Why is the Spitfire Mk IX still unstable??

[bongodriver]

I know you think that but it is ok, really.

 

:thumbup:

[Crumpp]

Not quite what I was getting at, I have argued from the beginning that stability increases with forward CG, something that Crumpp has denied in the case of the MkIX, I also understand the function of the elevator balance.

The elevator mod I mention does allow an increase in aft CG range according to provided documentation though, the same modification is present on the Fighter collections MkVB EP120.

 

The elevator modification allows exactly what Yo-Yo says.

 

It has nothing to do with the rear CG limit. It has to do with moving the forward CG limit allowing the elevator to raise the nose on landing with the longer/heavier engine.

[Crumpp]

No, there was a wartime modification of the elevator that increases the area by including balance horns.

 

 

 

By taking away area from the Horizontal Stabilizer....

 

The horizontal portion of the tail area remains unchanged result in NO movement of the aircraft's AC and no increase in the stability margin required to move the Rear CG limit. This would allow the forward CG limit to move. That does not effect the aircraft at normal to aft CG.

 

The angle of incidence change in the horizontal stabilizer fills the function of the bobweights by increasing the stick force per G and the pilot's perception.

Edited October 23, 2015 by Crumpp
Added the reason why the Rear CG limit was moved in the Spit MK IX

[Friedrich-4B]

By taking away area from the Horizontal Stabilizer....

 

The horizontal portion of the tail area remains unchanged result in NO movement of the aircraft's AC and no increase in the stability margin required to move the Rear CG limit. This would allow the forward CG limit to move. That does not effect the aircraft at normal to aft CG.

 

The angle of incidence change in the horizontal stabilizer fills the function of the bobweights by increasing the stick force per G and the pilot's perception.

 

How about Crumpp provides that report on the Spitfire IX's stability that he claims to have, so that 18 pages of debate can be brought to an end? No doubt, it will satisfactorily vindicate Crumpp's POV, thus ensuring that the said POV will be respected and not open to further debate, should the subject come up again. At this point, still waiting. :music_whistling:

[Crumpp]

Fredrich asked:

Crumpp do you have a definitive report or reports that prove that the Spitfire IX was longitudinally unstable? Yes/No

 

Yes and those reports and proof is posted. This is all measured and quantifiable Fredrich.

 

Crumpp says:

Already been discussed in my very first post starting this thread. It does not increase the area of the tailplane and therefore does not shift the stability margin.

 

It simply adds another form of balancing to the elevator.

 

Why is an airplanes elevator balanced? To shift the control forces to something more controllable under unstable conditions....

 

Let's see:

 

 

1. A million different bobweights of various sizes tried and experimented with...

 

2. Multiple attempts at other forms of balancing...

 

3. Multiple elevator redesigns and an obsession with elevator manufacturing tolerances on test aircraft.....

 

4. Post war area added to shift the stability margin (the correct fix and what should have been done in the first place)

 

5. Post war aircraft all have with restricted CG limits compared to wartime variants; even have specific longitudinal instability behaviors noted on some the type certificates!

 

And most damning...

 

No change in the relationship between the CG limits and no design changes to move the Aircraft's Aerodynamic Center from the Mk I to the Mk IX.

 

 

And yet we have pages and pages of staunch defense that the NACA conclusion was not correct and the aircraft was not longitudinally neutral to unstable at normal to aft CG.

 

[Friedrich-4B]

Yes and those reports and proof is posted. This is all measured and quantifiable Fredrich.

 

Yeah, right :smilewink: ; the only "reports" on the IX posted by Crumpp are a few paragraphs from Morgan & Shacklady, most of them dealing with a Spitfire IX tested with full rear fuselage fuel tanks and hand-made elevators, plus the report, courtesy of Mike Williams, that deals with the latter - in other words, no typical wartime Spitfire IXs are dealt with throughout Crumpp's entire "presentation".

