Aerodynamics of high-winged fighters.

peceed · Jan 9, 2024

tomo pauk said:
What aircraft of the two was without a supercharged engine?

P.8, its quoted maximum speed is on ground level.

It is also worth to mention, that the performance was not the reason the gull wing was introduced, but pilot visibility.
Metal construction was introduced for its higher resistance of airframes to harh field conditions.
So P.1-P.24 are not determinant of sole "high gull wing with struts" aerodynamic efficiency.
For that reason "modern" design should be created, using all technologies available in 40's and retracted landing gear.
I suppose that speed loss would be around 3-5%, and empty mass lowered by 10-15%

tomo pauk · Jan 9, 2024

peceed said:
P.8, its quoted maximum speed is on ground level.

Okay, thank you.

Shortround6 · Jan 9, 2024

There were two PZL P.8s and then things get murky and that is being kind.
The PZL P8/I used a Hispano Suiza 12M engine and that did not have a supercharger, at least it doesn't appear that any 12M had a supercharger.

Be careful, some drawings show a different exhaust pipe arrangement but that is artistic license. No Hispano engine ever used 3 pairs of exhaust pipes, they were always 1-2-2-1.
The 3 lower opening in cowl appear to be the air intakes for the 3 carburetors on each side. and there is a photo that shows this rather well, no supercharger.

The PZL P8/II the Lorraine 12H Petrel engine had here is where things get wonky.

Petrels came both without supercharger (?) (a few early ones) and with superchargers. Most photos of the P8/II show and exhaust duct/pipe? or at least you cannot see exhaust ports except for one photo and that doesn't have the correct number (there should be 6 per side evenly spaced?)
Now a problem is the 3 screens/intakes/patches? on the side of the engine cowl. The Lorraine's never used a 3 carburetor per side intake set up even on the unsupercharged engines of any type.
Next problem is that air intake/box just in back of the engine about 1/2 the height of the fuselage (between the struts), that is not there on P8/I. Supercharger intake? Something else?
Now this is a bit of a side track.

The problem with the whole PZ series was the wing.

From Wiki and there are versions of far greater detail.

File:PZL P.11c '39 - 2' cockpit detail (14360865064).jpg - Wikimedia Commons

commons.wikimedia.org

You have
the corrugated skin surface (what does that do the surface area?)
the diagonal rows of rivets.
the longitudinal seams/rivets
the overlapping joints, not butt joints.

bf109xxl · Jan 9, 2024

peceed said:
675 hp without supercharger and ram effect.

"PZL Fighters Part One: P.1 through P.8 (Monograph No.2)" by W.A.Ebersbacher and J.P.Koniarek, Phalanx Publishing, 1995
I-15 at sea level demonstrated 315 kph. M-25's power reached 730 hp at 3000m. Nevertheless, the difference in top speed at sea is too small considering all the circumstances.

peceed said:
And don't forget that total wing area matters, it is 18m2 vs. 21.9m2.

Yes, surely. The lager the wing square the higher the drag.

peceed said:
With same engine power and ceiling it would be 394 vs. 367 kph - 27 kph adventage.

I haven't figured out how you got those values.

peceed said:
23% higher wing area in case of I-15, 21% higher third power of speed in case of P.8. No magic here.

The magic, however, should by here: biplane I-15 with lager wing square, additional struts, etc., with a large radial engine performs better than P.8/2. I suppose it was a very challenging task to degrade the wing aerodynamics so much that a monoplane with a more powerful V-engine with a much smaller midsection would perform worse.

peceed said:
Quite equivalent airframes using struts, but P.8 prototype is ready 2 years earlier and not developed to production aircraft (without aerodynamic tweaks).

Does this fact change anything about the evaluation of the P.8's aerodynamic perfection?

peceed said:
Why do you think that metal means faster? Actually wooden surfaces were usually much smoother in the era.

Metal surface can itself is much smoother, requiring less processing than wood. It is more resistant to aerodynamic effects - e.g. better maintains the wing profile at high speed. And I-15 was fabric-covered (!!!!).

peceed said:
In polish fighteres there were rearview mirrors. Sudden attack from behind was impossible. And with eyes level aligned with wing surface the arc covered by wings is very minimal, you can see that wing part close to fuselage became very thin for the purpose of increased visibility.

