"simple" rule to build spaceplanes?

[Gooru]

I really love this simple method to build rocket launcher for any given payload. Thanks to kerbiloid for it.

Is there something similar for spaceplanes?

I watched a lot of videotutorials how to build planes, but most of them are just "build this! and it will fly!" without further instructions or hints.

I´d like to have a "set of rules" to estimate the total liftrating, thurst and delta-V i need for a given mk2 plane hull for example.

How do you build your planes?

Edited September 13, 2015 by Gooru

[Supernovy]

Figuring out a simple method for planes will definitely be harder than one for rockets. In a rocket, whether you lift off or not only depends on your thrust and your weight. For a plane, it'll depend on the amount of wing, the weight, speed, angle, and air density.

Though I have heard "1.2 lift rating per tonne of mass" before as a rule of thumb. That may have been for pre-1.0, though.

[selfish_meme]

1 lift per 10t

1 rapier per 16t max (20+ for pros )

Do not use external struts or fuel lines

Put very low drag things in front of everything something like shock cones.

You must achieve at least 1200ms on air by 20000.

Rapiers are not working properly until you are over 400ms. So go fast low

Flying Rapier powered spaceplanes

A spaceplane designed by those principles, takes a full orange tank to orbit on four rapiers and a whiplash

Jet/Rocket powered is basically the same though you don't need to get over 400ms down low, try and hit 1000ms by 10km, 1300ms by 20km, switch to rockets and follow a little behind the prograde marker till you are out of atmosphere (35km+) and then on the prograde marker until you reach your desired apoapsis. It should take virtually no dV to circularise.

Edited September 7, 2015 by selfish_meme

[RizzoTheRat]

How do you build your planes.

Badly

I've been following a pretty basic evolutionary approach. Started with a small atmospheric craft and discovered that I could hit about 20-22km and 1000-1100m/s with the Whiplash ramjets. Then I added rockets and found it took a lot more dv than I expected to hit orbit (in previous versions you could could hit orbit with very little rocket power), so I added more rocket fuel and found I needed another Whiplash to get the speed/altitude, then I found I needed more wing as I had to have such a high AoA it was to draggy...

I shall be watching this with interest as I could do with some simple rules. I think in 0.9 I used to reckon 1 lift rating for every 2 tonnes, but I haven't quite figured out an optimum wing loading in 1.0, looking at other people's designs many seem to be using more engine and less wing than me at the moment.

[GoSlash27]

Gooru,

The ratio of parts required varies with the parts you're using. An early career passenger shuttle with Mk2 parts is a different beast than a late career tanker with Mk 3 parts.

For a simple early career crew shuttle it goes like this:

for every 5t cargo (everything that isn't either engine, fuel, oxidizer, tank, or wing) you will need roughly:

1 Whiplash

2 LV-909s

10t lf&o to feed the rockets (450/550)

400 fuel to feed the Whiplash (about 1.76t)

Put that all together as aerodynamically cleanly as you can (don't forget the ram air!) and then total up your mass. You should be around 19t per 5t payload.

For wings, there's a surprisingly wide range of ratios that can work. The important thing isn't so much "lift to mass", but rather "zero nose incidence at Mach 1". You can do this with small wings at high incidence or large wings at low incidence.

A good starting point would be mass/3 with 2° incidence (3 clicks of fine rotation).

This is good for roughly 26% mass efficiency (payload/ total mass)

High tech tanker to follow...

- - - Updated - - -

for a High tech Mk3 tanker/cargo design:

1 RAPIER for each 10t cargo

1 shock cone per RAPIER

1t LF&O for each tonne of cargo (err to the high side a little).

2.8t jet fuel per 10t payload

Same deal with the wings; it's all about the angle of attack. It's more important to minimize wing panel count to avoid strutting than worry about an exact wing/ mass ratio. You can make up for small wings with incidence... up to a point. mass/10 at an incidence of 10° will work, or you can do larger wings at lower incidence like mass/3 at 2°.

As you move away from these "extreme efficiency" designs towards higher t/w designs, wings and aerodynamics in general become less critical, but you will need to increase the ratios of jet fuel, rocket fuel, and engines to payload to compensate.

This is good for roughly 31% mass efficiency

At the other extreme, the high t/w vertical RAPIER lifter.

One RAPIER for each 1.5t of payload

2t LF&O per RAPIER

.75t jet fuel per RAPIER

and of course wings are unnecessary.

This yields roughly 23% mass efficiency.

Best,

-Slashy

- - - Updated - - -

Badly

I've been following a pretty basic evolutionary approach. Started with a small atmospheric craft and discovered that I could hit about 20-22km and 1000-1100m/s with the Whiplash ramjets. Then I added rockets and found it took a lot more dv than I expected to hit orbit (in previous versions you could could hit orbit with very little rocket power), so I added more rocket fuel and found I needed another Whiplash to get the speed/altitude, then I found I needed more wing as I had to have such a high AoA it was to draggy...

