Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Sachs on June 15, 2002, 01:17:05 PM
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A lot of data has been thrown out in the last week about MW-50 and GM-1. When wil Pyro help out here and explain some of these to us. I am really curious as to know what we have and don't have. Pyro any chance of a chime in anytime soon?
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Yup
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...and ban someone ?
gdr ;)
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Guys, this whole A4/A5 with Mw50 arguement has been done many times before. No one yet in the 8 years I've been flying online flight sims has yet to produced a good reference doc that shows either plane had MW50.
And to be honest, you haven't in this latest round either.
Its very rare for Pyro to chime in on these arguements, and it usually takes substantial "definitive" proof to get something changed.
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Vermillion,
I think at this point it is just an academic exercise. It's interesting.
I am not looking to have anything changed.
F.
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Nor am I looking to have anything changed.
I do however trust Otto Stammberger when he says they used Water-methanol injection, wether it was on all 190's or just his or just some in his squadron I do't know but obviously he used it and this was prior to the 190 A8.
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If it's a quest to have something changed in the game, then the most you can expect is probably a yes or a no. In that case you'll need to pose some yes and no questions. :)
If it's an academic exercise, then don't expect a comment. We may well be covering ground that Pyro covered by himself years ago. And even if we are finding something new, I'm not sure it's in HTC's best interest to comment or to share research. I'm pretty sure they are an entertainment software company, not a provider of educational services. :)
I don't pretend to speak for Pyro here. This is just my best guess based on what I know about HTC and this business.
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Originally posted by Vermillion
Its very rare for Pyro to chime in on these arguements, and it usually takes substantial "definitive" proof to get something changed.
Wich kind of Proof?
Proof, for instance, such as showing a Focke Wulf chart of the Fw190A5, showing that AH's 190A5 is 10 to 15 mph slower than what it should be at sea level and low altitudes?.
I did that some months ago and still there is nothing new on the issue coming from HTC, at all.
No,Verm, showing proof isn't enough to see an answer coming from Pyro. And I say it without anger neither with any kind of desire to stir the pot, as I no longer care about it.
I just point at the fact.
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there have been several instances where substantial proof has ben offered to total scilence on pyros part. the compression on the d9 compaired to the a8 proplem was proven to be wrong by naudet . responce none at all. criticism is not allowed so i wont.
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Last summer I went and visited the HTC offices. Several of us (I was in the 56th FG at the time) discussed FM's and such with HiTech. He said something that made a lot of sense, and it has stuck with me every since:
"You can't argue with physics."
AH is a complex game, blending virtual physics, graphics, etc....into a playable game.
HT mentioned the 205 and performance data they had received on it. Once they plugged all the physical data into the system (engine HP, thrust, drag, etc.) none of it matched the "expected" performance. I believe in HTC. I believe they know enough about physics and aerodynamics to build a believable FM. So either the data they received was skewed, or.........
If the FW190 is slower in AH than what charts show it should be, don't be so quick to blame HTC. The guys do a whale of a job at this. Could be the test data is in error. Remember, the environmental conditions in AH are set, unlike in RL where varying barometric conditions can and do have an effect on instrument readings.
Just my thoughts...............
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Originally posted by eddiek
If the FW190 is slower in AH than what charts show it should be, don't be so quick to blame HTC. The guys do a whale of a job at this. Could be the test data is in error. Remember, the environmental conditions in AH are set, unlike in RL where varying barometric conditions can and do have an effect on instrument readings.
Just my thoughts...............
I don't buy it. Aces high's Fw190A8 performance matches Focke-Wulf performance charts almost milimetrically, but Aces Hihg's Fw190A5 performance doesn't match an IDENTICAL performance chart.
So, one yes, the other no?. Nope, eddiek...sorry but I simply don't buy it.
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Wilbus, nothing against Otto but consider several things. For one, its been at least 60 years and memory is not perfect. Especially when you consider that between 1942 and 1945, they probably changed aircraft versions (not to mention different aircraft within the unit) at least every 6-8 months. So who's to remember the exact difference between a A5 in late 1943 or early 1944 and a A8 in early 1944 to late 1944 when its wartime (ie its quiet a hectic time) and your memories are 60 years old. Plus most of these guys were pilots, not engineers or even mechanics. I've talked to many many WWII vets who flew combat, and commonly when I ask a very technical question regarding an aircraft I get a response like "I don't know, I just flew them".
