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Old 04-04-2019, 01:57 PM   #11
Mike Sebastien
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Re: Boomerang Sprint Conversion to Gas


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Standard formula for Gas engines: Air exit is 3 x intake area

On large gassers cooling is always a issue. Ducts around the head to route air is a solution. Also more oil in the Gas mix helps also as the excess oil carries away the heat.
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Old 04-04-2019, 11:16 PM   #12
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Re: Boomerang Sprint Conversion to Gas

Cool stuff. Think you should strap a big ‘ole tuned pipe on it so it can make serious power/rpm.

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Old 04-05-2019, 05:28 PM   #13
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Re: Boomerang Sprint Conversion to Gas

Well the firewall wall is in. Used a full tube of Hysol to glue the firewall, reinforce all of the fuselage joints I could get at plus the gear mounts. Having previously owned two Sprints I decided it would be wise to also put Hysol on the gear mounts as well, so I cut open the tops of the wings to get at them..

The firewall has been cut out below the mounts to increase the airflow to the engine from the intakes. I think it's going to be ok for cooling. I'm putting in a Jeti R14 along with a Jeti Mbar to monitor the air system for the Behotec gear. I'll set it up so if the pressure drops below 50 lbs the gear will be automatically lowered. The motor will also have a choke servo.

The gyro will be a Cortex.
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Old 04-05-2019, 10:04 PM   #14
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Re: Boomerang Sprint Conversion to Gas

Looking at the average Center of the gasser in comparison to the average center of the JM VT80 Turbine and the gasser is at least 6 inches further back meaning a whole bunch of lead up front. I used the balance on the spar tubing on mine although guys have gone a little further back. As for turbine start battery and gas ignition battery I don’t know if there is a ton of weight difference, couple of oz ....maybe.
And then there is the prop weight ; way back...... not being negative here but realistic . Yes it will be interesting to see what the all up balanced weight will be even with a smaller fuel tank and all.
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Old 04-14-2019, 09:39 AM   #15
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Re: Boomerang Sprint Conversion to Gas

Well it's finished and ready to fly all except the Graphics which should be along shortly. The instal was ready quite easy and I am really pleased with the outcome. Because of my concerns re cooling I installed a Jeti Cylinder head temperature gauge. Also installed is a Jeti Mbar to monitor the air pressure system. The model weighed in at 18.5 lbs total without fuel and took 2 lbs and 2 oz in the nose to balance . I used the recommended C of G of 10 inches forward from the trailing edge but after further investigation realize that its well forward and can be easiily moved aft to reduce the nose weight.

The propeller is a Xoar 18 x 10 pusher and i'm expecting to get about 7600 rpm.

Finished pictures and flight test report to follow.
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Old 04-14-2019, 02:58 PM   #16
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Re: Boomerang Sprint Conversion to Gas

Hey Brian, hope all goes well, looks like you have a winner there. a gal of fuel and you will fly all weekend. Nice work. Maddoggie
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Old 04-15-2019, 11:34 AM   #17
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Re: Boomerang Sprint Conversion to Gas

Decided to move the C of G back to 9 inches ( 228mm) forward from the trailing edge for the test flights. Took out 10 oz of nose weight.
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Old 04-17-2019, 06:52 AM   #18
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Re: Boomerang Sprint Conversion to Gas

Ran the RCGF 35RE yesterday and was not happy about Cylinder head temps I was getting. 180C. The problem being that the rear exhaust setup blocks off the air flow to the engine and any air the cylinders do get is heated by the muffler. Quickly decided to order the RCGF 32CC side exhaust. It's basically the same as the 35 but with the exhaust off to the side. Much better cooling as the ram airflow is now unrestricted. The side muffler also fits inside the Sprint airframe with a little cutting.

The flaps holes can now be filled in.

The RCGF 35RE is perfect for my next year's winter project ( Icon N West Stinson Reliant) and I didn't want to risk ruining the engine by test flying the Sprint. Should have the new engine in a week.
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Old 04-17-2019, 07:34 AM   #19
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Re: Boomerang Sprint Conversion to Gas

Looking forward to hearing how you make out. I’ve got an abused boomerang intro, and maybe a good candidate for a dle30.
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Old 04-17-2019, 07:54 AM   #20
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Re: Boomerang Sprint Conversion to Gas

That's a great idea Mike. I don't know what gear height you will get with the Nano but I get 1.5 inches of propeller clearance with the tail booms touching the ground swinging a 18 inch prop.

The 30 DLE would probably give you more than 1 to 1 power to weight thrust. Hover time with all that airflow over the elevator and rudders.
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