One radical thing you could try if you wanted is to bump up the number of ports from 8 to 10. Most designs try to maximize the intake region with less space between each petal. Probably not on your jet but sometimes people use slender fuel lines for gasoline and then expect the same diameter to work with methanol and the line pressure or resistance over a length will not allow enough flow to feed the engine no matter what size the metering jets are. If you had some nitro you could blend up a 15 or 20 percent mix with methanol to get more power. But then your metering jets and all would have to be wider than with methanol.
The little Tiger jet is said to produce 2 1/4 pounds of thrust using gasoline and the Dynajet on regular gasoline 4 1/4 pounds from an old schematic Don Laird sent me. I noticed the Tiger jet tail pipe is a few centimeters longer than the Atom even though it is smaller. Maybe one of those slight variables in length would be something to consider if you even have the time to try all that. The Japanese also made a second version of the Tiger with a slightly shorter tail pipe. Imagine how tricky it all gets because when you change one thing, you change many things in a sense, or rather throw off what might have been optimized for some other function on the jet.
On the Dynajet there's not a whole lot of overlap on the reeds either, just enough to cover the ports and a slight bit more. When I look at the Atom diagram, it "almost" looks like you could put eight more ports on it, the 8 holes are so far apart.
But 2.86 pounds of thrust is not bad for a little jet really.
How much thrust?
Moderator: Mike Everman
Re: How much thrust?
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Re: How much thrust?
Upon looking at the schematic more closely (again), the ports are 7 mm and the reeds 9 mm. The drawing though kind of exaggerates the coverage, the size/perspective of the ports compared to the reeds. Don Laird in his economy used to sell a plate you could put over the ports I believe that would cancel out one port, in the event you had one damaged reed, you could still fly on nine instead of ten. He said something about losing a little bit of power and that with two ports covered the Dynajet wouldn't run. I wonder though if he tried all the variations where two different ports were covered?
The Japanese version of the Dynajet sold their reeds in banks of 5, in that way if you lost a reed, you need only replace half a flower petal.
The Japanese version of the Dynajet sold their reeds in banks of 5, in that way if you lost a reed, you need only replace half a flower petal.
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Re: How much thrust?
I once bought a 23/64 drill bit thinking I would make a Dynajet. Then I read the way you make the ports is to use a smaller bit and then ream them to the exact diameter. I didn't know about reamer bits back then.
Rough estimates...
If you look at the Bailey jet or Dynajet the ports are .359ths and there are ten of them.
If you look at the Atom jet, the ports are ~.276ths in diameter and there are eight of them.
If you look at the Tigerjet, the ports are .256ths in diameter and there are ten of them.
Now the amount of square inches in the first case works out to 0.101 square inches per port times 10 petals, gives about 1 square inch of valve area.
In the Atom pi r squared case 2, .276ths comes out to 0.060 square inches and that figure times eight yields .48 square inches of valve area.
Lastly, the Tigerjet port of .256ths, has an area of 0.051 square inches. That times ten is .51 square inches of valve area.
Note, I am negating the ellipse in the ports because that would be more math, so adjust your expectations accordingly. ha
Now notice the Tigerjet combustion chamber is close to 1.75 inches outside diameter and the Atom jet is 2.125 inches in diameter yet the valve area is slightly greater in the Tigerjet even though it is smaller. The Dynajet and Bailey jet combustion chamber are 2.5 inches in diameter, again with the 1 square inch total valve area IF you don't count the ellipse effect of the angled hole.
My apologies to the metric world.
To continue...
The Atom tail pipe is 1.1 inches in diameter and the Tigerjet's tail is .866 inch according to the schematic on this site. A diameter of 1.1 inches would yield a tail pipe surface area of .95 square inches, and the Tigerjet .589 square inches.
The Dynajet schematic I have lists a tail pipe diameter of 1.25 inches although being formed of two blanked pieces, it is not a round shape. A 1.25 inch diameter tail pipe would have 1.227 square inches of surface area. I didn't count the flare of course.
I'm very tired so if I have bungled these numbers, forgive me.
http://www.csgnetwork.com/circlecalc.html
http://www.convertunits.com/from/mm/to/inches
http://www.csgnetwork.com/drillsizeconvert.html
Rough estimates...
If you look at the Bailey jet or Dynajet the ports are .359ths and there are ten of them.
If you look at the Atom jet, the ports are ~.276ths in diameter and there are eight of them.
If you look at the Tigerjet, the ports are .256ths in diameter and there are ten of them.