RAM, yes proof as in a technical document issued by either FockeWulf or the Luftwaffe that shows the use of production usage of MW50 in a A5 (or even an A8 for that matter) and a performance chart like I sent you for the A8 and the A8 with GM1. If it was used in production aircraft there would exist the exact same aircraft handbook, as I sent you for the A8.
Lord Dolf Vader, definitive proof of what??? That there is a physical difference between the handling of a D9 and a A8? Ummm guess what. There SHOULD be a difference. You have the same wing, but a different CG plus a different moment arm about which the elevator works, in other words the distance from the aerodynamic chord of the wing to the elevator is different. This will cause a different pitching moment. I'm admittedly no expert in aerodynamics or the modeling of aircraft, and I may have used a term incorrectly in this description, but I've learned alot lately on the subject. Now, is what we have in AH correct? I don't know. And no one has presented information to suggest that the D9 is wrong, just that its different from the A8. Which is correct.
And don't think I'm against you guys, I'm very interested in the subject myself, and I frequently fly the 190's myself, they're my favorites. I'm just trying to keep a perspective on the issue and look at it subjectively. :)
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Originally posted by Vermillion
RAM, yes proof as in a technical document issued by either FockeWulf or the Luftwaffe that shows the use of production usage of MW50 in a A5 (or even an A8 for that matter) and a performance chart like I sent you for the A8 and the A8 with GM1. If it was used in production aircraft there would exist the exact same aircraft handbook, as I sent you for the A8.
I'm not talking about MW50, Verm, but about the Fw190A5's speed, is too low according to the data of this chart.
(http://212.73.32.211/hosting/0003d/ebringas/a5speed.gif)
is a chart almost identical to that of the Fw190A8's speed in the A8's handbook you own, and which you sent me (which btw, I still own you a beer for it...someday :))
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Verm, very very true, however, I don't think he remembers wrong about water-methanol as it was what brought them up to speed once again.
One more thing, he said it was introduced quickly after the spit 9 entered service, thus being late 42/early 43 sometime. Might have been his + a few other planes only though.
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Ram,
That chart says the A5 could do 655 km/h (407 mph). It would do 416 if there was no such thing as compressibility. How much slower is the AH model?
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Originally posted by wells
Ram,
That chart says the A5 could do 655 km/h (407 mph). It would do 416 if there was no such thing as compressibility. How much slower is the AH model?
1 to 2 mph at the best altitude. I checked it the other day, Fw190A5 makes less than 407mph@21500feet. Nothing like 416mph.
[edit] ran the test again, 407mph exactly at 21500feet. Film at http://212.73.32.211/hosting/0003d/ebringas/a5speed.ahf
USAAF tests said FW190A5 did how much?. 416mph at optimal altitude (being it 21000 feet or something like that)?. No way it's that fast at AH. You can see it in the film.
Luftwaffe charts says FW190A5 hits how much?. 350mph on the deck (in fact 565km/h=351mph). No way it's that fast at AH, where it does 335mph.
[edit 2] I repeat that when I say that Fw190A5 is too slow, I'm talking about LOW ALTITUDES ONLY. Please, wells, compare the deck-to-10K feet speed on the chart, and compare with AH's performance. You'll see what I mean. Fw190A5 should be as fast as a fw190A8 on the deck -in fact, 1mph faster-, but it just hits 335mph (barely).
We have a Fw190A5 too slow according to USAAF data at high altitudes
we have a Fw190A5 too slow according to Luftwaffe data at low altitudes.
I've been repeating it for months.
Need more proof?. Well, I just can't find more, because I found all evidence possible.
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ya sure it's just an even 416? I hate to ya get ripped off that extra 3/10 ths :p
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Hey intrepid, Fw190A5 is in fact 1mph SLOWER than what it should be at proper altitude (I don't care about it), and between 10-15mph slower than what it should be at low altitudes (I DO care about it).
Proof is in chart and in film.
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The rightmost curve says 352 mph on the deck for Fw 190A-5. It is A LOT slower in the game.
Can anyone translate what is written in the chart ?
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Originally posted by RRAM
Hey intrepid, Fw190A5 is in fact 1mph SLOWER than what it should be at proper altitude (I don't care about it), and between 10-15mph slower than what it should be at low altitudes (I DO care about it).
Proof is in chart and in film.
Was it a brand new AH 190, or had it seen a few hours?