 

And nothing measured and quantifiable, except some stuff about Mk Is and VAs that relate to the Spitfire Mk IX only insomuch as they belong to the same family. (Closest Spitfire relatives to the Spitfire IX are the VC, from which the IX was derived, and the XVI)

 

Why is an airplanes elevator balanced? To shift the control forces to something more controllable under unstable conditions....

 

Let's see:

 

1. A million different bobweights of various sizes tried and experimented with...

 

:lol: How about making it "10 million" or even "100 million bobweights" just to emphasize that some experiments were conducted and the bobweights rejected. The only bobweights adopted were on some Spitfire Vs to help overcome poor loading practices on some squadrons. The bobweights were removed when the new elevators (mod. 789) were introduced on the Mk IX.

 

2. Multiple attempts at other forms of balancing...

 

3. Multiple elevator redesigns and an obsession with elevator manufacturing tolerances on test aircraft.....

 

As if the Spitfire was the only WW2 fighter to experiment with or alter elevator design and balances; nor is there anything unreasonable about being concerned about manufacturing tolerances on such vital components. To claim it was an obsession, based on one report, is as much of an overstatement as Crumpp's "A million different bobweights".

 

4. Post war area added to shift the stability margin (the correct fix and what should have been done in the first place)

 

The only evidence posted by Crumpp is the certificate for one restored Spitfire V - otherwise this continual assertion, implying that Supermarine were too stupid to fix the Spitfire IX's purported longitudinal instability until post-war, is rubbish. There was no problem to fix.

 

And most damning...

 

No change in the relationship between the CG limits and no design changes to move the Aircraft's Aerodynamic Center from the Mk I to the Mk IX.

 

Except for redesigned wings and elevators, plus the longer fuselage and heavier powerplant, including the propeller, engine and cooling system - most of which Crumpp mentioned in his OP, waaay back then:

 

In order to change the stability margin, we have to change airplane.

The short answer is we have to change the design of the wing, horizontal stabilizer, or length of the fuselage.

 

Funny, too how the Mk IX needed to be ballasted to restore the original handling characteristics...plus there were those pesky modified elevators that helped shift the forward CG limit, as well as enabling the aft limit to be moved back to 9".

 

So, no cigar for Crumpp.:smoke:

Edited October 23, 2015 by Friedrich-4/B
Tweaking

[bongodriver]

By taking away area from the Horizontal Stabilizer....

 

The horizontal portion of the tail area remains unchanged result in NO movement of the aircraft's AC and no increase in the stability margin required to move the Rear CG limit. This would allow the forward CG limit to move. That does not effect the aircraft at normal to aft CG.

 

The angle of incidence change in the horizontal stabilizer fills the function of the bobweights by increasing the stick force per G and the pilot's perception.

 

You just don't know when to give up.

 

Elevator mod 789 is the horn balanced late war type as described in your opening post.

 

 

you can see clearly that the Fighter collections MkVB EP120 has the late war elevator design.

 

 

now have a little think about life as you read through its Airworthiness note, paying particular attention to the weight and balance where it specifies the elevator specific modification as the reason for increase in CG range, note the specific detail of 'no' bob weight installation.

 

http://www.caa.co.uk/AANDocs/29299/29299000000.pdf

Edited October 23, 2015 by bongodriver

[JtD]

I don't think the rearward limit of the permissible CoG range is really equivalent to the neutral point of a design or something like that. Modifications that effect the rearward limit may or may not effect the neutral point. They might as well just effect the controllability in the rearward range of CoG positions, but not stability as such. So I think there's little point in using permitted CoG ranges to discuss small margins of stability. Might be a rough indicator, but that's it.

[Crumpp]

I don't think the rearward limit of the permissible CoG range is really equivalent to the neutral point of a design or something like that. Modifications that effect the rearward limit may or may not effect the neutral point. They might as well just effect the controllability in the rearward range of CoG positions, but not stability as such. So I think there's little point in using permitted CoG ranges to discuss small margins of stability. Might be a rough indicator, but that's it.

