109 Flaps

[Crumpp]

If Guppy's quote is right, not even the prop is the stopper. It has been shown that the measurements were ok.

Sure Angus.

We can bend physics for your favourite plane.

[Nashwan]

The mach 0.89 chart is for the same aircraft, but not on the same dive as when the prop came off. I don't know what speed was reached in the flight when the damage occured.

The RAE report that records the mach 0.89 dive was written in January 1944. It notes that all the flights were carried out by Sq ldr J R Tobin. As Guppy points out, the flight where the prop seperated was in April 1944, and Sq ldr Martindale was flying.

It was the same plane, though.

Oh, as a sidenote, - 606 TAS is how much IAS at 20K?

441, according to the chart I use. On the dive chart I've got, though, 606 was achieved at close to 29,000 ft. Speed was down to 510 TAS at 20,000 ft.

[F4UDOA]

TAS to IAS

Looks like 433MPH IAS = 606MPH TAS at 20,000FT.

[Crumpp]

Which is the placard limits.  Keep trying, I am sure you Spitfans can find a way to bend physics for your favourite plane.

606 TAS is how much IAS at 20K?

Which comes out to mach .85 using the 1976 standard atmosphere as the base.  Of course this standard did not exist in the 1940's.

Just reducing speed in a conservative 3% error for atmosphere and instrumentation yields mach .82 on the standard atmosphere.

Is it more likely the Spitfire could bend physics or more likely the difference is in the yardstick used to measure??

All the best,

Crumpp

[Nashwan]

Keep trying, I am sure you Spitfans can find a way to bend physics for your favourite plane.

I do find it a bit strange that mach 0.83 is fine in a P-47, but 0.89 in a Spitfire is "bending physics".

Which comes out to mach .85 using the 1976 standard atmosphere as the base. Of course this standard did not exist in the 1940's.

Where does the 606 mph at 20k figure come from? In the RAE chart I have, maximum speed was 606 mph at 28,820 ft. Speed at 20,000ft was down to 510 TAS, and the pullout was underway.

Just reducing speed in a conservative 3% error for atmosphere and instrumentation yields mach .82 on the standard atmosphere.

Is it more likely the Spitfire could bend physics or more likely the difference is in the yardstick used to measure??

So 3% faster for the Spitfire is "bending physics"?

[Crumpp]

I do find it a bit strange that mach 0.83 is fine in a P-47, but 0.89 in a Spitfire is "bending physics".

Nashwan,

Just the fact it has a prop on the front cast serious doubts on any claim over Mach .8.  

Instrumentation error can account for many claims over mach .8 as well.  Read Widewings post.

So 3% faster for the Spitfire is "bending physics"?

Between, the likely and unlikely, it is more likely to be instrumentation error than the Spitfire magically being able to overcome the drag of the propeller.

Where does the 606 mph at 20k figure come from?

F4UDOA says:

Looks like 433MPH IAS = 606MPH TAS at 20,000FT.

Limits of the Spitfire Mk IX in IAS(knots) from the POH:

    * S.L. and 20,000ft. - 450 (385)
    * 20,000 & 25,000ft. - 430 (370)
    * 25,000 & 30,000ft. - 390 (335)
    * 30,000 & 35,000ft. - 340 (292)

Nashwan why don't you post the full report if you have it.

All the best,

Crumpp

[Angus]

So, what is 500 mph ias at 20K? If you can do that in a ..hurry...
And Crumpp, what about those Spitfire pictures, where they broke up? Were they V's or other?

[Angus]

Oh, for Crumpp,,,again:
"Just the fact it has a prop on the front cast serious doubts on any claim over Mach .8.

Instrumentation error can account for many claims over mach .8 as well. Read Widewings post.


quote:
--------------------------------------------------------------------------------
So 3% faster for the Spitfire is "bending physics"?
--------------------------------------------------------------------------------




Between, the likely and unlikely, it is more likely to be instrumentation error than the Spitfire magically being able to overcome the drag of the propeller."

Ahem.
1. Special instruments for speed tests. Maybe a secret precise science only in the US and with the LW?
2. Not a normal fighter version Spitfire. No cannon bulges etc.
3. No prop any more.....
4. Did anybody look into the mach difference at alt?

[Crumpp]

Special instruments for speed tests. Maybe a secret precise science only in the US and with the LW?

No Angus,

It was a technical barrier for all.  As I have said from the begining, Angus.  No sides here.

The pics are not needed for this yet another silly gaming argument that boils down too:

Please make my plane do something it could not, even though it was physically impossible.

Nor do you have the "right" that I take the time to scan and post them.  They come form open source publications so you should be able to find them without a problem.

All the best,

Crumpp

[Crumpp]

So, what is 500 mph ias at 20K? If you can do that in a ..hurry...

Why don't you do it??

[justin_g]

500mph IAS at 20k? Assuming no P.E.C. ie: IAS = CAS, then using a handy-dandy NACA chart from 1943 for standard atmosphere conditions: 500mph IAS at 20k = 650mph TAS, 0.92M.

[Knegel]

Originally posted by Nashwan
................, according to the chart I use. On the dive chart I've got, though, 606 was achieved at close to 29,000 ft. Speed was down to 510 TAS at 20,000 ft.

Hi,

if this chart is right( i never saw it), it clearly show that the measurement must have been wrong, cause in general the highest speed can get reached in around 12000ft.
This is cause with decreasing temperatures the mach numbers increase, so i dont see a reason why the Spit should reach mach 9 in 29000ft, but less in 20000ft. The reson for this strange result probably is a measurement problem.

