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The Moki project. . .
11-04-2010, 07:54 PM
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The Moki project. . .
This whole idea started with the USRA Giant Scale pylon guys opening up a class for the 80" H9 Sundowner.
I put a plane together just in time for the class to be eliminated (since H9 stopped making it)
So, a big plane, a big engine, and now what?
We go faster for the hell of it (hopefully)
I've made friends with one smert fella down in AZ that owns a machine shop and took to seeing what it takes to wring out a Moki 210. He's had quite a bit of success. A 16x14 APC at 9600rpm on 60%nitro isn't too shabby! Tore the wings right off the plane one afternoon.
I've essentially duplicated his engine. (he was kind enough to share the notes with me) Although I'm at roughly half the elevation I've never been able to get the RPM he was/is so I've taken another tract. I too own a machine shop. . .
The positive displacement blower project begins. . . I spent a few hours on the phone with engineers from Whipple, Eaton, B/M, and Blower Drive Service. I've gotten a good understanding of what needs to happen now. I've got my bearings, gears, drive belts, and a few CAD doodles. I've also aquired materials.
Here's the basic rotor geometry: Rather than invest a huge effort into a helical rotor setup that is much more complicated to make I'm first going to keep this simple by machining a straight two lug rotor setup.
Here's a few pics as I'm running the rotor program right now as we speak
CAD doodles
chunk of 7075 T6 certified aerospace forged billet aluminum.
Some tool paths. Doesn't look like much yet as I have to get the bulk of this out of the way first. It'll start to make sense here soon enough.
More to follow.
Chad
I put a plane together just in time for the class to be eliminated (since H9 stopped making it)
So, a big plane, a big engine, and now what?
We go faster for the hell of it (hopefully)
I've made friends with one smert fella down in AZ that owns a machine shop and took to seeing what it takes to wring out a Moki 210. He's had quite a bit of success. A 16x14 APC at 9600rpm on 60%nitro isn't too shabby! Tore the wings right off the plane one afternoon.
I've essentially duplicated his engine. (he was kind enough to share the notes with me) Although I'm at roughly half the elevation I've never been able to get the RPM he was/is so I've taken another tract. I too own a machine shop. . .
The positive displacement blower project begins. . . I spent a few hours on the phone with engineers from Whipple, Eaton, B/M, and Blower Drive Service. I've gotten a good understanding of what needs to happen now. I've got my bearings, gears, drive belts, and a few CAD doodles. I've also aquired materials.
Here's the basic rotor geometry: Rather than invest a huge effort into a helical rotor setup that is much more complicated to make I'm first going to keep this simple by machining a straight two lug rotor setup.
Here's a few pics as I'm running the rotor program right now as we speak
CAD doodles
chunk of 7075 T6 certified aerospace forged billet aluminum.
Some tool paths. Doesn't look like much yet as I have to get the bulk of this out of the way first. It'll start to make sense here soon enough.
More to follow.
Chad
11-05-2010, 08:42 AM
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RE: The Moki project. . .
There!
Sorry, camera settings were changed.
Finished up the 1st op on the rotors last night. Now it's onto the 2nd op. So far so good. . .
Sorry, camera settings were changed.
Finished up the 1st op on the rotors last night. Now it's onto the 2nd op. So far so good. . .
11-05-2010, 04:54 PM
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RE: The Moki project. . .
Just got off the phone with the "Gawd" from MAC tuned exhausts. Were workin up a custom header and stinger for this bugger.
Should be cool (hopefully, fingers crossed. . .)
Here's a few more pics of getting the header set up sorted out.
Should be cool (hopefully, fingers crossed. . .)
Here's a few more pics of getting the header set up sorted out.
11-05-2010, 04:57 PM
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RE: The Moki project. . .
One rotor 1st op done:
There's about .0006" taper across the rotor's width when measuring the outside to outside swept arc. (the big imaginary circle this creates while spinning) .0006" taper isn't as close as I'd like but I'm going to live with it. I'm running my rotor clearance at .005" and case clearance at .008" so it shouldn't hurt anything. Twin lobe rotors aren't very efficient when compared to the multi flute helical setups in modern superchargers. I'll leave them alone for the time being and just stick with this. Progressing slowly, but dilligently.
More to come. . .
