# Rocket airplane building cost

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#### oriol

##### Well-Known Member
Hi everyone!

I was surfing the net and I found out that the cost of manufacturing or converting/modifying from conventional aircraft to rocket racer (for the rocket racing league) is 1 million dollars worth per airplane.

It s extremely expensive!
I´m not saying that an old quicksilver could do the trick but, the rocket racing airplanes aren t supersonic. I don t know maybe you need to reinforce them or do some modifications for weight and balance. You may even need to build them from zero even if there s no difference form outside if you compare it with the conventional aircraft with reciprocating engine.

Now if we consider the engine costs design, without entering on difficult maths, thermodynamics. It s like the ramjet engine, an engine without moving parts. So it s a lot easier to build than a, for example 2 stroke engine.
I ve seen many rocket bikes on the net, this guys don t have very rich sponsors supporting them, they are not the NASA.

Maybe the data I red on the net about the rocket racer was wrong. I think those airplanes have enough fuel for a 4min flight. Is it that hard to do it? Is it that expensive because of insurance costs?

I know the germans did that during the war but, they we re so desperate during those days they took all the chances, many pilots were killed testing those airplanes.

I would apreciate any comments from you,

thanks!

Oriol

##### Well-Known Member
Solid fuel rocket engines are way cheaper to make than aircraft engines. Basically just a pipe, nozzle and some fuel. (Liquid requires very expensive pumps)

The problem is in safely handling the fuel and mostly in making the rocket safe enough for human flight. While you could probably buy the components and manufacture a whole engine for a few thousand dollars, getting them safe enough might be virtually impossible.

The racing league uses LOX+kerosine I think. That requires very high pressure pumps (a rocket motors sees a few dozen to over 100 bar of pressure in the combustion chamber) which is expensive and complex.

#### delta

##### Well-Known Member
A couple of solid boosters might be nice to have in an emergency situation, or to get your speed up enough to kick in the ram/scram jets. I don't know who's got 'em in stock at an affordable price though.

Rick

#### oriol

##### Well-Known Member

I m not a rocket design specialist but there are plenty of powerplant options for a rocket engine: solid, liquid, gas.

I think most of the propellants and oxidisers are safe if they´re stored apart form each other. The suppliers sell you the gas and give you the bottle to keep it inside, everything is homologated tested, looks like a diving bottle.

The problem is when you put them together on the airplane. I know what happens in the combustion chamber is not like mixing hot water and cold water on the shower.

You can make it simplier if you don t use pumps and benefit form the pressure at wich the gases are stored. You can have constant Thrust, although the pilot won t apreciate that as much as the designer.

I m just wondering: maybe the option they choose is quite efficient from the physical point of view, transformation of energy... but I m sure you can get very good performances with much less investement, KISS rule!

Oriol

#### orion

##### Well-Known Member
And let's not forget the cost of re-engoneering the airplanes. None of the airframes were designed for that use nor for the speeds they see. As such, the conversion needs to cover aerodynamics, structure, control system, etc. Then you add a new system for storing fuel and all the associated systems of the engines and you have a pretty hefty project ahead of you.

#### oriol

##### Well-Known Member
A mix with rocket for take off and ramjet for cruise looks pretty cool!
The thing would be to save some from fuel from the rocket to have a safer landing.

I haven t heard of something like these being done.

The french s have flown a ramjet airplane during the 50´s for testing, it took off from a big airplane in flight.

#### oriol

##### Well-Known Member
I m focusing on how to lower the expenses, without considering in detail all the safest issues.

If you don t want to redesign an airplane to fly at 500Km/h (the speed of the rocket racers) then buy a fouga, Saeta or similar old training jet airplane. They re pretty cheap cause they burn a lot of fuel for sport aviation standards.

Now for the engines if dragster bikes can do that then it must have to be reasonably possible to adapt it for an airplane.

#### Propshaft

##### Well-Known Member
How about hybrid rocket motors, that run on nitrous oxide/some solid fuel.

I used to have one of those educational models that work on a cartridge used in whipped cream apparatus.
Those rockets had basically no moving parts, high output, and not as much explosion probability as pure solid fuel rockets have when there are cracks in the fuel grain.

