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Wing bending measurements during turning flight of nose-driven prop types

Wing bending measurements during turning flight of nose-driven prop types

Wing bending measurements during turning flight of nose-driven prop types

(OP)


Hello everyone,

I would like to know if anyone knows of any in-flight wing bending measurements made of any kind of nose-driven single engine propeler aircraft type, preferrably of low-wing configuration and high power, and most importantly carried out during a series of sustained horizontal turns, at various speeds and G loads if possible.

My understanding of the issue is that in-flight wing bending measurements are taken with a wing strain gauge and are typically done by diving then pulling out of the dive, the wing bending then being measured from the force of the pull-out.

My question concerns not this kind of test, but a similar test that would involve strictly sustained-speed horizontal turns at a constant G (but done at different Gs and speeds). My interest concerns primarity WWII fighter types, and I woud like to know if any such test were carried out at the time or since, and if similar aircraft types have had these wing bending measurements taken during turning flight while correlating to a given G load.

It seems to me the correlation would be a bit more complicated to do with horizontal turns, since matching the wing bending load to the altimeter data would not work. The movements of the controls or voice recording would have to be used...

It would also be of interest to know how the wing bending in flight was correlated to static wing bending tests on the ground.

I know very well jet or multi-engine propulsion is supposed to offer the exact same data, as are dive pull-outs, but my interest is specifically for tests with low-wing nose-driven types during horizontal turns... My general impression from my research so far is that these aircraft types are usually low-cost/low-tech aircrafts that are not often subjected to these types of fairly elaborate tests (vintage aircraft operators, for instance, never use wing strain gauges in the air, at least none of those I could find)...

So I would like to find an instance of such a specific kind of sustained-speed wing bending test during a prolonged horizontal turn of known G, with a low-wing nose-driven monoplane prop type, regardless of its significance or uselfulness. The closer in configuration, power and weight to a WWII fighter type, the better.

Thanks in advance.

Gaston



RE: Wing bending measurements during turning flight of nose-driven prop types

"regardless of its significance or uselfulness" ... Y, oh Y ?

is this a practical problem, or a student exercise ?

i doubt there's too much information out there ...
OEMs who would do this test if they had too probably don't have the resources/budget for it. the usual approach is for aero loads to be developed, and applied to a model of the structure (could be FE, could be hand calcs) to demonstrate that the structure should be able to withstand the loads. then ground testing proves the structure is good (there are plenty of s/gs on the test article) and flight tseting shows that handling is acceptable. i think it's rare that they'd s/g a flight test plane for loads validation.

now the military folks have plenty of budget (courtesy of you tax payers) and want to maximise performance, so i'd expect that they'd s/g flight test planes.

now, with your interest in WW2 planes, you can probably find a museum or such that'd be interested in helping you.

Quando Omni Flunkus Moritati

RE: Wing bending measurements during turning flight of nose-driven prop types

(OP)


Thanks!

Can you give me a link to the NACA/LARC research database?

I am not a student, but a simulation board game designer. My interest is to explore my own theory that nose length on nose-driven types may affect handling and wing lift through the sustained assymmetry of incoming airflow into the prop disc during level turns.

This is based on the real-life observation of large jumps in turning performance when the same aircraft type gained a much shorter nose (La-5 or Ki-100), this despite the change making them slightly heavier than the previous longer-nosed version.

Also, some WWII fighter pilots note an increase in the available low-speed sustained turn rate performance when power is reduced, which seems somehow related to the above, and yet in theory is something that should not happen.

Gaston

RE: Wing bending measurements during turning flight of nose-driven prop types

Have you already considered the effects of the change in 'keel area' and the effect of the change on the moment of inertia? It's not just mass, or even overall CofG that can affect some aspects of handling.

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RE: Wing bending measurements during turning flight of nose-driven prop types

(OP)


I don"t know how the keel area would affect the turn over several 360s. What I did observe from pilot accounts is that the advantage of the shorter nose seems strongest in indefinitely sustained low speed turns of around 3 Gs, while it seems to disappear in abrupt high speed short-lived turns of 5 Gs or more (where the weight divided by wing area equation seems to gain more validity in predicting the hierarchy of outcomes between aircraft types).

In other words, a heavier aircraft with a shorter nose will not out turn a lighter aircraft with a longer nose at high speeds and 5-7 Gs of short-lived turns (one full circle or less), but it will, with many types, out-turn the lighter aircraft in prolonged low speed horizontal turns at am "indefinitely" sustained-speed G value of around 3- 3.4 Gs.

