Why is the Spitfire Mk IX still unstable??

[bongodriver]

Heres an interesting certification for a MkXVI (essentially a MkIX) with full wartime CG limitations and it is the bubble canopy version which was understood to present lateral (directional) instability at rear CG limits, not significant enough to limit it's civilian operations clearly.

 

5. WEIGHT AND BALANCE

The aircraft has been weighed and a new weight and C of G schedule raised. CG datum is indicated by a plate on the port side of the fuselage near the fireproof bulkhead and is at the junction of the centre line of Frame 5 and the horizontal datum line which is parallel to and 3 inches below the thrust line.

Service limitations included:

Normal operational flying max. weight 7900 lb Overload max. weight for gentle manoeuvres and takeoff from hard smooth runways 9500 lb CG range 3.5" to 9.5" AOD Maximum landing weight 7450 lb

Page 10 of 11

The normal operation and overload weights above were as applied to this aircraft. More usual limits were 7800lb and 8700lb respectively.

This aircraft has 2 ballast weights (35 lb total) installed on the aft battery tray (and five ballast weights in the standard location over the tail wheel), such that with a 200 lb pilot + parachute, maximum achievable weight is 6803 lb and cg range 4.27 to 5.27 inches AOD. The limit weights and cg range achievable by this aircraft are therefore within the service limits.

6. FLIGHT TEST

The aircraft has been test flown to CAA Flight Test Schedules 2 and 233 with satisfactory results, i.e. consistent with other Spitfires. FTR 7938Y dated 14 July l99l refers. The aircraft is acceptable with respect to performance of aerobatic manoeuvres with the exception of intentional spinning and manoeuvres likely to lead to inadvertent departure from controlled flight

 

http://www.caa.co.uk/AANDocs/21359/21359020000.pdf

[Crumpp]

Ok, heres some quantifiable data on the approval of full wartime CG limits on a modern MkIX Spitfire, sorry it takes me time, I don't have any of this stuff pre prepared to satisfy any obsessive campaign and I have to look it up in real time.

 

Yes it has full wartime CG limits but nothing showing it has a wartime elevator and horizontal stabilizer.

 

Where is that information? It will list that on the actual Type Certificate. What you posted is the supplemental type for replacement of the spar booms.

 

This Addendum to the Airworthiness Approval Note No 17661 Issue 4 serves to record and substantiate the replacement of spar booms fitted to the above aircraft after a landing gear collapse at Le Touquet Airport France in June 1999. Detail of the incident was recorded on Mandatory Occurrence Report dated 10 June 1999.

 

So it is not a complete picture or type certificate.

 

It is very far from the "proof" you think. We need more details but since it is a Fighter Collection aircraft, I am sure Yo-Yo can get them.

 

I have no doubt, the post war war elevator modifications have increased the stability margin of the design and would have allowed for safe limits.

 

Do you have more details as the ones I have posted are the wartime elevator and horizontal stabilizer designs.

 

Normal wartime elevator and horizontal stabilizer

 

The tail section of the fuselage is a separate unit with integral fin, bolted to the main structure. The tailplane is made in halves which are then fitted to the tail section. The rudder and elevators and trim tabs (fitted to elevator and rudder only) are of metal with fabric

covering but ailerons have a light alloy skin. Pneumatically operated split flaps are incorporated. Control runs consist of high tensile cables and levers.

 

CG range limits 3.5“ to 7.0” aft of the datum point

 

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

 

 

The original tail unit is fitted having been refurbished by Fairoakes Aviation in 1979 under the supervision of Mr D.R. Melton.

 

CG range +3.5 in to + 6.39 in AOD.

 

http://www.caa.co.uk/aandocs/22416/22416000000.pdf

 

 

 

 

http://www.caa.co.uk/AANDocs/29100/29100000000.pdf

 

This one is another Fighter Collection aircraft and does not state the Cg limits but it has some non-standard modifications.

 

789 - Introduction of increased horn balance elevator

 

591 - Alternate construction of tailplane

 

Due to the forward of C of G, ballast weights have been fitted at Station 230 (aft of

tailwheel) in accordance with strike command Service Instruction Volume 50 Part III (Reg.

