well...my idea wasn't so original after all!

[Elapid]

I attended Balls13 this weekend and had the opportunity to chat with Dr. McCreary for a bit. I mentioned my idea of Smelly Motors, and to my surprise, he said he had done exactly that, though it didn't work out in that particular case due to the particular ester that was tried.

hehehe!
i really enjoyed picking his brain, and consider that one of the highlights of the event. I picked up a copy of his book and a box of AP supplies from Aerocon Systems.

lots of reading to do...

 

[DynaSoar]

Originally posted by Elapid
I attended Balls13 this weekend and had the opportunity to chat with Dr. McCreary for a bit. I mentioned my idea of Smelly Motors, and to my surprise, he said he had done exactly that, though it didn't work out in that particular case due to the particular ester that was tried.

Having ideas that others have already had and tried is a good thing. It means you're thinking like the pros. I can't count the number of times this has happened to me. Even my major contribution to brain imaging used a 100 year old concept (amplitude modulation, from AM radio). It just hadn't been used on brain waves before. Keep at it and you'll eventually be first. I did. Hopefully I can patent it.

 

[Elapid]

i really wish i had read his book BEFORE i talked to him...
it's cool, though, since he is extremely friendly and approachable and said if i had any questions on anything to feel free to email him.

how cool is that!

Re: ideas
i got another one, but i'm not sure if it would be worth the hassle...non-cylindrical motors...
several flavors come to mind...angular, prolly some nasty failure modes...tapered, not sure there's an advantage...and the other idea was going from a core-burner early on, with an end-burner at the forward end...

i guess i'll get back to reading. I have lots to learn!

 

[DynaSoar]

Originally posted by Elapid
Re: ideas
i got another one, but i'm not sure if it would be worth the hassle...non-cylindrical motors...
several flavors come to mind...angular, prolly some nasty failure modes...tapered, not sure there's an advantage...and the other idea was going from a core-burner early on, with an end-burner at the forward end...

Shapes: Not being a powderhound I can't say for sure, but I think anything other than round would tend to smooth out any humps in the thrust curve because stuff farther from the center would take longer to finish burning.

Tapered, now there's a possibility. The best shape for punching through the Mach wall is a cone, and not just a nose, a real long smooth cone. If an engine were made to fit such a beast it'd up the efficiency by eliminating wasted diameter, but by making use of it.

I'd be interested in hearing if multiple nozzles are possible. Anything with a big base has a lot of base drag. If the exhaust were spread out across the base instead of being just in the center, it would fight against this.

 

[Bill]

Originally posted by DynaSoar

Tapered, now there's a possibility. The best shape for punching through the Mach wall is a cone, and not just a nose, a real long smooth cone. If an engine were made to fit such a beast it'd up the efficiency by eliminating wasted diameter, but by making use of it.

I'd be interested in hearing if multiple nozzles are possible. Anything with a big base has a lot of base drag. If the exhaust were spread out across the base instead of being just in the center, it would fight against this.

Consider an aerospike nozzle. A cone in the front, a cone in the back and flames somewhere in the middle. That would be one cool rocketship.


Bill

 

[GL-P]

What would be real cool, I don't know if Dynarsoar was describing this, but a rocket motor with a pinched in centre like an hour glass would be cool. You'd have to screw it together in the middle though. The hole point would be to lower supersonic drag by using what is known as the equal area theory (or something like that) they use on aircraft, like a coke bottle.

 

[BlueNinja]

I don't see how the shape of the motor will affect teh aerodynamics of the rocket.... sorry for any ignorance....


And, GL-P, the Hypertek motors are just what you are describing.

 

[GL-P]

Ahh, yes!!! Yeah, it's hard to explain in a 1000 characters or less. Just look at high speed aircraft. Where the wings are the body pinches in a little. If only i could get an airframe to fit this shape.

 

[AlexM]

If anyone here has ever seen the T38 up close, I am pretty sure that is the shape he is talking about.

Hard to see in the pic, but if you look at it from the top, you can see the coke bottle shape.

 

[GL-P]

Yep, that's it.

 

[Stymye]

ok I'm lost,
what the heck does the shape of a fighter have to do with casting various shaped motor grains?..I don't see the correlation.

 

[GL-P]

on minimum diameter rockets the airframe is as small as it can get. you can't physically do the coke bottle shape without increasing body diameter at the front and rear end. if the motor and grains had an hourglass shape, you could change the airframe shape to use this technique. A fighter is just the large scale application of this effect

 

[solrules]

Originally posted by GL-P
Ahh, yes!!! Yeah, it's hard to explain in a 1000 characters or less. Just look at high speed aircraft. Where the wings are the body pinches in a little. If only i could get an airframe to fit this shape.