 

The Neutral point determines the rear CG limits. That is not the same thing as the Neutral IS the rear CG limit.

 

That limit is set according to modern stability and control standards at the onset of instability.

 

The Spitfires limit was pretty much set during the war based on pilot opinion on what he thought he could control.

 

That is why all the normal wing Spitfires have restricted CG limits compared to their wartime counterparts.

 

The Spitfire stability and control was not designed under a set of standards. It was designed by collaboration of the engineers at Supermarine and a small group of company test pilots. It is based on those pilot's opinions and subject to their ego.

 

That is how most airplanes were designed in the late 1930's which is why the NACA tested so many when it adopted standards.

[MiloMorai]

Must have been a real female dog for the squadron engineering people when changing the wing tips on the Spitfire. The whole squadron would be non operational while the W&B of 20 plus a/c were calculated and the maintenance people made the adjustments required to the a/c.

[Crumpp]

You just don't know when to give up.

 

Elevator mod 789 is the horn balanced late war type as described in your opening post.

 

 

you can see clearly that the Fighter collections MkVB EP120 has the late war elevator design.

 

 

now have a little think about life as you read through its Airworthiness note, paying particular attention to the weight and balance where it specifies the elevator specific modification as the reason for increase in CG range, note the specific detail of 'no' bob weight installation.

 

http://www.caa.co.uk/AANDocs/29299/29299000000.pdf

 

It is clipped wing...

 

Already discussed that changing the wing area will move the AC and change the stability margin. Once more, we do not have a weight and balance sheet for a clipped wing aircraft to see what the wartime CG limits were set too.

[JtD]

Must have been a real female dog for the squadron engineering people when changing the wing tips on the Spitfire. The whole squadron would be non operational while the W&B of 20 plus a/c were calculated and the maintenance people made the adjustments required to the a/c.

Luckily enough they simply added the wing tip modification to the weight and balance table and left the CoG range untouched. For instance, the Spit VIII went with the 3.5 to 7 range no matter what, but changing wingtips (here extended vs. elliptical) changed weight 20lb and moment by 270"lb.

[Crumpp]

Must have been a real female dog for the squadron engineering people when changing the wing tips on the Spitfire. The whole squadron would be non operational while the W&B of 20 plus a/c were calculated and the maintenance people made the adjustments required to the a/c.

 

 

Weight and balanced is calculated every time you fly, Milo. Once more, in the military, Part 135, and Part 121 the pilot has to sign off on the flight acknowledging that the weight and balanced was checked.

 

So it is not any different than any other flight, different numbers but no additional steps required regarding weight and balance.

 

They would not be recalculating the limits either, they would be told the standard limits for that configuration.

 

[Crumpp]

Luckily enough they simply added the wing tip modification to the weight and balance table and left the CoG range untouched. For instance, the Spit VIII went with the 3.5 to 7 range no matter what, but changing wingtips (here extended vs. elliptical) changed weight 20lb and moment by 270"lb.

 

If it was the same for the Spitfire Mk IX....

 

It would be listed on the Spitfire Mk IX weight and balance sheet as well.

 

Read AP-2095. You follow the specific instructions for each aircraft as outlined in its instructions.

 

The Spitfire Mk VIII wingtips are not the same as removing the tips on a standard wing to convert it to clipped wing.

 

he Spitfire VIII was essentially an unpressurized Mk VII incorporating the universal wing with extended tips

 

http://www.spitfireperformance.com/spitfire-VIII.html

Edited October 23, 2015 by Crumpp

[Crumpp]

Fredrich says:

The bobweights were removed when the new elevators (mod. 789) were introduced on the Mk IX.

 

Yes...the AC was not moved and with the same CG limits neither was the stability margin.

