1941: the best airframe for a single engined fighter

Cola said:

@drgondog,
109G-1 - 700km/h - 7km/23k ft - ~1150 hp/AtA1.42
P51B - 679km/h - 7km/23k ft - ~1270 hp (high and low blower)
Now, what?

@tomo,
forget about Merlin.
My mistake since I didn't figure, that 51A flew with some hybrid Allison...normal -81 was rated at 1200hp/SL, according to manufacturer's table.
Funny detail; plane was specially washed prior to flight. Hardly a wartime maintenance standard.

Ain't so.
Luftwaffe had top racers when they needed them.
They didn't bother to go over 700km/h until '43, since they didn't need it and they could hang heavy weapons, at expense of performance.
Most data you got for 109Fs and 109Gs are flown with AtA1.30 and it was '42/'43 (depending on model), when Allied 700+km/h fighters started to arrive in tactically significant numbers, when Luftwaffe lifted AtA1.42, limit.

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Beim-Zeugmeister shows a top speed for the Bf-109G-1 to be 700 km/h, plane being equipped with 2 LMGs, 1 x MG-131 (firing through the prop!) and 2 x MG-151/20 in the wings. So we have the mysterious G-1 with 5 gun's openings achieving 700 km/h. Neither such a high speed figure, nor the 670 km/h for the Bf-109F-4 is to be found in any flight test charts.

The -81 was not a 'hybrid' type. The V-1710 subtypes with 9,60:1 supercharger drive ratio were mounted on P-51A, P-39M/N/Q, P-40M/N, from late 1942/early 1943 on. In 1943 the production/installation of the V-1710s with 8,80:1 ratio was discontinued.

So, 'Luftwaffe lifted the 1,42 ata limit'? If your engine is fit to deliver the declared output, why would you limit that during the major war? Did they just decided that they don't like the limit, or it took Marseille's death to see that the 1942-vintage 605 has issues, limit the engine, work hard to find the culprit, manufacture the needed/better parts, install the de-bugged engines and THEN to lift the limit for the DB-605? The BMW-801s were experiencing the same limitations, both in fighter and bomber installations.

The Bf-109 that was able to fly faster than 700 km/h was the K-4, and that's second half of 1944, not 1943.
added: despite being a fine interceptor, the K-4 still carried far less of armament weight (if it's to fly above 700 km/h) and less than half of the fuel - the usability, an important category of a weapon of war, was far smaller than of the contemporary P-51.

GregP said:

Who protected anyone else when Soren was insulting them?

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You note the similarity too I see

cimmex said:

As an engineer I used to say: Tell me the result you want and I'll find the right calculation to present the proof....
cimmex

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In the US you would be a civil litigation trial attorney. As engineers we still try to run the calcs and let them tell us the result.

In the US the joke is when looking for an accountant ask him how much 2 + 2 is. When you find one that says "what did you have in mind" you know you have found your man

drgondog said:

In the US you would be a civil litigation trial attorney. As engineers we still try to run the calcs and let them tell us the result.

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Except when it comes to cost. All the B-2 managers were sent to take a course in cost estimating computer program which the government was levying on all subcontractors, Price M or something. I remember sitting in the class while the instructor was presenting his explanations and I was busy figuring out how I could manipulate the assumptions to get the number I wanted. I knew better than any machine how much it was going to cost to deliver my product.

Enough about P51s already! I propose that in debating the best airframe (and fighter) of WWII we apply the following yardsticks.

1.Economy of construction and ease of service (okay, the Mustang does look pretty good from this perspective, I admit, but so do the Bf109 and Hawker Hurricane)
2.Historical contribution to the course of the war (Mustang looking even better... as do the other two)
3. Success in air to air combat defined in number of kills

Mustang takes third place behind the Bf109 and Hurricane.

GregP said:

Who protected anyone else when Soren was insulting them?

