questioning F15 FM in crosswinds (track attached)

[gamerman972]

hi,

As the title says I am questioning either the f15 FM in cross winds or my technique. I doubt it's my technique (I have practiced extensively, probably more then a real pilot :) ).

Cross winds: 5 m/s @ 227 degrees (landing at tablisi luchine using summer clouds and wind weather template)

If I try to land a fully loaded f15 in cross winds if am able to successfully land 1 out 3 times (I crash or break the landing gear the other 2 times :) ).

I have better luck by jettisioning the fuel tanks (no crashes or breaking of landing gear (5 out 5), but the skidding on the runway seems very dangerous and probably not something we would see in real life) - watch the track in F2 (outside mode) facing the front of the plane (looking at the nose and the cockpit).

Cross winds of 5 m/s (11 knots) shouldn't be that bad given 30 knots cross winds should be possible.

Any thoughts about the flight model or advise to improve my landings in cross winds? in know the technique (crabbing and the sliping (rudder to align the nose to the runway + bank in the wind to level the plane)

Thanks

SummerCloudsAndWindTakeoffsAndLandings.trk

[fitness88]

Lots of complaints about it in the F15 forum.

 

http://forums.eagle.ru/showthread.php?t=166382

 

BTW, what is the procedure for reporting these sort of problems?

Edited May 15, 2016 by fitness88

[SinusoidDelta]

Another previous thread here

http://forums.eagle.ru/showthread.php?t=162079

 

My understanding is that any flight model issues should be posted in this sub. That being said I haven't seen responses (aside from GG) from the developers/testers team confirming issues or indications that they will be addressed.

 

I have a feeling correcting these somewhat minor FM issues such as ATT Hold, ALT hold, engine low idle thrust, ARI deactivation on wheel spin up, takeoff trim, and 0 AOA performance are very low on the priority list for the ED team.

 

Edit: @Gamerman972 Thank you for posting your track!

Edited May 15, 2016 by SinusoidDelta

[fitness88]

If the developers/testers team are aware of it that's a start. I just wonder if some of this can be easily fixed through the .lua files.

[SinusoidDelta]

I've tried modifying the landing gear model lua under the suspicion that insufficient spring force was causing the left/right main gear to compress unequally inucing a yawing moment on the nose gear. I don't really understand the variables though and it had no benefit when tested in a crosswind.

[fitness88]

I've tried modifying the landing gear model lua under the suspicion that insufficient spring force was causing the left/right main gear to compress unequally inucing a yawing moment on the nose gear. I don't really understand the variables though and it had no benefit when tested in a crosswind.

 

What about the nose wheel?

I posted this on another thread:

Possibly a tweak in this file may help correct the issue.

 

C:\Program Files\Eagle Dynamics\DCS World\Mods\aircraft\Flaming Cliffs\FM\F15/config.lua

 

Is this where you looked?

[SinusoidDelta]

Yes sir, thats where the constants are stored for the landing gear model. The only equation commented out is for force. I think it's some kind of simplified oleo strut compression equation. Regardless, us end-user's simply don't have enough information about the nuts and bolts of the FM to understand how ground reaction forces are being generated.

[gamerman972]

Well, so after some practice I am able to land fully loaded f15 in 5m/s cross winds in a consistent manner. it's challenging, require focus but it's fun. see the attached track. it gets easier as plane gets lighter. So with that said, I think the flight model seems fine.

 

I do have a question. so when I land i disengage the nose wheel steering and can keep the plane in control for the most part. The challenging part is below 80 knots. after that point the rudders became ineffective at controlling where as nose wheel become the better choice from this point onwards for keeping the plane aligned to the runway. however re-engaging the nose wheel steering is very challenging. That is because say my rudder is control via 50% pedal press. but if i am to engage the nosewheel it needs more like 10%. And suddenlty when i engage the nose wheel steering it swings because the rudder pedal press was at 50%. That is the challenge 1. Second challenge is since the nose wheel is disengage the nose wheel is spinning out of control. So there is luck factor involve when re-engaging the nose wheel steering because the nose wheel may be at 45 degrees which may result in plane going out of control. Therefore, my usual practice is to let the plane slow down below 40 knots before reengaging the nosewheelsteering becase at the point it is more manageable.

Helps me keep the plane aligned. I wonder if my approach is what real pilots take as well. how do they control the plane on runway as it lands in crosswinds?

TakeoffsAndLandings.trk

[fitness88]

gamerman972: With the FM as presently designed I've decided I have best control by leaving the nose wheel engaged from touchdown to rollout to stop. The trick is keeping yourself straight at all times, once under 50kts you can better control the steering.

The real challenge is taking off in multi-player with any crosswind, that is really a problem, but only in multi-player not single-player.

