Spitfire - Elevator and rudder at low speed

[Blackhawk_FR]

The Spitfire got a pretty strange behavior at low speed. 

Elevator loose all its effeciency while rudder stay as much effective/reactive as it is at normal/high speed. 

 

Somes may tell me "did you flew a Spitfire to know what you are talking about". Of course not, unfortunatly, but it's more about comparing the Spitfire's behavior with others aircrafts from the same simulator. From my experience it's the only one that suffer from this FM characteristic. 

 

 

Edited April 1, 2019 by F/JG300_Faucon

[Blackhawk_FR]

Am I the only one having that strange and unusual behavior? 

[Pict]

10 minutes ago, F/JG300_Faucon said:

Am I the only one having that strange and unusual behavior? 

 

It would help if you were more specific about what you are experiencing, as in;

 

Which Spitfire, Mk.Vb, Mk.IXe or both?

What speeds?

What altitudes?

Temperature?

 

Load outs (inc fuel) & trim settings?

 

and other stuff, like what hardware (joystick), and how you have it set up?

 

That way someone with a similar setup might be able to test and see if they are having a similar experience.

 

 

Edited April 2, 2019 by Pict

[Blackhawk_FR]

It's more noticable with Spit 9 (5 looks "normal"). 

 

You can try like this: 

 

- Start a looping with 270kmh (170mph), at low altitude, normal trim.

- Pull normally, quite close to the stall AoA.

- When you're getting close the top of the loop (~150kmh or 90mph), notice that you can't stall wings even with full back stick pressure.

- In the same time, "play" with rudder (left-right-left-right inputs) to notice it's as much reactive as it is at high speed, and that the aircraft stay also very stable on its yaw axis. In other words, at very low speed, rudder react like we were flying at normal/high speed.

- It's getting noticable under 200kmh, whatever the maneuver, whatever the altitude, whatever the loadout.

- Try the same exercice with Spit 5 or any other aircraft just after. You will notice that you can stall wings at the top of your loop (elevator still have some authority), rudder is less reactive, aircraft is less stable on yaw axis 

Edited April 2, 2019 by F/JG300_Faucon

[Guest deleted@50488]

Don't know if it's correct but:

 

.) Spitfire has neutral pitch stability at most power / speed / aoa configurations;

.) Propwash at the top of the loop could give live to your tail surfaces (rudder and elevator), depending on your power settings.

 

Try performing the same maneuver with an iddle or dead engine. Climb to 10k', kill the engine, perform your loop after reaching sufficient entry speed.

 

I'll try it too and report back ASAP when near to my IL2 machine ?

[Blackhawk_FR]

55 minutes ago, jcomm said:

Try performing the same maneuver with an iddle or dead engine.

 

That was interesting to try. 

 

It shows that without power:

- Elevator have a bit more authority ().

- Rudder is less effective, and aircraft less stable on this axis.

[Guest deleted@50488]

Thx for the feedback @Faucon.

 

Still far away from simming PC and time slot ?  Maybe later tonight ...

 

Anyway, strange indeed that you find the elevator has more authority with a "killed" engine ( ??? ).

 

Will report back after testing. My only ( long ) experience from RL is on gliders, and there we do not have propwas helping us at the top of a hammer head ? so the right amount of speed in the climb is the "secret" to getting to nail it ...

Edited April 2, 2019 by jcomm

[JG27*PapaFly]

On 4/2/2019 at 9:40 AM, F/JG300_Faucon said:

It shows that without power:

- Elevator have a bit more authority (). 

- Rudder is less effective, and aircraft less stable on this axis. 

Have a look at the slip indicator. If you allow the plane to slip slightly to the right at the top of the loop, the minute gyroscopic effect modelled for this plane will suffice to generate a force opposing your elevator input (you pull the stick) this can lead to the impression of insufficient elevator authority.

 

Have a look at my vid, you'll see what I mean. It gets even better: if you drop flaps the plane will become a UFO that will only stall if you specifically want to, and will instantly recover with full right rudder, fully pulled stick, and out-of-spin ailerons. This crap even works when missing one flap and one aileron.

 

 

[Haza]

Hopefully these FM issues do get addressed before BoBp is released officially.

 

 

 

[Blackhawk_FR]

On 4/5/2019 at 8:23 PM, JG27_PapaFly said:

Have a look at the slip indicator. If you allow the plane to slip slightly to the right at the top of the loop, the minute gyroscopic effect modelled for this plane will suffice to generate a force opposing your elevator input (you pull the stick) this can lead to the impression of insufficient elevator authority.

 

Wait I'm not sure to see what you mean. If you pull, the gyroscopic effect will push your nose to the right. Not in the opposite direction (and so, NOT inducing a force against your elevator authority). 

