Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 86241 times)

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #420 on: September 12, 2019, 04:23:36 PM »
With lower performance engines running pumper carbs, an IV bag works fine.  However, we had lots of problems getting a modified Walbro WYK carb to pump enough fuel in an engine like Jim's.  Lower pop off pressure and a Perry pump got us by.  Pipe pressure systems on nitro engines act like a simple throttle body fuel injector.  As the power goes up, the pipe pressure increases, increasing the fuel flow.  The double tank system helps maintain a consistent fuel flow at the carb like Jim explained.   

Jim, are you running a pumper carb?  Does the pressure regulator still handle the increased pressure and meter fuel well?

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #421 on: September 12, 2019, 05:48:23 PM »
Petertha,

Sorry about the confusion caused when I used the word "bladder". I was not referring to the rubber bladder type fuel systems used in the  past on some speed planes. I was referring to the hospital type IV bags adapted by many model boaters to replace metal or blow molded seamless type tanks. The blow molded, heavy duty type, tanks can be used for continuous pressurized fuel systems above 5 psi. The engine RPM's, tuned pipe total volumes, stinger ID's & lengths are some key factors that will determine how much pressure can be developed at any throttle setting. I am running a pumper type carb with the tuned pipe pressure. The maximum measured pressures generated with my tuned pipe designs are approximately 4 psi (110 ounces of water) at WOT.

Lohring,

Extensive dyno testing of my gas engines operating at RPM's above 21,000, with an "adequate" tuned pipe pressure, showed me that no change was necessary to the pop off pressure. In fact the tuned pipe pressurized system works in a similar manner on both gas & nitro engines, providing the tuned pipes design is "CORRECT". I can assure you that tuned pipe volumes that are to small combined with stinger diameters that are to short & to large WILL NOT WORK!!

Note: Present day pylon racing planes also use the pressure generated from a tuned muffler to provide an adequate fuel flow at RPM's of approximately 30,000. The measured pressure for a .45 cu in engine is approximately 90 inches of water at WOT.

Jim Allen
« Last Edit: September 12, 2019, 07:13:47 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #422 on: September 17, 2019, 04:19:57 AM »
3" OD pool noodles are used for flotation after their ends were sealed with Goop. I used Nokorode Black Silver Soldering Flux & Aufhauser Silver Alloy 45 (1370* F - 1550* F) for the tuned pipe pressure fittings, any tuned pipe joints & 1/8" of the cable's end that goes into the collet. The aluminum heat sink fixture prevents any heat from traveling past its end point. Silver soldering the cables end eliminates uwinding problems. This same heat sink will be clamped approximately 1.250" from the cables end. Lucas-Milhaupt 400* F solder with Lucas-Milhaupt Tec Flux is used to make the entire 1.250" end of the cable a solid.

Jim Allen

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #423 on: September 20, 2019, 12:01:33 PM »
Going back to the Piano wire drive shaft: As your engine appears to reach higher rpms that the one you are basing your design on have you considered the need to move the support bearings closer together to reduce the risk of whirling?
Best regards

Roger

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #424 on: September 20, 2019, 03:52:24 PM »
I would be interested in a comparison between the cable versus the wire drive.  It looks like you are planning to be able to run both.

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #425 on: September 20, 2019, 07:17:12 PM »
Roger & Lohring,

There are many unsubstantiated & unproven claims about the advantages of wire type drives. Claims of a 5 MPH increase in the maximum speed of a boat may be very possible because of the inherent drag of a "longer length", 1/4" OD, flexible, cable type system. The original purpose of using a wire drive was to allow the propeller's strut to be adjusted in depth & angle. As boats became larger & longer, wire type drives were replaced with solid shaft (3/16" OD) drives with ball & pin universals. Kalfus developed precision, very high quality, ball (.2812" OD) & pin (.1250" OD) type universals which I adapted to .65 cu in engines. Next came solid shaft (1/4" OD) drives with ball (.3125" OD) & pin (.1562" OD) type universals which I use for the .90 cu in geared twin setups. All of the solid shaft setups have very low friction amounts. There is no "shaft whirling or sine wave" activity to be concerned about if the shafts used are straight & they are "moderately supported". This is true at tested RPM's of 30,000+! Keep in mind that very few people have the expertise, knowledge or equipment to manufacture what would be necessary to build even a simple system!!

Jim Allen