CM/Spitfire/010/STC dated 1.2.74). Additional ballast has also been installed on the

redundant radio rack behind the pilot between frames 13 and 14, in accordance with the

relevant RAF A & P document.

 

http://www.caa.co.uk/aandocs/20279/20279000000.pdf

 

It is just a fact that the Spitfire does not meet modern standards for longitudinal stability and cannot be operated to its wartime CG limits as a result without modifications.

[Crumpp]

cg range 4.27 to 5.27 inches AOD.

 

The MK XIV is a different animal from the Spitfire Mk IX. Most of them had metal elevators and the tailplane area increased. Of course we know increasing the tail plane area moves the AC and increases the stability margin.

 

That is why wartime Mk XIV were limited to an aft CG of 5.9 inches so our limit is still restricted on this example but not by much. We can't tell why without knowing more details of this particular aircraft.

[Crumpp]

Heres an interesting report showing how a MkV Spitfire with absolutely miniscule adjustment to the wartime rear CG limit had all the minor adverse conditions presented by instability cured.

 

http://www.caa.co.uk/AANDocs/21053/21053000000.pdf

 

 

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 be declared as 7.76 inches AOD and this will be stated in the Supplement to the Pilot Notes for G-MKVC.

The maximum speed achieved during these flight tests was 340 KIAS. VNE will be declared at this value although the original clearance was to 390 KIAS (450 MIAS).

 

They restricted the CG limits to eliminate the longitudinal instability and the Vne......

[bongodriver]

The MK XIV is a different animal from the Spitfire Mk IX. Most of them had metal elevators and the tailplane area increased. Of course we know increasing the tail plane area moves the AC and increases the stability margin.

 

That is why wartime Mk XIV were limited to an aft CG of 5.9 inches so our limit is still restricted on this example but not by much. We can't tell why without knowing more details of this particular aircraft.

 

I haven't linked a doc for a MkXIV, that was for a MkXVI.

 

Here is one for a MkXIV which is even less restricted than your estimation.

 

http://www.caa.co.uk/AANDocs/26870/26870000000.pdf

 

5.5.3 Weight and Balance

The aircraft has been weighed; Loadmasters report reference 02MA1134 dated 20th March 2002 and a new weight and C of G schedule raised. CG datum is indicated by a plate on the port side of the fuselage near the fireproof bulkhead and is at the junction of the centre line of Frame 5 and the horizontal datum line, which is parallel to and 3 inches below the thrust line.

Service limitations included: Normal operational flying max. weight 8600Lbs Overload max. weight for gentle manoeuvres and take-off from smooth runways. 9900Lbs CG range 3.5” to 6.5” AOD Maximum Landing weight 8600Lbs

The limit weights and cg range achievable by this aircraft are generally within the service limits. A pilot weighing less than 175lb (with parachute) will find the forward of cg limit is exceeded, as fuel state becomes low. A placard warning of this will be installed.

 

interestingly though going back to your theory, yes they increased the tailplane area on the Grifon powered Spits yet that proved to limit the stability margin even more, yet another inconsistency to your theories.

[bongodriver]

They restricted the CG limits to eliminate the longitudinal instability and the Vne......

 

No, they limited Vne because they only tested up to 340KIAS, they limited the CG by .5 inches which is nothing (sorry if that makes you insecure) to eliminate completely the adverse effects of instability.

[bongodriver]

Yes it has full wartime CG limits but nothing showing it has a wartime elevator and horizontal stabilizer.

 

Where is that information? It will list that on the actual Type Certificate. What you posted is the supplemental type for replacement of the spar booms..

 

it is the addendum to the last issued type certificate where the rear CG limit was increased because it has the rear fuel tanks fitted, really nothing to do with elevator design.

 

 

So it is not a complete picture or type certificate.

 

complete enough.

 

It is very far from the "proof" you think. We need more details but since it is a Fighter Collection aircraft, I am sure Yo-Yo can get them.

