Basic Aircraft Design - Explained Simply, With Pictures

[CaptRobau]

Amazing stuff. Really helped me build some diverse designs. Only thing missing is probably a section on tail assemblies. The wiki article shows some interesting things you can do with tail assemblies, but what that info really needs is the keptin treatment.

[keptin]

I was original planning to include something on empennage, but thought it would guide players into more traditional tail assemblies rather than coming up with their own [possibly insane, but functional] designs and learning through experimentation. So instead, I drew a variety of control surface arrangements on aircraft throughout the tut to start with some ideas. It's enough to get players off the ground, but it's up to them to perform some trial & error testing.

The other reason that an empennage section wasn't included is that the advantages and disadvantages of different arrangements aren't well represented in KSP due to the simplistic fluid model. For example, lifting surfaces aren't any less effective in KSP if they're interacting with turbulent air from a forward wing or engine, so a T-tail is more aesthetic than functional. We also can't recreate a deep-stall associated with T-tails in KSP.

[KerbMav]

I keep reading and hearing stuff about landing gear has to be vertical to the runway, but I also see lots of designs that ignore this?

Also, is there reason to put the front gear on backwards - other than aesthetics?

[Cruzan]

I keep reading and hearing stuff about landing gear has to be vertical to the runway, but I also see lots of designs that ignore this?

Also, is there reason to put the front gear on backwards - other than aesthetics?

If you're talking about Camber then that's okay as far as I can tell. Toe is something that KSP does not tolerate so you need to be careful about that with your gears. You might still run in to problems though if your gears aren't perpendicular to the ground as things tend to vary from launch to launch

As for mounting the front gear backwards, this usually just help to ensure that your plane won't flip forwards when landing. If the front gear is too close to the CoM that could happen and mounting backwards helps place the contact point farther from the CoM

Edited November 5, 2013 by Cruzan

[RocketPilot573]

Nice tutorial!

But I have one question:

I have a 70 ton aircraft whose landing gear will not work. Going any faster than 10 m/s causes the gears to buckle. Despite the fact that they are perfectly straight, have like 100 struts, and that there are THREE gears on BOTH sides, and two in the front. Seriously, is there anyway to fix this? I have tried everything that this tutorial says, well except the last one! Rater than veering off the runway, the gear literally collapses...

[KerbMav]

As for mounting the front gear backwards, this usually just help to ensure that your plane won't flip forwards when landing. If the front gear is too close to the CoM that could happen and mounting backwards helps place the contact point farther from the CoM

Of course ...

I have a 70 ton aircraft whose landing gear will not work. Going any faster than 10 m/s causes the gears to buckle. Despite the fact that they are perfectly straight, have like 100 struts, and that there are THREE gears on BOTH sides, and two in the front. Seriously, is there anyway to fix this? I have tried everything that this tutorial says, well except the last one! Rater than veering off the runway, the gear literally collapses...

If your aircraft is that heavy, you might want to take a look at modded sturdier gears or create a slightly enlarged more robust version of the stock gear yourself.

But somehow I have the feeling that there has to be something in the design of your craft - care for a screenshot?

[keptin]

Try attaching small cubic struts directly to the wing-fuselage root (the fuselage part where the wings attach) and placing the gear below them. Alternatively, you can attach the gear directly to the fuselage. Don't forget to reinforce the fuselage so it doesn't twist.

This sucker weighs around 480 tons and that did the job.

[RocketPilot573]

Here's a picture:

This thing is already 350 parts, so it would be great I could remove some of those struts...

[KerbMav]

Try to add one of the modular girder segments - put them under the craft and put your gears neatly in a row onto it - try again, first without strutting.

btw.: Love the use of the tail connectors here - should use them more often myself!

[RocketPilot573]

Wow! Those cubic struts are strong! The gear if now perfectly stable at speeds over 100 m/s! Unfortunately, it cannot handle landing, I'm bringing it in at 90 m/s, which is the minimum speed that it can maintain level flight. The gear instantly explodes/breaks off, even when descending at only like 3 m/s... Any ideas? (Besides adding more lift)

[briansun1]

very nice...

[keptin]

Wow! Those cubic struts are strong! The gear if now perfectly stable at speeds over 100 m/s! Unfortunately, it cannot handle landing, I'm bringing it in at 90 m/s, which is the minimum speed that it can maintain level flight. The gear instantly explodes/breaks off, even when descending at only like 3 m/s... Any ideas? (Besides adding more lift)

The parts your gear are attached to are likely the weak point. Try using the fuselage. As always, a gentle, slow landing is ideal.

[KerbMav]

Tried a last-second-drogue-chute to slow you down a few meters above ground?

With low enough drag it should not instantly flip your front gears into the surface.

[Snarfster]

Very good post, love the way how complex issues are explained in a simple way. + rep for you.

[Keloooe_Pest]

Very, very nice work Keptin! Now to change my landing gears on my planes...

[Prometheus]

Would you mind adding a section on tail design if you can? You have a section covering wing designs and what each one achieves, but nothing on designing a tail...

