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Plane veers on Runway at speed.


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I'm working on spaceplanes, yet again.

The MK3, my latest attempt, keeps veering off to the side on the runway when it gets up to 110m/s or so.

I've checked the wheels angle, and I can't see anything wrong.

The braking power on the front wheel is set to zero.

I don't even touch the controls, and it does this every time.

Any advice?

EDIT: I've added the 'blueprints'. All advice welcome. I don't even know if lift is possible, because I can't get it up to speed on the runway yet.

8P5TtoN.jpeg

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5BplJVy.jpeg

x4HsLGN.jpeg

UooEtlN.jpeg

Edited by stephensmat
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  • Solution

So, a few things are jumping out at me right off the bat here.

  • First, the spaceplane look HEAVY. Like, really heavy. This could certainly be working against you rather than in your favor.
  • Second, I notice that your engines are very high up. None of the images seem to indicate the "center of thrust", but if it's too far above your center of mass, then it's causing a pitching down moment, which would put pressure on your nose gear, and would cause tilting and skidding, as well as make it extremely difficult for you to even lift the nose off the ground.
  • Third, you might try increasing the angle of attack of the main wings by rotating them upwards slightly, so that the wing is attacking the air at a greater angle than your nose. This will give you added lift before you even get the nose off the ground.
  • And finally, I am not sure how you have your control surfaces set up, but that main wing won't do much to help you pitch. Your only hope would be the canard wing near the nose. Make sure it's large enough, and bound to the pitch axis.
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40 minutes ago, EndeavourCmdr said:

So, a few things are jumping out at me right off the bat here.

All good points. I need teachers, more than I care to admit. Most Spaceplanes I've seen are long and thin, and mine is short and wide.

The thing is, I really want to keep the docking port in the centre rear. I plan to dock it with a 'drive section' for a Grand Tour.

With the exception of Eve, the only thing the jet engines are useful for is getting off Kerbin. I'm giving serious thought to just mounting it on a rocket booster.

It's just infuriating that I can't seem to make an ssto successfully.

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I mean, you CAN make an SSTO, but the question you might want to ask is: "why am I building an SSTO?". If I recall, the only reason that we ever tried to build SSTOs in the first place was cost savings. Because having parts burn up or get destroyed on every launch wasn't cost efficient. But that's not really the case now, with companies like SpaceX returning their booster stages back to the pad. And realistically, there isn't much actual benefit to SSTOs either, as you end up carrying a lot of dead (unneeded) mass along for the rest of the ride, which only hurts your Delta-V capacity.  And to offset that loss in Delta-V, your only option is to carry more fuel, which itself is just more weight that you are bringing just to burn off a lot of for a few hundred extra m/s.

That said, by all means, continue to practice and try it just for "the funs". It's a good learning and engineering exercise, nonetheless. 
But honestly, the best bet IS to stage parts that you no longer need. The less mass you carry into orbit, the better.

Edited by EndeavourCmdr
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10 hours ago, EndeavourCmdr said:

I mean, you CAN make an SSTO, but the question you might want to ask is: "why am I building an SSTO?".

Well, there's always the '10 Kerbals to Eve and Back' mission.

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On 4/8/2024 at 7:59 PM, EndeavourCmdr said:

So, a few things are jumping out at me right off the bat here.

  • First, the spaceplane look HEAVY. Like, really heavy. This could certainly be working against you rather than in your favor.
  • Second, I notice that your engines are very high up. None of the images seem to indicate the "center of thrust", but if it's too far above your center of mass, then it's causing a pitching down moment, which would put pressure on your nose gear, and would cause tilting and skidding, as well as make it extremely difficult for you to even lift the nose off the ground.
  • Third, you might try increasing the angle of attack of the main wings by rotating them upwards slightly, so that the wing is attacking the air at a greater angle than your nose. This will give you added lift before you even get the nose off the ground.
  • And finally, I am not sure how you have your control surfaces set up, but that main wing won't do much to help you pitch. Your only hope would be the canard wing near the nose. Make sure it's large enough, and bound to the pitch axis.

All good advice. i tried taking it to heart:

 

 

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  • 3 weeks later...
On 4/8/2024 at 10:31 AM, stephensmat said:

I'm working on spaceplanes, yet again.

The MK3, my latest attempt, keeps veering off to the side on the runway when it gets up to 110m/s or so.

I've checked the wheels angle, and I can't see anything wrong.

The braking power on the front wheel is set to zero.

I don't even touch the controls, and it does this every time.

Any advice?

EDIT: I've added the 'blueprints'. All advice welcome. I don't even know if lift is possible, because I can't get it up to speed on the runway yet.

8P5TtoN.jpeg

KcTlRuO.jpeg

5BplJVy.jpeg

x4HsLGN.jpeg

UooEtlN.jpeg

The spaceplane seems quite heavy, which could be working against you. Additionally, the high engine placement likely causes a pitching down moment, putting pressure on the nose gear and making it difficult to lift off. Try increasing the angle of attack on the main wings slightly to generate more lift before rotation. Also, ensure the canard wing is large enough and properly bound to pitch controls to help with rotation. Reducing weight and lowering the engines may also help balance the craft.

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On 4/28/2024 at 11:38 PM, leos101 said:

The spaceplane seems quite heavy, which could be working against you. Additionally, the high engine placement likely causes a pitching down moment, putting pressure on the nose gear and making it difficult to lift off. Try increasing the angle of attack on the main wings slightly to generate more lift before rotation. Also, ensure the canard wing is large enough and properly bound to pitch controls to help with rotation. Reducing weight and lowering the engines may also help balance the craft.

Literally the same advice I gave him several posts up, lol

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