# R/C Jet Video / Air Breathing Booster

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#### Bruce

##### Well-Known Member
This video,

shows a lightweight turbine powered model plane.

I especially liked the high alpha and smoke.

If the whole plane has a 2 to 1 thrust ratio, couldn't you make a rocket which would be simpler and lighter and have a 3 to 1 thrust ratio?

Maybe use Joe Barnard's gimbal system?

Boost a small rocket up to 40,000 feet and ignite it at that altitude?

Use the oxygen in the atmosphere for the motor for the first 40,000 feet which are the hardest aerodynamically to get through anyway...

Probably more complex and expensive than just brute forcing it with a large rocket booster though, right?

Turbo-jets are very expensive. This is something that you don't want to loose. There is a lot less oxygen at 40,000 feet, so performance will be a lot different at altitude. What are the FAA requirements and other regulations?

#### Bruce

##### Well-Known Member
Turbo-jets are very expensive. This is something that you don't want to loose. There is a lot less oxygen at 40,000 feet, so performance will be a lot different at altitude. What are the FAA requirements and other regulations?

Agreed, jet turbine engines are expensive. But an O motor that could lift a rocket to 40,000 feet wouldn't be too much cheaper...

Don't jet airliners routinely fly to altitudes approaching 40,000 feet? Their engines must have some way to adjust the air to fuel ratio to compensate for less oxygen at altitude. I think an SR-71 flew up to 85,000 feet and the Russians did even better, so they must have it figured out.

I don't know how the FAA would view an air breathing booster. My guess is that they'd call it a model plane and limit it to 400 feet. Any other opinions?

TRF recently had another thread similar on this topic. Someone posted on that thread an interesting article from Apogee.

#### David Schwantz

TRF Supporter
A Jetcat P200-sx make 52 lbs of thrust. Weighs 5.5 lbs. Burns 25 oz fuel/minute. Is 5.12" dia. On a rocket that will hit 40k, how much do you think it will weigh? How long will it take the Jetcat to get it there? Do you think the rocket can hold that much fuel? H$ll, I actually put a P-120 on a walmart plastic sled, but that was at sea level #### Attachments • 37.8 KB Views: 20 #### Bruce ##### Well-Known Member A Jetcat P200-sx make 52 lbs of thrust. Weighs 5.5 lbs. Burns 25 oz fuel/minute. Is 5.12" dia. On a rocket that will hit 40k, how much do you think it will weigh? How long will it take the Jetcat to get it there? Do you think the rocket can hold that much fuel? H$ll, I actually put a P-120 on a walmart plastic sled, but that was at sea level
Of course, you're right, that the weight of fuel needed to get to 40,000 feet could adversely affect the rocket's ability to take off in the first place...

The sled idea was brilliant! How fast did it go?

#### David Schwantz

##### Well-Known Member
TRF Supporter
Every year we had a chilli fly in on New Years Day. AMA limits us to 200 mph. But the sled was about 10 mph

#### Bruce

##### Well-Known Member
That's interesting that the AMA now has limits on maximum speed. I didn't realize that.

Back in the day, I remember control line speed events where they tried to go as fast as possible. I think the C division and pulse jet racers were nearing 200MPH?

#### David Schwantz

##### Well-Known Member
TRF Supporter
They only limit turbines to 200 mph.

#### G_T

##### Well-Known Member
Sailplanes have been transonic.

For the turbojet, you'd want to adjust the design to optimize it more for operation at lower atmospheric pressure and temperature, and/or perhaps add an afterburner. My guesstimator is you might end up burning about a pound of fuel per mile of altitude gain. At least at the lower altitude levels that's quite feasible. A turbojet has a much greater ISP, even if you run an afterburner, than a rocket motor. You just have to have a thrust to weight ratio greater than perhaps 1.2:1. Or you'd have to have wings.

We're just not allowed to do such things, or I'd already be working on them.

Gerald

#### Michael L

##### Random Pixel Generator
TRF Supporter
The compressor section on the front of the turbine provides the oxygen. Have you ever heard of a high bypass turbofan? Most commercial airliners in service today use them. Some of the thrust comes from the fan (the bypassed part) and some comes from the turbine (the turbofan part). The military uses low bypass turbofans, which are afterburner capable. Different mission.

SpaceX has a good idea

Not my file. Attribution per creative commons license. Also not from SpaceX so there may be errors:
<a href="https://commons.wikimedia.org/wiki/File:Raptor_Engine_Unofficial_Combustion_Scheme.svg">