Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Wmaker on November 10, 2010, 12:10:58 PM
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With the recent talk about the Me410, here's something I've been wondering...
Mosquito Mk.VI tops out at 356mph on the deck with WEP (+18lbs boost, 2x~1540hp, based on this chart: http://www.wwiiaircraftperformance.org/mosquito/merlin25-powercurve.jpg (http://www.wwiiaircraftperformance.org/mosquito/merlin25-powercurve.jpg)) in AH. Here's a chart from data set which pretty closely matches with AH performance: http://www.wwiiaircraftperformance.org/mosquito/hj679-dh-level.jpg (http://www.wwiiaircraftperformance.org/mosquito/hj679-dh-level.jpg)
Maximum speed at sea level for Me410 is usually given as 315mph on different sources. Here's chart originally posted by Moot. It can also be found from the document Krusty posted to the recent Me410 armament-thread on this forum:
(http://i46.photobucket.com/albums/f147/Wmaker/Me410.jpg)
So, the chart shows a sea level top speed of 304mph at 9,5 ton flying weight with climb and combat power (2x1558,5hp). Extrapolating speed for the WEP power output (2x1726hp) using aircraft speed equation and the 304mph figure comes out almost exactly 315mph. So that figure that can be found widely from the literature seems to be consistent with the chart above.
So here is the thing I can't quite get my head around. Mosquito is whopping ~40mph faster on the deck using roughly ~370hp less power and having ~6sqm more wing area. :confused: I'm sure that the Mosquito has clearly smaller drag coefficient but....40mph??? Other explanations? Considerable larger induced drag due to quite high wingloading (at these speeds...doesn't seem likely)? Significantly poorer prop efficiency (I doubt that)? It must be something that I'm missing since after all, the data is there and it is from flight testing (/calculation in Me410's case?).
And this brings me to the last part of my post...
The Me110G-2 tops out at bit over 320mph on the deck in AH which is ~5-6mph faster than the 315mph figure for the Me410. Here's a chart from Monogram's Close-up series Me110-volume:
(http://i46.photobucket.com/albums/f147/Wmaker/Me110G-2.jpg)
And here are the speeds in AH:
(http://bbs.hitechcreations.com/scores/genchart.php?p1=63&p2=-1&pw=2>ype=0)
I don't know the original source for the speed curve depicted in the Monogram book or the power setting that matches it but we can a**ume it's either WEP or climb and combat power. Anyway, there's quite difference between it and AH performance. I'm not saying this chart is wrong or right nor am I say anything about AH performance because the data I have is rather incomplete and limited.
Anyway I think here's some food for tought.
Comments, suggestions, discussion?
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What are the agreed on CD for the three airframes in discussion?
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What are the agreed on CD for the three airframes in discussion?
I don't have them, at least not right now. I might calculate some reasonable estimates later/look for the values from possible primary sources.
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I generally think that all things being equal, the CD is the answer to your question. The mossie really does not have as many bits in the wind as the other two airframes. I will add that I am an Engineer, just not an aero guy, so there are probably some others on the BBS that will have much more insight. I will look at my stuff when I get home as well.
--Crusader
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I generally think that all things being equal, the CD is the answer to your question. The mossie really does not have as many bits in the wind as the other two airframes. I will add that I am an Engineer, just not an aero guy, so there are probably some others on the BBS that will have much more insight. I will look at my stuff when I get home as well.
Like I said, I'm sure that the Mosquito has smaller drag coefficient. But so much smaller that it enables it to be 40mph (!!) faster with less power. Just doesn't pass my smell test. I'm sure it is a combination of several factors.
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Well to contrast that point, look at the payoff a lower CD has on E retention for the brewster in the vertical vice a K4, despite a 1000HP advantage.
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IIRC the Me 410 chart shows a lower power setting. Think it's Steig- und Kampfleistung (climb and combat power) as opposed to Start- und Notleistung (takeoff and emergency power). Edit - But you knew that.
Other thing to bear in mind is that the Merlin 25s made their best power down low. Full throttle heights were about 5k feet and 12k feet, as opposed to the 410's 11k feet and 21k feet.
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The power output I recall for the Merlin 25 at +18lbs boost was either 1625 or 1640hp, not the 1540 you list.
Do you know if the Me410 had ejector stacks or flame dampers in the tests you are showing?
Edit:
Keep in mind, to get 356mph on the deck in the Mosquito VI in AH you have to be completely clean in pure fighter mode, without even the mountings for bombs or drop tanks. How often would an Me410 be in that condition and how condition was the tested one?
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Lots of figures, so bear with me:
Depending on the reference, SL power for the Merlin 25 at +18 lbs is generally given as 1,610 or 1,620 hp. Rolls-Royce charts indicate power is actually just under 1,620 hp at sea level.
Peak output in MS is generally given as 1,640 hp at 1,950 ft or 1635 at 2,250 ft (again, sources differ). RAF placard is for 1,635 hp at 2,250 ft. Rolls-Royce curves credit the engine with just shy of 1,640 hp at 1,800 ft
Full FS power is 1,515 hp at 6,400 ft, again according to Rolls-Royce charts.
The RAF data sheets for Mosquito Mk VIs with Merlin 25s at +18 lbs and 5,500 ft gives a placarded MS top speed of 352 mph, when with 2 x 500 lbs bombs on wings and 2 x 500 in the belly. With bombs gone this increases to 362 mph.
Clean speed would be better again. Even with bombs gone, the external bomb racks are going to slow the aircraft somewhat. Sharp & Bowyer estimate the effect at about 5 mph.
The difference in speed between SL and 5,500 ft with Merlin engine powered is about 15-20 mph (closer to 20 usually, give or take a few mph on either side).
By inference, SL speed for a Mk VI with Merlin 25s at +18 lbs would reasonably expected to be about:
332-337 mph fully loaded (2 x 500 internal, 2 x 500 external),
342-347 mph bombs gone
347-353 mph clean, no bombs, no racks
This tracks quite well with known Mosquito performance tests. A Mk VI with saxophone exhausts and drop tanks was tested as capable of 332 mph at SL. Adding multi-stub exhausts was reckoned to add 10-15 mph, getting rid of external tanks up to 10 mph.
