AboutPaul Soderman Expertise Aeronautics, Fluid Mechanics, Aeroacoustics, Noise Control, Muffler Design, Wind Tunnel Research.... I know nothing about India - do not ask about schools, jobs, application requirements, career choices, etc. for India. Please, no text message verbiage; I prefer full words in full sentences. Thanks.
Experience 38 years as research engineer at NASA
Publications AIAA, NASA
Education/Credentials B.S. and M.S. Aeronautical Engineering - U. of Washington
Graduate work Standford U.
Awards and Honors AIAA Associate Fellow (American Institute of Aeronautics and Astronautics)
Question QUESTION: I need help beginning my research on the effects of using steel deflectors on a farmer propeller when its the triangular shape as used by Roland Gaross. Can you please tell me how this would effect the flow of air around the propeller and how it can effect the plane's capability on pitch and yawing. If you can please refer me to a book or website that can help me study the subject better because I am writing a paper comparing the Fokker E III and the Morane-Saulnier Type L with steel deflectors in terms of maneuverability. Thank You
ANSWER: Terri
You haven't told me what the steel deflectors looked like. In general, adding anything with significant thickness to a propeller would compromise the performance of the propeller. One thing in Gaross's favor was that the steel deflectors must have been put on the airfoil lower surface, which is less critical than the upper surface. But changing the airfoil shape is not good and could reduce thrust and increase torque required due to drag increase. The other factor is the mass of the deflectors which would have added angular momentum to the propeller. That would make it harder to maneuver a light aircraft just as moving a gyroscope is resisted by the angular momentum of the spinning mass and introduces new forces. In other words, a command to pitch the aircraft would introduce a force and moment in another direction. These things can be computed.
I don't know what book might help except a basic physics or dynamics book that would describe the forces and moments on a spinning body. Do a Google search on gyroscope. Likewise, propeller performance charts may give a clue as to how airfoil shape changes propeller performance, but if it was a simple protuberance it might be difficult to find data that matches.
Paul
---------- FOLLOW-UP ----------
QUESTION: The actual steel deflectors that were originally added on by Saulnier are not described anywhere that I've looked so far but what garros added on was a triangular shaped steel deflector that protruded from the back of the propeller so that if a mounted machine gun in front of the cockpit would be able to fire through the arc of the propeller and the bullet would ricochet off the deflector at a forward angle instead of towards the pilot. There sketches of the garros steel deflector on google I tried copying it over so I could give a visual aid but it wouldn't let me.
p.s The gyroscope helped a lot with the basic physics of a propeller however this triangular add on complicated things for me and I was unable to imagine how this could effect slippage in a way that I can prove theoretically within my paper as required by the teacher.
Answer Now I understand a little better. The triangular shape is what you would see looking along the surface from tip to hub. That would deflect the bullets away from the aircraft. It also suggests that the deflectors would be thick and potentially bad for propeller performance, though the spanwise length could be fairly short so maybe the performance hit was small.
I'm not sure what you mean by slippage. From the gyroscope equations you can compute the change in force and moment induced by the added mass subject to a pitch or yaw rate if you know the rpm.
