Spitfire IX Stick Forces

[Kurfürst]

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.

 

Its somewhat of an odd description and akin to describing a peg legged pirate (at best neutrally stable without the peg leg... :lol: ) having a so-called advantage in a knife fight due to that 'extra' stability the peg leg provides. On the Spitfire they simply used it as a band aid, since the aircraft's design had small stability margins to start with, and the managed to practically loose it as extra equipment kept creeping into the fuselage by mid war.

 

It just makes a plane with neutral stability characteristics to behave more like a stable aircraft and handle more intuitively. Also, there is not much point to it if your aircraft is stable in the first place, as the bob weights had poor reputation with the pilots and some complained that it "destroying the feel" of the aircraft. Still, for most pilots, bar the most experienced ones it was more easy to control a more stable aircraft in pitch since you only had to hold it on the edge, and not literally bringing it back from it.

 

It should be born in mind that neutral stability is not necessarily a bad thing, in a way it improves maneuvering reaction and would be for example useful for aerobatics, but for most applications, including combat flying it was un-preferred because of the less natural control characteristics and back and forth stick movements. Some planes with such characteristics could do wonderful things, trouble is that most of their pilots couldn't.

 

Its neutral or negative stability is quite akin to oversteering in cars. Could be a blessing for racing and rally drivers but a serious inconvenience to the average driver who does not know how to properly keep the tendency in check.

Edited May 25, 2016 by Kurfürst

[Nerd1000]

Its somewhat of an odd description and akin to describing a peg legged pirate (at best neutrally stable without the peg leg... :lol: ) having a so-called advantage in a knife fight due to that 'extra' stability the peg leg provides. On the Spitfire they simply used it as a band aid, since the aircraft's design had small stability margins to start with, and the managed to practically loose it as extra equipment kept creeping into the fuselage by mid war.

 

It just makes a plane with neutral stability characteristics to behave more like a stable aircraft and handle more intuitively. Also, there is not much point to it if your aircraft is stable in the first place, as the bob weights had poor reputation with the pilots and some complained that it "destroying the feel" of the aircraft. Still, for most pilots, bar the most experienced ones it was more easy to control a more stable aircraft in pitch since you only had to hold it on the edge, and not literally bringing it back from it.

 

It should be born in mind that neutral stability is not necessarily a bad thing, in a way it improves maneuvering reaction and would be for example useful for aerobatics, but for most applications, including combat flying it was un-preferred because of the less natural control characteristics and back and forth stick movements. Some planes with such characteristics could do wonderful things, trouble is that most of their pilots couldn't.

 

Its neutral or negative stability is quite akin to oversteering in cars. Could be a blessing for racing and rally drivers but a serious inconvenience to the average driver who does not know how to properly keep the tendency in check.

It is interesting that the Spitfire is often described as being relatively easy to fly in spite of its 'on the edge' neutral stability. At the same time the 109, an aircraft that AFAIK is very stable (so stable that you need all your strength to pull out of a high speed dive) is described as 'difficult' by many authors.

[Kurfürst]

Such descriptions are probably born in the authors own mind since the actual trials in 1940, and in fact, common sense, comparing the two state the exact opposite characteristics.

 

"Easy" and "difficult" are of course very simplified descriptions of complex control and handling characteristics. Which is a difficult, which is easy? A plane with heavy pitch control forces, high longitudinal stability, good but overall heavy control harmony, excellent stall recovery characteristics and mild stall, but rather high stall speed,low directional stability, or a plane with extremely light pitch control forces, poorly harmonized control forces, neutral at best longitudal stability, good stall recovery but violent stall characteristics but low stall speed, and medium directional stability..? Sometimes easy and difficult co-exist.

[Krupi]

Please can we get back on topic before anymore snide comments are thrown about.

 

I am still looking for data on stick forces.

 

Thank you.

[Kurfürst]

4 lbs/g for pitch, and 50 lbs stickforce for maximum aileron deflection at 200 mph IAS and above for variants with metal ailerons.

 

The former can be considered very, very light the latter is considered excessively heavy.

[Nerd1000]

4 lbs/g for pitch, and 50 lbs stickforce for maximum aileron deflection at 200 mph IAS and above for variants with metal ailerons.

 

The former can be considered very, very light the latter is considered excessively heavy.

Got anything on aileron input vs roll rate? As I understand it the original spitfire wing is very 'twisty', so the ailerons get less effective at high deflection (the wing twists the other way, partially cancelling out their effect). The problem was fixed by a new wing on the Mk 21, but it isn't really a WW2 plane.