How many hours did the engine have, and how many till its next check? What kind of fuel did you use and how well refined was it? How many hours did the airframe have again? What was the weather like when you tested (then again it'd be in the film wouldn't it). Did you use the AH FW test aircraft, or a front line issue aircraft? A prototype? The USAAF test aircraft? Was it armed?
Tronsky
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"Lord Dolf Vader, definitive proof of what??? That there is a physical difference between the handling of a D9 and a A8? Ummm guess what. There SHOULD be a difference. You have the same wing, but a different CG plus a different moment arm about which the elevator works, in other words the distance from the aerodynamic chord of the wing to the elevator is different. This will cause a different pitching moment. I'm admittedly no expert in aerodynamics or the modeling of aircraft, and I may have used a term incorrectly in this description, but I've learned alot lately on the subject. Now, is what we have in AH correct? I don't know. And no one has presented information to suggest that the D9 is wrong, just that its different from the A8. Which is correct. "
the thread was "190A vs 190D" ill bump it cause reading it made me wonder why they didnt answer at all . physics is a pure science. who has the phisics degree at htc again ?
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Originally posted by -tronski-
Was it a brand new AH 190, or had it seen a few hours?
How many hours did the engine have, and how many till its next check? What kind of fuel did you use and how well refined was it? How many hours did the airframe have again? What was the weather like when you tested (then again it'd be in the film wouldn't it). Did you use the AH FW test aircraft, or a front line issue aircraft? A prototype? The USAAF test aircraft? Was it armed?
Tronsky
You're joking, right ?
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who has the phisics degree at htc again ?
you don't need a physics degree to understand physics.
LDV, you do nothing to help your cause. You just become a mildly annoying buzzing sound that gives other LW fans a bad name.
Feel free to engage in friendly discussions of the relative performances of different aircraft, but realize that HTC does not have any generic malice towards the LW planes they create.
F.
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Originally posted by Hristo
You're joking, right ?
Obviously
Tronsky
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I missunderstood it the first time tho. sorry ;)
But the question of deck speed for AH Fw 190A-5 vs its real life counterpart is still open !
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The "190A vs 190D" thread was based on a serie of online tests in DA between these planes and some others. Acceleration (at lo level), roll rate, and elevator authority were all tested for these planes.
The result was that A series roll noticeabily better than D9 at any speed, they also have much better elevator authority at hi speeds. Typhoon and SpitIX surpassed all of them (A and D) by a very wide margin in elevator control at hi speed. Nor typh neither spit needed trim adjustements to exit a 8k vertical dive. In that dive, repeated several times, D9, La7 and G10 kept augerin in the sea over and over. Anther tested factor was the sensibility to trims, all 190s demostrated to be very sensible to trim adjustments while, in real world, they only needed a +-5 degree elevator trim control.
As a matter of fact, these tests derived in two threads, "190A vs 190D" and "190D elev auth".
There was no demostration justifying the advantage in roll rate of A series over D9, nor about the lack of elevator control above 350mph.
And yes, HTC kept radio silence.
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Tried the 190A-8 in il2 ? ;)
Is a blast !
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Originally posted by Hristo
The rightmost curve says 352 mph on the deck for Fw 190A-5. It is A LOT slower in the game.
Can anyone translate what is written in the chart ?
The written text in the charts are explanations and formulas to translate the incorrect speed readings (because instrumental error) at different altitudes, to correct ones. That's why each curve is split in two, the rightmost one is the "instrumental reading", the left one is the true corrected airspeed.
BTW, this is something I dont know if it is done in AH, in other planes. We might have a Fw190A5 making 407mph@21500 and not 416mph for that reason, but what about the rest of the planes?. Have all of them speeds compensated for instrumental error or is just the Fw190A5 the only plane in AH which takes that in account?.
Anyway, question remains: FW190A5 should run at 351mph@SL. It does 335mph@SL. 16mph is A LOT.
Will it get fixed?.
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I really hope so Ram, I really really hope so...
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So, if I got it right - the graph consists of 3 pairs of 2. Each pair has right curve as instrumental reading and left curve is corrected to TAS ?
So, each pair converges at the deck, where there is no correction.
OK, bring 352mph deck speed for Fw 190A-5 to AH !
To be honest, this thing alone would make the A-5 ride of choice among many FW types.
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"Tried the 190A-8 in il2 ? "
yea i have and it amazes me how different it and all the other aircraft are in il-2 compaired to ah.
best comparison i can give is il2 is to ah as wb was to aw. as far as flight model.
and german planes dont suck.
