Ramjet

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I know it's not a rocket, but I've always been awed by the simplicity of a ramjet. Launch on rocket till ramjet lights. Is this feasible in small scale?

This is an RAF Bloodhound rocket/ramjet combo. It makes me drool.

1920px-Bloodhound_SAM_at_the_RAF_Museum.jpg
 

Funkworks

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I think you’d need metals to withstand the high pressures and temperatures so, while maybe feasible on a small scale, I’m not sure it would respect the rules.
 

shockie

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since AIR is not compressible at subsonic speeds, RAM Air rocketry is probably out except for those HPR rockets that can attain and maintain supersonic speeds. On the other hand, air-augmentation of model rockets might be feasible. The Augie and Augie II were air-augmented rockets and they date from the 60's....
 

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since AIR is not compressible at subsonic speeds, RAM Air rocketry is probably out except for those HPR rockets that can attain and maintain supersonic speeds. On the other hand, air-augmentation of model rockets might be feasible. The Augie and Augie II were air-augmented rockets and they date from the 60's....
I've previously designed a booster just to test electronics - Small & Simple. With the right H motor, I can get 1.7MACH (simmed) which is enough to light this bad boy. I wonder if I could launch under "experimental"?
 

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I've previously designed a booster just to test electronics - Small & Simple. With the right H motor, I can get 1.7MACH (simmed) which is enough to light this bad boy. I wonder if I could launch under "experimental"?
you would have to get to mach 1.7 and stay there for a while to see any ram air effects. Maybe a 2 stager with a very high thrust to get you up to speed fast and then a long burning sustainer to keep you at speed.....
 

shockie

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here's a previous post that has some great ideas in it: https://www.rocketryforum.com/threads/ramjet-pod-functionality-and-design.164087/

it's kinda funny now , but back in the 50's people who used those Jetex "rocket" engines, also used venturi tubes to supposedly increase the thrust of those Jetex motors. I don't think ti was ever proved they did anything other than increase the weight of the models and make them look cool. Check out that JetMaster:

 
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The one pictured above - about the size of a dollar bill - is fueled with Jet B - 25% Kero, 75% gasoline. I'd love to say it was designed by me, but it was designed by a Naval Academy postgraduate for a Thesis to operate at mach 4.
 

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It is actually possible to get a start on a ramjet at speeds as low as about 100 knots, but it will not develop any significant thrust until speeds of .5 Mach or so.

Several ramjets were tested on prop aircraft and early subsonic jets.
 

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It is actually possible to get a start on a ramjet at speeds as low as about 100 knots, but it will not develop any significant thrust until speeds of .5 Mach or so.

Several ramjets were tested on prop aircraft and early subsonic jets.
very interesting. I didn't know that
 

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Ramjets work really good at supersonic speeds, because compressible effects are the exact opposite of the flow equations at subsonic speed. At supersonic speeds the air coming into a diffuser that has a decreasing cross-sectional area actually slows down and increases in pressure. This is exactly what is needed to go into a combustor, i.e., low air speed and high pressure. A turbo-jet is no longer needed to increase the air pressure in the combustor. At subsonic speed the air speed increases and pressure decreases in the convergent section of a nozzle prior to the throat.
 

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I find it fascinating, all the reading & learning about ramjets. For an engine that has no moving parts, a ton of stuff has to line up correctly for them to actually work & produce thrust. 99% of what I have found on the internet are simply glorified propane torches.
 

tab28682

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Think about the loadings on the wings as a result of the ramjet thrust.. and how the wings were never designed to have loads of that type.

Really interesting, thanks for posting.
Moet people do not know this, but in general, there is more aerodynamic force pushing the wing forward while in flight than there is pushing to the rear from drag effects. Think of the wing as a watermelon seed, being squeezed forward by “fingers”, which are the effect of the air as the flow rejoins behind the wing.

My recollection was that these ramjets on the P-51 were not all that powerful. I googled it and one reference shows that they were 800 lbs of thrust, each.

For more info, you will have to google around.
 
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tab28682

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Hey tab have any references you can point me to? Not pics but reports
Nope. Google might turn one up.

During WWII, Sanger in Germany put a fairly large version of his ramjet design on top of (I think) a Dornier Do 17.
 

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Just sharing - this is a functional design that I had converted from paper drawings to Solidworks, just in case someone wants to take this to the next level, just PM me and you can have the solidworks files. (won't let me post them direct). If I start playing with it, I'm afraid it will be a black hole I never emerge from.

All of the angles, lengths, sizes are correct & wind-tunnel tested. Jet is smaller than a dollar bill.
 

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