I shall be watching this with interest as I could do with some simple rules. I think in 0.9 I used to reckon 1 lift rating for every 2 tonnes, but I haven't quite figured out an optimum wing loading in 1.0, looking at other people's designs many seem to be using more engine and less wing than me at the moment.

Rizzo,

Just for you, here's how I evolve a design:

First off, all rules of spaceplane construction apply. You want balance, low drag, minimal strutting/ piping, etc.

You can expect roughly 4 tonnes of spaceplane for each tonne of payload (varies with efficiency), so just scale it up.

Decide what combo of engines you want and plan accordingly.

Now here's the trick: Build the entire thing out of fuel tanks. No payload, just fuel.

The objective is to get it supersonic, then hypersonic at altitude, then finally into orbit.

See how much mass you can get on it until you can't do it anymore, then back it off.

You always want to find ways to improve efficiency and eliminate unnecessary weight and drag rather than adding engines or fuel.

Whatever mass of fuel and oxidizer you have left in orbit (minus your reserve for orbital maneuvering and deorbit) is how much payload that design can handle.

Once you're satisfied, take note of all the ratios you used to accomplish it and build another with actual payload replacing the unused LF&O.

Best,

-Slashy

Edited September 7, 2015 by GoSlash27

[GoSlash27]

I knocked together a quick and dirty "cheat sheet" for RAPIER powered spaceplanes.

Lower payload per RAPIER makes a very fast trip to orbit and less emphasis on clean aerodynamics. Higher payload per RAPIER means that being aerodynamically clean is much more critical and the trip will take longer, but has higher efficiency.

So for example:

You have 20 tonnes of payload and decide to use 5t per RAPIER; 4 RAPIERs.

You would refer to the chart for jet fuel and multiply that number by your payload.

.43*20= 8.6t of jet fuel.

Same for rocket fuel. 1.2*20= 24t of rocket fuel

You would build this, then note the total mass. (somewhere around 80t)

multiply this by the lift value (.14) to get the total lift value of wings; about 12.

This is rough, but should get you in the ballpark.

Best,

-Slashy

[Just Jim]

Wow.... I've been working on a smaller SSTO the last few days, and this thread just answered a ton of questions I had.... thanks!!!!

[tbarcello]

1 lift per 10t

1 rapier per 16t max (20+ for pros )

Do not use external struts or fuel lines

Put very low drag things in front of everything something like shock cones.

You must achieve at least 1200ms on air by 20000.

Rapiers are not working properly until you are over 400ms. So go fast low

Flying Rapier powered spaceplanes

A spaceplane designed by those principles, takes a full orange tank to orbit on four rapiers and a whiplash

Jet/Rocket powered is basically the same though you don't need to get over 400ms down low, try and hit 1000ms by 10km, 1300ms by 20km, switch to rockets and follow a little behind the prograde marker till you are out of atmosphere (35km+) and then on the prograde marker until you reach your desired apoapsis. It should take virtually no dV to circularise.

Wow! That is completely different from my ascend, when I'm trying to escape thick atmosphere asap and then choking at 7k. No wonder I can't get them to orbit! Thank you so much!

- - - Updated - - -

Wow.... I've been working on a smaller SSTO the last few days, and this thread just answered a ton of questions I had.... thanks!!!!

Feel ya, bro!

Edited September 8, 2015 by tbarcello
Hate mobile typing

[Tarheel1999]

GoSlash27 - Question about incidence. Are you referring to the angle of the wings (anhedral/dihedral) or are you referring to the position on the fuselage? And if angle I assume you are referring to dihedral and if position I assume you are suggesting placing the wings slightly higher than the center of mass. Please correct me if I've misunderstood.

[Starhawk]

GoSlash27 - Question about incidence. Are you referring to the angle of the wings (anhedral/dihedral) or are you referring to the position on the fuselage? And if angle I assume you are referring to dihedral and if position I assume you are suggesting placing the wings slightly higher than the center of mass. Please correct me if I've misunderstood.

[Tarheel1999]

The angle of incidence referred to is completely different from anhedral/dihedral.

With angle of incidence, the leading edge of the wing is higher than the trailing edge. This gives the craft some lift even when the fuselage is pointed directly prograde.

Happy landings!

Thanks. So the answer was none of the above. Doh! I blame lack of coffee for my silliness.

[Just Jim]

OK, after reading this thread and taking some notes last night, I re-designed my SSTO prototype. The new one hit 1200 m/s at 22,000 meters... at a 20 degree incline!!! I could have gotten her much faster if I leveled out a little, but there was a storm rolling in, so I stopped at that point. She still needs more testing, but this one is finally close.

