Best way to fly the Whiplash

[Wemb]

Been playing KSP a while now - but have pretty much avoided flight, and completely avoided SSTO's till now.

Have been watching Scott Manley's lastest vids and have built something basically the same as his Blackbird-inspired spaceplane - two LV-T45's, surrounded by a pair of Whiplash engines.

My trouble is that it's taking forever, and pretty much most of my fuel to get high and fast enough for the whiplash's do anything more than barely manage 300 in level flight.

What's the best way to fly this engine? I've noticed that when it does go supersonic it does go off like a rocket (well, Ramjet) - but what's the best way to get upto speed? Is my SSTO too heavy perhaps? Is it worth trying to boost it to supersonic speeds right off the deck with some SRBs? Should I be trying to go as fast as possible at low altitude, or get up into thinner air above 10,000m before trying to accelerate above 300+?

Any pointers would be gratefully received!

Wemb

Edited July 3, 2015 by Wemb

[Sharpy]

Not enough power. Too heavy or too draggy plane for just two engines.

Whiplash has a funny power curve: it climbs quite well towards 300km/h, then its power drops until some 400km/h, where it becomes a power demon until 1000km/h, where it begins to weaken again, making reaching 1300km/h a feat.

If you fall into the 300km/h hole and can't climb up to 400, due to drag, you won't reach the hypersonic speeds. You could dive to speed up, but it's much better to either make your plane lighter or less draggy, or add more Whiplashes.

[A_name]

Not enough power. Too heavy or too draggy plane for just two engines.

Whiplash has a funny power curve: it climbs quite well towards 300km/h, then its power drops until some 400km/h, where it becomes a power demon until 1000km/h, where it begins to weaken again, making reaching 1300km/h a feat.

If you fall into the 300km/h hole and can't climb up to 400, due to drag, you won't reach the hypersonic speeds. You could dive to speed up, but it's much better to either make your plane lighter or less draggy, or add more Whiplashes.

Seconded.

[Prepper-Jack]

Engineering an appropriate TWR is important for the whiplash. As Sharpy said ... with too little, you're not going to go hypersonic. However, the other direction is even more disastrous- as too much engine can easily lead to detonations below 10km if you don't hold back on the throttle. That said, you still want enough to climb at 45 degrees and hit peak speed before 25km or so - which can be close to 1500 m/s with enough turbos.

[selfish_meme]

They are talking about the rapier, the whiplash is the turbojet engine. Two should have no trouble getting a small plane to 1000m/s at 10km in level flight. Are you talking about the whiplash or the rapier?

[Sharpy]

@Selfish: Rapier has a little more power than Whiplash (something of order of 10%).

Considering the use of LV-T45, that sounds definitely like Whiplash (there's really little point to take two Swivels if you have Rapiers on board already.)

[Wemb]

The Whiplash - haven't unlocked the rapier yet. Certainly haven't been able to get my thing going fast enough to disintegrate, so I'm guessing I've built it too heavy - certainly am taking into orbit, when I finally get there, too much oxidiser - so I might try emptying on the fuel tanks - feeds so counter-intuituive though, since I'm already using almost all fo the fuel in my payload's tank, let alone the launch vehicle.

Thanks everyone.

[Sharpy]

Yes, SSTOs are tricky. SST&FO are even trickier. You'll grind your teeth and rip your hair before you get any considerable payload to the orbit - either it's too heavy, or too flip-happy, or doesn't turn into a good climb after gaining the speed, or overheats too fast, or can't reach orbit in time due to too weak rocket engines, or eats up all fuel before reaching the orbit due to too fuel-hungry engines, then you get the rockets right and your Whiplashes are too weak again, then you add whiplashes and it becomes flip-happy again...

And then, you grin happily when you reach the orbit, perform the reentry burn, and realize you've only made it halfway through the challenge yet.

[xtoro]

When you're at the point of trying to hit 400m/s, you can also toggle your rockets on for a bit just to get up to speed and then shut them off once the jets start screaming. This can save you some time and LF for finicky planes that can't go on jets alone.

[Wemb]

When you're at the point of trying to hit 400m/s, you can also toggle your rockets on for a bit just to get up to speed and then shut them off once the jets start screaming. This can save you some time and LF for finicky planes that can't go on jets alone.

Ooo - good idea - hadn't even thought of doing that...

Thanks again.

[capi3101]

The old rule of thumb used to be 15 tonnes per Turbojet (a.k.a. Whiplash engine) for the souposphere at takeoff; to the best of my knowledge, it still applies. If you can't get above 300-400 m/s within that limit, it's definitely time to look at how much drag you've got going on.

Can we take a look at some screenies of your craft, purdy please (preferably a side shot, top down shot and aft shoft in the SPH)? We might be able to give you more specific advice if you do.

[Wemb]

I'm not at my PC at the moment - but as I said, I took, err, inspiration, from this video - figuring if SM can do this, the design should be sound - but he does seem to be able to point it at ~30deg off the deck and accelerate at the same time. albeit without a payload.

[ajburges]

I find that the new drag rules throw most old rule of thumb wisdom out the window. Best to just try it out once you understand and can fly the generic flight profile.

In aerobic flight, the most demanding point on engine power is the sound barrier. If you can pass that, you can get to the edge of aerodynamic performance. If you are on the edge of power requirements, a shallow dive can give you the additional energy needed to advance to Mach 2. RAPIERs have some of their best power to pressure at 10 km so plan your dive to be at 400 m/s at that height. Whiplash engines don't have an obvious height to dive through, but it can be difficult to maintain a climb past angels 12 if you need that dive for power.

Anerobic mode design is simply a matter of having 1600 m/s or more dV and unity or better TWR.

[selfish_meme]

I have not noticed whiplashes having a significant acceleration hump, unlike the rapiers, which is why I am confused. This has gone to orbit and returned, I am sorting out payload now (it turns out I probably no longer need so much room). It weighs around 80t wet and achieves 1250m/s at around 11-12k on just the whiplashes. It doesn't even need the nuke (in fact is a lot better balanced) without, it was just there for a mission idea I had which probably won't work out. This was based on my payload fraction challenge entry, just .....expanded. The frontmost fuel tank needs to be disabled during ascent to balance the nuke. Once in space transfer all fuel to the large tank in front of the cargo bay.

Edited July 2, 2015 by selfish_meme

[Wemb]

I have not noticed whiplashes having a significant acceleration hump, unlike the rapiers, which is why I am confused...

It's the change in versions - Scott Manley, whose design I ripped off, has just posted a video describing exactly what I'm seeing in the new version - his design can't be flown as agressively in the latest version as before - I'll drop a fuel take and dump some oxidiser which was a problem with my design - this looks to be the solution that SMs doing to.

Thanks for all the advice guys - I'll mark this as answered as soon as I read how to mark this as answered.

Cheers, Wemb