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North American Aviation Stored Energy Propulsion System

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I hope everybody else knows about this, and has lots of supporting documentation to post... This display model represents a small, single-seat, single-engine, proof-of-concept jet aircraft by North American Aviation (Columbus, Ohio division), designed to demonstrate the Stored Energy Propulsion System.

Was that some kind of rubber band? A bag of hot air? Steak and eggs? Even JP4 is technically "stored energy", so the designation is rather cryptic. The only unusual feature visible on the model is a pair of odd-shaped, side-mounted protrusions that is also an enigma (to me) -- see red arrow on picture 3.
 

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Sundog

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Any idea what year this is from? The only thing I can think of is maybe some sort of jet propulsion that uses a solid propellant, similar to a rocket motor? Maybe it was a form of early hybrid rocket jet, where the rocket part powers the turbine which than powers the compressor, only using a solid fuel propellant? Maybe the stubs on each side are for a propellant "log" to be placed in the airframe? It would make refueling very simple and rapid. Granted, I'm doing a LOT of guessing here, but this is the first I've ever heard of this concept.

It's a very pleasant looking aircraft. Thanks for sharing, hopefully someone will have some answers.
 

Stargazer2006

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Very interesting design and a totally unheard of concept! Thanks for sharing.
The design looks early 70s-ish...
 

Abraham Gubler

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circle-5 said:
Was that some kind of rubber band? A bag of hot air? Steak and eggs? Even JP4 is technically "stored energy", so the designation is rather cryptic. The only unusual feature visible on the model is a pair of odd-shaped, side-mounted protrusions that is also an enigma (to me) -- see red arrow on picture 3.

The protusion looks like a pressure valve (a la fire hydrant) and combined with the exhaust nozzle indicates (self supporting indicates that is) that the 'stored energy' could be a high pressure, compressed gas of some sort?
 

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Abraham Gubler said:
t the 'stored energy' could be a high pressure, compressed gas of some sort?

If so, my guess would be steam. Fill a titanium tank with water, heat to about 400 F, and open a valve. Works as a simple-yet-crappy rocket engine (see: Evel Kneivel's "Sky Cycle"). Blow the steam past a tip-turbine, and you can generate some fair thrust for a short duration.

Green is an odd color for a research vehicle like this.
 

overscan (PaulMM)

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http://www.google.com/patents?id=SWdfAAAAEBAJ

Here's a North American Aviation patent from 1966 for a flywheel suitable for use in a plane as a stored energy source. No idea if its relevant to the topic however.
 

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Sundog said:
Any idea what year this is from?

An educated guess would be between 1958 and 1965. This is based on the type of hardware (base, swivel, NAA logo) used on this model, which is almost exclusively consistent with A3J-1 through RA-5C Vigilante model fabrication at the Columbus shop.

So far, we have compressed gas, a flywheel, a steam tank and a propellant log. Until hard facts surface about this project, this is anyone's guess, so keep the ideas coming! I like the log idea, because the location of the extrusions would place them right in the air intake ducts. Perhaps these are cryogenic logs, which would increase thrust by supercooling the inlet air, making it denser (like some long-duration water injection)...
 

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Another signifciant item of design is the undercarriage. It is located in pods mid wing. Why not locate the gear in the fuselage? Maybe because the fuselage is a large pressure containment vessel? So you can knock holes in it for gear storage.
 

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Yeah, stored pressure makes sense, in that you would probably need a large pressure vessel. I find the steam aspect interesting, but, without looking it up, IIRC, isn't water's energy density much less than that of fuel per unit volume? Perhaps it was using pressurized methane? This is definitely a mystery.
 

Abraham Gubler

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Sundog said:
Perhaps it was using pressurized methane?

AKA liquefied natural gas (LNG), in which case it would still only have 60% of stored energy of heavy fuels.

Well the other Sherlock Holmesian thing about this model is its painted green. Because of the likely date this probably doesn't have any environmental movement significance. However it may correspond to the colour of the 'stored energy' or its exhaust flame.
 

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Maybe they intended to use gases spilled from the jet in cruise mode to drive a compressor of some inert gas (helium ?) in a tank, and use it to mechanically superdrive the turbine again in landing. The same could be done before taking off running the engine on taxi. In this way they could reuse it fom a lot of times. The same principle is used in some experimentl hybrid cars, where you use the cruise Otto engine to compress air in a tank and use it to drive mechanically the wheels in the urban cycle.
 

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Nobody else noticed the resemblance to the Harrier? and those protuberances are in the right place to be vertical lift nozzles (though perhaps not the right shape).

I know this doesn't answer the stored energy question - oh well.

