1941: the best airframe for a single engined fighter

[Vincenzo]

drgodong i tried to understand your formulas in 138th post in this thread (so for do calculation for others fighters). but i've a data problem the wetted area, there are some on line sources for this data?
and a logical trouble the thrust formula .85*Powerhp*550/(speedmph*1.467) following this more a plane is slow and more has thrust, this is right?
my physics study are too far in the time and limited (only first 2 years of high school) for help me

 

[CobberKane]

b

 

[drgondog]

drgodong i tried to understand your formulas in 138th post in this thread (so for do calculation for others fighters). but i've a data problem the wetted area, there are some on line sources for this data?
and a logical trouble the thrust formula .85*Powerhp*550/(speedmph*1.467) following this more a plane is slow and more has thrust, this is right?
my physics study are too far in the time and limited (only first 2 years of high school) for help me

Vincenzo - a couple of years ago I put the Lednicer VSAERO computer simulations on this site and I believe Tomo found them and presented the wetted area from the near last page of the report. Lednicer developed all the lines and airfoils from the actual data from NAA Drawings and consultation with the key aerodynamicist (having a senior moement - can't recall his name - not Schmeud). Go back to ~ page 8 of this forum but also go the Mustang Data section in the forum archives.

And yes, the Thrust does increase as V decreases, as counter intuitive as it seems, but be careful about accepting the equation unless you carefully examine propeller performance ..

 

[CobberKane]

Hello Cobberkane and welcome

I applaud your intent to try and get some air under the wings of this debate, and i am not about to embark on a tirade to denigrate any of the three aircraft that you selected. All three in their own right were truly great aircraft that contributed very greatly to the course of the war. but whilst I agree with the laudable objectives, I think in delivery your post falls at the starting gun.

Why do you think the Mustang comes in behind the other two? You raise three main points in your post which I comment on as follows



The 109 was cheaper to build but not by much, and it suffered a much higher attrition rate to the Mustang, and a lower serviceability compared to the Mustang. Mustangs suffered about 18% attrition rates per month to all causes from mid-1943 to the end of the war, compared to about 37% per month for 109s based in Germany in that same period, and close or above 50% outside of Germany (mostly Eastern Europe) which went up or down depending on the season. There were many extraneous reasons for that, but your statement was a blanket "its cheaper to run a 109 unit than a Mustang unit"....not true, whatever the reason, the Germans had far higher wastage of aircraft, and therefore far higher costs to maintain a given unit equipped with a 109 over a Mustang.



This is a highly subjective statement, and has the potential to attract endless argument and counterrargument. I obviously dont agree with the implication present in your comment....."the Mustang had a lower historical contribution to the war than either the 109 or the Hurricane". if that is your opinion, I disagree pretty strongly. All three made major contributions, but of the three, it was the mustang that made the most, followed closely by the hurricane. The only reason the hurri is of lesser importance than the P-51 is because it did not have a big role in the Pacific, whereas the P-51 did.

For reasons not entirely related to the aircraft, it was the Mustang that forced the wholesale redeployment of German fighter assets back to germany, leaving their frontline armies under protected. The 109 equipped fighter units of the LW, along with all other fighters, were unable to stem the carnage being meted out on Germany, and lost in the order of 5 or 6 fighters for every fighter they shot down. There were many reasons of which those that relate to the actual aircraft themselves are relativbely minor, but you did not qualify your statement in that way.
I would argue that of the three types, the Mustang had the greatest impact on the outcome of the war ( in all TOs and in all the roles it was used for)



Without a doubt, the 109 has this part of the market cornered, yet the numbers I have seen take a withering beating when you look at the figures closely. on the eastern front, some in this place have tried to claim that the 109 was responsible for shooting down at least 25000 IL-2s. Wrong. A closer estimate is about 1500-3000 1943-5, with about as many again prior to that. A high kill ratio, to be sure, but a drop in the ocean compared to what the russians were able to put in the air overall, and gained at a pretty hefty price in lost machines overall. The 109 was the most prolofic shooter of the war....it was also at least one of the most prolific losers of the war.......thats the problem with fighters.....to shoot aircraft down, you lose a whole bunch more the moment you take to the air whatever your inherent advantages. As the Germans found out to their cost, fighters dont win wars, they may reduce your losses, but they cant win wars, and when your opposition can swamp your defences, all you are doing by putting your fighters up is increasing their costs whilst also increasing your own. Fighters can plow the ground for your bombers, they can increase the losses for your opponent, but they cannot except in exceptional circumstances in you air superiority or air supremacy, and thats what was needed to win wars.

