Cheap Contest Series?

guest blogger john hare

The friends I know in the rocket industry are too busy running businesses and fulfilling contracts to work cheap or free on the unproven concepts that I find interesting. It has come to my attention that there are a lot of other groups out there doing rockets that can use even very small amounts of money to move their projects forward. For them to go after it, those small amounts of money would have to be attached to something simple, interesting, in line with their current projects, and with the potential for much higher returns on their time.

We may have a common ground for some projects. I have suggested all sorts of wild ideas in the interest of serious fun. If they work, I am serious, if not it was just in fun. 🙂 A few of the concepts didn’t get busted and have serious profit potential. The compensating nozzles in particular address an issue that has been neglected for development in this field. I want to throw out the simplest one I had to see if anyone would find it worth fooling with.


 The boot compensating nozzle idea could be tested without destroying the hardware that cost so much time and money. The concept is that an over expanded nozzle has an external subsonic inlet attached to half the perimeter. When the flow is trying to separate at low altitude, the inlet smooths the way for air to flow into half the nozzle to fill the bell so that the main exhaust has full expansion for that chamber pressure and altitude.

The economic reason for exploring this concept is that it can be tested with available engines and launch vehicles. Down to the HPR and Tripoli launches if the test stand results are positive. Most other compensating nozzles are just too expensive to test. Too expensive to test means they stay on the wish list indefinitely, as in aerospike. The NGLLC competitors could certainly have used some compensating nozzles for their flights this month. It wouldn’t hurt the Lynx or Falcons either if it could be proven quickly and inexpensively.

A subsonic inlet in this case is made from a piece of pipe or tubing laying around as scrap. Material properties of the material are unimportant as long as it can stand a few second characteristics burn before melting. The important thing is that it create a situation in which atmospheric air preferentially enters the nozzle to separate the rocket  flow in exactly the manner intended. Look at airliner jet inlets for what I have in mind. Ideally you would have half of one of them instead of dumpster stock, but this will be a cheap contest if it happens at all.

If the offer was for the first data set that compared the same  over expanded nozzle unmodified and modified in two runs, how much would it take? Results with pictures on your website with no travel or hardware sent. How would it be verified that the test took place? How would you know that I would or could pay up? Is there an organization interested in handling contests for stuff this small that can be trusted? and so on.

I am looking for real world ways of confirming or busting some of my concepts within my budget. Would $250.00 get some interest, or would it take $1,000.00 or $10,000.00? One I could do next week, one in a month or two if nothing goes wrong, and one never. I’m looking for feedback on if this series can and should be started.

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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About johnhare

I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.
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14 Responses to Cheap Contest Series?

  1. Joe Latrell says:

    A prize of $500 to $1000 would be a good incentive to a lot of people. The $250 maybe not so much. If you want these tested within commercial HPR ranges, recouping most of the costs would be paramount since you will have to static test everything to get good values.

  2. john hare says:

    So I put that as $500.00 for the static data and $500.00 for flight data at a minimum? Flight contest only if the static tests confirm the concept of course.

  3. Tim says:

    Hi John, have you considered CFD? It might be worth offering say $100 for a CFD model before moving onto hardware testing.

  4. jsuros says:

    Could you finance these cheap contest prizes by forming a nonprofit organization and asking for donations?

  5. john hare says:

    I think CFD is a lot of work and shaky for poorly understood concepts like this, but I’ll put up a hundred if somebody can confirm or bust it that way.

    If a few of the ideas pan out and add value to the industry, then that would be a good idea. People moving forward in this business would probably find it worthwhile to contribute.

    At this time though, I wouldn’t put my credibility high enough to ask others to send contributions my way. On the gripping hand, if there is an idea that somebody thinks feasible and useful, there is no reason they can’t add a few bucks to the jackpot to be sent directly to the winner(s). If somebody wants to do that, they can suggest the format and concept for me to follow.

  6. Habitat Hermit says:

    I was thinking of how to test the concept (maybe on a tiny rocket sled) and I’m wondering if I’ve found a serious flaw. The idea might well work at speed (however drag might/should be an issue) but what about liftoff when there isn’t any or much moving air to deflect into the nozzle? Doesn’t for example booster rockets or a first stage defeat the purpose of the solution?

    About small prizes (like for example the N-Prize which is small in most ways) and so on I wanted to air the idea that some of the concepts might be better off as joint projects (smaller than the Sugar Shot 2 Space project) or sponsored academic study (i.e. offer to sponsor them for engineers looking for thesis material).

  7. john hare says:

    The air should be sucked into the nozzle by the lower pressure created by the overexpansion of the nozzle. If it works, it will work best as a static test article. By mach 1, it should be nearly worthless, as it can only access the boundary layer air that has been slowed to relatively low velocity.

    It seems to me that a joint project might be beyond the time frames that interest me. If I can make this one attractive, many teams are able to fabricate and test it in a single weekend. This particular concept has the single strength that it can be validated or busted without changing the core hardware at all.

    I give this one less than 10% chance of working right on the first set of tries. I would put several other concepts much higher in probability though equally higher in time and material costs. A fast turnaround at minimum cost is my priority.

    How much would a sponsored acedemic study cost? For something as complex as the ejector/injector, it might be worth looking into.