 

You keep overlooking that fact attempting to turn the argument into something it is not whilst trying to imply I am an idiot.

[MiloMorai]

Extended wingtips

 

Pointed, triangular wing tips were designed especially for high-altitude versions of the Spitfire, starting with the Mk. VI. The enlarged wing area they provided resulted in better climb rate and slightly improved ceiling at the expense of manoeuvrability in combat on “normal” altitudes. The idea with both clipped and extended wing tips was taken further in Mk. VIII production, when the tips became easily interchangeable and theoretically could be swapped to suit the preferences of an individual pilot or tactical requirement.

 

 

The Spitfire Mk VIII wingtips are not the same as removing the tips on a standard wing to convert it to clipped wing.

from the link

 

Early models featured an extended wing of 40’2". Later models had the standard span of 36'10" or were clipped to 32'2".

[Crumpp]

Except for redesigned wings

 

There is no change in the normal wing design from the Spitfire Mk I to Mk IX that affects the aircrafts AC.

 

and elevators,

 

Changes were done to change the stick force per G for controllability.

 

plus the longer fuselage

 

No increase in the arm from the wing AC to the horizontal stabilizer/elevator AC = No movement of the Aircraft's AC.

 

Increase the frontal fuselage length simply increases the moment about the CG required. The tailforce lift was increased.

 

This has the same effect as dialing in some trim increasing the stick forces per G at a specific point. There is some stabilizing effect from horizontal dihedral but it is obviously not much gauging from the reduction in CG limits of Modern flying examples of the Spitfire Mk IX.

[Crumpp]

Extended wingtips

 

Pointed, triangular wing tips were designed especially for high-altitude versions of the Spitfire, starting with the Mk. VI. The enlarged wing area they provided resulted in better climb rate and slightly improved ceiling at the expense of manoeuvrability in combat on “normal” altitudes. The idea with both clipped and extended wing tips was taken further in Mk. VIII production, when the tips became easily interchangeable and theoretically could be swapped to suit the preferences of an individual pilot or tactical requirement.

 

 

from the link

 

Early models featured an extended wing of 40’2". Later models had the standard span of 36'10" or were clipped to 32'2".

 

Interesting information and thanks for sharing it.

 

Now, just find where it mentions the clipped wings on the Spitfire Mk IX weight and balance sheet and it will give you the instructions.

 

Otherwise, the weight and balance sheet is not referring to clipped wing variants if it is not mentioned.

[bongodriver]

It is clipped wing...

 

Already discussed that changing the wing area will move the AC and change the stability margin. Once more, we do not have a weight and balance sheet for a clipped wing aircraft to see what the wartime CG limits were set too.

 

So clipped wing Spits were perfectly stable, that was the magic bullet all this time?

 

Anyway this is a Spitfire MkVc G-BUWA, I think it has now moved on from the UK and is N registered, plain to see are the regular wingtips and elevator mod 789.

 

 

Lets see the difference between clipped wing and regular wing shall we?

 

I see the regular wingtip version is allowed an extra 2" forward CG but has the same 9" aft CG.

 

Oh and it still has no inertia weight.

 

http://www.caa.co.uk/AANDocs/23951/23951020000.pdf

 

I really can't wait to hear the next excuse :wallbash::wallbash::wallbash:

[Pilum]

When an design is changed or reconfigured, adding ballast simply corrects the CG back to its original location to prevent possible adverse loaded condition.

 

It has nothing to do with changing the CG to new limits and simply maintains the stability and control characteristics of the original aircraft.

Ok Crumpp, I thought explaining that since the Spitfire Mk9 had ballast in the tail this would help you understand that it was not unstable but apparently a more detailed explanation is necessary:

 

If we start off with the aircraft in a configuration that you above call the original CG location this can be either:

 

a) Stable

b) Neutral

c) Unstable

 

Now in your example above the aircraft is changed and the ballast is added to move the CG back to it's original location to as you say "maintain the stability characteristics of the original aircraft", i.e. maintain one of the states a), b) or c).