So in numerous cases, the heavier (but shorter-nosed) type seems favoured by low speeds, contrary to what one would expect.

Also at low speeds, reducing power in nose-driven types, or having an underperforming engine, seems to provide an advantage in sustaining faster constant-speed turn rates at low speed, this accross all types, but especially pronounced on long-nosed types...

Numerous pilots mention reducing throttle to instantly gain performance in low speed indefinitely sustained turn rates (meaning without any delay from deceleration, and this from well below the type"s Corner Speed), sometimes adding that they would put the propeller on full coarse pitch at low speed for extra benefit (not all types allowed this, owing to a pre-set prop pitch vs throttle power setting on some types, but here just downthrottling was still a benefit)...

At high speeds in high G turns, the inferiority of the heavier aircraft will remain even if its control forces are unusually light compared to the lighter aircraft, because the heavier aircraft, despite comparatively lighter controls at high speeds, could then "mush" outward to a surprisingly extreme extent: On one type, from a 40 degree dive from 1200 m, the heavier aircraft, after pulling up to a nose-level attitude, will "sink" tail-down a further 220 m from the nose-level point, despite being, from then on, in a slight nose-up attitude.

The lighter longer-nose type will exhibit no sinking on dive pull-out, easy to understand given its 30% lighter wing loading, yet in low-speed horizontal turns this obvious advantage disappears completely against the heavier aircraft, precisely where one would expect its advantage to be strongest...

This seems like a disparity in handling behaviour going from the vertical plane and or high speeds to the horizontal plane and or low speeds. The first matches expectations, but the second confounds them consistently, even within the same exact type if the long nose-mounted engine became shorter (from inline to radial) as in two cases: The LaGG-3 to the La-5, and the Ki-61 to the Ki-100.

On the one example where the fighter"s nose went from short to long (FW-190A to FW-190D), the low-speed horizontal handling became noticeably worse, while the high speed handling seemed to remain at least equal if not better.

It seems to me those disparities could be reflected by the wings bending differently under various circumstance, since one difference between a dive pull-out and a sustained horizontal turn is that the prop disc surface is "unloaded" in a dive, while it is loaded assymmetrically during a horizontal turn (through assymmetrical air inflow). I don"t know how this could change the loading of the wings, or deform the airflow around the wing to change the load, but if the load is not changing in any unexpected way, then the idea that something is happening that is poorly understood would definitely be proved wrong... Hence my interest in seeing horizontal turn wing bending measurements that would prove this notion wrong on nose-driven types.

Gaston

RE: Wing bending measurements during turning flight of nose-driven prop types

My only knowledge of aerodynamics does not extend beyond what I've picked up as a private pilot. It seems to me that if you are focused on effects from varying the length of the nose, you cannot draw any conslusion across different aircraft types. Across models, there is so much viariability in details of construction, arrangemet of control surfaces, distribution of weight, and engine power that I don't see how you'd narrow the cause down to the length of the engine nacelle.

In theory, there is no difference between theory and practice; experience suggests that in practice, there is.

RE: Wing bending measurements during turning flight of nose-driven prop types

(OP)

Don't forget these are all single-engined WWII fighters of similar configuration. I don't know if the engine power egg could be called a "nacelle" on those... To my mind it is the extreme nose location of the thrust that introduces an unknown effect under airflow assymmetry.

Don't forget also it is the varying effects of different nose lengths across a nose length-inverse amount of wingloading, for similar configuration aircrafts. Short-nose/Heavy vs long-nose/Light.

Wingloading is usually considered the dominant factor in low-speed sustained turns, along with thrust as a supplement, but it seems to me only a wing bending test while in turning flight would confirm this dominance on these kinds of aircraft configurations.

Furthermore, all else being equal, lower thrust up to an optimal point (mentionned as barely 55 MPH above stall, 160 mph, by one Me-109G-6 pilot), seems to provide a low-speed sustained turn rate advantage, completely at odds with accepted theory: Slower-speed turns, with reduced power, that are so much smaller in radius they result in a higher sustained turn rate at a slower speed, despite the aircraft being well below, at 160 mph, its Corner Speed of over 300 mph.

