Need some expert help with airfile editing

[mrogers]

I've been making new airfiles with Airwrench for a couple of fs2004 planes. Both are taildraggers, and I'd like the tails on these planes to rise early and quickly when throttling up in takeoff mode. Sometimes I do have to make individual adjustments in the airfile itself where fine tuning is needed after using Airwrench. Where can I adjust in the airfile to cause the tails to rise up early? Could someone knowledgable in advanced airfile editing enlighten me please? Been trying to work that out myself for ages with no luck, so it's got to the point where I've run out of ideas.

[Tom Clayton]

I don't remember ever seeing anything about horizontal stab lift in any of the air file entries, only elevator effectiveness in the cfg. The only thing I can think of would be to make sure the CG isn't too far aft.

There's also a "htail_area" entry in the [airplane_geometry] section. Seems to me that gently increasing that would help with raising the tail earlier.

[mrogers]

Thanks Tom I'll try that. What I'd like to do is to have the tail rise by itself at a specific airspeed with full throttle with minimal elevator use if possible.

[Milton Shupe]

Hi Mark,

No expert here; assuming that your wing area, htail/elevators square footage are correct, root chord, and CoG are correct (25% MAC), you can inch rearward the CoLift a bit (in table 1534) to see how that helps. (I do mean inches - maybe 1-2) Don't overdo it. It is stated in feet so a -0.1 to -0.2 shoud be more than enough. After each change test your rollout.

Although it should lift the tail sooner, it will also not want to lift off by itself if you get too far back. You have to find the balance of tail up and rotate / lift.

You should be using a test panel from Mudpond.org or AFSD to test the effects.

[SOLOBO]

I've been making new airfiles with Airwrench for a couple of fs2004 planes. Both are taildraggers, and I'd like the tails on these planes to rise early and quickly when throttling up in takeoff mode. Sometimes I do have to make individual adjustments in the airfile itself where fine tuning is needed after using Airwrench. Where can I adjust in the airfile to cause the tails to rise up early? Could someone knowledgable in advanced airfile editing enlighten me please? Been trying to work that out myself for ages with no luck, so it's got to the point where I've run out of ideas.

Hi Mark, what planes ?

... I'm not an expert, I begin to know and explore flight dynamics, and I already worked on this sort of problem...

[fliger747]

An interesting quest. Part of the problem you are having here stems from the way FS calculates pitch moments for the aircraft, it does not really treat the horizontal stab and elevator as separate entities responding to the slipstream in a different way than the wing. The tail will usually come up at some fairly high percentage of the takeoff speed, as it,s effect is really tied to the lift of the wing. Back many versions ago (some cfs?) here was an entry but it seems to no be effective now. It does help to have the CG and main wheel contacts close together, but this makes it easy to nose over! The FR Supercub uses a gauge to do this in FSX Accel, I once did an invisible lightly sprung extra tailwheel FO an Alpha of Miltons P47J, which sort of worked.

Without legerdemain you are unlikely to achieve say a spitfire that requires ground crew to sit on the horizon stab during a runup to keep the tail from rising.

Good luck! T

[SOLOBO]

In this case, some adjustments are possible. Are they 100% realistic ? I don't know exactly...

[Milton Shupe]

Tom makes an excellent point above that I forgot to mention. Main gear needs to be set fairly close to the CoG.
You can experiment with +4-8" forward of CoG depending on the aircraft, maybe more. Tipping from brakes may be an issue.

[mrogers]

Hi Mark, what planes ?

... I'm not an expert, I begin to know and explore flight dynamics, and I already worked on this sort of problem...

The one I'm doing at the moment is the Stinson 108-3 Voyager by Brian Gladden. The original airfile wasn't good and didn't do this nice model justice, so I thought I would make a new airfile from scratch, using Stinson specifications, references, stall speeds, other speeds, reading about its flight handling etc.

