Maggie Muggs Site

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ronchie
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Maggie Muggs Site

Post by ronchie » Tue Jul 19, 2005 2:54 am

Hi i just have a couple questions. I already read the website thats explains how to build one, but sime things where not stated. What size or for what engine is the needle valve assembly used from in your project? I found several on towerhobbies.com

http://www2.towerhobbies.com/cgi-bin/WT ... =GMG&V=SUP

And my second question is what liquid fuels can i use? r/c nitro fuel? gasoline? id like to stay away from propane.
Oh and before i forget theres no picture of the orientation of the flameholder. bottom of the dish facing exhaust or intake(by bottom i mean where say the water would exit if it where in a sink)

One last thing, there wouldnt be a problem welding this all up with a MIG, right?

Thanks for the help,

Al

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re: Maggie Muggs Site

Post by mk » Tue Jul 19, 2005 7:38 am

A MIG should work indeed.
But thin stainless is a bit tricky. Go for short spot like welds. Holes are burned through quite rapidly, but try it out for yourself.
mk

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re: Maggie Muggs Site

Post by larry cottrill » Tue Jul 19, 2005 1:19 pm

ronchie -

Note the dashed line indicating the flameholder in the side-view drawing - that should clarify it. Also, study the order of the steps shown in the site photos. The rear edge of the diffuser butts directly against the strainer top rim.

Yes, definitely weld it up if you are comfortable with that. It is going to be tricky, though, with such thin metal - the mug shells are thinner than a manila folder! With the glued construction, it was easiest to attach the strainer onto the diffuser shell first, since that was almost a perfect fit. The tail 'cone' fits over this with a fair amount of gap all around; for welding, you should provide a SS ring of some sort to fill this in, even if it's just a ring of thin tubing. I got some 1/4-inch OD 316 tubing that would have worked for this, once it got rolled around something to shape it.

I would guess that it's that LXFY29 - that one would certainly be usable. I have the actual needle valve part number somewhere at home, but not here at work. It is a Super Tigre needle valve for a large engine, like a .49 or some such. What I would do if you're in a hurry is print the closeup photos below and take them with you to the local hobby shop and tell them you want the "biggest Super Tigre needle valve that looks like this". How I got mine was a guy at the hobby shop sat down at the computer with me over his shoulder and we looked at what was available until I saw what I liked and special ordered it. It was about $18 US, making it easily the single most expensive part of the whole project! Amazingly, I had it in my hand about 3 or 4 days after ordering!

Good luck! Please note all the testing hints and test plan down on the third site page:
http://www.cottrillcyclodyne.com/Maggie ... gie_3.html
Most important: You'll need all the blower you can get!

L Cottrill
Attachments
Fuel_pipe_finished_crop1.jpg
Finished fuel pipe / needle valve assembly. This has the extra tubing parts attached. Photo Copyright 2003 Larry Cottrill
Fuel_pipe_finished_crop1.jpg (21.72 KiB) Viewed 8574 times
Fuel_pipe_parts_crop1.jpg
Parts of the fuel pipe assembly. The two tubing pieces are what you add on; the little section at bottom center is what was cut off the Super Tigre stock part. Photo Copyright 2003 Larry Cottrill
Fuel_pipe_parts_crop1.jpg (29.88 KiB) Viewed 8573 times
Maggie_engine_scale_1.gif
Original Maggie Muggs scale drawing. Note hidden line showing the flameholder orientation. Copyright 2003 Larry Cottrill
(24.73 KiB) Downloaded 509 times

ronchie
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re: Maggie Muggs Site

Post by ronchie » Tue Jul 19, 2005 2:06 pm

Yes i do feel more comfortable welding it all up. ive welded 22g steel without a problem. say i cant find the mug or would like to use a suitable container i find(for free trying to save money)of the same or similar dimensions. as long as the same principles are there it should work, i think.

also you didnt reply to me about what liquid fuels can be used? gasoline? mix? r/c nitro? Please help me with this one.

Once again thanks for your time and help

Al

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Re: re: Maggie Muggs Site

Post by larry cottrill » Tue Jul 19, 2005 2:59 pm

ronchie wrote:Yes i do feel more comfortable welding it all up. ive welded 22g steel without a problem. say i cant find the mug or would like to use a suitable container i find(for free trying to save money)of the same or similar dimensions. as long as the same principles are there it should work, i think.
Yes, you can use different shaped mugs. Here's what you need to remember:

The function of the two sections of your engine are exact opposites: The front end diffuser section must increase in area as the air flows rearward. This slows the flow velocity and actually increases the pressure! The combustion chamber / nozzle section does just the opposite - it converts increased pressure [due to expansion from combustion heat] to high velocity. What you need in the diffuser is a shape that leads as smoothly as possible from the intake into a significantly larger area at the flameholder. What you need in the rear section is a large area region for gas expansion, smoothly blending down into a somewhat narrower nozzle section. In terms of areas, I would use 2-to-1 as a limit for both parts, at least for a low speed engine like this. It is a mistake to try to get the ratios too high, in my opinion.