(Note the assumption of a 6 G Corner Speed of around 240 mph on a P-51D (minimum speed needed to reach 6 G in this case), was proven to be completely wrong by the test of the "Association of Experimental Test Pilots" in 1989: The 6 G Corner Speed -in actual horizontal turns, not dive pull-outs as tested before- they found to be at around 320 mph, not around 250 mph, and seemed to always match closely the maximum speed available at a given power in all WWII fighter types...

They also found the P-47D tracked targets better than the P-51 in turning, seemingly implying it turned better than the P-51, again at odds with theory and many wartime tests, but not combat accounts.)

So I think the aircrafts are indeed comparable, it is the "unknown" factor that makes them different. Many complicated factors seem to come into play: For my suspicion of a propeller-related effect on the wingloading to be even possible, it requires the CL moving in front of the CG almost instantly: Otherwise the propeller's -assumed- resistance to being tilted back into assymmetric air inflow would be very obvious to the pilot: If, however, the CL moves in front of the CG, the pilot would then feel no resistance tilting back the prop, as the tighter he turns, the more the CG and CL work in opposite directions, the scissor action in effect "supplementing" his elevator effort in proportion to the angle of attack, hiding the prop's resistance to tilting.

My theory is that all these nose-driven low-wing types are much more heavily wingloaded in horizontal turns than the G value the pilot actually feels in those turns, but some more than others, hence a turn performance hierarchy that makes no sense presently.

For this to work, the wing must somehow generate a lot of extra lift, maybe again related to the assymmetrical air inflow of a horizontal turn, which would be detectable by measuring wing bending in turns but not in dive pull-outs, as usually done, since the unloaded prop disc in a dive nullifies its presumed "wingloading" effect.

If horizontal turn wing bending strain gauge tests and measurements do exist on these generally similar types, and show no relationship to the prop's output, then the whole idea is proven wrong, and some other factor must be at play, including keel area, detail airframe differences and such...

However, the enormity of the wingloading differences, up to 50% in some cases, that are ignored and even reversed in combat, at a near 100% correlation against expectations, seems to be by far the single biggest difference between these various aircraft types, and so the more likely root of what causes this disparity between theory and actual outcomes.

Gaston

RE: Wing bending measurements during turning flight of nose-driven prop types

I'm confused by the short nose heavy V long nose light comments.

If I recall correctly then typically an air cooled radial engine as used in the short nose versions was lighter than a liquid cooled V as used in the long nose versions you refer to.

Now if the position of the engine C of G is brought closer to the A/C Center of Lift then that has to be corrected to keep the overall A/C C of G correctly located so ballast of some kind may be added up front.

For instance, when a Fairey battle was converted from Merlin to Hercules for testing I believe they had to extend the length of the nose to match C of G. If you want to keep the short nose they you'd need to add ballast or equivalent.

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RE: Wing bending measurements during turning flight of nose-driven prop types

(OP)

I know in the Ki-100 case they simply removed ballast from the tail, and that restaured the balance point perfectly. I read an account of the project manager.

Most of these WWII fighters had something like 50lbs of ballast in the tail, sometimes in the form of a thick aluminium armor plate. They tended to be very nose-heavy: One or two men could tip one on its nose: It took twelve to fifteen men to tilt it back...

I don't know what they did to the tail ballast on the La-5. What I do know is that it is a common mistaken assumption to think the Ki-100 or La-5 were hundreds of pound lighter than their inline-engined predecessors: They were actually 100 to 200 lbs heavier but with significantly more power (I don't know if this was all due to the engine itself, but with 300 to 400 extra hp, it seems likely that it contributed): In both cases with about 1500 hp vs 1200 previously.

But, as I describe above, I don't think the extra power helped in their horizontal maneuverability (but it did reap huge dividents on the vertical, and possibly in diagonal climbing maneuvers as well: Climbing while turning).

Again, contrary to popular belief, the longer-nosed FW-190D was inferior in low-speed handling to the FW-190A, but not in high G unsustained speed maneuvers, where it seemed to perform better and without the extreme high-speed "mushing" I described for the A... The D carried 500 lbs less in guns and ammo than the A, but had some engine armor added...

The P-47D had its nose lengthened 8 inches from the B model (unknown effect on handling, but the space was badly needed for other reasons), and, despite being a radial, it does not have a particularly short nose in raw dimensions: It does have a proportionately longer tail: I think it might be the leverage ratio between the tail and nose that plays a role in how the CL "shifts" in front of the CG (assuming this happens at all).

