F-86F handling BELOW stall speed

[=Mac=]

The F-86's flight model in low G with low air speed is considerably miscalculated. Climbing snap roll inputs from the joystick hit an invisible limit on pitch when approaching stall speed which prevents the conversion from the snap to a flat spin. Normal flat spin characteristics are not modeled correctly, either. Is it possible the inertial calculations are off at these sensitive speeds?

 

Is the flight model scripted in such environments?

[effte]

What should happen, and according to what source?

 

The aircraft seems more reluctant to spin than what I would have anticipated, based mainly on anecdotal evidence, but I would have to have better source material to call it considerably miscalculated. It appears you have found souch sources? Please share, it would be very interesting to read. Ditto for the flat spin characteristics, which I haven't seen described in detail anywhere, leading me to assume that flat spins weren't easily entered.

 

Rgds,

/Fred

[=Mac=]

I fly on a different computer than this one so I will have to upload the track and Tacview later.

 

I flew into a vertical, induced a snap roll which, as air speed drops, allows for a "climbing" flat spin. In the P-51, (considering the huge torque for the Merlin), such an aerobatic maneuver is easily accomplished. I have also done such a stunt in the A-10C, although it's not as impressively spinning as the prop-job.

 

In doing this maneuver in the Sabre, the inputs are the same but once the nose begins to "pull" into the flat spin (while going up), the Tacview shows the aircraft hitting that "limit" that keeps it in a slow conical spin rather than a flat one. Seeing that limit hit is what caused me to note the miscalculations in my post.

 

Once wind flow loses its influence on a spinning air-frame, inertia begins to take over and completes the motions. In the F-86, this does not occur properly. Basically, the aircraft doing this maneuver are in zero G or close to it.

 

As I have said, the Tacview clearly illustrates the lack of inertia in all axes and I will fly the maneuver in several aircraft and upload it all later, once I am on the sim-machine.

 

I found a YouTube video I did in the summer of 2012 in a P-51 that shows the maneuver. Keep in mind that the P-51 can do this very easily because of the engine torque. However, I also can get the A-10C to do it, albeit a bit slower in the spin because of those two massive vertical stabilizers. Link to follow:

 

 

Another demo of it. (Not my piloting):

 

Edited November 2, 2014 by =Mac=
Added a second video link

[cofcorpse]

While waiting tracks to see, is there some RL videos of such maneuver? Especially with jets. My quick search didn't find anything

[effte]

Ah, now I see what you mean.

 

Absolutely crazy, but interesting.

 

I suspect it will never have been tried intentionally in real life. :D It's pretty dynamic though, so the actual results would probably vary a lot.

 

I'll make sure to watch the videos later.

[=Mac=]

The climbing flat spin is difficult to find in RL. This is because, if you are in an aircraft capable of aerobatics, the Lomcevak is much more impressive so everyone does that, instead. I submit the following YouTube links of Lomcevak maneuvers.

 

A familiar jet doing it

 

 

From the cockpit. Lomcevak starts at 1:52

 

 

 

It should be noted that these are real life stunt flying aircraft and braced heavily for such maneuvers. I have yet to get a good Lomcevak in the DCS P-51. But I believe it can be done. I just need to quit my day job!

[SgtPappy]

I fly on a different computer than this one so I will have to upload the track and Tacview later.

 

I flew into a vertical, induced a snap roll which, as air speed drops, allows for a "climbing" flat spin. In the P-51, (considering the huge torque for the Merlin), such an aerobatic maneuver is easily accomplished. I have also done such a stunt in the A-10C, although it's not as impressively spinning as the prop-job.

 

In doing this maneuver in the Sabre, the inputs are the same but once the nose begins to "pull" into the flat spin (while going up), the Tacview shows the aircraft hitting that "limit" that keeps it in a slow conical spin rather than a flat one. Seeing that limit hit is what caused me to note the miscalculations in my post.

 

Once wind flow loses its influence on a spinning air-frame, inertia begins to take over and completes the motions. In the F-86, this does not occur properly. Basically, the aircraft doing this maneuver are in zero G or close to it.

 

As I have said, the Tacview clearly illustrates the lack of inertia in all axes and I will fly the maneuver in several aircraft and upload it all later, once I am on the sim-machine.

 

I found a YouTube video I did in the summer of 2012 in a P-51 that shows the maneuver. Keep in mind that the P-51 can do this very easily because of the engine torque. However, I also can get the A-10C to do it, albeit a bit slower in the spin because of those two massive vertical stabilizers. Link to follow:

 

 

Another demo of it. (Not my piloting):

 

 

Those look amazing! Well right now the rudder doesn't work at all in the F-15 or Sabre, so perhaps the lack of proper yaw inputs/reactions means you can't do the maneuver.

 

Yaw might be a little screwy for now altogether. It's a WIP anyway for now.

[SUBS17]

I fly on a different computer than this one so I will have to upload the track and Tacview later.

 

I flew into a vertical, induced a snap roll which, as air speed drops, allows for a "climbing" flat spin. In the P-51, (considering the huge torque for the Merlin), such an aerobatic maneuver is easily accomplished. I have also done such a stunt in the A-10C, although it's not as impressively spinning as the prop-job.

 

In doing this maneuver in the Sabre, the inputs are the same but once the nose begins to "pull" into the flat spin (while going up), the Tacview shows the aircraft hitting that "limit" that keeps it in a slow conical spin rather than a flat one. Seeing that limit hit is what caused me to note the miscalculations in my post.

