Help with spaceplane. :(

[Cruzan]

Nice! Reducing weight is definitely one of the better ways to go

[Smidge204]

Just 'cause:

http://www.youtube.com/watch?v=itU81I_kckc

It's a fairly capable craft if all you want to do is get into LKO and home again.

=Smidge=

[Vanamonde]

Hey look! It's my plane, and it's all working and stuff! That settles it; while there's certainly room for improvement in the design, my real problem seems to the way I'm trying to fly the things. I'll study your video, Smidge204.

It's a fairly capable craft if all you want to do is get into LKO and home again.

Yes, I made this one to figure out how it's done, not even attempting to carry any payload or do anything useful while it's up there.

Thanks for all the suggestions and feedback, folks. I'm going to mark this answered while I experiment with your advice.

[Nao]

Nice video Smidge204

Some thoughts after watching it (for Vanamonde):

I think the attitude was too big after engaging rocket motor, a shallower ~30deg attitude got me almost half a tank in 81x81 orbit (almost enough fuel to reach Mun).

One little trick to stop nosediving at landing is to actually remove front wheel from "braking" command in the action groups.

If you want to avoid spinning at flameout, remove the engines and place them again making sure the last engine to place to be the middle one, that way when flameout occurs it will be the middle engine.

And one more little nitpick: it would be nice to strut the fuselage (rocket fuel tanks) to sidepods so that it does not wobble that much

[Vanamonde]

One little trick to stop nosediving at landing

I've had that problem with other planes, but not this one. If you are experiencing that with this plane, I'm puzzled.

the last engine to place to be the middle one, that way when flameout occurs it will be the middle engine.

I'm aware of that trick, and that is what I did with this craft. The left engine still seems to cut out first, for some reason.

strut the fuselage

It's a work in progress. I have a slightly improved version in which I did do that.

[numerobis]

Looking forward to your success

Minor design point: Someone (Nao?) mentioned being able to fly vertically for the first 10km. That implies you have way too much jet thrust -- which in turn means extra mass. Drop one of the engines, and you'll be able to fly with 1.2t less dead weight at high altitude.

[Vanamonde]

Thanks numerobis, but the high-thrust is an intentional design feature. I'm hoping to zip up to apoapsis on the jets and then circularize with the rocket. Which doesn't seem to be working, but it is the goal of this design. Besides, when I tried removing the upper engine, it made a mess of the balance and would have required a substantial rebuild.

[Nao]

I've had that problem with other planes, but not this one. If you are experiencing that with this plane, I'm puzzled.

I'm aware of that trick, and that is what I did with this craft. The left engine still seems to cut out first, for some reason.

It's a work in progress. I have a slightly improved version in which I did do that.

Haha i saw it nosedive and snap at the end of the Smidge204's video, so just pointed that out

I'm aware of that trick, and that is what I did with this craft. The left engine still seems to cut out first, for some reason.

Try removing the engines completely and then placing fresh ones (without "alt" cloning) it should fix this (it fixed it in my test). I think this has something to do with part "number" that each part gets when it's created (that is being used by game engine to determine which part should be updated first each physics step), and sometimes new part can have lower number for whatever reason. (reloading the craft in SPH and just replacing engines seems to fix that)

Also If you ever want to have an stock early warning system for engine stall, I've found out that adding closed radial intakes can create some sort of "buffer" zone where engine thrust and fuel consumption goes down instead of flaming out. Ram intakes have very low drag and mass when closed so the don't impact actual performance almost at all.

For example adding 6 closed ram intakes to your craft (that normally flames out at 26,4km and 1.15ram intake air) have given me another 300m of altitude and a warning in lowered thrust on one of the engines before the flameout with 1.05 ram intake air.

[numerobis]

If you're using jets to zoom up to high altitude and then circularize from a near standstill, that would be why you're having trouble. You actually want to fly like a plane up to your service ceiling (the top full-throttle altitude), then build up speed there, as per the descriptions earlier. And if you do that, you find that having more jets doesn't improve your top speed: either you fly lower, where drag eats up the entire benefit of the extra jet, or you throttle back, and you get no extra thrust. So, at high altitude, more jets => more mass with no benefit.

At low altitude, you need to make sure you can get up to high altitude. That's what drives how many jets you need. TWR of 0.7 is very comfortable; TWR 0.3 is getting tricky.

[numerobis]

I've found out that adding closed radial intakes can create some sort of "buffer"

I wonder if that's related to the bug about not being able to fetch the last dribbles of air from the intake (a bug that is listed as fixed for 0.23).

[Vanamonde]

actually want to fly like a plane up to your service ceiling

I've tried that again and again for 1.5 years, without success. That's why I'm trying the other method. And I don't mean going straight up, but trying to find a good compromise between forward speed and climb rate. Like I said, it's not working, but at least it's failing in a different way, which is a nice change of pace. And Nao, I'll try that with the engines.

[koshelenkovv]

Small spaceplanes are quite easy to build and fly.

Keep it light, use 1 engine, or 2 for heavier models, put 3-4 intakes per engine.

