Why is the Spitfire Mk IX still unstable??

[bongodriver]

Missed this...

 

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

 

apology accepted

[Crumpp]

Apology for what? Having a late war tail modification? Why do you think the RAE was so concerned with manufacturing tolerances for the elevators?

 

 

Air Repair of Bicester re-fabricated the tailplanes,

strengthening the spar, improving the shrouds, allowing for

elevator horn balance and increasing the gauge of the plating,

this embodied modifications 591, 442, 789, 1025 and 1142

 

5. Flight Test

The aeroplane has been flown by several pilots and the results collated

under CAA flight test report reference FTR/6958Y dated 20 January 1989.

This report covered flight with the aeroplane ballasted to achieve four

loading conditions, one yielding an aft CG of 8.85 inches AOD at

6389lb. The original aeroplane limits were 3.5 to 9.0 inches AOD at

weights up to 7300 lb. At this aft loading it was found:-

1. that the aircraft would gently auto rotate into the 1g stall.

2. that above 3g a push force was required to prevent the turn

tightening.

3. turning stalls required a push force as the aircraft gently

auto rotated into the stall.

With the aircraft ballasted to 7.76 inches AOD these adverse

characteristics were not present and since the aeroplane will normally

be operating with the CG about 5 to 6 inches AOD the aft CG limit

will b declared as 7.76 inches AOD and this will be stated in the

Supplement to the Pilot Notes for G-MKVC.

 

http://www.caa.co.uk/aandocsindex/29016/29016000000.pdf

 

Looks like G-BUWA got one of the "good manufacturer tolerance" elevators the RAE was so worried.

 

:thumbup:

[bongodriver]

Apology for what? Having a late war tail modification? Why do you think the RAE was so concerned with manufacturing tolerances for the elevators?

 

Yes, arguing against it despite all the evidence.

 

 

 

http://www.caa.co.uk/aandocsindex/29016/29016000000.pdf

 

Looks like G-BUWA got one of the "good manufacturer tolerance" elevators the RAE was so worried.

 

:thumbup:

 

None of the stuff you just quoted appears in the AAN for the MkIX you just linked to, you are just making stuff up now.

[Friedrich-4B]

None of the stuff you just quoted appears in the AAN for the MkIX you just linked to, you are just making stuff up now.

 

Crumpps "information" in #203 (either on a Mk IX, G-ASVJ or Mk. VC G-BUWA? Crumpp seems to be mixed up on this) actually comes from a restored Mk. VC, G-MKVC, which has been rebuilt to completely different specifications to G-BUWA, and has been given completely different conditions for flying.

 

In fact, the following applies to G-BUWA (ex AR614) (From the Airworthiness Approval Note 23951 issued in July 1999):

 

8. Limitations/Concessions

AP1565E PN contains recommended minimum entry speeds for aerobatic manoeuvres. The following limitations shall apply and items marked with an asterisk shall be placarded in the cockpit (or appropriately marked on gauges):

*1. Aerobatics are permitted in accordance with the Pilots Notes (with the exception of flick manoeuvres).

*2. Spinning is prohibited.

*3. No Smoking.

4. Maximum take-off and landing weight authorised 7300 lb

CG range (elevator is to mod 789 standard) 3.5" to 9.0" AoD

CG Datum is marked on the port side of the fuselage near the fireproof bulkhead

(frame 5).

*5. Airspeeds

VNE 405 mph IAS

 

So much for all post-war/restored Spitfires not being allowed to fly with the original CG limits. :music_whistling:

 

And what Crumpp's throwaway comment

Looks like G-BUWA got one of the "good manufacturer tolerance" elevators the RAE was so worried.

means is anybody's guess. :smilewink: Edited October 24, 2015 by Friedrich-4/B
Condense links

[Pilum]

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.

 

Nope, the ballast is the needle that pops your "The Spitfire Mk9 is unstable" balloon. :smilewink:

 

Your attempt to connect the ballast ONLY to the empty weight CG is the red herring. The ballast affects the CG for ALL load conditions. Since you are so fond of "maths" why don't you calculate the effects at different load conditions? You will find that in all cases the CG is moved back. Since a lot of discussion has been concerning the CG without fuel in the rear tanks I calculated that and it turns out the CG is shifted circa 0.5" back in this particular case.

