Longditudinal/Pitch Stability Spaceplanes

[timpossible]

As an aspiring aerospace engineer (yea right) I spend a majority of my time in SPH.

i am getting pretty good at making really easily controllable planes that look ugly

or Nice looking planes that fly like pieces of crap

So i request a good method of increasing pitch stability, while still looking nice

Looks nice = Bad control

Looks Average = Great Handling

[bsalis]

From my experience, planes with stable pitch often have....

* The CoM near the center of the craft

* The CoL and CoD behind the CoM

* Long craft length

* Ample control surfaces

* Control surfaces further from the CoM

* Control surfaces at the rear and front

* Forward control surfaces should not be further from the CoM than the rear

So basically if you build something like a Lockheed U-2, but with the addition of canards at the front (but not too far), it should work great.

[timpossible]

thanks for that ^

but how well does the physics engine process drag? would i be able to have a positive stability on the elevators, so it will naturally want them to be parallel with the AoA. like a dart? help prevent spins and tumbling?

[Autochton]

timpossible: Don't go thinking the stock KSP flight model is significantly related to actual aerodynamics. It may adequately model what happens when something moves through something, but it sure ain't planes moving through air! :-)

The craft threads have many examples of the kinds of planes that will fly in stock KSP - but my eyes always hurt a little looking at them. If you want a more realistic flight model, I suggest getting a hold of the Ferram's Aerospace Research mod - colloquially FAR - which replaces the flight model wholesale. It causes issues with some mods that use the base drag numbers, but the planes that fly well end up looking like planes more often than not.

[KerbMav]

Your "arrow" looks way "cooler", sure - but your doublewinged hopper has its own charme - so I am not sure which one would be the ugly one?

[GROOV3ST3R]

While the simplified drag model does make it nearly pointless to actually build aerodynamic craft, it also provides us with some really interesting opportunities. Try this on for size:

It's length is about 2 Mk1 fuel tanks. I did use debug menu to put on 2 ram air intakes on each engine and one right behind the cockpit. As a result, this craft is able to circumnavigate Kerbin at least 4 times in a single flight and has a maximum useable altitude of around 47km. Also it flies at over 2150m/s or mach 6.5

It doesn't look terribly aerodynamic, nor like a hypersonic jet would. Sometimes I have to point it downwards and it still gains altitude. But then it's tricky to get off the ground, needs a whole runway and practically requires jet engines for a safe flight. Oh and I never managed to land it :S

The lesson here is: Use Avionics, adjust Trim to keep the nose pointing in the right direction and fly as high as you can.

About building a craft, try to keep the control surfaces as far away as you can from the CoG. Also, if you have trouble keeping the nose pointed upwards, it means your craft is too nose-heavy. Balance the CoG and CoL together. Make sure that as fuel drains from the craft, it doesn't destabilize it too much. CoG Will shift as tanks become empty. If possible, stack them laterally and not longitudinally.

If you prefer a more conventional design, look at this:

Note canards at the front help keep the craft pointed the right way up. Vertical control surfaces are angled so they also provide SOME lift and stability. Keep all lifting surfaces pointed EXACTLY in the direction of travel. Do NOT turn wings upside-down as this flips the direction in which they generate lift downwards.

On the side:

Try out this craft if you prefer something that is insanely useful in every single way as well as cool looking and capable of pretty much everything.

http://forum.kerbalspaceprogram.com/showthread.php/24734-Amphibious-VTOLSSTO-%28Image-heavy%29?highlight=VTOL+SSTO

Edited July 6, 2013 by GROOV3ST3R

[SDIR]

Actually, so far as I know, the wings in KSP do not actually provide lift, rather, you need to use angle of attack to keep your plane in the air. And yes, your planes in KSP will look strange but making them functional is the main priority.

[bsalis]

Actually, so far as I know, the wings in KSP do not actually provide lift, rather, you need to use angle of attack to keep your plane in the air. And yes, your planes in KSP will look strange but making them functional is the main priority.

Actually in RL, airfoils don't really produce much lift without some angle of attack. Lift increases up to typically 16 degrees where you suddenly go from max lift to stall! In KSP, lift increases to a max at 30 degrees then goes down again, with no stall. In both cases, higher angle of attack increases induced drag.

I don't know why people keep banging on about how it's not possible to build a realistic looking and flying plane in KSP (without FAR). Since I can do this just fine. Do people actually know about how real planes are built anyhow? For example RL plane wings have some angle of attack "built in" (ie. Angle of Incidence). Also, the tailplane actually creates a downwards force.