Advanced designs

[kool kitty89]

Oh, and I checked again and the Meteor III was ~1000 kg heavier than the Mk I, though still somewhat lighter than the Mk IV. But the Wing area figures are corect, and even the Mk IV and F-8 had lower wingloading than the 262 despite increased weight and decreased wng area. (374 ft2 to 350 ft2)

Though the heavier Mk IV and F-8 may have been worse at turning based on airframe alone, improved roll-rate and thrust largely made up for this, thogh this comparison isn't valid anyway since Derwent V type engines weren't available until 1946, among other reasons.

And the Meteor III with long-chord nacelles was capable of 520 mph with 2000 lbf Derwent I's and 493 mph with 1,700 lbf Welland engines. (it was limited to ~450 mph with short nacelles)

 

[Arsenal VG-33]

The periods between the last year of the war, and immediately after the war, from 1943 to 1947 have always been the most fascinating, for me at least. During these years, we have just a very few of the new jet designs and copies thereof, and having so few powerplant designs forces engineers to be more creative and imaginative when it come to airframes designs.

My favorites of the immediate post-war years are those sleek little Yak 15-17-23 series. I also like the lines of this Arsenal aircraft, the VG-70:

Arsenal VG-70 - Expérimental - Un siècle d'aviation française

I always thought that a true air race would be one in which all participants must use the same powerplant, and letting the better airframe design win.

 

[delcyros]

Seriously, Delcyros, that is incorrect. The automatic LE slats start to deploy already at low AoA's, that's fact.

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.



Incorrect. The airframe is the limit, which means 8.5 - 9 G's.

What the slats do is allow the Me-262 to reach its limit earlier in the speed range than the Meteor. At very high speeds it all becomes equal as a max performance turn will either rip the wings off the a/c or make the pilot unconcious.



And that is downright wrong. Automatic LE slats do NOT increase drag at all Delcyros. What you're thinking about is fixed LE slots.

Automatic LE slats function by means of airpressure, extending gradually as the pressure on the top of the wing gradually decreases as AoA is increased. There will NOT be any "stepped" increase in drag when the slats deploy, only at the point where even the slats cannot prevent the wing entering a stall, this is at the critical AoA, but that goes for all wings, with or without slats. When the critical AoA is reached drag is suddenly and violently increased and now overcomes lift, creating a stall.

But, the tighter your turn the more the drag, and that is universal. So when the Me-262 turns tighter than the Meteor it is whilst generating more lift also generating more drag.



Again you're incorrect, by virtue of its clean design the Me-262 has much better energy retention in maneuvers than piston engined a/c. Furthermore energy retention is NOT acceleration, it refers to the rate of energy loss in maneuvers, and here the ME-262 retains its energy much longer than any piston engined fighter.

LuftWaffe test-pilot technical inspector Hans Fay:
"The Me-262 will turn much better at high than at low speeds, and due to its clean design, will keep its speed in tight turns much longer than the conventional type aircraft"

Me-262 POH, Flight characteristics:
"(2) The airplane holds its speed in tight turns much longer than conventional types"

LE-slats, unlike flaps, do not increase the Cl-max of the wing at low to medium AoA´s, Soren. I really don´t understand why You pretend them to do so. They do work by airpressure and by delaying boundary flow seperation, both is only the case at high AoA´s, at low AoA´s there is no danger of boundary layer seperation for most airfoils. Usually, LE-slats do only cover the outer part of the wing (at the area of the ailerons), that is to improve the stall behavious (the outer part of the wing still produce lift, while the inner part of the wing is turbulent, that is to give A) plenty of stick warnings for a stall and B) to ensure aileron authority during a stall), You don´t want a stall to happen on the outer wing , it´s much more violent and will induce a strong spin. Full span LE-slats (Me-262 only) increase the flyable angle of attack and due to this increase, allow more Cl-max. The downside of this is increased drag (both, by the airfoil, as drag is in relationship with angle of attack and, to a less important degree, by the deployed LE-slats itself and their higher friction resistance, respectively).
LE slats -my key phrase was "if deployed"- increase drag substantially. That indeed is the case and can be verified by various AoA-drag charts.
If You have a solution where more lift can be generated without additional drag on basically the same wing, You would push the laws of fluid dynamics beyond their limits.

