Performance of the Fw 190A on the Deck?

[Harri Pihl]

Originally Posted by Crumpp

Go back and re-read.

Graham's original point was clearly not a reply to your statement. period.

Originally Posted by Crumpp

We see the magnitude of the affect of weight in our parametric study.

Nope, it gives too high magnitude for this specific problem.

Originally Posted by Crumpp

Why do you think the forumla is there under the portion explaining the affects of weight in the aerodynamic textbooks?

The formula is mainly for calculating cruise speeds at L/D max, just like Graham pointed out earlier. It assumes constant Cl so it is not a good method for our problem here.

[Crumpp]

Wonder why it is such a hard concept to grasp that although the speed difference is small, the weight affects are extremely significant because it means every performance parameter of the design has been reduced?

[Kurfürst]

Effect of weight on Bf 109G maximum speed:
http://kurfurst.allaboutwarfare.com/...fect_speed.jpg

[Juha]

Thanks a lot Kurfürst!
if I understood right, 500kg (appr. 1100lb), from 3000kg to 3500kg, increase dropped 109G speed at SL 3 km/h.

Thanks
Juha

[Holtzauge]

Originally Posted by Juha

Thanks a lot Kurfürst!
if I understood right, 500kg (appr. 1100lb), from 3000kg to 3500kg, increase dropped 109G speed at SL 3 km/h.

Thanks
Juha

That is my understanding to. But that is for a weight increase of roughly 16% (from 3000 to 3500 Kg) If we use this info to make a ballpark estimate of a 6% increase as was the case for the Mustang (from 9680 to 10280 lb) we discussed earlier, we get around 1 Km/h for the Me109 from Kurfurst diagram.

That tabs pretty well with the 1.4 Km/h that Harri and I calculated for the Mustang previously and shows that weight within reasonable bounds is not an issue at low level high speed flight.

Q.E.D

[Harri Pihl]

Originally Posted by Holtzauge

That tabs pretty well with the 1.4 Km/h that Harri and I calculated for the Mustang previously and shows that weight within reasonable bounds is not an issue at low level high speed flight.

I got pretty much exactly same values as the chart at sea level varying the weight. At FTH I got slightly lower reduction than chart but difference is not big, at 3500kg a bit over 1km/h. Given that at clean configuration the weight was never that high, the estimation appear to work pretty well

[Juha]

I almost forgot
one more theory on seemingly inconsistend performance at deck. FW 190A had air cooled radial but for ex Typhoon, Spit and P-51 had liquid cooled engines. According to Finnish tests on Bf 109G-2 fully open radiator flaps could decrease speed up to 50 km/h at low level, in LaGG-3 case the effect of the fully open radiator flap was appr. 15km/h.

Juha

[Jukka Juutinen]

Good point. Would be interesting to know the effect on especially the Typhoon. Also would be interesting if there is info on which one of the above was affected most by the ambient temperature. After all, didn´t Finnish test show that e.g. the SB had to pull back on power even on relatively mild conditions (Finnish summer vs. e.g. tropics or desert) as even fully opened rad flaps didn´t provide adequate cooling at FT.

[Crumpp]

I have no interest in derailing this thread with discussions about 50' obstacle clearance, Cdp or some other issue which has nothing to do with the issue at hand.

Well start another one....

[Juha]

Hello Harri
Quote: “I took values from the "Lentäjän Näkökulma IV" and got 423,66km/h at 5000m for 8600kg. Assuming e=0,8, n=80% and 120kp exhaust thrust (Do 17Z seem to have ejector outlets). So while not exactly accurate, the ballpark appears to be correct.”
You are too modest, your result is well inside normal variation between individual a/c.

I thought that result of 500 lb weight increase should be fairy insignificant and even if I remembered Do 17Z tests I tried to look some fighter results and got the idea to look Spit Vc, which was some 400 lb heavier than Vb when armed with 4 Hispano cannon but found out that the max speed of the Vc tested was between the speeds of the first 2 Vbs I checked. So I thought that I must look something more substantial weight increase and checked Spit IX, 900 lb heavier and 30 mph faster at was that 2000 ft. Now I knew that that was more complicated because of different nose contours and because of bigger (and dragger) radiator in IX, I found out power curve for Merlin 61 and was looking one for Merlin 45 when I checked this thread and found out Kurfürst’s message and saw that there was no need for more effort.

Quote: “Do 17Z seem to have ejector outlets”
Most seemed to have but not all, at least DN-54 and one other, was that DN-64, anyway one Z-5, ex Z-3 a/c, seemed to have older system, ie 2 exhaust pipes which came through upper part of NACA ring.

Juha