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Offline DoKGonZo

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109 Flaps
« Reply #165 on: January 31, 2006, 12:48:43 PM »
Quote
Originally posted by Kev367th
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Originally posted by Angus
NEIN; ES KANN NICHT PASSIEREN, EIN SPITFEUER IN SCHNELLSTURZFLUG SO NAH VOM BODEN OHNE ABSTURZ, DASS GEHT EINFACH NICH.

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Your father was a hamster, and your mother smelt of elderberries?


Bzzt ... nope ... that's the French Castle from Holy Grail, not the Tobaccanist Sketch.
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Offline niklas

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« Reply #166 on: January 31, 2006, 02:02:17 PM »
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Originally posted by gripen
Niklas,
The tests were part of long term high speed research project and instrumentation improved (as well as corrections and methods overall) a lot during testing, the first tests were done some time late 1942 and testing continued still after war (at least until 1946).

gripen


Well, the problem is: They can be off in a special part of the analysis, and this can affect all measurements. No wonder that all results seem to be good then.
In the report of the dive test they mention that they corrected speed down from 0.95 to 0.89 by an altitude correction. 0.06 near mach 1, this makes a huge difference. But what if there has to be taken additional effects into account ? Another correction down by 0.06?
The report says the tube showed neglectable error up to 0.90. Fine, if you mount it in a windtunnel and calibrate it maybe. But mounted on a wing? Did they not take other influences into account except for simple raise of compressibillity according to standard tables (e.g. like shown in the fw-190 IAS/TAS char, which ends at 700km/h for example - right there where at high alitude the mach effects shows up btw... understand?)
Unfortunatly no IAS is given only EAS.
Why did they stop in ´46 btw ? At this time jets got ready and the real importance to understand high speed effects started. Did they understand that their efforts were somewhat wasted because they were off in the past?

niklas
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Offline Crumpp

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« Reply #167 on: January 31, 2006, 02:05:26 PM »
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Offline gripen

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« Reply #168 on: January 31, 2006, 02:26:12 PM »
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Originally posted by niklas
Well, the problem is: They can be off in a special part of the analysis, and this can affect all measurements. No wonder that all results seem to be good then.


It's quite unlikely that there is large systematical error to one direction simply because several different measuring devices were used (like rakes etc.).

Besides there in some cases there is plenty of variation specially in early measurements. Good thing is that RAE published corrections to earlier measurements once the methods improved. As an example wind tunnel measurements were corrected with new kind of blockage corrections afterwards (BTW NACA adopted same corrections).

Quote
Originally posted by niklas

Why did they stop in ´46 btw ? At this time jets got ready and the real importance to understand high speed effects started. Did they understand that their efforts were somewhat wasted because they were off in the past?


I don't know when they did actually stop, I have studied tests only on prop driven planes and the last report I've seen on Mustang was from year 1946. Wind tunnel data contains stuff also on planes like the Supermarine Attacker so apparently project was going on with jets.

gripen
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Offline niklas

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« Reply #169 on: January 31, 2006, 03:05:20 PM »
Quote
Originally posted by justin_g
From "Spitfire IX, XI & XVI Pilots Notes"
52. Flying limitations
(i) Maximum speeds m.p.h. (knots) I.A.S.
Diving (without external stores), corresponding to a Mach. No. of 85:
Between
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)


That´s interesting. I just tried to the machnumber for the 20k value by the fw-190 chart formula. It comes very close to the chart formula. That means up to mach 0.85 they did not take any further influences into account to correct IAS. Imo a bit optimistic...

niklas
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Offline niklas

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« Reply #170 on: January 31, 2006, 03:09:19 PM »
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Originally posted by gripen

Besides there in some cases there is plenty of variation specially in early measurements. Good thing is that RAE published corrections to earlier measurements once the methods improved. As an example wind tunnel measurements were corrected with new kind of blockage corrections afterwards (BTW NACA adopted same corrections).
gripen


I alredy said that you can compare allied tests in a kind of closed group. But comparing it to the german tests is not possible as long as we don´t have both reports and both correction methods available for a comparison.
Hehe, the outdated 2213 airfoil from the early 30ies the ultimative highspeed solution. I wonder why the X1 was not equipped with it.

niklas
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Offline Crumpp

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« Reply #171 on: January 31, 2006, 03:13:07 PM »
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Imo a bit optimistic...


Yep.  But it is fun to watch the fans post all kinds of "evidence" as to why the speed measurements were accurate.

Someone needs to call NASA, I think we can solve many of the debates right here in these forums.

All the best,

Crumpp
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Offline Crumpp

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« Reply #172 on: January 31, 2006, 03:20:34 PM »
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It's quite unlikely that there is large systematical error to one direction simply because several different measuring devices were used (like rakes etc.).


There is not until we approach the transonic realm.  

During the war, the limits were around Mach .8
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Offline Angus

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« Reply #173 on: January 31, 2006, 06:06:05 PM »
Oh dear we're already up to Mach .85 ;)

Where's the .80 wall?

and:

"Hi,

the Spitfire manual give a dive limit of around 1030km/h????"

Yes id did ;)....apparently
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It was very interesting to carry out the flight trials at Rechlin with the Spitfire and the Hurricane. Both types are very simple to fly compared to our aircraft, and childishly easy to take-off and land. (Werner Mölders)

Offline Crumpp

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« Reply #174 on: January 31, 2006, 07:20:27 PM »
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Oh dear we're already up to Mach .85


Accuracy of measurement, Angus.  

They measured mach .85 but that does NOT mean the aircraft achieved it.  It's doubtful simply due to the fact the plane has that big propeller disc on the front!

The accuracy of any measurement above mach .8 is doubtful on ANY aircraft from WWII.

All the best,

Crumpp
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Offline Grits

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« Reply #175 on: January 31, 2006, 10:21:06 PM »
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Originally posted by DoKGonZo
My hovercraft is full of eels.


You are hereby charged that on the 28th day of May, 1970, you did willfully, unlawfully, and with malice of forethought, publish an alleged English-Hungarian phrase book with intent to cause a breach of the peace.
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Offline justin_g

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« Reply #176 on: February 01, 2006, 01:47:30 AM »
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The accuracy of any measurement above mach .8 is doubtful on ANY aircraft from WWII.


There is ABSOLUTELY NOTHING to substantiate this "claim" in the NACA documents you linked. PROVE IT.
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Offline justin_g

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« Reply #177 on: February 01, 2006, 02:07:51 AM »
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Originally posted by niklas
That´s interesting. I just tried to the machnumber for the 20k value by the fw-190 chart formula. It comes very close to the chart formula. That means up to mach 0.85 they did not take any further influences into account to correct IAS. Imo a bit optimistic...

niklas


I don't follow. Are you talking about compressibility corrections?
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Offline gripen

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« Reply #178 on: February 01, 2006, 02:44:28 AM »
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Originally posted by niklas

Hehe, the outdated 2213 airfoil from the early 30ies the ultimative highspeed solution.


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
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Offline Angus

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« Reply #179 on: February 01, 2006, 03:02:28 AM »
It is quite thin. Looks about as thin as anything I've seen on a WW2 fighter.
BTW, wonder what speed demons like the Fury could do. Now there's a thin wing as well.
Neville Duke was in the racings after the war. Gonna page his book a little to see if I come up with something.
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It was very interesting to carry out the flight trials at Rechlin with the Spitfire and the Hurricane. Both types are very simple to fly compared to our aircraft, and childishly easy to take-off and land. (Werner Mölders)
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