Stability and Control characteristics of the Early Mark Spitfires

[Crumpp]

Now let's get back to the NACA report so there is a better understanding of the issue.

We will look at a condition of flight essential to a dogfighter. The ability to make abrupt turns.

The pilot must be able to precisely control the amount of acceleration he loads on the aircraft. All aircraft performance depends on velocity. In order to get maximum performance out of the aircraft above maneuvering speed, Va, he needs to be able to make a 6 G turn and not exceed that load factor to prevent damage to the airframe. Below Va, the pilot needs to control the acceleration so that he does not stall the aircraft making the abrupt maneuver as well being able to maintain a maximum performance turn.

Doing that in an early Mark Spitfire was difficult and something only a skillful pilot could perform.

First the NACA report. Abrupt 180 degree turns were conducted at various entry speeds to gauge the level of control the pilot had in maintaining steady accelerations. The turns were also done to the stall point in order to gauge the behavior and amount of control.

"In turns at speeds high enough to prevent reaching maximum lift co-efficient" means turns above Va.





"By careful flying" a pilot can hold a steady acceleration. That agrees with the Operating Notes warning for the pilot to brace himself against the cockpit to get better control when making turns.

Now lets look at the measured results.



Here we see in a rapid left turn performed at 223 mph the test pilot is unable to hold constant acceleration on the airframe. Very small variations in stick movement and stick force changes of 1-3lbs results in large fluctuations in acceleration.

Next let's look at the pilots ability to control the accelerations in the pre-stall buffet.



Here we see the pilot was able to load the airframe to 5G's in 1 second to reach the pre-stall buffet 3 times. The smooth positive sloped portion of the curve represents the aircraft flying while accelerations are increasing. The top of the acceleration curve represents the pre-stall buffet. The bottom of the curve represents the stall point.

The take away is:

1. The large accelerations change for very little elevator movement.
2. The very rapid rate at which the pilot was able to load the airframe to 5G's.
3. The equally rapid rate at which the airframe unloaded down to 2G's when the pre-stall buffet was encountered. In 1 second, the aircraft went from 5G's to 2G's due to buffet losses. This means a rapid decay in turn rate resulted.
4. The violence of the pre-stall buffet combined with the longitudinal stability and control caused large fluctuations in the accelerations on the aircraft.


Last part of the NACA we will cover for today is the stick force travel. The amount of stick travel as measured by the NACA was not acceptable.




Next let's look at the opinion of Stability and Control Engineers on the Early Mark Spitfires.









Tomorrow I will post some of the plethora of references to this same issue of longitudinal instability as found in the Spitfire Mk I Operating Notes from July 1940. You will see the same references or similar to the same issue the NACA measured in the Spitfire Mk II Operating Notes.

There is no doubt that the Air Ministry was aware of the longitudinal instability of the early mark Spitfires.

[MiG-3U]

Originally Posted by Crumpp

Which has what to do with the MAC on the weight and balance sheet?

It gives exact location of the leading edge needed for calculation (p.7).

Originally Posted by Crumpp

Spitfire K-9788 shows an aft CG that is 33.2%.

The most aft MAC with the Feb 1944 revision is 31.7%.

I claimed normal service load:

7.7" at normal service load 1939
7.9" aft limit for DeHavilland without inertia device
7.5" aft limit for Rotol without inertia device

This means that on normal combat load there was only change in the case of the Rotol prop assuming that aircraft was properly loaded.

Besides, the revised limits were originally issued sometime around 41/42.

Otherwise you seem to have chosen same tactics as in the FTH discussion so my part end here now.

Cpt Doggles, you see my point now.

[Fenrir]

You present this like it's some revelation Crummp.

If you have done *any* research you'll have read Quill's book, which you should have done considering you're talking about the Spitfire and it's flying characterisics as it's practically source point one - he test flew the aeroplane in all it's marks over 10 years and countless hours - this makes him somewhat more credible than you, so you'll forgive me if I take his word over your clearly subjective posts.

The point is addressed fully and sufficiently in there to make all your posting here as redundant it is cherry picked.

I'm not going to bother posting it here, if you're serious about research, and truly objective you'll read it and come back here and retract some of this frankly irksome Spitfire smear campaign.

[Crumpp]

Otherwise you seem to have chosen same tactics as in the FTH discussion so my part end here now.

What "tactic" is that?

You mean showing you the question on an A&P exam?

If a turbo engine is rated at 310 HP up to 18,000', the altitude specified is pressure altitude?


False, the altitude specified is density altitude

http://quizlet.com/2496371/print/


Start another thread on the weight and balance or send me a PM. I would be happy to walk you through the steps in determining percentage MAC.

It is not that hard to do. You will understand it and see how ridiculus the theory the NACA could not do one really is!!

In presenting a February 1944 weight and balance document and for the purposes of this discussion on 1940 Spitfires:

You have presented the solution to the problem in an effort to claim the problem never existed.

[NZtyphoon]

Originally Posted by Crumpp

That empty weight CG for that specific aircraft then has its specific range for foward and aft limits based on its authorized configurations. That is why the weight and balance is part of the Pilot's Handbook for that aircraft. It is required documentation and just like the Handbook, propeller logs, engine logs, and airframe logbooks follows the aircraft throughout its life.

