Jet Lifting Challenge

[numerobis]

People often ask how many turbojets they need for their plane. Let's answer that question. The challenge: fly as much mass to near-orbit as you can, on turbojets alone. Divide the launch mass by the number of turbojets, that's your score.

More precisely, this is how you complete the challenge:

• Get a periapsis above 40 km.
  
• Show your spacecraft above the atmosphere.
  
• Show the mass of your spacecraft on the ground.
  
• Use turbojets only.
  
• Use a single stage.
  
• Information and autopilot mods as you wish; just say what they are. Otherwise, stock parts.
  
• Tell us something about how you built the plane.
  
• Tell us your flight plan.
  

For example, here's my submission:

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The plane has 30 small control surfaces. The bulk of them are on the top and bottom of the fuselage acting as lift only; they're angled down 10 degrees. Only a few actually act as control surfaces. Also, 17 intakes, and one turbojet.

I flew at full throttle, 30 degrees pitch until 20km, then I maintained between 40-60 m/s vertical speed until air ran thin. Then I pointed prograde and allowed MechJeb to throttle back automatically.

Launch mass is 17.307t on one turbojet, and that's your number to beat!

Edited January 12, 2014 by numerobis

[numerobis]

Thanks but no.

[ihtoit]

um... yeah, with that many control surfaces, 1096bimu, even at that weight you have infiniglide.

I've managed to make a 40-ton behemoth very similar to yours take off with no jet or rocket power - just using the six control surfaces as you have.

(FWIW to achieve "infiniglide" all you need is enough thrust from your control surface movements to a: overcome drag and b: achieve enough lift to, well, lift your aircraft. Given enough lifting surfaces (wing elements which add up to "Buttloads of lift" fill this requirement nicely - 9 pairs is ample for even heavy loads), you could lift to orbit with a single ion engine or a single pair of control surfaces).

Numerobis: perhaps you should make a rule, as in: maximum of two control surfaces. I think you might have an infiniglide problem with your design as well, but I can't be bothered to put 15 pairs on a tube to find out.

[numerobis]

ihtoit, you're getting a 40t plane off the ground with just seven control surfaces? I have my doubts. Infinigliders I've seen have several control surfaces per tonne of mass, and they're hard to control. I still haven't worked out the math on how they work.

1096bimu's plane is reasonable of a sort; it falls down at the "sit on the tarmac and burn off fuel for several hours" bit. It also fails to get Pe above 40km or show the spacecraft outside the atmosphere, but those could be fixed by another run.

[Dispatcher]

While I'll not be competing in this challenge, here are some stats and test info on the turbojet engine. Thrust: 225 kn, iSP at surface is 800 and while the Wiki says 1200 in vacuum, that would be zero in practical terms, since it cannot function in a vacuum. The average iSP is 1000 and more realistic as you near flame out. The Wiki listed its max dV as 11760. Its TWR is listed as 12.7. Launching vertically with no aerodynamic parts, it is able to lift about 5.651 tons (including its own 1.2 ton mass) and carry the non fuel mass up to about 23729 meters with a single simple air intake.

Its fairly fuel efficient. Using only one small octagonal tank of fuel (which in turn carries unused oxidizer as well), the vertically launched turbojet engine can get its very small non fuel payload up to 10526 meters altitude. For the interested, it generates an electric charge of 5 units per second.

From the above, it appears that one could succeed in the challenge on two "fronts"; by spamming air intakes and of course using aerodynamic parts for lift: the greater the surface area of a single pair of wings, the need for fewer wings overall, with their attendant drag. I'm guessing that one might use one of two approaches in flight. Either max your horizontal speed before attempting to thrust higher, or spam the jet engines for enough thrust to brute force your momentum up to the target altitude.

Good luck to you who accept the challenge!

[numerobis]

It complies with every rule and is a valid entry, now add it in.

Nope. I'm looking for reasonable responses to a reasonable challenge.

If violating the spirit of the rules excites you, then I invite you to pursue a career in law or finance.

[ihtoit]

ihtoit, you're getting a 40t plane off the ground with just seven control surfaces? I have my doubts. Infinigliders I've seen have several control surfaces per tonne of mass, and they're hard to control. I still haven't worked out the math on how they work.

1096bimu's plane is reasonable of a sort; it falls down at the "sit on the tarmac and burn off fuel for several hours" bit. It also fails to get Pe above 40km or show the spacecraft outside the atmosphere, but those could be fixed by another run.

An earlier challenge based on a Manley experiment was proven when I wingspammed a solar-ion plane. Turned out I didn't need the ion engine, just the two small control surfaces was all that was needed to achieve the 31m/s to take off and take the 6 ton aircraft (one rectangular lifting segment and I think it was 6 swept wings connected end-to-end in two triplets, all covered topside in small panels) to a very slow PE60km.

[BSI]

OK, got my plane into the air for the first test. Surprisingly, it flies like a dog, stalls HARD with no warning and, even more shocking, should prove to be a viable, stable and adaptable platform for future airplaneology.

The parts ditched on the runway are a MK1 can (0.6t), a radial decoupler (0.05t) and 2 separatrons(0.15t), for a total mass of nearly 200t.

Using B9, Kethane, KW Rocketry and F.A.R. ( I dunno if you have a different leaderboard since I'm using FAR). Basically, it's the two biggest KW tanks (the smaller one on the front is the same as a default orange tank), with the latest in Kerbal Aerodynamics. It's still very much WIP - I'm running the Basic Jet engine, but at low speeds I have more than enough thrust to reach take-off speed, so that'll be a turbojet next flight, and I'll need to add more intakes for high-altitude flight and some RCS for control at high speed. Though to be honest this thing never made it past 40m/s in testing so far, so high speed may be optimistic.

On the plus side, 200t divided by 1 jet should yield a recent score, and it has enough fuel to fly basically forever.

[numerobis]

Can it reach orbital speeds? IIRC you can't get fast enough in FAR using the stock turbojet.

I intended this to be a stock challenge, which is why I specified that information/autopilot mods were OK. I've clarified that rule now. B9 and KW don't offend me, and I'll take your result into consideration.

I don't have a problem with using a command seat and sloughing off some parts to get around the fact you're not allowed to start with a Kerbal in the seat, so that's fine despite the single-stage rule. That said, I wonder what the point is -- more mass is good in this challenge!

[BSI]

If a stock jet can't do it in FAR, then I suppose I better ground the program then (this was news to me, I hadn't been using the 2 stock jets since I started using FAR). I always knew there'd be a problem getting it up out of the atmosphere, but lifting it to 20km+ wasn't as hard as I thought (so much wing area).

It might be able to do it if I intake spammed enough and built up speed over several flying orbits (the plane itself should be good for dozens of round-the-world trips, just very slowly).

[numerobis]

The fastest FAR jet in the MachingBird challenge just barely makes it to the requisite speed, so it's not hopeless. Good luck!