Okay, I'll admit it - I was being a little tongue in cheek. My intention was to give the 109, P51 and Hurricane a draw in the first two gatagories (ease of construction, historical contribution) but rate the Mustang third in air to air kills, which I think is historically correct. My point being that the outcome of the comparison depends on the criteria we use - how else could you assert that the Hurricane had a 'better' airframe than the Mustang, an aircraft a generation more advanced?
I don't think I asserted that the Hurricane's historical contribution was better than the Mustangs, but now you mention it i think i could make a case for it. The Hurricane won the Battle of Britain for the RAF. Without the Hurricane, Operation Sealion probably would hace gone ahead. With the UK off the board Barbarossa probably would have succeeded - game over. Everything you say about the Mustang is true, but it wouldn't have been in any position to make the contribution it did without the preceeding heroics of the Hawker Hurricane.

 

[CobberKane]

Why?
Personally, I find it very interesting.
You get to understand drives behind particular construction decisions and their consequences on the flight behavior, etc...well, if you're interested in that kind of stuff.

Yeah, yeah - I know....It's just that sometimes I think you could start a thread on Jessica Alba's undies and three posts later we's all be talking about P-51s! I am reminded of CS Lewis' criticism of Tolkein - "Oh God, not another elf!"
Maybe I just need to get out more.

 

[parsifal]

Yeah, yeah - I know....It's just that sometimes I think you could start a thread on Jessica Alba's undies and three posts later we's all be talking about P-51s! I am reminded of CS Lewis' criticism of Tolkein - "Oh God, not another elf!"
Maybe I just need to get out more.

I promise if you start a thrread on her underwear, I will not mention P-51 even once

 

[CobberKane]

I promise if you start a thrread on her underwear, I will not mention P-51 even once

Okay, but this is probably going to get me banned...

 

[parsifal]

what were we talking about? i forget.....

 

[Vincenzo]

Vincenzo - a couple of years ago I put the Lednicer VSAERO computer simulations on this site and I believe Tomo found them and presented the wetted area from the near last page of the report. Lednicer developed all the lines and airfoils from the actual data from NAA Drawings and consultation with the key aerodynamicist (having a senior moement - can't recall his name - not Schmeud). Go back to ~ page 8 of this forum but also go the Mustang Data section in the forum archives.

And yes, the Thrust does increase as V decreases, as counter intuitive as it seems, but be careful about accepting the equation unless you carefully examine propeller performance ..

thanks for the clear
i think you missinterpreted my first point i did not trying to check your data i was looking for data (wetted area) for others fighters.

 

[davparlr]

Based on the initial premise,

In other words, this time on we should discuss the capabilities of the airframe, independently from the engine it was mounted on it. What designer/manufacturer got it best? The capabilities to be accounted for are "upgradedeability", structural strength, capacity for decent firepower fuel tankage, suitability for engines different that the original, adaptability to work as bomber and/or reccon plane, pilot protection, ability to lend itself for the mass production etc. The carrier-borne planes yield no points for such capabilities.

I would pick the following airframes based on potential air combat capabilities, growth potential for power, and size adequate for weapons and fuel upgrades.

1. P-51 Overall aircraft efficiency offered performance and size and strength provided combat growth.
2. Fw-190 for similar capabilities
3. F4U. Big and powerful with great potential in many roles.
4. Typhoon (and its follow-on designs, the Tempest and Sea Fury). Had to evolve but seems to be a great design

Even though I rated each, I think one could mix up the numbers and not lose much, if anything, no matter how it turned out.

In my opinion, while outstanding performers, both the Spitfire and Bf-109 were limited by their size to effectively expand to different roles.

