Motorjet

Moderator: Mike Everman

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

re: Motorjet

Post by larry cottrill » Wed Jul 05, 2006 4:41 pm

superhornet -

I have always thought that some experimentation would lead to a really good motorjet. That seems especially likely now that there are some really good little ducted fans available/affordable. I think your plan is basically a good one - just a couple of changes I would make:

Try to build your ramjet by getting it welded up, rather than by trying to use the original bonded (glued) Maggie Muggs construction. The reason is, you want to use all the air from your fan to drive the engine, which leaves you with no cooling airflow around the engine exterior! Of course, it will get some cooling once your vehicle starts moving, but that won't be enough if you're using an epoxy like J-B Weld for construction.

Alternatively, you could build your Maggie with something more high-temp, like some kind of muffler patch resin or some such. That's probably what I should have done with Maggie to begin with, but then the whole thing was just experimental, anyway.

A smooth cone for the diffuser section would be just as good as, if not better than, the 'Coca Cola glass' shape that I used on the original. So, don't worry if you can't get exactly the same shape for the parts. The important thing is to get a good fit around the rim of the sink strainer flameholder where it all comes together. Then, make sure you get adequate cooling air so the really high temps will be held well back in the chamber.

I certainly hope you go forward with this project! Be sure to document everything with pics you can post here. I assume you have seen my earlier comments and visited the link I presented (someone who's actually tried it):
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2067

I have also seen the motorjet called a 'thermojet', but that is a poor word for it, since that was a trade name for Melenric's valveless pulsejet designs, and should really be exclusively used for clones or further developments based on those designs. I think 'motorjet' is a perfectly fine term for the engines we're talking about here.

Good luck!

L Cottrill

Zippiot
Posts: 1190
Joined: Tue Nov 15, 2005 7:55 pm
Antipspambot question: 0
Location: california
Contact:

re: Motorjet

Post by Zippiot » Sat Jul 08, 2006 6:38 am

modified maggie muggs running near motorjet operation :)

I say neart b/c I stuck a nozzle on my 5hp shop vac and stuck the nozzle right into the modified intake of the ramjet...
It makes near 0 thrust but is quite loud, with a little math and experimentation you can prolly get over 8 pounds with this set-up
Attachments
674698992_m.jpg
startup, running rich
674698992_m.jpg (3.9 KiB) Viewed 13199 times
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
Sailing Student- Yes
Me- Then its too loose!

A.G.G.
Posts: 36
Joined: Sun May 08, 2005 7:11 pm
Antipspambot question: 0
Location: mexico guadalajara

re: Motorjet

Post by A.G.G. » Sun Jul 09, 2006 12:08 am

my motor jet / ram jet
Attachments
DSC00047.JPG
(344.65 KiB) Downloaded 1202 times

A.G.G.
Posts: 36
Joined: Sun May 08, 2005 7:11 pm
Antipspambot question: 0
Location: mexico guadalajara

re: Motorjet

Post by A.G.G. » Sun Jul 09, 2006 12:14 am

chamber combustion
Attachments
mi edf 2.JPG
(1.03 MiB) Downloaded 1208 times

A.G.G.
Posts: 36
Joined: Sun May 08, 2005 7:11 pm
Antipspambot question: 0
Location: mexico guadalajara

re: Motorjet

Post by A.G.G. » Sun Jul 09, 2006 12:19 am

ducted fan
Attachments
mi edf 3.JPG
(1020.88 KiB) Downloaded 1165 times

El-Kablooey
Posts: 723
Joined: Tue May 31, 2005 3:39 am
Antipspambot question: 0
Location: Northwest Georgia, USA

re: Motorjet

Post by El-Kablooey » Sun Jul 09, 2006 1:32 am

Interesting, AGG. Does it produce an increase in thrust over the ducted fan alone?

Najm
Posts: 120
Joined: Sun Apr 03, 2005 9:59 am
Antipspambot question: 0
Location: Karachi,Pakistan

re: Motorjet

Post by Najm » Sun Jul 09, 2006 4:43 am

my motor jet / ram jet
Did you measure what thrust it's producing?

Zippiot
Posts: 1190
Joined: Tue Nov 15, 2005 7:55 pm
Antipspambot question: 0
Location: california
Contact:

re: Motorjet

Post by Zippiot » Sun Jul 09, 2006 7:38 am

Wicked nicer than my pos :)
I should redesign the flameholder intake and nozzle...which in a ram/motor-jet is pretty much the entire thing!