Interestingly, there is no reason you can't use exactly the same mug shell type for both ends! I just wanted a shortened form for the front end for the sake of making the design more compact, but I could have used a longer "Coke glass" shape just like the rear section [cut back a couple of inches to get a smaller diameter to fit the rim of the strainer]. Again, have a look at Page 3 of the site - note that Ben Koopman's mug shells were completely different in design from mine. But also note how the shapes meet the reqirements I've just described above!

Incidentally, the pressure tap in the diffuser section is purely optional. You probably won't find a gauge sensitive enough for the slight pressure rise, anyway, although you could use a water manometer [U-tube] to measure it, if you're really interested.
also you didnt reply to me about what liquid fuels can be used? gasoline? mix? r/c nitro? Please help me with this one.
Sorry, I forgot to comment on that. I wouldn't use R/C fuels UNLESS you can get a version that has NO lubricating oil! Vegetable oils like the Castor oil in model fuels dry to a very gummy, even hard, residue that will really mess things up unless you want to clean it out carefully with strong alcohol after every run! Instead, you can use plain alcohol such as methanol [like Heet brand de-icer] or gasoline. Kerosene would probably be just as good as gasoline and much safer to handle [that's why it's used for jet fuel in the big engines!].

I would start out with your resting fuel level slightly below the needle valve, open the valve a few turns and see if the blower will draw fuel in. If it doesn't, set up your fuel so you can adjust your fuel tank up and down quickly in relation to the needle valve. [I'm thinking of something like those vertical rod stands and clamps used in Chemistry Lab at school.] Changing height is a very easy way to vary the pressure. If you want 'tighter' needle valve settings, you can experiment with a squeeze bottle, as Ben's teacher is doing in the pictures. Though that method sounded tricky to me, he and Ben liked it because the squeeze bottle gave them instant control over pressure and flow. I'll bet using it effectively took some practice, though. I personally would prefer having a small electric pump [maybe like a windshield washer pump] giving more-or-less constant pressure, and controlling flow with the needle valve. That's really how it was intended to be used.

And remember, NEVER stop the air flow while fuel is flowing into your engine! Always start the air first and shut it off last. If your blower ever quits during a run, your first concern is stopping the fuel flow IMMEDIATELY, so make sure you provide a way to accomplish that.

I hope this helps.

L Cottrill
Last edited by larry cottrill on Tue Jul 19, 2005 3:10 pm, edited 1 time in total.

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Re: re: Maggie Muggs Site

Post by larry cottrill » Tue Jul 19, 2005 3:06 pm

I should have mentioned that I really prefer propane vapor for preliminary testing, because I consider it very safe and easy to use. A simple regulator gives perfect pressure stability, so you can adjust very accurately [and repeatably] using the needle valve.

L Cottrill

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re: Maggie Muggs Site

Post by ronchie » Tue Jul 19, 2005 4:12 pm

Thanks for the quick responses larry youve been a great help. is it mandatory i test with propane? i cant just start out with kerosene? id rather not mess with propane. yeah i thought about something like those vertical chemistry stands for the bottle. i didnt think squezeing the bottle is a safe idea unless there where a vent hole. actually as i wrote this my father explained to me a very functional way to use the squeze bottle method safely! i drew up a little sketch in paint to explain. if the bottle were in use it would be upside down thus the vent tube must reach to the bottom. when u want to add pressure simply cover the vent tube with your finger and apply pressure to the bottle. when you want to stop pressure uncover the vent tube and the bottle will safely recover air. the purpose of this design is not only for safety but function as well.

thanks

Al
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jet fuel bottle 1.JPG
fuel system
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Last edited by ronchie on Tue Jul 19, 2005 7:40 pm, edited 3 times in total.

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re: Maggie Muggs Site

Post by larry cottrill » Tue Jul 19, 2005 6:00 pm

Al -

Propane is just a preference of mine because I'm properly set up for it and have used it now for a while on pulsejets. There's no reason you can't start out with a liquid fuel. Go with kerosene, I'd say. It's safer than gasoline, especially if there are accidental leaks or spills.

The little bottle rig looks like a nice design! I think there might be things something like that for filling model fuel tanks and so on. Keep in mind that in the inverted position as you have it shown, fuel will flow freely if you forget and un-block the vent! You might want to use a little shutoff valve rather than just your thumb over it - sort of a 'two handed' requirement for safety.

