Stability and Control characteristics of the Early Mark Spitfires

[robtek]

The problem is, that crumpp doesn't present claims, he presents documented facts!

The claims are coming from those, who are unwilling to accept those facts.

To recapitulate those facts, as i understood them, in concentrated form:

1. The early Spitfire marks had a inherent longitudal instability which led to the manufacturer-fix with bob-weights.

2. The stick forces for the elevator were extraordinarily small in the Spitfire.

3. The stick travel was extrordinarily small for large reactions.

It really doesn't matter how good the pilots then were able to cope with those circumstances, it should be reflected in game that the plane doesn't fly itself, but has to be flown, and that with precise, small inputs for the elevator.

Also the tests shown by crumpp say that if one doesn't ride the buffet in a turn, but gets into the buffet, the turn performance is reduced drastically.

It is up to the fm programmer to make it possible to feel the difference in game.

Every aircraft has its quirks, and i think we want them all represented in this game.

[taildraggernut]

The problem is, that crumpp doesn't present claims, he presents documented facts!

No, he presents documents and interprets them to an extreme, with Crumpp this apparent instability is 'total' and should render the Spitfire dangerous to fly, simply not true.

The claims are coming from those, who are unwilling to accept those facts.

Funny how despite a similar weight of documented evidence is labeled aas 'claims' when on the other side.

1. The early Spitfire marks had a inherent longitudal instability which led to the manufacturer-fix with bob-weights.

in the MkV which had a different engine, all up weight etc.....oh and was about to go into service with the US air force....who apparently heard it was a bit 'unstable'

2. The stick forces for the elevator were extraordinarily small in the Spitfire.

Yes, as my link to the NACA report showed 'desirably light'

3. The stick travel was extrordinarily small for large reactions.

as a real life pilot I can say that sounds like a perfect situation, who wouldn't like a responsive ride?

It really doesn't matter how good the pilots then were able to cope with those circumstances, it should be reflected in game that the plane doesn't fly itself, but has to be flown, and that with precise, small inputs for the elevator.

I must be using a different game, it certainly isn't a hands off aircraft in game, but I sure would like some more of that responsiveness.

Also the tests shown by crumpp say that if one doesn't ride the buffet in a turn, but gets into the buffet, the turn performance is reduced drastically.

Which is quite true of any aircraft, luckyly the Spitfire was so responsive that a pilot barely needed any effort to take the aircraft out of the buffet.

It is up to the fm programmer to make it possible to feel the difference in game.

Every aircraft has its quirks, and i think we want them all represented in this game.

Yes, I agree, I am really looking forward to the promised 109 topic.

[robtek]

Originally Posted by taildraggernut

No, he presents documents and interprets them to an extreme, with Crumpp this apparent instability is 'total' and should render the Spitfire dangerous to fly, simply not true.

I still have to find crumpps claim that the Spitfire is dangerous to fly, failed so far.

Funny how despite a similar weight of documented evidence is labeled aas 'claims' when on the other side.

Well, none of this evidence said different from crumpps documents

in the MkV which had a different engine, all up weight etc.....oh and was about to go into service with the US air force....who apparently heard it was a bit 'unstable'

Yes, the MK Va with the same flying characteristics as the Mk I / II as the airframe is identical apart from small changes.

Yes, as my link to the NACA report showed 'desirably light'

I haven't found your link, but i found that in the NACA report:

In turns with speeds high enough to prevent reaching
maximum lift coefficient because of the excessive accelerations
involved, the small static longitudinal stability
of the Spitfire caused undue sensitivity of the normal
acceleration to small movements of the stick. As shown
by the time histories of high-speed turns (figs. 15 to 1,
it was necessary for the pilot to pull back the stick and
then ease it forward almost to its original position in
order to enter a turn rapidly without overshooting the desired
normal acceleration. Although this procedure appears
to come naturally to a skillful pilot, flight records
from other airplanes show, that a turn may be entered rapidly
and the desired normal acceleration may be held constant
by a single rearward motion of the stick, provided
the static stability of an airplane is sufficiently large.
By careful flying, the pilot was able to make smooth turns
at high speed, as shown by figures 17 and 18. Ordinarily,
however, small movements of the stick caused appreciable
variations in the normal acceleration, as shown in figures
15 and 20.

as a real life pilot I can say that sounds like a perfect situation, who wouldn't like a responsive ride?

Now, that is pure blandishing.

I must be using a different game, it certainly isn't a hands off aircraft in game, but I sure would like some more of that responsiveness.

Yes, more in the elevators, much less in the ailerons.

Which is quite true of any aircraft, luckyly the Spitfire was so responsive that a pilot barely needed any effort to take the aircraft out of the buffet.

As it barely didn't need any effort to get into the buffet if not careful flown.

Yes, I agree, I am really looking forward to the promised 109 topic.

Me also.

[taildraggernut]

I still have to find crumpps claim that the Spitfire is dangerous to fly, failed so far.

One only has to look at the bigger picture the chap is painting to realise it, by carefull examination you will see he is suggesting 'extreme care' must be taken to fly it, the penalties for not doing so range from complete loss of control to airframe failure, so even though the specific words were not used the ultimate impression Crumpp is giving is of a 'dangerous' aircraft.

Well, none of this evidence said different from crumpps documents

and thats the craziest part, it's only Crumpps own interpretation of those documents that paint such a dire picture, the most noteable instance has been the graphs showing the various stability tests, all of which show an aircraft with a very gentle divergent amplitude which is in technical terms 'unstable' but not to any degree as to be of concern, so Crumpp's own evidence works against him.

