Vintage Ramjet Model Engine Plans [e-Bay]

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larry cottrill
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Vintage Ramjet Model Engine Plans [e-Bay]

Post by larry cottrill » Tue Dec 21, 2004 5:13 pm

Have a quick look at this - it certainly has simplicity in its favor:

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 57814&rd=1

But, I wonder how aluminum holds up? It kind of looks like an inner ramjet shell and an outer streamlined shell with fuel filling the gap and boiled fuel vapor driving the process via ejector action in the venturi ... or something ... but, I don't think I'm willing to buy it to find out for sure.

Anyone familiar with this plan? Forrest ... ?

[Please try to be forgiving if someone's already posted this long ago or something, and I missed it!]

L Cottrill

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by Bruno Ogorelec » Tue Dec 21, 2004 8:14 pm

I've been bequeathed -- by a very kind and enthusiastic fellow -- a set of cutaway drawings of experimental 40s ramjets that flirted with pulsating combustion, including ones with rotary valves...

Far more interesting and tantalizing than the stuff these people sell.

I wonder how much those would bring on eBay.

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by WebPilot » Wed Dec 22, 2004 2:05 am

Larry,

It's a pressure jet.

I have this plan. I think, I saw it for my first time on Paco's site. I have subsequently found it again in another publication where it was photographed spinning on a stand - impressive.

My take on this is:
  • the fuel tank is in the hollow outer shell
  • the tank is heated with lit cotton wadding shoved into the venturi
  • as the tank heats, the alcohol vaporizes and spews from the jet
  • the vaporized alcohol ignites, thus heating the tank
  • the cotton wadding is removed prior to forward motion.
Its a reaction engine - it's throwing mass out the back end thus propelling the jet forward. Clever, though, about its utilization of heat regeneration. It operates similarly to a Hero's steam engine.

I know, some of you want to believe it has created a stationary flame front, and the air coming in is heated, expanded, and thus accelerated out the back. Well, I don't know about all that - I don't think the jet accelerates to that high of a velocity. I think the open fore end is there to merely insure enough air gets inside to keep the fuel burning.

It does appear to be a neat little engine - using aluminium, obviously, makes it weigh less. I'd use thin steel for a prototype - you'll be doing a lot of hammering over forms.

Later,

-fde

PS Hmmm. Are these guys really making money from plans I have found in old magazines?
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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by Bruno Ogorelec » Wed Dec 22, 2004 3:04 pm

WebPilot wrote:Are these guys really making money from plans I have found in old magazines?
Quite possibly. The web is so huge that you can find customers for everything, including stuff that can be had for free elsewhere. The cost of doing business is low, too.

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by mk » Wed Dec 22, 2004 6:55 pm

WebPilot wrote:Larry,

It's a pressure jet.

I have this plan. I think, I saw it for my first time on Paco's site. I have subsequently found it again in another publication where it was photographed spinning on a stand - impressive.

My take on this is:


* the fuel tank is in the hollow outer shell
* the tank is heated with lit cotton wadding shoved into the venturi
* as the tank heats, the alcohol vaporizes and spews from the jet
* the vaporized alcohol ignites, thus heating the tank
* the cotton wadding is removed prior to forward motion.



Its a reaction engine - it's throwing mass out the back end thus propelling the jet forward. Clever, though, about its utilization of heat regeneration. It operates similarly to a Hero's steam engine.

I know, some of you want to believe it has created a stationary flame front, and the air coming in is heated, expanded, and thus accelerated out the back. Well, I don't know about all that - I don't think the jet accelerates to that high of a velocity. I think the open fore end is there to merely insure enough air gets inside to keep the fuel burning.

It does appear to be a neat little engine - using aluminium, obviously, makes it weigh less. I'd use thin steel for a prototype - you'll be doing a lot of hammering over forms.

Later,

-fde
Being a kind of pressurejet as Forrest wrote here, it reminds me on the M.E.W. 601 engine and my inspired "rebuild" (it's not an exact rebuild; just guessed and thrown together from stuff laying around).
It was and still is an impressive little fuel burner for me. An eye-catcher also for other people. Simply fascinating.

