Need help with building spaceplanes!!

[SilentGunner13]

I've been moderately successful in designing planes. And by moderately successful I mean they don't fall to bits or explode on physics load. However. Getting it off the runway is another matter entirely. I have a few problems.

Firstly, I don't know what the heck is the deal with my engine. I'm using the basic jet engine with B9 air intakes. My normal takeoff config is to keep on the brakes, stick the jets to full throttle and wait for them to reach peak thrust. When the jets begin to defeat the brakes, I come off the brakes and start rolling. However, as soon as I do, my thrust drops and so too does my acceleration. Even if I get airborne it still drops gradually. At some stage this usually ends in an explosion of some description. Usually in a botched takeoff abort attempt at the end of the runway. How do I stop my thrust from suddenly dropping? Is it something to do with Ferram Aerospace? Do I need even more intakes? Or is it something else entirely?

Also, I find that my aircraft very rarely fly in a straight line. I think it may be to do with my wing placement. I usually find that my aircraft violently pitch up or pitch down with no control input. Are my wings off? Again, I'm using Ferram Aerospace and also B9 Aerospace parts.

Thanks for the help!

[Geschosskopf]

Hmmm...

The violent pitching is usually a sign that your CoM and CoL aren't in the right relative positions. You want the CoL just a hair behind the CoM. But remember that the CoM will change during flight as you burn fuel, unless you carefully built the plane so this doesn't happen. Getting all this nailed down isn't complicated, it's just tedious and time-consuming.

Note that the Basic Jet Engine isn't a spaceplane engine; it works best at low-ish altitudes and speeds. You really want the Turbojet or RAPIER to get to space.

Anyway, I'm puzzled by the reported loss of thrust. Do you have the right-click menu open and are actually seeing thrust decrease there despite the throttle remaining at full? This might have something to do with FAR's aerodynamics.

But OTOH it could be B9. B9 hasn't had an official update in a long time, since 0.22 at the latest, so in its natural state it doesn't really work well in 0.24 (and with the 0.24 version of FAR). There are some patches other folks have made for it since then but they're hard to find sometimes and I can't vouch for them. I would seriously research this issue before using B9.

[Agifem]

About the throttle : I'm lacking an explanation. Maybe a little more intake will help, but i think any small plane can fly with a single intake. Maybe you are reaching terminal velocity at takeoff (about 100 m/s at sea level), and your single small engine fails to fight the heavy mass of your plane. Someone more knowledgable might help.

About the handling : Activate SAS, it's really not an option. If that's not enough, check your center of mass (CoM) and center of lift (CoL). They should be close to each other, with the CoM a little more to the front if you want the plane to be more stable at high speeds.

About the brakes : Even if jet engines take a moment to start, holding the brakes has never been necessary for me.

About Ferram : No idea what that mod does. Maybe that's the problem. I play with stocks.

[SilentGunner13]

The violent pitching is usually a sign that your CoM and CoL aren't in the right relative positions. You want the CoL just a hair behind the CoM. But remember that the CoM will change during flight as you burn fuel, unless you carefully built the plane so this doesn't happen. Getting all this nailed down isn't complicated, it's just tedious and time-consuming.

Thought so, I figured the fact that I mount my wings low to try and keep my landing gear level had something to do with it.

I'm puzzled by the reported loss of thrust. Do you have the right-click menu open and are actually seeing thrust decrease there despite the throttle remaining at full? This might have something to do with FAR's aerodynamics.

Yes, I have the menu opened and I usually see a drop in thrust, starts quickly and then slows down, but still drops. The most baffling thing is that this happens only when the brakes are let off and the craft begins rolling. Until then thrust still rises! It could be FAR or it could be B9 intakes. I'm using community fixes on the B9 parts as there hasn't been an official release since 0.22. The cockpits, gear and wings seem to work fine, but it could be the intakes. I'm no coding genius. I'll try the stock intakes and see if the problem persists.

[Jebadiah Kerban]

hu send me the craft and can fix etc but is ur plane wings or what? cos the wings must be at least the length of the plane if its big. what ever pm me

[Wanderfound]

Screenshots. From the top and the side, in the SPH with CoM/CoL/CoT indicators turned on.

We can't help you if we can't see what we're dealing with.

[Agifem]

I figured the fact that I mount my wings low to try and keep my landing gear level had something to do with it.

I'm not sure mounting the wings low is a good idea. I think it's necessary your center of lift is aligned with your center of thrust.

Also, your landing gear should not be leveled. The front part should be lower than the rear part, so that the plane points up a little as it rolls along the driveway. It gives the plane a natural incentive to take off without any pilot intervention.

[O-Doc]

By loss of thrust do you mean the throttle goes down or, the plane doesn't move. If it's the former then you are dealing with a bug. I've seen similar behaviour myself. If it's the later then, you might have something blocking the engine exhaust.

[Hodo]

The loss of thrust is not a bug in FAR. Ferram4 nerfed the way jet engines work with FAR, so no more overpowered jets that can fly to the Mun if you slap enough intakes on the craft. The basic jet loses power very fast, the closer you get to the speed of sound, the less power it will make, unlike the turbojet which makes less power but sustains it at higher speeds.

Your flight control and flight stability issues, wont fly in a straight line, are related.

If you have your wings at an odd angle, they may induce unwanted roll or yaw, same for your vertical stabilizer, if you have one. Also the lack of or over abundance of control, if you have not set your control surfaces to certain jobs, roll, pitch and yaw, you maybe having an overcontrol/undercontrol issue.

Post a few pics of the craft as Wanderfound asked and I am sure that we can find the problem.

[SilentGunner13]

Sorted the pitching by moving my wings to align the CoM and CoL.

By loss of thrust do you mean the throttle goes down or, the plane doesn't move.

My throttle is still at 100%. But the thrust in kN falls. I built a small plane with a single jet, two stock radial intakes, wings etc and the problem still occurs. I had built my thrust up to 120kN, but as soon as I set off it dropped and it took only 20 seconds to drop to 40kN. It's an odd behaviour and I can't see what is causing it. I'm going to post to Ferram Aerospace and see if anyone else has this problem.

[SilentGunner13]

and I don't think screenshots of a craft are necessary, because this problem is occuring with every craft I build, not just a single one. Regardless of size, number of engines or intakes.

[Hodo]

The engine power falling off is a FAR thing, it is the way engines are supposed to work.

[SilentGunner13]

The engine power falling off is a FAR thing, it is the way engines are supposed to work.

The thing is that the dropoff is so drastic that I can't build enough speed to get my craft airbone

[Hodo]

The thing is that the dropoff is so drastic that I can't build enough speed to get my craft airbone

How fast are you going?

How big is the craft?

Does it have enough wing to actually lift?

Is its gear set so you have a point of rotation?

Do you have air for the engine?

Are you using RAM intakes, Radials, or Circular?

These are all questions that could be answered with a picture of the craft so we can see if it is an actual aircraft or a brick with some wings slapped randomly on it.