90hp cruise props - Sensenich vs. McCauley

[coldwxflyer]

I bought my 90hp PA-18 with a McCauley climb prop on it, and it cruises about 80mph at 2200 rpm. I don't fly out of short/ rough strips, regular airports only (paved and grass), and no floats, so don't really need the climb prop, and would like to try a cruise prop for better cruise. Questions: which gives better performance, the McCauley or the Sensenich? I believe the Sensenich cruise prop is the 76AK-2-46, but does anyone know the "new" designation for the approved McCauley cruise prop for the 90hp? I'm sure a bunch of you have done this switch - what are your experiences? How much higher cruise speeds can I realistically expect? Or is this just going to be a $3,000 exercise that will only yield a few measly mph?

 

[gbflyer]

Or is this just going to be a $3,000 exercise that will only yield a few measly mph?

IMHO, yes.

I think the McCauley you are referring to is the 1B90CM71XX. I have a 7148 I got with my C90 powered -11 that is set - up and weighs pretty close to a PA18-95. That prop will cruise about 90-95 depending on tires. The 7141 climb prop I have on now cruises 85-90, again depending on tires. I cruise at a littler higher rpm than you've posted, around 2400 'cause my engine seems to like it there better.

The longer Sensenich 76AK-2-XX should pull a bit harder and cruise slower in theory since it's 74" instead of 71". That seems to be the propeller of choice for the seaplane guys. I have personally never tried one, but I'd sure like to.

JimC on this site has done a bunch of testing on props, I think mostly on lighter J3's but with similar horsepower. I think his emphasis was more on performance than speed, but his numbers might interest you nonetheless.


gb

 

[cruiser]

I don't know how long it will take Sensenich to get them certified but that composite prop would be the best of both worlds. Pitch changes take about 20 minutes. floats, wheels and cruise to the Bahamas all in one prop. http://www2.sensenich.com/discuss/messages/570/570.html?1216724277 Jim

 

[willyb]

coldwxflyer what prop are you using now?You may want to just re-pitch what you have.
Have you tried more rpm in cruise?
Running at low revs with a coarse prop is not necessarily better than turning more rpm with a flatter pitch.
I find a lot of cub guys have this thing for low rpm.
Engine load vs thrust produced is the key to the correct prop.You want minimum load on the engine for the most thrust you can get.
Load can be measured with a manifold pressure gauge plumbed into the intake spider.
Your 90 is restricted to less rpm than my 0-200 but it is basically the same engine and I run 2550 in cruise with a 75-35 prop.I get 92 mph no wind at 5gph leaned.
If JimC posts I know he will have a recommendation.He has tried a lot of props.

Bill

 

[coldwxflyer]

I have a McCauley 7143 on there presently.

You raise a good point about just running it at a higher RPM. Think of what we all do with constant speed props on Cessna 180s and 185s, namely making sure your MAP isn't too high for the RPM setting. For instance, we always run the prop up to the flat pitch setting turning final, so in case we have to firewall it for a go around, we use all that power in as efficient a manner as possible. That's what we're doing with a Super Cub with a climb or seaplane prop, except we have the prop in that pitch setting all the time! I've tried that with the Cub, cruising at 2400 instead of 2200, and I do get a bit more speed (maybe 3-5 mph), at the cost of increased noise and higher oil temps (about 10-15 degrees higher).

 

[willyb]

coldwxflyer
I spoke with McCauley product support .1B90CM/71-46,71-50 are what they list for the C-90.
I also checked the TCDS and the 1B90CM is what's listed with min static rpm 2200 and max 2350 with no pitch specified.You can use any pitch as long as you observe the static limits.This from McCauley.

The Sensenich M76AK-2 is also on the TCDS with a max diameter of 74" and the same rpm limits.

I would re-pitch what you have.It is pretty inexpensive compared to a new prop.At the rpm you want to run I would not expect more than a 5mph increase in speed.
Good luck,Bill

 

[bob turner]

I run the lowly C-85 at 2350 in cruise. Doesn't seem to hurt it.

 

[coldwxflyer]

If 71-46 and 71-50 are the props McCauley shows for that engine, then I'm pitched low with the 7143. Of course, the C90 was (is) used on a variety of airframes, and the McCauley prop numbers are a one-size-fits-all kind of thing. The 90hp PA-18 is probably one of the slower airframes on which the 90 is used (for example, compare it with the Cessna 140A and the later Luscombes, both of which are 10-20 mph faster). It's beginning to look like the just-run-it-at-2400rpm-and-be-happy idea may be the best and cheapest one of the bunch...

 

[gbflyer]

I think you're on the right track there. These little engines don't seem to mind being run a little harder. On the other hand, most prop shops only charge a couple hundred bucks to re-pitch one that is in good shape to start with.

I'd say your -43 pitch is a pretty good compromise between cruise and climb.

gb

 

[JimC]

I usually run a 7142 on an O-200 J3, cruising at 2350 rpm (well under 75% power). That gives me a cruise right at 79-82 mph and a fuel burn of 4.3 gph at an altitude of 3000 feet (including fuel used during the climb up from 310 MSL).

At WOT in level flight (depending upon density altitude), with the
7142, I get 118 mph max speed
7441, I get 115 mph max speed
7535, I get 110 mph max speed

My hunch is that a 7440 would be the best all-round prop for my personal goals (short takeoff and good climb with reasonable but not fast cruise). My 7441 has been repitched to 7440, but I haven't had a chance to fly it. It has been used in a static pull test, and rpm for rpm it will outpull a 7535 up to about 2750 rpm.

I like to cruise at about 80 mph, so whatever prop I'm running at the time, I just turn the rpm's needed to make 80 mph.
JimC

 

[JimC]

By the way, I recently had the chance to ride in a Just experimental with a 120 hp Jabiru 3300. The Just weighed 705 pounds and was running the Sensenich composite prop. The J3 weighs 789 pounds. With the 7142 prop, the J3 can get off and land shorter than the Just, climb at about 100 to 150 fpm greater rate of climb, cruise slightly faster, and top out about 8 mph faster. I wasn't impressed with the Just engine/prop combination, but don't know if the engine is overrated, or the prop was poorly pitched.
JimC