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We did. We removed the problem...

drgondog,
How do you figure friction and induced drag components?
Using 50%, 30% of total drag, respectively?

and wing area is THE common frame of reference

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I know, but it still doesn't make it right, since you can have Mustang's, or Liberator's fuselage in between...the results will differ.
You can use it when working with wing increments on the same fuselage, to illustrate differences.

as the induced drag increment due to rounded tip versus the 51 tip/chord ratio sets up a reasonaly close spanwise lift distribution, the aspect ratios are close

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Well that's a matter of perspective and it may be reasonably close compared to Mirage III, but makes significant difference between these two models and their respectful performance.
So, as we know Mustang was less draggy at top speeds, we also know that it probably produced more of induced drag, throughout the rest of the speed envelope.
It's a trade off and my original point, regardless of actual amounts of each and you don't measure L/D ratio only on top speed, but along the whole envelope when assessing "airframe efficiency".

Once again - anything at .5-55M during WWII introduces noticable instrumentation errors and there is no mention of algorithms or even attempts to make TAS corrections...

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How's so?
These guys do it..."Anzeige" - IAS, "Wirklich" - TAS
Also, I found on several places, manufacturer/Luftwaffe listing performance on a standard (ISA?) day, so there was some standardization, back then.

only the 'real Hp' delivered is interesting because that is the basis for free body diagram to solve for gross Drag. Yes?

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I agree, but "real Hp" in that case vary with propeller and its net thrust and you can't draw conclusions about aerodynamics from that.
It's like comparing turbojet and turbofan of the same thrust installed on the same airframe and then trying to blame aerodynamics, when turbofan comes second at top speed.
Also, there's a point of trim drag, which isn't a sole property of aerodynamics, but weight distribution as well and is one of the major players at top speeds, too.

As for the critical Mach number, it seems that general consensus is it didn't occur until M.7+, which generally wasn't a problem in level flight and I don't see what does the compressibility has to do with anything...what do you mean?


@tomo,

The -81 was not a 'hybrid' type. The V-1710 subtypes with 9,60:1 supercharger drive ratio were mounted on P-51A...

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Well Allison lists V-1710-81 as a 1200hp/3000 RPM/SL - 1125hp/3000RPM/FL146 and the one from the chart develops almost 1500hp.
Also, in the drgondog's link, there's an item that mentions an experimental carburetor being fitted.

If your engine is fit to deliver the declared output, why would you limit that during the major war?

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To conserve it, a major item in any military of any age.

The Bf-109 that was able to fly faster than 700 km/h was the K-4, and that's second half of 1944, not 1943.
added: despite being a fine interceptor, the K-4 still carried far less of armament weight (if it's to fly above 700 km/h) and less than half of the fuel - the usability, an important category of a weapon of war, was far smaller than of the contemporary P-51.

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Ah ok...but are we making a religion now, or follow the body of evidence?
Now, as for your comment of the weapons...
K-4 had 2x15mm cannons and 1x30mm cannon and not Mk108, but its big brother Mk103.
Also, K-4's cannon battery was fixed in the nose, making it both very precise and accurate (engine used as a recoil absorber and no necessity for rifling convergence), so you don't get to compare it linearly to other, wing armed, planes.

CobberKane said:

Enough about P51s already! I propose that in debating the best airframe (and fighter) of WWII we apply the following yardsticks.

1.Economy of construction and ease of service (okay, the Mustang does look pretty good from this perspective, I admit, but so do the Bf109 and Hawker Hurricane)
2.Historical contribution to the course of the war (Mustang looking even better... as do the other two)
3. Success in air to air combat defined in number of kills

Mustang takes third place behind the Bf109 and Hurricane.

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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

1.Economy of construction and ease of service (okay, the Mustang does look pretty good from this perspective, I admit, but so do the Bf109 and Hawker Hurricane)

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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.

2.Historical contribution to the course of the war (Mustang looking even better... as do the other two)

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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)

3. Success in air to air combat defined in number of kills

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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.

CobberKane said:

Enough about P51s already!

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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.

Cola said:

drgondog,
How do you figure parasite and induced drag components?
Using 50%, 30% of total drag, respectively?