Likewise, a Mk IX, with Merlin 72s that were marginally less powerful at low altitude, achieved 328 mph at SL with external bombs. The effect of the external ordnance was estimated at 15-18 mph, putting the aircraft in the 343-348 mph range at SL.
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Well to contrast that point, look at the payoff a lower CD has on E retention for the brewster in the vertical vice a K4, despite a 1000HP advantage.
I won't comment for the "E retention" as the issue isn't that simple even if the Brewster had the lower Cd, which it doesn't. Based on my simple calculations and NACA-data, Brewster's Cd is a bit below 0,03 while the value I've seen for the Bf109G is just slightly over 0,024.
Other thing to bear in mind is that the Merlin 25s made their best power down low. Full throttle heights were about 5k feet and 12k feet, as opposed to the 410's 11k feet and 21k feet.
The power output I recall for the Merlin 25 at +18lbs boost was either 1625 or 1640hp, not the 1540 you list.
Karnak,
Generally, Brits listed the engine power at the lower FTH, Germans used the sea level output (fluid clutch SC). For example the emergency power figure (1475ps) for the DB605 series is the output at sea level while it develops close to ~1580ps at ~2km alt.
Here are the powercurves I used for these engines:
Mosquitos' RR Merlin 25:
(http://www.wwiiaircraftperformance.org/mosquito/merlin25-powercurve.jpg)
Me410's DB603A:
(http://i46.photobucket.com/albums/f147/Wmaker/DB603A_powercurve.jpg)
Do you know if the Me410 had ejector stacks or flame dampers in the tests you are showing?
Edit:
Keep in mind, to get 356mph on the deck in the Mosquito VI in AH you have to be completely clean in pure fighter mode, without even the mountings for bombs or drop tanks. How often would an Me410 be in that condition and how condition was the tested one?
No certain idea about the flame dampeners/exhaust stacks, Nor really about the exact loadout either. The chart lists A1, A-2, A-3 variants, which doesn't really help much considering the naming practice Germans used but 9,5ton flying weight would suggest rather lightly equipped aircraft. Quick look at the loading plan shows that that weight includes roughly 50% fuel and the basic stock armament. Also, Me410 had its war load most of the time confined inside the bombbay. Those wing root SC50 racks were rare.
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Nice one, Jabberwocky.
:salute
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To differentiate from Jabber, I'm using in-game performance, not real world RAF testing.
I think that comparing speeds on the deck and only the deck gives you a very narrow picture of the real performance. Look at the F4u-1D, and its ram air effect below 2k. It's very interesting, but you compare it to something like the F6F and without this ram air effect there wouldn't be much difference between the 2 on the deck, but it alone adds about 15-20mph.
So, looking at the Mossie, the 110G, and the 410, I think deck speed alone won't be the answer.
Mossie 6 pretty closely matches a 190A5 in-game all the way up to 13k. Above that it drops off sharply while the 190A5 gains another 50mph at about 20k.
I think it's really a matter of the power curves, the supercharger dips and spikes. FTH on the 410 looks about 368 mph (19k). FTH on a MossieVI is about 375 (13k). Different alts, different power curves, but only about 7 mph off from each other.
The lower peaks show about 370 mph on the mossieVI (7k), but only 337mph for the 410 (10k)
I'd say it's a matter of the engine output at lower alts. Much like the Spit1 gained significant speed below FTH with the change to 100 octane fuel, I think it's just part of the power plant and part of the characteristics of the plane. You look at most DB engine power charts and it's much smoother, like a segmented line. You look at Merlins' curves and you get a serious negative dip between the peaks.
I think that just skews low alt (or perhaps "favors low alt" is better) for the mossie.
EDIT: Forgive me. I realize it sounds a bit redundant after re-reading Jabberwock's post.
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So, looking at the Mossie, the 110G, and the 410, I think deck speed alone won't be the answer.
Answer to what? I'm comparing apples to apples using speeds and power outputs at certain altitude.
I think it's really a matter of the power curves, the supercharger dips and spikes. FTH on the 410 looks about 368 mph (19k). FTH on a MossieVI is about 375 (13k). Different alts, different power curves, but only about 7 mph off from each other.
It is not about "supercharger dips and spikes" when I'm looking at a speed with maximum output the aircraft is capable of at that particular altitude. Mosquito in game is roughly ~40mph faster on the deck with less power output compared to the Me410 data point I know. No need to make this any more complicated than it is.
I think it's just part of the power plant and part of the characteristics of the plane. You look at most DB engine power charts and it's much smoother, like a segmented line. You look at Merlins' curves and you get a serious negative dip between the peaks.
Eh?
Single altitude. Single power output at a single power setting for two aircraft.
Take a look at the powercurves I posted.
<sigh>
...can't be that difficult...
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Answer to what?
The question about the speed difference.
You were asking "other than drag" why might this be. I was answering it might be that way because of the different predispositions in German engines vs RAF engines.
Just a thought, if you don't think that fits, then never mind.
EDIT: I answered in the spirit of "other than drag" but I think the drag is the real reason. The 410 looks nice, but is bulky, square, and not overly smooth. It's got giant radiators under the wings, a flat squared-off nose, little nooks and crannies all over to slow it down. IMO that is the reason.
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Was the 315mph at maximum power, WEP?
I would have expected the Me410 to do more like 330-335mph on the deck based on the British combat report I had read against it. A Spitfire Mk IX (most likely an LF.Mk IX) in Italy chased one down in a long tail chase on the deck.
That said, like all combat reports we don't know all of the factors that occurred. Not even the altitude as it happened over land.
The question about the speed difference.
You were asking "other than drag" why might this be. I was answering it might be that way because of the different predispositions in German engines vs RAF engines.
Just a thought, if you don't think that fits, then never mind.
He says he is comparing sea level power ratings for the engines though, so that should be accounted for, unless the German engines are blowing a lot of that power on something else, such as driving superchargers that are doing nothing at sea level.
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German engines and RAF engines have never really been all that par with each other. German designs were really meant to minimize the amount of precious metals they consumed, as Germany had little access to replace it. They squeazed more horsepower out of less space, often sacrificing aerodynamic consideration. The RAF could afford to tackle a resource-rich design and make it larger, then smooth that over with aerodynamic panels. Comparing them at similar power may yield similar results, or you may be nowhere close. Too many variables to just list horsepower.