A sudden attack was always possible regardless of the presence or absence of a rearview mirror. It doesn't matter how thin was the wing, you have to consider its projection depending on view angle.

peceed said:
And thats why idiot-engineers are using them all the time?

if you use something improperly, you obtain corresponding results.

peceed said:
Strut lowers a weight at the expense of increased drag. If is a clear tradeoff!

I spoke only about the aerodynamic effects.

peceed said:
For fast aircrafts with heavy (high total mass fraction) engines that tradeoff became not favorable (actually the important thing is mass of engine, propeller and fuel with all installations).

The effect of flight weight on maximum speed is incomparably lower than the effect of aerodynamic perfection.

Shortround6 · Jan 9, 2024

bf109xxl said:
View attachment 756687
View attachment 756688
"PZL Fighters Part One: P.1 through P.8 (Monograph No.2)" by W.A.Ebersbacher and J.P.Koniarek, Phalanx Publishing, 1995
I-15 at sea level demonstrated 315 kph. M-25's power reached 730 hp at 3000m. Nevertheless, the difference in top speed at sea is too small considering all the circumstances.

Trouble is, like a lot of stuff in the P.8 Saga. this does not correspond to other data.

EarlyEnginesL

"The 12H Petrel engine series, released in 1930, consisted of water-cooled, direct-drive or geared, supercharged, 60° V-12s with 145 mm (5.709") bores and strokes, resulting in 28.733 l (1,753.39 in³) displacements. The original 12H normal rating for both direct-drive and geared types was 500 hp at 2,250 rpm. The direct-drive engine produced 675 hp at 2,200 rpm; the geared engine produced 702 hp at 2,200 rpm. The 1930 geared and supercharged 12Hars produced 700 hp at 3,000 rpm and weighed 650 kg (1,433 lb); 65 were produced. The 1931 geared and supercharged 12Hdrs geared and supercharged produced 720 hp at 2,300 rpm and weighed 635 kg (1,400 lb); 350 were produced. The 1934 geared (17:11) and supercharged 12Hers with its 6.0:1 compression ratio was rated 720 hp at 2,650 rpm, a power level that was maintained up to 4,000 m (13,000 ft). The 12Hers weighed 474 kg (1,045 lb), was 1,859 mm (73.14") long, 795 mm (31.29") high and 709 mm (27.90") wide. The 1935 geared and supercharged 12Hfrs and 12Grs with their 7.0:1 compression ratios produced 815 hp at 2,800 rpm and weighed 650 kg (1,433 lb); 50 were produced."

Not saying that this is the last word on Lorraine engines but it doesn't look like Lorraine was offering an 800hp engine in 1932-33.
In fact very few people were. Hispano took until 1933-34 to get the 12Y up to over 800hp and that was a larger engine than the 12M that is said to have been used in the P.8.

peceed · Jan 9, 2024

Shortround6 said:
The direct-drive engine produced 675 hp at 2,200 rpm; the geared engine produced 702 hp at 2,200 rpm.

The opposite. Gearbox efficiency is around 96% and it perfectly matches data.

Shortround6 said:
The 1930 geared and supercharged 12Hars produced 700 hp at 3,000 rpm and weighed 650 kg

Impossible rpm, inconsistent with power. The fastest Petrels were running 2800 rpm. Weight obviously too big - 700 hp from 650 kg would be a disaster that couldn't be sold on market.

bf109xxl said:
Does this fact change anything about the evaluation of the P.8's aerodynamic perfection?

It shows that P.7, P.11 and P.24 could be faster by 20-30 kph by using better wings.

Shortround6 said:
Not saying that this is the last word on Lorraine engines but it doesn't look like Lorraine was offering an 800hp engine in 1932-33.

There was no fuel for that (except special racing compositions).

bf109xxl said:
The effect of flight weight on maximum speed is incomparably lower than the effect of aerodynamic perfection.