Thanks all for the great info here!!!

It's really helped me pin down what I've been doing wrong.

[Gooru]

Wow! Thanks for the great answers. This was exactly what i was looking for

[Gooru]

My plane has a mass of 32t, 2 whiplash and a liftrating of 7.

I´ve got problems with the angle of incidence.

When i tilt my wings up as described it gets harder to lift off.

The nose always wants to go down. I can´t even fly the thing.

It also gets nearly impossible to reach mach 1.

It seams the wing simply works like a pitched down elevator

Edited September 9, 2015 by Gooru

[Edax]

Another simple rule is that when your SSTO is traveling 850-1450 m/s via air-breathing engines is to keep the front pointed prograde as much as possible, as during the phase, the spaceplane will be very sensitive to drag and pitching the plane could cause a large loss in delta-v.

[The_Rocketeer]

My plane has a mass of 32t, 2 whiplash and a liftrating of 7.

I´ve got problems with the angle of incidence.

When i tilt my wings up as described it gets harder to lift off.

The nose always wants to go down. I can´t even fly the thing.

It also gets nearly impossible to reach mach 1.

It seams the wing simply works like a pitched down elevator

Angle of incidence has unusual effects on the relationship between CoM and CoL depending on your whole craft's attitude - it's not quite as simple as the two points moving completely relative to each other, because the direction of lift also changes - think about the effect that has when you move an engine and shift the CoT. To try to understand the issues you might have with pitched wings, experiment with tipping the whole craft in the VAB and look at the where the CoL/CoM are after you've tipped it. You might find that getting a clean take-off means rethinking your gear layout and rearranging fuel mass.

[GoSlash27]

My plane has a mass of 32t, 2 whiplash and a liftrating of 7.

I´ve got problems with the angle of incidence.

When i tilt my wings up as described it gets harder to lift off.

The nose always wants to go down. I can´t even fly the thing.

It also gets nearly impossible to reach mach 1.

It seams the wing simply works like a pitched down elevator

Gooru,

You usually have to move the wings forward a bit after increasing the incidence to keep your balance.

Best,

-Slashy

[Val]

My plane has a mass of 32t, 2 whiplash and a liftrating of 7.

I´ve got problems with the angle of incidence.

When i tilt my wings up as described it gets harder to lift off.

The nose always wants to go down. I can´t even fly the thing.

It also gets nearly impossible to reach mach 1.

It seams the wing simply works like a pitched down elevator

There are a couple of things you can try.

(Having not seen your plane, I'm assuming from your description, that your wings are mostly behind CoM)

- Move the wings forward or CoM back until it becomes pitch neutral again.

- If you have canards/elevators in the front of the plane, give them Angle of Incidence, too (if you didn't already).

Hope it helps.

Edit: Ninjaed by Slashy.

[Gooru]

What is wrong if my plane flips over backwards and the CoL is behind the CoM?

Should i turn SAS on or off?

Should i turn torque on or off?

Edited September 9, 2015 by Gooru

[The_Rocketeer]

What is wrong if my plane flips over backwards and the CoL is behind the CoM?

At what speed? If your speed is too high at low altitude, drag can cause you to flip.

CoL, CoM and CoT all (ideally) need to be in line with each other as well as being in the right order. Having any out of vertical alignment could cause problems, in the situation you describe possibly CoT being below CoM.

It could also be excessive steering input. Try setting your engine gimbals to locked.

Edited September 9, 2015 by The_Rocketeer

[Gooru]

I instantly flip over on takeoff. CoL, CoM and CoT are in line. CoL slightly behind CoM.

[GoSlash27]

Gooru,

There's a lot of things that could make that happen. We'd need to see a pic of your spaceplane. Preferably in the hangar with the CoM and CoL showing.

Best,

-Slashy

[Just Jim]

I finally got one into orbit!!! WOOHOOOOOOO!!!!!!!!!!!!!!!!!!

I can't thank the OP enough, and everyone else that chimed in on this thread, for all the great information! SSTO's have been the one thing I couldn't tackle, but this thread really helped me figure out what I was doing wrong!!!

Kerbal players are the best!!!

Thank you everyone!!!

[GoSlash27]

JustJim,

Congrats!

Best,

-Slashy

[selfish_meme]

I finally got one into orbit!!! WOOHOOOOOOO!!!!!!!!!!!!!!!!!!

http://i.imgur.com/qIsOpo7.png

http://i.imgur.com/5jDt3TP.png

http://i.imgur.com/T7VPiy6.png

I can't thank the OP enough, and everyone else that chimed in on this thread, for all the great information! SSTO's have been the one thing I couldn't tackle, but this thread really helped me figure out what I was doing wrong!!!

Kerbal players are the best!!!

Thank you everyone!!!

Well done!