Aerodynamics of high-winged fighters.

[GregP]

High-wing, single-seat fighter.

Granted, not a piston ... but still, high wing and a fighter. Well, maybe an interceptor.

 

[GrauGeist]

Actually P.1 and P.7 had so strong wing (around 20 g), that the following models didn't need to increase strength as their weight was growing up.
In practice pilot didn't need to think about structural strength in any circumstances.
P.11c had diving limit 600 kph IAS while having very draggy airframe.
And was extremely resistant to battle damage.

It is simply not true. High wing allows to use struts that save a lot of weight.

No contemporary fighter had them. In case of P.1-P.24 line the opposite is true: the main fuel tank was detachable in emergency situations, so they were the safest fighters of the era in the case of fire. Greece P.24 got armored windshield and armored plate behind pilot.

In short, a high wing (or parasol) fighter lacks the benefit of the wing's spars passing through the fuselage for strength.
The struts create drag.
The wing blocks the pilot's view (which can be a fatal handicap).

The high wing configuration is perfect for recon (ground observation), but not for combating enemy aircraft.

 

[V1710]

What about the P-38?

 

[bf109xxl]

The LaGG-3 was not that large of an airframe amd accepted the Su-2's engine/cowling well enough.

The cowling of LaGG-3M-82 (LaG-5, future La-5) had nothing to do with the Su-2 one. The Gu-82 - a Gudkov's attempt to improve LaGG by powering with the M-82 - had a Su-2-like cowling, but this airplane was just an experimental one. The best variant of M-82 cowling at that time was developed by Polikarpov, who was obliged to transfer his drawings to other design bureaus. There are confirmations of the transfer of drawings to Yakovlev, Mikoyan/Gurevich (reliably), and posibly Gorbunov. But there is no confirmation that the documents were transferred to Lavochkin - the latter developed the cowling rather independently. Seems, that this version of the cowling was less optimal than the Polikarpov's one.

 

[swampyankee]

In short, a high wing (or parasol) fighter lacks the benefit of the wing's spars passing through the fuselage for strength.
The struts create drag.
The wing blocks the pilot's view (which can be a fatal handicap).

The high wing configuration is perfect for recon (ground observation), but not for combating enemy aircraft.

The spars can most certainly pass through the fuselage in a high-wing fighter, or any other high-winged aircraft. Struts are not needed; note that they don't seem present on many current high-winged aircraft or some aircraft of the WWII era, like the DC-5.

The issues with a WWII-era high-wing, piston-engine fighter include, as you said, visibility, plus things like landing gear placement. Very few designers concluded that a modern (the PZL.11 and PZL P.7 are the only [eta]high-winged [/eta] ones to see WWII-era service) fighter or single-engine fighter would be practical, because of the issues of visibility and packaging.

 

[GrauGeist]

The cowling of LaGG-3M-82 (LaG-5, future La-5) had nothing to do with the Su-2 one. The Gu-82 - a Gudkov's attempt to improve LaGG by powering with the M-82 - had a Su-2-like cowling, but this airplane was just an experimental one. The best variant of M-82 cowling at that time was developed by Polikarpov, who was obliged to transfer his drawings to other design bureaus. There are confirmations of the transfer of drawings to Yakovlev, Mikoyan/Gurevich (reliably), and posibly Gorbunov. But there is no confirmation that the documents were transferred to Lavochkin - the latter developed the cowling rather independently. Seems, that this version of the cowling was less optimal than the Polikarpov's one.

So you're implying that Gorbunov of did not mate an Su-2's engine and cowling to the nose of a LaGG-3 airframe during early 1942?

 

[bf109xxl]

So you're implying that Gorbunov of did not mate an Su-2's engine and cowling to the nose of a LaGG-3 airframe during early 1942?

It was Mikhail Goudkov (Gudkov) who tried to install M-82 on the LaGG-3 in the early 1942 - I mentioned it already. No documents on transfer of the cowling design from Soukhoi (Sukhoi) to Goudkov have been found until now. The design of the Gu-82 cowling was a bit similar to the Su-2 one, but in no way exactly the same.

 

[peceed]

In short, a high wing (or parasol) fighter lacks the benefit of the wing's spars passing through the fuselage for strength.

While gives different structural benefits that save weight overall.

The struts create drag.

The wet area of struts is very small and they can be optimized even further than historical.

Struts are not needed; note that they don't seem present on many current high-winged aircraft or some aircraft of the WWII era, like the DC-5.

