pulse jets as alternative propulsion

i have been looking into pulse-jets and ram-jets with the idea of using them to aid a rocket motor, and providing much longer burn times. They also have cheep fuel, compared to solid rocket fuel.
In my browsing i have found that while not common, pulse jet use for RC airplanes is not unheard of.

Next step; build one or buy one? (there is one you can buy from hobby king, but it does not look like a good option for various reasons)
I understand the principal of how Pulse jets work, and i think i could build one. I also know that there would be some problems with putting one in a rocket.

What i want to know is: has any body tried to put one in a rocket, and if so do they have helpful information?

thanks
Julian

https://www.rocketryforum.com/showthread.php?59628-How-about-a-gas-powered-pulse-jet-engine

https://www.rocketryforum.com/showt...ocket-first-flight-(ever-)&highlight=pulsejet

V-1?

To answer your question, it is out of the scope of the hobby, air scoops, liquid fuel, igniting manually, ect.

But it wouldn't be difficult, good valves, good air routing, and a light/strong airframe would make it fly, but not as a rocket. You'd be hard pressed to make it higher than 1:1 T:W on the pad. That's why the V-1 had wings and took off at a shallow angle.

Hobby King do one and its cheap. 1.6KG of thrust as well.

i am. thinkin to use 2 in addition to a rocket motor, guess what a ...BOMARC...a ...large one


Gesendet von meinem iPad mit Rocketry Forum

legranddudu said:

i am. thinkin to use 2 in addition to a rocket motor, guess what a ...BOMARC...a ...large one


Gesendet von meinem iPad mit Rocketry Forum

Click to expand...

That would be insanely cool! Please do!

it would be very probably illegal and dangerous at landing. need to find a dry lake first ....but a great theoritical challenge. especially with pulsejet start in flight..


Gesendet von meinem iPad mit Rocketry Forum

Look up Vanderbilt USLI. I know they carried some ramjet as a payload for a number of years as part of the NASA USLI competition (sponsored by NAR). I'm not sure of the scope of what they did with ramjets, though I suppose I could feasibly look it up...

The vids I saw of the hobby pulsejets is they get very, very and very hot. That's why they were mounted on pods out in the breeze. Would be difficult to use with a rocket type design. Nice thought though. Kurt

I thought about the possibility of doing this a while back but I never acted on it. It seems like it wouldn't be too hard to do. Put the fuel in the rocket on the CG, run the lines down to the jet engine which is mounted in the open on the bottom. Maybe even get a nose cone and put it on the rear as a tail cone. You could also if you really want to get fancy add in electronic stabilization! Okay maybe with all that it'd be fairly difficult but not impossible! 😊

Please realize that there are lots of things which could be done. However, only some of them fit under NFPA 1127, and are covered under NAR and/or TRIPOLI in the US, or other appropriate regulation and governing bodies in other countries.

Gerald

Nothing prohibits pulse jets in the US. They are also flown in Europe. It is not out of the scope of this hobby. There are a lot of "legal" activities going on beyond the scope of most who are on this forum. Not everything falls under NAR or Tripoli rules.

Someone has already done it, and as you can see, the performance wasnt too impressive. But still go for it, would love to see a pulse jet rocket! [video=youtube;abr2Pt7SGi4]https://www.youtube.com/watch?v=abr2Pt7SGi4[/video]

ksaves2 said:

The vids I saw of the hobby pulsejets is they get very, very and very hot. That's why they were mounted on pods out in the breeze. Would be difficult to use with a rocket type design. Nice thought though. Kurt

Click to expand...

Maybe mount three or four in outboard fin pods.

ksaves2 said:

The vids I saw of the hobby pulsejets is they get very, very and very hot. That's why they were mounted on pods out in the breeze. Would be difficult to use with a rocket type design. Nice thought though. Kurt

Click to expand...

Actually, some were building scale jets powered by a pulse jet in the early 1960's. The internal engine was isolated from the balsa fuse by a thin aluminum tube.

the issue is not of technical order to me ...but the scale. I am researching a short pulse jet. even if you would build a 8" BOMARC (uuuuhhh???)...the pods would not be long enough to hide a standard pulse jet engine properly. Of course it shall be also strong enough to continue pushing a 50lb bird in full rocket flight for a while, even if not enough to accelerate. Furthermore I would try to start them in flight, 1 or 2 secs after rocket start. Main engine of course hybrid *LOL....an M CLUSTER or... what about that legendary 152mm contrail? And 3 D actively stabilized of course...

just saying...all of this is not going to happen.