There does seem to be something fundamantally different about the distribution of mass of radials that has a noticeable effect, yet the CG could not be far from the same place at roughly 1/3 of chord from the wing leading edge...

An interesting case is the Spitfire Mk V compared to the 5-6 inch longer nose Mk IX, with much more power (1800hp vs 1500hp), 20% more power for 5% more wingloading (7000 lbs vs 7400 lbs): In theory the Mk IX should sustain turns slightly wider but much faster: In WWII tests no difference was found in horizontal turns, even at high altitudes where the Mk V had over 30% less power.

According to my theory, the Mk V should sustain slower speed but faster rate sustained turns, given its several inches shorter nose and less power. Wartime British tests are inconclusive in that respect, but show no advantage to the extra power on the horizontal during turns, but a huge advantage on the vertical and in climbs.

I have it from good sources within the "Planes of Fame" flying museum, which once operated both types concurrently, that the more powerful Mk IX could not sustain turns with the less powerful Mk V. This indicates to me the wartime testing, that showed parity, was "optimistic" in favour of the Mk IX.

This is an important point, because if 20% more power cannot overcome 5% more weight, it does seem there is something odd at play...

In my experience of researching this for 15 years, I have found much WWII flight testing, and especially their conclusions, correlates very poorly with combat accounts. Combat accounts also show much greater consistency in the hierarchy among types in turns, even accross the broad spaces of different theaters and circumstances.

So there is something very odd going on: I have an account where 8 P-47Ds fought 15 Me-109Gs close to the ground, and they more than held their own in horizontal maneuverabiity near the ground, shooting down 3 to their one damaged... They were on a bomb run and felt confident enough about their handling to keep their bombs on during the entire dogfighting event...

These bombs were not the the 500 lbs variety either: The bomb load in this case was nothing less than a pair of 1000 lbs bombs: 2000 lbs of dead weight per aircraft... The P-47D's wingload is a good 30-40% over the Me-109G-6 40 lbs per square foot wingload according to Wikipedia. Maybe the difference was only 25% in some configurations, but that would definitely mean without the bombs...

So wingload (or powerloading in the case of the Spitfire Mk IX vs the Mk V), at least as we understand these things right now, seems unusually non-predictive.

Gaston



RE: Wing bending measurements during turning flight of nose-driven prop types

Gaston, unfortunately the NASA technical reports site is being sanitized: "The NASA technical reports server will be unavailable for public access
while the agency conducts a review of the site's content to ensure that it
does not contain technical information that is subject to U.S. export control laws and regulations and that the appropriate reviews were performed.
The site will return to service when the review is complete.
We apologize for any inconvenience this may cause".

I find this thread to be fascinating. Thanks for initiating it. Your comment about pulling a tighter turn with reduced power is interesting. I'm sure you are aware of the account of a P47 pilot where using war emergency power improved turning performance and gave him victory over an ME109 that had been out turning him. Nevertheless, if higher power increases speed it can widen the circle even while pulling more G and reducing power could do the opposite. And, the tighter circle should prevail in a dogfight despite the fact that it might involve a slower air speed and less G.
BTW, what is the "corner speed" in this context? And, would you please list the hierarchy of turning performance you mentioned?

RE: Wing bending measurements during turning flight of nose-driven prop types

(OP)


According to the 1989 test by the SETP, the Corner Speed in horizontal turns, at 6G, is always very high on these WWII types, and around 320 mph for the P-51 at METO, or near whatever the top speed is at a given altitude... That is for horizontal turns however, and note that, I am told from one apparently reliable source, that this is contradicted by frequent warbird experience, where they pull 6 G quite often under 260 MPH...

However note how these high Gs are pulled by Warbird operators: By pulling out from a dive (thus unloading the prop by diving), as this is the easiest way to achieve such high Gs... At no point was it confirmed to me that 6Gs below 260 MPH was achieved by a P-51 in horizontal turning, and I did ask...

If this horizontal/vertical "minimum speed to reach 6G" disparity is confirmed, which is not a certainty at this point (as the SETP could still be wrong in their 1989 claim), that alone could indicate a problem with our unsderstanding of flight physics: In theory both the horizontal and vertical limits should be at the same speed...

Except that, according to me, on the horizontal the prop is working much harder, and doing things to the wingloading...