  8. Habitat Hermit says:

    My misunderstanding there. Just to be sure I’ve understood the concept is it aiming to stabilize the flow separation “pattern” inside the nozzle? I.e. limit the underpressure to one specific part of the nozzle thus establishing a region where inflow can mitigate the underpressure more easily? In a way related to the idea behind things like vortex generators only for the inside of a nozzle (but doing so from the outside)?

    I don’t know what a sponsored study would cost but I think a modest amount of funds could be useful and welcome as an additional incentive if the hardware costs aren’t too high. Jonathan Goff and others around here would know much better than me. It was merely meant as a suggestion and possibility but for example the concept we’ve been talking about here (or very closely related ones) seems like it should be interesting to anyone doing research and papers on fluid dynamics (and finding a thesis subject can be difficult).

  9. john hare says:

    The concept is that the normal crisp edges on the nozzle exit discourage separation of the flow until quite low pressures are reached through overexpansion. The smooth aerodynamic shape on half the exit allows air to flow into the nozzle up to ambient pressure. If it works, it will allow air pressure on one side of the flow to optimize true exit pressure up to optimum expansion ratio in the same manner as an aerospike. The rounded aerodynamic section will need to be dropped then to get crisp separation of the flow at higher altitudes.

    I think if anyone was really interested I could think of a few thesis subjects. From where I sit, it is hard to picture the difficulty of finding interesting problems. If a very few bucks would move things along, it would be interesting to work something out.

    There may be a credential problem in me making the thesis suggestions though, I don’t have any. I might be the only one here that actually did drop out of elementary school.

  10. Eric Collins says:

    If the purpose of the boot is to encourage the flow of ambient air into the low pressure region of the nozzle, then at static conditions, there should be very little improvement over air just being sucked back in past the edge of the nozzle. Even with the ambient air moving past the nozzle at subsonic speeds, the best you might be able to do is move the separation point for the ambient air a little bit further towards the inside of the nozzle. At worst, the blunt surface might allow the separation point to oscillate, which would lead to vortex shedding.

    Looking back at your original article on “Notchbell and the Boot Compensators”, it seems that you are trying to actively force ambient air into the nozzle in a direction which is against the exhaust gasses. While you might succeed in slightly increasing the pressure along one side of the nozzle, you could possibly be introducing more instabilities into the flow where the two streams meet. Not only that, but in redirecting the ambient air, you are effectively reversing its momentum just to push it into a nozzle where the exhaust gasses will have to turn it around again. It seems to me that you will be suffering losses at both turns. Is the increase in performance really going to be enough to offset the increase in drag that would result from redirecting the ambient air against the direction it naturally wants to flow?

    It would appear to me that the thrust augmented nozzle concept is probably one of the best ways to mitigate the low pressure regions in the over expanded nozzle. At least in that case, the gasses introduced into the nozzle are heading in the right direction and are adding energy and momentum to the exhaust rather than contributing further to aerodynamic losses.

    I also remember now that several rocket engines, which I’ve seen on display, have the exhaust from their turbo-pumps redirected into their nozzles. In light of this discussion, I can begin to see some additional advantages that might be obtained from this.

    Of course this is mostly speculation on my part. I should stop doing CFD in my head and actually do a few runs to see what would really happen. I’ll let you know if I ever get “a round tuit”.

  11. john hare says:

    As per Tim’s suggestion, I’ve put up a hundred for the first to do a CFD of the concept to confirm or bust it. While I think that is a totally inadequate sum for the work I think is involved, it’s all I can see putting up for something that would have to be confirmed with hot fire anyway. If you like CFD as much as I like thinking around corners though….

    The purpose of the boot is to persuade the exhaust to detach from one side in a very smooth predictable manner. Normal overexpanded nozzles can suffer from irregular separations that are potentially damaging. It is not the goal to entrain the air, just have it push the exhaust against one expansion wall in an altitude scheduled manner, exactly like a linear aerospike in operation. The air just has to take a detour on the way.

    When there is no separation, overexpansion costs thrust on the ground when you really need it. If we can get a 5% thrust increase, payload benefits can be a multiple of that percentage.

    I finally worked out a means of demonstrating the concept with compressed air. Hopefully in a week or so I will be able to test and then youtube a dynamic demonstration. (in the sense that it will be moving) The yarn tuft methods of aircraft should provide a good indication of the nozzle operation. If that part goes well, then an instrumented hot fire contest is in order with a few bucks to make it interesting

  12. Bob Steinke says:


    If the prize were $500 for a static test I would try for it with the current Laramie Rose monopropellant engine. I calculated that if we turn down the chamber pressure until the throat is just barely choked then we would see 60 lbf with the current nozzle, and 130 lbf with a properly expanded nozzle. Even if the actual difference is only half that it should be measurable.

  13. john hare says:

    I am not sure if I am on the same page. Half of the difference between 60 and 130 lbf, or half the difference between 60 lbf and what the engine would reach with a optimum expansion at that flow rate? I am thinking that this concept, if it works, will gain between 5 and 15% when compensating for moderately overexpanded nozzles. If that is about right, then you may be looking for 5-10 lbs difference at the low flow rates of the 60 lbf run.

  14. Bob Steinke says:

    130 is what the engine would reach with optimum expansion at that flow rate so the maximum improvement that’s theoretically possible is to go from 60 to 130. But we probably won’t get that much improvement. It might not be stable if we get that close to the throat unchoking, or maybe the plume will separate all by itself at that low pressure. I meant that we might get half of the improvement, +35 instead of +70. 35 pounds difference should be measureable.

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