An interesting question would be, how much THRUST did they have? 410s had larger prop blades, I believe. Yet, they are still slower. It must really be clawing it's way throug the air compared to the Mossie.
Like I said, I think the drag is really the answer. Compare a P-38 to a 110G, and I think you get the same comparison as a Mossie to a 410. One sleek, smooth, curved, rounded, the other just sheer brutality.
It has an elegance, don't get me wrong. But "slick" it ain't.
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With the recent talk about the Me410, here's something I've been wondering...
So here is the thing I can't quite get my head around. Mosquito is whopping ~40mph faster on the deck using roughly ~370hp less power and having ~6sqm more wing area. :confused: I'm sure that the Mosquito has clearly smaller drag coefficient but....40mph??? Other explanations? Considerable larger induced drag due to quite high wingloading (at these speeds...doesn't seem likely)? Significantly poorer prop efficiency (I doubt that)? It must be something that I'm missing since after all, the data is there and it is from flight testing (/calculation in Me410's case?).
Comments, suggestions, discussion?
Well there is one missing piece of information that Krusty and Karnak has both failed to explain. After doing some rough calculations on paper and pencil, I made some pretty logical conclusions. Given that the Mossie can achieve ~40mph faster with less power in comparison to the Me410 and Bf110, one would think something would be amiss. But, my friend, I promise you, it isn't what it seems. My fast calculations show that the Mosquito has a 59% greater sex appeal than the two German planes. It's true! The Mosquito is simply that sexy! It just doesn't need all that excess horsepower for that top speed.
Here are my my calculations to prove it:
Bf110 - Is it sexy? No.
Me410 - Is it sexy? Not quite.
Mosquito Mk.6 - Is it sexy? Friggin yeah!
So in conclusion:
Sex appeal > raw horsepower
:D
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^ lol
Anyhoo, I've had a quick squizz at a docco I have re: the balance between thrust and drag for the Mossie prototype - it talks about back pressure, power abosrbed by airscrew, airscrew efficiency, ejector exhaust power, radidator heat regeneration, basic drag, induced drag, carburetor air collection and cooling drag.
So I suppose any of those could be out of balance in comparing the two aircraft.
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Was the 315mph at maximum power, WEP?
Just like I stated in my original post, yes.
I would have expected the Me410 to do more like 330-335mph on the deck based on the British combat report I had read against it. A Spitfire Mk IX (most likely an LF.Mk IX) in Italy chased one down in a long tail chase on the deck.
I would expect the cap between the Mosquito and Me410 to be smaller. That's why I started this thread. I'll calculate some Cd estimates later but right now it looks like that the Me410 would have to have almost twice the Cd that Mosquito has... :eek: Like I said, very hard to get my head around that fact. For comparison, Brewster has a Cd bit under ~0,03 and 109G ~0,024. Other is an inline engined fighter and the other has a large diameter radial...
unless the German engines are blowing a lot of that power on something else, such as driving superchargers that are doing nothing at sea level.
Well, superchargers are obviously accounted for but things like hydraulic pumps and electric generators do eat power but the differences in these should be neglible.
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Might (might, ah say *might!*) help if you show us the aircraft speed equation you referred to, as well.
The other possiblity is that the Me 410's actual sea-level top speed at Notleistung was measured higher than you've calculated, but I've never seen any such measurement.
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An interesting question would be, how much THRUST did they have? 410s had larger prop blades, I believe. Yet, they are still slower. It must really be clawing it's way throug the air compared to the Mossie.
It's a matter of prop efficiency. I have a couple prop eff curves for the VDM prop of the 109G (DB605A-1). But the differences on this front can't really be big enough to have a huge effect. Well, obviously seeing Mosquito prop eff curves would help...
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P = ½ρv3ACd
P ∝ v3ACd
410 and mossie both ~1550hp, so:
3043(ACd)410 = 3563(ACd)mossie
(ACd)410 = 1.60(ACd)mossie
thats saying that the 410 has 60% more drag than the mossie at those speeds. the mossie was an exceptionally clean design so its feasible.
the calc also assumes that both aircraft are equally efficient at turning hp at the flywheel into thrust, a big assumption. ejector stacks and radiator output design can both add thrust, aero design for the nacelles, cowling and wing can reduces losses. if the mossie scores better on these (I suspect it does), it reduces the 60% difference in ACd.
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Thanks for that, but are you using a speed of 356 at sea level for the Mossie? Surely that's the WEP speed, vs the 304 for the Messer, which is at Mil speed?
Or, are you using that HP as Mil for the 410 and WEP for the Mossie?
P = ½ρv3ACd
P ∝ v3ACd
410 and mossie both ~1550hp, so:
3043(ACd)410 = 3563(ACd)mossie
(ACd)410 = 1.60(ACd)mossie
thats saying that the 410 has 60% more drag than the mossie at those speeds. the mossie was an exceptionally clean design so its feasible.
the calc also assumes that both aircraft are equally efficient at turning hp at the flywheel into thrust, a big assumption. ejector stacks and radiator output design can both add thrust, aero design for the nacelles, cowling and wing can reduces losses. if the mossie scores better on these (I suspect it does), it reduces the 60% difference in ACd.
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from the OP charts, at sea level:
Me410: 2x 1558hp (Mil), 304mph
Mossie: 2x 1540hp (WEP), 356mph
:)
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Cheers.
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thats saying that the 410 has 60% more drag than the mossie at those speeds. the mossie was an exceptionally clean design so its feasible.
Well this is where we somewhat disagree. I don't quite see the 60% difference plausible. But since we are still more or less guessing here it doesn't really matter. :)
The prop eff difference could make a difference and yes the airframe geometry behind the prop is rather important. But I'd say both of them had rather neatly cowled inline engines. I'm sure the underwing radiators of the Me410 reduce reduce the air velocity for the prop below the wing somewhat. Well, it would need some serious CFD stuff to unravel these things in detail.
Anyways, I did some quick calcs using 2x~170lbs as exhaust thrust for the DB603As (values are based on the exhaust thrust chart for the DB605). I came up with 0,036 Cd for the Me410 at 315mph on the deck. That's not a zero lift Cd but includes both induced and parasitic drag. Anyway, 0,036 sounds pretty brutal.