There's about .0006" taper across the rotor's width when measuring the outside to outside swept arc. (the big imaginary circle this creates while spinning) .0006" taper isn't as close as I'd like but I'm going to live with it. I'm running my rotor clearance at .005" and case clearance at .008" so it shouldn't hurt anything. Twin lobe rotors aren't very efficient when compared to the multi flute helical setups in modern superchargers. I'll leave them alone for the time being and just stick with this. Progressing slowly, but dilligently.
More to come. . .
11-05-2010, 07:54 PM
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RE: The Moki project. . .
Oky doky,
1st op on the rotor halves is finished. Both are within a couple tenths for taper and OD. Not too shabby for a dumb farm kid.
Tomorrow or next week I'll start on the 2nd operation. I've got a rifle to get started on for a client so it may have to wait a bit.
Nite gents.
C
1st op on the rotor halves is finished. Both are within a couple tenths for taper and OD. Not too shabby for a dumb farm kid.
Tomorrow or next week I'll start on the 2nd operation. I've got a rifle to get started on for a client so it may have to wait a bit.
Nite gents.
C
11-06-2010, 08:38 AM
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RE: The Moki project. . .
Afraid there's a bit more to this than just building boost.
As I've come to learn "huffing" a front rotary valve 2C engine isn't as easy as it would seem. The issue comes with keeping the charge in the cylinder. The exhaust port is the first thing that opens as the piston is on its way down after firing. This compresses the mixture in the crankcase. After the exhaust piddles out the spent stuff the transfer ports begin to open and the new intake charge gets squirted up into the combustion chamber. In a boosted condition it's very likely the bulk of the charge will run right out the exhaust port.
I have a couple options. One (most complicated) is to design a new head/liner with a poppet valve that's driven off a camshaft for the exhaust. The second (more realistic) is some creative use with a tuned pipe. The pipe works by taking the sound energy generated and reflecting it back towards the exhaust port to literally stuff the piddling intake charge back in the cylinder. Done correctly it's quite powerful. Tuned exhausts on 125cc motorcross engines are capable of making the combustion chamber displace up around 180cc's of intake charge volume. It makes the powerband quite narrow though as the length of the pipe determines the RPM range/broadness. This is why the "revy" 125's are often picked on as being "peddled" around the track by the gear shift lever. (to keep the thing in the optimal RPM range for max power)
What I'm learning is the trick is to get that charge shot up there with enough velocity to adequately fill the cylinder while avoiding an overly "quick" charge that'll tend to run out the exhaust. If I can get the intake charge "just fast enough" then hopefully it'll fill the cylinder and loiter around while the piston changes direction and closes off the exhaust port.
This leads to another challenge. The actual displacement of the engine isn't exactly correct. (Bore x bore)x stroke x .7854 is the old school displacement formula. Unfortunately it's a bit skewered for a piston port engine. The ports are open for the bulk of the rotation cycle. Actual displacement (usable) is significantly less as anything that really matters takes place from TDC (top dead center) on the piston to when the exhaust port starts to open. The trick with high nitro content is to get enough exhaust timing. This means raising the port- sometimes considerably. Doing so reduces the effective "pressure cycle" in crankshaft degrees as the pressure in the cylinder drops off pretty quick once the port opens. Raising the port elevates the effective RPM powerband of the engine. It has to run faster to make the same power as the shorter port did. Not a bad thing so long as components inside (crank, rod, piston) are able to tolerate it.
I know my stock Moki 210 ran a 16x16 APC at 7400 rpm on 15%. Through extensive tinkering I was able to bump that up to 7900 rpm with 58% nitro. (I had to buy a hydrometer and learn how to blend my own fuel) What kicks my butt is my buddy down in AZwas able to run a 16x14 APC at over 9600 on the ground with 60%. I figured I should have been in the low to mid 8's with the 16 pitch. Makes me think I did something wrong but I can't find out what it is. With smaller props I got as high as 10,200 rpm (14.4x13 APC) My performance goal is to be able to spin that 16x16 at 10,000. That should really wake this engine up. If I get it then I'll look at a custom prop with more pitch.
200mph is the speed target for this bugger. A bold undertaking. I doubt I'll get it without having to really tear into the airframe but who knows? Stranger things have happened.
Ok, back to work. This morning's agenda is to finish the rotors. Gear sets and all.
More to follow as time allows.
