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Using flaps and spoilers in FAR


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Hello everyone. After spending some time making SSTOs in stock i have finally graduated to FAR. However, i am having a bit of trouble with the current sp i am working on pictured here:

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After doing some reading i heard that i would be able to use flaps to increase lift (at the cost of increased drag i understand) and get my plane off the runway in <100m/s with a low AOA. As it is now i would need approx 20 degrees to fly level. So... can anyone provide the info (preferably some pics to help) on how i can use flaps and eventually spoilers to improve performance when needed?

edit: in case anyone was wondering, my COM and dry COM are in the exact same position. (thank you RCS build aid)

Edited by cadaverific
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You'll want the rear flaps to deflect down, but that introduces a pitch-down moment to the plane. You can counterbalance that by setting the canards as flaps, too. Adjust them so that the y-intercept of the Cm curve is the same (usually 0) both for flaps at 0 and 3. My Skathi does this.

You'll almost certainly need action groups for the collective flap setup.

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Firstly: have a dig through https://github.com/ferram4/Ferram-Aerospace-Research/wiki/An-Example-SSTO-Design-Process

Reading that while you play around in the SPH should help you make sense of the data provided by FAR.

You don't need to use the aerodynamic analysis tools (my first few dozen designs were done purely by eyeball and flight testing, and they worked just fine), but they do make it easier once you get your head around them. In particular, pay attention to the part of the link above that discusses how to work out what speed and angle of attack you need for liftoff. You want the speed to be within what you can reach before the end of the runway, and the required angle of attack below 10°.

Very short flaps/spoilers tutorial:

Flaps and spoilers are both ways of temporarily enhancing the deflection of control surfaces. Flaps deflect down; they increase both drag and lift. Spoilers deflect up; they increase drag but reduce lift. Flaps ease takeoffs and allow your craft to fly at a slower speed without stalling. Spoilers ease landings by pushing the plane down onto the runway and enhancing braking on the ground. Either can also be used to increase drag during reentry.

Control surfaces can be set to work as flaps or spoilers, but not both. By default, spoiler activation is linked to the "B" key, with the spoilers off unless triggered. By default, flaps are on unless deactivated through action groups or right-click menus. If you're using flaps, it's generally a good idea to set one action group to increase flap deflection and another to reduce flap deflection.

You may find it helpful to have a well set up example craft to reverse engineer. Have a go with http://forum.kerbalspaceprogram.com/threads/90747-Kerbodyne-SSTO-Division-Omnibus-Thread?p=1398173&viewfull=1#post1398173

That one uses both flaps and spoilers, and takes off very easily if flown right, despite its large size and relatively low air-breathing thrust.

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Thank you both for your input. This is what i ended up with for the time being:

Imgur hates me right now

Tao: Looking through your flight instructions was very helpful. Thanks for the link.

Wanderfound: I actually started with the first link, but the way it was worded was a bit confusing at first(which prompted me to post here. i should have mentioned that in the op). Thats where i got the idea and AOA values to look for. I understand a lot of the necessary values in the tools which should help my success rate on new designs greatly.

I'll stick with the smaller design for the time being until i get the hang of it but this plane is my WIP for the Laythe Capitalism Challenge. (the weight and passengers will be increasing hopefully)

Edited by cadaverific
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Thank you both for your input. This is what i ended up with for the time being:

Imgur hates me right now

Tao: Looking through your flight instructions was very helpful. Thanks for the link.

Wanderfound: I actually started with the first link, but the way it was worded was a bit confusing at first(which prompted me to post here. i should have mentioned that in the op). Thats where i got the idea and AOA values to look for. I understand a lot of the necessary values in the tools which should help my success rate on new designs greatly.

I'll stick with the smaller design for the time being until i get the hang of it but this plane is my WIP for the Laythe Capitalism Challenge. (the weight and passengers will be increasing hopefully)

Below 8° AoA and a 100m/s takeoff speed; nicely done. :)

A lot of successful FAR design seems to be a matter of unlearning bad habits induced by the soupmosphere, most of which is about reducing excessive drag (e.g. airhogging, wingstacking, etc). Streamlining is key.

I couldn't make sense of anything in that link either, until I went through it on my tablet while simultaneously experimenting in the SPH on the laptop. It could certainly use a bit more in the way of worked examples.

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Thanks thanks.

Its amazing how different FAR is for planes(i've only used it for rockets untill now). I'm not used to how few wings are needed to be effective, not to mention no need to arihog.

Actually while ive got you here here a quick question. Ive been flipping through a few of your ships and i was curious: how big do you think you could go for an interstellar ship? i'm just interested in a ballpark that would be effective. Id love to hit up duna with FAR and max out my cargo to Laythe.

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Thanks thanks.

Its amazing how different FAR is for planes(i've only used it for rockets untill now). I'm not used to how few wings are needed to be effective, not to mention no need to arihog.

Actually while ive got you here here a quick question. Ive been flipping through a few of your ships and i was curious: how big do you think you could go for an interstellar ship? i'm just interested in a ballpark that would be effective. Id love to hit up duna with FAR and max out my cargo to Laythe.

Assuming you meant interplanetary?

As big as you like, really; the limiting factor is "can you get it into orbit?". Especially if you're willing to refuel in Kerbin orbit, you can get just about anything just about anywhere, even if you don't use LV-Ns.

My Longreach can lift off from the KSC runway, fly to Minmus, do a VTOL landing there and return to the KSC runway, all without refuelling. Add an orbital refuel and most of the others could manage that as well.