Basically the same system they use on spaceship one/two. Thrust can be controlled by adding more nitrous to the fuel.

However I think making a system for human flight based on any kind of rockets is soliciting for a Darwin award.

#### oriol

##### Well-Known Member
However I think making a system for human flight based on any kind of rockets is soliciting for a Darwin award.
It s a big challenge no doubt, but aviation has know many challengers, wright brothers, de la cierva, lilienthal, Rutan...

It s sad to realize that no major improvements have been made since WW2 on the subject, rocket propulsion is still restricted to high budgets or military purposes.

#### Propshaft

##### Well-Known Member
By any means, all forms of space/rocket travel are very dangerous. At least compared to any other form of transport (as number of movements).

Did you slip a decimal point or two? It's hard to build even an ultralight for $10K. Rockets are cool for racing, but they're inherently inefficient and impractical for atmospheric flight. And expensive, no way around it... liquid fuel rockets require high pressure high volume turbopumps, which gave NASA lots of headaches in the 1960's. Pumps like that aren't something you can buy off the shelf, and the engineering required to build one is not trivial. -Dana Money does not buy happiness. But poverty really sucks. #### oriol ##### Well-Known Member No insurance company would ever insure one. The rocket racers will have to have some very restrictive event insurance that will cost 10's of millions per event. When I was at university a teacher told me once that the most expensive thing of a rocket launch is the insurance. #### autoreply ##### Well-Known Member Driving a motorbike is dangerous, even moving in bicycle in barcelona is dangerous. Sure you know someone who happened to have an engine failure in flight. All kind of transportation have its inherent risks. True, but the numbers are "slightly" different. In roughly 3000 hours on a motorcycle I never came close to killing myself. An engine failure on a conventional aircraft has nothing to do with a few hundred pounds of explosives, exploding a few feet from your head... About 1 in a hundred rockets fail if you only look at the professionally designed ones. Fly it 15 times and you've just done your first shot at Russian roulette. If you look at amateur rockets, you're probably down to 10% failure. That's almost as good as Russian roulette with 6 chambers... I tried not to magnify all the safety issues to avoid and endless discussion about the almost infinite things that can go wrong with any design flyable or not. Being the case of such an unconventional airplane the thing to be expected by much more wise people than me is:¨No it won t work it s too dangerous, you need to be a pro with a lot experience and even if it s the case....." The reason for that attitude is that most pilots have been to a considerable number of funerals of close friends, of children, husbands and so on who died in an aircraft crash. Mind you, those died in very safe, proven and properly designed aircraft. If you don't do the necessary years of study and learning, in the end spend a fair amount of money on them or take failure modes and safety VERY serious, we're no longer discussing risk or a lack of safety. We're talking certain death. Don't get me wrong, rocket propulsion can work for small aircraft. But it's neither cheap, simple or safe. #### wsimpso1 ##### Super Moderator Staff member Log Member Only going to point it out once. The reason people compare engineering projects against "rocket science" is because rocket science is fairly high up on the scale of engineering difficulty. Engineering difficulty means money to design, to build, to test, to redesign, to test, and so on. If the one supplier of engines, pumps, valves, tanks, and controllers says the price is$1M per set, well, who out there is going to invest and then compete with them and drive the price down...

Reasonable efficiency liquid fuel rocket motors have very high pressure in the combustion chamber. Saturn rockets used in Apollo were 3000 psi (400 bar for those who live in SI). That is 1960's technology. Space Shuttle was twice that.

So, you have some decisions about how you are going to push fuel and oxidizer into the combustion chamber:

You can run huge pressure bottles of gaseous fuels and oxidizers at pressures quite a bit higher than Combustion chamber to enable using most of the fuel and oxidizer. Well, the bottles get big, and very heavy. Then there is how to regulate the flows of both gases in correct ratios, and so on. Gases are kind of tough to manage;

You can run big gas bottles at higher pressures in series with liquid fuels. Now you have gas bottles and fuel bottles that all have to carry big pressure, but at least the fuel bottles are smaller and much lighter. You still have to regulate the flows to the combustion chambers. Not trivial;

The solution performed by the space agencies of various rich countries is to use high pressure gas to spin turbines that run turbine pumps to move fuel and oxidizer to the combustion chamber. The fuel is stored at ambient pressure and is metered as a function of turbine speed, so weight and control is workable.