 

So again, as shown in post #195, the only plausible reason they did this was to lower the stability of an already stable aircraft. However if you want to prove that the Spitfire Mk9 was unstable already without the ballast and that they added ballast in the tail to shift the CG even further back thus increasing instability even further then knock yourself out! :joystick:

Edited October 24, 2015 by Pilum

[Yo-Yo]

Nope, the ballast is the needle that pops your "The Spitfire Mk9 is unstable" balloon. :smilewink:

 

Your attempt to connect the ballast ONLY to the empty weight CG is the red herring. The ballast affects the CG for ALL load conditions. Since you are so fond of "maths" why don't you calculate the effects at different load conditions? You will find that in all cases the CG is moved back. Since a lot of discussion has been concerning the CG without fuel in the rear tanks I calculated that and it turns out the CG is shifted circa 0.5" back in this particular case.

 

So again, as shown in post #195, the only plausible reason they did this was to lower the stability of an already stable aircraft. However if you want to prove that the Spitfire Mk9 was unstable already without the ballast and that they added ballast in the tail to shift the CG even further back thus increasing instability even further then knock yourself out! :joystick:

 

Stop. As the speculation are based only on suggestions, why don't you use the very simple logic: as MkV was presumed good in stability/controllability and as Mk IX got heavier engine some ballast was added TO RETURN its CG to limits for V. Could you directly compare not the allowed CG positions but ACTUAL positions based on weight and balance charts for both Mks?

[Kurfürst]

For the winner, I'll buy an ice cream.

[Pilum]

Stop. As the speculation are based only on suggestions, why don't you use the very simple logic: as MkV was presumed good in stability/controllability and as Mk IX got heavier engine some ballast was added TO RETURN its CG to limits for V. Could you directly compare not the allowed CG positions but ACTUAL positions based on weight and balance charts for both Mks?

I use very simple logic: Crumpp claims the Spitfire Mk9 is unstable. My claim is you don't add ballast in the tail to a plane which is unstable. You add ballast to REDUCE stability, ergo the Spitfire Mk9 is stable. You don't agree?

 

You could of course calculate and compare the Mk5 and the Mk9 CG locations as you say but I don’t see that you need to: If we take the Mk9, the designers added 17.5 lb ballast, not 5 or 25 lb but exactly 17.5 lb. Now they had the option to abstain or add whatever amount of ballast they wanted but elected to add exactly 17.5 lb. I agree with you that they added the ballast to return to a WANTED level of stability. This CG position may or may not be like the Mk5. However I don’t see we need to do the detailed calculations for each mark since they obviously added what they thought necessary to achieve the flying qualities they wanted in the Mk9. Now we could of course assume that they added the ballast in the tail to get the instability that Crumpp claims plagues the Mk9 but why would they?

 

Really, this thread is now over 20 pages and Crummp’s theory is looking more and more like Bertrand Russel’s proverbial teapot. Looks like it’s time to remind ourselves that it’s not we who should prove that Crumpp’s teapot does not exist but Crumpp who should convince us it’s out there orbiting the sun somewhere.

Edited October 24, 2015 by Pilum
Added the Mk5 & Mk9 comparison and the teapot!

[Pilum]

For the winner, I'll buy an ice cream.

 

Thanks, I'll have the vanilla! :thumbup:

[Yo-Yo]

I use very simple logic: Crumpp claims the Spitfire Mk9 is unstable. My claim is you don't add ballast in the tail to a plane which is unstable. You add ballast to REDUCE stability, ergo the Spitfire Mk9 is stable. You don't agree?

 

You could of course calculate and compare the Mk5 and the Mk9 CG locations as you say but I don’t see that you need to: If we take the Mk9, the designers added 17.5 lb ballast, not 5 or 25 lb but exactly 17.5 lb. Now they had the option to abstain or add whatever amount of ballast they wanted but elected to add exactly 17.5 lb. I agree with you that they added the ballast to return to a WANTED level of stability. This CG position may or may not be like the Mk5. However I don’t see we need to do the detailed calculations for each mark since they obviously added what they thought necessary to achieve the flying qualities they wanted in the Mk9. Now we could of course assume that they added the ballast in the tail to get the instability that Crumpp claims plagues the Mk9 but why would they?

 

Really, this thread is now over 20 pages and Crummp’s theory is looking more and more like Bertrand Russel’s proverbial teapot. Looks like it’s time to remind ourselves that it’s not we who should prove that Crumpp’s teapot does not exist but Crumpp who should convince us it’s out there orbiting the sun somewhere.

