Aerospike Motor Test Successful by Binder Design October 23, 2003 Web posted at: 12:49 PM EDT
(ROL Newswire ) -- The first documented successful test of a composite fueled aerospike motor has taken place on 10/22/03, by Mike Fisher, owner of Binder Design. Mike has been developing the nozzle for EX use, and it has gone through three redesigns. This latest version was a complete success, and the photos and video from the test clearly show typical aerospike behavior. There will be ongoing testing from K to M class motors, with flight tests to follow shortly.
Mike hopes to show significant flight performance increases using the aerospike nozzle as compared to the standard bell nozzle. Look forward to a webpage coming soon featuring detailed reports and pictures at the Experimental link at Binder Design's website at
It gives a bias toward liquids and theoretically aerospikes.
Theoretically.
Turns out the Aerospike effect is speed dependent and this is crappy at liftoff.
Doing drop tanks on liquids is a practical suggestion if the motor itself can be optimized for so many conditions. One of the main reason for 2 or 3 or even 4 or 5 stage rockets is not only mass reduction but thrust profiling.
Aerospikes we have tried had marginal benefits. However I am willing to waste my time and resources proving his aerospike is the exception to the rule if he is interested. I have a launch window to 50k and booster motors suitable to optimize its potential and good data recorders are now commonplace.
Not *entirely* true. You can get orbital flights with lower Isp's if you're willing to increase the amount of fuel you burn, as an overall fraction of the vehicles' weight. A LOX/kerosene rocket with an Isp of 320 will need to be 90% fuel to do the same job as a LOX/LH2 vehicle with an Isp of 420 and 80% fuel.
The fact that the LOX/Kero vehicle will be *smaller* than the LOX/LH2 one, and thus more robust, is lost to many people. :-)
Actually, aerospikes are favoured because they don't require the large, heavy 'bell' behind the combustion chamber. That makes for a lighter motor.
Expansion-deflection nozzles are an often-forgotten in-between step... a combination of a deLaval nozzle and an aerospike.
I didn't make that statement, Jerry did. I agree. The nozzle should be at optimum expansion no matter what the altitude. BUT, the ideal situation to operate it in to see any large increase in performance would be at high speeds to burn it through as much altitude as possible, i.e. sustainer, not a booster.
Unless you are serious about SSTO, but even then, very little perfomance increase should be seen early in the flight.
I'm skeptical that very much performance gain will be seen in our small hobby motors, but it is an interesting exercise that will give us some answers.
Besides, at a visceral level, "It's just cool."
BTW, ...J. Steven York....the writer? Didn't you used to fly with us in the NW? Where'd you go?
So are you saying an aerospike is as efficient as a traditional solid (this was a solid aerospike) at even altitudes under 20,000 feet and speeds under M1?
I'm expecting lower numbers for the aerospike on the test stand, typical of multi throat nozzles compared to a single bell or conical nozzle. So, I suspect the above to be true.
Someone about a year ago or so claimed 20% or better increase in performance in flights conducted at less than mach and to a few thousand feet......pure BS.
It's the fact that the LOX/kerosene vehicle IS smaller that is important since it has lower aerodyanamic drag losses for a given total propellant load impulse and therefore higher effective specific impulse. In space all you need to worry about are thrust loads. In the atmosphere the aerodyanamic loads can be huge and located inconveniently. You therefore want a high average propellant density when drag losses are important, making density x Isp the figure of merit. It's why von Braun went with LOX/kerosene on the Saturn V S-I and why the shuttle uses APCP for the SRB's. APCP is dense stuff. LH2 has such a low density (like whipped cream) that the intrinsic Isp advantage of the propellant mixture is lost when in the atmosphere due to increased vehicle drag. It's part of why the SSTO NASP was really a non-starter and also why they wanted to use slush hydrogen - an act of desperation.
While a LOX/kerosene vehicle would be smaller, I would expect the design margins on loads and allowable stresses to be about the same for the whole vehicle (i.e. pretty slim), so vehicle scale doesn't have alot to do with robustness per se because this is a design target. Most fighters, for example, are designed to take something like +9/-3 g's (dictated by the presence of the pilot) and unless it's a really small vehicle you're not going to add any more capability or weight than what is minimally necessary to meet the design criteria. It's going to take more structure to build a big draggy LH2 tank to a given set of structural criteria than a smaller tank with shorter spans and lower aero loads, but the smaller tank also encloses less propellant. The structural mass fraction could therefore end up about the same, but the effective Isp based on the net accelerative force doesn't if significant aerodynamic drag is present - advantage: solids.
The aerospike is inefficient at low speed because the external flow doesn't confine the exhaust very well (or at all at takeoff). In fact the ejector-type pumping that occurs below Mach 1 can actually increase the drag on the vehicle. You may therefore have to increase the engine size significantly for sufficient take-off thrust margin, which will then result in significantly oversized engines and the need for deep throttle-back capability or premature shutdown of some engines (which may then be dead weight hauled to orbit) to prevent excessive aerodynamic or acceleration loads later in the flight. Complexity adds weight, and weight is the first, second, and third most important factors in building aerospace vehicles. There are good reasons why NASA and DOD haven't flown an aerospike engine.
That's not to say we should stop doing research, its just that what we have now (shuttle, EELV's, etc.) is actually difficult to beat when you look at the whole system, payload needs, and current flight rates. Rutan isn't trying to assemble a space station, for example, and if he was he would need a Much bigger and more expensive vehicle. At some point, you really have ridden a technology about as far as it will go and a breakthrough is needed somewhere else to get significant new capabilities, like automobiles versus horses. I don't think the aerospike falls into that category but nuclear thermal might.
Don't forget, though - an overall smaller vehicle, given the same 'empty' vehicle weight, can use thicker structural components everywhere. Rather than having to rely on bleeding-edge composite technologies, aluminum and titanium could be used.
But it's not the volume of the propellant that matter, but rather the mass. Kerosene is twenty times denser than liquid hydrogen, but only 15% lower performance. That makes for smaller feed lines, smaller tanks, etc. - and since there's no need for insulation around kerosene, that weight can be eliminated altogether.
I think the idea is that the expantion ratio is more self optimizing to the flight conditions, rather than fixed as in most bell nozzels.
I think Lockheed proposed the linear aerospike because it would push R&D and the novel coolness factor. They knew that NASA did not want to pay for a shiny new low tech delivery truck.
Optimum expansion is not everything. A conventional nozzel opimized for sea level will still produce additional thrust as the air presseure drops, just not as much more as as a fully expanded exhaust.
I'd bet on the conventional optimized nozzel for a given altitude. Although an aerospike nozzel may be more efficent overall on typical assent profiles. IF you have a movable nozzel plug, you may be able to throttle the engine more efficiently as well.
always!
But an HPR aerospike motor is of interest first for the R&D, and second for the novelty sales potential.
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