Build an MK3 Spaceplane after 0.90 update

[Fire-Dragon-DoL]

I'm having a few troubles, expecially even with micro amount of fuel, I find myself missing THRUST. I'm experimenting with rapier engines, but I really miss enough thrust to even lift off this guy...

Any suggestion? Did anyone try to build a spacecraft with those pieces?

I would like to avoid applying simple rocket engines, defeat the entire purpose

Edited December 29, 2014 by Fire-Dragon-DoL

[Rakaydos]

Supposedly the design would be more efficient with only 1 layer of wing/secondary hull, but I managed to brute force this thing from 1400m/s to orbit on raipers alone.

[Anquietas314]

This was a design I managed to get to orbit (after adding a whole bunch of intakes):

It just barely made it off the runway in one piece though.

I don't have a newer screenshot of it handy - I made it in sandbox a few days ago.

[Fire-Dragon-DoL]

Need a few suggestions, where did you put the rear wheels? It's a bit hard. Also, on the first picture, how did you stack 2 mk2 tanks one over another? It's very weird shaped (p.s. the first screenshot is really cool O.o)

The second guy is a big fatty beast, but that's definitely a great space station refueler, which is what I'm aiming for

[Anquietas314]

Need a few suggestions, where did you put the rear wheels? It's a bit hard. Also, on the first picture, how did you stack 2 mk2 tanks one over another? It's very weird shaped (p.s. the first screenshot is really cool O.o)

The second guy is a big fatty beast, but that's definitely a great space station refueler, which is what I'm aiming for

In my case the wheels were on the rocket fuel tanks nicely spaced (the ones with grey stripes)

It actually makes a horrible station refueler because it took almost all of the fuel to get to orbit.... and that cargo bay only has an empty orange tank in it.

Edited December 20, 2014 by armagheddonsgw

[Fire-Dragon-DoL]

Are there anything something like a "lift calculator"? It's quite hard to calculate how many wings I need to keep this fat guy in air

[Fire-Dragon-DoL]

In my case the wheels were on the rocket fuel tanks nicely spaced (the ones with grey stripes)

It actually makes a horrible station refueler because it took almost all of the fuel to get to orbit.... and that cargo bay only has an empty orange tank in it.

Oh THAT'S A CARGO BAY, I thought it was fuel!

I can definitely confirm, we need a new engine for this beast. Or we make a very small spaceship like the first one.

[Rakaydos]

You can use the Offset gizmo to move the Mk 2 tanks up and down the side of the Mk3 hull

My 4 rear wheels are all 1 snap off center of the lower Mk2 hulls, 1 snap rotated, so they are vertical and all the same height. Then I offset them 1 snap into the hull so they didnt stick out.

[Fire-Dragon-DoL]

So this guy can't lift off, damn.

Probaby more wings considering the TWR is ok, but it's getting somewhat insane.

[Anquietas314]

So this guy can't lift off, damn.

Probaby more wings considering the TWR is ok, but it's getting somewhat insane.

https://dl.dropboxusercontent.com/u/762638/Files/Images/Screenshots/mesorotshots/2014-12-20_21-17-38.jpg

It's quite common for planes to not be able to "lift off" the runway. As long as you can get moving upwards before you hit the ground after flying off the edge, you're fine (in the case of mk3 spaceplanes, "hitting the ground" = plane falls to bits and goes boom)

Also, I would recommend swapping some of the rapiers for turbojets. They're more fuel efficient for getting to orbit and have higher thrust, plus you really don't need that much TWR in space

Edited December 20, 2014 by armagheddonsgw

[Brownhair2]

I'm currently having trouble getting a normal Mk 3 plane off the ground, I think using the Mk 2 parts is a good idea, since they provide lift and fuel.

As for a new engine, I was actually doing some research for this very purpose, and I found most jet engines are actually only as strong as the Basic Jet Engine. The most powerful engine I could find was the General Electric GE90, which actually is pretty powerful, but is a turbofan. Still, something like it in KSP would help.

[JTpopcorn]

Try raising the height of the front wheel, it should help you take off before the end of the runway. Also make sure the rear wheels arent to far back. Also for those discouraged look at this https://www.youtube.com/channel/UCR_h4FgyRszrWfo0-LJAm6A

As for a new engine, maybe a 2 meter jet, like b9 would work, but turbofans really should be added.

[Hodo]

http://i.imgur.com/rTFjCL4.png

Supposedly the design would be more efficient with only 1 layer of wing/secondary hull, but I managed to brute force this thing from 1400m/s to orbit on raipers alone.

It would have been more efficient to not make a biplane.

[Rakaydos]

It would have been more efficient to not make a biplane.

Isnt that what I just said in your quote?

[Hodo]

Isnt that what I just said in your quote?

I meant to say more but was side tracked by work...lol.

But yes, as Ferram said in the FAR thread biplanes are just not that great at supersonic speeds. They create more drag then lift at that point. You would be surprised at how much better the craft would fly with a bit more actual wing to the craft, you shouldn't have any problem with getting higher. I have a much larger SSTO that can reach Geosync orbit from the ground it has a bit to much in the way of wing area and actually was able to land at just above 60m/s with a rate of decent of less than -2m/s.

I know it isn't the new Mk3 parts but I have only JUST updated to .90 because most of my mods are finally updated.

