"Pusher" powered

Here is an excellent article on the issues with pusher design:
http://www.djaerotech.com/dj_askjd/dj_questions/pushtractor.html

dirk gently wrote:Here is an excellent article on the issues with pusher design:
http://www.djaerotech.com/dj_askjd/dj_questions/pushtractor.html

Very interesting read!! It seems that "propeller" efficiency suffers; in most.. if not all designs.. where the airflow forward of it is disturbed by the airframe. Lots of issues for full-scale designs. Flying wings were mentioned as being better candidates. After reading the article, I can certainly understand why there aren't a lot of pusher-designs out there.

Thanks for posting the link Dirk.

This guy has a lot more interesting articles on his site. He actually explains stuff that you can find in any aerodynamics handbook, but actually does that in a way that let's someone with some modelling experience, but perhaps with no PhD in physics understand it.

The problem with a pusher is that your engine goes rich rather than lean when entering maneuvers. This is a result of the tank being in front of the engine. Not a good thing when you need the power. My friend Dan resolved this issue when he built his scale Farman Bipe. Here's a picture I took of him when we entered a "Fun Scale" at Palisades Park, New Jersey a few years ago. Dan custom built a shaft for the LA .46 which utilized a rag joint similar to a steering column joint. The engine was in the nose with the shaft running directly through a tunnel just like a rear wheel drive car. The tank was constructed with a hull like appearance in which the shaft ran through it. It was remarkably engineered and it worked flawlessly. The plane met it's demise  when the wind came over the trees where we fly at on the weekends. It pretty much splatted the plane into the ground. Ken

That's always sad to hear about Ken. It must have sucked to see happen. I've seen that airplane before.. probably a different model.. but I remember it. I really like bipes... and "tripes" for that matter. I'm trying to visualize the tank in that Farman bipe. Was it like a "saddle" arrangement? Did the extended prop-shaft run over.. or under it? Just curious. I'm sure it was a good size tank for the .46. It looks like the engine is mounted upright with it's cylinder just forward of the wing's leading-edge? It's hard to tell from the photo. Were there any engine cooling issues?

This "rag-joint" I am curious about. Can you elaborate a little bit on the materials Dan used? I've been toying in my mind with extended-shaft drives.. where there would be at least one angle to deal with. One such drive is a "marine" application.. but the other is aircraft. The aircraft is a 1/2A "Stiletto" control-line model.

This plan references a steel universal joint.. pillow-block/bearings type set-up... but there doesn't appear to be any angular changes in the drive-line. Maybe this helps with any slight misalignment when building?



Of course.. we're talking 1/2A here.. as compared to a big .46.. but I'm just curious about what the coupling consisted of.. and whether Dan ran his shaft in a sleeve.. or whether he used a pillow-block/bearing set-up? I can't imagine trying to flip-start that .46 with those tail-booms in the way..

That's always sad to hear about Ken. It must have sucked to see happen. I've seen that airplane before.. probably a different model.. but I remember it. I really like bipes... and "tripes" for that matter. I'm trying to visualize the tank in that Farman bipe. Was it like a "saddle" arrangement? Did the extended prop-shaft run over.. or under it? Just curious. I'm sure it was a good size tank for the .46. It looks like the engine is mounted upright with it's cylinder just forward of the wing's leading-edge? It's hard to tell from the photo. Were there any engine cooling issues?

This "rag-joint" I am curious about. Can you elaborate a little bit on the materials Dan used? I've been toying in my mind with extended-shaft drives.. where there would be at least one angle to deal with. One such drive is a "marine" application.. but the other is aircraft. The aircraft is a 1/2A "Stiletto" control-line model.

This plan references a steel universal joint.. pillow-block/bearings type set-up... but there doesn't appear to be any angular changes in the drive-line. Maybe this helps with any slight misalignment when building?



Of course.. we're talking 1/2A here.. as compared to a big .46.. but I'm just curious about what the coupling consisted of.. and whether Dan ran his shaft in a sleeve.. or whether he used a pillow-block/bearing set-up? I can't imagine trying to flip-start that .46 with those tail-booms in the way..

Roddie, the shaft ran under the tank. The shaft indeed was in a pillow block with a bearing and yes cooling and also alignment was an issue to the point that it cost Dan 3 LA .46's until he got it corrected. The engine is mounted inverted and starting the 11 x 4 was certainly an issue. I would start the plane many of the times. You wouldn't really flip the prop like one would conventionally on a open nose stunter. I would grab the prop by the center section and flip it backwards with my thumb and forefinger like I was trying to snap my fingers. It would light off pretty quickly. The joint itself coming off of the engine utilized a couple he made that threaded onto the shaft with a mating flange. The shaft also had this flange and this rubberized cloth he attained was in between the flanges. This assembly was also balanced. Dan and Bob Zambelli worked on this project together. It really was a neat piece of engineering. The tank and shaft still exists and he mentioned that some day he might build another. The struts in the rear were carbon arrow shafts. The projection that you see in front of the leading edge in the picture is Snoopy. Ken

Ken Cook wrote:Roddie, the shaft ran under the tank. The shaft indeed was in a pillow block with a bearing and yes cooling and also alignment was an issue to the point that it cost Dan 3 LA .46's until he got it corrected. The engine is mounted inverted and starting the 11 x 4 was certainly an issue. I would start the plane many of the times. You wouldn't really flip the prop like one would conventionally on a open nose stunter. I would grab the prop by the center section and flip it backwards with my thumb and forefinger like I was trying to snap my fingers. It would light off pretty quickly. The joint itself coming off of the engine utilized a couple he made that threaded onto the shaft with a mating flange. The shaft also had this flange and this rubberized cloth he attained was in between the flanges. This assembly was also balanced. Dan and Bob Zambelli worked on this project together. It really was a neat piece of engineering. The tank and shaft still exists and he mentioned that some day he might build another. The struts in the rear were carbon arrow shafts. The projection that you see in front of the leading edge in the picture is Snoopy. Ken

Thanks Ken. I'm always interested in knowing about how modelers overcome obstacles.. when building an unorthodox model.