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I did some quick aerodynamic calculations based on some of the above data. Here's what I found:
Assuming 407mph is the top end A-5 speed at 21K ft:
(1) Quick estimation of drag=thrust assuming .80 prop efficiency and 1800 engine BHP:
If top end speed @ SL= 335mph, drag = 1611 lbs
If top end speed @ SL= 351mph, drag = 1538 lbs
If top end speed @ 21k= 407mph, drag = 1326 lbs
(2) Using the above drag estimations, approximations for CD0 are:
CD0= .026 at 335mph SL
CD0= .023 at 351mph SL
CD0= .027 at 407mph 21k ft
(3) Assuming CD0=.023 is the correct form drag coefficient, I did a calculation of what the expected max level airspeed should be at 21k ft. Assuming 1326 lbs of drag at 21K ft (from original assumption that 407mph as the topend speed at 21k and the said engine data) and using CD0=.023, the max level speed would be a whopping 451 mph.
CONCLUSIONS:
The first observation is that a 351mph max level speed at sea level is suspect since it is out of line with the CD0 of .027 assuming and that a max level speed at sea level of 335mph is much closer in line aerodynamically. CD0 should remain fairly constant. Clearly the CD0 for 335mph SL ~ CD0 at 407mph 21k where as CD0 at 351mph SL is lower than expected given the thrust and drag assumptions.
The 2nd observation is that if CD0=.023 then the max speed at 21k feet should be much higher than 407mph and closer to 451mph given the thrust and drag assumptions.
Based on some of the math I would have to say the 351mph SL max level speed doesn't make aerodynamic sense if the max level speed at 21K is 407mph.
Please feel free to check my math.
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
The 2nd observation is that if CD0=.023 then the max speed at 21k feet should be much higher than 407mph and closer to 451mph given the thrust and drag assumptions.
Well, if the engine was delivering same power at SL than at 21.5k feet I won't say a word, Dtango... but you know, BMW801D-2 was powerful as hell at SL, but it lost most of its power at medium to high altitudes. I don't see you taking this into account in your calculations.
BTW, and just as another example,even more dramatic, to show you're wrong:
La7 makes 380mph@SL. It tops out 405mph@20k
Power outputs change drastically with altitudes. Sorry but your math may be correct but is not appliable as long as you don't take engine power output variations with altitude in account.
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Thats true. I believe that takeoff power was at 1700HP and at 18,700 feet 1440HP.
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nope ,senna, according to a performance chart I have, is more like 1775hp@SL and 1425hp@20000 feet
[edited, link was incorrectly written]
(http://212.73.32.211/hosting/0003d/ebringas/bmw.gif)
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RRAM, I was listing the numbers I found in one of my books. The figures are pretty similar taking into account the slide. I dont think the book was quoting SL hp, more so around 3 and 4k ground level. Also if you take 18,700ft into mind, it shows about 1440 hp.
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Yup, senna I was pointing at the SL power being higher than 1700hp rather than to the 18k one wich I already thought was correct :).
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RRAM:
Thanks for the data on the alt variation on BHP. Here's some recalcs based on the Engine BHP figures you provided. Again bear in mind that these are approximations.
(1) Drag = Thrust approximations
@ SL with BHP 1775, .8 Prop Eff..
If max level speed = 335 mph, D= 1590 lbs
If max level speed = 351 mph, D= 1517 lbs
@21K with BHP 1425, .8 prop eff...
if max level speed = 407 mph, D= 1050 lbs
(2) Parasite Drag Coefficient Approximations
Using the above estimates:
SL max level speed 335 mph, CD0=.026
SL max level speed 351 mph, CD0=.022
21k max level speed 407 mph, CD0=.021
[EDIT: just to be clear, Di was factored in and I applied the CD = CDi + CD0 equation to derive CD0]
(3) Expected Max Speed at 21k using CD0=.022
Assuming 1050 lbs drag, max level speed at 21k = 406mph
(4) Expected Max Speed at 21k using CD0=.026
Assuming 1050 lbs drag, max level speed at 21k = 379mph
CONCLUSION:
Very interesting indeed. First it would appear with the modified BHP #'s that CD0~.021, .022 is more accurate. 2nd with a CD0=.022, the resulting max level speed at 21k gets you the appropriate max level speed of 406 mph.
