Comment

Comment by Bruce Woodry on March 9, 2011 at 8:27pm

Thanks for all your comments. We settled on the Jabiru 3300 for the HP/Weight and price. Will let you all know how it works out.

Bruce

Comment by Bob McDonald on January 10, 2011 at 8:13am

All

I do not know where the info regarding a Rotax 912S gear box not being capable or swinging a 72" dia WARP prop is coming from? I spoke with George Hurt at Kodiak Research (Rotax distributor North America) and Bob Robertson (Light Engine Services Rotax Dealer Canada) about which prop to use for my CH750 principally on floats. There is no issue swinging this diameter prop on the Rotax 912S. I chose this prop based on the recommendations of the Rotax people. Remember if you put a heavier engine on the airframe, you reduce your useful load..."simple math". The extra weight of the engine consumes extra horsepower just to stay airborne, and it consumes extra fuel which is again extra weight in its operation. The extra fuel consumption has both the effect of reducing your useful load and reducing your flying range....and extra $ costs / hr flown which will realy add up in todays soaring fuel costs. Build your aircraft (regardless of model) as light as possible and it will be a delight to fly and out perform the heavier version.

Comment by Bruce Woodry on January 6, 2011 at 10:11am

Thanks, Chris. The main issue in the numbers is to make sure we have sufficient payload to stay within ELSA. Plane will take higher loading. Not too worried about staying STOL, as we think that the 300' takeoff will slide out to a 400-500' splash, which is still ok. We are obviously trying to optimize, as you never know when you may need the extra performance, and a bit more up front work might be worth the time for a plane that we will live with for quite a while. Maybe the fixation on accuracy is the engineer in me.

Comment by Chris Aysen on January 6, 2011 at 9:59am

Well, if you can stay under the FF recommended installation weight you should not have to much of a problem with payload (as far as affects because of engine weight). The problem (lack of better word) is the addition of the floats. I don't believe in getting too tied up in numbers. You have obviously put alot of research into it. I agree with you about the 3300 or the 350i with a wide cord prop. But because of the added weight; and subsequent drag; you may have to sacrifice some STOL perfomance. But then you may not need it? 

Comment by Bruce Woodry on January 6, 2011 at 9:18am

Here is some of the technical information:

Specification/Engine	Lycoming O-320 D	Lycoming O-233	Jabiru 3300	UL Power 350IS	Rotax 912 ULS
Technical
Number of cylinders	4, horizontally opposed	4, horizontally opposed	6	4, horizontally opposed	4, horizontally opposed
Displacement:	319.8 cu in	233.3 in³ (3.82 L)	200 cu.in. (3300 cc.)	3503 cc (213.8 cu.in)	82.6cu.in. 1352cm³
Compression:	7.0:1	8:1:1	8.3 : 1	8.6 : 1	10.5:1
Prop Rotation:	Clockwise	Clockwise	Clockwise	Clockwise	Counter Clockwise
HP (cont)	150	100 hp (75 kW) at 2400 rpm	107 hp @ 2750 rpm	120 hp (86.3 KW) @ 2800 rpm	95 HP  @5500
HP (peak)		116 hp (87 kW) at 2800 rpm	120 hp @ 3300 rpm	130 hp (95,6 kW) @ 3300 rpm max. 5 minutes	100HP@ 5800 RPM for 1 minute
HP/Weight	.54	.51	.60	.67	.68

Comment by Bruce Woodry on January 6, 2011 at 8:38am

Thanks, Chris. Most are recommending more ponies under the cowl for the 200lb heavier 750 with floats. If we were looking at principally wheel flight, we would bolt on the 912 and not look back. Our engine picks are below, and the challenge is bolting on enough HP and having enough payload to take more than one guy along. We have done a bunch of research on the engine weight vs. installed weight, and get substantially conflicting information, so if you, or anyone, has better numbers than below, we certainly would like to know it.

Comment by Bruce Woodry on January 6, 2011 at 8:28am

Here is a snapshot of our short list of engine picks. We are having difficulty getting the manufacturers to give us real weights, as everyone likes to play the "mine is lighter than yours" game. If anyone has better numbers, please let me know. :

 

Specification/Engine	Lycoming O-320 D	Lycoming O-233	Jabiru 3300	UL Power 350IS	Rotax 912 ULS
Installed Weight	268??	215	182??	172.8?	168.1
o-200 Deduct	-220	-220	-220	-220	-220
Amphib Floats	200	200	200	200	200
Amphib rigging with pump	25	25	25	25	25
Wheels deduct	-50?	-50?	-50?	-50?	-50?
Empty Weight aircraft	775	775	775	775	775
Ready to fly, dry, floats	973.0	920	912	902.8	898.1
Fuel (24 gal)	144	144	144	144	144
Oil (@1.88 lb/qt)	15	15	6.9	5.6	6.0
Empty, wet	1132.00	1079.0	1062.9	1052.4	1048.1
Gross	1430	1430	1430	1430	1430
Payload (elsa)	298.0	351.00	367.1.0	377.6	381.9

Comment by Chris Aysen on January 6, 2011 at 8:07am

Bruce - The physics you quote on the prop as per Rotax is right. It tells us that a shorter prop will produce less inertia on the gear box. However, past experience has proven that Rotax engines are well capable of swinging props in the 72" range with little or no adverse affects. I do agree with your assessment of a wider cord on the prop which would be conducive with a smaller diameter prop. You may have a point there in your particular situation. I can tell you, however, I have the 912 ULS and I love it on my 701. Its very relaible, quiet, fuel efficient, and easy to maintain (although expensive). But my 701 is not your configuration. The 1440 gross plus floats provide a different challenge. I don't know what FF weight limit on the 750 is; I believe around 225??? The 3300 Jabiru may be a consideration but from what some of the owners have been posting don't expect advertised TBOs. The ULs look promising but I agree with you; just not enough flying..... But this is the experimental world and Gus seems to be a knowledgable fellow. Best of luck!!

Comment by Paul Bonasera on January 5, 2011 at 10:55pm

My plan is to put the CH 750 on an amphibs. it will be licenced with 1320 gross on wheels and 1430 on floats should still have pleanty of room for 2 people and fuel, I want to keep it light sport leagle. My engine will be Lyc.

0-235 and warp drive prop w/nichel leading edge. Zenith said this weight increase is ok with the edition 1 plane.

Hope this helps to eather clear things up or make more choises

Comment by Bruce Woodry on January 1, 2011 at 8:51pm

Thanks Stefan and Bob.

 

We have the new CH 750 kit with 1440 gross, 1430 ELSA gross.We have inquired as to the take offs for wheels and adders for amphibs/rigging, but no answer yet.

 

The Rotax is a good package, proven, with a good FF kit, few installation problems. Bob, are you swinging a 72" prob? We called Rotax and they have recommended against anything greater than 66" due to the rotational intertial breaking the gearbox. We also favor longer, wider cord props for float operation, and will certainly reconsider our position on the Rotax if our assumptions prove incorrect. 

 

We like the UL 350, best HP/Weight ratio, but there are only a few in US operation and a couple hundred in Europe, few, if any, have made it to TBO yet. We are looking for a FF kit, and don't think the UL 350 has one, but would be intrigued if it did.

 

We are currently leaning to the Jabiru 3300, and emailed Giuseppe for his comments. 

 

None the less, it would be great to take more than my dog and a sandwich of Lake Superior missions.

 

Thanks again for your comments.

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