Check out http://www.pulse-jets.com/phpbb2/viewtopic.php?t=916

Of course the tank pressurization with a single flame only (no pan needed) is much nicer.
I squeezed the ejector pipe to improve a burner/engine of my "rebuilds"; The shape became similar to the burner/engine shown in the ebay link.
Probably the size of the fuel jet at my rebuilds was or rather is way too big for working resonably.

It caught my mind again...
mk

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by larry cottrill » Thu Dec 23, 2004 6:29 pm

Forrest, Marten et al -

A hideous and dangerous thing has just occurred to me:

I have a piece of hardware that is strikingly similar to the interior part of this 'pressure jet', including the fact that it is aluminum. It is much larger, though. It is in fact, the venerable 'instrument gyro venturi' ...

The picture below indicates how I thought of using it as a carburetor in a valveless engine. If the inside part were tweaked into becoming a spout for fuel vapor, it would kind of do what we're told the little "ramjet" is doing, and also rather like the tail end of the MEW 601.

L Cottrill
Attachments
Venturi 1.jpg
Aircraft instrument venturi as carburetor - not that far from a crude 'pressure jet'? Drawing Copyright 2002 Larry Cottrill
Venturi 1.jpg (96.87 KiB) Viewed 10284 times

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by larry cottrill » Thu Dec 23, 2004 6:35 pm

mk wrote:Being a kind of pressurejet as Forrest wrote here, it reminds me on the M.E.W. 601 engine and my inspired "rebuild" (it's not an exact rebuild; just guessed and thrown together from stuff laying around).
It was and still is an impressive little fuel burner for me. An eye-catcher also for other people. Simply fascinating.
Marten -

Since you enjoy firing it up, why not make a simple thrust stand and measure the thrust? You might be surprised at what it does!

When I had a couple of the 601s, I never bothered to try this, and it has bothered me ever since that I never confirmed whether the tail tube, or for that matter, even burning the ejected fuel, added anything over the simple reaction force from the fuel being sprayed out!

It would be fascinating to figure out ways to optimize the action of such a crude device, and get some form of it that could actually be used to drive small models. The little "ramjet" form eliminates carrying the firepan around, so there's part of the problem licked, already.

L Cottrill

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Self Regulating???

Post by larry cottrill » Thu Dec 23, 2004 7:03 pm

Here is one thing I thought of about the most obvious difference between the so-called "ramjet" and the MEW. The big difference, of course, is that in the MEW 601, the heat for boiling the fuel is independent of the heat of combustion in the jet tube, while the aluminum "ramjet" uses the waste heat from combustion for its pressurization.

But, consider - this might mean that the little aluminum wonder is actually self-regulating and protected from over-pressure! To wit:

As pressure increases, the boiling point of the liquid goes up! [This is why you use pressure cookers to boil eggs if you live in Denver.] Now, what this means is [well, if I'm right, anyway] that if the fuel vapor pressure climbs significantly in the top of the chamber, the fuel will temporarily stop boiling [reducing combustion heat] until the pressure can drop a little. Thus, the thing is actually a thermal-feedback fuel pressure regulator as well as a boiler!

(Hey, don't laugh - it isn't everyone that comes up with this stuff! ;-)

L Cottrill

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by mk » Thu Dec 23, 2004 7:08 pm

Considering the original M.E.W. 601 with a tiny fuel jet:
I think you want hot(?) liquid fuel entering the fuel jet and a spray of hot(?) liquid fuel forming just after the fuel jet outlet.
Then vaporization hapens after the pressure drop, while or rather a bit after the fuel spray is forming (- after passing the fuel jet outlet if you will). Otherwise the liquid fuel spray is vaporised through combustion heat partially before and partially while burning.


Hmmm...the shown simple kind of ramjet or rather pressure jet seems to establish a flame front just after or at the venturi neck, but my M.E.W. 601 "rebuild" assembled with the (I think) too large fuel jet needs the pan flame for operating, not only for pressurizing the fuel tank.

