[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[ferram4]

@DaMichel: A known issue where the drag of very short adapters is much higher than it should be. I've had a lot of trouble coming up with ways to fix it though. The docking port error is due to the fact that the origin of the docking port is just slightly inside the bounds of what the cargo bay checks for parts to cancel drag on; it should only affect small parts in that exact situation though, and the alternative is that things that are on the ends of the cargo bay that should be shielded aren't.

@rhoark: You'll find more information Googling either longitudinal or lateral stability and looking from there. There is a relatively new Scott Manley video posted in the OP that covers a lot of stuff. There's also the help windows, added specifically for this purpose.

[MAKC]

Say I wanna use a foreplane canard, how would I go about making it stall earlier than the main wing?

[Shad0wCatcher]

@MAKC best thing I can think of is find the stall angle of the plane and increase the Canard's AoA limits above it while leaving the rear control surfaces untouched. Otherwise I'd say find the point where drag intersects/overcomes lift and do the same.

[ferram4]

You've got two options:

1. Pitch it up at a slightly higher angle of attack (~5-10 degrees) than the main wing. That offset in AoA will help make the canard stall sooner, but it won't help too much if you get the main wing to stall and will be detrimental if you get it to stall during a pitch-down maneuver. This is your only option if you're working with stock canards or B9 canards.
   
2. The better option is to use pWings to make a canard with a much higher aspect ratio and less sweep than the main wing; this will make it stall at a lower angle of attack overall, but it will have a better lift slope to compensate. This method will help even if the main wing stalls and doesn't care about pitching up or down. This is also the proper way to do this sort of thing.
   

In general, if you have two lifting surfaces on a plane, you want the forward surface to have less sweep / higher aspect ratio than the rearward surface, since it causes the forward surface to stall sooner and push the plane out of the stall.

[MAKC]

@ferram4

I honestly don't see the point in not using pWings in general. They're just plain better. Thanks for the pointers & back to the drawing board for me.

[werk62]

I really miss the old axis assignment. I am trying to make a (somewhat) accurate F4 Phantom, but with the new axis controls I can't get the speed brakes right. You see, the F4's speed brakes are on the bottom of the wing, but without the negative deflection option, they always deploy upward. Any way to fix this?

[werk62]

To clarify, I am using the procedural wings control surfaces. I do not use the B9 air brakes because they are way too effective. They will stop a craft dead in the air from 300m/s.

[ferram4]

I'll add the negative deflection amounts back, but it'll require some testing to make sure that it clamps to certain values properly.

[DaMichel]

@DaMichel: A known issue ... snip

Okay, thanks for the info. It is easy enough to avoid once one knows about it.

[werk62]

@ferram4 Thank you so much!

[ada221]

im really liking how this mod makes me build really cool/realistic rockets (and actually making me think about what im doing)

http://imgur.com/mriGtq1

i also found out that its better to use more of the smaller engines rather than the mainsail or skipper because you can get more thrust per area (note that the above picture demonstrates this fact)

Edited January 22, 2014 by ada221

[MiltiTrace]

Hello Ferram!

My rockets flying not so good:), so i wanted to check fairings, and how they working under FAR:

Alt and speed almost have not changed, but there is a huge difference in drag. This is normal or should I make changes (and what i need to edit) in cfg of fairings?

Edited January 22, 2014 by MiltiTrace

[autosave]

Made this with using FAR and B9 for a the Fastest plane under 1000 m Challnge

[Hyomoto]

I have a question concerning flaps. I understand the basic principle is to increase the distance air travels over an airfoil in order to improve lift at lower speeds. However, in practice, the only thing this has ever done for me is apply a pitch down, they might as well be another set of elevators. Which means, obviously I'm not using them correctly. However, I get the feeling few people are using them at all because there hasn't been significant discussion in this thread on the topic. Either everyone gets it, or no one has admitted to not getting it. So I'm trying to wrap my head around the concept.

But I have a theory. Is it perhaps because my wings have enough lift to begin with, and that adding more is simply causing them to push up against the center of mass (hence the nose down)? If that's the case, is there some measurement I should be using to know how much lift an aircraft should have? I doubt people are just eyeballing this. I've tried reading up on various wikis, talking to flight engineers and going over the help in your mod but when I try to put it into practice they just don't seem to do anything useful. What am I missing?

[ferram4]

@Miltitrace: That's close to correct, but it's mostly due to the size and shape of procedural fairings, which are less blunt than the nosecones, reducing drag quite a bit. If your rockets look anything like that test rig, they're too short and wide and need to be made taller for them to be stable.

@Hyomoto: Odds are that you don't have enough flap surface, combined with the flaps being too far behind the CoM. Most flaps do cause a pitch-down tendency, but the elevators have enough control authority to counteract this. Ideally, you want a plane where the flaps are exactly on the CoM, with the tail making it stable.