For a slat see:
f63
the chart gives CL-increase ONLY AT HIGH ANGLES OF ATTACK. In comparison a normal high lift device like flaps:
f65
the chart shows CL-increase FOR ALL ANGLES OF ATTACK.

On top of all this, You failed to mention the actual airfoils and their CL-max potential. The LE-full span of the Me-262 do give 25% advantage against an Me-262 wing without them, not more. The Airfoil of the Meteor does start with a notable Cl-max advantage over the thinner -262 wing.

Furthermore, with "energy retention" I do not mean loss of energy due to turning but "stockpiling energy" in order to keep turning. Any turn is an acceleration by definition of physics and requires energy. Planes with high acceleration will quicklier reload their energy after turning. The Me-262 unfortunately does need more acceleration ellbows than it´s piston prop adv.
Basically, in a high aoa condition (where the deployed full span LE-slats give some 25% advantage in Cl-max), the drag is substantially increased, too. At this condition, the Me-262 depletes her energy rapidly due to increased drag. The Me-262 has an excellent energy retenetion if the turn is large in diameter (=low aoa, less energy needed to sustain the turn, LE-slats not deployed) due to the clean airframe and this has been verified by various pilot accounts. That is due to the low thrust to weight ratio. The Me-262 is simply badly underpowered to sustain high aoa-turns without either rapidly loosing it´s energy or trading altitude.
This is the reason why the Me-262 were successfully engaged in dogfights by piston prop A/C (f.e.Kozhedub said post war that he was only able to kill the Me-262 on feb.17th, 1945 because the driver was stupid enough to engage a turning fight instead of using energy tactics)

 

[Soren]

Delcyros, instead of dodging try actually reading what I wrote.

Like I said with higher lift comes higher drag, that is inevitable, simple law of physics. So like I said, the tighter your turn the higher the drag, and that is universal. So when the Me-262 turns tighter than the Meteor it is whilst generating more lift also generating more drag.

And yes the Me-262 does have poor low speed accelleration, however as speed reaches ~400 to 450 km/h the Me-262 starts to out-accelerate propeller a/c fast!

Also remember that we're comparing the Me-262 Meteor here, not the Me-262 and piston engined fighters, thus the energy loss in a tight turn will not be any higher than that of the Meteor, actually it will be lower because of the higher AR wing.

And about energy retention, well like I said it refers to rate of which energy is lost in maneuvers, nothing else. What you're talking about Delcyros is the rate of which energy is regained AFTER maneuvering - two completely different things!

Now about the automatic LE slats, well in fear of repeating myself; NO they do NOT increase drag Delcyros, and I have no clue what ever gave you that idea. As explained 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. There will NOT be any "stepped" increase in drag when the slats deploy, only at the point where even the slats cannot prevent the wing entering a stall, this is at the critical AoA, but that goes for all wings, with or without slats. When the critical AoA is reached drag is suddenly and violently increased and now overcomes lift, creating a stall.

And yes the slats start to deploy early on in the AoA range, they're dependant on air-pressure and thus the speed level of they're deployment is dependant on this pressure. Try flying a real a/c equipped with this device, you'll see that the slats start deploying very early on.


So these are the simple facts:

1. The automatic LE slats start to deploy already at low AoA and gradually extend until fully deployed at around the airfoils critical AoA and increasing it by an additional 25% percent.
2. The slats do NOT increase drag
3. The tighter the turn the higher the drag

 

[kool kitty89]

The slats will also be extended in level flight at low speeds (such as in take-off and landing) as well due to the low airpressure on the slats, correct?

From my general (albeit limited) understanding of automatic LE slats, the improve stalling characteristics for both low speeds at low AoA (or level flight) and at high AoA even at hih speeds. (ie when ever airpressure decreases the slats begin to deploy which results in a relative increase in lift) But if lift increases so should drag, though the Lift to Drag ratio may stay the same.


Another thing to considder, which I had forgotton about, is that the Me 262's fusalage was designed to utilize some airfoil characteristics and actually generate lift itsself, how affective this was I'm not sure.

 

[delcyros]

Like I said with higher lift comes higher drag, that is inevitable, simple law of physics. So like I said, the tighter your turn the higher the drag, and that is universal. So when the Me-262 turns tighter than the Meteor it is whilst generating more lift also generating more drag.

True.

And yes the Me-262 does have poor low speed accelleration, however as speed reaches ~400 to 450 km/h the Me-262 starts to out-accelerate propeller a/c fast!