Now the amount of square inches in the first case works out to 0.101 square inches per port times 10 petals, gives about 1 square inch of valve area.
In the Atom pi r squared case 2, .276ths comes out to 0.060 square inches and that figure times eight yields .48 square inches of valve area.
Lastly, the Tigerjet port of .256ths, has an area of 0.051 square inches. That times ten is .51 square inches of valve area.
Note, I am negating the ellipse in the ports because that would be more math, so adjust your expectations accordingly. ha
Now notice the Tigerjet combustion chamber is close to 1.75 inches outside diameter and the Atom jet is 2.125 inches in diameter yet the valve area is slightly greater in the Tigerjet even though it is smaller. The Dynajet and Bailey jet combustion chamber are 2.5 inches in diameter, again with the 1 square inch total valve area IF you don't count the ellipse effect of the angled hole.
My apologies to the metric world.
To continue...
The Atom tail pipe is 1.1 inches in diameter and the Tigerjet's tail is .866 inch according to the schematic on this site. A diameter of 1.1 inches would yield a tail pipe surface area of .95 square inches, and the Tigerjet .589 square inches.
The Dynajet schematic I have lists a tail pipe diameter of 1.25 inches although being formed of two blanked pieces, it is not a round shape. A 1.25 inch diameter tail pipe would have 1.227 square inches of surface area. I didn't count the flare of course.
I'm very tired so if I have bungled these numbers, forgive me.
http://www.csgnetwork.com/circlecalc.html
http://www.convertunits.com/from/mm/to/inches
http://www.csgnetwork.com/drillsizeconvert.html
Presentation is Everything
Re: How much thrust?
The Tigerjet port of .256ths, has an area of 0.051 square inches. That times ten is .51 square inches of valve area.
The Tigerjet's tail is .866 inch diameter according to the schematic which works out to .589 square inches.
Valve area divided by tailpipe area is ~87%, close to the Dynajet of 83%.
But look at the Atom jet. .276ths port diameter comes out to 0.060 square inches and that figure times eight yields .48 square inches of valve area. The Atom tail pipe is 1.1 inches in diameter which would yield a tail pipe surface area of .95 square inches.
Valve area divided by tailpipe area is a lowly 50% ratio.
The Tigerjet's tail is .866 inch diameter according to the schematic which works out to .589 square inches.
Valve area divided by tailpipe area is ~87%, close to the Dynajet of 83%.
But look at the Atom jet. .276ths port diameter comes out to 0.060 square inches and that figure times eight yields .48 square inches of valve area. The Atom tail pipe is 1.1 inches in diameter which would yield a tail pipe surface area of .95 square inches.
Valve area divided by tailpipe area is a lowly 50% ratio.
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Re: How much thrust?
Hi Mark, interesting comparisons, I wonder why the guy who designed the atom gave it such a small port area, if I was to make a new valve head with 10 larger ports would I have to increase the size of the venturi also to maximise the gains? I have increased the thrust of my jet to 3 pounds, stll using methanol and the same flowjector sizes but slightly increased petal lift, an extra four screws equally spaced with the four already holding the valve head on and I have done away with the starting air tube so as to flow more air, it starts so easily that the starting tube is not nesassary. Now that I have 3 lbs thrust I am going to stop chasing more thrust and concentrate on a fuel bladder and cut off valve, the guy who is redesigning the plane on his cad program has nearly finnished so the build will commence soon, I am going to test my fuel tank and cutoff valve on a dolly and also get an idea of acceleration at the same time should be loads of fun, I will post a vid of the test for you all to watch and have a good laugh. Phil.
Re: How much thrust?
I can't answer why the Atom has a lower valve ratio than the other two jets listed. One thing I like to do though is work with volumes, how much thrust a jet gets using so much volume. I put water in the Dynajet and it held around 20 to 21 ounces of water. And the Bailey jet held an even 3 cups or 24 ounces. Yet both have the same valve head sized ports and same length. Maybe some kind of volume to thrust ratio would be the most telling. The Tigerjet holds about 9.5 ounces of water. Recall too that the Atom is a few centimeters shorter than the Tigerjet, even though it is a larger jet.
Here's a tidbit from some Cornell Aeronautical Laboratory study. "It may be observed that for each combustion-chamber diameter a maximum value of specific impulse is obtained in the range of the tailpipe length investigated. The irregular nature of the specific impulse curves appears to be typical of this type of device and indicates extreme sensitivity to small changes in configuration. Changes in tailpipe length as small as 2 percent produced changes in specific impulse values as large as 10 percent."