 

I'm also curious as to how the change to the heavier and longer griffon engine changed the elevator response. It presumably moved the CoG forward a bit.

[Friedrich-4B]

Its somewhat of an odd description and akin to describing a peg legged pirate (at best neutrally stable without the peg leg... :lol: ) having a so-called advantage in a knife fight due to that 'extra' stability the peg leg provides. On the Spitfire they simply used it as a band aid, since the aircraft's design had small stability margins to start with, and the managed to practically loose it as extra equipment kept creeping into the fuselage by mid war...blah, blah, blah...

 

Just guessing that Kurfurst, who for years has been such a dedicated Spitfire enthusiast, can provide good documentation that proves that the sad, slow old Spitfire IX was a bit of a cow for the average RAF pilot to handle, in much the same way that an oversteering race or rally car could be considered tricky for an average driver. :thumbup:

 

No doubt Kurfurst can also provide documentation that shows that all wartime Spitfire IXs used inertia weights to band-aid the aircraft's purported longitudinal instability?

 

Otherwise, what is the point of Kurfurst's post? Is Kurfurst implying that ED's Spitfire IX will be an oversteering cow that only the more experienced players will be able to handle properly? Or is he claiming that Yo-Yo's statement

 

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.

 

is wrong, because Kurfurst knows that ED's Spitfire IX will oversteer into the nearest tree at every opportunity without a skilled pilot at the helm? :dunno:

[Krupi]

4 lbs/g for pitch, and 50 lbs stickforce for maximum aileron deflection at 200 mph IAS and above for variants with metal ailerons.

 

The former can be considered very, very light the latter is considered excessively heavy.

 

That is just not right isn't it! 50lbs for metal ailerons is way way too high for 200 Mph :megalol: from what I have read the metal ailerons reduced the force significantly up to 300-350 mph

 

4-6 lbs per G seems about right for elevators though.

Edited May 26, 2016 by Krupi

[Kurfürst]

How did metal ailerons "reduce" the stick forces Krupi?

 

Why do the Spitfire roll curves (RAE figures) in the summary report NACA 868 show the break at 200 mph?

 

 

Perhaps another NACA report will help you figure out.

 

[Krupi]

Simple the fabric ailerons would balloon at high speed increasing drag and therefore increasing the force required to push the ailerons! It is very obvious how metal would remove the balloon issue.

 

If you look at the NACA report for a worn out (Robert Stanford Tuck said that) Spitfire Mk V they give the max force required at 200mph 40 lb, 300mph 50 lb.

[Krupi]

What Spitfire Mk is the top graph?

 

The second is definitely an early Spitfire with fabric ailerons IIRC and at 30 pounds

Edited May 26, 2016 by Krupi

[Krupi]

Honestly I think my question is too simple for what is a complex and ever changing equation...

 

Basically I am trying to find a reliable figure at around 300mph to help me with a control column I am making.

 

I am thinking that a good starting point ~15lb for the elevator and ~30lb for ailerons would simulate the lack of harmony found in the Spitfire.

 

Obviously the forces change too much depending on a lot of external factors which I will not be feel in a static ground level simpit :lol:

 

P.s.

I am currently waiting for some data to come through on stick forces that a pilot took in a 109 and Spitfire it should be interesting, I will post it here when I have received it.

Edited May 26, 2016 by Krupi

[Kurfürst]

What Spitfire Mk is the top graph?

 

The second is definitely an early Spitfire with fabric ailerons IIRC and at 30 pounds

 

Actually both are Mark Vs with metal ailerons. The first one was tested by RAE, and the figures they obtained were included by the NACA summary report - you can see the the max. aileron deflection was obtainable with 50 lbs up to 200 mph, ie. the straight part of the roll curve. Same thing with the second graph (Mark V w. metal ailerons tested in the US), only that it only shows with 30 degree stick force.

 

Now as for the fabric ailerons, the stick forces per se do not seem to have changed much (no particular reason to think so unless gearing or aileron shape was considerably changed). The trouble with the fabric ones was that no matter how hard you deflected them, they lost their effectiveness at high speed. Since the metal ailerons did not balloon, their effectiveness (roll rate obtained for given deflection) did not diminish so rapidly with speed. Of course subjectively this would seem to the pilot that the ailerons were lighter, considering the same force now yielded greater effect in rolling.