Anyhoo, I've had a quick squizz at a docco I have re: the balance between thrust and drag for the Mossie prototype - it talks about back pressure, power abosrbed by airscrew, airscrew efficiency, ejector exhaust power, radidator heat regeneration, basic drag, induced drag, carburetor air collection and cooling drag.
That doc sounds really interesting and would probably help to make some basic calcs for the Mossie more accurate. Would you be kind enough to share if I PM'ed you my e-mail addy?
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Well this is where we somewhat disagree. I don't quite see the 60% difference plausible.
I used your numbers so, assuming they are right, the 60% difference exists. the interesting question is why. :)
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I used your numbers so, assuming they are right, the 60% difference exists. the interesting question is why. :)
Yes, exactly.
I'm just saying that the difference can't be all drag. Just for comparison Cd0 of the Sopwith Camel is listed as 0,0378 not a big difference when compared to the 0,036 value for the Me410 that I got. Yikes!
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That doc sounds really interesting and would probably help to make some basic calcs for the Mossie more accurate. Would you be kind enough to share if I PM'ed you my e-mail addy?
No worries, go ahead and PM me.
As per the above, I reckon there's more happening than just drag. What does that note top-right of the DB603A power curve chart say? I get it includes both static and dynamic (pressure?), but what's the rest? Does not take account of - is Rueckstoss engine back-pressure or exhaust thrust? If it's the former, it might begin to explain things.
On the face of it, it's very strange, 2x44 litres vs 2x27 litres. What's the "standard cruising power" from that graph? FWIW, the Mossie VI cruised at 240 mph or so with flame dampers, more without, think at +7 lbs/in2 but don't quote me.
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Yes, exactly.
I'm just saying that the difference can't be all drag. Just for comparison Cd0 of the Sopwith Camel is listed as 0,0378 not a big difference when compared to the 0,036 value for the Me410 that I got. Yikes!
Well, the discussion would be more sensible by using the drag area (flat plate area) for the comparison. The Camel has a lot of wing area for a small and light plane so the Cd might look small. For a good reference in finnish I suggest Raunio's article serie in SILH couple years ago.
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yup, the drag area or reference area is the A in ACd above.
considering the dimensions of the 410 and mossie and their frontal projections, Amossie and A410 look pretty similar to me, the mossie is a little bigger but a little less chunky.
I still reckon the difference in Cd values is the biggest factor here.
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Is it possible the power output of the German engines is being reported as higher than it really was? False claims from manufacturers to the German government were not unknown. We have performance tests of both aircraft that seem unlikely to have been falsified and power output claims for their respective engines that seem to not be able to be matched to their demonstrated performances.
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Could the 410's Cd be calculated with small enough error margins by just giving a CAD model to someone with access to one of those CFD virtual tunnel apps?
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Cd? Co-efficiency of Drag?
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Could the 410's Cd be calculated with small enough error margins by just giving a CAD model to someone with access to one of those CFD virtual tunnel apps?
Basically, yes. My experience with CFD software is limited to two hour excercise :D but I'm sure there shouldn't be much file-format conflicts in general considering that analysis of this kind of nature is done all the time in the industry. It would obviously have to be rather accurate model to gain accurate results and takes quite a time to compute depending on the computer.
Something you might find interesting: http://www.hobbybokhandeln.se/j22/CFD.htm (http://www.hobbybokhandeln.se/j22/CFD.htm)
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I approve of Moot's bump :aok
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I'm willing to do the model if anyone can pass it on to someone who'll run it thru CFD..
Thanks WMaker, that's one of the things I was looking for.
... That's great!.. That software looks free to the US public... Bummer.. It's only for Mac. But at least there ought to be someone who can use it with the model one of us would make.
Guess I'll do it on 3DSMax. Seems like a safe bet format wise.. ?
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http://www.public.iastate.edu/~akmitra/aero361/design_web/airfoil_usage.htm
Messerschmitt Me 410, NACA 23018-636.5, NACA 23010-636.5
Might be of some help...
Can you guys use an existing model? Eg. from IL-2? I'm sure the conversion alone will be a hefty job to do. Then again could be easier to do one from scratch...
-C+
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thats a pretty massive modelling task to get any meaningful numbers out of it. :O
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RTHolmes I haven't started yet, but if you can definitely say it's not feasible, let me know now :D
It seems the second Me 410 book by Petrick has a clear picture of the plane that was modified for high altitude interception: no radio mast and no barbettes. Maybe some valuable clues can be found if its performance is mentioned somewhere. A better pic than this one:
(http://farm6.static.flickr.com/5137/5496710768_9a054e1580_o.jpg)
Will have to look into Il2 game models..
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RTHolmes I haven't started yet, but if you can definitely say it's not feasible, let me know now :D
I can't say I speak from experience or even with much knowledge...take it what it's worth...but...
...if the numbers that come out from the CFD-analysis are within 20-30% of the calculated numbers you really haven't solved much IMO. Numbers from the theoretic, smooth 3D-model will always be better than reality. Although I'm sure that just like in any mechanical engineering field there's plethora of multipliers/coefficients that can be used to account for manufacturing imperfections and to create safety marginals between normal stresses and failure of a structure. Ie. I'm sure there are surface roughness multiplyers etc. to account for how a real manufactured aircraft would perform but setting these multiplyers is obviously kind of "guess work" in this situation. Obviously there aren't any "black and white" answers to be found as every aircraft is an individual...especially 60 odd years ago.
What goes without saying is that it would be an awesome learning experience and you would come out of it knowing helluva lot more than you know now. For that alone it would be more than worth it but IMO you shoudn't be doing it for the results alone as you might be dissapointed with the lack of conclusive results.
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^ thats what I reckon. getting the 3D models detailed enough will be a huge task, if its even possible. small tweaks to the shape can yield large differences in aero effects.
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I think the short answer is that the Mossie was designed to be fast and that was the primary design criteria to the point where it was considered too radical and initially rejected. Since drag is exponential small differences in Cd mean bigger speed differences than similar differences in thrust.
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I only have enough time to make a model about as good as enthusiast blueprints and other references will allow. I won't have time to get into the CFD (don't know where to find a CFD app yet) till late this summer.