 

The logic can be even simplier: we have two planes with the same AC. We also have measured stability margine for 5 as well as CG position. We also have CG position for 9. Then, the scoolboy calculation gives the answer.

But. Only for gliding. Excessive 300-400 hp can change things for TO conditions.

[Cripple]

I use very simple logic: Crumpp claims the Spitfire Mk9 is unstable. My claim is you don't add ballast in the tail to a plane which is unstable. You add ballast to REDUCE stability, ergo the Spitfire Mk9 is stable. You don't agree?

 

You could of course calculate and compare the Mk5 and the Mk9 CG locations as you say but I don’t see that you need to: If we take the Mk9, the designers added 17.5 lb ballast, not 5 or 25 lb but exactly 17.5 lb. Now they had the option to abstain or add whatever amount of ballast they wanted but elected to add exactly 17.5 lb. I agree with you that they added the ballast to return to a WANTED level of stability. This CG position may or may not be like the Mk5. However I don’t see we need to do the detailed calculations for each mark since they obviously added what they thought necessary to achieve the flying qualities they wanted in the Mk9. Now we could of course assume that they added the ballast in the tail to get the instability that Crumpp claims plagues the Mk9 but why would they?

 

Really, this thread is now over 20 pages and Crummp’s theory is looking more and more like Bertrand Russel’s proverbial teapot. Looks like it’s time to remind ourselves that it’s not we who should prove that Crumpp’s teapot does not exist but Crumpp who should convince us it’s out there orbiting the sun somewhere.

 

Strictly speaking that isn't logic... :P

 

So, we are suggesting that the correct weight was added to give "necessary to achieve the flying qualities they wanted in the Mk9", yes? That doesn't mean it magically became "stable". Nor can we assume that raw "stability" was foremost in the minds of those who added the weight. Actually, we can't assume anything, can we?

 

I agree that we should essentially be using Occum's Razor to simplify this discussion down. However you seem to be adding more (unsubstantiated) suppositions to an already muddied field. Nae ice-cream just yet... :smartass:

[Pilum]

The logic can be even simplier: we have two planes with the same AC. We also have measured stability margine for 5 as well as CG position. We also have CG position for 9. Then, the scoolboy calculation gives the answer.

But. Only for gliding. Excessive 300-400 hp can change things for TO conditions.

 

Yes well I'm quite convinced Supermarine engineers are past the schoolboy calculations stage so no worries there. Sure things change with different power settings but let me get this straight: Are you saying the Mk9 is unstable in all but gliding conditions?

[Pilum]

Strictly speaking that isn't logic... :P

 

So, we are suggesting that the correct weight was added to give "necessary to achieve the flying qualities they wanted in the Mk9", yes? That doesn't mean it magically became "stable". Nor can we assume that raw "stability" was foremost in the minds of those who added the weight. Actually, we can't assume anything, can we?

 

I agree that we should essentially be using Occum's Razor to simplify this discussion down. However you seem to be adding more (unsubstantiated) suppositions to an already muddied field. Nae ice-cream just yet... :smartass:

 

Strictly speaking I don't agree but if that's how you feel them I'm OK with that and I can do without the ice-cream as well if you're not sharing. :)

[Yo-Yo]

Yes well I'm quite convinced Supermarine engineers are past the schoolboy calculations stage so no worries there. Sure things change with different power settings but let me get this straight: Are you saying the Mk9 is unstable in all but gliding conditions?

 

As i begin to work on i will give the answer.

[Pilum]

As i begin to work on i will give the answer.

 

Well I look forward to seeing the results and hope that the DCS Spitfire Mk9 will be just as pleasant to fly as most pilots who have had the pleasure to fly it in real life seem to agree on. :smilewink:

[Crumpp]

The logic can be even simplier: we have two planes with the same AC. We also have measured stability margine for 5 as well as CG position. We also have CG position for 9. Then, the scoolboy calculation gives the answer.

But. Only for gliding. Excessive 300-400 hp can change things for TO conditions.

 

:thumbup:

 

Looking forward to the finished product!

[bongodriver]

Strictly speaking that isn't logic... :P

 

So, we are suggesting that the correct weight was added to give "necessary to achieve the flying qualities they wanted in the Mk9", yes? That doesn't mean it magically became "stable". Nor can we assume that raw "stability" was foremost in the minds of those who added the weight. Actually, we can't assume anything, can we?