Fly to 15-20 km and start building your speed while keeping vertical speed about 100 m/s, then 50 m/s, then in almost level flight.

Speeds up to 1700 m/s could be achieved easily, and with some experience you will get over 2000 m/s at altitude about 35 km.

Then start your rockets (at angle about 30-45 deg.) and kick Ap to 75-80 km and coast.

Use 2 separate action groups to close all intakes and to shutdown jets.

Closing intakes helps greatly reducing drag.

If you using 2 engines and one got flameout, then disable engines, not cut throttle by X. (When you cutting throttle there is still some residual thrust while engine spooling down.)

Edited November 30, 2013 by koshelenkovv

[iceman_gobbi]

Looks like you have some CoT vs CoM problems.

With that engine mounted on the top it will move your CoM up slightly but your CoT will change drastically when you switch to rockets. This is why you are pitching up.

I would start by trying to move that top engine downwards into the body of the ship or move another rocket engine up to it so you keep your current CoT.

Guys! Hey guy? Just do what I do with my very fly whale, my mania of decentralizyng center of mass just for build 4 atmo engines BELOW wings and not in the middle, always result in some of both: 1-stability problems uping the nose of ship dangerously or:

2- Pushing de nose down.

I try all, realign all engines, follow some tips of a lot "specialists" in aeroplanes, try add a lot of rcs thrusters (because as less atmosphere, less control about my dear Espinhenta I have), but it was just I turn on rocket mode and in matter of seconds happen a catastrofic lost of control (almost till splashdown in ocean), always the same think, when I am about to give up and literatly delete all saved versions, I think:

"Well.. If there are to much thrust going from down of the ship, but, JUST A LITTLE BIT in comparisson with all thrust that engines could generate, WHY NOT PUT JUST ONE OR 2 LITTLE RADIAL ENGINES! THEY EVEN ARE ORANGE AND STYLIST! WHY NOT TRY?!"

So, I put 2 rockomax at very middle (dorso) above the plane, and just for garantee more 2 of the same engines BELOW rocket engines, but almost in the center line just in case the thrust of the first 2 engines be much stronger, ok, result it was: THE BLACKBIRD TURN IT INTO A PERFECT AEROSPACE SHIP!! I swear guys, in the moment I turn the little 20kn engines, alll look like heaven! Looks like never some part it was builded far of center line!! But.. Is still a difficult plane to pilot, "she" (Espinhenta) claim/drain alll talent a pilot should have!! Lol

But, in "aeroplanes mode", far away from vertical rockets, I'm just a newbie anyways!!

Still thinking: its not so hard just try put one engine and set one key in action groups for the opossite side the nose points, dont you guys, think?!

Just 0,09t but the rest of the "girl" is aalll very very light weigth (allways my major concern!)

[Mr. Speed]

Thanks numerobis, but the high-thrust is an intentional design feature. I'm hoping to zip up to apoapsis on the jets and then circularize with the rocket. Which doesn't seem to be working, but it is the goal of this design. Besides, when I tried removing the upper engine, it made a mess of the balance and would have required a substantial rebuild.

I downloaded your craft and reached orbit fine with more than enough fuel to do some orbital ballet. Afterwards it put it on a diet, I took all the beams off and also removed the top engine and put the turbojets under the wings without the pylons. it is only slightly unstable when empty, I had to be careful with landing. I usually fly my spaceplanes at the top of their flight ceiling to pick up speed, take a very shallow dive to get a little bit more air and then pitch up until I have to light the rocket. That works fine with this plane but the high climbing angle trajectory you want is probably easier to do with the small jet engines and no additional jet fuel, just rocket fuel. The smaller jet engines are lighter and give more thrust early on which is good since you are not going to stay for a long time in the atmosphere. since a steeper trajectory gives you less time to gain speed with the jets you need more burn with your rocket, so it is a very fine balance between thrust and fuel you are looking for.

Here is a pic of the XSP-32 that went on a diet. It is about 4 ton lighter so a bit more fuel remains after reaching orbit.

[Vanamonde]

I put 2 rockomax at very middle (dorso) above the plane

That can work, but also adds mass to the plane, which I'd like to avoid.

Mr. Speed, how are the wings attached without those central struts?

[Mr. Speed]

You drag the wings to the top of the fuselage with double symmetry and snap angle on, then flip them over with the qweasd keys so they are horizontal and attach them. Good luck!

[Vanamonde]

Progress report: I suck.

Col_Jessep, I can't handle your plane! I found it very difficult to steer, but it got to orbit with fuel to spare. I do not understand why. Still studying.

Sirine, I tried those planes, and now I am depressed because they work so much better than mine.

[Sirine]

Progress report: I suck.

Col_Jessep, I can't handle your plane! I found it very difficult to steer, but it got to orbit with fuel to spare. I do not understand why. Still studying.

Sirine, I tried those planes, and now I am depressed because they work so much better than mine.

Try figure it out both plane characteristic. The share the following common:-

1) Lots of lift. (Wings)

2) Light. (They have less fuel).

3) RAM Air-intake. 6~8 of them per engines.

4) Cheat, 'Close' Radial Air Intake.