Refuel the Longreach and it'll easily go interplanetary. And have a peek at the pictures accompanying the Migration for an example of how easy it is to hit Kerbin escape velocity. That was just a bit of sillyness done to show off, but if you fly sensibly (i.e. get out of the atmosphere before doing it) it could easily make that with plenty of juice still in the tanks.

If you want long-haul plus heavy cargo ability, see the Kerbodyne Brutus. I normally avoid LV-Ns for self-imposed-handicap reasons, but they essentially double your range.

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Is there actually a point in using spoilers? My understanding is that they are supposed to push your plane to the ground on landing and improve the efficiency of the wheel brakes; but the only thing that seems to do in KSP is increase the risk of your landing gear buckling and crashing your plane. Are they only supposed to be used together with flaps to nullify their effect, or is there something else I'm missing?

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Is there actually a point in using spoilers? My understanding is that they are supposed to push your plane to the ground on landing and improve the efficiency of the wheel brakes; but the only thing that seems to do in KSP is increase the risk of your landing gear buckling and crashing your plane. Are they only supposed to be used together with flaps to nullify their effect, or is there something else I'm missing?

The braking effect is slight, but it is there. The other use in landing is in order to prevent "floating ten feet above the runway until it runs out" issues; they let you drop the last bit of altitude without pitching down.

They also come in handy as reentry air brakes.

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The trick with placing flaps on aircraft is simple.

Place them as inline with the CoM as possible.

It is hard to tell in these pictures but here is a couple of my craft that have flaps on them.

oBt7iPN.png

This one is the easiest to see them on, but it is also a swing wing design.

D9oaQsP.png

This one you can see where the flaps are but they are not deployed, the airbrake is though and it is right over the CoM of the craft.

TujJClB.jpg

This one you can't see them in this picture but that is because I mounted them under the wings inline with the CoM.

cr6k3KJ.jpg

Most delta wing aircraft wont have flaps.

This craft from my RO install is not an SSTO but it is a very nimble fighter, it uses leading edge slats instead of flaps.

PASsq41.png

Bl1lokf.png

And here is a picture of my Cessna in my RO install.

9CVVfKO.png

it has its flaps in a traditional possition.

Hope I helped a bit more.

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You'll want the rear flaps to deflect down, but that introduces a pitch-down moment to the plane. You can counterbalance that by setting the canards as flaps, too.

I tried that on one of my SSTOs and it doesn't seem to be not a good idea. Using the canards as flaps increases their angle of attack and makes it easier for them to stall; as a result, with flaps activated I actually lose control over the plane at higher speeds than without them.

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I tried that on one of my SSTOs and it doesn't seem to be not a good idea. Using the canards as flaps increases their angle of attack and makes it easier for them to stall; as a result, with flaps activated I actually lose control over the plane at higher speeds than without them.

You shouldn't need flaps at higher speeds. All of my flaps are fully raised by 450kts and don't come down again till well below that.

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Hodo: Thanks for the advice, and more importantly the pictures. Its helped me with my flap placement a great deal.

I tried that on one of my SSTOs and it doesn't seem to be not a good idea. Using the canards as flaps increases their angle of attack and makes it easier for them to stall; as a result, with flaps activated I actually lose control over the plane at higher speeds than without them.

As Hodo said, the flaps are only used to help the the plane off the ground and to help it glide before landing. I cant imagine any other uses for them (except maby slowing down re-entry).

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As Hodo said, the flaps are only used to help the the plane off the ground and to help it glide before landing. I cant imagine any other uses for them (except maby slowing down re-entry).

I wouldn't suggest using flaps to slow down on re-entry, they may come off your craft due to the dynamic pressures at those speeds once you hit the lower atmosphere where you would encounter most of the drag needed to slow down.

I suggest using spoilers and air brakes.

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I wouldn't suggest using flaps to slow down on re-entry, they may come off your craft due to the dynamic pressures at those speeds once you hit the lower atmosphere where you would encounter most of the drag needed to slow down.

I suggest using spoilers and air brakes.

I only use use flaps in the upper atmo. Usually when pressure is around 50k i take them off, but before then they do a pretty good job. I can add spoilers but it would mean changing design... which can be done but im lazy. btw, what mods add air brakes? All i have right now is FAR and SP+ as far as aerodynamics and parts.

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As far as my exp goes,

The flaps don't quite work as they do as in FSX or XPlane10

and since in most of the cases, the spaceplane won't be having insufficient runway to stop after touching down (OP brakes), I don't care about the landing speed,

Hence I don't use the flaps functionality.

And I bet many of us do the sake too.

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I only use use flaps in the upper atmo. Usually when pressure is around 50k i take them off, but before then they do a pretty good job. I can add spoilers but it would mean changing design... which can be done but im lazy. btw, what mods add air brakes? All i have right now is FAR and SP+ as far as aerodynamics and parts.

Air brakes are in Firespitter, and in B9.

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As Hodo said, the flaps are only used to help the the plane off the ground and to help it glide before landing.

I never said I used them for anything else. My point was that using the canards as flaps on my plane seems to require greater landing speeds than using no flaps at all, because as soon as the canards stall, the plane will nosedive into the ground.

Yes, using them to take off a little bit faster might work, but is low-priority for me, since there's plenty runway to accelerate on. Landings are the difficult part.

since in most of the cases, the spaceplane won't be having insufficient runway to stop after touching down (OP brakes), I don't care about the landing speed

Yes, but wheel stability is an issue. Planes can easily skid out of control and shred themselves to pieces on the runway if attempted to be landed too fast.

Edited by Hurry, Starfish!
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