schneider

I have a question for all the engineering/aerodynamic types. As a result of too many Novel's laying aroung, too much time on my hands, and too many drill bits calling my name, I enlarged my Norvel .061 r/c (BigMig) throttle to 9/64's, drilled out the exhaust outlet nipple, and tried out various props. On 35% NVX, I am getting 17,700 on a Tornado 6x3.... 19, 900 on a Cox 5x4...... and 25,700 on an old Testors 3 blade what I would guess to be a 4x2 (?) (and yes, I am now officially deaf after that run!) Given the rpm that each prop is spinning, which one will give the best real-world top speed versus vertical climb? The Cox and Tornado felt to have about the same static pull, maybe a slight advantage to the Cox, and to be honest I only let the Testors run long enough to get a tach reading and I dont remember how it felt (I was a bit nervous letting a 25 year old prop spin that fast so close to my persona.) The plane is a Ripmax Coyote glider ( http://www2.towerhobbies.com/cgi-bin...?&I=LXAHP1&P=7 ) thats weighing in at right around 22 oz. (without fuel).

Msaint

My Feedback: (5)

Keep in mind going back on pitch while it increases rpm does not actual mean it is the most efficient. If you want a true measure setup a static thrust test stand. I would also try a 6x4 as well as a 7x2. heh about all the 4x2 will do is throw a rod. I dont know that it would even generate enough thrust to pull the plane

AndyW

My Feedback: (1)

schenider,

Agree with Msaint. Spinning faster doesn't necessarily mean more thrust or power. You have to load the engine properly to absorb the torque. All things considered, for Norvel .061s, I've found that the BLACK Tornado prop to do many things well. The white Tronados do OK but flex robs power. They're good if you smack the ground a lot. I've found that the Cox 6 X 3, despite being the same dia. and pitch, tend to load the Norvel a bit too much. More blade area on the Cox is the thing. Norvels like to spin faster than Coxs.

Msaint,

Where can I get a 7 X 2 prop? What brand?

Bipe Flyer

I've played with Tornado white and black, COX grey and black, APC, MA in sizes 5X3, 5.7X3, 6X2, 6X3 and 6X4. I prefer the APC 6X2 for thrust and the APC 5.7X3 for a little more speed.

I would also be interested in finding a 7X2. I think it might just be the perfect size for either the .061 or .074.

schneider

Thanks all for the input.....I'm glad you mentioned the Cox 6x3, I wanted to tach it next but my glow plug battery was dying. I wanted to see just how much the Cox loaded the engine versus the Tornado being that they were both 6x3. I, also, prefer the black Tornados over the whites. The black 6x4 always seemed to fly the plane the best.

I put the old Testors 3 blade into the "bad idea" category pretty much before I even tested it. I didnt think a 2 pitch would be too efficient at that high of an rpm, plus the inefficiency of 3 bladed props in general. I really did it more for the entertainment value (noise) more than anything, and just to see what it would tach at. My interests are migrating from the .40 size planes more to the 1/2a's and I find screwing around with the engines almost as much fun as flying them! At the rate I am going I'll probably end up pulling one of my Testors control line biplanes off the basement wall and getting dizzy with it in the back yard......

Msaint

My Feedback: (5)

I have ONE 7x2 prop it is wood no idea what brand as 7x2 is marked on it in marker. I at one time had 2 the other one is now part of a corn field. I picked them up in a box of old props at Central Penn Swap meet a few years back from a guy that had a mess of old engines and free flight stuff. Think I paid like 5 bucks for a box of like 10 used props.