BMW Question for vliegvark

[Biggles of Africa]

This one is probably for vliegvark.
I am embarking on my first project, and am tossing ideas around for the power plant, I would really like to use the BMW R100 engine if this is viable, I have searched all the posts relating to the BMW power plants, and it seems that the 1100 or 1200 is the way to go as opposed to the older R100 motors, but due to a number of factors, $$$$ being one of them, I would like to use the R100 if possible, here are a few aircraft specs:

Max all up Wt: 540lbs
Single seater
Wing area: 117 sq ft, modified Clark - Y
Vne: 85mph
Cruise: 60 - 65mph
Motor: 35 - 40 Hp
Fuel Quantity: 5 USG

with this in mind, i do not think that I would require all the power of the new 1100 or 1200 engines, but I think the R100 should be well capable of doing the job without breaking into a sweat.
the aircraft will be operated up on the Reef in the big smoke.
Why I want to run a BMW motor.
I like the idea of a 4 stroke over a 2 stroke
Cost
Ease of Maintainence & cost
The plans call for a 447 Rotax or similar, but I m not keen on half the engine sticking out the top of the cowl in my veiw, the pots of the BMW out the side would take care of that issue.
I have read that cooling these motors is a problem area, as they are 70% air cooled and only 30% oil cooled.
I will be leaving the pots out in the free airstream behind the prop, kinda like a J3 Cub, surely this should take care of the cooling issues?

All thoughts would be greatly appriciated.

[Abe]

Hi Biggles!
Yes, I think your project is imminently feasible.
Yes, the BMW is heavy, but your wings and design are just the kind that should carry that with ease. (And it will sound great!)
Moreover, considering your budget constraints, I could supply all the bittys necessary to convert that motorcyle engine to flight status, even heads and dual ignition, at neglible cost. (failed R100RS project, a guy with a USA accent was involved, 'nuff said.)
FlySafe!
Abe
ohaighttwooniner260585

[Biggles of Africa]

Hi Abe
Thanks for the insight, as soon as I have done the homework, and am have been satisfied that the R100 power plant will be suitable, I will most definitely take you up on your offer.
Many thanks

[vliegvark]

Biggles you can give me a buzz on 0h aight 3 sex sevan aight dbl2 dbl3

typing is my down fall

[Henni]

I will be leaving the pots out in the free airstream behind the prop, kinda like a J3 Cub, surely this should take care of the cooling issues?All thoughts would be greatly appriciated.

Hi Biggles,

Countrary to what may seem logical, a cowled air cooled engine with proper cooling baffles is cooled much, much better than one that just having it's heads hanging out in the free air flow.

A good example of this is the KRII which suffers from serious overheating when flown without a cowling.

Henni

[Griffin]

There was a Bush Baby hangered at FAFK with a BMW R100 motor. I did not fly it but the owner was very impressed with the performance and it sounded wonderfull. I think the owners name was Kobus Du Plessis and I seem to remember he moved the plane to Worcester. Louis at Aerosport may still have his details if you want to contact him.

[Biggles of Africa]

Hi Henni

Yes, I do understand the concept of having the engine cowled and baffling to direct the airflow to where you want it, and also to force it through between the cylinders, you are quite right, but in the case of the R100 motorcycle engine which was designed to have the pots hanging out in the airflow, and maintain it's cool, without being cowled, also living under much harsher conditions than it would in an aircraft, just think of 40mins in stop start traffic with very little, if any airflow, by design the cooling fins on the motorcycle engine are designed to cool the engine adaquatly by absorbing the heat and radiating it into the free air around.
I may be wrong, but that is just logical to me, you also do not have the situation where you have a rear pot to cool.

[Oupa-G]

You cannot compare the R100 with the later oil heads. The R100 in purely air cooled with heat bottle necks and all sorts of vibration problems The R1100,1150,1200gs are completely different engines.If you are going to take the trouble converting then use the oilhead We have successfully converted with dual independant ignition systems and dual fuel. The 1200GS delivers 100hp. My 1100 has now done 200hrs no problems.

[Oupa-G]

You cannot compare the R100 with the later oil heads. The R100 in purely air cooled with heat bottle necks and all sorts of vibration problems The R1100,1150,1200gs are completely different engines.If you are going to take the trouble converting then use the oilhead We have successfully converted with dual independant ignition systems and dual fuel. The 1200GS delivers 100hp. My 1100 has now done 200hrs no problems. Papa-G father of vliegvark

[Biggles of Africa]

Hi Papa-G
Not what I wanted to hear, but, yes, I do hear you, and that is why I posted, to get the input of those who know better than I.

Unfortunately the later engines that you speak of are just sooo far out of my budget right now that is not an option, that is why I was looking at an old R100, and seeing that I would only be looking for about 60 horses, I hoped that it would be fine for the application.
Oh well, I guess, when the time arrives, I will be hunting for a cheap and nasty 503 to drag it through the air.
The plans call for a 447, so a 503 should be plenty up here in the big smoke.
Thanks guys, for all your input, it is invaluable.