 

[drgondog]

thanks for the clear
i think you missinterpreted my first point i did not trying to check your data i was looking for data (wetted area) for others fighters.

Well - he also analyzed the Spit IX and FW190D-9 and presented those full surface areas also. The references for all wetted areas were also presented. The wetted area for the 109G according to Hoerner was 590 sq ft.

As always context is important. In considering friction drag (or profile/form/vortex drag) you have to ask nagging questions like how much of the surface is in the 'Laminar flow' region, versus full blown turbulence - or where on the wing does the boundary layer separate enough that average surface roughness behind the 'datum' for the adverse pressure gradient start?

So both the wing and total areas provide context when looking at total frag versus lift related drag - and we aren't anywhere close to looking at lift of the fusleage/wing combination..

I looked at a lot of Soviet fighter types (Mig 15, 17, 19 21, etc) at Nellis AFB and was amazed at the gaps (some and not consistently in same specifc area) between sheet metal skins, for example, in the regions aft of the wings - an area you could expect a lot of vortex drag and little laminar flow. On purpose? I don't know.

 

[tomo pauk]

I'm not following you here:

and my point was that you can't linearly compare number of barrels and ROF, for 109 and winged installations, in response to tomo's assertion.

 

[tomo pauk]

Hi, David,

The thread covers the 1941, so we should divide the airframes in service from the airframes in prototype phases. So maybe the Fw-190 should be the 1st choice here (it is in service), and along the prototype/pre-series fighters I hold the P-51 in the high regard.
The Typhoon features rather different wings vs. Tempest, a notably different fuselage, so it should be regarded as a separate entry - the late war Hawkers are way out of this thread. Typhoon was unable to provide the RAF with a fighter of greater performance over most altitudes vs Spitfires with two-stage engines (tick wing was flatly a wrong choice), the combat range was found wanting, the tail needed reinforcement. I'd rate Spitfire as a far better airframe.

 

[tomo pauk]

For some reason, the post made at 7:11 is listed the one at 6:11 (post #192), so I'll post again:

I'm not following you here:

and my point was that you can't linearly compare number of barrels and ROF, for 109 and winged installations, in response to tomo's assertion.

 

[Cola]

And speed was recorded at both 1200hp/sea level rating (Military power) and the 1460-1480hp level (WEP) just make sure the manifold pressure is included in the speed listing to be sure which is which.

Good point.
No argument there, since it explains stuff.

"Conserving" the engine, when it may give a military advantage, is just as poor a policy as flagrantly blowing up engines to no purpose.
How many allied planes escaped or German pilots died while "conserving" their engines during this period?

Or it just tells you, that "military edge", as you call it, wasn't needed in relation to price, in observed timeframe.
Again, in reality these things are called contracted lifetimes and are expressed in working hours, at pre-set load.
So, the goal of manufacturer is to produce contracted number of HP over a pre-set lifetime.
Obviously, the engine can give significantly more power, but at the expense of lift time and maintenance.
Now, I won't speculate on Luftwaffe's decision to limit the engine performance, but we do have evidence that it was available as early as in '41 (as per links I've provided), so you're free to assume OKL was a bunch of irresponsible cowboys, but I'm more inclined to think, they didn't really need it at that time.
Ofc, I got no proof for either, but anyone that ever served any kind of army, will tell you pretty much the same thing.

The "body of evidence?" ROFLMAO

Now, this is pretty immature response, because you're ROFLMAOing at Mr.Christopher Chant and he gets payed for what he writes. You?
He may be wrong though and I can agree that such a configuration was comparatively rare, but even so 109G's standard battery was deadly for a fighter sized aircraft, due position and construction and my point was that you can't linearly compare number of barrels and ROF, for 109 and winged installations, in response to tomo's assertion.
If you have objections on that...let's have them.

Got one shred of proof (like a photo) that the K-4 EVER carried the guns you list into the air? Or even had them fitted in a firing trial on the ground?

No, but neither have you for the contrary and I'm more inclined to believe official publications, than forum myths.

@drgondog,

None of the above. I thought I presented Induced Drag of both the 109 and 51 earlier.