Why not do the SpaceShipOne routine? It is a solid rocket motor with modest oxidizer support. It is still complex, expensive and with the nitorus oxide pressurized, pretty heavy and slow to refill. And the solid rocket fuel can not be replenished until the chamber cools. The rocket racers are planning pit stops to refill LOX and ethanol tanks.

So, where is this going to be cheap and simple? You are dealing with "rocket science".

Billski

#### oriol

##### Well-Known Member
So, where is this going to be cheap and simple? You are dealing with "rocket science".

Billski

Wikipedia :"Bipropellant liquid rockets are simple in concept but due to high temperatures and high speed moving parts, very complex in practice."

I didn t find detailed specifications of the rocket bikes, all I have is wikipedia saying that rocket dragster cars can achieve super high speeds at a price: tmax = 20 seg.

If we assume dragster rocket cars engines to be reliable still we ll have not enough time to make something practical with an airplane. Me 163 range 40 Km, Ohka 35 Km.

The only "practical thing" would be, as pointed out previous in this thread, a ramjet airplane with a rocket engine for taking off.

Still the acceleration would be so great! Not many passengers would volunteer for a ride.

#### Propshaft

##### Well-Known Member
Did you slip a decimal point or two? It's hard to build even an ultralight for $10K. -Dana Money does not buy happiness. But poverty really sucks. No, I did not. A nitrous canister, with a controlled valve a titanium tube and graphite nozzle can be made for that money. Like I said, I don't think you'd survive, but for that money, I'm very sure you could make a motor like that, not if you want to develop it in any way towards efficiency and safety. But I made one for$20 that weighed about 150 grams and went up at least 200ft.

Now you're right 10k isn't any serious amount. But if you had to build a rocket powered plane, I'd go with a hybrid rocket. For limited number of parts and control.

Rocket planes are cool through history, but dangerous, expensive, and inefficient. Unless you can come up with a throttle-able motor, power is all or nothing; not a soft acceleration.
As nitrous oxide is the oxidizer, as is air in a combustion engine, shutting/reducing the flow of nitrous to the solid fuel core/nozzle will effectively stop or reduce the burn of the hybrid rocket engine.

But overall I'm skeptical you can do it without big bucks, and even so, I wouldn't sit in it.

//You might as well have fun, while doing things.

#### bmcj

##### Well-Known Member
HBA Supporter
I was surfing the net and I found out that the cost of manufacturing or converting/modifying from conventional aircraft to rocket racer (for the rocket racing league) is 1 million dollars worth per airplane.
You may indeed be able to build a cheaper rocket aircraft, but if I recall correctly, the Rocket Racing League's approach is for a standardized engine and aircraft so that the race is won primarily on the merits of the pilot's skill. Their version of engine, aircraft, and customized electronic race navigation equipment and software (all of which has already been engineered) may indeed add up to a million dollars. Of course, there may even be some membership and registration fees for the RRL built into that number.

Bruce

#### bflynt

##### Member
It was my understanding the Rocket Racing League had already selected the engine for the planes.

The initial engine was a LOX/Kerosene engine from XCOR
XCOR Aerospace Rocket Engines -4K14 LOX_kerosene_engine

Now it seems they have switched to a LOX/Methanol from Armadillo

My understanding is the RRL has to use a liquid motor because the engines will not be run continuously. The engine just serves to boost the plane up where it will coast down then re-light again to boost back up, etc.

I'm not sure a hybrid rocket motor would have the performance necessary to compete against a liquid motor. The grain is used relatively quickly and continues to degrade from heat even after the motor is shut off. In addition, unless your using some exotic fuel/oxidizer the specific impulse is relatively low when compared to bi-propellant liquids.

Bryan