Cheers, Woody
 

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I dont think it is V/STOL related. If nothing more, than the air intakes are simply too small to ensure sufficient amount of the air. I agree that the fuselage seems to be optimized as the big gas tank, but consider that you must place the engine somewhere, also the cockpit requires its space so the only place for the tank is the fuselage between the end of the cockpit and wing leading edge and under the fuselage.

To be honest, I must say that after I read the topic title and then saw the "pair of odd-shaped, side-mounted protrusions", this is what first comes to my mind. List it as another option :D
 

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OK, a wind-up spring. Why not?

After reviewing the stored energy flywheel patent uncovered by Overscan, I'm wondering if that might be the right answer. The date fits (1966) and the patent comes from North American Aviation, with a similar name. I had never heard of flywheels for storing energy in aircraft applications (weight penalties come to mind) but the performance is impressive: 2,000-hp from a 12-inch flywheel running at 54,000 rpm (the rim speed would be bi-sonic).

Protrusions on the model could be external air or hydraulic ground run-up connections. Interestingly, these appear to be located at the CG, a good spot for a flywheel or two. Of course, the method by which all this stored energy gets converted into propulsion is still a mystery. In addition, there would probably be gyroscopic side effects during flight, unless that's exactly the point -- to somehow harness this kinetic energy into usable bursts of maneuverability, perhaps by tilting the flywheel(s). To be continued...
 

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Weight penalty was also my answer to the "why not?" question. You can have suprisingly high power, but it takes only a short time and after that you will only have a dead weight. So the next logical step would be to think about purpose and mission profile of that kind of plane. Short site - by - site city transport perhaps?
 

Abraham Gubler

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circle-5 said:
After reviewing the stored energy flywheel patent uncovered by Overscan, I'm wondering if that might be the right answer. The date fits (1966) and the patent comes from North American Aviation, with a similar name. I had never heard of flywheels for storing energy in aircraft applications (weight penalties come to mind) but the performance is impressive: 2,000-hp from a 12-inch flywheel running at 54,000 rpm (the rim speed would be bi-sonic).

You wouldn't need a big external crank to turn an internally mounted flywheel. Plus the weight of a flywheel is huge. Another Sherlock Holmesian point about this aircraft is the wings are tiny. So this means either a very high wingloading or a very light weight aircraft.

Another potential use for side 'plugs' could be something associated with nuclear power. Obviously not a reactor but the 'stored energy' could be something to do with radioactive decay. Said decay being used as a heat source for turbine? No need for fuel to be burnt in the engine...
 

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Abraham Gubler said:
Another potential use for side 'plugs' could be something associated with nuclear power. Obviously not a reactor but the 'stored energy' could be something to do with radioactive decay. Said decay being used as a heat source for turbine? No need for fuel to be burnt in the engine...

Even today's best radioisotope thermal generators produce only enough energy to power a light bulb (in hard-to-reach lighthouses) or some electronics (as in the LEM or unmanned spacecraft, like Cassini). On the plus side, RTGs can run for many years, but to propel an aircraft with the atom requires the energy output of a reactor. There was boundless optimism back then (remember the Ford Nucleon, the family car you could refuel every 100,000 miles?) so I wouldn't rule out the option of a small reactor.
 

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I am so thankful we don't have nuclear cars driving around right now. Makes me shudder to even think of a body count if 9-11 had been conducted with a group of nuclear cars as oppposed to conventional airliners.

As far as the aircraft in question is concerned, do you think fuel cells could have played a part?
 

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I am so thankful we don't have nuclear cars driving around right now. Makes me shudder to even think of a body count if 9-11 had been conducted with a group of nuclear cars as oppposed to conventional airliners.

Or, just the highways on a Memorial Day weekend.

This stored energy can only be a few things.
I discount the fuel log, because rocket power or some sort of combustion power would not be considered "stored energy" in the context. This leaves stored-
1. Mechanical energy -flywheel, mainspring, rubber band, etc.
2. Electrical energy- some sort of battery
3. Heat energy -compressed fluid or steam

The first two forms would probably supply the propulsion in some form of propeller. I do not see any. Also, wouln't a flywheel storing such a massive amount of mechanical energy cause a lot of gyroscopic headaches?

All of these are technically possible, but I can't see them as anything more than a novelty in aircraft use. Look at the automotive world. The weight penalty is less restrictive, yet none of these power systems have ever advanced in post WWII years beyond prototypes or limited production (until recently with electric cars, of course)
 

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Since the center fuselage doesn't have any landing gear and there are two intakes, there's a large space for a big object at the center of gravity.

I'm leaning towards a spherical pressurized tank, enabling vertical takeoff. Sorta like the German zero length Starfighters. The protrusions would be steerable nozzles for the takeoff.

