Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 85814 times)

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #405 on: August 18, 2019, 10:18:34 PM »
I finally decided on the position & method to mount the trim tab servos. The final position is setting as low as possible, 1/8" away from the bottom inside of the sponson bottoms & as close to the hulls balance point as possible. A solid type mounting system would have definitely been easier. However, the clockwise, counterclockwise rotation of the Hitec D956WP servos used allows for the easy mirror machining of right hand side & left hand side mounting systems. A total of 4 duplicate machined pieces make up each side, including the G-10 fiberglass base plates. The servos are shock mounted with the molded grommets provided. Next will come the direct linkages to the trim tabs.

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #406 on: August 19, 2019, 11:26:08 PM »
The simple drill jig shown allows for the precise location of the holes in both sides of the transom. The two holes are not only precisely located but they are at the correct angles for the brass tubes which hold the rubber sealing boots that are used outside & inside of the transom wall. I use an end mill mounted in a drill chuck, turned by hand, to cut the holes through the thick carbon fiber transom. Notice how the 5/32" piano wire rod lines up perfectly on the right hand side.

The last two photos show how the drill jig is used to hold the brass rubber seal mounting tubes for glueing inside the uneven transom surfaces. They will also be glued with a doubler block on the outside.

Jim Allen

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #407 on: August 20, 2019, 02:58:43 PM »
I've never run adjustable trim tabs on anything, so I'm going to be interested in how they work.  I once considered a full width tab across the tunnel area between the sponsons, but didn't find it helped.  On the full size Dry Martini the tabs and the outdrives were adjustable.  There the adjustment was very helpful for trimming the boat to the conditions.  In that case you had some very sensitive on board sensors (the crew) to check the settings.

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #408 on: August 21, 2019, 02:02:06 AM »
I'm also very interested in seeing how these things are going to work Lohring! They can be slaved to move with the rudder movements or moved independently. A very capable Australian model boat builder who runs several oval & straight away record catamarans encouraged me to do these modifications. He also explained how the trim tab system can effectively be used in the oval & straight away. Each completed system gets me closer to starting with the engine modifications for the rear exhaust QD. The 27 cc engine will have my 2.155" (54.695 mm) connecting rod with the 16 roller bottom end. No roller is used in the top end of the machined piston. Many engine builders use longer rods but they never receive the full advantage of this modification without moving the wrist pin hole higher up in the piston. My wrist pin hole is .403" from the piston crown & my single ring piston is 1.250" high compared to 2.210" for the stock piston.

The same drill jig is used again to securely hold in place the brass rubber seal mounting tubes & the 1/8" thick carbon fiber doubler piece on the outside of the transoms. An additional brass tube with a clamp ring sets the depth of each seal mounting tube. A white machined teflon sleeve is placed inside the mounting tube along with the 5/32" rod that is connected to the servo to ensure the alignment is correct. The angled hole in the doubler piece fits tightly on the brass seal mounting tube. Clamping of all the pieces involved ensures perfect alignment until the J-B Kwik weld cures.

Jim Allen



Jim Allen
« Last Edit: August 21, 2019, 02:42:17 AM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #409 on: August 27, 2019, 01:32:07 AM »
The trim tabs are now complete except for the two simple machined pieces that attach the trim tabs to their 5/32" piano wire actuation rods. The trim tabs were machined & then carefully bent to match the angle of the sponson's rear surfaces. The trim tabs are set at the correct angle & depth with the wedges shown. Mounting the trim tabs to there 3/16" thick carbon fiber bases, with the grommets & hardware to be used, & then glueing these entire assemblies, guaranteed their exact location. The same hardware mounting base plate was used again. No holes were drilled through the boats sponson's rears surfaces! Testing the movement that the grommets would allow, before mounting, showed a movement of approximately 1/4" up or down with very little force being applied. I can't wait to test the things out!

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #410 on: August 28, 2019, 11:05:19 PM »
I will be setting up & testing a 3 mm (.1181") piano wire drive that is an exact copy of the the type used by Ed Kalfus in his record setting tether boats. He fully developed this technology in 1937 & 38 using ready available K & S piano wire which is still available in most hobby shops. The same type & size , precision ground "single split" collet assemblies, were used to effectively clamp 3 mm, 1/8", 3/16", 1/4" solid, as well as flexible 1/4" cable drives. I will be making a comparison between the 1/4" flexible cable & the 3mm piano wire drive with a set up that will be interchangeable at the lake site. The photos show how some 1/4" size hardened & ground, precision single split collets, were easily made. This type of single split collet mounted in its hardened & ground clamping body, with a 32 pitch OD thread, never wears out & will maintain its precision forever! Notice the machined spring steel thrust washers which allows severe tightening of the 32 pitch ID clamping nut against the collet.

Jim Allen
« Last Edit: August 29, 2019, 09:45:28 AM by strictlybusiness1 »

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #411 on: August 29, 2019, 11:48:12 AM »
I feel like several off your previous resent post are in the category, the motorcycle racing crowd call "Power is useless without control" .... and without any experience to ask good questions on the subject.

This last post get me curious though. I have never seen a prop shaft and engine without a cupling between them to compensate for mis-alignment .... this off cause robs some power, so I can understand why you want to avoid it - but how do you ensure a perfect alignment ?   An ajustable engine mount or ...?