 

Proof enough that you are incorrect about restrictions on wartime CG ranges, this aircraft is now with planes of fame I believe, maybe you have more opportunity to investigate.

 

I have no doubt, the post war war elevator modifications have increased the stability margin of the design and would have allowed for safe limits.

 

Post war elevator modifications that don't exist on these marks?

 

Do you have more details as the ones I have posted are the wartime elevator and horizontal stabilizer designs.

 

they all have standard elevators.

 

It is just a fact that the Spitfire does not meet modern standards for longitudinal stability and cannot be operated to its wartime CG limits as a result without modifications.

 

many WWII fighters don't, including German ones, I have already linked a MkI certificate with no restriction on CG range and it is operated in wartime configuration guns and all, there is no mention of elevators being of a modified specification, I guess you need to get in touch with our authorities and tell them that they are just wrong.

[Crumpp]

No, they limited Vne because they only tested up to 340KIAS, they limited the CG by .5 inches which is nothing (sorry if that makes you insecure) to eliminate completely the adverse effects of instability.

 

You are selectively reading it and missing important details.

 

The limits on the Spitfire Mk V were the same as the Spitfire Mk IX.

 

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.

 

Crumpp says:

<A push force in the turn is longitudinal instability>

 

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 be declared as 7.76 inches AOD and this will be stated in the Supplement to the Pilot Notes for G-MKVC.

The maximum speed achieved during these flight tests was 340 KIAS. VNE will be declared at this value although the original clearance was to 390 KIAS (450 MIAS).

 

9in reduced to 7.76in is 1.24 in representing a 16% reduction in the CoG aft limit.

 

Once more, the aircraft limits were adjusted to eliminate the onset of longitudinal instability.

 

bongodriver says:

Post war elevator modifications that don't exist on these marks?

 

Yes, there were post war modifications to the tail plane that would have increased the stability margin allowing for an increase in CG limits.

 

Your document does not give any details as to what was done. It tells us nothing.

 

bongodriver says:

I have already linked a MkI certificate with no restriction on CG range

 

You do not pay attention to the details Bongo, that is what is killing you on this issue.

 

The MkI you linked below has balanced elevators. That means the CG range was 9.0 in for this aircraft during the war and is restricted to 7.9 in post war to eliminate the longitudinal instability.

 

Read the type certificate....

 

 

http://www.caa.co.uk/AANDocs/29100/29100000000.pdf

 

Crumpp says:

Anything Spitfire Mk XIV

 

Is off topic and irrelevant to the Spitfire Mk IX.

[MiloMorai]

Yes, there were post war modifications to the tail plane that would have increased the stability margin allowing for an increase in CG limits.

 

These post war mods would be ...................

[Crumpp]

These post war mods would be ...................

 

57% increase in the horizontal stabilizer and elevator area.

[bongodriver]

57% increase in the horizontal stabilizer and elevator area.

 

Not the case, no merlin powered spitfire has an increased elevator and taiplane, and the size increase on griffon powered spits is not a post war modification, there is no such thing as a griffon tail plane on a merlin spit.

[Crumpp]

bongodriver says:

Not the case, no merlin powered spitfire has an increased elevator and taiplane, and the size increase on griffon powered spits is not a post war modification, there is no such thing as a griffon tail plane on a merlin spit.

 

If you know this then why do you post the Spitfire Mk XIV data in this thread trying to prove the wartime limits are in effect for Spitfire MkIX's being operated today?

 

As for the Merlin powered Spits, the modification was certainly tested and improved the longitudinal stability.

 

As for what was specifically done to the one you posted...I do not know and neither do you.

 

Something was done however as no post war Spitfire can operate unrestricted with the longitudinal instability of the wartime variants.

 

We have seen enough detailed type certificates to establish that. So far you have been able to produce only ONE aircraft with unknown modifications and only half of the rear fuselage tank installed that comes close its wartime CG limits.

