McCulloch 72 Prop

[Roberd42]

Hey guys,

I'm new to the forum with a few technical questions. I currently have a 48in. unlabeled prop on my gyro (72hp mac bensen) that is cracking at the lamination near the hub. I also have another prop, in great shape, that is labeled Aerial Propeller Co. that is also 48in. Not sure of the pitch (seems similar to my current prop) and was wondering if this prop would be OK to run on the Mac. Seems like all replacements avail for purchase are 50in. However I have all of the original Bensen documentation calling for a 48in. prop. Can someone please fill me in on the performance difference and which is better? Thanks. -- William

[All_In]

I don't have the experience to answer your question, but I'd get a scale and do a thrust test before and then after you change the new prop. Then you would know for sure.

[Karl Hagström]

I got my prop from R&D.
Mr "Red" concluded i should have a Prop 50" X 24 (pitch)
As I understood it is better to have o shorter prop if you want the 72 hp to give you more power available stat over a greater rpm span, a longer prop gives you more thrust, but your 72 hp may not have the extra energy you need to quickly adjust your thrust. So 48" might be just the right one for you if the pitch is right. But I wouldnt use this information as the truth, Ask Red or someone else before you go for it.

Good Luck!

[GYRO J]

50x28 tenn.prop or 50x26 tenn.prop

[Caribean_gyro]

50x30, sterba, lake oswego, We use 30 on pitch will be slower on T/O but will cruse at 3500. so engine run cooler

[Steve Weir]

I thought a Bensen could swing a 52 inch prop, maybe 52x26. Anyone using or have used a 52 inch prop on a Bensen Mac?

[gyromike]

I use a 52x26 Tennessee Prop on my 90 Mac, and my Bensen is built according to plans with stock engine mount and stock mast. I cruise ~2900 rpm @ 55mph.

On the 72 I would use a 52x24 Tennessee Prop.

[Roberd42]

I talked with Red and he said I should be fine with the 48in prop on the 72hp mac. Only test flying will truly tell I guess.

[James]

I used a 52/26 on my Mac, am using the same thing on my direct drive Subaru.

[billygyro]

I used a 52/26 on my Mac, am using the same thing on my direct drive Subaru.

Hello James, question for you? how is the Tennessee Prop on the direct drive soob work for you? and what kind of numbers are you getting out of it? Just today I talked to Tennessee prop and was informed that they could do me a prop 54x26 that would give me 3600 to 3700 rpm's on the engien and produce about 350# of thrust. what do you think about that?

[Mike Schallmann]

Billy -Im really hesitant about getting involved in this -but I think this information is important--


First I need to talk about your engine. If its in good shape it will put out about 65 HP in the RPM range of 3600 RPM. Also if it has been "cammed" I dont think that will help, but it probably wont hurt. A stock EA82 is set up to run best in that range from the factory. When you "cam" an engine you are altering the valve lift and valve timing slightly --usually to bring the torque and power curve up into the higher RPM ranges.

Can you get 350# of thrust from that engine --the answer is PROBABLY -that is based on the fact that a DD EA81 will get an average of 325# of thrust in a DD setup--and the EA82 has slightly more power -so it should get a little more thrust.

Now about the prop. Tennessee Prop is a good reputable company -and if anybody can make a prop that will put out 350# of thrust for that engine they can do it -- but they CANNOT guarantee that is enough thrust to fly the gyro. So if you buy the prop -make sure its returnable if it dont work out.

So heres the bottom line. With 350# of thrust --on a cool day with a relatively low DA you can PROBABLY get the gyro airborn and out of Ground Effect. But it WILL be EXTREMELY sluggish and operating very close to backside of the power curve --it will be very dangerous and I do not recommend it.

The ONLY DD EA81/82 powered machines that I have seen fly are EXTREMELY BASIC--no pods ,no frills, no bells, no whistles . And no electric starters --most dont have prerotators --and usually the pilots are relatively lightweight--the AUW is right at the 550# mark

You need 400# of thrust to make YOURS fly reasonably well -as your AUW is approx 750#-any less will not provide the desired results. I can only give opinions -and these opinions are based on my experiences---

Billy I wont plague you anymore with responses-- I think Ive stated my position adequately--The decision is yours--Good Luck