Ben Buckle Fokker D8 - Engine choice

[David Germany]

Hi, I'm building a Ben Buckle Fokker D8 from an old kit, it will be built with no dihedral but with ailerons with wing mounted mini servos. Originally I had intended to fit an ASP 40FS but I do have the option of a Saito 45 Special. If I need a shed load of lead to balance with the ASP then I guess I may as well use the Saito, Would the extra weight / power of the Saito require more strengthening to the front end ? I hope to keep the overall weight as low as possible to keep the flying speed low.

Any advice on the engine options would be appreciated.

[brokenenglish]

David, respectfully, IMO your power estimations are way too much!

The BB Fokker D8 is Earl Stahl's design (early forties). The original weighed 28 oz all up and was powered by a 1940 Ohlsson 23 turning a 12" prop. (I'm looking at the original magazine article as I type this).

The plane is very lightly constructed and an OS 20 or 26 FS would be just about perfect. Assuming that you're using modern lightweight RC, then your RC hardware will probably be lighter, or at least no heavier, than the spark ignition system used in the original plane.

Obviously, the plane needs to be built very light at the rear, so do exactly that and stop thinking that a load of nose ballast is unavoidable. That's not true. You need to forget "RC sport" culture a bit. The rear end needs to be built like a free flight model if you want to keep the model light and fly slowly.

It won't be an all-weather flier but you'll have a great plane for calm evenings.

[J D 8]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Recommended is 20 two stroke or 30 four stroke.

Aircraft of this early era do not care for to much power, they do not want to go faster but do want to climb like the proverbial homesick 

Cheers, John.

,

 

Edited By J D 8 on 07/12/2020 18:18:47

Edited By J D 8 on 07/12/2020 18:22:20

[kc]

In recent years RCME published several articles by Nigel Hawes which contained details of how he electrified this D8. I cannot remember the details now but he went to some trouble to keep all the weight up front, including putting the lipo at the very front.

I remember also that the plan already has a longer nose or cowl compared to scale.

[David Germany]

Thanks Guys, I'll stick with my original choice then (the 30FS) and keep it light and slow. I was hoping for a similar flying speed as my Junior 60 which also has an ASP 30FS. Also, on checking the fit of the Saito 45 I would have to lengthen the cowl even more than the plan which would detract even further from the scale outline.

Thanks again, just needed some reassurance after being distracted by some of the t'internet content.

[Jon H]

I flew one of these a club mate built and it originally had an enya 25 2 stroke fitted. Flew like a dog, so i suggested a 40-52 4 stroke as it was bloomin heavy. He fitted a 46 2 stroke instead and it still flew like a dog, just faster.

Further inspection revealed it was massively nose heavy and with that sorted it flew well. Its likely the original 25 2 stroke would have been plenty had the balance issue been spotted earlier as it was well over powered by the 46.

Your 30 4 stroke will be fine but you could use the saito 45 and fit a big prop. My Flair nieuport 17 has a saito 45 non special and i turn a 15x5 prop at low revs. Works nicely but i have to be careful with the throttle or i will toast the engine. If you went this route the firewall could be moved back so you dont have to alter the cowling.

While i agree that a model like this should not be over powered a 45 saito is not going to be excessive and if you team it up with a 15x4 or 14x5 prop it would be perfectly ok. The fine pitch will keep the speed down and still give plenty of thrust.

 

Edited By Jon - Laser Engines on 08/12/2020 10:14:43