 

6. Conditions Affecting This Approval

This aircraft is fitted with modification 1335 which introduces rear fuselage tanks (only the

upper tank is fitted to this example). The weight and CG limitations of the Permit to Fly

should be revised to read:

9.2 Loading limitations

Maximum total weight authorised (normal) 3402 kg (7500 lb)

CG range limits 3.5 inches to 10.5 inches aft of datum

Maximum total weight authorised (overload) 4309 kg (9500 lb)

CG range limits 3.5 inches to 12.5 inches aft of datum

Datum is defined in the Pilot’s notes and a plate on the port side of the fuselage.

9.5 Other limitations

At weights in excess of 3402 kg (7500 lb), gentle manoeuvres only.

 

http://www.caa.co.uk/AANDocs/17661/17661040100.pdf

 

The operating restriction of "gentle maneuvers only" at weights above 7500lbs and the fact it only mounts 1/2 the rear fuselage tank certainly does not make it comparable to a wartime aircraft.

 

Those restrictions do ensure this aircraft will not have the handling issues of it wartime examples.

[Friedrich-4B]

57% increase in the horizontal stabilizer and elevator area.

Please show, with documentation, that post-war Spitfire IXs and XVIs had their horizontal control surface areas increased by 57%.

 

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

5.5.1 Pilots Notes

The aircraft is to be operated in accordance with Pilots Notes AP1565J, P and L.

‘Pilots Notes for Spitfire IXB Registration G-ASJV’ was raised to cover procedures

for operation of the long range wing fuel tanks.

 

6.1 Aerobatic Limitations

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

Spinning is prohibited.

 

It is just a fact that the Spitfire does not meet modern standards for longitudinal stability and cannot be operated to its wartime CG limits as a result without modifications.

 

It is just a fact that restored Spitfires are not operated to wartime standards because, like any other restored WW2 aircraft, they are rare and extremely costly to repair or replace. It has nothing to do with purported "longitudinal stability" standards.

 

(From Spitfire: Return to Flight )

Edited October 22, 2015 by Friedrich-4/B
Spelling

[Crumpp]

CG limits have nothing to do with stress or wear on the aircraft.

[Decibel dB]

%5Bimg%5Dhttp%3A//i.imgur.com/kRTdMVz.jpg?1[/img]

 

This is MJ627 a MK IX that was converted as a two seater after the war by removing the aft tank and replace it with a seat. In tandem it does have a little instability and very sensitive in pitch. This is not the case in solo. I hope it help

[Friedrich-4B]

CG limits have nothing to do with stress or wear on the aircraft.

 

Nor is longitudinal instability mentioned as a reason why restored Spitfire IXs and XVIs are not flown to their wartime limits.

 

Now as I recall, right at the beginning of this year, Crumpp assured us that he had at least one definitive report stating that the Mk IX suffered from longitudinal instability

 

http://forums.eagle.ru/showpost.php?p=2279493&postcount=71

 

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

Yes...

 

So here we have a problem; surely it would have been far easier on everyone had at least some of this information been posted right at the start of this thread, instead of subjecting everyone to endless debate and speculation based on partial documents of earlier, single-stage Merlin Spitfires, and what has happened since to restored examples?

[bongodriver]

You are selectively reading it and missing important details.

 

The limits on the Spitfire Mk V were the same as the Spitfire Mk IX.

 

I selectively read the relevant information, I certainly do not miss or try not to miss the important details. clearly the limits on a MkV were not the same as a MkIX as we have all seen a MkIX type certificate showing aft limits of 10.5" and 12.5"

 

This is your claim on MkIX CG limitations from post No5

 

 

The NACA Flying Qualities investigation was only 4.8 inches aft of datum and the normal take off CG is 6.8 inches aft of datum in the Spitfire Mk IX.

 

 

Yet we see modern day MkIX's with CG at 7.0" and this is the most limiting, you also seem to be confusing MkIX's with MkV's again as there has been no NACA report on a MkIX shown.

 

9in reduced to 7.76in is 1.24 in representing a 16% reduction in the CoG aft limit.

 

Once more, the aircraft limits were adjusted to eliminate the onset of longitudinal instability.