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I think the short answer is that the Mossie was designed to be fast and that was the primary design criteria to the point where it was considered too radical and initially rejected. Since drag is exponential small differences in Cd mean bigger speed differences than similar differences in thrust.
I would agree,look at the various speeds found on the mossie of the same model! I recall reading about a paint job that took 8,10 mph off the airframe.The mossie being wood could be sanded to a fine finish that a rivited metal plane just couldn't attain.
Now I have a question,where would the effects of this drag be felt more,at low alts or at high alts?
:salute
PS: I'm not sure of the answer myself,so I'm not trying to be a smart a..... :o
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Drag increases the TAS loss as you go up. This from comparing drag on 109 gondolas and DT racks, the value always increases as you go up simply because TAS increases.
For IAS maybe it stays the same?
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I can't say I speak from experience or even with much knowledge...take it what it's worth...but...
...if the numbers that come out from the CFD-analysis are within 20-30% of the calculated numbers you really haven't solved much IMO. Numbers from the theoretic, smooth 3D-model will always be better than reality. Although I'm sure that just like in any mechanical engineering field there's plethora of multipliers/coefficients that can be used to account for manufacturing imperfections and to create safety marginals between normal stresses and failure of a structure. Ie. I'm sure there are surface roughness multiplyers etc. to account for how a real manufactured aircraft would perform but setting these multiplyers is obviously kind of "guess work" in this situation. Obviously there aren't any "black and white" answers to be found as every aircraft is an individual...especially 60 odd years ago.
What goes without saying is that it would be an awesome learning experience and you would come out of it knowing helluva lot more than you know now. For that alone it would be more than worth it but IMO you shoudn't be doing it for the results alone as you might be dissapointed with the lack of conclusive results.
I'd love to fail at trying to put it all together, but it sounds like I won't have enough time for it. I'm think I'm gonna find an aerospace professor and ask some questions in person..
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Morfiend since drag force is airspeed and air density I'm guessing it's about the same at various altitudes for a given IAS until you get into compressibility and wave drag which is more likely at higher altitudes.
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Thx FLS,
In my simple mind I assumed the drag would be higher in the "thicker" air down low and therefore have it's greatest effect at SL. Again to my simple mind I thought this might have something to do with the lower speeds attributed to the 410 vs the Mossie.
I know it's much more complex than that,drag squaring with speed and such but I wasnt sure how much if any the alt would effect this.
:salute
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The drag is certainly greater at low altitude when you compare it with high altitude at the same true air speeds. That's why the maximum speed of aircraft is not at sea level. But air density affects drag similarly on all aircraft. So all aircraft fly faster as the air gets thinner. Then engine performance starts to suffer from the thinner air, so unless the aircraft have the same engine, their relative speed difference will not be the same at all altitudes, because the drag vs thrust will not stay the same when the engines are not affected the same way by the thinner air. So it's likely engine differences that you see at altitude and not drag differences from the thinner air.
One you get into compressibility it gets more complicated and beyond my understanding.
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Parasite drag is the real killer for the 410
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Another possible explanation is simply the same problem as the RAE's initial tests on an undampered Merlin 25 Mosquito VI. It is possible the RLM was given a lemon to test.
In the case of the Mossie, said lemon was shaving 15-20+mph off of what it should have been doing.
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There's mention of the Me 410D (with DB 603 JZ) having a reworked cockpit/nose shape. Anyone have any idea what that reshaping looked like?
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I don't think it ever was built?
Plus any refernces I've read so far just showed it as an engine upgrade. Not sure on the nose change.
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No but a look at the projected shape could be some clue of how "Bad" the production nose is for aerodynamics.
I didn't write down where I read it about it.. damn
... Warplanes of the Luftwaffe Hitler something something: p.249, halfway down the right text column:
<< The Me 410D, with the new twin-wheel gears, annular-cowled 603 JZ engines and revised forward fuselage (which was expected to give better pilot view and lower drag). >>
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... I should have posted this here. A service 410A with no turrets and no antenna mast only gained 20kph "at altitude". So the turrets should count for at most 10-12 mph. This aircraft was supposed to have GM1 boost but it's not clear if GM1 was used on the flight +20kph was recorded; the turrets' and antenna mast's drag would only be smaller with it.
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Found both pictures of it.
(http://farm6.static.flickr.com/5257/5511673288_5715a4933a_o.jpg)
(http://farm6.static.flickr.com/5053/5514154507_b9f2c0327e_b.jpg)
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From Generalluftzeugmeister meeting notes, dated 6/15/43
"In the area of the Angriffsfuhrer England [Generalmajor Dietrich Peltz?], an Me 410 is said to have increased its speed by 40 kph [25 mph] through the use of filler paste, something which possibly indicates the potential of this measure, or the poor build quality."
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there ya go - the key factor is parasistic drag.
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piccies no workies
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From Generalluftzeugmeister meeting notes, dated 6/15/43
"In the area of the Angriffsfuhrer England [Generalmajor Dietrich Peltz?], an Me 410 is said to have increased its speed by 40 kph [25 mph] through the use of filler paste, something which possibly indicates the potential of this measure, or the poor build quality."
Very interesting, thanks!
Here's some Cds calculated based on these speeds:
(http://i46.photobucket.com/albums/f147/Wmaker/Me410MossieCD.jpg)
The exhaust thrust values are extrapolated from table values of a DB605A-1 for the DB603. For the Merlin I don't remember if I used those those DB605 values as basis or if I based them on one reference on Griffon's values I've seen on the literature. I'll double check them later. Prop efficiency is based on the 109G prop eff charts and Mossie's is based on the doc Scherf kindly posted for me. The Cd value includes both parasitic and induced drag at the speed mentioned to simplify the calculation as I didn't have accurate Cl or Oswald's effiency for these aircraft. Of course some fairly good estimates could be made but it really won't change things much considering the general accuracy of the calculation and for the purposes of this thread.
P.S. Sorry Moot, I'll try to reply to your PM soon.
EDIT/Prop eff for the faster Me410 would change a bit aswell, forgot to change that value but it won't change much anyway./EDIT
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No hurry on PMs, I'll be burried in research and studying till Wednesday.
