Me262 vs. P-80

[drgondog]

I always thought that automatic LE slats were for slow speeds, not all speeds and definitely not at high speed.
As for the high AR of the 262's wing, it would certainly have a lower induced drag (but a higher parasite drag). However, higher AR wings have a lower roll rate and putting the heavy engines on the wing doesn't do you any favours on the roll rate, only helping to slow it down.
The best place for the engines is in the centre of the plane, no question and it’s also causes less drag. I believe the Russians instead of copying the 262 came up with an aircraft which had two engines in the fuselage because of the reduced drag.

This bit is a guess on my part, but my guess is that the LE slats were to assist in the problem of loss of lift that happens with swept wings at slow speed. With a swept wing the airflow tends to be 'swept' to the wing tips instead of going straight over the wings. This causes a loss of lift at slow speed and one of the things that the LE slats will do is assist with the slow speed handling.
The 262 was built for speed not agility and the Germans would have found this problem out in tests, had considerable experience in LE slats and would have known how to address the problem

Glider, I can't speak definitively for Mtt but you are 100% correct with respect to functional reason for LE slats on F-86 - stability at low speed (as in final approach) for swept wing config. The MiG15 solved that problem with large wing fences to assist flow in straight (more or less) flow over wing.

I would also believe the drag would be higher for two nacelles than for an engine imbedded in fuselage - which is a primary reason twin engine fighters ALL are designed that way. I'm really having a hard time recalling a fighter with T/E imbedded in (or suspended) wing that started design after 1950.

That said, boundary layer control into a 'cheek' inlet has always been a strong focus for aero guys - particularly for high transonic to supersonic flow in which the mach (and shock wave angles) change significantly.

Compressor stalls were harder to prevent than a nacelle config engine mount.

I suspect (without proof) that the reason for the two engines on the Me 262 and Meteor was that no single engine was of high enough thrust at time airframe design started, to give the airframe the hoped for performance... and that the P-80 was the first that had an engine design on the horizon to cause Kelley Johnson to go with imbedded fuse engine.

[kool kitty89]

I think the Yakovlev Yak-25 - Wikipedia, the free encyclopedia was the last fighter (albeit an interceptor) with outboard nacelle-mounted engines. Yakovlev Yak-25 - Wikipedia, the free encyclopedia

Also the Me 262 was considered in having wing-root buried engines (a design incorporated in the HG III, somewhat similar to the P-59A's layout, albeit much more streamlined) but the external surfaces of 004's got too hot for this placement iirc, and required regular maintenance which nacelle placement facilitated.

The original concept of the 262's design was to have engines that were far smaller than those that developed (closest was the HeS-30, 006) and were to be mid-mounted in the wing, similar to the Meteor, but much smaller.

I'm not sure where Soren is getting this info on the 262's agility, and that comparison he sites is insubstanciated and possibly a comparison to the original Goblin-(under)powered XP-80 (2,400 lbf); a completely different design (the L140) of which only one prototype was made (now at the NASM adjacent to a Me 262 and FH Phantom), the XP-80A (L141) was a drastic improvement in aerodynamics (more streamlined with rounded wing and tail tips and thin "knife edge" wings), technology, and performance. Pluss that "comparison" he sites doesn't even say the 262 is more maneuverable, only faster and with better acceleration, climb, and crit. Mach number. (which it certainly would compared to the XP-80 which barely broke 500 mph and had fairly thick wings and low thrust/weight)

Though I certainly don't agree with Geezer either, the Me 262 was certainly viable! And it had flown with 004A's nearly 3 years before the original XP-80 (though only months prior to the rather poor, as it was, XP-59A) But the 262 had been in development since late 1939! The major problem was the engines, a problem exacerbated by the cancelation of Heinkel's class-1 engine designs. Otherwise the 262 (and/or the He 280) could have been in production by early 9943 and in active service by the end of that year.
And though .50's were certainly better for dogfighting than Mk 108's (note: this is a 30mm weapon, not 37mm as was wrongly stated, a 30mm shell is ~1/2 the size of a 37mm) the rof of the M2 was only ~20% higher so this would result in less firepower lead-wise. The reason for the superiority is the higher velocity and better ballistics, as well as the higher volume of fire. Mk 103's would be good but were heavier, slower firing, and with a much higher recoil. Personaly the Brits 4x 20mm Hispano Mk V cannons were one of the best of the war. The MG 151/20 was good, but with a lower muzzel velocity, ROF, and poorer ballistic shape. The best dogfighting gun of the war was probably the 15mm MG 151/15, with high ROF (comperable to the M2), excelent ballisics, very high Muzzel velocity (considderably more than the M2 BMG) with the very powerful 15mm round. Immagine a Me 262 sporting 6 of those! Even the faster-firing M3 machine gun was of limited use in Korea, while still quite powerful, was virtually inaffective aganst almost every part of a Mig 15, except the engine. 20mm cannons or .60 calliber guns (incedentaly, developed from the MG 151/15, but with similarly improved ROF to the M3) would have been a better choice fot the ASAF fighters.


