Spit/109 sea level speed comparisons in 1.08 beta patch

[MiG-3U]

Originally Posted by TomcatViP

@Mig

Always the same, always bragging ... When did I post my "stuff" ? Tell me.

Post #516

Originally Posted by TomcatViP

Your Holtzauge did not post detailed calculation or discuss his method. I pointed one source of error. Tht's it.

Exactly the same calculation is used on the Mtt test on the prototype V15a to calculate speed at higher power at sealevel (blatt 5) posted several times here. I used the same calculation for demonstration on the post #448 and noted that it's a crude, unaccurate and partially wrong way to calculate it. However, it's good enough for small differences.

Originally Posted by TomcatViP

This is the basis in Sciences. Put it down and submit to what ppl think.

Yes, of course. But why do you complain about Holtzauge's calculation now but not about Mtt calculation which has been here much longer (or mine which was posted 3 weeks ago)?

Originally Posted by TomcatViP

ANd you just hve to open a NACA chart to see the drag rise for the specific airfoil. You don't hve to pick bit of info here and there. It's free and available.

Actually I'm refering tests of entire airframe, tunnel and flight tests. And yes, many are available. For Hoerner's Bf 109G analysis, get his Fluid Dynamics book. Some are freely available, here is one for few aircraft including Spitfire I. Below is also a Cd/mach number chart from that report attached, you can see that up to Mach 0.5-0,6 there is rather minimal drag rise due to compressibility.

Originally Posted by TomcatViP

And by the way, 10% of drag raise (outsourced from my memory) is equal to what a fully open rad will do on Seversky P-35.

Hoerner's number 10% is for entire speed range from mach 0.3 up to 0.55 ie speed changes 250-300kmh while we are talking here about 15kmh speed difference around mach 0.4, that means that drag rise is certainly certainly less than 2%, probably less than 1%.

[TomcatViP]

Originally Posted by MiG-3U

Post #516

No. Again lack of modesty in your assumption. Take a look on Youtube searching TcViP and related variables. You'll see that I posted that last time almost 3 years ago. Good Hunt

...Obviously you won't but that show you how personal arguments hve nothing to do on a forum. Even if that behavior seems rather popular Lol

Originally Posted by MiG-3U

Exactly the same calculation is used on the Mtt test on the prototype V15a to calculate speed at higher power at sealevel (blatt 5) posted several times here. I used the same calculation for demonstration on the post #448 and noted that it's a crude, unaccurate and partially wrong way to calculate it. However, it's good enough for small differences.

Small diff... Yeah. But not small diff at max speed for this kind of plane !

Originally Posted by MiG-3U

Yes, of course. But why do you complain about Holtzauge's calculation now but not about Mtt calculation which has been here much longer (or mine which was posted 3 weeks ago)?

All this story abt the 109E not reaching 500Kph is ridiculous. Juts like other big themes fairly popular here. Nothing new here so you can past those line.

Originally Posted by MiG-3U

Actually I'm refering tests of entire airframe, tunnel and flight tests. And yes, many are available. For Hoerner's Bf 109G analysis, get his Fluid Dynamics book. Some are freely available, here is one for few aircraft including Spitfire I. Below is also a Cd/mach number chart from that report attached, you can see that up to Mach 0.5-0,6 there is rather minimal drag rise due to compressibility.

Didn't I say local mach number ???? Again when your plane is traveling at Mach 0.5, your wing see a peak of high subsonic speed for a 15% airfoil section. Same with the fuselage, especially the bottle neck effect at the rear par. Yes, the 109 was very well streamlined but your calculation need to be repeatable to other type

Originally Posted by MiG-3U

Hoerner's number 10% is for entire speed range from mach 0.3 up to 0.55 ie speed changes 250-300kmh while we are talking here about 15kmh speed difference around mach 0.4, that means that drag rise is certainly certainly less than 2%, probably less than 1%.

Compare to what ?

Wil hve a look to your doc cited as refs. hoping that I won't lost my time wit another bunch of lifting line and alike theo.

If you are interested in the matter you shld read the books from Karman directly.~

A good one and easy to reach (amazon - very cheap):
Aerodynamics - Selected Topics in the Light of their Historical Development, Cornell University Press, Ithaca, 1954

The university of Warsaw hve also a very good list of PDF doc posted on theit website. Doing some Google searching you sld found it easily.

[MiG-3U]

Originally Posted by TomcatViP

No. Again lack of modesty in your assumption. Take a look on Youtube searching TcViP and related variables. You'll see that I posted that last time almost 3 years ago.

Well, I rely on what you have posted on this thread. At the post 519 you suggest that the calculation is ok "to estimate the time of accel from Stall speed to 200mph". But that is actually not true because the Cl and the hence Cd changes in large degree during acceleration as well as thrust. However, for a quick estimate for a small change as discused here, the calculation is good enough.

Originally Posted by TomcatViP

Didn't I say local mach number ???? Again when your plane is traveling at Mach 0.5, your wing see a peak of high subsonic speed for a 15% airfoil section. Same with the fuselage, especially the bottle neck effect at the rear par. Yes, the 109 was very well streamlined but your calculation need to be repeatable to other type

The testing of a whole airfame accounts all these and we know, based on Hoerner and other sources, that around Mach 0.4 the compressibility effects are minimal in the case of Bf 109G, there is no reason to believe that the Bf 109E is much different because the wing profiles are almost the same as well as the fuselage.

Originally Posted by TomcatViP

Compare to what ?

We can safely use the same rate of drag rise as given by Hoerner for assuming Cd change from 460 to 475kmh. And because the speed change is so small and we are around Mach 0.4, we can safely assume that the Cd rise is just a small fraction of that 10% given by Hoerner, probably less than 1%.

[TomcatViP]

Ok 3 post and nothing new.

I hve been tricked liked that alrdy for hundred of pages. End of conv. for me.

Here is the link to the book I cited for the reader that would be interested to get a quick snap of what are aerodynamics forces, as told by a Jedi master:

http://www.amazon.com/Aerodynamics-H...+Topics+karman

Much better read than hanging here, sadly..

May the Force (of flows) be with you.

[JtD]

If you were right, the Mach related drag increase on the 109E would happen only somewhere between 498 km/h and 537 km/h, as the top speed in first charger gear (537 km/h, 2150m, 1115 hp) and in second charger gear (575 km/h, 4850m, 1100hp) are in perfect agreement.

A plane doing 498km/h at 1018hp at sea level, should do around 555km/h at 1115hp at 2150m and 600km/h at 1100hp at 4850m, give or take a percent or two.

These figures happens to be pretty much spot on Bf 109F performance, which either means it did not suffer the E model Mach effects, or it means the problem with the data is elsewhere.

Google searching you sld found it easily