None of the above. I thought I presented Induced Drag of both the 109 and 51 earlier. The formula is to divide Cl squared by AR*e*pi. Parasite drag includes skin friction, surface imperfections (rivet heads, gaps, protuberances ('blisters', antenna, exhaust stacks, gun barrels, radiators, etc). Vortex drag (zero lift level flight) include the wing body effects - generally minimum with mid wing construction, flow separation due to turbulence/boundary layer.

In a design build up from a PD standpoint the first thing you look at is the wing - and say for a 109 you would break it down to look at estimates for the slat gaps, the radiators, the construction of the leading edge and airfoil/wing section for at least 40% of chord as this is the most critical area for friction drag - then you would look at the different components of parasite drag like incomplete wheel covers, radiators, etc so that you have a sense for major drag factors of the wing.

Ditto for tail/eppenage as this is another aeodynamic surface region of importance.

The fuselage is broken down in a similar fashion.

Friction drag has to be looked at as a function of Reynolds number then you look at estimates for Vortex drag at Zero lift for baseline and futz around with AoA related form/profile drag increases due to increasing angle of attack.

For an aircraft like a 109 or 51 that does penetrate .50M you need to think about compressibility. This is a different aspect OTHER and SEPARATE from Critical Mach/Wave Drag which seems to elude you for the moment. Before we dive into this any deeper I gotta ask whether you are a pilot, an engineer/non-aero, or an interested dabbler.


I know, but it still doesn't make it right, since you can have Mustang's, or Liberator's fuselage in between...the results will differ.
You can use it when working with wing increments on the same fuselage, to illustrate differences.

Same question - aero engineer or dabbler? I can use Wing area as a common frame of reference for CD, Cdi, CL because that is the language of aerodynamics and each of the terms have foundation physics behind the equations, and wing area is the foundation for expressing Lift and Induced Drag - whether B-24, Mirage III, 109 or 51.



Well that's a matter of perspective and it may be reasonably close compared to Mirage III, but makes significant difference between these two models and their respectful performance.
So, as we know Mustang was less draggy at top speeds, we also know that it probably produced more of induced drag, throughout the rest of the speed envelope.
It's a trade off and my original point, regardless of actual amounts of each and you don't measure L/D ratio only on top speed, but along the whole envelope when assessing "airframe efficiency".

Cola - you are confusing me. On one hand you know the terms and have a sense of what is going on relative to the forces at work on an aircraft in flight. On the other hand you make statements above that simply aren't true - and further, you could discover the fact based comparisons by understanding the physics and do the calcs.

I showed you the math for Induced Drag and showed the derivation for CL. Two critical factors. Wt/WingArea and dynamic pressure q. for the 109F-4 flight test at SL the W/S = 2900/172 = 37.18 psf, for the P-51 (with two cannon and -39 at 363mph - not polished with 400 grit sandpaper - or washed) W/S = 8100/235= 34.46. Go back and look at the respective 'q'. You will note that the denominator for the 51 CL calc is greater than the F-4. You will note that the numerator (WL) for the 51 is smaller -------------> for these two aircraft at max speed the P51 CL is lower. I am not gonna do the math for you but that relationship holds until way down the timeline for WWII, that relationship holds until the G-10/K4 relative to the 51D - but once again falls behind the P-51H - and it gets worse when the 109 extends slats and raises the CL.

Once you get past the high speed runs you need to look at pre slat deployment for the 109 and compare against the 51 - as long as the two aircraft are in level flight, no slat deployment, the 51 will be operating at lower CL for both traveling at same speed. This is F-4 versus first Production P-51 1942.

As to L/D, it is one 'measure' of aerodynamic efficiency, but in truth L/D is most important when trying to compare relative efficiency of movement in the air - and most important in the drag bucket where Total Drag is at a minimum - not at landing speed (where Induced Drag peaks) and not at top speed (where parasite drag peaks) per se. In that region on the drag polar, parasite drag and induced drag are equal. It is in this region where you toy with Gross Weight and optimal speeds for max range estimates for variable altitudes.