[fitness88]

Yes sir, thats where the constants are stored for the landing gear model. The only equation commented out is for force. I think it's some kind of simplified oleo strut compression equation. Regardless, us end-user's simply don't have enough information about the nuts and bolts of the FM to understand how ground reaction forces are being generated.

 

SinusoidDelta I've changed line 20 to read from: anti_skid_installed = false,

to read: anti_skid_installed = true,

 

Let me know if you found landing more controllable. In single player I did. However in multi-player there is still the same problem with swerving while taking off:mad:

[Dr.Goose]

Interesting that this topic came up.

 

I just practiced some crosswind landings this weekend and I must say that the effects of a crosswind were just slightly higher then I would have expected. I too experienced some skidding but not the excessive (nose wheel) skidding like I saw in gamermans track.

 

A 12knot 90°* crosswind was literally no issue using proper crab technique.** (Keep in mind that formation landings are prohibited above 10knots of crosswind and formation takeoffs at 15knots***)

 

A 22knot 90°* cross was difficult (and well out of comfort) but again (with proper technique) doable.**

 

Though I failed to preform a 32knot 90°* crosswind landing as I constantly tipped over on landing (even tough I used full into wind aileron)**

 

To sum it up.

This performance is not all to unexpected for an Aircraft like the F-15 as it has a fairly narrow track and a large high wind resistance body which makes it susceptible to cross winds.

 

* 90° means a 90°+-5° relative wind to the runway (basically a pure crosswind)

**this data is for a clean configurated F-15 with 5.000-12.000lbs of fuel.

***AIR FORCE INSTRUCTION 11-2F-15 Volume 3; 18 September 2014; F-15--OPERATIONS PROCEDURES; pages 15 and 28 "http://static.e-publishing.af.mil/production/1/af_a3_5/publication/afi11-2f-15v3/afi11-2f-15v3.pdf"

Edited May 17, 2016 by Dr.Goose

[fitness88]

Interesting that this topic came up.

 

I just practiced some crosswind landings this weekend and I must say that the effects of a crosswind were just slightly higher then I would have expected. I too experienced some skidding but not the excessive (nose wheel) skidding like I saw in gamermans track.

 

A 12knot 90°* crosswind was literally no issue using proper crab technique.** (Keep in mind that formation landings are prohibited above 10knots of crosswind and formation takeoffs at 15knots***)

 

A 22knot 90°* cross was difficult (and well out of comfort) but again (with proper technique) doable.**

 

Though I failed to preform a 32knot 90°* crosswind landing as I constantly tipped over on landing (even tough I used full into wind aileron)**

 

To sum it up.

This performance is not all to unexpected for an Aircraft like the F-15 as it has a fairly narrow track and a large high wind resistance body which makes it susceptible to cross winds.

 

* 90° means a 90°+-5° relative wind to the runway (basically a pure crosswind)

**this data is for a clean configurated F-15 with 5.000-12.000lbs of fuel.

***AIR FORCE INSTRUCTION 11-2F-15 Volume 3; 18 September 2014; F-15--OPERATIONS PROCEDURES; pages 15 and 28 "http://static.e-publishing.af.mil/production/1/af_a3_5/publication/afi11-2f-15v3/afi11-2f-15v3.pdf"

 

The issue is mainly crosswind takeoffs in multi-player...same 5kt takeoff in single player has no exaggerated skidding/swerving issue.

[gamerman972]

Good feedback

 

Interesting that this topic came up.

 

I just practiced some crosswind landings this weekend and I must say that the effects of a crosswind were just slightly higher then I would have expected. I too experienced some skidding but not the excessive (nose wheel) skidding like I saw in gamermans track.

 

A 12knot 90°* crosswind was literally no issue using proper crab technique.** (Keep in mind that formation landings are prohibited above 10knots of crosswind and formation takeoffs at 15knots***)

 

A 22knot 90°* cross was difficult (and well out of comfort) but again (with proper technique) doable.**

 

Though I failed to preform a 32knot 90°* crosswind landing as I constantly tipped over on landing (even tough I used full into wind aileron)**

 

To sum it up.

This performance is not all to unexpected for an Aircraft like the F-15 as it has a fairly narrow track and a large high wind resistance body which makes it susceptible to cross winds.