Btw, which moment in the video? It's quite long ^^

Edited April 8, 2019 by F/JG300_Faucon

[JG27*PapaFly]

5 hours ago, F/JG300_Faucon said:

If you pull, the gyroscopic effect will push your nose to the right.

The nose moving to the right will induce a gyroscopic force that is odd to your pulled stick. In short, you must counter the nose swing to retain elevator control authority.

 

Throughout the vid you see the effect every time that I apply full power while maintaining full right rudder and full elevator applied. Adding power (prop rpm) in that condition acts as if I released some back pressure on the stick, instantly recovering from a stall

 

[Blackhawk_FR]

2 hours ago, JG27_PapaFly said:

The nose moving to the right will induce a gyroscopic force that is odd to your pulled stick. In short, you must counter the nose swing to retain elevator control authority.

 

Ok, see what you mean. But whatever if you have a slip indicator to the right, or to the left, or centered, the elevator still loose a lot of efficiency. 

[JG27*PapaFly]

1 hour ago, F/JG300_Faucon said:

But whatever if you have a slip indicator to the right, or to the left, or centered, the elevator still loose a lot of efficiency.  

What I have observed so far is that pitch-up authority is reduced while sideslipping in Spits. This is odd because it points to a slip- induced loss of lift being modeled for the tail surface (which is nothing but an inverted wing which generates lift in the opposite direction than the actual wing). This effect is known for planes with T tail configurations, e.g. F-104 and many gliders, but should not really affect planes with classical tail configurations. There, one part of the elevator is being shaded, while the other part gets increased airflow during sideslips.

[Haza]

 

@JG27_PapaFly,

 

Have you managed to carry out further flap tests on any of the other aircraft in the sim?

 

 

[Guest deleted@50488]

https://www.aerosociety.com/media/4953/the-aerodynamics-of-the-spitfire.pdf

 

https://apps.dtic.mil/dtic/tr/fulltext/u2/a801513.pdf  ( see page 7, 2nd paragraph, and onward... )

 

Looks like the model we have in IL-2 Great Battles, even if not "perfect" is still very good IMO...

Edited April 9, 2019 by jcomm

[JG27*PapaFly]

On 4/9/2019 at 12:59 PM, Haza said:

 

@JG27_PapaFly,

 

Have you managed to carry out further flap tests on any of the other aircraft in the sim?

 

 

Hi, I haven't had time for more tests lately.

[Blackhawk_FR]

Another way to show this rudder efficiency problem: When taxiing slowly (~10%, 1200 rpm), it's possible to make turns only with the rudder. 

 

At the end I believe it's just a "WIP effect" and that Spitfire's FM will be improved. 

[ZachariasX]

18 minutes ago, F/JG300_Faucon said:

At the end I believe it's just a "WIP effect" and that Spitfire's FM will be improved. 

Dogfighting on the MP servers will look very different once this general trend is mended throughout the hangar. The Spit doesn't do anything that any other aircraft wouldn't do in BoX, just to different extent. All this goofing around at obscene AoA when stalling with twisting and turning... That will be a thing of the past. People will not be very tempted anymore to use flaps on any aircraft in combat (exept for the combat flaps) as only a good maneuvering speed will keep you alive. Once you're near stall, you lost most of your maneuvering possibilies and you're a sitting duck. But it's already so much better now than in RoF.

[Psyrion]

8 hours ago, F/JG300_Faucon said:

Another way to show this rudder efficiency problem: When taxiing slowly (~10%, 1200 rpm), it's possible to make turns only with the rudder. 

 

At the end I believe it's just a "WIP effect" and that Spitfire's FM will be improved. 

Disregarding the rest of this thread but that does sound perfectly normal to me. Why shouldnt you be able to turn with only rudder at normal taxi speeds?

[Blackhawk_FR]

1 minute ago, Psyrion said:

Disregarding the rest of this thread but that does sound perfectly normal to me. Why shouldnt you be able to turn with only rudder at normal taxi speeds?

 

Because not enough propeller blast to have an efficient rudder.

[Psyrion]

Just now, F/JG300_Faucon said:

 

Because not enough propeller blast to have an efficient rudder.

Got anything to back that up? Not trying to argue, just sounds wierd to me since from what I understand the speed you get at 1200-1300 rpm is pretty normal for taxiing and in taxiing you use rudder for normal turns and brakes only when needed.

[Blackhawk_FR]

- Experience on tailwheel aircrafts

- Asked to a display Yak9 pilot (same brake system)

- All manuals will say you need brakes to turn

An example: https://forum.keypublishing.com/forum/historic-aviation/74484-supermarine-spitfire-take-off-and-landing-guide

 

In fact rudder is just very slightly effective, due to the weak propeller blast on the rudder compare to the weight of the aircraft.