 

Thus the main limiting factor with later metal ailerons on the Spit were (i) high aileron forces limiting deflection (ii) wing twisting under the load induced by aileron deflection countering the aileron effect (so much so that some 65% of the roll was lost at 400 mph), since the whole wing started to twist and act like a huge aileron. Hence why the theoretical aileron reversal speed (at which point the twist would be so severe that the twist would roll the plane to the opposite direction) was rather low, 510 or 580 mph IAS. This required a complete redesign of the wing with the Mark 21 series.

[Talisman_VR]

Its somewhat of an odd description and akin to describing a peg legged pirate (at best neutrally stable without the peg leg... :lol: ) having a so-called advantage in a knife fight due to that 'extra' stability the peg leg provides. On the Spitfire they simply used it as a band aid, since the aircraft's design had small stability margins to start with, and the managed to practically loose it as extra equipment kept creeping into the fuselage by mid war.

 

It just makes a plane with neutral stability characteristics to behave more like a stable aircraft and handle more intuitively. Also, there is not much point to it if your aircraft is stable in the first place, as the bob weights had poor reputation with the pilots and some complained that it "destroying the feel" of the aircraft. Still, for most pilots, bar the most experienced ones it was more easy to control a more stable aircraft in pitch since you only had to hold it on the edge, and not literally bringing it back from it.

 

It should be born in mind that neutral stability is not necessarily a bad thing, in a way it improves maneuvering reaction and would be for example useful for aerobatics, but for most applications, including combat flying it was un-preferred because of the less natural control characteristics and back and forth stick movements. Some planes with such characteristics could do wonderful things, trouble is that most of their pilots couldn't.

 

Its neutral or negative stability is quite akin to oversteering in cars. Could be a blessing for racing and rally drivers but a serious inconvenience to the average driver who does not know how to properly keep the tendency in check.

 

This Spitfire can shave its own peg-leg and even with this modification it is remarkably stable :D

 

http://www.featurepics.com/StockImage/20070419/spitfire-pencil-sharpener-stock-picture-289698.jpg

[Friedrich-4B]

Honestly I think my question is too simple for what is a complex and ever changing equation...

 

Basically I am trying to find a reliable figure at around 300mph to help me with a control column I am making.

 

I am thinking that a good starting point ~15lb for the elevator and ~30lb for ailerons would simulate the lack of harmony found in the Spitfire.

 

Obviously the forces change too much depending on a lot of external factors which I will not be feel in a static ground level simpit :lol:

 

P.s.

I am currently waiting for some data to come through on stick forces that a pilot took in a 109 and Spitfire it should be interesting, I will post it here when I have received it.

 

Too right. I have the full NACA 868 report: the summary presented with the graph shown by Kurfurst is as follows (quote from pages 37-38 ) :

 

Rolling performance. - Data have been collected on the rolling performance characteristics of a number of fighter airplanes of American and foreign manufacture....Comparisons are made on the basis of the helix angle pb/2V and the rolling velocities obtainable at 10,000 feet altitude with a 50 lb stick force (figs. 46 and 47). An accurate rating of the balanced ailerons is not possible from the data presented. The only conclusion to be drawn perhaps is that good performance can be obtained from ailerons having any of the various balances, providing sufficient care is exercised in the design and development. The wide variations in the performance of planes having Frise ailerons may be an indication of the well known fact that Frise ailerons are extremely sensitive to each of a large number of design parameters.

 

The report:

[ame]http://naca.central.cranfield.ac.uk/reports/1947/naca-report-868.pdf[/ame]

Edited May 26, 2016 by Friedrich-4/B
add paragraph heading to quote

[Krupi]

Actually both are Mark Vs with metal ailerons. The first one was tested by RAE, and the figures they obtained were included by the NACA summary report - you can see the the max. aileron deflection was obtainable with 50 lbs up to 200 mph, ie. the straight part of the roll curve. Same thing with the second graph (Mark V w. metal ailerons tested in the US), only that it only shows with 30 degree stick force.

 

Now as for the fabric ailerons, the stick forces per se do not seem to have changed much (no particular reason to think so unless gearing or aileron shape was considerably changed). The trouble with the fabric ones was that no matter how hard you deflected them, they lost their effectiveness at high speed. Since the metal ailerons did not balloon, their effectiveness (roll rate obtained for given deflection) did not diminish so rapidly with speed. Of course subjectively this would seem to the pilot that the ailerons were lighter, considering the same force now yielded greater effect in rolling.

