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Commissioner Tadpole

I've designed an airplane, but it doesn't work as intended

Question

I've been planning to set up a base on Laythe, and one of the things I intend to send there are plane-rover hybrids to explore the myriad of islands across the moon. However, upon designing such a plane and testing it on Kerbin, it displayed severe flight issues, such as:

• Flipping out of control when taking off - airplane must taxi at ~70m/s and make a jump, then shove throttle to 100% to accelerate quickly. It will spin out and crash when doing a conventional takeoff.

• Easily losing control when turning around on the atmosphere - When turning around, it'll wackingly spin around and then go back to its initial position. To steer, you must do so slowly and carefully.

• Hard time landing - It's hard to properly orientate the plane because it will not budge when steering unless doing a full bank turn, and when trying to land, it will bounce right up and start spinning uncontrollably.

I'd like to fix the problems I have with the plane, so if anyone could point out some bad design choices I did, it'd be welcome. I have taken five screenshots from the plane in order to help.

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Solar power is very weak on Laythe compared to Kerbin. And panels are draggy. I'd go for FuelCells or RTG.

A "car"-type landing gear, with the rear landing gear far back, is generally very unstable on aircraft. Put the Landing gear beneath CoM and Rover wheels further back.

3 engines is a lot for such a small craft. Here's a single engine super sonic craft inspired by yours.

yJQmqoL.png?1 TNvtKBa.png?1

It's stable as an aircraft both on the runway and in the terrain and as a rover on rover wheels. Quite forgiving and robust as you can see in these videos.

Download

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Commish,

 I'd recommend moving the rudder further back and adding elevators/ canards (whichever trips your trigger).

Best,
-Slashy

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Second Slashy's advice. Look at the position of your vertical stabilizer. It's practically right on top of your CoM, which means it has very little lever arm to work with and therefore provides practically no yaw stability. It needs to move much farther back.

Also, be sure to disable roll authority on the vertical stabilizer; otherwise it ends up fighting itself and loses much of its effectiveness.

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The rover wheels are adding a bunch of drag to the front of the plane that the SPH CoL isn't accounting for, which may also be contributing to your lateral stability issues.

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For take off and landing stability, have you considered a set of retractable aircraft landing gear? If its placed to extend below the rover wheels when lowered, you won't have to fight the rover wheels speed limitations. When landed, retract them and use the rover wheels. They should be strong enough to lift the aircraft up when transitioning.

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4 minutes ago, SinBad said:

For take off and landing stability, have you considered a set of retractable aircraft landing gear? If its placed to extend below the rover wheels when lowered, you won't have to fight the rover wheels speed limitations. When landed, retract them and use the rover wheels. They should be strong enough to lift the aircraft up when transitioning.

 

He's got that.

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16 minutes ago, foamyesque said:

 

He's got that.

Sorry, I didn't see.

Note to self: don't look at screenshots on mobile phones if you want to comment :confused:

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11 hours ago, Commissioner Tadpole said:

• Flipping out of control when taking off - airplane must taxi at ~70m/s and make a jump, then shove throttle to 100% to accelerate quickly. It will spin out and crash when doing a conventional takeoff.

Do keep in mind the units system you're working in. The "taxi" speed you're describing is 156 mph. If that's not enough speed to generatee lift, you may also need more wing. Canards might be helpful.

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2 hours ago, pincushionman said:

Do keep in mind the units system you're working in. The "taxi" speed you're describing is 156 mph. If that's not enough speed to generatee lift, you may also need more wing. Canards might be helpful.

^ This.

When I need to build "flyable rovers", I've found that biplane designs work pretty well-- it's an easy way to double the wing area, without making the wings stick out farther to the sides and therefore become more vulnerable to bonking into terrain when turning.  It has the added bonus that if you put your wings widely spaced (i.e. lots of clearance between the top and bottom wings), it leaves the left and right sides of the craft unobstructed, which can be a convenient place to mount things such as engines or other miscellaneous paraphernalia.

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None of the solutions worked. Pushing the vertical stabilizer back hardly had any effects, while adding canards gave the plane so much lifting force that steering it even as softly as possible causes it to spin uncontrollably - and unless I'm very high up in the air, this'll result in me crashing.

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Can you drop the .craft file in here, please? I'd like to take a closer look at the guts of this thing.

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22 hours ago, Val said:

Solar power is very weak on Laythe compared to Kerbin. And panels are draggy. I'd go for FuelCells or RTG.

A "car"-type landing gear, with the rear landing gear far back, is generally very unstable on aircraft. Put the Landing gear beneath CoM and Rover wheels further back.

3 engines is a lot for such a small craft. Here's a single engine super sonic craft inspired by yours.

yJQmqoL.png?1 TNvtKBa.png?1

It's stable as an aircraft both on the runway and in the terrain and as a rover on rover wheels. Quite forgiving and robust as you can see in these videos.

Download

That worked. It's a little stiff and seems to want to stall at times, but I have that problem with all planes, so it's okay. Thanks!

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