FINE! A creative way to use flaps and spoilers

[DivisionByZero]

So, I've been struggling and struggling with space planes in a certain career-mode save of mine that utilizes Ferram and a number of other mods (think Scott Manley Interstellar Quest mod list). I really haven't bothered with space planes at all in my KSP games but I kept seeing them come up and I can recognize the advantage for reusable vehicles of this type. Anyway, most of my planes would either have trouble taking off, or break up due to aerodynamic forces, or I'd lose control on re-entry. It was not pretty. Did I mention vanguard ejection seats are very important?

Just now, finally, I was able to complete an entire mission and make a perfect landing on KSC and I used flaps and spoilers to boot! Now I will tell you how so you can use these nifty items as well.

So I was struggling and struggling and decided I'd replicate Scott Manley's space plane from episode 28 of the Interstellar quest series. Basically, it's a B9 Mk. 2 pod with a 2m cargo bay and LFO tank as the main fuselage. I needed to put a new satellite into a polar orbit so I replicated the mission objectives as well. You can see an image of the space plane below alongside a shot from the satellite after launch.

Javascript is disabled. View full album

You'll probably notice the fact that I have 3 different control surfaces on each wing: 1 2m control surface and 2 1m control surfaces. The 2m control surface has flaps enabled and the innermost control surface has spoiler enabled. The maximum deflection is graded so that the innermost surfaces can deflect ~10 and the outmost can only deflect about 5-7. Now, here's how the flaps and spoilers work:

Flaps basically increase the size of the wing by extending downward. This increases lift and drag of the wing. You can find a bunch of youtube videos explaining flaps if you want more information. Now, the new lift surfaces result in a net pitching moment downward if your wing is in line with the center of mass (CoM) of the ship. This can sometimes be compensated for with elevator control during flight, but what I had experienced is that only with the first flap setting you can do this. You have to set up an action group to control the flaps and spoilers in flight. I have action groups 1 and 2 as increase and decrease the flap setting respectively. The flaps alone are difficult to control on anything other than the first flap setting.

Then, I realized I didn't know what spoilers did, so I put some on my plane. Actually, originally I had only 2 control surfaces on each wing and set one on flaps and one on spoilers. However, when I looked at the static stability results, anytime I put spoilers on I would be unstable at low angles of attack (AoA). Not good. This led me to set up the spoilers on a smaller control surface (1 1m control surface closest to the fuselage) with flaps on the outermost and largest control surfaces. Now when I looked at the static stability, I could engage the spoiler at low speed as well as the flaps in settings 2&3! There are images in that album I linked.

So, what do spoilers do? They actuate the control surface in the opposite direction than the flaps. This results in tending to pitch the nose up if all you had were the spoilers. That means, they tend to counteract the downward pitching action of the flaps. So, by engaging both a spoiler and the flaps, you can dramatically increase the lift and drag of the wings and avoid the difficult control situation that usually comes in using the flaps alone! Basically, I was able to come into KSP and make a landing at 100m/s, very gentle with my flaps engage at setting 2-3 with the spoilers engaged and my RAPIER engine at 10-20% power. It was a piece of cake and I had NEVER landed anything before!

So, there you have it: some information on how to use flaps and spoilers with your space-planes.

Cheers!

PS: could someone tell me how to make nice embedded imgur albums?

Edited May 17, 2014 by DivisionByZero
fixed link... ok, not the "right" way to use flaps and spoilers...

[NathanKell]

['imgur]uwd5t['/imgur]

Remove the ' and note the letters between the tags are the letters that correspond to your album's link.

Regarding flaps and spoilers themselves, though: your problem is you're using them on a delta wing; flaps (or spoilers) in *that* position are essentially just action-group-controlled elevators.

If you want to use spoilers (whose effect, btw, is to reduce lift; any pitch moment is a side-effect, just like with flaps) on a wing layout like that you need to place them mid-wing. You can't do the same with flaps...

Anyway, your best bet is to stay away from flaps and trailing-edge spoilers on a delta or canard-delta. They're really for traditional-wingplan wings.

[ferram4]

You've got the right idea for the flaps, but you're completely wrong for spoilers.

Spoilers are just supposed to reduce the overall lift of the vehicle while adding more drag; flaps happen to be great for slowing the plane down, but they also tend to produce a little too much lift when you're, you know, trying to put the plane on the ground (or keep it on the ground). So spoilers are placed (near the center of mass of the vehicle) to reduce the lift produced by the wings while still allowing a draggy enough configuration that it slows down.

What you've got going on is a pair of action group controlled elevators, not spoilers. Which is great, but that's not what they're intended for; generally getting lots of pitching tendencies from spoilers is considered a bad thing.

In practice, flaps don't tend to be added to delta wing vehicles, except in rare circumstances, since they're acting as elevators at the same time. The only exception I know of is the Tu-144, which had a pair of canards extend to counteract that at low speeds.

[DivisionByZero]

KAHN!

Well poo. And here I thought I was being clever. Have you guys written these things up somewhere so people can avoid these embarrassing situations down the road?

[DaMichel]

Not to my knowledge. Some of it is scattered in Ferram4s thread and there is an excellent thread about general plane design in the Tutorials section which is mostly for stock planes though.

I'd like to add that you can set your elevators/canards to be flaps, too. And moreover, you can set a negative deflection strength. If you do this right your pitching moment hardly changes when flaps are deployed because the elevators, set up as flaps, move to compensate. It will be like an automatic trim if you like to see it that way.

Btw. The Firespitter mod has a part which lets you save trim settings and recall them with action group buttons. I never really used it, but this might be something to have a look at.

[DivisionByZero]

Thanks for the tip about the firespitter part for trim settings. As I'm trying to fly these space planes I'm finding that setting the trim is very helpful at different stages of the flight so I may check it out.

I think I need to look quite a bit more at all these little tweakables since I didn't realize you could set negative strengths. Your idea on the canard trim sounds like the right answer. Thanks!

[phoenix_ca]

I'd like to add that you can set your elevators/canards to be flaps, too.

D'oh! So if I set the canards at the nose of a delta-wing aircraft as flaps, and some flaps at the back of the wings, the whole thing should stay stable-ish?

[DaMichel]

Yep.

Just tweak the deflection strength of your canards so that the x-intercept of the cm curve (usually @ 0 Deg. AoA ofc.) is the same for retracted and deployed settings.

[aristurtle]

The Colibri is pretty neat, but does anyone have any tips on doing an actual vertical landing with it?

[Alshain]

The Colibri is pretty neat, but does anyone have any tips on doing an actual vertical landing with it?

This is a really old thread and I'm not sure your question has anything to do with it's topic.