Help needed Using jets for ascent, air intake, and TWR

[sdrevik]

I'm having difficulty figuring out how to use jets for ascent and things not following what I see other people posting.

I have a 25t craft with three Whiplash jets, with a circular air intake and three additional radial intakes each, for max airflow.

On the ground at Kerbin, it reports a TWR of 1.42, with each engine generating about 110kN thrust.

Thrust starts to fall off rapidly as it ascends, 80 each at about 3500m, and TWR drops below 1 at about 4000m. More air intakes don't seem to help.

What am I doing wrong? Or is this the best that jet engines will do?

[Workable Goblin]

Whiplashes have a very strongly speed-dependent thrust; if you can get to be reasonably supersonic (~400 m/s), then they'll run away and start generating ridiculous amounts of thrust. If you're not seeing that, my suspicion is that you're pitching up very sharply and not allowing them to speed up (which is okay anyways, you don't really want to be going supersonic at low altitudes in most cases due to drag and heating). Try staying more level and you should see a great performance increase.

It would be helpful to know whether you're trying to use them on a vertical or horizontal takeoff vehicle, too. Your strategies are going to be rather different then.

[sdrevik]

[QUOTE=

It would be helpful to know whether you're trying to use them on a vertical or horizontal takeoff vehicle, too. Your strategies are going to be rather different then.[/QUOTE]

Thanks, I'm working with them purely in vertical ascent mode, in lieu of a booster. Planning to use for landing and initial takeoff on Laythe.

Max vertical velocity probably tops out at about 150 m/s before TWR drops below 1.0. I tried the Rapier, it was worse. The original jet didn't even have TWR > 1 on the ground.

Tried posting a photo but dropbox is under maint. :(
[IMG]https://app.box.com/s/uhcqm432cyz6qeql6y6q79zh43xg8fdn[/IMG]

[IMG]https://dl.dropboxusercontent.com/u/40956047/KSP/jet.jpg[/IMG]
[IMG]https://dl.dropboxusercontent.com/u/40956047/KSP/jet.jpg[/IMG] Edited November 21, 2015 by sdrevik

[Workable Goblin]

[quote name='sdrevik']Thanks, I'm working with them purely in vertical ascent mode, in lieu of a booster. Planning to use for landing and initial takeoff on Laythe.[/quote]
Well, that's part of the problem; they're really a lot better used in a horizontal vehicle that can tolerate TWRs below 1 while reaching a height/speed profile where you can really run away with them. That being said, however...

[quote name='sdrevik']Max vertical velocity probably tops out at about 150 m/s before TWR drops below 1.0. I tried the Rapier, it was worse. The original jet didn't even have TWR > 1 on the ground.[/QUOTE]
Then your problem is not having enough of them (or, even better, rockets). You [i]really[/i] have to get Whiplashes up to supersonic speeds before they're at all good.

I get a 404 when trying to access your picture, incidentally.

[sdrevik]

I was trying to duplicate Scott Manley's lander in this video- I can't tell what's different, but I can't even see where his air intakes are for the jets, unless it's the black circles on top. At about 6 minutes, you get a close in view of the craft.

[URL]https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwi35OL-iaLJAhVMmh4KHeEFAekQtwIIHTAA&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D4m7oyrbNH58&usg=AFQjCNH6cucJw0WJBvKG1Z7hmqAVo2I1Bw&sig2=rV6QBLGyDfN1WDPBz3vtGg[/URL]

[DeMatt]

On 11/21/2015, 10:51:09, sdrevik said:

I was trying to duplicate Scott Manley's lander in this video- I can't tell what's different, but I can't even see where his air intakes are for the jets, unless it's the black circles on top. At about 6 minutes, you get a close in view of the craft.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwi35OL-iaLJAhVMmh4KHeEFAekQtwIIHTAA&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D4m7oyrbNH58&usg=AFQjCNH6cucJw0WJBvKG1Z7hmqAVo2I1Bw&sig2=rV6QBLGyDfN1WDPBz3vtGg

...that's a three-year-old video, there's been several major changes, both to the Whiplash and to the atmosphere, since that was recorded.

Try doing a seaplane instead of a VTOL instead, the latest changes to oceans make them viable: https://www.youtube.com/watch?v=ofkH4Z80IrY if you want a Scott Manley demo.

Edited November 30, 2015 by DeMatt
New forum formatting.

[sdrevik]

[quote name='DeMatt']...that's a three-year-old video, there's been several major changes, both to the Whiplash and to the atmosphere, since that was recorded.
.[/QUOTE]

Ah, well that explains it.