...and in return will find itselfe beeing outaccelerated by the Meteor....

Also remember that we're comparing the Me-262 Meteor here, not the Me-262 and piston engined fighters, thus the energy loss in a tight turn will not be any higher than that of the Meteor, actually it will be lower because of the higher AR wing.

While AR-ratios beeing a case for importance, Your statement in context of our comparison is pure speculation, Soren. AR-ratio differences -the way You used them- are only true for wings with identic properties as to AIRFOIL, REYNOLDS-NUMBER and basic planform (except chord-span relation). Are You going to say that Meteor and Me-262 have the same airfoil, same chordlength, same planform? In orcer to support Your claim You need the EXACT aerodynamic properties of each wing, respectively.

And about energy retention, well like I said it refers to rate of which energy is lost in maneuvers, nothing else. What you're talking about Delcyros is the rate of which energy is regained AFTER maneuvering - two completely different things!

Indeed but nontheless important, too. I a going to stress the opinion that the Me-262 is no turnfighter. Turning at such high aoa´s will bleed off the remaining energy quickly. And the Me-262 has a harder time to get the ernergy back...

As explained 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. There will NOT be any "stepped" increase in drag when the slats deploy, only at the point where even the slats cannot prevent the wing entering a stall, this is at the critical AoA, but that goes for all wings, with or without slats. When the critical AoA is reached drag is suddenly and violently increased and now overcomes lift, creating a stall.

Nor did I ever spoke of a "stepped" increase in drag. The slats do NOT increase CL-max per se, they just allow a higher angle of attack to happen due to delying of boundary layer seperation. higher angle of attack = more Cl-max = more drag. BTW, there is additional drag due to the increased surface of deployed slats and related friction resistance.

And yes the slats start to deploy early on in the AoA range, they're dependant on air-pressure and thus the speed level of they're deployment is dependant on this pressure. Try flying a real a/c equipped with this device, you'll see that the slats start deploying very early on.

Slats are dependent on air pressure, correct. However, THEY DO NOT INCREASE CL-MAX AT LOW AOA´s , deployed or not. You have Your own charts to proove this. If You doubt this, feel free to submit Cl-max-aoa charts, which say the opposite. I have provided such charts above. You won´t find any supporting lift increase at low aoa´s. Therefore, it´s pretty irrelevant if LE-slats deploy at low aoa´s, if they deploy, they do add only friction drag, not lift. LE-slats are useful at high (better say extreme) aoa´s, when the wing -in other conditions- would have been long stalled. They do DELAY boundary layer seperation, they don´t make the boundery layer thicker or so. THE 25% CL-max INCREASE IS ONLY AVAIABLE AT HIGH AOA´s.
That means in return that maximum sustained turn rate and minimum steady state turn radius are at or near stall speed, a regime any sane pilot in a badly underpowered A/C will avoid in combat.

 

[Soren]

Delcyros,

No, the slats do NOT increase CLmax at low AoA, and I never claimed that they did. However the slats DO start to deploy at low AoA, that's fact, and this was the issue we were discussing, but you've seen your mistake now so all is OK.

...and in return will find itselfe beeing outaccelerated by the Meteor....

No that is again wrong Delcyros.

Answer me which is faster, the Meteor or the Me-262 ? That's right, the Me-262 is, significantly so, and so at 400-450 the Me-262 will quite easily out-accelerate the Meteor.

The Me-262 also had a decent climb rate advantage at 3,900 ft/min.

While AR-ratios beeing a case for importance, Your statement in context of our comparison is pure speculation, Soren. AR-ratio differences -the way You used them- are only true for wings with identic properties as to AIRFOIL, REYNOLDS-NUMBER and basic planform (except chord-span relation). Are You going to say that Meteor and Me-262 have the same airfoil, same chordlength, same planform? In orcer to support Your claim You need the EXACT aerodynamic properties of each wing, respectively.

While it is true that the exact figure is only obtainable emmidiately when comparing wings with the same airfoil planform, we do nonetheless know that everything else being equal the higher the AR the higher the Clmax and the lower the Cd0, increasing the L/D ratio, which is VERY important to the turn performance of the a/c. Also we can conclude with certainty that the planform of the Meteor's wing is inferior as the engines terminate allot of wing area by being mounted in the middle of the wing.

