Stability and Control characteristics of the Early Mark Spitfires

[Igo kyu]

Originally Posted by Glider

I totally agree with your friend. Ask him what he thinks about theories that have no support, I am confident that he will consider it a theory no more and no less.

No it's not. It is a hypothesis, which is the early stage of a theory.

[Glider]

Originally Posted by Igo kyu

No it's not. It is a hypothesis, which is the early stage of a theory.

point taken

[MiG-3U]

Originally Posted by 6S.Manu

If you provide a method to identificate which poster are part of the "blue side"...

Well, I see blue side planes on the signatures, is that a poor indicator? Sorry if you feel offended.

Originally Posted by 6S.Manu

Anyway it's not a smart question: "why only the blue side want the the feature modelled?" can easily become "why only the red side don't want the feature modelled?"

Actually I'm asking why you, regardless your color, are demanding that the longitudal stability and elevator control of the early Spitfire's after the worst case scenario?

The worst case scenario means here a Rotol propeller and CoG behind the aft limit for that configuration, like in the NACA tested Spitfire.

Note that typical pre war or BoB service CoG for a Spitfire with DeHavilland propeller ok even for the Spitfires flying today. Actually even the CoG NACA used for a Rotol propelled variant is ok with the DeHavilland prop... but not with the Rotol prop.

And the manual containing control reversal warnings is for the Rotol propelled variant.

Originally Posted by 6S.Manu

Do you mean that the test in the first post is not real?

Of course it's real but if you question pilots comments, you should also apply the same standard for all the data, including that report:

1. They did not know the CoG for military load.
2. They tested just one CoG position.
3. The CoG they used, 31.4" behind leading edge at the root is 7.8" aft datum. The rear limit for the same configuration is 7.5".

Originally Posted by 6S.Manu

No... There is a ton of documents in this thread... I don't think to have questioned them all.

Actually you should, and more precisely, put things on right contex. Yes, there is plenty of documentation posted, including critics on NACA test (even wartime critics by RAE).

[Crumpp]

They did not know the CoG for military load.
2. They tested just one CoG position.
3. The CoG they used, 31.4" behind leading edge at the root is 7.8" aft datum. The rear limit for the same configuration is 7.5".

31.4%....MAC

[ATAG_Dutch]

[Crumpp]

The worst case scenario means here a Rotol propeller and CoG behind the aft limit for that configuration, like in the NACA tested Spitfire.

Fixed Pitch Wooden Airscrew

Longitudinally, the aircraft is stable with centre of gravity forward, but is unstable with centre of gravity normal and aft with engine 'OFF' and 'ON'. Longitudinal stability records are attached.

http://www.spitfireperformance.com/k9787-fuel.html

[Crumpp]

Note that typical pre war or BoB service CoG for a Spitfire with DeHavilland propeller ok even for the Spitfires flying today.

Not with the longitudinal instability......

[NZtyphoon]

Originally Posted by 6S.Manu

Mine was a compliment.
OT: BTW Can I ask if you know a source for the RR Merlin family? I'm trying to develop a framework about engines and I'm interested to have some data.

I'm not asking you to do my work: I need only a clue about a website or a book. Thanks!

No problems: a reasonable starting point can be found on this site:
http://www.spitfireart.com/merlin_engines.html

Some valuable articles can be downloaded from Flight Global:
eg: http://www.flightglobal.com/pdfarchi...42 - 0449.html
http://www.flightglobal.com/pdfarchi...42 - 2609.html
or
http://www.flightglobal.com/pdfarchi...0-%200164.html

or for the Griffon

You can download a Merlin 61 Maintenance Manual Here (via DepositFiles)

One really good source for books is the Rolls-Royce Heritage Trust

Hope this helps.

[NZtyphoon]

The worst case scenario means here a Rotol propeller and CoG behind the aft limit for that configuration, like in the NACA tested Spitfire.

Originally Posted by Crumpp

Instead of just being smart and making rolleyes how about proving, with documentation, that this statement is incorrect. Prove that you are not making a worst-case scenario out of just two documents: Prove that the Spitfire had such bad longitudinal stability characteristics that it affected its abilities in general flight and in combat and, above all PROVE that this can be replicated in a flight sim made for PCs.

[Crumpp]

Instead of just being smart and making rolleyes how about proving, with documentation,

This is the second or third time in this same thread the same argument has arisen.

The instability existed in all early mark Spitfires at normal and aft CG until it was fixed with the inertial weights.

It is a function of the tail design and elevator, static margin, and fuselage length.

The Operating Notes are full of warnings about it. It was not limited to one propeller or a specific load.

It was at NORMAL and AFT cg.

NORMAL....

Noun: The usual, average, or typical state or condition.

Your whole premise of the Constant Speed Propellers being the "most adverse condition" is just plain wrong.

Which do you think is heavier? A three bladed CSP or a two blade fixed pitch wooden propeller? The correct answer is the CSP.

What do you think happens to the CG when you add weight to the front of the aircraft? Do you think it shifts forward or back?