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Here's some Cds calculated based on these speeds:
(http://i46.photobucket.com/albums/f147/Wmaker/Me410MossieCD.jpg)
wow thats an even bigger difference than my back-of-envelope calc earlier :confused:
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Shouldn't the power and the Cd for the Mossie both be a touch higher? The data card for the M25 FB.VI says the Merlin we have was making 1635 hp at 2,250 feet. Or am I dreaming again.
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Shouldn't the power and the Cd for the Mossie both be a touch higher? The data card for the M25 FB.VI says the Merlin we have was making 1635 hp at 2,250 feet. Or am I dreaming again.
My comparison is at sea level (air density 1,25kg/m3). The power output of the Merlin is based on this chart:
(http://www.wwiiaircraftperformance.org/mosquito/merlin25-powercurve.jpg)
Brits usually gave the power output value figures at the first FTH where as Germans for example gave the figures at sea level.
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(http://www.warbirdphotographs.com/LCBW4/Me410-A3-67.jpg)
Nice find moot.
I mentioned in another thread I've suspected what we see in the Me410's max level speed performance is mainly due to parasite drag increases due to the shape of it's fuselage. If you look at the 410 the fuselage shape looks to me like it would promote a longer adverse pressure gradient along the fuselage resulting in more drag due the degree of thickness and curvature in the front 1/4-1/3 of the airplane.
What does all that mean? Pressure distribution follows the curvature (camber) of the shape in the air-flow. Where camber increases pressure tends to increase. Where camber decreases pressure decreases. Peak pressure occurs where fluid flow velocity is the highest. Pressure increases up to the point of peak pressure (following the increase in camber of the shape). But after the peak pressure point pressure decreases until it reaches the pressure of free-stream airflow at the trailing edge of the shape.
The area of decrease is known as the adverse pressure gradient. Viscous forces cause back pressure against the boundary layer in the adverse pressure gradient which eventually leads to separation. The more forward the pressure peak is on the shape, the longer the adverse pressure gradient is, the more turbulent the flow & the easier separation occurs. All this conspires to increase parasite drag. Essentially the similar principle was being applied for laminar airfoils vs. conventional and that is to reduce drag by moving the pressure peak further back along the chord of the airfoil.
Alas I have no desire to crack out some CFD or computing using DATCOM to estimate the effects on the 410 so don't ask :D.
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(http://www.warbirdphotographs.com/LCBW4/Me410-A3-67.jpg)
Nice find moot.
I mentioned in another thread I've suspected what we see in the Me410's max level speed performance is mainly due to parasite drag increases due to the shape of it's fuselage. If you look at the 410 the fuselage shape looks to me like it would promote a longer adverse pressure gradient along the fuselage resulting in more drag due the degree of thickness and curvature in the front 1/4-1/3 of the airplane.
What does all that mean? Pressure distribution follows the curvature (camber) of the shape in the air-flow. Where camber increases pressure tends to increase. Where camber decreases pressure decreases. Peak pressure occurs where fluid flow velocity is the highest. Pressure increases up to the point of peak pressure (following the increase in camber of the shape). But after the peak pressure point pressure decreases until it reaches the pressure of free-stream airflow at the trailing edge of the shape.
The area of decrease is known as the adverse pressure gradient. Viscous forces cause back pressure against the boundary layer in the adverse pressure gradient which eventually leads to separation. The more forward the pressure peak is on the shape, the longer the adverse pressure gradient is, the more turbulent the flow & the easier separation occurs. All this conspires to increase parasite drag. Essentially the similar principle was being applied for laminar airfoils vs. conventional and that is to reduce drag by moving the pressure peak further back along the chord of the airfoil.
Alas I have no desire to crack out some CFD or computing using DATCOM to estimate the effects on the 410 so don't ask :D.
Awesome and very interesting photo! :aok
Thanks for you input Tango! Very much appriciated.
Yeh, I've been thinking that tadpoles look like they do for many other reasons than low water resistance. (Well, tadpole is slightly slower than Me410 and it moves ina fluid that's almost 100 times denser so the flow stays attached better.) :D :D :D Anyway, I *still* thought that it wouldn't be as big of a difference. The production quality and therefore poor fit of the panels, bombay doors, panel seams etc. For example looking at the Me410 that's preserved in England those things are pretty evident. Obviously do cause that extra bit of drag in reducing the speed according to the account Moot posted. Ie. reducing the speed from ~340mph to 315mph. Considering the power outputs even 340mph is low compared to the Mosquito and that can be largely due to the overall geometry of the airplane. Looking at the test flight data that 356mph figure for the Mosquito also seems to be pretty much the "best performance that was achieved".
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My comparison is at sea level (air density 1,25kg/m3). The power output of the Merlin is based on this chart:
(http://www.wwiiaircraftperformance.org/mosquito/merlin25-powercurve.jpg)
Brits usually gave the power output value figures at the first FTH where as Germans for example gave the figures at sea level.
I thought you'd be using that chart. That one confuses me, as the peak power output is lower, and the altitude at which it develops it higher, than what I've read otherwise.
Try your calculation with this one:
http://bbs.hitechcreations.com/wiki/index.php/Image:Merlin_25_and_23_Power_Curves .jpg
Shows 1610 or 1615 or so for the Merlin 25 at sea level.
You should also have a look at this document:
http://bbs.hitechcreations.com/wiki/index.php/Image:The_Aircraft_Performance_Data _Book_AVIA_28-3030_.jpg
Shows a Coefficient of drag for the Mosquito F.II (outwardly identical to the FB.VI) of 0.0224.
(Tosses head, bats eyes, "Honestly, I don't know why I upload these things if people aren't going to use theh.")
My little daughter would like to say ":banana: and :rock from Daddy."
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Looking at the test flight data that 356mph figure for the Mosquito also seems to be pretty much the "best performance that was achieved".
This is true, at least for 100 octane fuel, which is the relevant fuel to this discussion and to the AH Mosquito performance.
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You can't mention CD without factoring in frontal area to arrive at CX.
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pah, links above to AH wiki no workie. Will do the photobucket thing.
(http://i937.photobucket.com/albums/ad212/mhuxt/Merlin_25_and_23_Power_Curves.jpg)
(http://i937.photobucket.com/albums/ad212/mhuxt/The_Aircraft_Performance_Data_Book_AVIA_28-3030_.jpg)
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(http://www.warbirdphotographs.com/LCBW4/Me410-A3-67.jpg)
Nice find moot.