BTW, there is additional drag due to the increased surface of deployed slats and related friction resistance.

Wrong again, now you're just making assumptions. Automatic LE slats do NOT add any drag when deployed, they rather drastically decrease it by increasing the critical AoA by 25%. The only additional drag that is created when the slats deploy is that which originates from the higher lift generated because of the increase in the AoA.

Remember that at the same angle of bank and velocity two fighters make exactly the same turn.

 

[kool kitty89]

The acceleration of the Meteor III would be dependent on weight and thrust values and if long chord nacelles were fitted. Thrust/weight of the with derwent I engines would be about the same (actualy slightly higher) as with the 262 and at dogfight speeds quickly reached in maneuvers (dropping below below 600-650 km/hr) the Meteor would likely accelerate better, particularly if Derwent II or IV engines were used. (which, as said, would have been available before the end of the war--and even if they weren't used for whatever reason, they easily could have been fitted to later production Meteor III's and retrofitted to others like was often done with the new nacelles).

As for climb, I havent seen any specifications for the Meteor III's values, but with similar thrust/weight (and much higher thrust than the Mk.I as well s better aerodynamics) and much lower wing-loading, the Meteor III shuld outclimb the Me 262. (with more weight and less wing area and much more thrust the F.Mk IV and F-8 had initial climb rates of 7000 ft/min, 2134 m/min)

 

[kool kitty89]

I've seen very few comprehensive specifications and statistics on the Meteor III. Some say ~493 mph top speed, others as high as 520 mph but never specify altitude or if long-chord nacelles were used. (although with any speeds over 450 mph would imply long-chord nacelles) The use of the more powerful Derwent II or IV engines (2,200 and 2,450 lbf) which would have been available for late model Mk. III's aren't mentioned either. The weight figures also seem to vary.
The Gloster Meteor sites that "The new nacelles increased the redline speed at altitude by 120 KPH (75 MPH), even without new powerplants." but the speed with short nacelles isn't sited (except for the Mk.1) and it isn't clear if "without uprated powerplants" refers to Wellands or Derwent I's. Meteor, Gloster / Armstrong Whitworth has some useful info, and it sites that 493.7 mph (795 km/hr) was reached with 1700 lbf (770 kp) Welland engines, so it would make sense that the 520 mph figure would be with Derwent I's.

Does anyone have reliable info on the Meteor III?

The same sight also says: "the ailerons had been deliberately wired to be "heavy" to prevent aerobatic maneuvers from overstressing the wings, and pilots complained that flying the aircraft could be very tiring; this had not been a problem with the Meteor I, since it hadn't been cleared for aerobatic maneuvers." So the Meteor III was cleared for aerobatics, in fact the heavy wiring of the ailerons was to facilitate clearance for maneuvers.

But one thing I've wondered is why they didn't clip the wings for the Mk.III, such as was done with early Griffin-engined Spitfires as an intrim for strengthened wings, or why not just limit the range of motion of the ailerons but not wire them heavy. (which would still limit roll-rate, but would make things alot easier on the pilot)

 

[kool kitty89]

And again, the empty (equipped) weight of the Meteor III should be 4771 kg and combat weight around 13,800 lbs (6,265 kg) (a load of 1494 kg of internal fuel only). Wing area was 34.74 m2. And assume the Me 262 has a fuel load of 1838 kg and a weight of 5638 lbs. (due to ~23% lower fuel efficiency)

So if you use the same calculations with loaded weights you get:

Me-262
weight: 5,638 kg
Wing area: 21.7 m^2

Wing loading = 259.80 kg/m^2

Gloster Meteor
weight: 6,265 kg
Wing area: 34.74 m^2

Wing loading = 180.34 kg/m^2

Soren Said:
"Now let us ignore the increase in CL the higher AR causes and alone consider that the Me-262 benefits from a increase in lift critical AoA by 25% because of its automatic LE slats:" Assuming this is correct; with the new values it gives:

259.80 kg/m^2 * 0.75 = 194.85 kg/m^2 Significantly higher than the Meteor III.

Although the Thrust/weight of the 262 would allow better linear acceleration. (although 2,200 lbf Derwent II's would put them equal and 2,450 Derwent IV's would put the Meteor ahead, though by the same thought 004D's would have to be considered; I'm not even considering if HeS-30's had been fully developed and produced, or if 2,700 lbf Goblin I engins were fitted to the Meteor)