Reuseable rockets

[Jonfliesgoats]

What are thoughts regarding a vertical launch and horizontal landing at sea?  You don't have to carry any fuel or parachutes, but you have to carry enough wing area to land at sea at a surviveable speed (50m/s) horizontally.  Has anyone determined whether it takes more mass to lug wings for a seaplane landing?

Right now, 20tons dry rocket only needs two or three parachutes followed by a very small amount of fuel to arrest the descent before splashdown.

[Rune]

31 minutes ago, Jonfliesgoats said:

What are thoughts regarding a vertical launch and horizontal landing at sea?  You don't have to carry any fuel or parachutes, but you have to carry enough wing area to land at sea at a surviveable speed (50m/s) horizontally.  Has anyone determined whether it takes more mass to lug wings for a seaplane landing?

Right now, 20tons dry rocket only needs two or three parachutes followed by a very small amount of fuel to arrest the descent before splashdown.

Well, that's probably the lightest recovery system of them all. That booster of mine we have been talking about for a while now has exactly 1.48mT in aerodynamic surfaces (I opened the game to check), and a dry weight of 29.15mT. Now, that doesn't mean that you can land it at less than 50m/s (it glides about the same way the shuttle did), but water (and land) landings are all about vertical speed. Keep a bit of energy, flare up at the last second, and >70m/s hitting the water should be just fine. Then again, 100% recovery means getting to the runway, and that means landing gear, with is another 0.545mT.

 

Rune. Still, peanuts, and you can land dry, meaning you only need to keep some fumes to deorbit and keep the fuel cell running.

Edited October 30, 2016 by Rune

[Technical Ben]

It is only lighter than the fuel, if your tank is a wing. Otherwise the wings weigh more than the fuel and/or parachute (at least as far as I know IRL, KSP may be different).

[Jonfliesgoats]

Exactly where I am heading, rune.  Glide angle is determined by lift/drag, not lift itself.  All things in equilibrium it usually pays to fly at the angle of attack and associated airspeed that gives you either the best angle of glide or a little more slowly for minimum sink rate.

Higher performance aircraft don't just look at glide performance, however.  Margins above various controllability limits need to be maintained and adequate speed maintained for maneuvering and gusts.  One of the practical reasons for flying high performance aircraft at speeds above Vld is soyou have enough total force available due to maneuver the aircraft into a satisfactory flare.  This is why reference approach speed is not always 1.3 or 1.23 approach speeds.  Flight testing and engineering may determine a given airframe's reference approach speed should be much higher so, as Rune as described, you can flare!

You're doing Boeing's work for them, Rune! 

Anyway Rune is more concise than I am, but a low performance glider, like the Space Shuttle (in equilibrium) can maneuver into a nice flare given enough speed (dynamic pressure for nerds).  The rub is how fast you can go before a fast landing turns into a slow crash.  If you land so fast your tires break, gear detaches and aircraft balls up, the landing doesn't do you much good.  So there is a minimum wing area (we won't go into airfoil design and lift devices) required for a given brick to flare and touch the ground at a survaveble speed.

Since we don't have any control over the airfoils in KSP, we only have a couple variables to play with.  We know Cl max for our modular wings and those wing s should stall around an alpha of ten to twelve degrees (seems that's what I have observed).  So we can't really benefit from vortex generation as we would in real life, but the upshot is our math gets easier!

This is great stuff!  Thanks all!

Edited October 30, 2016 by Jonfliesgoats
Delete reference to Lockheed

[Jonfliesgoats]

So I ran the numbers on my graphing calculator for a pair of swept wing type B.  I assumed the lift value for those wings was the Clmax.  These are theoretically determined stall speeds and are the slowest speeds possible for touchdown since KSP doesn't simulate ground effect.  Ran the lift equation using 2.26 for cl max and checked myself against the stall speed equation.  These numbers are valid at sea level on Kerbin.  A few thousand meters up, your true airspeed will be higher due to lower freestream air density.

10t  26m/s

20t  36m/s

41.5t 50m/s

 

Anyway, assuming my math is correct a theoretical 20t rocket would be right around the mass where you could either use a few parachutes and a retro burn or horizontally land at sea.  What gets interesting is for a 30 something ton lifter, you actually save a lot of mass by horizontally landing at sea!

These are returning, dry masses, the actual weight of our craft on the pad could be much higher.  

Landing a heavy rocket, say after capturing a payload may present some interesting engineering and operational challenges.

What we have here, gents is what corporate hacks call a paradigm shift!  I love it!

Edited October 30, 2016 by Jonfliesgoats

[Jonfliesgoats]

I typed a lot.  I got really excited there.