Spitfire IX Stick Forces

[Krupi]

Hi Chaps,

 

I am hoping someone here can cast a bit more light on this particular topic.

 

I am trying to find some information regarding the forces required to deflect the ailerons and elevator around cruise speed. I knew from reading various sources that the Spitfires control were incredible light and that the elevator and ailerons were not harmonized with the former tending to be very light at all speeds and the ailerons becoming heavier especially above ~300mph.

 

Currently my efforts to read into this have led me on a merry goose chase. :doh:

 

I asked the same question over at "The Aviation Forum" and have been given some great information to read through from a very helpful chap over there which I am currently trailing through.

 

http://forum.keypublishing.com/showthread.php?138819-Spitfire-Mk-IX-Stick-Forces

 

At present the most compelling evidence I have found comes from a NACA 868 report on the Spitfire MK Mk V from which I have the following...

 

Ailerons - ~ 40 lbf at ~300mph

 

Elevator - ~ 5 lb per g in a turn

 

However I have read that the NACA Spitfire Mk V was in a pretty sorry state, apparently this statement came from Robert Stanford Tuck who was over in America for a tour.

 

Anyway if anybody has some more documents to trawl through I would be grateful.

Edited May 21, 2016 by Krupi

[Ala13_ManOWar]

Interesting question, specially how can a disharmonization like that be modelled into our joysticks.

 

I am trying to find some information regarding the forces required to deflect the ailerons and elevator around cruise speed. I knew from reading various sources that the Spitfires control were incredible light and that the elevator and ailerons were not harmonized with the former tending to be very light at all speeds and the ailerons becoming heavier especially above ~300mph.

The funny thing is the only time I could flew in a Tiger Moth this happened indeed, with a really light like hell pitch control and quite heavy ailerons but I guessed biplane made that. May be one of the chaps around here flying Moths regularly can talk to us about that.

 

 

I'm really eager to ride the Spitfire with its quirks :pilotfly:.

 

S!

[Friedrich-4B]

Hi Chaps,

 

I am hoping someone here can cast a bit more light on this particular topic.

 

I am trying to find some information regarding the forces required to deflect the ailerons and elevator around cruise speed. I knew from reading various sources that the Spitfires control were incredible light and that the elevator and ailerons were not harmonized with the former tending to be very light at all speeds and the ailerons becoming heavier especially above ~300mph.

 

Currently my efforts to read into this have led me on a merry goose chase. :doh:

 

I asked the same question over at "The Aviation Forum" and have been given some great information to read through from a very helpful chap over there which I am currently trailing through.

 

http://forum.keypublishing.com/showthread.php?138819-Spitfire-Mk-IX-Stick-Forces

 

At present the most compelling evidence I have found comes from a NACA 868 report on the Spitfire MK Mk V from which I have the following...

 

Elevator - ~ 40 lbf at ~300mph

 

Ailerons - ~ 5 lb per g in a turn

 

However I have read that the NACA Spitfire Mk V was in a pretty sorry state, apparently this statement came from Robert Stanford Tuck who was over in America for a tour.

 

Anyway if anybody has some more documents to trawl through I would be grateful.

 

The difficulty with relying on the NACA report on a Spitfire VA is, as mentioned elsewhere, the elevators had been redesigned for all but the earliest IXs.

 

BTW (and slightly OT) Yo-Yo has described how the FM will handle in this thread:

 

:)

 

Fortunately, Mk IX is slightly stable, anyway, the required stick travel is not high... but nothing extraordinary.

 

Very pleasant to fly, very controllable, predictable and steady.

 

Some day I will try to shift CoG to Mk V or Mk IX with rear tank position... but do not think it will be a kind of trouble.

 

none of the longitudinal instability that some self-proclaimed "experts" have insisted the Spitfire IX supposedly exhibited. :thumbup:

[Nerd1000]

The revised elevators on the Mk IX appear to increase the balance area, which suggests that Supermarine were actually trying to reduce the force needed to move the elevators.

 

That makes me suspicious of claims that the elevators were perceived as too light at the time. Surely if the elevator forces were too light they would have reduced the balance area rather than increasing it?

[Krupi]

The revised elevators on the Mk IX appear to increase the balance area, which suggests that Supermarine were actually trying to reduce the force needed to move the elevators.

 

That makes me suspicious of claims that the elevators were perceived as too light at the time. Surely if the elevator forces were too light they would have reduced the balance area rather than increasing it?

 

The extended hornbalance from what I have read were introduced to bring the cog back to where it was on the MkV and earlier however it was not fully fixed until the introduction of the extended rudder. Later Mk IX had them.

