Todd You are correct. In some cases you do not need a gear box. I know of at least one aircraft that simply bolted on a V-6 Buick to the front of his plane,,, straight from the car..attached a prop...and merrily and reliably flew about for several years. The owner was satisfied with the performance but was always aware that the restricted RPM used to keep prop speeds manageable also robbed him of the potential HP that the Buick had at higher RPM. Explanation;..If the Buick is rated as 180HP at 5500RPM and you restrict it's use to 3400rpm, you get perhaps 100 HP. (I am exaggerating all figures for illustration). NOW, is 100HP acceptable for an engine that ways 250 lbs.??...or 2.5lbs/HP My question then is this: What is the rated HP of your BMW and at what RPM? What is the weight of the engine? What is the actual HP at 3400 RPM (prop)? Will it turn out to be 40HP and 145 lbs in weight??...or 3.6 lbs/HP. Will 40HP satisfy you in a KR1?. Don't laugh, it might! In the early years of VW use in homebuilts, 40-50 HP was common. I once did a KR2 with 1800cc VW and I doubt very much that it yielded more than 50HP. Yes, of course you can do all of the things that you imagine. If the engine is light and you wish to make a longer motor mount or forward fuselage,...easily done! I did that once, just for looks. But I did extend the tail section aft and ultimately put my battery behind the seat. This is what you will do, work it out!! It's really as simple as you imagine it to be. There is a thrill in doing what you imagine and a wonderful self-satisfaction in working out the basic math. To some extent the following is true;, The larger the prop, the faster you'll go but how do you keep the tip speed down. Run a large prop around 2200 RPM, design an engine that runs optimally at the speed giving you all of the power you need for SAFE, FAST, EFFICIENT flight. I recall in the past that BMW engines were being used in Europe so I suggect that you google it.
> In a message dated 7/2/2011 5:22:48 P.M. Central Daylight Time, > rdrace...@aol.com writes: > > Why would you need the gearbox? Couldn't you just attach the propeller > directly to the flywheel, or to the front of the crankshaft somehow. I > have > ridden BMW twins for years, and they chug along quite comfortably at > 3200-3400 rpm. It seems like that would be just about right for a KR1. > and I > would think the light weight would be an asset. If C.G. is a problem > couldn't you just extend the front end a tad to give the engine more Arm > and > balance it out? > > Todd Thelin > Spanaway, WA > >
