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Taking off from water


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So I have an SSTO plane that I want to be able to land on the ground or the water. I haven't played for a while so the water is new to me. I managed to land in one piece consistently now, but taking off is another thing. Despite 4 RAPIERS, my top speed in the water is 30 m/s. I must be dragging a lot, although my underside is made of nothing but fuselage, wings and landing gear (which of course I have retracted), so there's nothing I can get rid of. And even if I could go faster, there's the problem of pitching up, it just won't. I suspect this is because my "fulcrum" is way behind my COM at the back edge of the wings (it's a delta wing design). So that's my problem, I'm hoping to hear some ideas on how to solve it.

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Unfortunately KSP's water is very thick. Getting a high speed in it is very difficult and not breaking anything at those high speeds is even more so. Before trying to get faster in the water to takeoff, I suggest writing down you takeoff speed in land, then landing as gently as you can in the water, while staying at that speed. This will determine whether or not you would be able to takeoff from the water without things breaking. 

If you can do that, then maybe try SRB's for water takeoffs? The mk2 expansion pack has radially attachable SRBs intended for speed bursts on takeoff, which then detach. You could either keep them in all the time or attach them with KIS when it's time to go. 

TL;DR version is

a) Test to see if you can takeoff in water with breaking

b) Try SRBs. 

c) Moving the fulcrum towards the centre of mass is also good. I normally try to get the centre of life just behind the centre of mass.

I hope I have helped,

Benji13.

 

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4 rapiers and 30 m/s? That's just nuts. Something must be wrong. Is this an MK2 design?

It is possible to create a hydroplane in KSP. You can put little fins on pylons, and they can raise the rest of the plane above the water -- or maybe just the front end to gain you some pitch.

If you can't pitch up, then my recommendation would be to pitch down. Go submersible, dive to 50 or 100 meters, then get the nose pointed up. You will come out of the water with a lot of speed and force -- probably quite a bit too violently, but it's something you can try anyway.

 

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Thank you all for your replies. First off, I want to share a few things I tried that didn't work:

I placed radial intakes, four at the back and two one at the front, hoping it would give me some floatability. They didn't, and only dragged me down reducing my top speed to about 25 m/s.

Then I used the large Big-S elevons placed in front of the COM and bound their deploy function to action groups to use as flaps to temporarily shift the COL forwards and force the nose up. This helped a little bit, the nose did pitch up like one degree, and I was actually able to hit about 35 m/s but sadly not enough to become airborne. I tried these with and without the intake floats, neither worked.

Minimum takeoff speed on the runway is 45 m/s.

 

2 hours ago, Benji13 said:

 

Unfortunately KSP's water is very thick. Getting a high speed in it is very difficult and not breaking anything at those high speeds is even more so. Before trying to get faster in the water to takeoff, I suggest writing down you takeoff speed in land, then landing as gently as you can in the water, while staying at that speed. This will determine whether or not you would be able to takeoff from the water without things breaking. 

If you can do that, then maybe try SRB's for water takeoffs? The mk2 expansion pack has radially attachable SRBs intended for speed bursts on takeoff, which then detach. You could either keep them in all the time or attach them with KIS when it's time to go. 

TL;DR version is

a) Test to see if you can takeoff in water with breaking

b) Try SRBs. 

c) Moving the fulcrum towards the centre of mass is also good. I normally try to get the centre of life just behind the centre of mass.

I hope I have helped,

Benji13.

 

 

I am able to land in the water without breaking. I get it down to just under 50 m at around 100-150 m/s, put on the air brakes and just hang out there keeping my vertical speed to -1 or 2 m/s while my horizontal speed dies out until I stall and fall in. It usually happens at about 50 m/s (my takeoff speed is slightly lower, but I attribute that to the RAPIER's thrust when pitching up.

I'll consider the SRB. Since I want to keep it stock, I'll have to attach it to the belly of the craft, which may or may not kill my aerodynamics when SSTOing. I'll have to try it.

 

1 hour ago, bewing said:

4 rapiers and 30 m/s? That's just nuts. Something must be wrong. Is this an MK2 design?

It is possible to create a hydroplane in KSP. You can put little fins on pylons, and they can raise the rest of the plane above the water -- or maybe just the front end to gain you some pitch.

If you can't pitch up, then my recommendation would be to pitch down. Go submersible, dive to 50 or 100 meters, then get the nose pointed up. You will come out of the water with a lot of speed and force -- probably quite a bit too violently, but it's something you can try anyway.

 

Yes, I also thought it was nuts! It's indeed a Mk2 craft. It weighs about 50 tons.

I'll consider the pylons, again, it may or may not kill my aero. But I do definitely look forward to trying the underwater launch approach!

 

21 minutes ago, AeroGav said:

What about making some hydrofoils?  So to the plane rises mostly out of the water as speed builds?

The aero :/. This thing is meant to SSTO and reenter the atmosphere. What kind of aerofoil design do you have in mind?

 

Please keep the suggestions coming!

 

Edited by A_name
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Well I was able to sole this by using hydrofoils. All it took was two small structural pylons mounted along the center of the fuselage, one just in front of the COM and the other further front near the cockpit, with two control surfaces radially on each pylon. It's still able to SSTO with the hydrofoils so the added drag was negligible.

I also tried the SRB approach. The Flea was too weak to push me out of the water and the next size (is it the Thump?) was too big.

I also tried the submersion approach, but sadly the plane was to buoyant to go under even though it was able to nose down.

Thanks again everyone!

Edited by A_name
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Hmmm. Well, just to see what would happen, I threw together an MK2 SSTO w/4 rapiers. 51 tonnes. Goes to orbit pretty nice, considering it was just thrown together. My version obviously has a bit less wing than yours, because my takeoff speed is around 80 m/s. I can just reach 80 in the water -- and just as I start to lift off, pieces of the plane start blowing up. But if we combine the two designs, you might be there. :wink:

JEaW9bG.png

 

I certainly see the problem, though. Getting from 30 m/s to 80 m/s in the water is not trivial. Gotta keep the nose from burying itself in the water. Gotta get the body to lift itself up out of the water. For seaplanes, I like putting one set of canards below the water level, to give myself a lot of pitch control for lifting and diving.

 

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