It is obvious, but lower weight can increase climb rate. In come cases it is much more important than maksimum speed, for example for naval interceptors.
My primary candidate to "remake" with gull wing is F4U. Looks like Bearcat competitor

peceed · Jan 9, 2024

bf109xxl said:
biplane I-15 with lager wing square, additional struts, etc., with a large radial engine performs better than P.8/2

It wasn't. P.8 had lower drag area around 20%. BTW, liquid cooled engines offered little advantage in total drag, because there was no pressurised coolant and coolers were bigger than in late 30's, and without Meredith effect (discovered 1935 IIRC).

bf109xxl said:
It doesn't matter how thin was the wing, you have to consider its projection depending on view angle.

View angle is exactly 0. It is a design feature of both P.1-24 line and Z-17.

bf109xxl said:
monoplane with a more powerful V-engine with a much smaller midsection would perform worse.

P.8 had weaker engine, without supercharger. If we take into account altitudes, power comparisons show that its drag area was 20% smaller.
But I-15 clearly had lower drag of landing gear, 2 shorter struts instead of 4 bigger ones (albait there were additional wires). Drag of 4 very small central struts can be comparable to interference drug of wing sections close to fuselage.

bf109xxl · Jan 9, 2024

peceed said:
It wasn't. P.8 had lower drag area around 20%. BTW, liquid cooled engines offered little advantage in total drag, because there was no pressurised coolant and coolers were bigger than in late 30's, and without Meredith effect (discovered 1935 IIRC).

It should outperform I-15 by maximum speed totally. Despite of less powerful engine, non-optimal radiator, etc. It is just not comparable - an all-metal monoplane with V12-engine and a fabric-covered biplane with a large bad-cowled radial engine. The difference must be huge - over 100 kph at any altitude. But it seems that Polish engineers spent too much effort to degrade the aerodynamics of the wing.

peceed said:
View angle is exactly 0. It is a design feature of both P.1-24 line and Z-17.

The angle of view may vary depending on the relative height difference with the opponent attacking from behind.

peceed said:
P.8 had weaker engine, without supercharger.

The difference by maximum speed at the sea level is too small even taking into account this fact.

peceed said:
If we take into account altitudes, power comparisons show that its drag area was 20% smaller.
But I-15 clearly had lower drag of landing gear, 2 shorter struts instead of 4 bigger ones (albait there were additional wires). Drag of 4 very small central struts can be comparable to interference drug of wing sections close to fuselage.

Seems, that I underestimated Polikarpov's efforts.

peceed · Jan 9, 2024

bf109xxl said:
an all-metal monoplane

It is not a guarantee or requirement for good aerodynamics. Look at Wibault 7 aircraft - PZL bought license for its stressed skin technology. "Not the best" is an euphemism. Then look at Mosquito. Or FFVS J 22.
Metal doesn't give better aerodynamic performance, just a little strength advantage (against torsion loads) and durability (especially before Cekol introduction).
Metal airframes can be build much quicker and on much bigger scale.

bf109xxl said:
The angle of view may vary depending on the relative height difference with the opponent attacking from behind.

I need to be more specific because you are ignoring context: View obstructed by wings is contained around 0 degree plane, +- few degrees.
You can see all the attacks from the height advantage, especially considering the fact that angle of attack is higher than 0.
P.1 was designed to have much better visibility in combat than biplanes. Z-17 was designed to have better visibility in combat than P.7 (the whole point of unusual layout).

Shortround6 said:
The PZL P8/II the Lorraine 12H Petrel engine had here is where things get wonky

There was a second variant (P.8-II-2), with 2 small coolers moved to sides of fuselage (cowling of landing gear was simply optional).

Shortround6 said:
The Lorraine's never used a 3 carburetor per side intake set up even on the unsupercharged engines of any type.

It is aircraft designer decision. Engine doesn't really care as long as there is a sufficient aspiration, and power of engines was very comparable - old setup could simply work.

bf109xxl said:
I suppose it was a very challenging task to degrade the wing aerodynamics so much that a monoplane with a more powerful V-engine with a much smaller midsection would perform worse.

