I can't spin a spit and FM concerns (vid)

[Wmaker]

In the vid, I have a nice tail slide even if the nose doesn't drop fast enough I think. Then I have that ' nose high wobbeling around' example, and finally I cannot make a dam Spitfire spin. I'm pretty sure they did when stalled while full rudder is applied.

https://www.youtube.com/watch?v=uSzvthRnx8o

What you guys think?

I've been wondering the same thing for quite a while. My personal hypothesis of it is that there might be excessive gyroscopic precession of the prop working together with the aerodynamic forces at play during a tail slide that cause this somewhat weird behavior. I doubt there's anything wrong with gyroscopic precession code itself but I'm suspecting that the parameters fed into the model might be the cause. For example, a case where the prop mass is too great or the angular velocity of the prop is too high (say, the crankshaft rpm instead the rpm of the prop end of the reduction gear) would cause greater precession force than what would occur in real life.

I want to emphasize that this is just a hypothesis and it would be pretty hard for me to explicitly prove it. One way to test the theory is to try tail slides with the I-16 which seems to have the worst symptoms of this. As the I-16 starts fall backwards at the top of the tail slide, without any control input, it takes a long while for the I-16s nose to drop close to parallel of the velocity vector when the engine is running at idle. With the engine off and prop stationary, the nose swings down quickly and uneventfully.

Before the prop mass of the Brewster was reduced, the plane could fall ~4000-5500ft down more or less tail first from a tail slide maneuver before the nose came down. After the reduction of the prop mass (granted, other changes were made as well) the nose drops down rather uneventfully.

The planes that in my opinion seem to suffer from this problem the most are:

I-16
Spit14
Ta152

[SFRT - Frenchy]

Is the 'can't spin a spit' thing serious, or am I missing some in-joke?

Just put the stick to 4-5 o'clock and apply full right rudder. You're spinning.

I'd love to see your video of it, or catch me in the MA, I'll observe you. By a spin I mean, nose down about 30 degrees doing a couple of rotations like you see at airshows.

Do you "spin" as in it stays spinning when you let the controls go neutral or that you can't get one wing to stall before the other?

Per Boscombe Down testing the Spitfire had to be held in a spin otherwise it would stop on its own.  IIRC the Mk XIV would do about 1080 degrees before ceasing to spin.

Did you look at the video? : I can't get to make it spin when stalling with full rudder deflection. I'll make a video for the P47 to explain (geezbus you guys are killing me).

[Karnak]

At work, can't see videos. 

[FLS]

I've been wondering the same thing for quite a while. My personal hypothesis of it is that there might be excessive gyroscopic precession of the prop working together with the aerodynamic forces at play during a tail slide that cause this somewhat weird behavior. I doubt there's anything wrong with gyroscopic precession code itself but I'm suspecting that the parameters fed into the model might be the cause. For example, a case where the prop mass is too great or the angular velocity of the prop is too high (say, the crankshaft rpm instead the rpm of the prop end of the reduction gear) would cause greater precession force than what would occur in real life.

I want to emphasize that this is just a hypothesis and it would be pretty hard for me to explicitly prove it. One way to test the theory is to try tail slides with the I-16 which seems to have the worst symptoms of this. As the I-16 starts fall backwards at the top of the tail slide, without any control input, it takes a long while for the I-16s nose to drop close to parallel of the velocity vector when the engine is running at idle. With the engine off and prop stationary, the nose swings down quickly and uneventfully.

Before the prop mass of the Brewster was reduced, the plane could fall ~4000-5500ft down more or less tail first from a tail slide maneuver before the nose came down. After the reduction of the prop mass (granted, other changes were made as well) the nose drops down rather uneventfully.

The planes that in my opinion seem to suffer from this problem the most are:

I-16
Spit14
Ta152

Nice observation. I've never tried it with the prop stopped.

[SFRT - Frenchy]

I think Wmaker as a good point, exploring further the engine runing at idle is what's screewing up the deal.

When I shut off the engine of the Spitfire I have a very nice spin either directions. When I leave the engine runing at idle, she does spin to the right but it's very choppy, like she's trying to get out of the rotation even when I keep the rudder full in. On a left spin, it's total nonsense to me. (vid loading up).

Maybe in AH, the idle power of the aircrafts and forces associated with them are far too strong, and they interfere with the aerodynamic laws? I wonder if it's why the nose acts all weird in wingovers and hamerheads.

https://www.youtube.com/watch?v=586lFSpIxsw

[colmbo]

I agree the Spit acts pretty weird when trying to spin it using a "standard" spin entry of aft stick to stall with full rudder in direction of desired spin.  Seems to only want to yaw in one direction regardless of rudder input.  Once "spinning" it hesitates as Frenchy noted, kind of like I've heard some flat spin modes described where rotation varies and the nose pitches up and down.  Occasionally it has gotten stuck settling nose high, otherwise recovery is consistent.

[SFRT - Frenchy]

Watch vid above Colmbo, so far on the planes I tries, the F4UD is the most magnificiant. On a stall/left rudder it will enter a very nice 'roll into the spin'. On a stall/right rudder she will not enter a spin, you can maintain her wings level-ish. That idle prop forces thingy.

The Ensign Eliminator syndrome I couldn't replicate it. I was ridding the stall full left rudder and jammed the throttle forward with no superhuman skill needed to accelerate straight and level.

For the old timers, I think it was Beta 4 maybe when the big FM change came? I liked it before better because you could actually run a stall fighter like a spitfire out of energy in a stallfight. But I disgress 

[Dragon Tamer]

I think I remember something in my P-47 manual about the aircraft stalling tail down. I'll have to take a look tomorrow and see if I can find it.

[Scherf]

Can't spin a Spit? Tried it in the Spit 1?

Once I had it in a spin from hi alt, had time to try everything twice, read the manual, try it again, make coffee, try it again, answer the phone, try it all again and still couldn't stop it.

[SFRT - Frenchy]

Maybe you were in space? 

[hgtonyvi]

I'm not really 100% sure of what frenchy is saying but if its a nose up stall and u are trying to bring the nose back down quickly u have to glimpse at the true air speed and average the plane that u are in when exactly is it going to stall. Before u are about to stall use your engine torque and rudder to catch back the air speed and true air speed at the same time so the aircraft will not struggle to retain back its normal stall speed. From the vids posted I think that's what the problem was. Most of u might not get what I am saying but from my experience and my flying point of views that is what I will assume.

[nrshida]

Can't spin a Spit? Tried it in the Spit 1?

Centre of gravity too far aft bug is my hypothesis for that one.

[Randy1]

On the P47 wing-over, with hard rudder, the timing of the throttle seems to be critical.  Too soon and it mushes out as you noted.  I do use manual trim.  I can't hit it every-time.  If it mushes, you are in deep po-po. I know that.  Might as well be a Christmas ornament, at a BB gun convention.

Maybe some of the P47 specialist can offer some good advice.  What I said is all I've got.

[colmbo]

On the P47 wing-over, with hard rudder, the timing of the throttle seems to be critical.  Too soon and it mushes out as you noted.  I do use manual trim.  I can't hit it every-time.  If it mushes, you are in deep po-po. I know that.  Might as well be a Christmas ornament, at a BB gun convention.

Maybe some of the P47 specialist can offer some good advice.  What I said is all I've got.

A wing-over is not a stall maneuver.  It's simply a steep climb - turn - dive.  Did you mean hammerhead?

[Scherf]

Maybe you were in space? 

Certainly felt like I was falling at a constant rate. If I'd managed to get my speed up to 25,000 mph or so before the stall, I'd have gone comfortably into orbit.