Yes, the MK Va with the same flying characteristics as the Mk I / II as the airframe is identical apart from small changes.

the same airframe with a different engine and all up weight, given that there were apparent differences between the MkI and MkII how can it be so?

I haven't found your link, but i found that in the NACA report:

Seek and ye shall find....

http://history.nasa.gov/monograph12/ch4.htm

Now, that is pure blandishing.

I fail to see where I am flattering you?

Yes, more in the elevators, much less in the ailerons.

Yes, I can go with that

As it barely didn't need any effort to get into the buffet if not careful flown.

Lucky all those chaps with 10 hours on type and 0 combat experience were very careful

Me also.

I have a feeling we are in for a long wait

[Al Schlageter]

I think it is worth re-posting the words of an aeronautical engineer who spent a lifetime practicing his profession over one who hasn't:

FIGURE 4.5. Supermarine Spitfire airplane. A high-performance fighter noted for its role in the Battle of Britain and throughout WW II, the Spitfire had desirably light elevator control forces in maneuvers and near neutral longitudinal stability. Its greatest deficiency from the combat standpoint was heavy aileron forces and sluggish roll response at high speeds.

http://history.nasa.gov/monograph12/ch4.htm

[robtek]

@ taildraggernut

ok, you've wrote at first NACA document, but you meant a Nasa-document about the Naca-document.
And you didn't flatter me, i meant sugarcoating, english is not my first language.
All those chaps with 10 h were those who did fly so carefully that they were outturned by 109's, maybe.

@ Al Schlageter
Of course light elevators ARE desirable, it's the combination with short stick travel which may cause problems for the less experienced.

[taildraggernut]

Originally Posted by robtek

@ taildraggernut

ok, you've wrote at first NACA document, but you meant a Nasa-document about the Naca-document.
And you didn't flatter me, i meant sugarcoating, english is not my first language.
All those chaps with 10 h were those who did fly so carefully that they were outturned by 109's, maybe.

@ Al Schlageter
Of course light elevators ARE desirable, it's the combination with short stick travel which may cause problems for the less experienced.

Does it matter much? does the fact it is a NASA document about a NACA document invalidate it? is it impossible to ascertain what I was refering to? I don't quite follow the need for that correction.

Sorry but english is my first and only language, I simply assumed you used such an uncommon word because you knew what it meant, I had no warning that you may not have understood the words you are using.

so none of the chaps survived an engagement with a 109? despite the fact....sorry anecdotal fact.....that new guys were told to turn as hard as they could in order to evade the 109?

with regards to short stick travel this is apparently another desireable quality, from another part of the same article, interstingly you will se that research was put into trying to make control forces 'light', now apparently this is what makes the Spitfire 'tricky', but what it actually did was compensate for the slight instability and made it more controlable.

The Quest for Reduced Control Forces

One of the most serious problems encountered by designers of military airplanes during WW II was keeping control forces desirably light while airplanes were being made with greatly increased weight, size, and speed. Flying qualities research had shown that maximum control forces should be kept below what a pilot could conveniently exert with one hand on the control stick or wheel. For ailerons, this force was about 30 pounds on a control stick or 80 pounds on a control wheel. Increasing the mechanical advantage of the pilot's controls was impossible because of the limited size of the cockpit and the lag in deflecting a control wheel more than plus or minus 90 degrees. Studies of aerodynamic balancing devices to reduce the aerodynamic moments on control surfaces became one of the main research objectives of wind tunnels involved in stability research.

Aerodynamic balance on most airplanes designed prior to WW II was usually accomplished by locating some control surface area ahead of the hinge line. Various arrangements of these balances are shown in figure 6.1. These balances had advantages and disadvantages from both mechanical and aerodynamic standpoints. In general, balances that were permanently located in the air stream were subject to icing that might jam the controls. Balances that broke the contour of the airfoil added drag. In addition to such practical considerations, balances had to be selected on the basis of the hinge moment parameters such as the variations of control surface hinge moment with angle of attack and with control deflection. These parameters had fundamental effects on the flying qualities. The effect on snaking oscillations of the variation of hinge moment with angle of attack has already been mentioned. To obtain light control forces, both of these parameters had to be reduced.

Theoretically, the control forces could be reduced to zero by reducing these hinge moment parameters to zero, but in practice this goal could not be attained. One problem was the nonlinearity of the hinge-moment variations. For example, a control surface that was properly balanced at low deflections might be overbalanced at large deflections. A second problem that limited the degree of aerodynamic balance on large and high-speed airplanes was the effect of small changes in contour due to manufacturing differences. These differences might be almost too small to detect, yet could cause quite large changes in the control forces. The Germans, in an effort to obtain very light aileron forces on the Me109 airplane, would test fly the airplane and try different sets of ailerons until one was found that would give forces in the desired range. The British, on testing the Spitfire, mentioned encountering "rogue" airplanes that had different characteristics from the standard airplanes, the reasons for which could not be detected.

As a result of these problems, a practical limit had to be set on the degree of aerodynamic balance, which was usually 25 to 30 percent of the forces produced by an unbalanced control surface. This degree of balance, however, was nowhere near what was required to provide desirable handling qualities on the largest or fastest airplanes. In some cases, forces would have to be reduced to about 2 to 4 percent of those of an unbalanced surface.