I mentioned in another thread I've suspected what we see in the Me410's max level speed performance is mainly due to parasite drag increases due to the shape of it's fuselage. If you look at the 410 the fuselage shape looks to me like it would promote a longer adverse pressure gradient along the fuselage resulting in more drag due the degree of thickness and curvature in the front 1/4-1/3 of the airplane.
So because of how blunt is the front-most part of the fuselage, IOW the nose surface and what's down-wind of it a bit, you've got something like
(http://i149.photobucket.com/albums/s58/tapakeg/birds/410/410agp01.jpg)
Where the boundary layer is somewhere along those green lines, and somewhere in the yellow area you've got some kind of turbulence... Where the yellow area grows (from the wind current's POV) much quicker than a less blunt shape would cause? And the parasite drag is much stronger in that yellow area, or due to it being so much larger?
This is the shape of the planned revised 410 front fuselage:
(http://i149.photobucket.com/albums/s58/tapakeg/birds/410/p311_1k.jpg)
So this shape would better "coax" the airflow around it, rather than bluntly deflecting it and then abruptly cambering back like the "forehead" part of the canopy does in the original fuze shape? Kind of like a motorcycle is "cleaner" when it's got a rider tucked in behind the windscreen, rather than an unmanned motorcycle?
.. And ideally you'd want the pressure peak as far back, so does that mean a pressure peak right at the trailing edge (just speaking hypothetically, dunno if it's possible) would be ideal?
It's really curious that back in WWII they hadn't (had they?) thought of wind tunnel with colored plumes fed into the air flow.
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the mossie is alot closer to the sears-haack shape than the 410 ...
(http://upload.wikimedia.org/wikipedia/commons/thumb/3/33/Sears-Haack.png/220px-Sears-Haack.png)
(iirc the germans had some excellent wind tunnels)
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That looks a lot like Skylon/LAPCAT's shape.
(http://i149.photobucket.com/albums/s58/tapakeg/birds/410/moss410_silh.jpg)
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Notes at the bottom of the "drag" file may be of some use:
(http://i937.photobucket.com/albums/ad212/mhuxt/stats1b.jpg)
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You can't mention CD without factoring in frontal area to arrive at CX.
What is CX?
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another fairly random thought on the mossie's aerodynamics: Ive always wondered if the mossies engine pods act as anti-shock bodies, they certainly look like they could. could it be that the design conforms to the area rule to some degree just by coincedence? or is the mossie not quite fast enough for wave drag to be an issue?
:headscratch:
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Ive always wondered if the mossies engine pods act as anti-shock bodies, they certainly look like they could.
I remember something from Sharp & Bowyer about the extended engine pods being modified and extended during development. I'll have to dig it up and look for the reason.
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Nacelles were extended back past the line of the trailing edge early on to cure some tail buffet, though some very early examples entered service with the original short nacelles.
Later models had nacelles which exteded further forwards due to the intercoolers on the two-stage (high-altitude) Merlins.
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This thread is getting me all excited about the 410. Great questions and discussion though. Since I am not anything related to an engineer...great introduction to concepts.
So when do we get the 410? And is the P-61 next?
Boo
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2 weeks after HTC decides to add it.
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another fairly random thought on the mossie's aerodynamics: Ive always wondered if the mossies engine pods act as anti-shock bodies, they certainly look like they could. could it be that the design conforms to the area rule to some degree just by coincedence? or is the mossie not quite fast enough for wave drag to be an issue?
:headscratch:
At sea level, not fast enough for wave drag to be an issue. At altitude, maybe a little, but as long as you're slower than about .7 mach, you can, for the most part, exclude wave drag entirely. That being said, it might be worth it to do an analysis where you break out the induced drag just so you can isolate the total difference between the two Cd0. But, looking at the shape of the 410 fuselage, the nose has to be a huge drag (pun intended) on the Cd0 of the airframe.
Also, if the prop efficiency on the Mossy is estimated at 80-82% as Scherf's diagram shows, there could be some slop in the Cd0 they came up with if the actual numbers differed--maybe not a lot, but some.
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I thought you'd be using that chart. That one confuses me, as the peak power output is lower, and the altitude at which it develops it higher, than what I've read otherwise.
Try your calculation with this one:
http://bbs.hitechcreations.com/wiki/index.php/Image:Merlin_25_and_23_Power_Curves .jpg
Shows 1610 or 1615 or so for the Merlin 25 at sea level.
You should also have a look at this document:
http://bbs.hitechcreations.com/wiki/index.php/Image:The_Aircraft_Performance_Data _Book_AVIA_28-3030_.jpg
Shows a Coefficient of drag for the Mosquito F.II (outwardly identical to the FB.VI) of 0.0224.
(Tosses head, bats eyes, "Honestly, I don't know why I upload these things if people aren't going to use theh.")
My little daughter would like to say ":banana: and :rock from Daddy."
Thank you very much Scherf you certainly didn't post those in vain! :)
With those power outputs the Cd is starting to get closer of that Cd0 in your document. I got 0,02122. I'm thinking that some of the difference is probably in the exhaust thrust because I used DB's exhaust thrust figures for the Merlin. Merlin probably has higher exhaust thrust than DB due to the fact that it burns more fuel at higher boost pressures. Call me crazy but I remember reading from somewhere that Spit 14's Griffon 61 produced something like 12kg of thrust per cylinder? I just can't for the life of me find it now that I tried to search for it. :headscratch: Reducing that Griffon's thrust to suit the Merlin's power output would bring the Cd sightly over that 0.0224 Cdo-figure and would mean we should be in the ball park...
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Heya,
No worries, glad we're in the ballpark on the Mossie.
Now, for the 410...
The 0.84 WMakeris referring to for prop efficiency was used in a separate test, on the Mossie prototype, and the relevant docco specifies "the Lock-Bufton method" was used to calculate it.
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Hi moot:
Your picture doesn’t quite describe what I explained. 1) The boundary layer doesn’t usually separate & re-attach like you’ve drawn it (though it can in certain situations but that’s another story!). 2) Turbulent flow in the boundary is different from boundary layer flow separation from the surface.