You guys asking for an increase of the A-5's speed to 351 mph at sea level may be on to something here. The approximations based on the engine data assumptions, resulting drag, and max level speed at 21k estimates appear to be in line with what you are indicating.
Of course I'm missing details such as thrust calculations aren't as straightforward as the T = BHP*PE * 550 / V that I was using nor are PE figures constant. However if the gets us with 85% of an accurate approximation then something may be amiss.
Pyro, HT- any comment?
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
Pyro, HT- any comment?
Frustrating, eh ?
WTG on the calcs tho !
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Me frustrated at Pyro or HT? Nah. I just tried to do a sanity check. It's one thing to have numbers. As EddieK mentioned earlier you have to take the next step to see if the numbers line up with the physics.
My sanity check of the physics could be way off. HTC does their homework pretty rigorously and I'm wondering more if I am missing something here. I'll leave it to others who are knowledgeable to take a stab at it. As far as I can tell though using the engine BHP figures that RRAM provided there might be reason to make a change in the SL speed of the A-5. This assumes that RRAM's data is very close to what HTC is using for their flight models.
Tango, XO
412th FS Braunco Mustangs
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dtango,
A very nice series of posts. No bias, redid your calcs, and friendly.
Refreshing.
F.
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Where's the damn antagonism, I miss it ;)
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Excellent calculations, Dtango. Thanks for doing them again taking the lower engine output at 21K into account.
:)
Well...once again: Proof's here (charts and film)...I now just hope they now live up to their promise (to look into the issue when proof is presented) and change the Fw190A5's speed curve in Aces High to the one in the speed chart. :)
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Yup, it would be an exciting feature in AH. To me it would overshadow any Pac plane addition ;).
Can't wait...
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I would rather see the 190A5 speed fixed then new planes added as well. SO i second that motion.
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Originally posted by Sachs
I would rather see the 190A5 speed fixed then new planes added as well. SO i second that motion.
You get nothing.
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Someone get Hernán Cortés here !! ;)
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Hristo, Cortés read my advice in the zuma's footer, he has better things to do ;)
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I don't know what he said...ignore list is SO useful! ;)
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Indeed it is Ram :)
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I think you luftwhiners are on Pyro's ignore list :)
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Up again for Pyro, or someone at HTC to say something :)
Also, please don't forget to look at the rollrate chart posted in this thread (http://www.hitechcreations.com/forums/showthread.php?s=&threadid=56342) :)
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Hi Dtango,
>As far as I can tell though using the engine BHP figures that RRAM provided there might be reason to make a change in the SL speed of the A-5. This assumes that RRAM's data is very close to what HTC is using for their flight models.
Have a look at the exhaust thrust: At sea level, the BMW801D provides 1740 PS in high speed flight, and another 75 kp of direct exhaust thrust. At 21000 ft, it's 1445 PS plus 110 kp of direct thrust.
Regards,
Henning (HoHun)
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Thanks Henning. I saw the exhaust thrust on RRAM's charts but didn't think it would factor in that much. Here is the analysis one more time - factoring in ~150 lbs exhaust thrust at SL and ~250 lbs exhaust thrust at 21K.
(1) Drag = Thrust approximations
@ SL with BHP 1775, .8 Prop Eff., exhaust thrust ~ 150 lbs
If max level speed = 335 mph, D= 1740 lbs
If max level speed = 351 mph, D= 1667 lbs
@21K with BHP 1425, .8 prop eff., exhaust thrust ~ 250 lbs
if max level speed = 407 mph, D= 1300 lbs
(2) Parasite Drag Coefficient Approximations
Using the above estimates:
SL max level speed 335 mph, CD0=.028
SL max level speed 351 mph, CD0=.025
21k max level speed 407 mph, CD0=.027
[EDIT: just to be clear, Di was factored in and I applied the CD = CDi + CD0 equation to derive CD0]
(3) Expected Max Speed at 21k using CD0=.025
Assuming 1300 lbs drag, max level speed at 21k = 431mph
(4) Expected Max Speed at 21k using CD0=.028
Assuming 1300 lbs drag, max level speed at 21k = 407mph
CONCLUSION:
Exhaust thrust makes an impact. Looking at the physics CD0 ~ .027-.028 seems to be in line while the CD0~ .025 is not. The math here says that if the SL topspeed of the A-5 is 351mph, then the expected 21k topspeed should be 431mph.