If do remember right, the video also shows how a part of the pan flame is succed into the ejector (that's why I did change/improve the rear plate of the pan, having a bent lid). Then the pan flame ignites the fuel spray.

What happens at the original M.E.W. 601? Is there established a kind of flame front or is the pan flame also necessary for a kind of "constant ignition" in the ejector (Larry [if I do remember right], you also replied under the "rebuild topic" that the ejectors glowing zone begins just a few milimeters behind the fuel jet outlet)?

I wonder if the presented ramjet or pressure jet would self-sustain then...hmmm.
mk

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by larry cottrill » Thu Dec 23, 2004 7:27 pm

mk wrote:Hmmm...the shown simple kind of ramjet or rather pressure jet seems to establish a flame front just after or at the venturi neck, but my M.E.W. 601 "rebuild" assembled with the (I think) too large fuel jet needs the pan flame for operating, not only for pressurizing the fuel tank.
I think the MEW only needed the pan flame for starting ignition, really - as long as the burn never got interrupted, it would keep going as long as fuel and air were available, I'm sure. All I'm saying above is that the combustion in the tube did NOT influence the boiling action in the tank.

Marten, in your video, as the thing runs low on fuel, it starts hesitating and re-firing for a few seconds. Did you NOT have the internal 'wick' to keep liquid fuel at the spray port? If not, that's probably why it's doing this, and it would also mean you end up ejecting some fuel as vapor, rather than an aerosol [fine droplets].
If do remember right, the video also shows how a part of the pan flame is succed into the ejector (that's why I did change/improve the rear plate of the pan, having a bent lid). Then the pan flame ignites the fuel spray.
Yes, it does that - but I think the only advantage to that is that it will automatically re-ignite if it dies briefly.
What happens at the original M.E.W. 601? Is there established a kind of flame front or is the pan flame also necessary for a kind of "constant ignition" in the ejector (Larry, you also replied under the "rebuild topic" that the ejectors glowing zone begins just a few milimeters behind the fuel jet outlet)?

I wonder if the presented ramjet or pressure jet would self-sustain then...hmmm.
The 'flame front' in the MEW was just the cone of fuel burning a mm or two aft of where it was ejected from the nozzle. The more forward heating of the tube was because the nozzle was so small that the fuel came out in about a 60- or 70-degree cone! It actually was a pretty decent nozzle for atomization of fuel.

I think the aluminum pressure jet would self-sustain, unless fuel flow was interrupted OR the air velocity just got too high for the flame to stay in the chamber - a blow-out. Jet velocity means a lot - when you light an acetylene torch [just the gas burning in air, no oxygen valved in] you can open the fuel valve until the "flame front" moves outward several INCHES from the nozzle, and it self-sustains perfectly. And you can gradually close the valve and bring it back in. I think most fuels in air will behave that way, just at differing degrees due to the different combustion speeds. So, there's no reason the little jet couldn't keep going, at least for low to moderate airspeeds.

L Cottrill

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by mk » Thu Dec 23, 2004 7:45 pm

Larry Cottrill wrote: [...] Did you NOT have the internal 'wick' to keep liquid fuel at the spray port? [...]
A "wick"?
I couldn't see any ejector tube interior shown in the drawings available on the forum. My ejector is just a hollow tube rolled from mild sheet metal.

Can you draw a scetch or give a closer description to me?

Larry Cottrill wrote: [...] it would also mean you end up ejecting some fuel as vapor, rather than an aerosol [fine droplets]. [...]
Ooops. A few times I wrote about "vapors" where I meant "aerosols".
But I think it isn't worth correcting my post; The impact wouldn't be (regarding to the post) or rather isn't (regarding to the burning process) too big.
Larry Cottrill wrote: [...] at least for low to moderate airspeeds.
Of course. It's more an fascinating little fuel burner for demonstration than a real engine for propulsive usage to me.
mk

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by larry cottrill » Thu Dec 23, 2004 8:22 pm

mk wrote:
Larry Cottrill wrote: [...] Did you NOT have the internal 'wick' to keep liquid fuel at the spray port? [...]
A "wick"?
I couldn't see any ejector tube interior shown in the drawings available on the forum. My ejector is just a hollow tube rolled from mild sheet metal.