One interesting thing though, is that the US has dever used fighters with outboard jet engines. The P-59 had the nacelles half-burried in the fusalage into the wing-roots. The Navy's FH Phantom and F2H Banshee had the engines burried in the wing-roots.

And about the LE slats, they were generaly retracted at high speeds, even often in maneuvers, but durring hard turns the LE of the wing would loose pressure, allowing the slats to extend, so turning would have been marginally improved by them.

One thing the P-80 had (again absent in the YP-80A) was air-breaks, this was an obvious advantage on the Me 262...

[Soren]

Glider & Bill,

The Me-262 & F-86 were both fitted with the LE automatic slats because of a desire to improve slow & high speed maneuverability in the horizontal plane. That they lower the stall speed and increase the controllability of the a/c close to the stall is why they're also very useful at landing & take off.

The LE slats work by delaying boundary layer seperation, increasing the critical AoA & CLmax of the airfoil by approx. 25% in the covered areas. The slats function by means of airpressure, as the the pressure starts to decrease on the top of the wing the slats start to deploy, the speed of which is completely determined by how quick the change in AoA is. Bf-109, Me-262 & F-86 pilots generally all loved this device because of its very positive effect on the turn rate & stalling speed of the aircraft.

Later versions of the F-86 featured an extended sharp leading edge instead which gave better high alt performance (6-3), but at the expense of decreased maneuverability in the horizontal and a higher stall speed. For this reason the Canadians kept the slats on their versions and in comparative tests the Canadair Sabre would always outturn their US counterparts. The later developed F-86F-40 went back to using LE slats for this reason, and it also decreased stalling speed by 21 mph compared to the earlier 6-3 equipped F-86F.

[drgondog]

[QUOTE=Soren;301213]Glider & Bill,

The Me-262 & F-86 were both fitted with the LE automatic slats because of a desire to improve slow & high speed maneuverability in the horizontal plane. That they lower the stall speed and increase the controllability of the a/c close to the stall is why they're also very useful at landing & take off.

Understood.

Having said that, Edgar Schmeud said it (F-86 LE slats) was primarily the mandatory design feature to keep the F-86 able to avoid tip stalls at practical design landing speeds. It specifically was not introduced to improve high speed turn capability

The LE slats were a bonus for manuever but unlikely to surface on the 86 had they not had the problems they had with low speed safety.[/B]

This was first USAF swept wing design in production fighter and drew heavily from Me 262 studies.

[drgondog]

[QUOTE=kool kitty89;301046]I think the Yakovlev Yak-25 - Wikipedia, the free encyclopedia was the last fighter (albeit an interceptor) with outboard nacelle-mounted engines. Yakovlev Yak-25 - Wikipedia, the free encyclopedia

QUOTE]

You are right. Instead of 1950 I should have stated 1951 as last time a twin nacelle jet fighter was designed.

[kool kitty89]

The 86 sure did rely heavily on research from the Me 262 program. Just look at how poor the XP-86 was doing with the original strait-wings based on the Mustang's (with much thinner chord), speed performance was wors than that of the much heavier P-84, which used the same engine and had thicker wings. (it was also worse than the P-80B and C)

[Soren]

And about the LE slats, they were generaly retracted at high speeds, even often in maneuvers, but durring hard turns the LE of the wing would loose pressure, allowing the slats to extend, so turning would have been marginally improved by them.

That is incorrect Koolkitty. As have already been explained the slats work by means of airpressure, deploying and re-deploying depending on the AoA being pulled, therefore they are AoA dependant devices, they are completely independant of speed.

And an increase in lift and critical AoA of ~25% is hardly something you can call "marginal" KoolKitty. The slats are infact hugely beneficial to turn rate at both high & low speeds, hence them being used on nearly every fighter since WW2.

A great invention indeed, kudos to Handley Page for being the first to patent it.

[Glider]

Soren
Can I ask if the slats on the 262 were spring operated?

[Soren]

They were not. They were essentially free moving devices, but in flight airpressure determined wether they were to deploy or re-deploy, the shifting airpressure gradually pushing them out as AoA increases or gradually pushing them in as AoA decreases.

[kool kitty89]

Sorry, I meant that in slow maneuvering (low G) the slats would not deploy, but with harder maneuvers the slats would extend to prevent a stall.

Thanks for correcting on the operation of the slats, I knew they were air-pressure operated but I wasn't sure if it was pressure on the LE of the wing or elsewhere. Sorry, I misspoke with the "marginal" comment...