[GoSlash27]

Are there anything something like a "lift calculator"? It's quite hard to calculate how many wings I need to keep this fat guy in air

If you're running stock, you'd want to have the sum of the lift coefficients of your wing sections to equal the aircraft mass in tonnes. That gives a good balance between lift and drag.

example: a 75 tonne spaceplane would need the lift coefficients of it's wing panels to total 75. You'll still be okay if you're over this; it doesn't have to be exact.

The large wing connecters and delta sections have a lift coefficient of "2" per panel, so you'd want at least 38 of these panels total, or 19 panels per wing.

Check out my basic spaceplane tutorial from 0.25 here:

http://forum.kerbalspaceprogram.com/threads/102182-So-you-want-to-build-a-space-plane

If you're running FAR, I have no idea.

Good luck!

-Slashy

Edited December 20, 2014 by GoSlash27

[Hodo]

For FAR you can run the diagnostic tool in FAR in the SPH. Set in the first tab, your desired test speeds in mach, I like to run up to mach 6 and leave it 0-50 test points.

This will give you your important information. The most important line to pay attention to is the green line on that graph.

As long as your L/D is above your C/D line you should be good. Ideally you want your c/D line to stay as low as possible this is the amount of drag your craft is generating as it goes faster. The L/D is lift vs drag. the higher this number the higher lift you are creating vs the amount of drag you are experience. Most of my craft have a L/D ratio of about 3:1 or better.

Edited December 20, 2014 by Hodo

[Rakaydos]

Actually, looking at my craft family in the editor... with the wings separated by the thickness of a Mk2 hull (so, a bit over 1.25m) and two delta wings long at the root (call it 6x 1.25m=7.5m), unless there's something weird going on with supersonic airflow, I shouldnt get any loss of performance until I hit an angle of attack of... (googles geometry from years ago)

CoTangent N degrees = adjacent/opposite = 1.25/7.5 =1/6 of 90 degrees, call it, 15 degrees.

Did my math fail me? is supersonic airflow doing weird things to simple geometry?

[Anquietas314]

Actually, looking at my craft family in the editor... with the wings separated by the thickness of a Mk2 hull (so, a bit over 1.25m) and two delta wings long at the root (call it 6x 1.25m=7.5m), unless there's something weird going on with supersonic airflow, I shouldnt get any loss of performance until I hit an angle of attack of... (googles geometry from years ago)

CoTangent N degrees = adjacent/opposite = 1.25/7.5 =1/6 of 90 degrees, call it, 15 degrees.

Did my math fail me? is supersonic airflow doing weird things to simple geometry?

Supersonic airflow is fairly well known for doing very weird things, so chances are your model's a bit too simplistic I have no idea the extent to which FAR accurately models real-world physics though.

(disclaimer: I am not a physics expert)

[Hodo]

Supersonic airflow is fairly well known for doing very weird things, so chances are your model's a bit too simplistic I have no idea the extent to which FAR accurately models real-world physics though.

(disclaimer: I am not a physics expert)

FAR does an extremely good job of it, it isn't perfect but it is way better than stock.

[Anquietas314]

FAR does an extremely good job of it, it isn't perfect but it is way better than stock.

Oh I know that part, I was referring specifically to the airflow physics - i.e. does it do some sort of particle-based simulation or just use a decent mathematical model?

[Hodo]

Oh I know that part, I was referring specifically to the airflow physics - i.e. does it do some sort of particle-based simulation or just use a decent mathematical model?

Mostly mathmatical, I believe.

[Anquietas314]

Mostly mathmatical, I believe.

Figures I guess. Detailed particle simulations are really hard to do in real-time, especially in a game like KSP where there's a hundred(thousand?) other things happening at the same time

[Fire-Dragon-DoL]

It's quite common for planes to not be able to "lift off" the runway. As long as you can get moving upwards before you hit the ground after flying off the edge, you're fine (in the case of mk3 spaceplanes, "hitting the ground" = plane falls to bits and goes boom)

Also, I would recommend swapping some of the rapiers for turbojets. They're more fuel efficient for getting to orbit and have higher thrust, plus you really don't need that much TWR in space

It's meant to be a refueler (that's why so much delta v), that's why rapiers, I don't need efficency in space, I just need to reach orbit.

About the plane I know, but in this case, it doesn't lift off at all: when I reach the end of the runaway (at 140 m/s), I can point the nose ~20° up, but the plane looses altitude in any case, it looks quite clear that I don't have enough lift, sigh

[Anquietas314]

It's meant to be a refueler (that's why so much delta v), that's why rapiers, I don't need efficency in space, I just need to reach orbit.

About the plane I know, but in this case, it doesn't lift off at all: when I reach the end of the runaway (at 140 m/s), I can point the nose ~20° up, but the plane looses altitude in any case, it looks quite clear that I don't have enough lift, sigh

Like I said, turbojets are more fuel efficient *in the atmosphere* that means you can reach orbit with more fuel! RAPIERs are nice on small planes because it means you don't need 2 kinds of engines. When you have loads of them that benefit disappears, so it's better to use turbojets (which will make it easier to get off the ground! more thrust!) for atmospheric flight and dedicated rockets for when you're ready to go to orbit. You can also get out of the atmosphere using only the turbos.