 

Yes, I did misread the magnitude of adjustment, the important piece of information to take away from this is that the longitudinal instability was 'eliminated'

with a minor adjustment of rearward CG, this completely flies in the face of your inherently unstable in normal CG ranges theory.

 

Yes, there were post war modifications to the tail plane that would have increased the stability margin allowing for an increase in CG limits.

 

No, there are no post war modifications, there are in service modifications which you have even included in your opening post that increase the stability margin and then in another post completely denied it and subsequently changed your mind again, not that you are backpeddaling to suit your agenda of course.

 

Your document does not give any details as to what was done. It tells us nothing.

 

it tells us plenty, it tell us that the elevator had no modifications, it tells us the aircraft is very close to full authentic wartime spec, it tell us that CG was unrestricted to any arbitrary civilian limitations

 

You do not pay attention to the details Bongo, that is what is killing you on this issue.

 

The MkI you linked below has balanced elevators. That means the CG range was 9.0 in for this aircraft during the war and is restricted to 7.9 in post war to eliminate the longitudinal instability.

 

Read the type certificate....

 

I have read the certificate, that is how I know it says nothing about a wartime limit of 9.0" and the actual rearward limit of 7.9" is bang on the money for a standard elevator with no inertia weight and a DeHavilland prop, standard elevator being the mass balanced and not aerodynamically horn balanced one.

 

Spitfire Mk I:

 

 

As we can see G-AIST has the early type standard elevators and not the horn balanced late revision (you know, the same one on the MkIX that would have increased its CG to 9.0")

 

 

So, it is a fact, the NACA report on the Flying Qualities of the Spitfire is applicable. Supermarine correctly followed the NACA's advice and did not choose mass balancing for the aircraft but instead choose to aerodynamically balance the elevator. This does represent a design change that moves the aircraft's AC.

 

Yes, yes it does, a wartime modified elevator that increased the stability margin.

 

 

Crumpp says:

Anything Spitfire Mk XIV

 

Is off topic and irrelevant to the Spitfire Mk IX.

 

This one baffles me, you quoted yourself and declared it irrelevant, and the quote is not even something you actually wrote, I am in complete agreement of course but it is curious, it does lead us nicely in to the prolonged agony that is waiting for you to actually provide the data on an actual MkIX you claim to have.

 

If you know this then why do you post the Spitfire Mk XIV data in this thread trying to prove the wartime limits are in effect for Spitfire MkIX's being operated today?

 

I didn't, I posted MkXIV data to illustrate further to you that wartime limitations are not restricted in civilian operations, I have posted data for most relevant marks highlighting this point that you so vehemently deny.

 

As for the Merlin powered Spits, the modification was certainly tested and improved the longitudinal stability.

 

A modification was tested yes, no modification was implemented, to date elevators remain to original wartime specification.

 

As for what was specifically done to the one you posted...I do not know and neither do you.

 

Oh but I do, you only have to look and see it is the late wartime aerodynamically horn balanced elevator.

 

 

Something was done however as no post war Spitfire can operate unrestricted with the longitudinal instability of the wartime variants.

 

Well we can clearly see now that you are incorrect on this, we even have videos of modern day pilots describing the mild effects of instability in an aircraft permitted to carry fare paying members of the public, I understand it is tough for you to let go of this fantasy of yours.

 

We have seen enough detailed type certificates to establish that. So far you have been able to produce only ONE aircraft with unknown modifications and only half of the rear fuselage tank installed that comes close its wartime CG limits.

 

I have produced several type certificates that detail precisely the configuration of the aircraft in question, there are no unknown modifications on the example in question, there is a full list of modifications and none involve post war revisions of the elevator design, half a rear tank is representative of a wartime aircraft with half a rear fuel load, you know, the configuration that combat was permitted.

 

http://www.caa.co.uk/AANDocs/17661/17661040100.pdf

 

The operating restriction of "gentle maneuvers only" at weights above 7500lbs and the fact it only mounts 1/2 the rear fuselage tank certainly does not make it comparable to a wartime aircraft.

 

Those restrictions do ensure this aircraft will not have the handling issues of it wartime examples.