 

Thus the main limiting factor with later metal ailerons on the Spit were (i) high aileron forces limiting deflection (ii) wing twisting under the load induced by aileron deflection countering the aileron effect (so much so that some 65% of the roll was lost at 400 mph), since the whole wing started to twist and act like a huge aileron. Hence why the theoretical aileron reversal speed (at which point the twist would be so severe that the twist would roll the plane to the opposite direction) was rather low, 510 or 580 mph IAS. This required a complete redesign of the wing with the Mark 21 series.

 

I have read quotes from Geoffrey Quill that states that the ailerons forces decreased with introduction of the metal ailerons, unfortunately I do not own the book and don't trust "quotes" from people on the Internet so I am going to purchase it.

 

Wing twisting I know of however that is not in the speed range I am enquiring about, most aircraft in WW2 had severely reduced aileron control at speeds over 400.

 

So yes we agree that the metal ailerons reduced stick forces :thumbup:

[Krupi]

Here is the piece which makes me question the NACA information

 

https://books.google.co.uk/books?id=Yf17NyVsJcIC&pg=PT144&lpg=PT144&dq=spitfire+aileron+lb+force&source=bl&ots=uuQUXfkv_j&sig=Edqct8_NiKkoPs_l2NZTUQHNGXI&hl=en&sa=X&ved=0ahUKEwiulebA3-TMAhVHNhoKHQYDDDoQ6AEIHDAA#v=onepage&q=9%20lb%20force&f=false

 

I am not sure how good this book is, however the metal ailerons are said to have reduced forces at 350 mph compared, only 9 lb compared to 43 lb of the fabric ones... Of course we don't know at what rate the roll was as it is not mentioned making comparison to the charts useless

 

I need to get Geoffrey Quills book that will hopefully go into this further.

Edited May 26, 2016 by Krupi

[Krupi]

Here is another NACA chart from the "worn out" Mk V...

 

 

1.2 rads is about 68 degrees a second.

Edited May 26, 2016 by Krupi

[Friedrich-4B]

Just for interest, I'm attaching a report on the effectiveness of the Spitfire's fabric covered ailerons

[Krupi]

Thanks Friedrich I was looking for that.

 

Page 3 is very telling, the mention again of metal ailerons reducing the stick forces required at high speeds.

Edited May 26, 2016 by Krupi

[Kurfürst]

Here is another NACA chart from the "worn out" Mk V...

 

 

1.2 rads is about 68 degrees a second.

 

Thank you for posting it, it shows very clearly how quickly the high the stick forces become on the Spitfire with metal ailerons, here there is already 60 lbs stick force when rolling to the left at 145 mph IAS, and the same force at 160 mph IAS when rolling to the right. Finding matching pair of ailerons on the Spitfire tended to be somewhat of a random affair through the war.

 

In any case, as far as control harmony goes it was a rather odd combination since applying the same force in pitch would likely overload the air frame. Some Spitfire pilots described this as handling the stick with a delicate fingertip in pitch, while arm wrestling the ailerons. I hope FBB controls will give some of that feeling back to our virtual pilots.

 

This might also help.

 

Edited May 26, 2016 by Kurfürst

[Ala13_ManOWar]

Thank you for posting it, it shows very clearly how quickly the high the stick forces become on the Spitfire with metal ailerons, here there is already 60 lbs stick force when rolling to the left at 145 mph IAS, and the same force at 160 mph IAS when rolling to the right. Finding matching pair of ailerons on the Spitfire tended to be somewhat of a random affair through the war.

 

In any case, as far as control harmony goes it was a rather odd combination since applying the same force in pitch would likely overload the air frame. Some Spitfire pilots described this as handling the stick with a delicate fingertip in pitch, while arm wrestling the ailerons. I hope FBB controls will give some of that feeling back to our virtual pilots.

Quite interesting feature to see in the Spitfire module, thanks!! :thumbup: But I can see people coming mad here saying, why is rolling left or right so different? :D

 

S!

[MiloMorai]

As manufacturing defects are not modeled, the ailerons will be matched.

[Ala13_ManOWar]

As manufacturing defects are not modeled, the ailerons will be matched.

If I understand correctly it isn't a defect but a feature, quirk, whatever you want to name it.

 

S!

[MiloMorai]

In the perfect world the DCS modules fly in, the ailerons would be matched.