Let’s sharpen our understanding.
Adverse Pressure Gradients:
When air flows around a cambered object it will accelerate & decelerate in relationship to the objects shape. Here’s a diagram to illustrate:
(http://thetongsweb.net/images/pressure_grad_airfoil.jpg)
In the above diagram we can see where air accelerates & decelerates around a shape. Where the airflow decelerates there must be a region of increasing pressure. This region is known as an adverse pressure gradient.
Adverse pressure gradients are greatly influenced by an object’s shape. The shape determines the amount of fluid velocity increase & decrease and where the peak pressure or transition from decreasing to increasing pressure begins. Here’s another diagram to demonstrate:
(http://thetongsweb.net/images/cpcompare.jpg)
We have 3 airfoils compared. The right-hand graph is a plot of pressure (Cp) vs. % of chord length (x/c) for all 3 airfoils. Annotated on the graph is also where the transition point between laminar to turbulent flow occurs.
We see the Cp curve goes up and then comes down toward the trailing edge for each airfoil. Where the curve descends & all the way to the trailing edge is the adverse pressure gradient. The downward slope of the curve is the degree of adverse pressure gradient; the steeper it is the greater the adverse pressure gradient.
The blue airfoil shape is thicker & more curved near the leading edge. Note on the Cp chart this results in a long, steep adverse pressure gradient compared to the others. Also note that the laminar to turbulent flow transition point is much further up toward the leading edge as well. These are all direct result of the airfoil shape. Why is all this important?
Parasite Drag:
Parasite drag consists of two fundamental components:
1) skin friction drag &
2) pressure drag
Skin friction drag is strongly related to boundary layer turbulent flow. Pressure drag results from boundary layer separation. Both turbulent flow formation (skin friction increase) & boundary layer separation (pressure drag) are strong functions of the adverse pressure gradient.
The Me410 has a similar conceptual shape like the blue airfoil above. The forward section of the Me410 fuselage has a large radius of curvature around the nose & cockpit & then tapers off. Like the blue airfoil it creates an adverse pressure gradient which moves the turbulent flow transition point closer toward the leading edge / nose of the aircraft. This results in more turbulent flow along the length of the fuselage which increases skin friction drag.
The adverse pressure gradient is also steep & long meaning the boundary layer will tend to separate earlier along the fuselage. Earlier separation of the boundary layer results in increased pressure drag.
I speculate these factors conspire to increase the parasite drag due to the shape of the adverse pressure gradient. Understand this is just an educated guess on my part, but a guess no less on why we are seeing the Me410 with a calculated drag coefficient we are from published performance numbers. I’d have to do some fancy maths with panel codes & the like to better estimate.
Loose Ends:
A couple of loose ends to tie up you asked about in your post: a) pressure peak placement, b) motorcycle rider analogy.
Yes pressure peak placement toward the trailing edge will help reduce parasite drag but it comes with a big trade off with other key variables such as degraded lift, etc. There's no free lunch in aero :).
As for the motorcycle analogy with the rider tucking, it's similar but not the same. In that instance the tucking of the rider is drastically reducing pressure drag for having a blunt shape in the oncoming wind. We're talking about smooth bodies here and how the pressure gradient is affected by the shape of the smooth body.
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Pressure distribution follows the curvature (camber) of the shape in the air-flow. Where camber increases pressure tends to increase. Where camber decreases pressure decreases. Peak pressure occurs where fluid flow velocity is the highest. Pressure increases up to the point of peak pressure (following the increase in camber of the shape). But after the peak pressure point pressure decreases until it reaches the pressure of free-stream airflow at the trailing edge of the shape.
For clarification & correction- I posted the above statements in my original post in this thread. It reads inaccurately. Actual pressure decreases, reaches the peak, & then increases. The reason I stated it the way I did is because Cp curves are usually graphed upside down like the Cp curves posted above where the y-axis gets more negative the higher up you go. Confusing aerospeek.
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I see from the various documents that the DB603 was designed for B4 fuel.
What say you Experten? Did it carry on with B4, or was the 603 capable of using C3? Did it do so?
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603 is listed in Mankau as having a C3, and C3+MW50 variant. The book is >< this close from saying they were never fitted operationally. They're described as preproduction .. And the 410 A&B both are listed as using plain -A engines almost everywhere. Even in the May 15th 1944 "operational & planned variants" (not a real quote, just my gist) pamphlet at the end of the Petrick/Stocker book.
.edit.. there was one retrofit: 603-G superchargers retro'd on -A's.
No post-hoc reports but planned as: 140 retrofits for June 44, 240 for July, and nothing after that since in Sept the Me 410 was canned. It was planned to be built with the 603E from that month on.
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Thanks for that, it's what I figured. IIRC the 410-B ended up with the same engines as the 410-A, despite plans for a 1900 hp (PS?) powerplant. I guess it was stuck with that bloody B4 stuff.
Tempted to say "it's a shame ... " but....
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It wasn't a shame but it is a shame :D hehe
For future ref.. A dedicated engine book might correct this but I reckon there isn't much to get wrong:
DB 603
First proposed Sep. '36
Contract voided by RLM March '37
Development continued on company dime, makes it to test bench in '39; RLM changes its mind
New contract for 120 units Feb '40
Full scale prod in '41
then: "Since the Me 209, 309, and He 177B never materialized and the 410 and Do 217 ceased production in '44, in fall '44 the situation arose whereby there was temporarily no suitable taker for the DB 603 [...]" So that leaves little room for the Me 410 being produced/mass-equipped with anything but variants of the 603.
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The whole family in detail:
A, B, C 1942 (http://i149.photobucket.com/albums/s58/tapakeg/birds/410/603_1.jpg)
A 44; AA 44; D, E, F 42; G, H, J 42; K, L, M 42; AE 44 (http://i149.photobucket.com/albums/s58/tapakeg/birds/410/603_2.jpg)
AM 44; AAM 44; E, F Apr.43; E Oct.43; E-2 44; G, K Apr.44 (http://i149.photobucket.com/albums/s58/tapakeg/birds/410/603_3.jpg)
G, K Oct.44; LA-0 44; LA-1 44; N 44 (http://i149.photobucket.com/albums/s58/tapakeg/birds/410/603_4.jpg)
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Many thanks for that.