 

What we must take away from all this research in to the modern day MkIX is that the CG range varies dependent on configuration, aircraft that carry more weight in the rear actually have less restricted CG rear limints, single seaters without rear tanks and standard elevators limited to the 7.0 to 7.2 range.

 

http://www.caa.co.uk/AANDocs/22416/22416020000.pdf

 

a single seater with no rear tank and no post war modifications of elevators with a 9.5 rear limit

 

http://www.caa.co.uk/AANDocs/26450/26450020000.pdf

 

and dual seaters getting up to the 8.0 range

 

http://www.caa.co.uk/AANDocs/19022/19022000100.pdf

 

http://www.caa.co.uk/AANDocs/20929/20929000000.pdf

 

and a single seater with rear tanks and standard elevators reaching 12.5" aft of datum

 

http://www.caa.co.uk/AANDocs/17661/17661040100.pdf

 

on investigation including other marks it does show an inherent limit in the Spitfire design where instability begins to manifest, this instability is at worst mild when the limit is slightly exceeded, the limit in this case seems to be approx. the 7.0" aft CG, most of these reports show that a 7.0" aft CG is a range that is very easily kept within for a standard loaded Spitfire (equivalent to full fighter loads) with single occupant and no rear fuel, no instability manifests whatsoever within that range hence why the 7.0" limitation is imposed, they simply don't need to go beyond it. in the more tail heavy Spitfires that need to go outside that CG range it is clear that a level of instability is deemed acceptable and controllable or they simply would not allow the paying public to get in to one and this limit is allowed right up to 12.5" aft in the hands of civilian pilots.

 

So Crumpp please, we emplore you, provide this mystery MkIX report you claim to have, I honestly would welcome it no matter what it proves.

[Crumpp]

Decibel dB syas:

This is MJ627 a MK IX that was converted as a two seater after the war by removing the aft tank and replace it with a seat. In tandem it does have a little instability and very sensitive in pitch. This is not the case in solo. I hope it help

 

Welcome to the discussion.

 

The front cockpit is moved forward in the tandem Spitfires otherwise the conversion would not be possible. Solo, it is a different animal from a Spitfire Mk IX and I have no doubt it falls in the forward of normal CG range for wartime Spitfire Mk IX.

 

Nor is longitudinal instability mentioned as a reason why restored Spitfire IXs and XVIs are not flown to their wartime limits.

 

By definition, the rear limit is determined by the onset of longitudinal instability in a modern aircraft stability and control standards.

 

 

That is why the CG are restricted from their wartime limits.

 

The modern definition of sufficient stability has changed as data and the pilot's opinion has been quantified.

 

 

bongodriver says:

I haven't linked a doc for a MkXIV, that was for a MkXVI.

 

Mk XVI horizontal stabilizer and elevator area was increased from the wartime 31.46M^2 of the Mk IX to 33.83m^2. This represents a stability margin increase so the Mk XVI is a different animal from a wartime Mk IX.

[Crumpp]

No, there are no post war modifications, there are in service modifications which you have even included in your opening post that increase the stability margin and then in another post completely denied it and subsequently changed your mind again, not that you are backpeddaling to suit your agenda of course.

 

There is a post war modification increasing the horizontal stabilizer/elevator area. It goes from the wartime area of 31.46m^2 to 33.83m^2.

[bongodriver]

Mk XVI horizontal stabilizer and elevator area was increased from the wartime 31.46M^2 of the Mk IX to 33.83m^2. This represents a stability margin increase so the Mk XVI is a different animal from a wartime Mk IX.

 

No, the MkXVI was a MkIX airframe in every way, the MKXIV that we are actually talking about is a Grifon Spitfire and has the larger tailplane accordingly, the point stands that CG limitations for that type are unchanged from wartime specifications.

 

it's odd how you have misquoted me in that post.

Edited October 22, 2015 by bongodriver

[bongodriver]

There is a post war modification increasing the horizontal stabilizer/elevator area. It goes from the wartime area of 31.46m^2 to 33.83m^2.