No idea, what you think you showed, but this is how this works in real world...(no IIRCs or assumptions):

Aircraft:

Mustang P-51A*
3084 kg - airframe
300 kg - fuel
100 kg - pilot
OW = 3484 kg

Bf109F-4*
2391 kg - airframe
300 kg - fuel
100 kg - pilot
OW = 2791 kg

(*I'm ignoring ammo, oil and other expendables due time/research constrains)


Flight conditions:
crusing speed: 500 km/h TAS (139m/s)
dynamic pressure: 11.78 kPa ISA
Altitude: deck (static pressure 101 kPa ISA)

Coefficient of lift:
Cl (P51A) = 0.134
Cl (109F4) = 0.144
(if you got Cl/alpha charts, you can figure alphas)

Induced drag coefficient:
Cdi (P51A) = 0.00097e^-1
Cdi (109F4) = 0.001e^-1

Induced drag:
Di (P51A) = 247e^-1 N
Di (109F4) = 190e^-1 N

Note, I expressed induced drag in a function of Oswald number.
Also, I gave Mustang 300 kg of fuel, out of 500kg (nominal internal capacity) only, while 109F4 got full internal tanks and if you wanna calculate both planes in loaded clean configuration (couldn't find reliable and verifiable data for P51A), you'll get in the 40+% neighborhood difference in induced drag.
Do you really need calculations to figure this out?

Now, as for the formula for power as basis for the rest of your story I already made a comment on prop's thrust lapse.
So, the assumption that 51's airframe is less draggy by "this" much, than 109's, while ignoring the 109 might have more draggy propeller, is well, another assumption.

Finally, the CG position isn't really an aerodynamic property.
In an airframe with constant aerodynamics features, CG point will shift as the expendables get spent (fuel/ammo/whatever) and your trim (drag) will change correspondingly.
So, the same airframe with same power has different top speeds without changing power or aerodynamic features for different trim settings and this is particularly pronounced at top speeds.
Hope, we're on the same page now.

Cheers

 

[drgondog]

@drgondog,

No idea, what you think you showed, but this is how this works in real world...(no IIRCs or assumptions):

The real world I lived in included undergrad and graduate school as well as Lockheed and Bell. We collectively did Ok using the theory extracted from the academic world and it was consistently applied as I applied it for you for subsonic aeordynamics for reciprocating engine aircraft.

Also in both the 'real world' and academic world we presented the 'problem to be solved', the 'given's and the solotion approach step by step for a.) ease of checking assumptions and .b) for checking the math. Whether you are a sage warrior of the real worl or not, nothing in the dissertation below would meet the hard eyed scrutiny of a design chief looking for evidence that you know what you are talking about

As you disdain such mundane methods, why don't give unenlightened cretins such as myself the the background of your brilliance and academic rigor, and perhaps drop a few pearls regarding your experience in preliminary design, or aero structures, or flight mechanics so that we may bask in your bright and shining light?

Aircraft:

Mustang P-51A*
3084 kg - airframe
300 kg - fuel
100 kg - pilot
OW = 3484 kg

Report number, aircraft preparation steps, Gross weight at take off, tables referencing TAS, Assumed Hp, throttel position, Rpm/ manifold pressure, altitude, any anomalies experienced during the test, etc.

Bf109F-4*
2391 kg - airframe
300 kg - fuel
100 kg - pilot
OW = 2791 kg

(*I'm ignoring ammo, oil and other expendables due time/research constrains)

Same as above - except if you are using the November 1941 LW Test results - you don't have to research, it's there. BTW it doesn't really matter what the ammo load was or wasn't - only the Gross Weight at take off is all you need to proceed to the next step of necessary 'Given's'- but you knew that from your real world, didn't you?

Flight conditions:
crusing speed: 500 km/h TAS (139m/s)
dynamic pressure: 11.78 kPa ISA
Altitude: deck (static pressure 101 kPa ISA)

Hp for the specified cruising speed? Throttle setting. You need that to get to thrust. You need thrust to quantify total drag in the Free Body equation for equilibrium. What efficiency did you arrive at? Can you show us how you derived the Propeller/Engine efficency? What assumptions did you use for developing 'eta' for the Thrust equation? for either ship? Why?