-this year-

ROFL


Gesendet von meinem iPad mit Rocketry Forum

I almost bought one of them from Hobby King a few years back just to fire it up for fun. But then I thought that my wife, dog,s and neighbors, would hate on me.

I built a pulse jet years ago, never thought of putting it in a rocket till now...

I would certainly launch it on a rocket motor to get it up to speed.

safety and regs are a concern...where would one even find that sort of stuff. On the other hand I could just use common sense and apply the NAR safety code to the rocket part of it.

I am thinking about using the propane lighter refill bottles because it self pressurizes (eliminating fuel pump) and it turns to gas when not under pressure, allowing a les that perfect fuel injection system.

Worth thinking about. Will work on it more and let you know about any progress

Julian

Common sense and regs, the twain shall never meet. Just joking.

You want to look through the NFPA codes. The rocketry we do under NAR and TRA in the US is under NFPA 1127. It is insured through NAR and TRA. If it doesn't meet what is outlined as acceptible practices for NAR or TRA, it isn't insured. If it isn't insured, you may well have to secure your own insurance to get a launch site. Good luck with that. Also good luck getting someone at an existing launch site to say ok go fly it. If it isn't under NFPA 1127 then it will be under some other NFPA regs - or not at all. To fly something along the lines of what you are envisioning, it would be Class 3 (or perhaps something else; I do not know the Class 3 restrictions), would require you to get a launch site, would require you to get signed waivers from the land owner and any surrounding property within range, would require you to get approval of the local fire marshal... Plus you'll need the FAA waiver to launch it.

Propane - let's see, essentially you are launching an overweight pyrotechnic bomb using a severely underpowered but very loud motor which is glowing red hot. It's not like there are not some things which can go wrong with this picture...

You'd be wanting to talk with FAR perhaps.

But frankly, if you were picking a jet engine, you picked the worst possible choice in most any regard other than cost. But a bad technical decision is still a bad technical decision. I suspect it is an even worse regulatory one.

I apologize for being blunt about my opinion on this one.

Gerald

It's a neat project, and I'm not trying to discourage you from pursuing it, but it's not a rocket. Technically speaking, your aircraft is a jet propelled missile with a rocket assisted launch where as our "rockets" are actually rocket propelled missiles. The NAR/TRA safety codes are very specific as to the propulsion systems that we can use, and we are restricted to non-air breathing rocket engines. Jets engines are air breathing propulsion systems and not covered under NAR/TRA rules. The AMA codes do include jet engine flights and also rocket glider flights so I believe AMA flight rules would apply and AMA insurance would be required for operations, but not at a NAR or TRA sanctioned event.

Bob

Pulse jets tend to not have the highest thrust to weight numbers, so keeping the jet stable during it's flight will require a fair amount of effort. It should be possible with enough design and effort to make a sufficient pulse jet engine to work with a rocket. But by the time you put that effort it might make more sense to go with a more conventional turbine since they have some better performance properties for what rockets need.

Also if I remember correctly, I am pretty sure that pulse jets and supersonic flows do not get along with each other. So a pulse jet might not be the most optimal air breathing engine to use for rockets, since even if you get a reasonably working pulsejet, you are going to run into it's limitations pretty quickly.

If it has to be stuck subsonic (like with a pulse-jet) then I'd go with a subsonic ramjet instead. Lighter, simpler so it ought to be more reliable, and far more thrust once it gets moving a bit.

But I don't think it will fit under any currently allowed category, so, that means leg work and paperwork, and patience with bureaucracies.

Pulse jets are most efficient at generating noise and heat. If you put the pulse jet inside a subsonic ramjet tube configuration just to use it as a heater, it would likely generate more thrust as a heat source than what the pulse jet originally had.

Gerald

This is a pressure jet engine. It uses propane liquid and tuned ports to operate with no moving parts. In the literature I got years ago one of the photos is of 4 130 pound thrust engines with the thrust pointing down lift a man on a platform but boy, do they get hot, make a pulse jet look like its blowing cold

[video=youtube;-jiy2Nr116M]https://www.youtube.com/watch?v=-jiy2Nr116M[/video]

Depending on your altitude I might be concerned with the decrease in oxygen as altitude increases. I have a valveless pulsejet that ran okay at ~150ft, but was noticeably more sensitive when I lugged it to Black Rock (~3900ft) a year ago. Granted, my pulsejet was never intended to be well-optimized, and a valved pulsejet (what you would use in this application, as it's more efficient) may have better characteristics anyway. Maybe this would not be an issue regardless, I don't know. Just a thought from my experiences. (Hmm, I see an excuse to build another pulsejet... )