L Cottrill

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re: Maggie Muggs Site

Post by Zippiot » Tue Nov 15, 2005 8:12 pm

i am having a few problems keeping my ramjet running. most likely it is my ful setup, its a mix of gasoline fumes with a little liquid fuel. it burns so hot that the brass fuel injection gets red hot (changing the color of the flame to green). i will probably change to propane soon, but until then any tips? maybe a cone in the front to compress the air more so i have less fire shooting out the front of it. my air supply is very powerful (5 hp shop vac) so i doubt that is the issue.
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Re: re: Maggie Muggs Site

Post by larry cottrill » Tue Nov 15, 2005 9:44 pm

Zippiot wrote:i am having a few problems keeping my ramjet running. most likely it is my ful setup, its a mix of gasoline fumes with a little liquid fuel. it burns so hot that the brass fuel injection gets red hot (changing the color of the flame to green). i will probably change to propane soon, but until then any tips? maybe a cone in the front to compress the air more so i have less fire shooting out the front of it. my air supply is very powerful (5 hp shop vac) so I doubt that is the issue.
Zippiot -

If you're getting flame in the front end of your engine, you don't have the air velocity it takes to get through your flameholder without a large pressure drop.

Is your flameholder exactly like the one I showed on the Maggie site? You've got to have almost more holes than steel! Can you post photos of what you built?

For it to be right, you should have just a slight velocity loss through the engine. This should result in no flame at all out in front of the flameholder. Try to borrow a big leafblower - the velocity will probably be higher than what you get from a shop vac, even a big one. But remember, you still have to have a LOT of your available air going over the outside of your engine! (How much depends on whether you glued or welded your build - which way did you build it?)

Try propane (which is slower burning). If you still have trouble with flame up front, do what Steve Bukowski did with his little engine - get the fuel piped in just BEHIND the flameholder in the turbulent zone. This will work very well with vapor fuel, at just a few PSIG, since the pressure in the chamber will not be very high even with the engine going full blast.

L Cottrill

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re: Maggie Muggs Site

Post by Zippiot » Tue Nov 15, 2005 11:59 pm

i borrowed my neighbors leaf blower, it makes much less airflow than the shop vac (the shop vac is as much bigger than my 36 inch tv). i am still getting a lot of flame though the front, i am using a stainless strainer as the flame holder, just like the one you used. my front end is actually pressure fitted to my rear, the two pieces almost fit so i heat up the rear and hammered the front end in. i cant get a pic up just yet, ill try rounting the intake behind the flameholder until then. maybe an augmentor in front of the thing will help?
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re: Maggie Muggs Site

Post by Zippiot » Wed Nov 16, 2005 5:46 am

so i made a few adjustments, and it works. i found a perfect diffuser, but i couldn't figure out how to attatch it. it was a cone made of aluminum. i was just rummaging around and i found a large thick washer that fit perfectly in the intake. i am amazed to report that it actually works. the thing is so loud that i need to wear ear protection, being mostly deaf that says something. i get a nice cone of blue flame that extends between 6 and 12 inches out the exhaust. the shop vac is sufficient for testing, but i can use a more powerful one. the plastic keeps melting away, i need to find a metal tube that i can use as a fuel line, unless anyone has a suggestion?
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re: Maggie Muggs Site

Post by larry cottrill » Wed Nov 16, 2005 3:26 pm

Zippiot -

Congratulations!!!

Get us a video, or some pictures ... we'd like to see that!

Make sure you look at Steve Bukowsky's TLAR Ramjet thread and the video he posted there. Exciting stuff!

L Cottrill

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re: Maggie Muggs Site

Post by larry cottrill » Wed Nov 16, 2005 3:40 pm

Zippiot -

One more thing. I thought about this last night, and I wonder if maybe that big shop vac isn't delivering TOO MUCH velocity for the type of flameholder Maggie has! What I'm thinking is, maybe it's actually choking the flameholder so you just get pressurized stalled air and a lot of the air just gets "bounced" back out the front, i.e. the diffuser area is full of turbulence.

Here's what I'd like you to try sometime, and report back in: Go back to the original form of the diffuser (in other words, get rid of your big washer) and try working your jet in from a distance of maybe 3 ft (1 metre) out in front of the nozzle of your blower. Gradually work it in, adjusting for more and more fuel as you go. I'll bet you'll find a point where it will run really well, but it will be quite a few inches out from the nozzle.

A powerful blower like that might actually be a reasonable air supply for a more "classic" or "textbook" ramjet design with conical flameholders, like the paper model shown in the photo below (rear end in hand).

Thanks for reporting your findings! All the best,

L Cottrill
Attachments
Model_ramjet_crop1_small.jpg
Model of classic "textbook" ramjet, designed for high subsonic velocity operation. Note conical flameholders. Photo Copyright 2005 Larry Cottrill
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Zippiot
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re: Maggie Muggs Site

Post by Zippiot » Wed Nov 16, 2005 5:51 pm

i found the perfect piece for that!! ill give it a try tonight, and it seems that it was making turbulence in front, the flame was being pushed out the front because the strainer made too much resistance. even with the shop vac pushed as close to the thing as possible some of the area in front of the flameholder got red hot.

a wierd thing that i cant explain is that the closer i bring the shop vac to the opening of the jet, the more the flames curl back towards the shopvac. my only explaintion is that the back of the jet is making high pressure from the heat and the shop vac with its high speed moving air is making low pressure. a vacume making a vacume...
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