Is this a Maggie?

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phonedzero
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Is this a Maggie?

Post by phonedzero » Mon Feb 09, 2009 4:46 am

Well is this what one should expect from this build? This one the second run, and now the little fire breather needs a rebuild. The cement although good for high heat is to brittle and cracks very easily!

http://www.youtube.com/watch?v=_opm6e7UO_Y

larry cottrill
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Re: Is this a Maggie?

Post by larry cottrill » Mon Feb 09, 2009 1:35 pm

phoned -

Man, I have to hand it to you -- THAT is impressive! The flame looks too rich, i.e. too much fuel for the air flow used. Try to adjust fuel flow for a nice blue flame (I realize that the video may not be showing it accurately, of course).

If anything, I'd say your air is TOO fast for this design (probably because of the fairly "steep" diffuser cone). The flameholder is probably working OK, but there's a lot more combustion behind the chamber than there should be, I think. After repairs, try it with the blower a little farther away, or at a lower speed setting (if adjustable). Remember, any given ramjet design will only be good for a fairly narrow speed range.

All that being said, you have the right idea, basically, and you've done a good job of building her and showing that she will in fact run.

Since you need to re-build (at least to some extent), this is a good time to consider replacing the diffuser with a longer, narrower cone. That should give stability with a higher inlet speed.

But anyway, nice work, man!

L Cottrill

phonedzero
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Re: Is this a Maggie?

Post by phonedzero » Mon Feb 09, 2009 1:43 pm

Thats great, I figured I was headed in the right direction! The blower was on its lowest setting so moving it back is my only hope to slow it down a bit, on all my runs fuel was barely cracked to achieve the effects seen! Can't wait to put the engine back together and have another go! Great design and sooo easy to build! Thanks again Larry!

phonedzero
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Re: Is this a Maggie?

Post by phonedzero » Mon Feb 09, 2009 4:47 pm

Hey Larry---Re the flame cone, if built properly should I be able to pull the cone down into something a bit tighter and more focused, and would it help to also flare the exhaust outlet. Is there a proper ratio inlet diam/body length/outlet diam, that I can follow seeing as how it can be difficult to gather the supplies as per your original design?

larry cottrill
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Re: Is this a Maggie?

Post by larry cottrill » Mon Feb 09, 2009 6:58 pm

phonedzero wrote:Hey Larry---Re the flame cone, if built properly should I be able to pull the cone down into something a bit tighter and more focused, and would it help to also flare the exhaust outlet. Is there a proper ratio inlet diam/body length/outlet diam, that I can follow seeing as how it can be difficult to gather the supplies as per your original design?
No, I wouldn't change the exhaust end or flameholder -- I think those are working for you. Refining the diffuser is probably the single best thing you can do. I think right now, your action is mostly from velocity rather than pressure. A longer diffuser should smooth things out at the front end of the chamber, and then you'll have more of the kind of burn you want. The key is the get the air flow "smooth and slow" going into the chamber at the flameholder location.

Again, the classic example of one running right is the video by Steve Bukowsky -- his little scale-down of the Hiller copter tipjet. Just scroll down in this forum a while and you'll find it, probably from two or three years ago.

EDIT: OK, it's right here:
viewtopic.php?f=4&t=1881#p21789
Just download the ZIP file and enjoy! This is exactly how they should run.

L Cottrill

larry cottrill
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Re: Is this a Maggie?

Post by larry cottrill » Tue Feb 10, 2009 1:40 pm

I'm always amazed at how many people have tried this idea (the Maggie Muggs basic plan). My older son David says it has a kind of "cult following". The idea is crazy, really: Build a jet engine with the philosophy you'd accept to build a model airplane -- glue a bunch of pieces together and hope for the best.

They don't last long once you try them out. But, apparently, they are cheap enough and fun enough that the lack of robustness doesn't matter to anyone. I would never have guessed that the idea of putting so much work into a "non-permanent thing" would be so gladly accepted!

