R100 BMW Gyrocopter

BMW R100 flying gyrocopterBMW R100 morotcycle engine for gyrocopter power

How many of us have been through the following? We purchase a KB2G gyroglider kit, assemble it and learn to fly it. After being towed up and down the runway many times and for many hours, we begin to think about adding an engine. We do not know what type to use. Do I use a McCulloch, a Rotax, a VW, a Subaru, or is there something else out there?

When the time came to look for an engine. I knew I didn’t want a two cycle. The VW was an option and the Subaru was just being developed. I wanted an air cooled engine but I thought the VW was too heavy and needed a lot of work to convert for use on a gyro. I have always thought the engine used in some of the BMW motorcycles would be an ideal aircraft engine.

The engine in the BMW R100 series motorcycles is an air cooled, two cylinder, horizontally opposed power plain with a displacement of 1000cc. It is a four cycle and develops about 55 Hp. The engine has a reputation of being very smooth running and rugged. It also has the advantage of having a built-in starter and alternator.

Flying BMW gyrocopter

Left side view of the powerplant installation. The reduction drive utilizes a Gates Polychain belt and stock, off-the-shelf sprockets. The original starter, alternator, and ignition system are retained for additional cost reduction. All-up weight of this neat powerplant is 125 lbs.

I purchased a low mileage, used engine and began to look at it to determine how to go about converting it to use on my gyro, I decided to use the original battery ignition system, alternator and starting system as well as the original carbs.

I figured that the original electric and fuel systems had been used with success for many years. The only thing that I would have to add would be an electric fuel pump since the motorcycles use a gravity feed system.

Now to find a reduction gear that could be fitted to the engine. I was unable to locate a reduction gear to lit my needs so I would have to have one made.

After talking with several people, I determined that a reduction gear based on the Gates Polychain would be ideal for what I needed. With a belt drive you have an infinite number of gear ratios available just by changing, the size of the drive pulley, the driven pulley and possibly changing the belt length.

The local Gates dealer was very helpful in providing me with the necessary information that I needed to work out the desired gear ratio. (I did not tell him what the ultimate use was going to be).

Not being an engineer or machinist, I was fortunate in finding a person who could take my ideas and design and make the unit for me. As you can see from the accompanying photographs, the unit turned out simple, compact, and light weight.

BMW R100 motorcycle engine to gyrocopter

Right side view of the stock Bensen gyro with the R100 BMW engine installation. An electric fuel pump mounted on the mast supplies fuel from a plastic tank. Engine mount is fabricated from 6061-T6 aluminum.

The reduction drive uses an 8mm pitch, 36mm (1.4 inch) wide Polychain belt. The reduction ratio is 1.7. Off-the-shelf Gates sprockets are used in the installation to keep cost at a minimum.

The engine mounts are my own design, made from 6061-T6 aluminum. I was able to make them with very little machining. I made the mounts to fit the existing holes in the airframe, so it was not necessary to drill any additional holes.

I almost forgot to include some important information. The engine weighs 125 lbs. complete with starter, alternator, and dual carbs. This is not exactly a light weight engine, but it should not be too heavy for the gyro. I should have a very smooth running, reliable engine that I will not have to be constantly tinkering with. Just think about it. No hand propping or pulling a rope – just say clear prop and push the starter switch.

BMW R200 powered gyrocopter

BMW R200 powered gyrocopter

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R100 BMW Gyrocopter
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2 Comments on "R100 BMW Gyrocopter"

  1. Larry Whalen | July 1, 2020 at 8:23 am | Reply

    I presently have two 1972 R75/5 (750cc) BMW motorcycles, one of which the engine is presently being fitted to a vintage Bensen B-8 M along with a redundant and strengthened mast as well as a set of new rotor blades and hopefully a design for a safety feature which will help eliminate PIO which has been tested on a large scale RC model with more than favorable results, but for me until a human is behind the controls, the reality is the tests mean nothing since the human element is required to fully establish what may still be needed to ensure it will function properly when the situation arises, also until I can get it protected it will not see the light of day since I’ve already had two designs stolen and three more somehow “duplicated”, (for lack of better words) and which are now being sold.

    One very nice feature of the older Boxer twin BMW engines is they are capable of having the displacement changed by merely removing the “jugs, or cylinders and pistons and then replacing those with the next step up cylinders and pistons, i.e. from 750 cc’s to 900 cc’s in a couple of hours and with a change of jetting you are in business, all of which was explained in an issue of “Cycle World” sometime around 1974 which made your Beemer capable of running off from a Kawasaki K-1000 much to the consternation of a few Kawasaki riders.

    Until this COVID 19 situation runs it’s course I’m unable to get a few items machined to finish my project and complete my tests – both for the engine and the “anti – PIO” feature, as well as one more surprise item I’m hoping will function as well as it did on my mockup.

    So until then it will be kept under wraps until I can be sure someone else doesn’t claim credit for my design and intellectual property, but will do my best to keep anyone interested in what’s going on with the gyrocopter itself.

    • Please, by all means, keep us updated. We are happy to publish any gyro stories. Kind regards, Adam

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