Having said this, another very important Aerodynamic 'efficiency factor' is the ratio of Useful Drag/Total Drag. In the words of Herr Professor Hoerner, Useful is categorized as 'necessary', 'required' or 'unavoidable'. Useful for a 109 would be the induced drag of the wing and by necessity - the wing with all the friction drag it brings. 'Potentially unnecessary' include parasite drag due to slats, parasite drag due to lack of complete wheel covers, drag due to shoddy manufacturing tolerances or rough camo paint, drag of radiators - all creating trade offs

I agree, but "real Hp" in that case vary with propeller and its net thrust and you can't draw conclusions about aerodynamics from that. It's like comparing turbojet and turbofan of the same thrust installed on the same airframe and then trying to blame aerodynamics, when turbofan comes second at top speed.

You shouldn't draw conclusions, initially, other than assume the mfr's rated Hp is reasonably accurate and that you have generated a good analysis regarding the propeller efficiency - both interesting variables in deriving Net Thrust, before even considering exhaust gas thrust. Having said that there is a foundation of math around propeller tube influences as well as a body of wind tunnel data to support them. Look to low speed characteristics of F4U and stall issues on left inboard wing.

Also, there's a point of trim drag, which isn't a sole property of aerodynamics, but weight distribution as well and is one of the major players at top speeds, too.

Why isn't trim drag a sole property of aerodynamics? All Aero basically starts with a free body diagram with forces resolved to cg - cg being influenced by weight distribution - but the trim required for level flight or even stability in pitch is readily extractable via aerodynamics. Certainly trim drag is a factor at high and low speeds. There is that ol cmpromise thing when considering elevator/horizontal stab incidence/trim tab area factors, etc - and Trim drag becomes More critical when dabbling in high power/high G/High CL manuevering in asymmetric flight (i.e turning in combat)

As for the critical Mach number, it seems that general consensus is it didn't occur until M.7+, which generally wasn't a problem in level flight and I don't see what does the compressibility has to do with anything...what do you mean?

There is a significant difference between 'compressible' and Critical Mach. Look them up and search NACA reports to examine drag rise regions versus Transonic versus Critical mach. Look to the F-4 report for German engineer awareness of the phoenomenum (and all aeros of the day). Do the calcs for a/c like the P-51B-1 with 1650-3 at SL and 29000 feet. Zero Lift Drag significantly increases at the high dash speeds which are in the .62-.65M range at 29K. Dig a little and compare the drag rise between say a P-39 and a P-51 or a P38 - and you will have a better handle regarding why the P-38 needed so much comparative power relative to a 51 to get to 425 mph at 25K.

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Do the math,then challenge my assumptions, rather than assume conventional wisdom based on flight experience or what you have read. I make mistakes in math when I don't much care if someone is checking for grades.

Cola said:

Well Allison lists V-1710-81 as a 1200hp/3000 RPM/SL - 1125hp/3000RPM/FL146 and the one from the chart develops almost 1500hp.
Also, in the drgondog's link, there's an item that mentions an experimental carburetor being fitted.

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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.

Cola said:

To conserve it, a major item in any military of any age.

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"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?

Cola said:

Ah ok...but are we making a religion now, or follow the body of evidence?
Now, as for your comment of the weapons...
K-4 had 2x15mm cannons and 1x30mm cannon and not Mk108, but its big brother Mk103.
Also, K-4's cannon battery was fixed in the nose, making it both very precise and accurate (engine used as a recoil absorber and no necessity for rifling convergence), so you don't get to compare it linearly to other, wing armed, planes.

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The "body of evidence?" ROFLMAO

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?

Cola said:

Ah ok...but are we making a religion now, or follow the body of evidence?
Now, as for your comment of the weapons...
K-4 had 2x15mm cannons and 1x30mm cannon and not Mk108, but its big brother Mk103.

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Oh dear not that myth, again.

drgondog said:

Do the math,then challenge my assumptions, rather than assume conventional wisdom based on flight experience or what you have read. I make mistakes in math when I don't much care if someone is checking for grades.

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DG you have the patience of Job and the wisdom of Solomon. Keep it up, you are doing fine.