[mrogers]

Tom makes an excellent point above that I forgot to mention. Main gear needs to be set fairly close to the CoG.
You can experiment with +4-8" forward of CoG depending on the aircraft, maybe more. Tipping from brakes may be an issue.

Thanks, Milton for the tips. I adjusted the CoG foward slightly, just on parallel with just behind the main wheels. Made sure I didn't go too far forward of course. It seems to have made a difference. The tail is up at 50mph instead of 60 and lifts off at 78-80 mph in 950ft of roll which is about right for the published specs.

[mrogers]

I don't remember ever seeing anything about horizontal stab lift in any of the air file entries, only elevator effectiveness in the cfg. The only thing I can think of would be to make sure the CG isn't too far aft.

There's also a "htail_area" entry in the [airplane_geometry] section. Seems to me that gently increasing that would help with raising the tail earlier.

Thanks Tom, I increased the Htail area but didn't seem to make any difference. Reverted back to original specs as no change was apparent. I think the CoG approach was apparently the best way to go.

[mrogers]

In this case, some adjustments are possible. Are they 100% realistic ? I don't know exactly...

It could be possible....

[mrogers]

An interesting quest. Part of the problem you are having here stems from the way FS calculates pitch moments for the aircraft, it does not really treat the horizontal stab and elevator as separate entities responding to the slipstream in a different way than the wing. The tail will usually come up at some fairly high percentage of the takeoff speed, as it,s effect is really tied to the lift of the wing. Back many versions ago (some cfs?) here was an entry but it seems to no be effective now. It does help to have the CG and main wheel contacts close together, but this makes it easy to nose over! The FR Supercub uses a gauge to do this in FSX Accel, I once did an invisible lightly sprung extra tailwheel FO an Alpha of Miltons P47J, which sort of worked.

Without legerdemain you are unlikely to achieve say a spitfire that requires ground crew to sit on the horizon stab during a runup to keep the tail from rising.

Good luck! T

Thanks fliger747, I've taken note of the CoG and the mainwheels, and made the appropriate changes. The nose will tip over only if you put too much pressure on the brakes at the end of the roll however at that stage it's slowed down so much there's no need to use the brakes that much.
Pardon me, but what is "legerdemain"?

[mrogers]

Still having to push the stick foward some to raise the tail up....that might be normal though. Seen photos and vids of taildraggers with their elevators down a bit on take off roll.

[Tom Clayton]

Glad it worked for you! I'm by no means a flight dynamics expert (obviously), but I do like to tweak when I feel improvements can be made. I had thought about moving the CG forward, but I've also had plenty of landings during my Corsair "phase" where I taxied in with bent prop blades and a cracked gearbox because I tried to get stopped too short!

Milton, is record 1534 an FSX only record? I opened up a few air files from my hangar and I don't see it.

[Milton Shupe]

Glad it worked for you! I'm by no means a flight dynamics expert (obviously), but I do like to tweak when I feel improvements can be made. I had thought about moving the CG forward, but I've also had plenty of landings during my Corsair "phase" where I taxied in with bent prop blades and a cracked gearbox because I tried to get stopped too short!

Milton, is record 1534 an FSX only record? I opened up a few air files from my hangar and I don't see it.


No, the 1530 series records have been around at least since FS9 came out.

Look in most any of my air files, most recently, the Avia 51. I used it to get the perfect tail lift and lift off for those aircraft. It is a finely tuned adjustment that must be used wisely because of other implications. You could also try adjusting the cruise lift scalar in the tuning section. 1534 should only be used after all the other factors are verified as correct. And if you really want to get technical I suppose you could play with 404 but that is too technical for me to work with.

EDIT: Forgot to mention you can copy 1534 or any section from any air file to yours with the Copy to Clipboard, and Add/Replace from Clipboard functions.