I believe it is called the 'coke bottle' effect in the aircraft industry. Sorry, no more details except that it helps aerodynamic flow.

 

[GL-P]

yeah, I know it works but not really how though...

 

[sandman]

This is a better example.

A B-58 Hustler supersonic bomber!

Man, could these things break windows on the ground!

 

[sandman]

Maybe this pic is better.

 

[DynaSoar]

Originally posted by GL-P
yeah, I know it works but not really how though...

What it is, is where there's something else that pokes out, the body goes in. Where the wins start, the body starts to narrow. As the wings get bigger going aft, the body gets narrower. As the wings end, the body goes back out. That keeps the profile in terms of square inches of area or whatever, approximately the same. This is also called "wasp waist".

On rockets, rarely is there anything in the middle that adds area. That's what happens at the bottom: the fins.

And, we do in fact do this in rocketry. Werner von Braun used it when he designed the V2. This is what a boat tail is. Where the fins start to stick out and add area, the body starts to curve inward. A boat tail does allow the airflow to fill in behind the rocket smoothly, decreasing base drag, but if properly designed it follows the equal area rule, the amount of inward curvature equalling the increase in finnage, which is NOT a word, but it is now.

So there's a design for you. A motor that fits in a boat tail.

 

[gerbs4me]

The B-58 Hustler is one awesome jet, sorry this is off-topic

 

[Elapid]

hehehe!

how about different grain compositions?

like with my core-burner to end-burner idea, i would think a high solids composition for the core-burner section, and low-solids compound for the end-burner to control temperature during the extended burn...

maybe i shouldn't give away ALL my ideas...
ok, if anyone flies with this, i want 10% of the gross!


ooohhhh...
i just got a KILLER idea!!!!!!!!!!!

 

[slim_t]

Originally posted by Elapid
how about...... my core-burner to end-burner idea,

This was the idea I liked. I don't pretend to know alot about rocket motors, but it seems this would be a good way to get a heavy rocket on its way fast and then still provide a long gentle boost after it was up to speed. ???

But this may already be in use. Does anybody know?

Tim

 

[jetra2]

I think the C5's by Estes were sorta like this.

Not sure though.

Jason

 

[DynaSoar]

Originally posted by slim_t
This was the idea I liked. I don't pretend to know alot about rocket motors, but it seems this would be a good way to get a heavy rocket on its way fast and then still provide a long gentle boost after it was up to speed. ???

But this may already be in use. Does anybody know?

Tim

(Core-burner to end-burner)

I don't know if this is how they do it or not, but any motor that gives a hard boost followed by a long low sustain is performing this way. Look at the thrust curve for the Apogee E6: https://nar.org/SandT/pdf/Aerotech/E6.pdf

Jet is right, the Estes C5 does too: https://nar.org/SandT/pdf/Estes/C5.pdf

"This bird? It's a Mars Snooper, mate. It's got BEAUTIFUL PLUMAGE."

 

[LMazza]

The very same core-end burning motor idea came to me about two days ago. I was thinking about altitude record attempts and how best to do them with a single motor. Anyway, how does an Estes C5 have a propellant core? The igniter sticks in just as far as any other Estes motor.

 

[DynaSoar]

Originally posted by LMazza
The very same core-end burning motor idea came to me about two days ago. I was thinking about altitude record attempts and how best to do them with a single motor. Anyway, how does an Estes C5 have a propellant core? The igniter sticks in just as far as any other Estes motor.

The igniter goes in until it's wedged against grain. The grain has a hole in the C5-3. I just took a paperclip and stuck it into a C5-5 and a C6-3 (and C6-5). It goes in 1/4" farther on the C5-3. The C5-3 does start out as a core burner.

 

[LMazza]

Ok, thanks for clearing that one up. I guess I never noticed that difference.

 

[Elapid]

Originally posted by DynaSoar
Shapes:

well, by reading, i have answered some of my questions on my own.

shapes... bad idea.
the surface area of burning propellant drops off radically when the burning propellant surface reaches the walls of the case, causing pressure to drop and burning of propellant to cease before it is all used up. the result is that the incomplete combustion lowers the delivered impulse of the motor.

no thanks.

 

[hokkyokusei]

Originally posted by slim_t
This was the idea I liked. I don't pretend to know alot about rocket motors, but it seems this would be a good way to get a heavy rocket on its way fast and then still provide a long gentle boost after it was up to speed. ???

But this may already be in use. Does anybody know?

Tim

There are some BP motors available over here in the UK from time to time that use this technique. Huge initial spike that tails away and burns for a long time.