"simple" rule to build spaceplanes?

[Val]

Thanks for all these advices!

About the cyan arrow, why both crafts, created differently had this asimmetric body lift? Something about the design? Do you have any idea what it might be?

About the craft, here it is without lights and without mk1cargobay. I used an almost empty tank to simulate its weigth, though. I think the main difference is that the tank is a "bit" longer than the two cargo bays...

About mechjeb, thanks, I'll try it (until now I've only used the node executor and the precise landing assistant)...

EDIT: Hey, Val, I've tried MechJeb and got a worse result (210m/s), removed two of the intakes and it got even worse (no orbit). I think my (space)plane takes too long to get to 300m/s. If you have time, can you please fly its stock version (above)?

Sorry, the craft still won't load in my install.

Both the game and KerbalX reports it as having mods still.

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[Van Disaster]

How do you build your planes?

I built planes with 1.0 aero just long enough to realise it was still soup & went back to FAR, but newAero is just enough on the realism side for the same principles.

Build the fuselage around the payload - balance tanks either side of the cargo bay so your CoM doesn't move when you empty them. Add wings until it looks like it has enough wings - just go stare at real life aircraft until you get some idea of proportions. Make sure you have enough control authority - that's surface area of controls X distance from CoM. Add engines until it's got about 0.4 jet TWR - if you're using Rapiers that will probably be plenty of rocket power. Launch it, fly it to 21km; if you're pitching up more than 15 degrees then add more wing.

That's it, basically.

[jlcarneiro]

Sorry, the craft still won't load in my install.

Both the game and KerbalX reports it as having mods still.

[---SNIP---]

Sorry! Forgot to delete one part. Could you please try this craft file? I'm really curious, I just can't make it get speed fast enough. Maybe it's just me, but could be a mistake, when you replicated the craft you inadvertently correct it...

- - - Updated - - -

[...]

Launch it, fly it to 21km; if you're pitching up more than 15 degrees then add more wing.

[...]

Hmmm! Interesting, I tried to keep its wings small (due to the high speed)... I'll try this idea, thanks!

[Van Disaster]

There is a point where you're causing more drag by pitching too much than you would by adding wing, that's the point you need to find. You'll use less fuel getting to 21km with more wing, too.

I should clarify: 15 deg AoA ( it's not a hard number, that's just the approximate limit I use ), but if you're at 21km gaining speed your AoA & pitch are going to be the same.

Edited September 27, 2015 by Van Disaster

[Val]

Sorry! Forgot to delete one part. Could you please try this craft file? I'm really curious, I just can't make it get speed fast enough. Maybe it's just me, but could be a mistake, when you replicated the craft you inadvertently correct it...

I got it to orbit with ~1250 m/s, but I had to make 2 small changes before it was flyable.

1. Landing gear was too far back.
   
2. Tail fin/Vertical stabilizer was too far forward.
   

CoL was also a little too far back, probably because the parts you replaced were shorter than the replacement, so this might not be a an issue on the original.

Craft file: Epsilon2 (Mk.2)

More details and ascent described in album.

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[jlcarneiro]

I got it to orbit with ~1250 m/s, but I had to make 2 small changes before it was flyable.

1. Landing gear was too far back.
   
2. Tail fin/Vertical stabilizer was too far forward.
   

CoL was also a little too far back, probably because the parts you replaced were shorter than the replacement, so this might not be a an issue on the original.

[---SNIP---]

Once again, thank you very much! As I suspected, I noticed some differences between "my" Epsilon2 and "your" Epsilon2:

1. Your landing gear is on the main fuselage, I put them on the wings.
   
2. Your plane stays at zero degrees, it seems only the wings' AOA is responsible for the lift (although the plane did not take off on its on, I had to lift the nose).
   
3. I'm definetely not a good pilot. Even with the help of Pilot Assistant (to keep que pitch angle), I was not able to get to 450m/s as fast as you did.
   

But I managed to get to orbit (250km/250km, the altitude of my future station) with about 300m/s dV left.

I have a LONG way to go yet, but as I said before, thank you very much!

EDIT: BTW, where can I find a guide telling me how far some dV will take me? I mean, if I'm on a 80x80 orbit and have 100m/s dV, how far can I go? And how much do I need to get back to Kerbin? Things like that... Those deltaV maps answer these kind of questions, but for a different (and much larger) scale...

Edited September 30, 2015 by jlcarneiro

[GoSlash27]

EDIT: BTW, where can I find a guide telling me how far some dV will take me? I mean, if I'm on a 80x80 orbit and have 100m/s dV, how far can I go? And how much do I need to get back to Kerbin? Things like that... Those deltaV maps answer these kind of questions, but for a different (and much larger) scale...

This can be answered by the uniform circular motion and vis-viva equations.

v= sqrt(GM/r)

where

v=orbital velocity in m/sec

G= universal gravitational constant 6.67x10^-11

M= parent body mass in grams

r= orbital radius in meters (from parent center, *not* altitude)

v= sqrt(GM(2/r-1/a))

same as above and

a=semi-major axis; the mean radius of your elliptical orbit

If you're in an 80x80 orbit then you have an orbital velocity of 2279 m/sec.

If you wish to deorbit, then the cost in DV depends on where you wish to set your periapsis. I usually go for 45km. Setting that up would require a retroburn of 30.3 m/sec.

If you wanted to set up an elliptical orbit with an 80 km periapsis with 100 m/sec DV, you could set your apoapsis to 214,000m.

You could do a hohmann transfer to a 144,000m circular orbit.

Best,

-Slashy

Edited September 30, 2015 by GoSlash27