Fellas looking to change the SL speed of the A-5, sorry for leading you guys on. I should have factored in the exhaust thrust. It looks like HTC has done their homework as usual. Like I said, I was more concerned that I was missing something. I should know better since I've asked others to remember to factor such things in as exhaust thrust into the equation.
This was a good exercise however. I didn't have the BMW801D charts and what I hope this serves as notice for others that you can't forget to factor in (a) alt impact on engine performance, and (b) other not so obvious variables such as exhaust thrust.
Tango, XO
412th FS Braunco Mustangs
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@dtango: Were did you get your propeller efficiency from? Or is it just a guess?
And a question about thrust:
thrust = engine output x prop efficiency
this should be roughly right, right?
And if this is so, can you calculate speed with thrust data without the incertainty of prop efficiency included in the calculation?
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Naudet:
Keep in mind the calculations are all approximations. Let me just say that anything having to do with thrust calculations can be incredibly difficult.
Were did you get your propeller efficiency from? Or is it just a guess?
Prop efficiency ~.80-.85 is about the best that any prop is going to get and is a common "standard" factor to use for approximations. If you wanted to be exact prop eff. varies based on a lot of variables. Constant speed props enables maximum prop efficiency across varying velocities. For my calcs, I'm assuming that at the highest velocity for the A-5 the prop is still at max efficiency.
thrust = engine output x prop efficiency
Actually thrust = engine output x prop eff / velocity
Thrust can be an incredibly difficult value to calculate. I'm using a simplified equation based on the above:
Thrust = ((Engine BHP * prop. eff. * 550) / velocity) + exhaust thrust
I'm assuming it is safe to use this equation for this case since:
(a) I'm approximating,
(b) we are analyzing at a specific point - max level-speed at some assumed max Engine BHP that we can see on BMW801D charts
(c) the velocity of the aircraft is a given and,
(d) we are analyzing a level-flight situation
Tango, XO
412th FS Braunco Mustangs
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Dtango, just one question. (since I am in wayy over my head when it comes to calculations like this)
What would the result be if you calculated with a speed of 416mph at 21k instead of the 407 mph figure you have used.
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Hi Naudet,
>And if this is so, can you calculate speed with thrust data without the incertainty of prop efficiency included in the calculation?
While we're at it, have a look at
http://jagdhund.homestead.com/DoraCharts.html
and specificially
http://server3003.freeyellow.com/jagdhund/FW190D-9/D9speedWeb_01.jpg
That's a newly posted chart that shows a speed of 611 km/h for the Fw 190D-9 using 1925 HP ("Schwebeleistungen im Schnellflug").
Regards,
Henning (HoHun)
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Hortlund:
What would the result be if you calculated with a speed of 416mph at 21k instead of the 407 mph figure you have used.
I'm at work and don't have access to my spreadsheets that I have set up to run the calculations so I can't easily run the calcs for CD0. However I can easily do some other calcs.
If top max-level speed = 416 MPH at 21K, then with a CD0=.025 (351mph SL max speed) the expected top speed at 21K would be 445mph vs. the 431mph.
For CD0=.028 (335 mph SL max speed) the expected top speed at 21K would be 420mph.
Just by rough comparison this still demonstrates that CD0~ .027-.028 which again points out that CD0~.025 does not meet the physics sanity check.
There are other questions/replies posed from the "other" thread that I would like to address. I'm at work and heading off into another meeting (this one 4 hours long) so give me some time and I'll respond to them when I get home.
Tango, XO
412th FS Braunco Mustangs
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What would the result be if you calculated with a speed of 416mph at 21k instead of the 407 mph figure you have used.
I've run the calcs. I goofed a little on trying to make the "easy" calcs in the post above. (I used the CD0 values and not CD). I tried to rush the calcs and missed a detail :). At any rate if the max speed at 21K was 416 mph (vs. 407 mph) then we find the following:
(1)@21K drag=thrust approximation:
D=1277 lbs (vs. 1300 lbs)
(2)Form Drag Coefficient:
@ 21k and 416mph topspeed, CD0 = .0263
(3)If SL topspeed = 351mph, @21K = 438 mph (vs. 431 mph)
(4)If SL topspeed = 335mph, @21 = 410 mph (vs. 407 mph)
So if we assumed 416 mph was the top speed at 21k, it really doesn't change the complexion much.
At any rate the 407mph is what RRAM's chart shows vs. 416mph factored in for compressibility as already previously noted by others.