[Voidryder]

Ok, I'll admit it, I'm a rocket man. Spaaaaaace Baby. Light the candle and get into The Black fast. I actually delete all aircraft parts from any downloads so I can add more rocket parts. ::looks at sky then stubs toe in dirt:: Ok, it's because I can't build a plane worth a rivet. That is till now. Just got my first little sucker off the runway without wheelbarrowing, flipping onto it's back or nosing into the drink. And it's thanks to you Keptin. ::two thumbs up:: Um...you wouldn't consider doing a pictural on landing, would you? Like soon? Only got quarter tank of fuel left and Bob is looking worried.

[keptin]

@Voidryder, Ha, thanks, I'm glad I could help. No plans to do a piloting tut as of yet, but maybe in the future.

@Prometheus, A few others asked about tail assembly as well. I might add something in the future, but I think leaving a certain amount for the players to discover through trial and error is better for learning.

[el_coyoto]

I loooove the "Eagle", truly a majestic and state-of-the-art aircraft!

The tutorial in itself is accurate, well written and lovingly drawn!

I'm almost sad that I've already discovered most of these tricks before (Scott Manley FTW), because this would have looked nice printed and hanged above my desktop...

Excellent job!

[qwertyx2y]

Great tutorial, only one i've ever read.

Otherwise it's Manly, But this is great! i have no more trouble with Jets.

[AGlassOfMilk]

About the part with the starting straight thing and the plane beeing to fat, tires getting buldgy and getting off the runaway, I do not agree with that part.

The problem is different as I experienced:

Especially with tiny light planes the problem becomes more obisious. As a real kerbal beginner if my plane doesn't lift, it needs just more powerful engines, solves every problem right? Well the problem is, that if you try to start your plane at max power, the engines start wobbling and thus not push straight forward anymore thus pushing the plane off the track. I think the drifting to the side forces the unstraight boost of the engine even further, pushing the plane more and more off the track.

The solution to the drift off the runaway in this and my only and most experienced problem is not to fix the tires, but to lower the force for the engines. I had to start my plane at 50% push. While the plane is driving slow/standing still, the engines boosting at full power apply a huge force to themself/their connection to the plane. When the plane is actually flying at fast speed, there isn't this huge force anymore and it will fly straight even if you are at max power. At least that is what I experience. So if you have problem with you plane going off the track, try to start with less power until you lift off (like 50-60%).

Indeed what also help is adding vertical wings, like fish fin at the wings to correct the drift off.

Btw, I first thought its a tireproblem and tried adding more tires (==weight) to the plane, but the problem was still there. So I think it's better to check for the overpowering liftoff before you try to fix other stuff on your plane.

[7499275]

I just want to express my apologies to the OP as I just posted a "Basic Aircraft Design" tutorial last night and didn't know realize this was here!

[Jobin]

Thanks for the infographic, I'll probably end up referring to it at some point when I take stability & control of aircraft next Fall semester :^) A much easier read than my Aerodynamics textbook.

Edited December 5, 2013 by Jobin

[Tank Buddy]

Moar moar moar

[Zephram Kerman]

Cool tutorial.

One thing you didn't mention is how you get different controlsurface setups. (elevators versus elevons)

If you place a control surface flat without symmetry you get an elevator, while if you place them in symmetry, they are linked together across that axis and provide roll control. You can't actually have a pure aileron in default KSP because an aileron is a control surface only hooked up to the roll axis and doesn't respond to pitch control - in KSP they are either hooked to both pitch and roll (if symmetrically linked) or just pitch. (you can have vertical surfaces linked with roll control too, but that is just weird )

Anyway, another KSP issue related to that - elevators behind the Center of lift (or mass?) seem especially ineffective in KSP, especially when attached to wings that are attached mid-fuselage. This mostly because of the lawn dart syndrome you described, because without canards, the CoL shifts back away from the CoM and marginalized the elevators on the wings. So a Delta-wing style plane (or something like the space shuttle, which only has elevons on the main wings) is very difficult to make in KSP.

Remember, KSP was originally designed for rockets. Winglets on the bottom of a rocket are set up to work in combination to provide pitch, roll, and yaw, in whatever arrangement we slap together. So it helps to think of the control surface behavior as being "mapped" in the same way as RCS thrusters.

The response of a control surface is dictated by its location relative to Center of Mass. The proportion of the response is a simple SIN(°) function. So if it is put on the tail, exactly centered, it will not respond to roll inputs, only pitch. If you put two surfaces, it doesn't matter if they are linked by symmetry or not. (Turn on part clipping, and put two surfaces in the center. When they are perfectly overlapped, they will not respond to roll input.)

Same thing with ailerons. If they are placed exactly even with CoM, they will not respond to pitch inputs. (The only way I can ever do this is by mounting them flush to the top or bottom of a wing surface, near the leading edge.) Since most people put them on the trailing edge, they are behind the CoM, so KSP treats them like rocket winglets.

I'm sorry, this would be much easier to understand with sketches or a video. But I need to run off to my job!

I am looking forward to tweakables, very much.