One day we will have these inside of r/c planes, soon if we keep making ones like that AGG, nice work!
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
Sailing Student- Yes
Me- Then its too loose!

Zippiot
Posts: 1190
Joined: Tue Nov 15, 2005 7:55 pm
Antipspambot question: 0
Location: california
Contact:

re: Motorjet

Post by Zippiot » Sun Jul 09, 2006 7:45 am

jet on its own, isnt very shiny anymore...
Attachments
Picture 042.jpg
looks pretty, wolf in sheep's clothing
(595.2 KiB) Downloaded 1163 times
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
Sailing Student- Yes
Me- Then its too loose!

A.G.G.
Posts: 36
Joined: Sun May 08, 2005 7:11 pm
Antipspambot question: 0
Location: mexico guadalajara

re: Motorjet

Post by A.G.G. » Mon Jul 10, 2006 2:33 am

hello

I do not speak English good

not measured the push but it is little :(
in fact he is not ducted fan is a fan of hair dryer

http://www.rcgroups.com/forums/showatt. ... tid=777461

Najm
Posts: 120
Joined: Sun Apr 03, 2005 9:59 am
Antipspambot question: 0
Location: Karachi,Pakistan

re: Motorjet

Post by Najm » Mon Jul 10, 2006 5:15 am

Any fan in a duct is a ducted fan.
I'm going after this project also.

Zippiot
Posts: 1190
Joined: Tue Nov 15, 2005 7:55 pm
Antipspambot question: 0
Location: california
Contact:

re: Motorjet

Post by Zippiot » Mon Jul 10, 2006 2:04 pm

Check out the pic I submitted above, you can see it works off of many differently shaped muggs. I dont think you will get the flow you want from a computer fan, as it takes a 5 hp shop vac for me to sustain the propper fuel to air ratio in my maggie muggs...
But try it out and see
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
Sailing Student- Yes
Me- Then its too loose!

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

re: Motorjet

Post by larry cottrill » Mon Jul 10, 2006 2:32 pm

hornet -

Here's the thing about the shape of the mugs: There's no reason you have to use the exact shape in my original drawings, BUT both the diffuser and the chamber/nozzle sections should be smoothly curved. The ideal theoretical shape for the diffuser would actually be a simple cone - the "Coke glass" shape I used is acceptable only because this is meant to be a very low speed form of ramjet. It is really important for the chamber to flow smoothly into the nozzle, too, if you want good thrust development. A "sharp" break from chamber to nozzle will work for an engine that's just an experimental demo, but the losses at the sharp nozzle point will be more than you really want for maximum efficiency. The sharp break will also crate a severe "hot spot" at that point which will be difficult to cool adequately. (For good cooling, the flow around the outside of your engine should be just as smooth as the flow inside!)

Your "flameholder" strainer looks exactly right - almost half the total area should be holes. When it's running, there will be a little flame cone behind every hole before they all blend together in the chamber.

The "ripples" in the rear section are unnecessary. I just liked them because they look cool. They also theoretically strengthen the very thin shell a little, sort of a corrugated culvert effect. But, the design will definitely work fine without them.

L Cottrill

Zippiot
Posts: 1190
Joined: Tue Nov 15, 2005 7:55 pm
Antipspambot question: 0
Location: california
Contact:

re: Motorjet

Post by Zippiot » Mon Jul 10, 2006 2:42 pm

Search the forums for axial flow turbine (you might still see it in the turbine section). I have a great sheet(s) of math for an axial flow, sorry to say it but a simple computer fan prolly wont work...
I say that b/c small axials are so picky it would be hard to get everything just right.

If you really want to start turbine check out this book, best thing you can do as first steps towards home built turbines!


http://www.amazon.com/gp/product/095105 ... 16?ie=UTF8

(I know its 60 bux but with that design you can build a working turbine for under 200!)
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
Sailing Student- Yes
Me- Then its too loose!

Zippiot
Posts: 1190
Joined: Tue Nov 15, 2005 7:55 pm
Antipspambot question: 0
Location: california
Contact:

re: Motorjet

Post by Zippiot » Tue Jul 11, 2006 6:48 am

I have gotten my muggs to 1200 degrees F. To be fair my "modified" muggs has no glue and is instead heat/pressure fitted to eachother (heated one mugg cooled the other and smahed them into eachother, works great!).
Mixing in some fiberglass can sometimes help with the heat and strength at heat issue, chop it up with scissors and mix it up good!
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
Sailing Student- Yes
Me- Then its too loose!

Post Reply