Even if the SETP claim of a 320 mph "Corner Speed" on the horizontal is wrong, it still appears wing bending on these aircraft configurations was only ever measured by doing dive pull-outs (if at all)...


As for the hierarchy in turns, let's say in sustained low speed horizontal turns below 240 mph (3.3 Gs or therabouts):

Top in Western Europe:
1-FW-190A (downthrottled, flaps out a little, even better with broad wood prop)
2-P-47 (Razorback early needle prop, no water boost, but no downthrottling either), maybe tied with Hurricane.
A significant margin between 2 and 3...
3-Merlin P-51 (downthrottled, flaps out 10-20°, prop on full coarse), very probably tied with downthrottled Me-109G.
4-Spitfire
5-Full power Me-109G (as usually flown)
6-P-47 Bubbletop with Paddle blade, maybe tied with Merlin P-51 at full power no flaps (both often flown like this).

Note the P-47 typically does better to left.

High speed unsustained speed maximum G unsustained turn or dive pull-out (around 5-7 Gs):
1-Me-109G trimmed tail-heavy, probably tied with all P-47 versions.
2-P-51 (might be even with Spitfire)
3-Spitfire
4-Me-109G trimmed nose-heavy. Much behind the first 3...
5-FW-190A (far behind the first four, due to tremendous nose-up "sinking": 220 m. in 1200 m. of 40° dive...)

Japanese aircrafts would generally be in front in the first list, but might be in front of only the FW-190A in the second list...

As for the account of a P-47 using boost to turn faster...

Yes I do remember reading a late P-47D Bubbletop pilot specifically saying that engaging his engine Water-cooling system gave him an extra boost of power, and then describing, as a consequence, a boost in the turn rate, which allowed him to gain on the Me-109 that was gaining on him.

The only thing I can say is that this is the only account I know of of this being described... And far more numerous accounts (easily over one hundred or more) seem to show the exact opposite: The P-47 having a natural advantage over the Me-109G in slow-speed turns, and easily gaining, especially in early '44.

Later Bubbletops seem to show a marked deterioration in sustained slow-speed turn performance compared to earlier Razorbacks, reason unknown... But they might still enjoy better and lighter elevator response at high speeds: In the account you mention, and I'm pretty sure we are talking about the same one, if the P-47 accelerated straight out of the turn for a while, the Me-109G would then have to straighten out to follow him, at which point, going fast now, if the Me-109G was not trimmed tail-heavy, its elevator forces could be very high: The P-47 with its light controls (excessively light even) could then do a harsh sudden high speed 6 G turn that would immediately place it behind the struggling Me-109 pilot if he was wrongly trimmed nose-heavy (it took a lot of turns to turn the big trim wheel, if not done in advance)...

To avoid this Me-109-specific problem, Me-109 pilots were often advised to trim their ship tail-heavy, so that to fly straight and level, they constantly had to push on the stick, something which novices did not appreciate apparently... This allowed instant high speed turn response to the Me-109, with little pilot effort... In this condition, the Me-109's fully moveable trim tailplane actually gave it a superior elevator response to Allied types, and this at very high speeds, and for obvious reasons, given the whole tailplane would move as it was trimmed (copied later by North American on the Sabre): It could pull-out first out of a fast dive compared to even a P-51D, with its heavy stick, while the light-stick P-47 might instead "mush" down with the nose up, a little like the FW-190A, but much less abruptly and severely... The P-38 could apparently pull-out better than almost anything, with the dive flaps on, even sometimes without, but this is not mentionned in the book "America's Hundred Thousand", one of the many obvious contradictions of flight tests (I'll go with combat accounts on that one)...

Then there is the account of "Boddenplatte" at Y-95 on the TV show "Dogfights", where, in the second half, an older P-47 Razorback (likely with paddle-blade prop) is gradually out-turning a Me-109 at low speed, on the deck, around a "slag pile" mountain, just as I would expect... Note however something very interesting happens here: The pilot himself narrates almost all of the encounter, except for one crucial part, where, for some reason, the "narrator" voice takes over and says this, just as the Me-109 starts to turn, and initially gains on him: "VOICE OVER INTERRUPTS NARRATION BY PILOT: "He engages water injection and suddenly the Me-109 stops gaining on him". And that's it: I do not count this as the pilot actually saying it... Quite the opposite in fact, because I happen to know in detail how slavishly devoted television is to simple and clear ideas presented by in-house "experts", even if the real world out there doesn't oblige... I wonder why the pilot had to be interrupted just at that moment, and words not spoken by him put in there...