As far as I can see - a not completely perfect alingment will rob power too and maybe even destroy parts ....

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #412 on: August 29, 2019, 03:12:22 PM »
I'm very interested in how a wire drive works on a gas engine.  The electric and nitro racers get a definite improvement over cable drives.  How are you connecting the wire to the prop shaft?  It's not clear from your pictures.

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #413 on: August 29, 2019, 04:45:18 PM »
Lohring & Admiral_dk,

Very astute observations to questions that can be easily answered.

Ed Kalfus' .90 cu in nitro engine produced 4.5 HP at 24,000 RPM. A 3 mm (.1181") piano wire drive would survive indefinitely while being supported with several (3 or 4) evenly spaced bearing brass bushings over a distance of approximately 17". The engine was solidly mounted & the bushings were soldered in the stuffing tube through small holes in the stuffing tubes OD.The brass stuffing tube that held the bushings went into the strut & the 3 mm piano wire went through the 3/16" X approximately 2.5" long prop shaft. The 3 mm piano wire was a heavy press fit into the prop shaft. The piano wire was  heavily peened where it exited at the threaded end of the prop shaft. Ed's propellers had a 1/2" hub length X 5/16" diameter. This system gave him a tunable strut in depth & thrust angle. It is very possible that the wire drive for a 27 cc, 8 HP, 23,000 RPM engine may have to be larger in diameter (1/8" or 9/64"), but the engineering principles would be the same. For the assembly of present day wire drives Loctite # 648 retaining compound with a light press fit would be sufficient.

I prefer to mount nitro or gas engines on solid mounts. If rubber mounts are used they are very high durometer (70+) type mounts that are used. Solid mounts are usually aluminum & G-10 fiberglass. A stuffing stub with solid shafts mounted is epoxied in place after the engine is mounted for these systems. This gives an alignment within + or - .002" at the engines collet.

When using solid shafts (3/16" or 1/4" OD) "precision" machined ball & pin universals give the least amount of friction loss & there will be no RPM loss because they are a constant velocity type of U joint.

Jim Allen
« Last Edit: August 29, 2019, 04:50:36 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #414 on: September 01, 2019, 10:28:30 PM »
The trim tabs with all their associated parts & linkages have finally been completed. I have not set the maximum downward movement amount as yet, however the last two photos show what could be expected. The two D956WP servos easily raise the entire rear end of the boat off the building fixture with very little effort. I used the same 5/32" OD piano wire rods with a .375" x .750" X 1.5" long aluminum interconnecting block which made any rod length adjustments a "piece of cake". The 5/32" piano wire rods have 5/16" long flats milled where the 8-32 set screws lock up.

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #415 on: September 06, 2019, 11:56:48 AM »
I machined these two 1/8" thick carbon fiber supports to eliminate the possibility of cracking the carbon fiber deck where there are no bulkheads. The two pieces weigh a total of 1.5 ounces. They are very rigid & provide a support distance of 8" under the deck cowl opening.

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #416 on: September 11, 2019, 08:29:55 AM »
Since I always use a tuned pipe pressurized fuel system, no bladder of any kind can be used. The 12 oz. main tank & the 4 oz. secondary tank both have custom removable mounts. The tuned pipe fits into the engine's header with a labyrinth type seal. There is no straight section inside the tuned pipe or the header section at this critical transition point. A teflon sleeve will be added to make this joint 100% air tight!

Jim Allen

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #417 on: September 11, 2019, 11:38:38 AM »
Jim I have two questions from your last post.

Is it the preasure pipe we see under the exhaust connection and that it ends up very close to the "wall" in the bottom of the picture ?

Is the reason for two tanks like some of the fly boys - the big one feeds the smaller so there never is any air in the one feeding the carb ?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #418 on: September 11, 2019, 05:00:41 PM »
The two titanium barbed fittings seen under the header pipe are water inlets for the engine. The barbed fitting for tuned pipe pressure with a gas engine is taken at the pipes mid-point. The barbed fitting for tuned pipe pressure with a nitro engine is taken at the header. The reason is because of the much higher engine exhaust temperature (approximately 900*F) for a gas engine compared to the engine exhaust temperature (approximately 500*F) for a nitro engine. The measured pressure in either case does not vary with the location of the fittings.

Not only is there no air in the secondary tank because the main tank is filled through it, but its position in relation to the carburetor can be used to eliminate the effects of "G" forces on the fuel supplied to the carburetor when turning the boat at maximum speed.

Jim Allen

Offline petertha

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #419 on: September 12, 2019, 03:06:22 AM »
Hi Jim. I was wondering about your pressure/bladder comment because I've seen boosted bladder tanks in RC, but always methanol. You are saying gasoline fueled are too hot for that? Interesting. Would engine running conditions benefit from a fuel delivered via pressure regulator type devices? I think some operated on kind of a micro oscillation check valve principle (Cline?) but I think the Perry had a diaphragm what took pulses off the crankcase & was regulated. Looks like the names are re either changing hands or going by the wayside? Have not heard of this one but I'm out of the loop
http://www.ironbaymodelcompany.com/ibmco%20recreational%20website_010.htm 

older Perry reference
http://saito-engines.info/pumps.html

I had a lot of running experience with the YS pressure regulator & they were great. But it was integrally designed into the engine.