 

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

 

 

 

Elevators

 

All except the initial production Mk. IXs had elevators with extended mass balance horns. Whereas the early Spitfires had a 45-degree break in the hinge line, this new pattern had an additional 45-degree break, resulting in the tip of the elevator pointing straight forward.

 

As a rule of thumb the early pattern is seen on Mk. IXs converted from Mk. Vs, and early original Mk. IXs. I’ve seen both patterns on aircraft in the MA serial range (Castle Bromwich – mid-1943 vintage).

[Crumpp]

I have read the certificate, that is how I know it says nothing about a wartime limit of 9.0" and the actual rearward limit of 7.9" is bang on the money for a standard elevator with no inertia weight and a DeHavilland prop, standard elevator being the mass balanced and not aerodynamically horn balanced one.

 

It does not have the standard elevator so the propeller type is irrelevant. I has the modified horn balance elevator so the Aft CG limit in wartime would be 9.0in.

 

Same limit as a wartime Spitfire Mk IX.

 

Notice the note above the propeller types...."with standard elevator". In otherwords, not horn balanced.

 

 

 

What we must take away from all this research in to the modern day MkIX is that the CG range varies dependent on configuration, aircraft that carry more weight in the rear actually have less restricted CG rear limints, single seaters without rear tanks and standard elevators limited to the 7.0 to 7.2 range.

 

The tandem Spitfire front cockpit is moved forward and the aircraft has a 9 1/2 lb bobweight. I cannot find the fuselage length specifications but I would venture it has a longer fuselage as well.

 

What you should take away is the fact the wartime Rear CG limit was too far aft under stability and control standards.

 

The NACA assessment was correct and applicable to the Mk IX series since the stability margin remained unchanged in the design. The aircraft was neutral to unstable at normal CG to the rear CG limit.

[Crumpp]

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

 

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.

 

:P

[bongodriver]

It does not have the standard elevator so the propeller type is irrelevant. I has the modified horn balance elevator so the Aft CG limit in wartime would be 9.0in.

 

a picture of the actual aircraft with the early standard elevator is not enough for you? it is the standard non horn balanced elevator as illustrated in a previous post, no Spitfire ever had a straight hinge line elevator, the earliest type has the 45 degree hinge break and is the standard.

 

Same limit as a wartime Spitfire Mk IX.

 

Absolutely not

 

Notice the note above the propeller types...."with standard elevator". In otherwords, not horn balanced.

 

 

So, you get it now?, no horn balance, meaning the standard elevator with 45 degree hinge break.

 

The tandem Spitfire front cockpit is moved forward and the aircraft has a 9 1/2 lb bobweight. I cannot find the fuselage length specifications but I would venture it has a longer fuselage as well.

 

No bob weights are fitted, fuselage length is the same but the front cockpit is moved forward slightly, look forward to the data you gather and share though.

 

What you should take away is the fact the wartime Rear CG limit was too far aft under stability and control standards.

 

I have not seen a single wartime limit that exceeds anything listed a modern example, so your claim here is just plain nonsense, we have however seen clear evidence of instability being eliminated at CG ranges of 7.0, this is not the normal range of a Spitfire and it does render your claim of Spitfire instability at normal CG range completely invalid.

 

The NACA assessment was correct and applicable to the Mk IX series since the stability margin remained unchanged in the design. The aircraft was neutral to unstable at normal CG to the rear CG limit.

 

it was correct for that specific MkV, it's applicability to the MkIX is very tenuous at best

[Yo-Yo]

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.

 

:P

 

The only one, short, natural and the right way to determine Mk IX stability having EXACT data for Mk V, that is, for sure, obvious for you, is:

Answer the question if 9 has the same wing (planeform and airfoil), stab area and its arm relatively to the wing MAC.

If so, the neutral point of the airframe is the same, and we are able to create the airframe model having stability charachteristics exactly as Mk V using measured data.

Changing CoG position corresponding the Mk IX docs.

Get it as is... :), profit.

And i am really amazed how many letters were typed during the discussion... :)

 

So, i very much appreciate your battle proving the engineering way of thinking! :)

Edited October 22, 2015 by Yo-Yo