Props

[gilligansae]

I have a McCauley 74/45 prop on my A-65. I have been told by one old timer or another and a couple of IA's that 45 is too much pitch and that it will cause the engine to run at a high manifold pressure at redline, causing exhaust valve damage with 100LL.

Any truth to this rumor? Forrest - Help?

Should I get the prop re-pitched to 43? a fellow T-carter told me that his is 74/43 and that his runs at 90 mph at 1960 rpm.

Please Advise...

[Robert Lees]

I also use a 74/45, an excellent all-round prop, 95-100 mph at 2200 rpm on my A-65.

How do you get up to redline...only in a dive? Static rpm should be around 2070 or so. Max continuous rpm is 2250, redline at 2300.

What is your actual diameter...there is a tolerance of 69.5" to 76" for the A-65 engine. The actual diameter will have a bearing upon the engine rpm and effective pitch of the prop.

43 I think would be a climb prop. Your fellow's 1960 rpm is probably not doing the engine any good. What is his static rpm, and does it meet the requirements of Type Certificate A-696?

In conclusion, I would suggest that unless there is something untoward with either the dimensions of your prop or the rpm limits, then stick with a good prop.

Rob

[gilligansae]

I agree with you. I think the prop is fine. My A&P says that I should be careful. I have always run it at the numbers you said, 95-100 mph at 2250. I can run from 1950-2050 static with it. I talked with the guy that has the 43 pitch and he never sees over 2000 static. He also never runs his tcart over 2000 in flight because he is content with going 80mph.

Jeff

[jgerard]

I prefer a prop that allows full rpm in level flight, that is the only way you can get full HP. Just because you have the throttle all the way to the stop does not mean you are making 65hp. Only at 2300 rpm do you get the full 65. And yes you can burn up cylinders by having too much pitch and over loading the engine. It does not cost much $150 or so to have the prop pitch changed. Give it a shot and let us know the results.

Less pitch means less throttle for the same rpm means less fuel burned. You won't loose much speed from a 45 to a 43. If you want that extra 3 mph back just open the throttle more. You will probably notice a drop in oil temp with a flatter pitch due to the reduced load on the engine. I always run at 2300 rpm everywhere I go and the oil temp is only about 80/100 degrees over ambient temp.


Still looking for a 74" prop, any for sale???

Jason
N43643

[alwaysoar]

prop

OK, You've got my interest. I have a wood 72-42, listed in all the ads as either a "standard" or "climb." Sensenich calls it a standard I think. I get about 2100 static, or a little under, I can get 2400 in cruise (just majored my engine so I was just checking to see), but I only get about 85 mph cruise. Is that all I can expect from a wood 72-42? I'm not really in a hurry, but if I should go faster and I'm not, I want to know why.

Ed @BTV VT
TF 527

[alwaysoar]

post script

ps: All the literature says you should cruise at static RPM. If that is so, then you guys are running way over. What's up with that?

Ed @BTV VT

[Robert Lees]

What literature is that, Ed? First time I've heard that.

Rob

[alwaysoar]

props

Rob,

The Taylorcraft Service Manual on page 18, "NOTE: Recommended cruising RPM should be static or the maximum RPM shown on the tachometer when the engine is run up prior to flight with the carburetor heat off." It also states in the paragraph above that note, "Recommended cruising RPM 2150."

Other folks besides you all on the forum have also said there is no problem running 2200 or 2250. With my 72-42 wood prop, where would you run it, and what kind of speed should I expect?

Ed @BTV VT
TF 527

[alwaysoar]

another post script

Also, Rob,

You give greater limits than the type certificate A-696 that states prop diam. not over 72" or under 70", yet owners are running 74" props. How is this legal? I know there's a resource I don't know about. You guys are the experts.

Ed @BTV VT
TF 527

[AlvinMcIver]

Prop

This is right on an issue over which I have been mulling for some time. In reviewing my log books, there is a notation that, in 1987, a new prop was installed:
McCauley 1A90
CF 7447
SN6929
There is no other mention in the log books of any work being done on the prop, but when I acquired Tommy a little over two years ago, the prop looked brand new, no nicks, (new labels) painted tips and etc.
Two weeks ago during the annual, there was occasion to remove the spinner which allowed me to check out the hub and lo and behold, all of the numbers matched. However, when I measured the prop, tip to tip, it only measured 72.5" (not 74).
Here is what I experience with my A65-8:
Static runup 1950-2000 rpms (tach has been checked and found within tolerances);
Cruise 2150-2200 rpms @ 102-105 mph IAS (ASI has been checked and found within tolerances) & Oil Temp = to Ambient + 100-110;
Max rpm of 2300-2325 with full throttle in level flight;
Climb is dependent upon the usuals, but it has always pleased me, regardless of density altitude, gross weight, and grass runways (although MN never gets too high).
Given the comments above, I'm guessing that, in addition to shortening the prop, it was re-pitched. When I use the "No Slip Propeller Estimator" in an aticle on props (which I copied from somewhere), it suggests that has a pitch of 51 - not likely. Now the question: how does one determine the pitch?
Thanks
Alan
PS: my wife's theory is that men are into quantity, women into quality; men measure, women evaluate. She says, if it pleases me, why do I care what size it is. Guess there is something to that, but I still would like to know.

[jgerard]

Regarding longer props, dig a bit deeper in to the T.C. information under alternate equipment. There you will find the listings for the 74" props.

Metal props are more efficient than wood for producing thrust because they are thinner.

McCauley and Sensenich measure the pitch of their props differently so don't expect a 74-43 McCauley and a 74-43 Sensenich to produce the same results. Metal props ONLY for this example.

Recommended cruise RPM??? 2300 from an A65 should be fine if you don't experience overheating problems. I think the recommended cruise rpm has something to do with max efficiency of the aircraft. I burn about 4.5 gallons/hr at 2300 rpm because I am not at full throttle with the prop I am using. Straight and level I can get 2450/2500 rpm, I usually climb for the first 30 seconds at 2400 rpm indicating around 50 mph and then pull it back to 2300rpm. I am swinging a 70-42 metal McCauley. My cruise speed is only about 90 mph at 2300 rpm. The guy at the prop shop says “A 72-42 and a 74-40 should produce about the same static rpm."

A longer prop is more efficient. (High aspect ratio like a sailplanes wing) Never cut your prop unless it has been damaged. Trade it off if you want a shorter one. A side benefit of the longer props would be more frontal surface area when wind milling during an approach to landing thus helping to slow the plane down.

Jason
N43643