 

I can't see how the hornbalance would really impact the stick forces and if it did it would not be a big impact.

Edited May 22, 2016 by Krupi

[Nerd1000]

I don't understand. When you say 'cog' do you mean Centre of Gravity? Or some part of the elevator mechanism?

 

edit: Okay, got it- they extended the horn balance to move the centre of mass of the elevator forward, possibly reducing flutter.

 

Increasing the area in front of the hinge will reduce stick forces because the area in front of the hinge is subject to aerodynamic forces just like the part behind the hinge. Therefore in an ideal case equal areas in front of and behind the hinge result in zero stick forces at all speeds. This is obviously not good, so planes with an all-flying tail (which is as close as planes come to the 'equal areas' scenario) often have some mechanism to prevent the pilot from over-controlling the plane, for example an anti-servo tab on the stabilator or springs and bob weights in the control system that provide artificial 'feel'.

Edited May 23, 2016 by Nerd1000

[Krupi]

Yes Centre of Gravity

[Yo-Yo]

Yes Centre of Gravity

 

Do you really mean that CoG of a body can be shifted adding a small area to the horn???

[Krupi]

This is just from what I read, to improve the stability the hornbalance was added as equipment was been added changing the cog. The same sources also said that the problem was not really fixed until the rudder from the VIII became standard on later Mk IX so clearly the extended hornbalance elevators were not a big enough change as you have queried :smilewink:

 

I was just pointing out that from what I have read there was no mention of a link between the extended hornbalance elevator and stick forces.

 

If you have another explanation I would be very interested :)

Edited May 23, 2016 by Krupi

[Krupi]

Apparently this is a quote from Geoffrey Quills book...

 

"In the meantime a 75-gallon tank was fitted in the fuselage of a Mk IX behind the pilot and we also fitted a bob-weight in the elevator circuit, so what with this and the large horn-balance on the elevator we hoped for the best."

 

What is clear is that apart from the first few converted Mk V aircraft all production Mk IX were built with the extended hornbalance.

Edited May 23, 2016 by Krupi

[Yo-Yo]

This is just from what I read, to improve the stability the hornbalance was added as equipment was been added changing the cog. The same sources also said that the problem was not really fixed until the rudder from the VIII became standard on later Mk IX so clearly the extended hornbalance elevators were not a big enough change as you have queried :smilewink:

 

I was just pointing out that from what I have read there was no mention of a link between the extended hornbalance elevator and stick forces.

 

If you have another explanation I would be very interested :)

 

THis part can not change the CoG... of course if you did not make it from solid uranium...

[Krupi]

THis part can not change the CoG... of course if you did not make it from solid uranium...

 

:megalol:

 

The quote from the Geoffrey Quill book suggests the extended hornbalance was more to do with longitudinal stability, however the bob weight would certainly move the CoG.

Edited May 23, 2016 by Krupi

[Alicatt]

A bob weight is used to counterbalance a mechanical moving part, generally they are as small as can be used. It is unlikely that a bob weight on a control linkage would be big enough to drastically alter the centre of gravity of an aircraft.

[DD_Fenrir]

:megalol:

 

.... however the bob weight would certainly move the CoG.

 

Must correct you there Krupi, the bob-weight was introduced to make the stick forces heavier with 'g' making applying too much elevator input more difficult and therefore increasing the effort required by the pilot to over-stress the airframe, it would have little impact on the CoG by and of itself.

 

As to the effectiveness of the redesigned elevator:

 

"The 'Westland elevator' [an experimental type not fitted operationally - DD_Fenrir], as it became known , demonstrated the way forward; but our aerodynamicists at Hursley Park thought that an even more effective answer could be obtained by enlarging the horn balance of the standard elevator and this we did by stages. The effect was astonishing. At last a way had been found to improve the basic static stability margins of the aeroplane..." from Spitfire by Jeffrey Quill, p237, ISBN0-09-937020-4

Edited May 23, 2016 by DD_Fenrir

[Krupi]

Ah okay thank you for the corrections chaps.

 

My apologies I thought it was just a ballast essentially, I didn't realise that bob weights were linked to the stick forces.

 

So how did they work, how did they increase the forces at high g?