 

* 90° means a 90°+-5° relative wind to the runway (basically a pure crosswind)

**this data is for a clean configurated F-15 with 5.000-12.000lbs of fuel.

***AIR FORCE INSTRUCTION 11-2F-15 Volume 3; 18 September 2014; F-15--OPERATIONS PROCEDURES; pages 15 and 28 "http://static.e-publishing.af.mil/production/1/af_a3_5/publication/afi11-2f-15v3/afi11-2f-15v3.pdf"

 

Thanks Dr. Goose,

i think we both agree that flight model is behaving as it should. I think the reason mine is skidding more then yours was probably because i was landing at higher speeds because of a fully loaded (3 fuel thanks + all those missiles) f15. I am sure i will get the similar results as yours if I go with an empty F15. I think i have the crabing technique mastered. It's the slipping technique at the very end that is trickly. slipping technique of using the rudder to alight the nose to the runway and using stick to keep the plane level. seems like a split second thing one has to do near the about a feet or two off the ground. am i right? what is the best approach?

Thanks

[SinusoidDelta]

According to the -1 you should maintain the crab until touchdown. My concern is almost entirely in regards to taxi and take off though. Is there a difference in weather effects from SP to MP? Such as dynamic weather?

[ShuRugal]

I do have a question. so when I land i disengage the nose wheel steering and can keep the plane in control for the most part. The challenging part is below 80 knots. after that point the rudders became ineffective at controlling where as nose wheel become the better choice from this point onwards for keeping the plane aligned to the runway. however re-engaging the nose wheel steering is very challenging. That is because say my rudder is control via 50% pedal press. but if i am to engage the nosewheel it needs more like 10%. And suddenlty when i engage the nose wheel steering it swings because the rudder pedal press was at 50%. That is the challenge 1.

 

I would recommend that, as your speed slows to where you need to re-engage NWS, you apply a momentary over-steer (IE, if you need 50% left, go 100% left for an instant) and then release rudder entirely, then engage NWS and apply steering as needed.

 

This way, you will "kick" the nose out a little bit, and then it will swing back in the second you are neutral before you turn NWS back on. If you time it correctly, you should be able to transition from rudder to NWS with very minor visible effects.

 

Alternately, you could steer with toebrakes as rudders become ineffective, and leave NWS off.

 

Second challenge is since the nose wheel is disengage the nose wheel is spinning out of control. So there is luck factor involve when re-engaging the nose wheel steering because the nose wheel may be at 45 degrees which may result in plane going out of control.

 

This sounds like a bug. If NWS is disengaged, the wheel casters to stay aligned with your direction of travel. Only time the nose wheel would ever be at 45 degrees is when making a sharp turn, in which case you should not be changing NWS (on or off) until the turn is complete.

[Nerd1000]

Thanks Dr. Goose,

i think we both agree that flight model is behaving as it should. I think the reason mine is skidding more then yours was probably because i was landing at higher speeds because of a fully loaded (3 fuel thanks + all those missiles) f15. I am sure i will get the similar results as yours if I go with an empty F15. I think i have the crabing technique mastered. It's the slipping technique at the very end that is trickly. slipping technique of using the rudder to alight the nose to the runway and using stick to keep the plane level. seems like a split second thing one has to do near the about a feet or two off the ground. am i right? what is the best approach?

Thanks

Just applying rudder and keeping the wings level will cause you to turn. The way I do it (no idea whether this is correct, especially for the Eagle) involves entering a sideslip on final approach- the plane is rolled towards the direction the wind is coming from, while heading is maintained with rudder. This way the plane flies a bit sideways and when you reach the runway your nose is already lined up. You then start to flare, level the wings while at the same time easing off the rudder and touchdown with minimal sideways speed.

According to the -1 you should maintain the crab until touchdown. My concern is almost entirely in regards to taxi and take off though. Is there a difference in weather effects from SP to MP? Such as dynamic weather?

I'm a little confused that the -1 says maintain the crab until touchdown. While the idea of drifting in my F-15 is compelling, wouldn't that risk blowing out the tires and potentially flip you over?

[esb77]

According to the -1 you should maintain the crab until touchdown. My concern is almost entirely in regards to taxi and take off though. Is there a difference in weather effects from SP to MP? Such as dynamic weather?

 

You can select dynamic or static weather in both SP and MP missions, it's part of the weather options for the mission editor. I make a lot of MP missions so that I can choose between multiple aircraft/vehicles at the start, and in a situation where the MP mission is running on the computer you're playing on, there's no apparent difference between MP and SP weather that I can detect from experience with copy-paste mission creation where I make MP and SP versions of the same mission and run them on my computer.

 

 

The interesting question is what happens if you're a client with high ping to a MP server? Even if weather is handled the same internally between SP and MP, the difference between 0 ping and lots of ping might produce a significant effect, just as it can for aircraft and missile positions.

 

I've never really seen the effect, but I typically look for MP servers with 200 ms or less ping in my connection.

 

What sort of ping do you usually get the Virtual Aerobatics server SinusoidDelta? Is it stable, or does it fluctuate a lot? Does the problem show up for you on severs where you have a stable connection at less than 100-150 ms ping?

Edited May 18, 2016 by esb77