Mr Ripley:
What's striking is that now Dtango's calculations based on guesses outrun the factory speed chart presented..
I can't see the logic there..
How does Dtango's exhaust thrust impact the original chart presented? One player presents a calculation estimate of flight performance that overruns the original chart?
I'm sorry you missed the logic. An aircrafts top-end level speed is mostly determined by form drag of the aircraft which is roughly constant for a given airframe. I'm using this aerodynamic fact to do a check against the factory speed chart. The calculations show that the form drag based on the charts have significant variance. This doesn't equate aerodynamically because form drag should remain roughly constant. If the speed at SL is 351mph like it says on the chart then based on the form drag the speed at 21K should be 431mph not 407mph as it indicates on the chart.
Hortlund:
And he is saying he is using approximations, surely that must have some effect on the calculations? I really know too little about this stuff, but I find it very hard to believe that the factory charts are so wrong.
The "approximations" I'm using are accepted common aerodynamic methods used for performance analysis. I warn that they are approximations in the since that they are not to the 99.99% precision and not what you would use for basing flight models off of. I would be surprised if they aren't in the 90-95% accuracy range though.
Are the factory numbers wrong? I can't say for sure. However I'm trying to point out that if you're going to base flight models on physics then the physics has to equate. In this case we find that the chart has a discrepancy vs. the physics. We've already corrected for alt. variations on engine output as well as exhaust thrust. I'm at a loss to explain the discrepancy. The other possible explanation could be prop. efficiency. If prop eff. ~.66 at 407mph then you could end up with what the charts indicate. This doesn't make sense however since we are talking about a constant speed prop and you would expect a much higher efficiency. I'll see if I can double check this.
Tango, XO
412th FS Braunco Mustangs
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@Henning: I know that calculations, as i own a hardcopy of that report (about 10 pages).
But as i have no clue of any flight performance calculations, i don't have any idea what those terms and facts mean.
can you explain me what the following are and what they mean?
Ca
Cwg*F
∆fs
Cwg/Ca
Va (i guess that is speed, and as all other speeds are given in TAS and have the index "w" i guess "a" stands for IAS)
and the last term i can really identify, looks like
Ns* did not work, but it said: Wurzel aus gamma durch gamma 0
would really help if i got a definition for em.
If possible in german so i get it all. :)
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Hi Naudet,
Ca: Auftriebsbeiwert = Cl: lift coeffecient
Cwg*F: Widerstandsbeiwert * Stirnfläche = Cd * A: Drag coefficient * frontal area
Delta Fs: Zusätzliche Stirnfläche bei erhöhten Anstellwinkel = additional frontal area at increased angle of attack
Cwg/Ca: Verhältnis von Widerstand zu Auftrieb = Cd/Cl drag to lift ratio
Va: Angezeigte Fahrt = indicated airspeed
Vw: Wahre Fahrt = true air speed
>and the last term i can really identify
That's power corrected for air density so that it applies to sea level.
Regards,
Henning (HoHun)
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Thanks alot.
Does that now mean that damned D9 flew at a mighty 611 km/h (~380 mph) with 1925PS at SL?
Cause i see no altitude given in the calculations.
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Hi Naudet,
>Does that now mean that damned D9 flew at a mighty 611 km/h (~380 mph) with 1925PS at SL?
Yes.
>Cause i see no altitude given in the calculations.
The calculations describe an equilibrium between weight and lift ("Schwebeflug") independend of altitude. You can see that as "Va" is stated, not "Vw". To find out the top speed of the D-9 for any altitude and any power, you just plug in the actual power value, select the corresponding line in the table, find the indicated air speed and transform it to true air speed. If you plug in 1925 PS @ 0 km, IAS equals TAS, so you get 611 km/h TAS.
Regards,
Henning (HoHun)
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OK, just to get it right:
Lets say i know the D9 engine would give 653 PS @ 7,5 km (to all folks, thats JUST an example), to get the speed, it would look along the 653 PS line, take the 402 km/h IAS, convert it to TAS and would have the max possible speed for the D9 with 653PS at 7,5 km?
right?
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Hi Naudet,
>right?
At least that's the way I understood that data sheet :-)
It does not contain complete calculations, though, but just certain data points that were considered important for future reference, so it's hard to decode.
Regards,
Henning (HoHun)
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Yes, as far as i understand this report, its presents just the results.
And only very important "corner" data is given.
Would be really cool to have the whole calculation step by step.