Lets use engine from M.S.405 on P.8-II - 860 hp on 4000 m .
Max speed will be ~~350 kph * (860/675/0.608)^(1/3) = 448 kph.~~ (was pressure instead of density)
350 kph * (860/675/0.668)^(1/3) = 434 kph.
Struts, no retractable landing gear, no canopy.
Morane did 435 kph on trials.
I hope this changes yourperspective.

Shortround6 · Jan 10, 2024

peceed said:
It is aircraft designer decision. Engine doesn't really care as long as there is a sufficient aspiration, and power of engines was very comparable - old setup could simply work.

It was the engine makers decision.
The aircraft designer didn't just start switching carbs around as the aircraft design saw fit.
The Aircraft designer could change the intakes/ducts leading to the carbs/air inlet.
The Aircraft designer did not yank off a pair of existing carbs and mount 6 smaller ones and new manifolds.

HS engines used two valve cylinders and they used Siamesed intake ports on the out side of the heads. Exhaust ports were also on the outside.

Lorraine engines used 3 or 4 valve heads (depending on model of engine) , exhaust ports on the outside and intake ports on the inside.

Aircraft designers had enough troubles without trying to turn into engine developers.

bf109xxl · Jan 11, 2024

peceed said:
It is not a guarantee or requirement for good aerodynamics.

In comparison to a _fabric-coated_ airplane - certainly it is a guarantee for _a better_ aerodynamics.

peceed said:
I need to be more specific because you are ignoring context: View obstructed by wings is contained around 0 degree plane, +- few degrees.

I told about the rear visibility on Z-17. Take into account the possible relative angles the planes are at to each other when maneuvering. The obscuration of the view by the wing will not be very large, but it will be much greater than zero for a low-wing plane.

peceed said:
Lets use engine from M.S.405 on P.8-II - 860 hp on 4000 m .
...
Morane did 435 kph on trials.
I hope this changes yourperspective.

This fact evidences only that the French engineers honorably won the competition with Polish engineers (it was definitely a desperate fight!) for the deterioration of aerodynamics. By the way, the Bloch monoplanes were also clearly under-speeding, considering the power of their engines.

peceed · Jan 11, 2024

bf109xxl said:
This fact evidences only that the French engineers honorably won the competition with Polish engineers (it was definitely a hard fight!) for the deterioration of aerodynamics.

You totally missed the point. P.8/II had similar drag area to aircraft that was 3 years younger, while having struts , no canopy and fixed landing gear (typical traits of the era).

With these 3 issues resolved drag of clean (CFD model) P.11c is lowered by 22.5%. If we treat it as proxy for quite smoof P.8, speed could be increased by 8.86%, and it is a lower bound - because of higher base effect (coolers on P.8 were optimized so it should have less drag than radial with Townend ring ).
So 434 kph on 4000 m (HS 12Y engine) is increased to 472 kph. Assuming inlet compression it can reach 482 kph on 4500 m. With good exhaust stack - 500 kph. All using basic aerodynamics of P.8, and making totally equivalent low-plane with canopy. As improvements we still have cooler using Maredith effect and constant speed propeller: 560-570 kph.
Now you have an apple to apple comparison of aerodynamic quality.

bf109xxl said:
In comparison to a _fabric-coated_ airplane - certainly it is a guarantee for _a better_ aerodynamics.

You are definitely confusing correlation with causation and ignoring timeline.

Shortround6 said:
Lorraine engines used 3 or 4 valve heads (depending on model of engine) , exhaust ports on the outside and intake ports on the inside.

This is the argument. Of course common manifold for 3 carburetors is possible, but it would be way less probable.

peceed · Jan 11, 2024

bf109xxl said:
By the way, the Bloch monoplanes were also clearly under-speeding, considering the power of their engines.

Fixed in MB.157.

bf109xxl · Jan 11, 2024

peceed said:
You totally missed the point. P.8/II had similar drag area to aircraft that was 3 years younger, while having struts , no canopy and fixed landing gear (typical traits of the era).

