Space plane help

[Nich]

My plane is both a lawn dart and unstable at the same time. Any suggestions?

[EladDv]

the tilted wings make the CoL behave weirdly and the engines might also apply torque if the thrust is not centered on the CoM X and Y axis

[Claw]

The Center of Lift is too close to the Center of Mass. Generally you want the CoL a bit behind the CoM. As for lawndarty behavior, that might be due to insufficient pitch authority.

Overall you could fix this by adding a tail, or shift the wings back some and add a canard. There are other ways though, that's just the most straight forward.

Also, you may want to consider a vertical stabilizer on back (vertical fin) to help with yaw control. You might experience some issues later with yaw stability, especially as you start to ramp up speed (assuming that's a spaceplane).

Cheers,

-Claw

[Alshain]

As mentioned, your biggest issue is the CoL is a little too forward. A general rule of thumb for spaceplanes is to have the CoL ball halved by the CoM. It doesn't have to be perfect but you need to see about half of that ball. I say "for spaceplanes" because they generally don't need a high degree of maneuverability. If you are launching into equatorial orbit, they don't really need to turn much at all except for minor inclination correction. Even if you are going polar, no need to turn on a dime, take your time doing it. Fighter planes and other jets you may want it a bit further in but you will lose stability for maneuverability.

Your vertical stabilizers are too far out on the wingtip to be useful for yaw and stability. Whether using one or two, it needs to be a little close to the body to be really effective and they might need to be a little bigger. This image was not made by me and I've forgotten where I got it, but I love using it as a reference for finding good tail designs that fit with everything else I'm trying to do. You should note again, dual vertical stabilizers are seldom useful on spaceplanes, unless space is just an issue. You will find the first three are used in real planes most often, and with good reason, they are simple and work best. (In fact I would almost say they are in order of most to least common)

Edited September 4, 2015 by Alshain

[GoSlash27]

Nich,

That spaceplane design has wandered off into the weeds like a drunk on a bicycle!

Please don't take that as any kind of disrespect; you know that *I* know that you are a steely- eyed missile man.

But I mean... look at it, amiright? It looks like it would be an unstable lawn dart.

Okay. Best advice I've got from this pic is to completely scrap it and start with a fresh sheet of paper.

Step #1 is to define the mission and thus payload capacity. Get a feel for the scale of it.

Step #2 is to build a simple SSTO in accordance with the ratios that you (and of course the rest of us) have established in previous designs, but build it completely out of fuel tanks. Tweak and adjust as necessary until you are successfully orbiting enough mass to account for the mass of your orbital mission payload (the mining equipment, fuel to get to Minmus, etc).

Step #3 is to take all this data in hand and build your spaceplane with the required parts, supplies/ etc. And build it like a proper spaceplane. Make it clean, efficient and well- balanced from the start.

If it's deficient, don't succumb to the urge to crutch it by tacking stuff on. Look for things that you can eliminate or design to be more aerodynamically stable, clean and efficient. Take it from the top if necessary.

What's wrong here isn't a technical deficiency in the design, but the philosophy behind how it was laid out, assembled, and adjusted.

Specific suggestions:

- a plane that light doesn't need that much wing with that much incidence. You just need enough to keep the nose firmly aligned with the prograde marker throughout the ascent. With all that t/w, you don't need that much wing *or* that much incidence.

- the vertical stabilizer(s) should be as far aft as you can possibly get it.

- don't stack bulky draggy equipment radially out in the slipstream. Find a way to shield it from the airflow.

- Don't add additional parallel stacks if you can help it.

Good luck!

-Slashy

Edited September 4, 2015 by GoSlash27

[ajburges]

One thing to note: with the different angles of incidence for the wings, your CoL will shift with AoA. Until the critical angle, the CoL will shift towards the greater magnitude aligned lift vector sum as AoA increases. That critical angle has crazy behavior though.

Given that your zero incidence surfaces are ahead of the CoM, your craft should have a stronger stabilizing response with AoA as long as you stay within the critical angle. However, once you pass that angle, the CoL will suddenly shift way forward. Once it does that, it will likely exceed your aerodynamic control authority. It would be very hard to return to controlled flight then.

[tbarcello]

Okay. Best advice I've got from this pic is to completely scrap it and start with a fresh sheet of paper.

No! Look at the shadow! All he needs is tail fings and he's golden! No scrapping, no nada!

...

I don't know though...