 

Since ballast is added in the tail this means that the aircraft (in our case the Spitfire Mk9) BEFORE moving the CG back to it's original location by means of the ballast, the CG HAD to be located further forward. I.e. the states were:

 

d) More stable

e) Somewhat stable

f) Somewhat unstable

 

Now from these states we add the ballast to states d), e) and f) to return to the original states a), b) and c).

 

So making a sanity check, when is it expedient to add ballast?

 

Let's begin with case f):

 

We add ballast to make an airplane that is somewhat unstable more unstable? Hmmmmmm, no that does not sound like a good option.....

 

OK, then, what about case e):

 

We add ballast to make an airplane that is somewhat stable neutral? Emmmmm......no, me no like going from a small stability margin to neutral...

 

So what about case d):

 

We add ballast to make an airplane that is more stable less stable? Hmmmm, yes that seems plausible....

 

But wait? What does this mean? Wait for it, Waaaaaaaaaaaaaaaaaaaaait for it:

 

It means, it means, the Spitfire Mk9 has to be stable!!!!!!!!!! :clown_2:

[Random]

Interesting that the merlin engined ones had ballast in the tail too. I've only seen griffon engined ones with the relevant panels removed. Was very surprised by the amount of lead!

[Crumpp]

G-BUWA

 

You mean this one with the clipped wings and modified elevator?

 

The one you are trying to pass off as having normal wings, no modified elevator by swapping the old UK CAA type sheet?

 

http://forum.keypublishing.com/showthread.php?20144-Spitfire-Crazy-Mk2

 

http://www.caa.co.uk/AANDocs/23951/23951020000.pdf

[bongodriver]

You mean this one with the clipped wings and modified elevator?

 

The one you are trying to pass off as having normal wings, no modified elevator by swapping the old UK CAA type sheet?

 

http://forum.keypublishing.com/showthread.php?20144-Spitfire-Crazy-Mk2

 

http://www.caa.co.uk/AANDocs/23951/23951020000.pdf

 

Yes, that one after it's conversion back to full wingtips and it's subsequent airworthiness approval note in 1999, 3 years after your attached photograph.

 

http://www.caa.co.uk/AANDocs/23951/23951000000.pdf

 

Nobody is swapping anything, you just seem to be referring to the AAN issue2 which is a document covering this aircrafts withdrawal from airworthiness, probably due to subsequent export.

 

this in in your issue 2 AAN

 

Issue 2 of this AAN has been raised to withdraw the approval of this aircraft for the issue of a UK Permit to Fly. If in future a UK Permit is required for this aircraft, a complete investigation of the build standard and a new E4 recommendation for the issue of a Permit will be required.

 

What you seem to be conveniently ignoring is the original issue AAN states clearly the non-clipped wings minus bob weight and it has the 3.5" to 9.0" CG range still, pictures show clearly it has elevator of the late war mod 789.

 

The mainplanes incorporate a light alloy skin with main D-spar, with auxiliary rear spar and ribs, secured direct onto the fuselage without any central section. Round span wing tips have been fitted. The wings are fitted with original spars.

Edited October 23, 2015 by bongodriver

[Crumpp]

Interesting that the merlin engined ones had ballast in the tail too. I've only seen griffon engined ones with the relevant panels removed. Was very surprised by the amount of lead!

 

Ballasting is a red herring.

 

It does not effect the CG limits and is used only to prevent adverse loading conditions from developing when the CG changes in flight for specific load conditions. Permanent ballast is used to bring the empty weight CG back to the same position it was before the equipment or configuration was changed.

 

The whole ballasting thing is just white noise that has little to do with the conversation.

[Crumpp]

CG range (elevator is to mod 789 standard)

 

Missed this...

 

http://www.caa.co.uk/AANDocs/23951/23951000000.pdf