Similar drag area was 20+% less. "The younger aircraft" was _BI_plane with LARGE DIAMETER air-cooled engine, fixed landing gear, no canopy, etc.

peceed said:
With these 3 issues resolved drag of clean (CFD model) P.11c is lowered by 22.5%. If we treat it as proxy for quite smoof P.8, speed could be increased by 8.86%, and it is a lower bound - because of higher base effect (coolers on P.8 were optimized so it should have less drag than radial with Townend ring ).
So 434 kph on 4000 m (HS 12Y engine) is increased to 472 kph. Assuming inlet compression it can reach 482 kph on 4500 m. With good exhaust stack - 500 kph. All using basic aerodynamics of P.8, and making totally equivalent low-plane with canopy. As improvements we still have cooler using Maredith effect and constant speed propeller: 560-570 kph.

And with a good jet engine it could even exceed the speed of sound - at least once.

peceed said:
Now you have an apple to apple comparison of aerodynamic quality.

The comparison of the maximum speed at sea level was quite enough to draw a conclusion.

peceed said:
You are definitely confusing correlation with causation and ignoring timeline.

I definitely do not confuse anything. From the I-16 story: the rigid plywood skin on the top of the wing gave an additional 25-30 km/h to the maximum speed - according to the results of tests of the pre-production prototype of the "type 24".

NevadaK · Jan 11, 2024

Thumpalumpacus said:
Generally speaking, monoplane fighters of the WWII era had low-mounted wings, rather than high-mounted. I imagine that that's for keeping landing-gear closer to the ground.

But was there any aerodynamic reason to favor low- over high-mounted wings?

Hi Thumpalumpacus,

I'm no aerodynamicist so I can't comment there, but my opinion is that the prevalence of low wing fighter aircraft has a lot more to do with pragmatics like minimizing landing gear weight and facilitate loading ammunition and mounting things to wing hard points. A lower wing position is just easier to fuel and arm. There might be a couple other reasons that haven't been brought up. First, as propellor diameters grew it becomes more difficult to provide ground clearance when you are tails up preparing for take-off. A low wing, provides a lower pivot point meaning that when the aircraft rotates to level the prop would travel less distance downward than it would with a taller pivot point. For a high wing aircraft with larger prop that would only add to the required length of the landing gear. Second, if I understand WW@ air to air combat, it largely involves maneuvering with positive G forces. Psychologically, it's easier to image forces pressing against something rather than pulling and aircraft designers might been inclined to place the wing lower on the airframe due to this bias. I admit the last one's a bit of conjecture.

peceed · Jan 11, 2024

bf109xxl said:
with LARGE DIAMETER air-cooled engine

Frontal area doesn't matter for low Mach number speeds, only wet area matters. I-15 is extremely short.

bf109xxl said:
_BI_plane

Biplane has exactly same parasitic drag as monoplane having the same wing area (ignoring struts and wires) , just lower lift due to interference, so it need to be bigger for the same lift. So there is no need to double count disadvantages that comes from "biplaness".
It is 23.55 vs. 18 m2 wing area, few wires instead of struts and much cleaner landing gear.

The biggest advantage of P.8 would be better energy retention during dogfight.

bf109xxl said:
I definitely do not confuse anything. From the I-16 story

I-16 is a good example: -5 was 40 kph faster on ground level. It is exactly the same speed as strutless P.8 with canopy and retracted landing gear would have.

bf109xxl · Jan 11, 2024

peceed said:
Frontal area doesn't matter for low Mach number speeds, only wet area matters. I-15 is extremely short.

What? Are you seriously?

peceed said:
Biplane has exactly same parasitic drag as monoplane having the same wing area (ignoring struts and wires)

We cannot ignore neither wires nor struts.

peceed said:
just lower lift due to interference,
so it need to be bigger for the same lift.

The I-153 had better lift as the I-16 with the same engine being of the same size but ca. 130 kg lighter.

peceed said:
So there is no need to double count disadvantages that comes from "biplaness".
It is 23.55 vs. 18 m2 wing area, few wires instead of struts and much cleaner landing gear.

Wing area INCREASES drag.

peceed said:
The biggest advantage of P.8 would be better energy retention during dogfight.

It has nothing to do with aerodynamical perfectness.

peceed said:
I-16 is a good example: -5 was 40 kph faster on ground level. It is exactly the same speed as strutless P.8 with canopy and retracted landing gear would have.