The weight of DC-5 was concentrated in the wings: they contained landing gear, engines, fuel tanks.
Fuselage was relatively light, g-limits low, so the benefits of struts would be minimal.
High-g fighter with mass concentrated in the fuselage can benefit much more, that's why high-winged fighters universally used struts.
Visibility and landing gear location is the main reason for low wing dominance in monoplane fighter designs.
Drug of struts is quite low, but it offsets structural benefits in high speed designs. Stronger engine in aircraft with struts (for the same performance) would be heavier and require more fuel hence more wing area - so there would be no weight benefit. And there can be no stronger engine available.

 

[swampyankee]

High-winged fighters didn't need to use struts; neither did low or mid-wing fighters. That the very limited number of high-winged fighters -- and I can think of none that were even vaguely modern beyond the PZL P.7 and P.11 -- used struts just showed that their designers thought that the struts were, overall, beneficial, most likely for weight savings, and accepting the increased drag (some of the fighter designers of the WWII era were also not very good at reducing drag. See, for example, the Bf109, which had much greater zero-lift drag than most of its contemporaries)

It is known that struts, even in transonic aircraft, can reduce drag in cruising conditions, but this requires very careful design, possibly involving CFD (rather challenging in 1942) There's a lot of reports on strut-braced wings for transonic speeds on ntrs.nasa.gov (see Search - NASA Technical Reports Server (NTRS)).

 

[bf109xxl]

While gives different structural benefits that save weight overall.

The wet area of struts is very small and they can be optimized even further than historical.

The weight of DC-5 was concentrated in the wings: they contained landing gear, engines, fuel tanks.
Fuselage was relatively light, g-limits low, so the benefits of struts would be minimal.
High-g fighter with mass concentrated in the fuselage can benefit much more, that's why high-winged fighters universally used struts.
Visibility and landing gear location is the main reason for low wing dominance in monoplane fighter designs.
Drug of struts is quite low, but it offsets structural benefits in high speed designs. Stronger engine in aircraft with struts (for the same performance) would be heavier and require more fuel hence more wing area - so there would be no weight benefit. And there can be no stronger engine available.

An all-metal high-wing monoplane was ca. 100 km/h slower than a low-wing monoplane (even a partially wooden one!) with a similar engine. Low-wing monoplane fighters outperformed high-wing fighters even with less powerful, larger diameter engines (e.g., the I-16 with its single-row Wright). Ok, you can point to the retractable landing gear as the major reason for the difference in performance, but we can compare P.24 to Japanese low-wing monoplane fighters of the mid-1930s with non-retractable landing gear. The latter outperformed it completely (except firepower) even with much less powerful engines. The P.24 was an archaism, suitable only for countries with very limited military budgets. The high wing had no design advantages if used on _piston-engined_ _fighters_ already in the early 30s, although Polish designers created excellent airplanes at the time of their adoption. These airplanes, however, had no future and very quickly became obsolete in contrast to the low-wing monoplanes which had much more reserves for further development.

 

[Shortround6]

Unless you very carefully select examples we are going to be going around in circles.

For wing design a braced wing can use a thinner airfoil than an un-braced (cantilever) wing.
What is the thinner airfoil worth?
What is the fuselage to brace interface (fairing) worth?
What is the brace to wing interface (fairing) worth?
What are the braces worth?
What is the disruption in airflow on the wing surface from the Brace/strut/fairing.

And so on.

Also let's remember that as speed increases, the disturbed air flows a bigger and last longer.
Biplanes have more drag than monoplanes of the same wing area because the down flows of the wings interfere with each other.
Do two struts have more drag than a single strut even if they have the same wetted area?

Go back to post #16 for examples of the Lockheed aircraft of the late 1920s and early 30s.
Nowhere else are you going to find a selection of aircraft using two wings with the same airfoil but slightly different sizes, mounted on identical fuselages, in three different locations and using a selection of landing gear (and fairings) and all/most of them using the same engine.

And take a look at the PZ 11.

Look at the fore and aft stringers/braces/strips every 15cm/6in on the wing. I have no idea what that did drag on spanwise airflow but it was something.
Or some of the other lumps, bumps, slots, screens and appendages.
Now in 1934 it was pretty hot stuff, compare to Boeing P-26 or Gloster Gladiator but trying to compare the drag to the layout of the wing when there is so, so much other stuff going on?

 

[swampyankee]

An all-metal high-wing monoplane was ca. 100 km/h slower than a low-wing monoplane (even a partially wooden one!) with a similar engine. Low-wing monoplane fighters outperformed high-wing fighters even with less powerful, larger diameter engines (e.g., the I-16 with its single-row Wright). Ok, you can point to the retractable landing gear as the major reason for the difference in performance, but we can compare P.24 to Japanese low-wing monoplane fighters of the mid-1930s with non-retractable landing gear. The latter outperformed it completely (except firepower) even with much less powerful engines. The P.24 was an archaism, suitable only for countries with very limited military budgets. The high wing had no design advantages if used on _piston-engined_ _fighters_ already in the early 30s, although Polish designers created excellent airplanes at the time of their adoption. These airplanes, however, had no future and very quickly became obsolete in contrast to the low-wing monoplanes which had much more reserves for further development.