Can you draw a scetch or give a closer description to me?
Look at the original plan that Bruno posted. The wick is that long, spindle-shaped thing near the boiling chamber. It was a cotton cord thick enough that when you stuffed the end of it into the backside of the nozzle, it would stay. Then what you did was fill the chamber with gasoline and lower the nozzle onto it while threading the wick down in. This would result in gasoline all over your hand, which you allowed to evaporate as you tightened the nozzle onto the chamber with a small, non-sparking wrench. ;-)

So what you ended up with was a chamber full of fuel, with a little cotton rope that fed the spray nozzle with liquid by capillary action. The wick would lie gravitationally in the bottom of the chamber, so liquid was always available at the nozzle. Once you lit the engine off, it would run very evenly until the chamber was almost bone dry, then simply quit!

Marten, I'm really sorry that this detail wasn't brought out while you were building yours! I guess I just thought you understood it from the original plans ...

L Cottrill

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by WebPilot » Thu Dec 23, 2004 9:53 pm

Image

Marten,

I, too, made one of these. I made mine back in the spring. The plan I followed made no mention of a tray.

Thanks for the info.

I am sorry I wasn't around and therefore, missed your post.

Later,

-fde
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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by mk » Fri Dec 24, 2004 10:48 am

Larry Cottrill wrote:Look at the original plan that Bruno posted. The wick is that long, spindle-shaped thing near the boiling chamber. It was a cotton cord thick enough that when you stuffed the end of it into the backside of the nozzle, it would stay. Then what you did was fill the chamber with gasoline and lower the nozzle onto it while threading the wick down in. This would result in gasoline all over your hand, which you allowed to evaporate as you tightened the nozzle onto the chamber with a small, non-sparking wrench. ;-)

So what you ended up with was a chamber full of fuel, with a little cotton rope that fed the spray nozzle with liquid by capillary action. The wick would lie gravitationally in the bottom of the chamber, so liquid was always available at the nozzle. Once you lit the engine off, it would run very evenly until the chamber was almost bone dry, then simply quit!
Then the "wick" is placed into the fuel supply, not into the nozzle/ejector tube. So the nozzle/ejector tube is hollow isn't it?
I noticed this detail, but thought it was a kind of filter (made out of fiber-glass[?]), so I left it out generously. Is it really made out of cotton? Or something else?
All in all a kind of misunderstanding the plan. These wicked details...

When I add a simple wick insted of a cotton(?) spindle to the fuel jet (srew with hole in this case) it might help stopping the overfueling action and the really dangerous fuel jet (jet of [burning] fuel coming out of the reservoir and passing the nozzle) at the very beginning. The spray pattern might also be improved this way (getting a wider angele in my case).

WebPilot wrote:I, too, made one of these. I made mine back in the spring. The plan I followed made no mention of a tray.
WOW! How much time did you spend building the engine exactly as shown in the plan? Just looking at the tiny sheet metal pieces the "spider" is made from...And the fuel reservoir, it's a CO2 or N2O cartridge, isn't it?
The engine is really much nicer than every single on of my "rebuilds".
mk

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Re: Vintage Ramjet Model Engine Plans [e-Bay]

Post by larry cottrill » Fri Dec 24, 2004 5:07 pm

Marten, yes, it is a wick that carries fuel to the spray nozzle. I doubt that it will improve spray performance much, though - the pressure will still be there, and that's what counts in terms of how the nozzle works. I think you need to re-make it with a smaller hole.

Yes, that one by Forrest looks exactly like it, except for the missing pan. The pan will be hard to duplicate - it was an unimaginably crude stamping, something that would knock Al Belli off his chair laughing.

L Cottrill

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