C
As I've come to learn "huffing" a front rotary valve 2C engine isn't as easy as it would seem. The issue comes with keeping the charge in the cylinder. The exhaust port is the first thing that opens as the piston is on its way down after firing. This compresses the mixture in the crankcase. After the exhaust piddles out the spent stuff the transfer ports begin to open and the new intake charge gets squirted up into the combustion chamber. In a boosted condition it's very likely the bulk of the charge will run right out the exhaust port.
I have a couple options. One (most complicated) is to design a new head/liner with a poppet valve that's driven off a camshaft for the exhaust. The second (more realistic) is some creative use with a tuned pipe. The pipe works by taking the sound energy generated and reflecting it back towards the exhaust port to literally stuff the piddling intake charge back in the cylinder. Done correctly it's quite powerful. Tuned exhausts on 125cc motorcross engines are capable of making the combustion chamber displace up around 180cc's of intake charge volume. It makes the powerband quite narrow though as the length of the pipe determines the RPM range/broadness. This is why the "revy" 125's are often picked on as being "peddled" around the track by the gear shift lever. (to keep the thing in the optimal RPM range for max power)
What I'm learning is the trick is to get that charge shot up there with enough velocity to adequately fill the cylinder while avoiding an overly "quick" charge that'll tend to run out the exhaust. If I can get the intake charge "just fast enough" then hopefully it'll fill the cylinder and loiter around while the piston changes direction and closes off the exhaust port.
This leads to another challenge. The actual displacement of the engine isn't exactly correct. (Bore x bore)x stroke x .7854 is the old school displacement formula. Unfortunately it's a bit skewered for a piston port engine. The ports are open for the bulk of the rotation cycle. Actual displacement (usable) is significantly less as anything that really matters takes place from TDC (top dead center) on the piston to when the exhaust port starts to open. The trick with high nitro content is to get enough exhaust timing. This means raising the port- sometimes considerably. Doing so reduces the effective "pressure cycle" in crankshaft degrees as the pressure in the cylinder drops off pretty quick once the port opens. Raising the port elevates the effective RPM powerband of the engine. It has to run faster to make the same power as the shorter port did. Not a bad thing so long as components inside (crank, rod, piston) are able to tolerate it.
I know my stock Moki 210 ran a 16x16 APC at 7400 rpm on 15%. Through extensive tinkering I was able to bump that up to 7900 rpm with 58% nitro. (I had to buy a hydrometer and learn how to blend my own fuel) What kicks my butt is my buddy down in AZwas able to run a 16x14 APC at over 9600 on the ground with 60%. I figured I should have been in the low to mid 8's with the 16 pitch. Makes me think I did something wrong but I can't find out what it is. With smaller props I got as high as 10,200 rpm (14.4x13 APC) My performance goal is to be able to spin that 16x16 at 10,000. That should really wake this engine up. If I get it then I'll look at a custom prop with more pitch.
200mph is the speed target for this bugger. A bold undertaking. I doubt I'll get it without having to really tear into the airframe but who knows? Stranger things have happened.
Ok, back to work. This morning's agenda is to finish the rotors. Gear sets and all.
More to follow as time allows.
C
11-06-2010, 01:55 PM
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RE: The Moki project. . .
1st op on the back blower case cover is done. Just a little fluff n buff to nick the burrs off.
Woo Hoo. It'll be a great "hood ornament" for my desk if nothing else.
11-06-2010, 05:06 PM
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RE: The Moki project. . .
I think without a new sleeve for timing change or preferably a actuated poppet exhaust valve, much of the boost would shoot right though and out. (a paraphrase of what you already said). To try and use a resonant intake and/or exhaust chambers with a boost device and not make internal engine changes may work but the math would need to be precise(luck?) and I would suspect the rpm working range to be vary narrow.
I think you got a heck of a challenge ahead of you, and I really hope it works.
When someone has a project, and asks me "can this be done?' I usually say "sure, it's only a mater of how much money and how long it takes"
I think you got a heck of a challenge ahead of you, and I really hope it works.
When someone has a project, and asks me "can this be done?' I usually say "sure, it's only a mater of how much money and how long it takes"
11-08-2010, 12:13 AM
#16
RE: The Moki project. . .
I can't help but wonder if that exquisite blower wouldn't be better off on a large 4-stroke such as a Saito. A more suitable cam profile would be a breeze for a man of your obvious talents and capabilities. Plus, none of the tricky problems inherent to a 2-stroke. The only real problem then is to discover how much boost they can take before something in the motor comes out through the case for a breath of fresh air.