A good way to figure out how much lift you need is to go to the Derivatives tab and take down the wing area. Then go to static analysis and take down the maximum Cl that you can achieve without a tail strike (you'll have to use your judgment for that). Multiplying them will give you lift area; multiply that by 0.5 * 1.225 kg/m3^3 * velocity^2 and you'll get the total lift at any velocity on the runway. Then take the plane's mass in tonnes (also in the Derivatives tab) and multiply that by 9.81 m/s^2 * 1000 kg / tonne and you'll have the plane's weight in N. Lift has to equal weight for liftoff; you can solve this out to get you:

velocity = Sqrt(mass_in_kg * 9.81 m/s^2 / (0.5 * 1.225 kg/m^3 * Cl * Area))

And it'll tell you the velocity you can take off at.

[Hyomoto]

Well, that's definitely the thorough answer I'd hoped for. Now let's see if I can do something useful with it!

EDIT: Hmm, when plugging the numbers, and this may have just been a snaff on my part, but I get nearly the same value as u0 under the derivatives tab. Is that correct?

EDIT 2: Well, putting it into practice seems to have worked though I'll need to work on my landings. My controlled crash became a crash. But your instructions worked and made sense, thank you.

Edited January 23, 2014 by Hyomoto

[Surefoot]

@ferram: you say ideally flaps should be around the COM, i suppose the same goes for control surfaces, including leading edge flaps ? That would enable delta wing / elevon designs where the trailing edge is quite far behind...

[ferram4]

@Hyomoto: U0 is supposed to be horizontal velocity in steady, level flight so that seems about correct.

@Surefoot: Leading edge flaps should also be as close to the CoM as possible, but they won't affect the pitch moment as much, so they're less important. Control surfaces should be as far from the CoM as possible so they have as much leverage as possible. Generally, delta wings and flaps don't seem to get along too well, though I haven't checked real life planes to see if that's perfectly correct.

[camlost]

One example of trailing-edge flap on delta wings

[Surefoot]

i was more specifically thinking of tail-less designs such as SR-71, Concorde, XB-70, Space Shuttle... How do they avoid the very violent pitch-down tendency i noticed when recreating said designs, and mach tuck effects ? I was thinking about leading edge control surfaces, and maybe some flaps... when i have more time i'll check out the designs for Concorde. For example the aborted Boeing supersonic had a very visible wing camber, which is very hard to reproduce in KSP due to too large angular increments when positioning wing elements.

[palker]

Well all that real planes have been thoroughly designed and tested in aerodynamic tunnels before ever taking flight. So if they found out that excessive pitch down moment is present they would correct it by any means available. The pitch down moment with extended flaps is unavoidable and it will always be there it size will depend on a aeroplane in question. For example L-29 Delfin trainer aircraft has mechanism that automatically changes tail plane incidence if flaps are extended because of the pitch down moment and many other aircraft use similar autotrim functions to prevent sudden changes in aircraft balance during flaps operation.

[a.g.]

You can actually add auto-trim like that in FAR too - or after the negative deflection for flaps is re-enabled, anyway. You just configure your elevators to be simultaneously flaps, with an appropriate small positive or negative deflection.

Of course, this only works if you have separate elevators which can be tweaked like this.

Edited January 23, 2014 by a.g.

[Surefoot]

Well all that real planes have been thoroughly designed and tested in aerodynamic tunnels before ever taking flight. So if they found out that excessive pitch down moment is present they would correct it by any means available.

And that's why i am trying to take inspiration from them, and see what "any means available" is actually, since they did find a solution.

My current problem with tailless designs is two-fold, first is an unrecoverable mach tuck, the other is constant pitch-down even at subsonic, to the point i cannot even fly up sometimes. I have quite some experience with FAR (and have very successful conventional designs, including SSTO's that can go to Laythe and such), it's just i think i am reaching the limitations of KSP modelling tools at the moment - i would need finer rotation increments (so far it's 15°) in order to create a proper cambered wing for instance, which seems to be a common feature of those delta-winged supersonics. Trying to compensate with leading edge control surfaces, the idea suggested by Ferram that they would be situated near COM has to be explored

[softweir]

Concorde didn't have flaps, only elevons - elevator/aileron dual-function control surfaces. In order to deal with Mach tuck, fuel was pumped from forward tanks to rearward tanks.

Trim by transferring fuel would be a neat feature for a KSP mod...

[Hodo]

Concorde didn't have flaps, only elevons - elevator/aileron dual-function control surfaces. In order to deal with Mach tuck, fuel was pumped from forward tanks to rearward tanks.

Trim by transferring fuel would be a neat feature for a KSP mod...

I use TAC Fuel balancer for that affect.