[napamule]

Tom,
Section 1534 is in AirEd v1.42 but (maybe) missing or 'scrambled' in AirEd v1.52. Here is how it 'reads':

(1534) //FS2000 Wing Center of Lift, record:
1=00,double,*CoL. Lateral Offset from MAC
2=08,double,*CoL Vertical Offset from MAC
3=10,double,*CoL. Longitudinal Offset from MAC
------------------------------------------------
1h=0.00 in Concorde
2h=0.00 in Concorde
3h=Center of Lift relative to MAC ( -63.00 in Concorde)

Chuck B
Napamule

[SOLOBO]

Still having to push the stick foward some to raise the tail up....that might be normal though. Seen photos and vids of taildraggers with their elevators down a bit on take off roll.

I installed the Stinson 108-3 Voyager by Brian Gladden and flew with it. It looks well, but yes, we have to push a little bit the stick forward... I think that is normal.

[Dev One]

You might also try setting the engine vertical position a bit higher, but be careful on the brakes with full throttle & especially with a forward C of G!
FS9 also seems to have too much power to the elevator trim - its almost as if its designed only for 'flying tails'. So that setting before take off can have a disproportional effect.
The air file does not seem to have the capability to angle the thrust line (upthrust/downthrust) so one needs to adjust the height relative to the centreline
Cm_dT (Thrust) in 1101 seems to have no effect.
I've just been experimenting with my current a/c in development.....so I have moved my mainwheels aft, added 1534 at -0.5 ft aft & raised the engines by 0.5 ft & now can get the tail to raise at about 38 KIAS, a reduction of 12 to 14 Kts with forward C of G (14%).
HTH
Keith

[Tom Clayton]

Thanks - I guess what I'd need to do is find a plane with that section and copy from there.

Edit: I found a couple of more advanced releases in my hangar that have 1534 installed - the mega-model Stearman and the B170 from the guys across the pond both have it.

[Milton Shupe]

Thanks - I guess what I'd need to do is find a plane with that section and copy from there.

Edit: I found a couple of more advanced releases in my hangar that have 1534 installed - the mega-model Stearman and the B170 from the guys across the pond both have it.


So, you do not have any of my taildraggers? :-)

I think the Howard 500 is th eonly one without 1534.

[Tom Clayton]

Have a bunch on the other 'puter, but with its "issues," I haven't fired it up in a while. I have FS9 installed on this laptop, but it doesn't run too well. I'm trying to decide if and how I can get back into the air on a regular basis, but for now I can at least use my current settup for digging up info and such. We just got our tax money back, but thanks to a hit and run about a year ago, I need to spend about $500 on a new front wheel for the bike. :isadizzy:

[mrogers]

Still experimenting with the CoG!
Trying to keep it within or close to MAC of 25%. Would that be the correct thing to do?

The 1534 is related to the CoL numbers it seems as I note after edjusting the CoL the same number appears in it.

[Dev One]

Don't forget that the C of G in the .cfg file is the EMPTY C of G position, so if you have any load forward or aft of 25% that will have a modifying effect & affect it in flight also - amount of elevator trim required etc.
Keith

[mrogers]

Thank you to all who helped with their tips and advice here, it's very much appreciated.
I think I've gone as far as I could go with the airfile for this plane, trying all the different ideas.. I think the best approach was moving the CoG foward a bit, closer to the mainwheels, but not too far forward. Fine tuning a bit more followed after that It's still requiring a bit of stick foward to lift the tail up, (would be normal practice for most taildraggers I guess) tail is up at 45-50mph and lift off at 70-75mph. A bit of trim up is needed. If you take power off too much too quickly while on approach the nose will drop down at 60mph so its important to have some power on above 60mph down to touchdown. Too much brake and the tail will rise! In all it's performing like how it would according to what I've read about the Stinson.
It's still a work in progress of course, but I feel satisfied with it so far and have really enjoyed hopping along the runway testing it.

Edit: Milton, I took the Avia 156 up for a spin recently, it's a beauty! Thanks Milton!