 

I agree that we should essentially be using Occum's Razor to simplify this discussion down. However you seem to be adding more (unsubstantiated) suppositions to an already muddied field. Nae ice-cream just yet... :smartass:

 

Actually it is logic, you don't add ballast in the back to increase stability, in this case the stability and controllability was the primary idea behind it, remember this is a fighter not a flying club aircraft.

 

in the case of the MkIX the increased weight in the nose from the bigger engine increased stability and this was in fact undesirable, if an aircraft becomes too stable it loses manoeuvrability because it becomes harder to control because the stick forces are heavier (like the Me109) and has other detrimental effects too, the adding of ballast in the rear of the aircraft was intended to 'reduce' the stability (which is a sliding scale) by shifting the CG back closer to the Centre of lift (the engineering elite will call this Aerodynamic centre (AC)).

 

A simple way to look at stability is:

 

CG forward of AC = Stable condition

CG equal to AC = Neutral condition

CG aft of AC = Unstable condition

 

The ideal situation would be close to Neutral, it gives absolute control without heavy stick forces and is not unstable, the down side is that the CG range must be carefully managed to ensure it won't slip too far in to the unstable range, and the aircraft is somewhat twitchy because of light controls, this is what the NACA MkV report suggests is the case.

Instability increases manoeuvrability but causes the aircraft to become less controllable because the aircraft starts to over react to control inputs, that is why modern jet fighters are designed to be unstable, they just have to have computers to actually control them, the pilot is simply making a request to that computer when he makes a control input, because these conditions are a sliding scale of varying degree that means slight instability is not inhumanly possible to control but flying an unstable aircraft means the pilot will be overloaded and using all his skill simply in the task of maintaining control the aircraft and will not have the spare capacity for much else like combat/aerobatics etc etc (that doesn't sound like the Spitfire now does it?) but that is what Crumpp would like to see, Spitfires spinning out of control because the pilot coughs.

 

 

This is a simplification, there are ways to overcome stability issues without messing with CG, but as we have seen in this discussion the thinking is based on the same airframe through the Merlin Spitfire marks, of course the MkV in the famous NACA report had an early elevator design so it's not as simple as taking MkV data and bingo we have a MkIX though I'm sure Yo-Yo is not telling us the full story of how he will achieve his results.

 

Here's another video explaining some of the basic principles, the engineering elite need not jump up and down in disgust, centre of pressure and aerodynamic centre are always getting mixed up in these simplified instructional videos for student pilots, the point is that stability is a balancing act between the lift induced components and the gravity induced components.

 

[NineLine]

So I took this thread as an excuse to crack open some of my Spitfire books again, just to read pilot stories and such, at first, just looking for items on this subject, but forgot how many great stories and such so I will admit I just ended up reading everything instead of scanning for specifics.

 

My take on the whole thing is everyone is sorta right. The Spitfire does seem to have some instability... BUT, these instabilities are, for the most part, not felt by the pilot. Obviously when you change the load-out, or the addition of the rear tanks, ect... can amplify the issue to where its noticeable, it seems a standard combat load-out that we will be flying wont really see these... or feel these that is.

 

I am excited to see what it will fly like, and look forward to the challenges the Spitfire will bring as we have seen from the previous 3, they each have their little quirks...

[Cripple]

So I took this thread as an excuse to crack open some of my Spitfire books again, just to read pilot stories and such, at first, just looking for items on this subject, but forgot how many great stories and such so I will admit I just ended up reading everything instead of scanning for specifics.

 

My take on the whole thing is everyone is sorta right. The Spitfire does seem to have some instability... BUT, these instabilities are, for the most part, not felt by the pilot. Obviously when you change the load-out, or the addition of the rear tanks, ect... can amplify the issue to where its noticeable, it seems a standard combat load-out that we will be flying wont really see these... or feel these that is.

 

I am excited to see what it will fly like, and look forward to the challenges the Spitfire will bring as we have seen from the previous 3, they each have their little quirks...

 

 

+1

 

And thanks for posting that article earlier. It will help a lot with the control-loading for my wee Spit.:)

[Ala13_ManOWar]

Well I look forward to seeing the results and hope that the DCS Spitfire Mk9 will be just as pleasant to fly as most pilots who have had the pleasure to fly it in real life seem to agree on. :smilewink:

The problem with that is, what do you call a pleasant flight? In a Chuck Yeager scale anything is a pleasant flight, while less gifted pilots would call the same experience a hell. A single sentence like that can't be any help in the module development and any of us should take those as matter of fact without further explaining what actually means a pleasant flight to the guy saying it.

 

S!