I'll note also that, while downthrottling to turn faster at low speeds is an infrequent occurence with the P-51 (but somewhat widespread and very corroborated in several details when mentionned, and more or less the same thing with Me-109s and FW-190As, all quite heavy two-handed elevator types depending on trim), downthrottling in a sustained low-speed turn is never mentionned with the P-47 or the Spitfire... I don't have much of a clue why that is, but the common trait of both the Spitfire and the P-47 is an elevator that, even at high dive speeds, is described as somewhat overly light, and prone to damage the airframe by bending if the pilot does not restrain his effort... Maybe at lower speeds, in a turn where you are held up on your side by Gs, they become so light as to become imprecise to use under stress, given their lightness, and so this discourages lowering speeds further, since that would mean to lose more feel?

Gaston



RE: Wing bending measurements during turning flight of nose-driven prop types

Obviously this vital performance area is determined by some rather subtle factors that could be exploited by skilled and experienced pilots and was not a simple consequence of wing loading and power.

You mention that some Japanese types would rank above #1 in sustained turns. I guess that reflects well on the Hellcat, Bearcat and Corsair which were competitive with them (?).

RE: Wing bending measurements during turning flight of nose-driven prop types

(OP)

Between the Spitfire and the FW-190 there is a 50% difference in wing loading... And yet not one account of the Spitfire out-turning the FW-190A, in sustained and clearly slow speed turns, has surfaced so far in my years of research...

Even at high speeds, there are only a small handfull of examples, all preceded by dives, or long straight lines at full power... All are also obviously high-speed short-duration turns with no mention of multiple circles or "lufbery" or "gradually gaining" or anything of that sort.

I have four separate accounts of the exact opposite, a FW-190A out-turning the Spitfire at slow speeds, gradually and inevitably, plus one pilot making a general statement that the Hurricane out-turned the Spitfire and Me-109, but was itself out-turned by the FW-190A. That in itself is worth more than one right there... Just how much can pilot skill overcome a 50% shortfall in wingloading? Just how invisible can that 50% be?

I would be very surprised if pilot skill -under the duress of combat- amounted to more than 5-10% of this basic maneuver: Level turning...

Furthermore, pilot skill in this case seems related not to perception finesse, but to basic method: The use of downthrottling and sometimes flaps seems prominent... True, determination could play a role, but the determination to live is pretty much the same in all people, wouldn't you say? And that makes this kind of pressure somewhat of an equalizer as to how far you are willing to go... This is precisely where period flight tests are more susceptible to a lack of motivation: Are you really willing to court trouble just to find out exactly how much more that fat heavy plane is out-turned by that light nimble one? Ie: USAAF P-47 vs P-51 conclusions...

The Bearcat was never used against the Japanese.

Of all the US Pacific fighters, the consensus among Japanese pilots was that only the Hellcat and the Wildcat would turn with them: Probably in part because they were the two slowest ones...

The Wildcat would sometimes hold its own in turns with a Zero, but was easily beaten if the Zero shifted to a vertical loop, if one Saburo Sakai account is to be believed. I know that the late model FM-2 Wildcats were absolutely fearsome adversaries, and even better than early Wildcats: I have read at least one account of an A6M5 Zero attacking an FM-2 eagerly in 1944, thinking this would be an easy target, and being instead shot to ribbons...

The FM-2 Wildcat had, by a huge margin, the most lopsided kill-loss ratio against the Japanese of all US fighters: Half again more than the 19:1 of the Hellcat itself: Somewhere around 32 kills to each loss...

Against the Germans the ratio was even more lopsided, since, if memory serves, it took no loss for a fair number of kills...

Here are the ratios:

FM - 32.46 to 1
F6F - 19.12 to 1 (4900 kills to the P-38's 1800)
PB4Y - 11.36 to 1
F4U/FG - 11.31 to 1
PB2Y - 7.00 to 1
PBM - 6.00 to 1
F4F - 5.08 to 1
SB2C/SBW - 2.39 to 1
TBF/TBM - 2.09 to 1
SBD - 1.75 to 1
PBY - 0.47 to 1

This indicates to me that the post-WWII dogma of using speed at all cost, and avoiding dogfighting, was not so universally practical at that particular time: Even against the unprotected, fragile Japanese aircrafts (favouring short bursts from a higher speed it would seem), the most successful fighters were the two slowest and most maneuverable in turns: The F6F Hellcat and the FM-2... Even those targets had to be peppered for a while...