Flywheels have better energy density, but they weigh a lot when the energy is expended. If you have two wheels spinning in the opposite directions, you can cancel the gyroscopic effects. You'd need a fan for it anyway, F-35 style.

A steam rocket could be much more effective, and is potentially very simple. You get a short high thrust impulse and are left with a light empty tank.

Springs have an awful energy density, definitely not that.
 

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imo, liquefied gas as a source of high energy can be viable. i think it worked for the air powered car so i guess it has good applications for aviation as well although they have less range.
 

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Some additional thoughts regarding stored energy:

It is easy to dismiss the flywheel option as being too heavy, etc., but the North American Aviation patent, while a bit arcane, clearly states: "This invention concerns energy storage devices of the inertia type identified generally as flywheels wherein lightweight and maximum efficiency are of crucial importance as in the case of aerial vehicles using such devices."

So it's a flywheel made specifically for storing energy in airplanes. And as mz correctly points out, counter-rotating flywheels could be made to cancel each other's gyro effects. But how did they plan to convert this energy into propulsion?

The next point concerns the project itself: why engineer and build a new airframe from scratch, just to test a simple thrust augmentation device, like a steam tank? That could have been tested on a B-47 or some other pod-engine jet for a fraction of the cost, so it must be something fairly substantial, integral to the airframe. The outboard undercarriage seems to confirm that.

And finally, all the assumptions here suggest the energy in question is stored on the ground, before flight. But what if this airplane can collect and store energy while in flight? Convair had a (very complex) way of doing that called LACES, but it could be as simple as recovering energy while braking or in a dive...
 

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I still like the steam idea, though I've no evidence for it. If the steam was exhausted out through Harrier-like nozzles on the side, it would presumably allow for a few seconds of very high thrust, enough - perhaps - to lob the plane vertically into the air and get it going forward. A reusable Zero Length Launcher of exceptional simplicity; a built-in VTO system of relatively low mass.
 

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I like the idea of a flywheel as well but that 'nozzle' shape just doesn’t support it. If you had a flywheel and you needed an externally driven crank to 'load' it with energy you wouldn't need anything outside the aircraft to attach this crank. Such an attachment could be recessed. Also the flywheel axis is most likely going to be the same as the longitudinal axis of the aircraft to minimise the stability effects of the flywheels. So if the crank came in from the side it would need a 90 degree gear box. Also the ‘nozzle’ has a 90 degree angle to it which if it was a crank attachment would mean another gear box. Which would be superfluous since the external crank could be aligned at 90 degrees to the aircraft’s longitudinal l axis for power transfer to this ‘nozzle’ if it was a crank attachment. We really need someone from NAA Ohio Div to post online just what this thing was...
 

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And to generate the steam - how about H2O2? NAA had experience with it as a fuel for the X-15 APUs and I think that it was used as the fuel for Bell's rocketpacks. By the mid-sixties, handling, storage and usage would be a known issue. In fact, most of the energy from the H2O2 decomposition could be extracted to spin up / "top off" the flywheels. The low energy exhaust would be blown overboard through the two small exhaust ports...

...any thoughts?
 

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Perhaps the stubs are the exhaust ports for whatever is "spinning up" the flywheels? Maybe they look like a cross between a flywheel and those early centrifugal compressor engine designs, with an axial turbine? Such that the fly wheel and centrifugal compressors are a single integral component? Maybe there is some sort of "tip burning" going on the tips of the centrifugal compressor to power the flywheel, or aid it, without the turbine doing all the work and that's exhausted at the stubs?

Just another pure guess on my part.
 

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aim9xray said:
And to generate the steam - how about H2O2?

Meh. If - and it's a mighty big "if" - this this is steam powered, the title is "stored energy propulsion," which indicates it's somethign out of the ordinary. A simple monoprop thruster system ain't that unusual. And if the design features a tank of compressed steam, it's easiest if the guys out in the field could use what's already available to heat the tank of water... electricity, jet fuel or deisel would be my guess.
 

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From Wikipedia description of the Westinghouse Mark 50 torpedo (a 1974 design):

"The torpedo's Stored Chemical Energy Propulsion System (SCEPS) uses a small tank of sulfur hexafluoride gas [oxidant] which is sprayed over a block of solid lithium, which generates enormous quantities of heat, in turn used to generate steam from seawater. The steam propels the torpedo in a closed Rankine cycle, supplying power to a pump-jet."

So, one could presumably use either the direct expansion of Li-SF6-heated air for jet propulsion (as do nuclear engines, like the GE X-211) or develop the SCEPS as the indirect cycle described above, driving a fan instead of a pump-jet.
 
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