[bongodriver]

The problem with that is, what do you call a pleasant flight? In a Chuck Yeager scale anything is a pleasant flight, while less gifted pilots would call the same experience a hell. A single sentence like that can't be any help in the module development and any of us should take those as matter of fact without further explaining what actually means a pleasant flight to the guy saying it.

 

S!

 

Trust us, he is not describing a 'Chuck Yaeger' version of pleasant, the Spitfire is loved by all it's pilots and they are not all 'Chuck Yaegers', I have never read an account of a pilot not enjoying the Spitfires handling qualities and if there are such accounts they are in a very significant minority.

[Ala13_ManOWar]

Trust us, he is not describing a 'Chuck Yaeger' version of pleasant, the Spitfire is loved by all it's pilots and they are not all 'Chuck Yaegers', I have never read an account of a pilot not enjoying the Spitfires handling qualities and if there are such accounts they are in a very significant minority.

Of course, but "they enjoy" doesn't means the Spit isn't tricky to fly. Look at the 109 forums with people complaining because somebody said once the 109 is pleasant to fly while they don't find the pleasure anywhere sitting in front of a PC... Lets see what the module is when it's out of course, but look at this thread foreseeing troubles we don't have yet :huh:. It's so complicated describing an own feeling about how this or that aircraft flies I don't think arguing so much beforehand is any good based on that.

 

S!

Edited October 26, 2015 by Ala13_ManOWar

[NineLine]

Trust us, he is not describing a 'Chuck Yaeger' version of pleasant, the Spitfire is loved by all it's pilots and they are not all 'Chuck Yaegers', I have never read an account of a pilot not enjoying the Spitfires handling qualities and if there are such accounts they are in a very significant minority.

 

Well the ones that didnt enjoy the flight qualities of the Spitfire might not have been around to write about them in the 1940's ;)

 

Most pilots talk about the Spitfire in comparison to its opponents, less about a leisurely flight. I could end up being similar to a race car, its designed to go fast, and be comfortable while doing so, but driving to back and forth to work might not be so comfortable :)

 

All that said, I to have not read too many accounts from Spitfire pilots that didnt absolutely love the aircraft, that doesnt mean it was easy to fly, but meant it was good at what it was intended to do.

[bongodriver]

Of course, but "they enjoy" doesn't means the Spit isn't tricky to fly. Look at the 109 forums with people complaining because somebody said once the 109 is pleasant to fly while they don't find the pleasure anywhere sitting in front of a PC... Lets see what the module is when it's out of course, but look at this thread foreseeing troubles we don't have yet :huh:. It's so complicated describing an own feeling about how this or that aircraft flies I don't think arguing so much beforehand is any good based on that.

 

S!

 

But that's the point, everyone who said they like the Spit say it because it's not tricky to fly, it is carefree in handling and gives plenty of warning of approaching stall.

The reason this thread exists is because the OP has a personal hatred of the Spitfire and is obsessed with trying to influence developers to make his interpretation of the FM.

 

 

Well the ones that didnt enjoy the flight qualities of the Spitfire might not have been around to write about them in the 1940's ;)

 

Most pilots talk about the Spitfire in comparison to its opponents, less about a leisurely flight. I could end up being similar to a race car, its designed to go fast, and be comfortable while doing so, but driving to back and forth to work might not be so comfortable :)

 

All that said, I to have not read too many accounts from Spitfire pilots that didnt absolutely love the aircraft, that doesnt mean it was easy to fly, but meant it was good at what it was intended to do.

 

There are people who flew the Spit in combat and loved it, there are people who flew aerobatics in the Spit and loved it, there are still people who fly Spits who aren't trying to kill anybody and they love it.

 

I think I'm just being wound-up now, nevermind, we will see what we get.

Edited October 26, 2015 by bongodriver

[NineLine]

There are people who flew the Spit in combat and loved it, there are people who flew aerobatics in the Spit and loved it, there are still people who fly Spits who aren't trying to kill anybody and they love it.

 

I think I'm just being wound-up now, nevermind, we will see what we get.

 

Not sure why you are getting wound up, I doubt we are saying anything different...

 

Love doesn't equal easy to fly. Thats all I am trying to get across, surely you as a pilot might have experienced that, maybe? An aircraft that you loved to fly, but was a handful to operate? And I am not saying the Spitfire is a handful, but I am sure its not something anyone can jump into and be an Ace pilot with either...

 

So take a deep breath and read what I am typing... it will be ok ;)