As to how the F6F compared to the F4U, don't subscribe to those WWII Navy tests that claims the F4U and the F6F were equal in turning ability: The 1989 test by the SETP showed conlusively the F6F could turn harder by quite some margin than all of the other 3 present: F4U (FG-1), P-47 and P-51. This correlates with what the Japanese pilots were saying...

The Wildcat was the best turning US fighter of WWII, bar none, and this was probably even more true of the FM-2...

I don't know where the US Navy types stand compared to the FW-190A in turns: I would not be surprised if the FW-190A fell in between the F4U and the F6F, but certainly it is not better than the FM-2 for sure... Ignore the near-identical pair of silly Navy comparison tests of the FW-190 with the F6F and F4U, which look like carbon copies of each other, and conclude: "The FW-190A is an interceptor-type aircraft not suited for dogfighting": Terminally ridiculous... They also claimed the F4U out-rolled the German fighter, something for which, surprisingly enough, the British RAE felt strongly enough to be compelled to send them a letter, during wartime, to counter that claim in strong terms, probably making the first ever typed WWII fighter performance argument I would say...

(Of note is that one FW-190A Western ace related that the FW-190A's ailerons were essential to its -all-important- slow-speed turning ability, as he could "catch" the wing-drop with them, and "ride the turn" on deflected ailerons... This was so important, 3 different types of ailerons were offered as choices, this particular pilot choosing the broadest chord one for low-speed, and supplementing this further by "spacing" it out with field-mounted spacers at the hinges, to "artificially" increase its chord further. He would also reduce the throttle well before the merge with P-51s, and used slow speed turns at reduced throttle almost exclusively, and this against all allied fighters including the Spitfire... If they did not try to turn with him, he would merely face them in repeated head-to-heads. With the broad wood prop, he supposedly reversed a tailing P-51D in only two turns on the deck...)

It is really stunning how utterly blind those Navy comparison tests were: They are almost comically contradicted by the Russian 1943 "Red Fleet" articles, which are based on months of observed combat... The US P-47 vs FW-190A comparison made by front-line pilots in Italy in 1944 is also excellent, and agrees beautifully with every improbable-seeming detail of the "Red Fleet" article.

They didn't always get them wrong...

Gaston

RE: Wing bending measurements during turning flight of nose-driven prop types

Gaston, When I mentioned pilot skill I do not imply that the pilot's efforts could change the flying characteristics of the plane, but tactics, choosing what to do and executing to maximize your chances in a fight are always a matter of both skill and experience. For example, poor training and an utter lack of experience killed a lot of Axis pilots toward the end where they otherwise might have fared much better. Another example of the effect of skill and experience from Korea is the claim that Russian pilots of Mig-15s had a strongly favorable kill ratio against F-86s while these pilots were most often veteran flight leaders also with the tactical advantage that leaders enjoy. And I can't forget Sakai's description of an escape from death at the hands of a flight of Hellcats where his ability to execute clever evasive maneuvers was the difference.
Again, a very illuminating discussion.

RE: Wing bending measurements during turning flight of nose-driven prop types

(OP)

I understand better what you meant now.

This "overall pilot skill" issue is why I don't give much credence to kill ratios to determine aircraft performance... Interestingly enough, in Western Europe, kill ratios by the 8th Air Force in 1944 were pretty lopsided, despite the fact that the enemy was mostly fighters. You hear ratios from 3 to 20+ to one, 3 being the P-38, and 20+ being the P-51...

But the P-38 had high altitude problems and training issues, and was grossly outnumbered initially, while the P-51 arrived in large numbers quite a bit later, and just at the right time to look infinitely better than it actually was...

This lopsided ratio in favour of the P-51 has at least two major contributing factors: The number of P-51 "Ace in a day" soared in May 1944, just as the P-47 was being massively shifted to low altitude ground attack (to prepare D-Day), and, coincidentally, this was also the time where the P-51 was finally vastly outnumbering the P-47, at a rapid rate, for high altitude bomber escort duties, after being a quite a minority element in the 8th Air Force for the first four months of 1944. (The P-47 got 160 of the 220 air to air kills of late February's "Big Week" -the remaining 60 being split between the P-38 and P-51!-, despite the P-47's short range with no wing drop tanks, only a belly drop tank!)