What assumptions did you use for extracting exhaust thrust? If equation, what variables and why?, If test data, where? Real worl, standard equations with variances depending on the engine. real world, BS?, what? If you wish to complicate, what about relative Meridith effects - what assumptions did you make?

The extraction of CL is not a great exercise but somehow even using your cryptic shorthand and no case develoment you seem to be way off. I could have mangled my own reductions of your metric examples to translate to Ft-pound format. I used .6214 for reduction of K/hr to M/hr and 2.205 for reduction of Kg to pounds

Coefficient of lift:
Cl (P51A) = 0.134
Cl (109F4) = 0.144
(if you got Cl/alpha charts, you can figure alphas) Duh, you can also figure out CDo for the wing if you have a CL/CD plot, etc etc

At SL, for V=500km/hr = at 455.8F/s, at : q= 1/2*rho*V>2, at S= 232 SF for P-51A. S=173.3 SF for 109F-4.

CL (P-51A) = 7682/(q*S) =.1324 (for 235 sf) and .134 (for 232 sf)
CL (109F4) = 6154/(q*S) = .1439-----------> 109 has CL 8.8% greater than P-51A

Assuming I translated km/r to feet/s =500x.6214x1.467 F/s incorrectly, take 'q' out as it is the same in this silly exercise, and just use the proportionsof GW/S -------> P51A=7682.2lbs/235sf=32.68; 109F4=6154lbs/173sf=35.6

The CL of the 109F4 is 8.8% greater than the P-51A for my calc and 7.5% greater for yours. I suspect yours is wrong for the data you have presented?

Induced drag coefficient:
Cdi (P51A) = 0.00097e^-1
Cdi (109F4) = 0.001e^-1
[
Rather than look to various references THE definition for AR is AR=b>2/S. I used Hoerner's generous AR for the 109F-4 but if you stay with the definition.

Ergo AR for the 51D is 37.25>2/235 = 5.90; if you use P51A 37.25>2/232=5.99. Use the Worst Case = lower AR = 5.9.

AR for the 109F4 = 32.23>2/173= 5.99.

Say e=.85 or make a case based on documented wind tunnel results if you believe differently
CDi (P-51A) = .1324>.2/(pi*AR*.85) = .0175/(3.14*5.9*.85) =.00111

CDi (109F) =.1439>2/(3.14*5.99*.85) = .0228/(3.14*5.99*.85) = .00129

The % larger Induced drag Coefficient of the 109 is .00129/.0111 or approximately 16.2% Greater than the 51A at this airspeed. .

Induced drag:
Di (P51A) = 247e^-1 N
Di (109F4) = 190e^-1 N

Nope. Di (51A) = Cdi*q*S = 117.37 pounds
Di (109F) =Cdi*q*S = 101.89 pounds

The net is that the 51 with 232/173.3 ratio of drag area (wing) (34% more) only has 15% more Induced drag to offset thrust than the 109 at that speed - net benefit 180 gallons of internal fuel in its wing over the 109F for very small drag penalty and a much cleaner wing

Note, I expressed induced drag in a function of Oswald number.

Couldn't prove it from your results so far

Expressed maybe in some real world way as yet untranslated to the unwashed industry/academic dolts

Also, I gave Mustang 300 kg of fuel, out of 500kg (nominal internal capacity) only, while 109F4 got full internal tanks and if you wanna calculate both planes in loaded clean configuration (couldn't find reliable and verifiable data for P51A), you'll get in the 40+% neighborhood difference in induced drag.
Do you really need calculations to figure this out?

Lol - do you? Trot out yours and flail away.

Now, as for the formula for power as basis for the rest of your story I already made a comment on prop's thrust lapse.
So, the assumption that 51's airframe is less draggy by "this" much, than 109's, while ignoring the 109 might have more draggy propeller, is well, another assumption.

