262 vs F-86

[drgondog]

T-2-711 and T-2-4012 and 711 crashed after engine failure.

As to 'no affect' to 4% reduction in Weight?  W=L ; the CL' (new CL) is a function of (1-.04)*W/(qS) = (1-.04)W/(1/2*rho*(*V')>>2)*S) where v' is slightly more than V at GW=14000.

I had a brainfart in carrying around the 1-.04 factor which only belongs to the reduced Lift from 14K to 13.5K

It ain't much but CL for the 13500 is less than CL for 14000 and CL>>2 is less for induced Drag, enabling higher speed for same thrust... and lower W/L and more excess power over drag for 13,500 vs 14000 which enables higher ROC.  I'm too lazy to run the iterations for v' and solve for CL'.

Summary - weight reduction consistent with structural integrity improves all key performance metrics.

[GScholz]

In other words you now agree that a 4% reduction in weight is insignificant with regard to top speed?

[Tank-Ace]

The thing about speed is that it gives one the ability to dictate the terms of the fight in large measure. I mean lets face it, if you just refuse to turn with an A6M and keep your speed up, they're about the most harmless fighters in the game.

Thats not to say they aren't good fighters, just that they lack the ability to force a fight on their own terms.


The same situation occures when one tries to engage a 262 with a slower aircraft from co-alt. You'll get one pass at most, that being a HO or extreme deflecton shot, and then he's gonna either stay away from you, or convert that 500mph into about 6-8k of altitude, and bounce you from above.

[bozon]

Thats not to say they aren't good fighters, just that they lack the ability to force a fight on their own terms.

Actually that does make them not so good fighters. Zekes, KI43, Brewsters and co. do somewhat well in the MA because of the very unrealistic conditions - they basically feed of scraps of the 1945 speed monsters. I remember many scenarios and special events of A6Ms vs. F4Us. The A6Ms never stood a chance when there were no fast fighters to force the F4Us to slow down and duke it out. In real life, a pilot in danger will simply dive to the clouds and happily RTB without kills, but with his life. In AH it is the exact opposite - most players will prefer to take a bad chance for a kill rather then spend 30 minutes buzzing about and RTB with nothing to their credit.

[Debrody]

In AH it is the exact opposite - most players will prefer to take a bad chance for a kill rather then spend 30 minutes buzzing about and RTB with nothing to their credit.

uhm, unfortunately thats not always true, there are many extraordinary timid pilots out there.
Otherwise, i pretty much agree with your post. AH is much more of an air quake than a realistic environment.

[drgondog]

The 262 carries approx. 3,200 lbs of fuel. Take one up offline set fuel burn to 0.001 and see how much of a difference there is in top speed with 100% and 25% fuel. You'll notice that the difference in top speed at SL is no more than 1-2 mph, and that's with a weight difference of approx. 2,400 lbs. You seem well versed in aerodynamic nomenclature, so I'm sure you know that induced drag only represents a minute part of total drag at such high speeds. A 4% reduction in weight would not affect top speed of the 262 in any measurable way; at least not with 1940s instruments.

You're right.

I ran the numbers for a test case - assuming top speed, level, on the deck at 510mph TAS and got ~ 2 mph with some assumptions, namely that the drag rise due to compressibility was less than a delta of .002 of total CD at .66M at STP and therefore not yet into the onset drag rise region of CD vs M for both the Me 262 and F-80.  Induced drag is low (CDi=~.000399 for 14K and ~, .00029 for 11.6K). Parasite drag will dominate until the wing moves into Mcr, where in a short time if V continues for both of these ships, Compressibility drag will dominate CD. Actually because of the Mach range for both the 262 and P80 flying at top speed neither will realize  benefit of losing 4-10% of their weights with same thrust of more than 2+ mph.  

That much weight reduction would positively affect climb rate significantly, however.

  

 

[drgondog]

In other words you now agree that a 4% reduction in weight is insignificant with regard to top speed?

Yes - CL reduced from .000399 at 14K to .000299 at 11,600 - which would ~ 1/2% change in CD at 510mph/SL

[GScholz]

 


Yes, climb rate would be affected, but at 4% it would be about 150 ft/min (correct me if I'm wrong). However, given the general poor condition of the tested 262s and the maintenance difficulties mentioned in the report I would not be at all surprised if those 262s underperformed despite any weight loss during testing.

[drgondog]

Yes, climb rate would be affected, but at 4% it would be about 150 ft/min (correct me if I'm wrong). However, given the general poor condition of the tested 262s and the maintenance difficulties mentioned in the report I would not be at all surprised if those 262s underperformed despite any weight loss during testing.

Let's back up a bit. We started at discussing differences in dash speed by reducing the weight from 14000 to Depending on the altitude and the Thrust for that altitude, It should be proportional to ~ W2/W1 14000/(1-.04)*14000 =  ~4.2 %higher ROC than at 14000 pounds.

ROC = V*Sin(Theta).  If you hold the thrust and Velocity constant for both GW's, and assume small variation in airspeed due to reduced Induced drag, then for 14000, (T*V-D*V)/W1=ROC1 in vertical component of Freestream velocity = (T*V-D-V)/14000..

Similarly at 13,440;  (T*V-D*V)/W2 = (T*V-D*V)/13,440= ROC2 for lower GW.  Of course its not precise because the lighter weight ship at same top end velocity is climbing at different angle from Theta@14000 pounds and vortex drag due to lift will play with Drag total by increasing it and cause the Me 260 to slow down a bit in the climb.

So, it 'depends' but the 'delta' ROC2 at seal level is closer to 187 fpm (3fps) from ~510mph and 4500 fpm at 14000 pounds (using a number quoted but not from that Test paper).   

As an aside One of the P-80s at Wright Pat undergoing tests was 44-85044 which was described in the 1946 Test Reports as the worst performing P-80A-1 in USAAF inventory.  Have no idea what aircraft were used.

Having said that, it was clear that T-2-711 and 4012 had issues with the engines as 711 crashed due to engine failure and multiple engine changes had to be made during the evaluation.

[GScholz]

If it helps, the best climbing speed of the Me 262 was about ~450 km/h IAS.

[drgondog]

If it helps, the best climbing speed of the Me 262 was about ~450 km/h IAS.

ahh, it doesn't really.  my 510mph was a guess 'best dash' at SL, pegging Drag = Parasite Drage + Induced Drag + Compressibility Drag + Wave Drag at that speed of .66 M, then stripping out everything but Parasite Drag in the assumptions, knowing that Drag in level flight is less than at a positive angle of attack in a climb... why should I obtain 'real data'? when I made so many assumptions..

I was looking for a rule of thumb/close enough type result.

[GScholz]

Ok, let's agree on 187 ft/min then. I bet that number is well within the variances of different 262 airframes and engines. After all, the 1945 ones that the Allies got their hands on were built from scrap under the open sky; some of them even had wrinkles and bumps.

[drgondog]

The best way to peg the potential performance is to put reliable 1900 pounds of thrust engines to the calculations but I have never seen a validated CD0 or a CD vs M drag plot....

And my 187fpm delta is a swag based on stripping some 390 gallons of jet fuel (and armament) from the loaded mission weight.

[titanic3]

uhm, unfortunately thats not always true, there are many extraordinary timid pilots out there.
Otherwise, i pretty much agree with your post. AH is much more of an air quake than a realistic environment.

Ain't that the truth.