Why where the P-51 kills suddenly soaring in May of 1944? Amazingly enough, the cause was two major doctrinal changes occurring at the exact same time, one Allied, one German, the German one probably being the more important:

-The Allied change was the Doolittle order to free the escort fighters from "shadowing" the bombers, instead allowing them to range ahead and sweep the sky ahead of the bombers, making it possible to disrupt enemy fighter formations as they were assembling (also giving the interceptors less time to climb up to the high bombers, given the much higher speed of the now unhindered escort fighters)

-The German change was even more significant: It was the catastrophic "Bombers only" directive of May 1944 (which was never relaxed, but probably followed more "loosely" later) that treated the Luftwaffe as essentially an "expendable" arm: German fighters were to ignore enemy escort fighters and concentrate on the bombers, in doing so enormously boosting US escort fighter confidence... As Galland said: "If I understand this well, the safest place in the sky is now in an American fighter cockpit..." Very little remaining overhead fighter cover was allowed to the German fighter pilots, who, amazingly enough, were obedient enough to let this order take full effect for a good while, allowing themselves to be slaughtered on a mass scale...

Many inexperienced P-51 pilots suddenly came back in May with almost unheard-of strings of five kills or more: This shows how profoundly doctrine permeates down to the tactical level...

When the air fighting shifted to lower altitudes, around D-Day in June 1944, these two new doctrinal attitudes lost quite a bit of their significance, since the altitude advantage (and large bomber streams) played a lesser role in tactical frontline fighting: As a consequence, the kill/loss ratio changed dramatically in the other direction: A figure I read claimed the exchange ratio was around 1:1 over France, despite worsening German training...

This is why many of the "ace in a day" occurences within the 8th Air Force are noticeably clustered around May of 1944...

Popular lore has it that the Luftwaffe barely showed up over the Normandy invasion front: In fact, it expended an enormous and unprecedented effort for months, but the vulnerability of its large bases, and the short range of its fighters, required dispersion in forward airfields, and the poor communications available in these forward fields, plus the numerical disadvantage, made the defense uncoordinated and diluted. Many of them just flew round and round not knowing where the action was...

If anything, I would say pilot skill is slightly overrated as a factor, at least for low-altitude fighting, which seems easier to master for a novice: In US combat reports of late 1944, I noticed that German pilots, who had to be less experienced for the most part, were actually giving more trouble against worse odds if they were at low altitudes: One of the reasons is they were flying more of the more maneuverable FW-190As... The FW-190A grew to represent 70% of the Western Front fighter force as 1944 dragged on...

But their tactical choices seemed better too, in late 1944, than in early 1944: The Luftwaffe institution as a whole gradually seemed to have learned how to fight US fighters by September, and despite having less well trained pilots, they were apparently giving them better advice. It's only when massively attacking high altitude bombers again in November (there was a sort of "resurgence" of the anti-bomber effort twice in November: Two occasions were the largest intercepting fleets ever were assembled: 600 + fighters) that the losses again became terrible: With big bombers around, the "bombers only" directive again took its toll...

These two failed November "mini Big Blows" were what killed off Adolf Galland's "Big Blow" idea of concentrating 1500+ fighters against the bombers: In the end, this preserved assembled force was used on the low-altitude "Boddenplate", but it had been trained for high-altitude fighting, which apparently did cause problems: It does show training does matter, but probably not to a hugely greater extent than doctrine...

In my view, "Boddenplate" was probably a better idea if the force had been trained for it, and if the effort could have been repeated (note the "exchange ratio" of "Boddenplatte" was still around 1:1, despite all the problems), leaving the high altitude bombers for the Flak or their jets. I think the Germans simply could not compete at high altitudes, where pilot training indeed seemed to matter more...

Also it so happened that the Luftwaffe's best mass-produced fighter, the FW-190A, was noticeably out of its best element above 20 000 ft: The P-51 seemed comparatively quite at ease in the thin air.

If anyone knows about in-flight wing bending measurements, while turning, on these types of aircrafts, note that I am still interested...:)

Gaston

RE: Wing bending measurements during turning flight of nose-driven prop types

Well thought out analysis. The dilemma for the Germans was that they HAD to do as much as they could against the bombers. And, concentrating on lower level combat with fighters even with a 1:1 kill ratio would always be a losing proposition against the increasingly overwhelming resources of the Allies at that point in the war.

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