Completely wrong, neither individual CG drawings, nor weight and balance sheets were issued with the Pilot's Notes - fighter pilots especially were rarely allocated their own aircraft and had to take what was made available. Pilot's Notes General, Section 7:


Each and every aircraft type used by the RAF and FAA had generic cg/w&b sheets printed, which had fixed fore and aft limits, beyond which the flight qualities started to suffer: Lancaster cg drawings:



Loading diagram up to L7532...


L7533 on...


Careful study shows the cg limits fore and aft were identical, despite different equipment and loadings - the airframe was the same, so the limits stayed the same - those fore and aft limits for ALL early Marks of Merlin engined Spitfires were identical, Mk I to Mk V and were not changed until the modified elevators with larger mass balances were introduced.

It was the responsibility of the groundcrew to ensure that the cg limits were adhered to. The only crews that needed to know the position of the cg were bomber crews with their large disposable loads and multiple crew positions

This is how the cg was calculated:







Relatively small changes in equipment weight and equipment position could still make a big difference to the final cg - a few kg a few inches aft of the rearmost cg position could upset the handling of an aircraft;

NACA made it quite clear that their calculations for the Spitfire may well have been in error - until Crumpp can prove that NACA had calculated the cg position correctly, according to early Spitfire cg data charts, the report needs to be viewed with some suspicion.

Originally Posted by Crumpp

Now let's get back to the NACA report so there is a better understanding of the issue.

We will look at a condition of flight essential to a dogfighter. The ability to make abrupt turns.

The pilot must be able to precisely control the amount of acceleration he loads on the aircraft.
Doing that in an early Mark Spitfire was difficult and something only a skillful pilot could perform.

Where did you get this nonsense? Show me accounts of even trainee pilots who found manoeuvring the early marks of Spitfire difficult - I repeat Supermarine's Chief Test Pilot Jeffrey Quill stated categorically that there was no problem with the longitudinal stability of early Mk I & II Spitfires.

[Glider]

A lot of words and a lot of effort into defend a position or a view but nothing to address the basic question:

You still have the question that has yet to be addressed. If in theory the Spitfire was so poor in its stability, why did all the pilots who flew it of every nation, sing its praises?

There is of course another inconvenient point that should be considered and that is have you done these calculations on the Me109E?

I say this because if you believe that the Spitfire to be dangerous and the German pilots considered the Spitfire to be much easier to fly than the Me109E, How dangerous do you think the Me109 was?

[gimpy117]

there's a difference between "singing praises" and having a stable aircraft. Data is not subjective, data is data. I'm sure once you got how to know the spitit was a wonderful aircraft...but as far as I know it's not an aircraft you can just "fly" and get maximum performance out of

[winny]

I have some questions. @ Crumpp
We're other contemporary aircraft also tested in this way?
It's all good and well saying the Spit did this, this and this but, how did other aircraft stack up?

Also, how exactly do you intend to model this phenomenon in CLOD?

It seems to depend on stick forces and stick forces aren't calculated in CLOD? Or are they? We all know that the controls on these aircraft stiffend significantly at high speeds, that's not accounted for either.

So really the most important point, considering where we are is, what would you expect to be done to the FM to replicate this?

[Crumpp]

We're other contemporary aircraft also tested in this way?

Yes, many other aircraft were tested. My plan is to do threads on the stability and control of all the main fighters involved in the game.

I am sure I will be hated by both "red and blue".

I don't want to de-rail my own thread so if you want an in-depth discussion we will start another one.

It's all good and well saying the Spit did this, this and this but, how did other aircraft stack up?

Well, subsonic incompressible flow theory for symmetrical airfoils will give a one dimensional picture of an aircraft. The stability and control characteristics help to complete the picture.

Stability and control was a new science during WWII. Many of the aircraft have issues and those issues should be modeled.

For example, a symmetrical airfoil analysis of the Spitfire and Hurricane would give the impression the Hurricane was the 2nd rate fighter. In fact, the Hurricane was the real workhorse and an airplane the Bf-109 pilot should respect. Why?

The Hurricane was a very stable and maneuverable aircraft. Air combat is not about fancy flying on a warm sunny day. It is about getting bullets on a target. The Hurricane did not have the convergence issues and was an airplane the average pilot could quickly get guns on target as well as accurately shoot from to destroy his opponent.

I am sure there is nothing you can teach a Spitfire ace about finessing an airplane or over controlling.

Also, how exactly do you intend to model this phenomenon in CLOD?

So really the most important point, considering where we are is, what would you expect to be done to the FM to replicate this?

Well that is up to the devs as I don't know the game engine. If they are using the standard Cm calcs, then it should be rather straight forward.

[Sandstone]

Originally Posted by Crumpp

In fact, the Hurricane was the real workhorse and an airplane the Bf-109 pilot should respect. Why?

The Hurricane was a very stable and maneuverable aircraft. Air combat is not about fancy flying on a warm sunny day. It is about getting bullets on a target. The Hurricane did not have the convergence issues and was an airplane the average pilot could quickly get guns on target as well as accurately shoot from to destroy his opponent.

Air combat is often about speed and climb rate. The Hurricane was effective against bombers but less so against the Bf-109 simply because it was significantly slower and had a poorer rate of climb than the German aircraft. I hope you aren't trying to argue that the pitch sensitivity of the early Spitfire actually made it less effective against fighters than the Hurricane. That would be a very odd thing to be claiming.