People may not understand or agree with you, but anyone who discounts your knowledge of things flying is ill advised in my opinion

SR6 and Milosh have covered the stuff, not too much for me to post.

The carburetor was actually one of the things that made single stage Merlin better than the single stage V-1710s. Those were featuring a carby with smaller throat area than Merlin (24,4 sq in vs. 38,3 sq in for s.s. Merlin). The net loss was easy to see wen comparing the altitudes where the 1100-1125 HP were achieved - Merlin 45 20 series were better for 3-4000 ft, vs, the late 1942 and on Allisons (ca. 18500 vs. 14,5-15,5 kft; all without ram effect). You can note that late war P-39 and P-40 were equipped with V-1710s that have had an almost 1000 ft altitude advantage vs. engine of the P-51A (15,5 kft vs. 14,6 kft), so any 'experiment' is excluded. The 15,5 kft was perhaps the highest altitude the single stage, single speed V-1710 was capable, for power of at least 1125 HP (maybe water injection would help, hopefuly someone could chime in with better assessment on this?).

Hi, CobberKaine,

Enough about P51s already! I propose that in debating the best airframe (and fighter) of WWII we apply the following yardsticks.

1.Economy of construction and ease of service (okay, the Mustang does look pretty good from this perspective, I admit, but so do the Bf109 and Hawker Hurricane)
2.Historical contribution to the course of the war (Mustang looking even better... as do the other two)
3. Success in air to air combat defined in number of kills

Mustang takes third place behind the Bf109 and Hurricane.

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This is about the best AIRFARME for single engine fighter (either in prototype phase, or those in service), not for the best FIGHTER, nor for the one that made the most kills. We have plenty of the 'best fighter' threads, check them out post there if you wish. As for this thread, you can check out the 1st post here to see what is looked after. You can start the thread at your liking, too.

parsifal said:

DG you have the patience of Job and the wisdom of Solomon. Keep it up, you are doing fine.

People may not understand or agree with you, but anyone who discounts your knowledge of things flying is ill advised in my opinion

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This is a post about drgondog. I agree whole heartedly. Obviously a man with loads of hands on experience in the aero world.

You forgot to credit him with the objectivity of Solomon as well. Or you kept that charisma for yourself ?

Lets not turn this thread into a pissing match with insults. This is not a kindergarten.

So far this thread has been really good, with opposing ideas discussing the topic peacefully.

jim said:

You forgot to credit him with the objectivity of Solomon as well. Or you kept that charisma for yourself ?

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There is no such saying and no i dont keep that "charisma" for myself. Neither do i give it to you, which is what I suspect is really galling you. I am at a bit of a loss why you would want to attack me on this thread Jim, as I am not denigrating the me 109. I think it was a fantastic aircraft, and a great airframe. This whole debate about the Mustang started because of adverse comments from yourself. You are obviously upset because a lot of people dont agree with you, and are displaying knowledge on the subject that is obviously showing that initial position to be unfounded. I am not speaking of myself. In my opinion you should be appreciative of the time, patience and wisdom being lavished on you, for your sake, but the best you have to offer is cabal and inflammatory rhetoric.

You have made some contribution to the debate, fair enough, but people have either found fault, or simply disagreed with it. thats fair enough as well. You can take the information, or reject it, its entirely up to you. You can bring additional information or opinion to the debate, which is welcome as well. But you may not bring insult and ill temper, as neither can I or anyone else.

So, do you have wisdom, opinion or knowledge that proves or suggests the 109 to be a superior airframe and/or the Mustange not? I would genuinely like to know why you believe the 109 to be such a vastly superior airframe and the Mustang so inferior, even if that means transgressing a little from the topic parameters and just telling why its such a superior machine.

My reasons for believing in the Mustang are related to its abaility to take on the 109, defeat it, but do it at ranges that other aircraft of the same role could never hope to achieve. in my opinion that makes the Mustang an exceptional aircraft.

jim said:

You forgot to credit him with the objectivity of Solomon as well. Or you kept that charisma for yourself ?

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I think Solomon was wise, not necessarily objective.