Cola - your comments have so far been unsubstantiated by any reference to any written discussion on the theory of propellers and the derivation of various efficiencies. You don'y know the relative merits of a 109 prop in their various forms, or any P-51 Prop. You haven't in any way substantiated that you know much of anything relative to the equations of aerodynamics, the equations of Propeller Theory (gathering Power Coefficient and Power Coefficients as function of power applied versus power available), or any structured way of breaking down Drag cmponents in subsonic flow.

You mutter nonsense about 'real world' but we don't know if you live there. maybe I just don't understand the genious that is obviously contained masterfully by you in these debates? If so, I humbly apologice for disturbing the fabric of your tranquil existance - but at any rate I will not respond to the bovine fecal matter comments.

Finally, the CG position isn't really an aerodynamic property.

Duh - we went around that before. It is however a frame of reference about which one may translate all aerodynamic and inertial forces

In an airframe with constant aerodynamics features, CG point will shift as the expendables get spent (fuel/ammo/whatever) and your trim (drag) will change correspondingly.

Duh. I believe this is wy we are all interested in weights and balances Before take off - not after rotation. That may be the reason that aeros are always looking for ways to get the storage of expendables as close to the cg as possible - ya think?

So, the same airframe with same power has different top speeds without changing power or aerodynamic features for different trim settings and this is particularly pronounced at top speeds.
Hope, we're on the same page now.

Cheers

I have the distinct feeling you are looking for pages to be on - but I am eqally sure we 'won't be on the same page'.

 

[drgondog]

P51A had a 5% smaller AR and 10% higher wing loading then 109F4, so the actual amount of drag reduction the Mustang's laminar wing produced in relation to higher alphas flown over almost all speeds, makes your claim very dubious, at best.
It's probably the other way around, but I wouldn't speculate at this point.

For the examples you just set, at 310mph with 51A GW =7682 pound, 109F at 6154 pounds the respective wing loadings were

P-51A = 7682/232 = 33.1, the 109F4 = 6143/173 = 35.6 You did mean that the P-51 had a WL of 95% of the 109 - not 110% as you said above? Or is it possible that WL changes depending on the Mission and point in the mission? Hmm

The AR once again is defined as span>2/wing area.
109F Aspect Ratio is 32.5*32.25/173.3 = ~ 5.99
51/51A Aspect Ratio = 37.25*37.25/232 = ~ 5.98

.

.

Where is the 5% 'extra' for the P-51A? The P-51D AR was 5.9 even that represents only 1.5% difference

 

[drgondog]

Got question to do with the hypothertical though DG. What would be your estimates of Mustang I airframe equipped with one of the earlier merlins? Performance, competiveness, perhaps even likely ranges in RAF service. Im looking for ballpark figures.

RParsifal - If you would pass a decent Hp vs Altitude and Delta weight for a 45 or a XX I could derive some in the ballpark dash speeds at those altitudes of interest.
Regards

 

[Shortround6]

Now, this is pretty immature response, because you're ROFLMAOing at Mr.Christopher Chant and he gets payed for what he writes. You?
He may be wrong though and I can agree that such a configuration was comparatively rare,

Mr.Christopher Chant writes books on a wide variety of military equipment including tanks and ships, and while I have a number of his books myself I don't think he is primarily a researcher.

A Mr. Anthony Williams does disagree with him (author of "Rapid Fire", and co-author of "Flying guns of WW I" , "Flying guns of WW II" and "Flying guns the modern era") see: BOOKS BY ANTHONY G WILLIAMS

Comparatively rare is actually non-existent.

No, but neither have you for the contrary and I'm more inclined to believe official publications, than forum myths.

What official publications?

you want me to prove a negative.

the only way I could prove that NO 109 had such an armament would be to have photos of every 109 airframe with serial numbers. Other wise what ever serial number plane/s is not in the photo collection would be the one/s that had this fictitious armament.

Nobody to date has come up with a photo or even good engineering drawings of such an armament or even a good explanation of how would even fit. There may have been trial installations of the MK103. the MK 151s in cowl are a while other story.

You talk about a body of proof, where is the body of proof concerning this armament?
30 websites all quoting each other or William Green's book from the late 50s do not make up a body of proof.

 

[FLYBOYJ]

Gentlemen, please play nice....