Probably in some cases, just the nature of the fuel used would dictate the optimum tailpipe length or diameter. There are so many variables that it's difficult to say the outcome is because of just one thing, and not taking into account many other things.
There was this neat experiment around the early 1900's that had a flame of hydrogen burning in an oxygen atmosphere. It was also shown that you could just as easily have a flame of oxygen buring in a hydrogen atmosphere. It illustrated how they're really just two reactants. Maybe instead of only tinkering with metering jets, one could also adjust the venturi diameter. Perhaps by having a variable venturi, you could better mix the fuel entering the jet for a particular fuel or conversely, be favoring one fuel over the other unfairly, one needing more thorough, accurate mixing.
So many variables. I would be curious to know how much water your jet holds, in that way we could make yet another comparison. ha
PS Here's one design for a fuel tank and fuel feed that's kind of clever.
http://jetzilla.com/Vol01Num01/jetZilla.html#Article_2
The author. http://www.btemodels.com/doublewhammy.html
Cline regulator http://www.billsroom.com/pcfs/
More tidbits.
"The pressurized fuel system that I use comes from Bruce and utilizes a Cline fuel regulator. I used wide diameter surgical tubing from McMaster Carr for a fuel bladder. You can use 45 cal shells for the end caps of the fuel bladder, but I machined mine out of aluminum. I would highly recommend the cline fuel regulator, especially if you plan on trying to fly the engine."
http://www.rcuniverse.com/forum/m_34615 ... tm#3466024
Here's a tidbit from some Cornell Aeronautical Laboratory study. "It may be observed that for each combustion-chamber diameter a maximum value of specific impulse is obtained in the range of the tailpipe length investigated. The irregular nature of the specific impulse curves appears to be typical of this type of device and indicates extreme sensitivity to small changes in configuration. Changes in tailpipe length as small as 2 percent produced changes in specific impulse values as large as 10 percent."
Probably in some cases, just the nature of the fuel used would dictate the optimum tailpipe length or diameter. There are so many variables that it's difficult to say the outcome is because of just one thing, and not taking into account many other things.
There was this neat experiment around the early 1900's that had a flame of hydrogen burning in an oxygen atmosphere. It was also shown that you could just as easily have a flame of oxygen buring in a hydrogen atmosphere. It illustrated how they're really just two reactants. Maybe instead of only tinkering with metering jets, one could also adjust the venturi diameter. Perhaps by having a variable venturi, you could better mix the fuel entering the jet for a particular fuel or conversely, be favoring one fuel over the other unfairly, one needing more thorough, accurate mixing.
So many variables. I would be curious to know how much water your jet holds, in that way we could make yet another comparison. ha
PS Here's one design for a fuel tank and fuel feed that's kind of clever.
http://jetzilla.com/Vol01Num01/jetZilla.html#Article_2
The author. http://www.btemodels.com/doublewhammy.html
Cline regulator http://www.billsroom.com/pcfs/
More tidbits.
"The pressurized fuel system that I use comes from Bruce and utilizes a Cline fuel regulator. I used wide diameter surgical tubing from McMaster Carr for a fuel bladder. You can use 45 cal shells for the end caps of the fuel bladder, but I machined mine out of aluminum. I would highly recommend the cline fuel regulator, especially if you plan on trying to fly the engine."
http://www.rcuniverse.com/forum/m_34615 ... tm#3466024
Presentation is Everything
Re: How much thrust?
Hi Mark, its very interesting that tidbit about about tailpipe length, the reason being that I have discovered that my tailpipe is 8mm to short! I dont know how it happened but it has irritated me a lot, I bet I am losing thrust because of this, just for you I will fill my jet with water and check out the volume. Thanks for the link to the jetzilla bladder tank article I have been meaning to look that up and also I will subscribe to jetzilla, the bladder tank set up is not a graet deal different to the one I am setting up at the moment, except for the cline regulator, thats a nice piece of kit and I can see the bennefit of it but so far this project has cost me the price of a few liters of methanol and I mean to go on without spending money just using the resources around me and my own ingenuity, so as when this project is complete with a really nice jet airplane that flies well I can say to myself, nice job something for nothing with real satisfaction, thats why I have not gone out and bought a load of drills for the petrol metering jets. Any way my fuel set up will have a needle valve in place of the cline and if the engine flames out I will hit the fuel cutoff switch on my transmitter. As for using 45 cal shells for the bladder end cap the bloody english government took my guns and gave me a pittance after the Dunblane school massacre in scotland.
Re: How much thrust?
Ok I admit it, I need a cline regulator, Phil.