Me110G-2, Me410 and Mosquito Mk.VI maximum speeds.

[Wmaker]

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) 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

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:


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. 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:


And here are the speeds in AH:


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?

[dirtdart]

What are the agreed on CD for the three airframes in discussion? 

[Wmaker]

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.

[dirtdart]

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

[Wmaker]

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.

[dirtdart]

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.

[Scherf]

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.

[Karnak]

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?

[Jabberwock]

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.

[Wmaker]

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:


Me410's DB603A:

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.

[Scherf]

Nice one, Jabberwocky.

 

[Krusty]

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.

[Wmaker]

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...

[Krusty]

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.

[Karnak]

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.