 

Once wind flow loses its influence on a spinning air-frame, inertia begins to take over and completes the motions. In the F-86, this does not occur properly. Basically, the aircraft doing this maneuver are in zero G or close to it.

 

As I have said, the Tacview clearly illustrates the lack of inertia in all axes and I will fly the maneuver in several aircraft and upload it all later, once I am on the sim-machine.

 

I found a YouTube video I did in the summer of 2012 in a P-51 that shows the maneuver. Keep in mind that the P-51 can do this very easily because of the engine torque. However, I also can get the A-10C to do it, albeit a bit slower in the spin because of those two massive vertical stabilizers. Link to follow:

 

 

Another demo of it. (Not my piloting):

 

 

Problem with that in an aircraft like the F-86 is the possibility of a flame out/compressor stall, I wonder what limitations the F-86 has in that regard or AoA?

[=Mac=]

Climbing Flat Spins in DCS aircraft

 

I flew the P-51, A-10C, F-15, Fw-190, and the F-86 this afternoon, made tracks, Tacviews, and short compressed videos then packed it all in a zip file. Link at MediaFire:

 

http://www.mediafire.com/download/1d692rbbatdz6vp/Climbing_Flat_Spins.zip

 

click the green download (147.56 MB).

 

I believe the error in not flying the flat spin in the F-86 just might be the pilot.

[aaron886]

Why would you assume every aircraft should be able to do that? :huh:

[=Mac=]

I wanted to see if they could. If they can't, why not? I cut my teeth on watching Bob Hoover create masterpieces in the air with his Yellow Mustang and gorgeous Aero Commander Shrike. Have you seen his Tea ceremony in his Shrike?

[cofcorpse]

I wanted to see if they could. If they can't, why not?

 

You assumed that: "The F-86's flight model in low G with low air speed is considerably miscalculated" because Sabre can't do climbing snap roll. Do I understand correct? Or are there another problems?

[=Mac=]

Hi cofcorpse,

 

No, it wasn't because the Sabre can't do a climbing snap roll, but because of the limit that I thought I saw going from the snap roll to a flat spin. In the track that I had (at the time), it was obvious that aircraft "wanted" to flatten out the spin but was limited. Unfortunately, the track and Tacview got deleted by my own fault. So, I flew the same maneuver in all the above listed DCS aircraft only to find the F-86 did NOT exhibit that limit I had seen. For now, the Sabre simply does not go into the flat spin and I attribute that to either my own piloting shortcomings or the designed attributes of the aircraft which cannot generate sufficient physics.

 

In short, I cannot duplicate what I saw the other night. Or... what I thought I saw.

 

The flights I submitted here in my zip file exhibit all the correct motion as would be expected of real aircraft.

 

I will continue to fly the Sabre, later, and if I can create the "limit" I thought I saw, I hope to post the track of it. Otherwise, please accept my apology for my making the initial, apparently unfounded, complaint.

 

Mac

[effte]

Why would you assume every aircraft should be able to do that? :huh:

 

That was my first thought as well, but =Mac= has a point. It is basic physics. The mass distribution of aircraft makes almost all aircraft strive for a flat spin, with aerodynamic forces acting against this tendency to create the various more common spin modes.

 

At the apex of a vertical climb, the air speed is zero so the only aerodynamic force is that from angular velocity, which should be pretty marginal. Hence, the spin should indeed tend to flatten.

 

As I wrote earlier, it is highly dynamic so the tendency may well be hidden among a plethora of other influences... but it is a very interesting application of flight dynamics in the DCS environment. :)

[aaron886]

I would have to see it, because descriptions in this thread are a bit bare, but I would assume tailplane stall might be what you're seeing. Regardless, this is a flight simulator, and they cannot model an airplane to do every conceivable weird thing you want to do with it that has never been tested in real life. The purpose was to create an F-86 that flies like an F-86, and I think that has been done admirably.

[cofcorpse]

Hi cofcorpse,

Mac

 

Thank you for explanation. Now I understand. If you find something wrong in your opinion, track, description and some data about correct behavior would be much appreciated! :thumbup:

[effte]

I would have to see it, because descriptions in this thread are a bit bare, but I would assume tailplane stall might be what you're seeing. Regardless, this is a flight simulator, and they cannot model an airplane to do every conceivable weird thing you want to do with it that has never been tested in real life.

 

Yes, and no. Yes, as it is most definitely outside of the flight envelope that I we can reasonably expect the simulation to cover. But also no, as the beauty of this is that it effectively removes the aerodynamic loads and reduces the problem to one of basic rigid body mechanics - which should most definitely be in place, and also appears to be there.

 

As far as I know, you only have the basic moments of inertia in the model though. This means that for any asymmetrical loadout where you also have products of inertia, the results will not mimic what they would be in real life. It's not something which would be obvious though - quite the opposite, I'd say!

 

The purpose was to create an F-86 that flies like an F-86, and I think that has been done admirably.

 

Very much agreed, and those who know me in these forums probably agree that I'm not among those who are easy to please or slow on the trigger. :badmood: :D

[=Mac=]

For the record, for pure flying enjoyment, the P-51 and the F-86 are my absolute favorites. Oh, and the Huey just has to be the closest thing to helicopter simulator heaven. Please don't take my commentaries as me being displeased with BST. I cannot emphasize enough how much Belsimtek and Eagle Dynamics mean to me. The work you guys are doing is not only extremely important to me, but to the rest of the aviation world, as well.

 

Please, please, please keep up the great works you are doing!

[drack]

An interesting point intelligently made MAC.

 

Interesting thread.

 

The FM does seem a bit dull in the spin.

 

It is still in Beta so we wait and see.........