I-16 is just a good illustration that rigid skin produces less drag than the fabric one.

peceed · Jan 11, 2024

bf109xxl said:
What? Are you seriously?

Sure, as long as you remember about local velocities. Of course Cx matters, teardrop is better than ball. But when your shape is "good enough" it is not important. Sometimes it is better to increase that area in order too obtain better shape. In first approximation the main problem with good radial aircraft is a bigger fuselage wet area.

bf109xxl said:
We cannot ignore neither wires nor struts.

I do not ignore them - just count them separately.

bf109xxl said:
The I-153 had better lift as the I-16 with the same engine being of the same size but ca. 130 kg lighter.

53% higher total wing area.
I-153 was aerodynamically perfected. Dual gull wing minimized interference drag with fuselage. It also increased vertical distance between wings, this reduces interference drag. Only 1 strut and 3 wires per side. Retractable landing gear.
But I do not see such a weight difference.
"Being lighter" implicitly refers to empty mass - 86 kg (I-16-18 - same engine and guns).

bf109xxl said:
I-16 is just a good illustration that rigid skin produces less drag than the fabric one.

Smoothness, not rigidity.

bf109xxl said:
Wing area INCREASES drag.

My point is that drag of I-15 is larger than P.8 in proportion to the wing area ratio. So they have very similar aerodynamic quality.

bf109xxl · Jan 11, 2024

peceed said:
Sure, as long as you remember about local velocities. Of course Cx matters, teardrop is better than ball.

A small ball is better than a large one.

peceed said:
But when your shape is "good enough" it is not important.

Please in numbers. What is "good enough"? Why even small difference by diameter was so important for designers that they prefer to install less powerful engines with a smaller diameter than more powerful, but larger engines?

peceed said:
Sometimes it is better to increase that area in order too obtain better shape. In first approximation the main problem with good radial aircraft is a bigger fuselage wet area.

The main problem of each radial aircraft is cowling. And it was far from optimal on the I-15.

peceed said:
I do not ignore them - just count them separately.

It is not correct - the I-15 cannot be considered without them.

peceed said:
53% higher total wing area.

And what? Same weight + same power =(approx.) same climb with the corresponding airfoil.

peceed said:
I-153 was aerodynamically perfected.

Better than the I-16?

peceed said:
Dual gull wing minimized interference drag with fuselage.

It was not dual. The interference drag was approximately the same as for direct wing. I already mentioned the discussion between Polikarpov and TsAGI/VVS.

peceed said:
It also increased vertical distance between wings, this reduces interference drag.

I-16 was a monoplane. It has zero interference effects from the second wing.

peceed said:
Only 1 strut and 3 wires per side. Retractable landing gear.
But I do not see such a weight difference.
"Being lighter" implicitly refers to empty mass - 86 kg (I-16-18 - same engine and guns).

The numbers are different in different sources. According to Shavrov the full weight of the I-153 was 1860 kg vs. 1765 according to Maslov, for the I-16 type 18 both sources report 1830 kg. The climb rate also differs: the same (5.5 vs. 5.4 min to 5000m) according to Maslov and 5.3 vs. 6.0 min for the I-153 and I-16-18 correspondingly according to Shavrov. Thus, the difference can be roughly estimated as negligible.

peceed said:
Smoothness, not rigidity.

Rigidity. The problem was the elastic deformation of the skin at high speed, which distorted the wing airfoil.

peceed said:
My point is that drag of I-15 is larger than P.8 in proportion to the wing area ratio. So they have very similar aerodynamic quality.

Taking into account much higher drag from poorly cowled air-cooled engine it may be concluded, that the perfection of the wing aerodynamics of the I-15 was higher.

peceed · Jan 11, 2024

bf109xxl said:
According to Shavrov the full weight of the I-153 was 1860 kg vs. 1765 according to Maslov, for I-16 type 18 both sources repot 1830 kg.

When you analyze structural differences you should compare the masses of empty aircrafts.

bf109xxl said:
It was not dual. The interference drag was approximately the same as for direct wing.

Leading edge seems to be gulf shaped, and place where spars where previously located is used by landing gear.
But there is no substantial increase of gap between wings.

Aerodynamics of high-winged fighters.

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