Though this still doesn't mean it will be more maneuverable than the P-80, it just means it will be more maneuverable than a 262 w/out slats.

Plus, as stated, the high-aspect-ratio wing, despite decreasing induced drag, increased parasitic drag, and both the P-80 and 262 have very thin (for the time) airfoils, its just that the AR of the P-80's was somewhat lower (but not by too much) and that the wing roots on the P-80 were thicker at the wing-fuselage junction. In fact, if you compare the wing-area and span of each craft, both are almost the same, the span is less than 3ft longer in the 262, and area is less than 5 ft2 more on the P-80, the shortness of the P-80's wings is exaggerated by the sharper taper of the wing.

Also these planes wouldn't be meeting at top-speed (probably ~480-500mph at the start of combat, assuming no dives) and speed would quickly drop tho the 400 mph range once maneuvering began, possibly even lower, so medium-speed handeling would be far more important...

[Soren]

Koolkitty,

A difference in AR of over 1.0 is considered much, esp. when looking at the change in the L/D curve. Plus the AR of the Me-262's wing is higher than 7.23 when you start to incorperate the sweep of the wing.

Parasite drag is completely irrelevant in maneuvering flight Koolkitty, while induced drag is very important being an absolutely essential factor to the turn performance of the a/c here. Parasite drag, which relates very much to frontal area, is important in straight flight as it has a great effect on the top speed of the a/c, but in maneuvering flight it is irrelevant.

So lets look at it;

The Me-262A-1a has a empty equipped weight of 3,800 kg, while the P-80 has a empty equipped wieght of 3,819 kg. Thats a wing loading of 175 kg/m^2 vs 173 kg/m^2 respectively, and now consider that the Me-262 has a CLmax approx. 20% higher than that of the P-80, when taken into consideration the result is a 35 kg/m^2 lighter wingloading for the Me-262.

[kool kitty89]

But role was certainly much better on the P-80...

And this comparison test:

The USAAF compared the P-80 and Me 262 concluding: "Despite a difference in gross weight of nearly 2,000 lb (907 kg), the Me 262 was superior to the P-80 in acceleration, speed and approximately the same in climb performance. The Me 262 apparently has a higher critical Mach number, from a drag standpoint, than any current Army Air Force fighter."[7] The Army Air Force also tested an example of the Me 262A-1a/U3 (US flight evaluation serial FE-4012), an unarmed photoreconnaissance version, which was fitted with a fighter nose and given an overall smooth finish. It was used for performance comparisons against the P-80. During testing in May-August 1946, the aircraft completed eight flights spanning four hours and 40 minutes. Testing was discontinued after four engine changes were required during the course of the tests, culminating in two single-engine landings.

With the gross weight difference of 2000lb statement (assuming this comparison test is real) they were obviously referring to the Goblin (under)powered (2,400 lbf) XP-80 which, as said before was a drastically different design, and it's top speed was barely past 500 mph and climb was barely past 3,000 ft/min.

I've never seen a comparison between the XP-80A or mention of agility...

[Soren]

Yes, the roll rate was better on the P-80.

[Glider]

There is no doubt that Induced drag is more important in manoeuvring as it comes into play at lower speeds. Obviously, the one thing that you lose when manoeuvring, is speed.
The problem for the Me262 is that induced drag is considerably higher for aircraft with swept wings, due to the greater upwash.

At the end of the day the 262 was designed for speed not manoeuvring. The swept wing has huge advantages for speed which can be translated into climb and acceleration. However the wing is not good for a turning fight.
The slats were I am sure a solution to the slow speed handling and may have helped to some degree at high speed but dogfighting a 262 wasn't playing to its strengths.

[kool kitty89]

The 262 was built for more speed than she could do in level flight... With some 004D/E engines it might have pushed her into the maximum designed range... Or maby if the HeS-30's (006) had been fully developed and used on her...

Still she was a good a/c, no doubt about that, I'm just not sure that she would have been the better dogfighter of the two... The 280 with better matching engines (fully developed HeS-8 engines, or preferably, HeS 30's) would have probably been the best dogfighter of the war, even capable of out-turning piston fighters. Optimised for medium speed maneuvering (realitively high speeds for dogfights at 400+ mph, with turn performance at 500 mph probably lower than the 262 or P-80) and with excelent wing-loading, thrust/weight (especially with 006 engines) and a good fighter armament. Wings fairly thick compared to the P-80 or 262, but thinner than the Meteor's (about the same as the Vampire's or Spitfire's) and with a decent Mach limit of .79 (same as the long-nacelle Meteor III/4 and the Vampire I). The eliptical wings also offered a good lift to drag ratio, particularly if they were also laminar flow.(not sure of the airfoil type, and the high lift:drag is an inherant quality of the eliptical planform iirc)