[DD_Fenrir]

"The object of this was that, when any g was applied to the aeroplane, the (bob)weight would react in the sense of pushing the stick forward thus counteracting g. Any tendency on the part of the aeroplane to tighten into turns was therefore immediately corrected by the elevators. When I tested the device extensively on N3297 it worked extremely well. It was worth about two inches' rearward travel of the centre of gravity and provided in good measure the increased stability margins we were seeking. In fact, our very first tests of this idea were done by weighting the trailing edge of the elevator; later we fixed a lever arm in the control circuit with a weight which could be varied and we sent the aeroplane to the A & AEE at Boscombe Down with the device fitted. We started with a 3.5lb bob weight and increased it to 7lb. The only side effect, so to speak, was that when taxiing over bumpy ground it showed a tendency to jerk the stick around a bit but this was a minor effect, and of no real consequence."

 

from Spitfire by Jeffrey Quill, p232, ISBN0-09-937020-4

 

There is a diagram floating about somewhere but cannot source currently.

Edited May 23, 2016 by DD_Fenrir

[Krupi]

Is that it?

 

http://aerolegends.co.uk/blog/spitfire-nh341-restoration/posts/november-2015/restoration-update-15

 

[DD_Fenrir]

Certainly looks like it!

 

IIRC it was mounted at the base of the control column perpendicular to said column with the bob-weight extending forwards toward the nose.

[Yo-Yo]

Aerodynamic compensation increases free-controls stability reducing hinge moment due to stab AoA.

[Friedrich-4B]

"The object of this was that, when any g was applied to the aeroplane, the (bob)weight would react in the sense of pushing the stick forward thus counteracting g. Any tendency on the part of the aeroplane to tighten into turns was therefore immediately corrected by the elevators. When I tested the device extensively on N3297 it worked extremely well. It was worth about two inches' rearward travel of the centre of gravity and provided in good measure the increased stability margins we were seeking..."

from Spitfire by Jeffrey Quill, p232, ISBN0-09-937020-4

 

There is a diagram floating about somewhere but cannot source currently.

 

Just a note that N3297 was initially the Mk III prototype, later converted to the first Mk IX

prototype.

[Ala13_ManOWar]

Aerodynamic compensation increases free-controls stability reducing hinge moment due to stab AoA.

My flight instructor said all the time, "trim isn't for pilot comfort only but to reduce pressure in control surfaces hinges". I think I'll nail in the face this sentence to some people out there.

 

S!

[Talisman_VR]

So, just for clarification, for the layman like myself, would it be correct for me to assume that the bob weight is good technology that has a positive beneficial effect for controlled flight and is not a bandage on a wounded aeroplane? In terms of technology (not exact function), perhaps on a par with something like wing leading edge slats?

 

Happy landings,

 

Talisman

[Krupi]

No, it is a simple device to ensure the pilot doesn't over stress the aircraft.

 

In this case as the G force increases the elevator stick forces becomes greater.

[Yo-Yo]

So, just for clarification, for the layman like myself, would it be correct for me to assume that the bob weight is good technology that has a positive beneficial effect for controlled flight and is not a bandage on a wounded aeroplane? In terms of technology (not exact function), perhaps on a par with something like wing leading edge slats?

 

Happy landings,

 

Talisman

 

The bobweight simulates stick forces that are distinctive for a stable plane. If tyhe plane is neutral with free controls (regarding stick forces), if you want to increase g you pull the stick encountering some resistance. then as you reach the desired g you must return the stick almost in the same position having the same force as for 1g flight. It's not intuitive and always considered as unpreferrable feeling and action, so this artificial force from the bobweight proportional to the g works for better feeling.

 

Generally, the free controls neutral margin is more forward in terms of CoG than fixed controls margin. Adding a bobweight we move the first one to the second one.

[Talisman_VR]

The bobweight simulates stick forces that are distinctive for a stable plane. If tyhe plane is neutral with free controls (regarding stick forces), if you want to increase g you pull the stick encountering some resistance. then as you reach the desired g you must return the stick almost in the same position having the same force as for 1g flight. It's not intuitive and always considered as unpreferrable feeling and action, so this artificial force from the bobweight proportional to the g works for better feeling.

 

Generally, the free controls neutral margin is more forward in terms of CoG than fixed controls margin. Adding a bobweight we move the first one to the second one.

 

Yo-Yo,

 

Thank you very much for taking the time to explain. So it would appear to be a relatively simple but sophisticated device that, amongst other things, can give an advantage to the pilot of a high performance combat aircraft that is regularly pushed in combat to fly to the very edge of the flight envelope.

I use force feedback joysticks and wonder how this might effect my feeling and experience of flying the Spitfire compared to non FF sticks in terms of the DCS model.

This is very interesting stuff. I love the way this hobby is educational in so many different ways :)

This is a great community. Thanks.

 

Happy landings,

 

Talisman