There are many, many examples showing negligible difference in the performance of well-designed high and low wing aircraft created for the same mission. There are advantages to low wings on fighters, mostly as a) better landing gear placement and b) better pilot visibility.

 

[bf109xxl]

There are many, many examples showing negligible difference in the performance of well-designed high and low wing aircraft created for the same mission. There are advantages to low wings on fighters, mostly as a) better landing gear placement and b) better pilot visibility.

What exactly aerodynamic flaws in the P.24 caused such a loss in speed? It's really not quite clear to me. For example, I could refer to the discussion between Polikarpov and TsAGI (Central Aerohydrodynamic Institute, the leading Soviet research center for aerodynamics) about the I-15/I-153 (gull-type) wing. Polikarpov proved that the gull-type scheme does not have the disadvantages attributed to it by TsAGI and provides similar parameters as the "straight" wing. The P.24 wing scheme has a clear similarity to the gull type, so the reasons for the high aerodynamic drag are not obvious to me. Airplanes with open canopy, non-metallic wing skin and worse wing profile fabrication (typical for Soviet airplanes) demonstrated a higher flight performance with less engine power. Even some biplanes with approximately equal engine power (with even larger diameter!) outperformed the P.24. Why? I have already spoken about the non-retractable landing gear. There remain struts - apparently, the drag created by them was higher than previously estimated. Or are there other factors? Cowling? It was just terrible on the I-16. What else?

 

[peceed]

Ok, you can point to the retractable landing gear as the major reason for the difference in performance, but we can compare P.24 to Japanese low-wing monoplane fighters of the mid-1930s with non-retractable landing gear.

The main reason was very draggy technology of stressed skin wing construction (Wibault). First on market, not the best in the late 30's.
P.24 had similar drag area to Gloster Gladiator biplane.

What is the fuselage to brace interface (fairing) worth?
What is the brace to wing interface (fairing) worth?
What are the braces worth?
What is the disruption in airflow on the wing surface from the Brace/strut/fairing.

Master thesis that can give some answers:
ANALIZA SIŁ OPORU AERODYNAMICZNEGO POSZCZEGÓLNYCH PODZESPOŁÓW SAMOLOTU PZL P.11c - Materiały Kompozytowe - Composite marerials
Struts gives 4.1%+4.4% of total drag.
So we can assume, that aircraft with struts is around 10% draggier. But low-wing allows for easy reduction of landing gear drag, so there is no surprise that it became prevalent.

The P.24 was an archaism, suitable only for countries with very limited military budgets.

It wasn't cheaper to produce than low-plane, and it wasn't bad plane in the time when it was designed and produced. It is simply previous generation, that was being replaced in 1939. Polish Air Force intended to replace them by PZL.38, multirole aircraft that required engines specially designed engine that happened to be a failure. Unfortunately there was no backup project for airplane, and no replacement for engine.

 

[bf109xxl]

It wasn't cheaper to produce than low-plane, and it wasn't bad plane in the time when it was designed and produced. It is simply previous generation, that was being replaced in 1939.

This generation was outdated no later than 1937. Whether the Poles underestimated their opponents or were too tight on funds - I don't have enough information. The engine (14K) was adequate and could provide 540-560 kph for all-metal aircraft.

 

[tomo pauk]

This generation was outdated no later than 1937.

Against the most likely opponents - Germany, Soviet Union - certainly.

The engine (14K) was adequate and could provide 540-560 kph for all-metal aircraft.

Please, do tell.

 

[bf109xxl]

Please, do tell.

Re.2000 - 530 kph, I-180 M-87B - 540 kph. Both were powered with 14K derivatives. I suppose, the I-180 with a closed cockpit canopy and more careful wing fabrication (e.g., better landing gear doors fit) could reach 560 kph.

 

[tomo pauk]

Re.2000 - 530 kph, I-180 M-87B - 540 kph. Both were powered with 14K derivatives.

Neither of these was powered by the actual 14K.

 

[bf109xxl]

Master thesis that can give some answers

I am not sure that you can obtain reliable coefficients by simulation in this case - were the simulations verified by the experimental data (e.g., wind tunnel blowing of the P.11 models)?

 

[bf109xxl]

Neither of these was powered by the actual 14K.

I doesn't matter. The difference by parameters (diameter, power) was negligible. M-87B had 950hp on 4000m, 14K on P.24 - 930, 14N on P.24F/G - 970.