Amazingly, I have never been slammed by anyone that actually built one of these and got it running, however briefly. And that, even though my original plan is never followed exactly, due to the difficulty of finding exactly the parts I used.

L Cottrill

phonedzero
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Re: Is this a Maggie?

Post by phonedzero » Tue Feb 10, 2009 3:00 pm

It is a great project for anyone interested in jets, rockets, fire, noise! I am going build one with my son next weekend. What you need to do Larry is put a kit together, two mugs, jb weld, fuel line and fitting, and a flameholder! Let guys figure out their own stand, 50 bucks a kit! For me it was a great way to break in my new shop, and I just love to build stuff, especially since I found out that you could build and run a jet engine in your backyard! Has any ever used larger stainless vessels ie. thermos bottles. I'm just thinking about how big one could make a Maggie with off the shelf products! This was defenitly the most fun I have had, playing with all these different engines and principles. A welder friend said he would TIG weld a Maggie together, I may do that just to have a permenant unit to pull out at a moments notice! My wife and friends think I am mazzo!

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Re: Is this a Maggie?

Post by larry cottrill » Wed Feb 11, 2009 8:38 pm

phonedzero wrote:It is a great project for anyone interested in jets, rockets, fire, noise! I am going build one with my son next weekend. What you need to do Larry is put a kit together, two mugs, jb weld, fuel line and fitting, and a flameholder!
Well, phone, there are a few (ha) problems with this plan.

Way back a few decades ago, there were lots of outfits making electronic kits -- low-distortion stereo amps and preamps, oscilloscopes and other test instruments, you name it. I built TWO Heathkit 25-inch color TVs for my dad and mom, one in 1966 and a nice all-solid-state one (that I still have) in 1976. From the time I was 10 years old until I was about 24 or 25, I built no less than two Heathkit products per year. I've also built Dynaco kits, Eico kits and even cheap little single-board kits sold off a pegboard rack in plastic bags! So where are these companies today? Just long gone.

The Heath Company was probably the all-around best, especially for beginners. Their motto was "We won't let you fail!" They had an entire phone-ready staff to answer questions and handle problems, and another staff to repair returned units. You'd better believe they saw some doozies, in terms of workmanship! And staffing a "help desk" costs real money. But that's the kind of service that's expected. Of course, most people who know me from the forums would know I can't provide that level of service -- you DO know I have a day job, right? But to sell a bunch of them to the "public" (and sure, I think that would be really cool), you HAVE to provide some level of service after the sale, or your reputation in the marketplace is quickly shot. A one-man show just can't do that, in my opinion. And remember, we're talking about something that could burn down somebody's shed or even their house!

The problem is basically that when you market kits to the public, you CANNOT ASSUME any certain knowledge or skill level. That impacts not only the building of the kit, but the potential liability incurred in getting it to work. Any good lawyer will tell you that you cannot realistically work around the liability issue, try as you might with "ironclad" disclaimers or whatever. If someone wants to, they will sue. If someone is physically hurt and sues, they will win. In some ways, kits have less potential liability, in some ways greater liability, than selling a finished product (where you at least have control over the quality at first run). Of course, you can argue that there's even SOME liability to offering designs on a forum. But at least, most of the interested parties are talking to each other and thus have some idea of the hazards involved, safety precautions, proper technique, etc. You don't usually have 9-year-olds diving in "blind" just because of a flashy ad in a magazine or on a Web page. But of course, there's nothing that can actually prevent that from happening, either.

The world gets weird quickly when you start offering dangerous toys to anybody that shows up with 50 bucks.

L Cottrill

phonedzero
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Re: Is this a Maggie?

Post by phonedzero » Wed Feb 11, 2009 8:53 pm

Understood! I always laugh at how we all made it through childhood without bike helmets, had Daisy air rifles, and 'be home before the sun sets', but seems impossible to occur in todays world!

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