602mph in 20000ft is around mach 0,91 depending to the temperature!
Dont sounds very credible as safe divespeed. lol
I would say this datas corespondent to the IAS, that the gauges show the pilot, with all measurement mistakes inclusive!!

btw, the step between mach 0,83 and mach 0,89 is very very big!! Its only 3% more speed, but around 50% more drag!!!!

Thats the reason why most planes with common wings and dragload have a max divespeed of around mach 0,8 (+-0,03).

The reason why the P47 probably could dive faster is its heaveyer weight in relation to its drag. The P47 had relative smal wings for its weight, same like the P39, both planes got measured with similar speeds.

The Spit was a pretty light plane in relation to its drag, but the weight is the only thrust in a highspeed dive.

Greetings, Knegel

[Nashwan]

if this chart is right( i never saw it), it clearly show that the measurement must have been wrong, cause in general the highest speed can get reached in around 12000ft.

If you start a dive at 40,000 ft, and pullout at 27,000 ft, highest speed is not going to be reached at 12,000ft.

The purpose of these tests was to investigate high mach speeds (subsonic, of course), as such dives were carried out at high altitude.

This is cause with decreasing temperatures the mach numbers increase, so i dont see a reason why the Spit should reach mach 9 in 29000ft, but less in 20000ft. The reson for this strange result probably is a measurement problem.

No, the reason for this "strange result" is that the pullout started around 28,000 ft. From pulling about 0.7 G (normal to path) in the dive, G went up to 1.42 at 27,240 ft, up to 2.12 at 22,190 ft.

602mph in 20000ft is around mach 0,91 depending to the temperature!
Dont sounds very credible as safe divespeed. lol

Where is this figure coming from?

The Spitfire manual notes
* S.L. and 20,000ft. - 450 (385)
* 20,000 & 25,000ft. - 430 (370)
* 25,000 & 30,000ft. - 390 (335)
* 30,000 & 35,000ft. - 340 (292)

430 at 20,000 ft is about 590 TAS. That's about mach 0.84 (and the manual says limit is 0.85)

In the dive test I have, speed at 20,080 ft was 510 TAS.

I would say this datas corespondent to the IAS, that the gauges show the pilot, with all measurement mistakes inclusive!!

The manual figure certainly does, as it was a guide for pilots.

btw, the step between mach 0,83 and mach 0,89 is very very big!! Its only 3% more speed, but around 50% more drag!!!!

For the same plane. But for a plane with a higher critical mach, and therefore later onset of mach divergent drag? It could be less drag.

The reason why the P47 probably could dive faster is its heaveyer weight in relation to its drag. The P47 had relative smal wings for its weight, same like the P39, both planes got measured with similar speeds.

It also had pretty thick wings.

The Spit was a pretty light plane in relation to its drag, but the weight is the only thrust in a highspeed dive.

At what speed? Once mach diveregent drag starts to increase sharply, it dwarfs all other forms of drag. A plane with a later onset of MDD can have much lower total drag at high speeds.

To nick an image from Nasa:


That shows the plane with the thinner wings having lower drag at all speeds, but that's not necessarily the case in all aircraft. Imagine a plane with thinner wings, higher drag at low speed, but entering MDD later:



Aes you can see, it has lower drag at low speed, but because it enters MDD at lower speed, it has higher drag at very high speed.

[Crumpp]

That shows the plane with the thinner wings having lower drag at all speeds

All a correct but mute point as we have drag polars of the Spitfire.  It was unremarkable for a WWII fighter.

All the best,

Crumpp

[niklas]

Originally posted by gripen
Absolutely not. The Spitfire wing showed typical unwanted characters at high mach numbers for the profile used ie loss of lift, steep decrease of Clmax, pitching moment changes, large increase of drag at higher Cl etc. But if compared to other planes using similar profiles (like the P-38), these characters were much less pronounced and delayded due to relatively thin profile.

gripen

gripen, you named naca reports etc. speaking in favour of the spitfire.
Why don´t you say that ALLl naca report  mention a thickness ratio of 30-40% to be favorable for high speed flight?

I just happened to be in England and by luck spotted a sign to an aviation museum which turned out to be tangmere. They have a spit5 there and some post war world record jet plains. The difference is SO obvious. The spitfire with 20% chord ratio, steep gradient right away from the edge (don´t forget it´s depth, the win is thicker than that one of a 109!). That gets even more pronounced because the 22xx is pretty flat on the lower side, so the vast majority of the whole thickness is achieved on the upperside.
After the max. thickness, the turn towards a decreasing thickness is also VERY pronounced on a spitfire.
Both features, steep gradient in the pressure gaining section and aprupt turn towards decreasing thickness is EXACTLY  the opposite of ALL late, post war and current designs who have all a shallow gradient due to 30-40% chord placement, a more symmetric layout on upper and bottom side and especially (and this is first mentioned in german sources during the war) a flat middle seciton on the topside to allow a gentle recover from supersonic airflow. Go to tangmere and compare the airfoils of the spit and the early jets there, it´s SO obvious!

Naaa, believe what you want. I respect the pilot who did the dive tests, regardless whether they were british, american, russians or german or any other country, but with such a desing claiming 0.89 can only be a hint that they had insufficent knowledge about interpreting transsonic flight results (at least in england).

niklas