The New Seaplane/Climb prop thread

[buzzlatka]

I have been searching the old posts and beating my head over what prop to put on the airplane to increase climb perf. I have the 7651.
Here are my options

1 Get the 8043 prop with the STC from kenmore.
If I go that route I buy the STC for 100, then buy a 3500 dollar 8042 and have it repitched to 43. (no 43's in stock anywhere).

2 Get the STC and the 8042.

3 Get the STC and 8042 and repitch to 45 or 47.

4 Repitch my existing 76 prop to 49ish?

I just thought of idea 4 as I was talking to american propeller and they said I would have to repitch the 42 becasue of availability.
Please weigh in with your ideas. Option 4 would be good because I would save money. But would I really get the climb performance?
How about the 8045 vs 8043. Is there really a difference? Could I still get good climb out of a 45 twist and not sacrifice as much cruise.

[GAHorn]

What static rpm are you getting with the 7651?
You can estimate that each 1" of pitch change will increase static rpm by X amount, and then have it re-pitched to acheive 2700 static (which will give you max 145 hp for takeoff.) Problem is, ... you'll then have to reduce rpm for cruise because the prop will then overspeed in flight.

[Bruce Fenstermacher]

George I'm SHOCKED that you might suggest something that is not approved. Or do you have another source of approval for the process you described? Or more likely you forgot about this limitation.

Per the tCDS:
Propellers and Propeller Accessories
1. Propeller
(a) McCauley 1A170 33lb. (-39) (-39) (-39)
Static r.p.m. at max. permissible throttle setting:
Landplane: Not over 2330, not under 2230
Seaplane (Models 170A and 170B): Not
over 2525, not under 2300.
No additional tolerance permitted.
Diameter: Not over 76 in., not under 74.5 in.

I read this to mean that regardless of the pitch you can flatten it but only to the point that you have 2330 static rpm at full throttle and no more.

And I could be wrong but that 2330 RPM will probably be obtained with the 51 pitch prop.

buzzlatka if I were you I'd get as accurate a reading of your current static RPM with your current prop what ever it is. I would use a digital optical tach for this. I would then have the prop shop repitch your current prop to what they think will give you the max static RPM allowed.

You may think you have a 51 pitch prop but it's not or perhaps a 50 would actually allow you to reach the peak static rpm allowed.

This would be the cheapest way to go to start.

[N3243A]

What do you really need the increase in climb for? Do you need the max you can buy to get out short and climb over obstacles or is it just a nicety? I bolted on an 80-42 almost 7 years ago and have never looked back. But I am probably operating in a different environment i.e. gravel bars and unmaintained bush strips.

The difference in cruise between an 80-42 and 80-43 is probably negligable. You can overspeed with the 80-42 in any descent if you are not carefull but it sure made a huge operational difference for me. Plan on right at 100 mph all-around cruise with an 80-42 even with bigger tires.

Bruce

[GAHorn]

George I'm SHOCKED that you might suggest something that is not approved. Or do you have another source of approval for the process you described? Or more likely you forgot about this limitation. ....

I didn't forget. I was addressing only the issue of increasing climb performance, ..not approval basis.
There's nothing inherently wrong with changing the pitch of the prop to increase RPM to the point of engine limitation in an effort to improve takeoff/climb. Any such work should be performed in an approved manner (by a prop shop) and documented.

It's probably a minor alteration, however.

Per FAR 43, Appdx A:
"(a) Major Alterations
(3) Propeller major alterations. The following alterations of a propeller when not authorized in the propeller specifications issued by the FAA are propeller major alterations:

(i) Changes in blade design.

(ii) Changes in hub design.

(iii) Changes in the governor or control design.

(iv) Installation of a propeller governor or feathering system.

(v) Installation of propeller de-icing system.

(vi) Installation of parts not approved for the propeller."
"Blade design" does not automatically prohibit a change in pitch of the blade. Prop mfr's have approved wide range of permissible pitches for each prop/blade design. The specifications in the TCDS are necessary in order to meet published performance. "No changes" does not always pertain to safety of flight or inherent airworthiness issues, it may also apply in order to meet performance guarantees.

As you know, just because the TCDS is written in ink, does not mean there aren't approved methods to alter the aircraft.

[Bruce Fenstermacher]

George I don't see a difference ignoring the limitations of the prop rpm in the TCDS and say tire size or engine model.

Or are you saying it is only OK to exceed the TCDS limits if the prop shop has some basis of approval to do so?

[GAHorn]

No, I'm only expressing an opinion that limitations of the standard prop as depicted in the TCDS is not applicable to any other approved propeller configuration, including approved propellers of different pitch.

Neither does the TCDS list all the propellers which are approved for the airplane.

If you have a standard propeller installed on a standard engine it must meet the TCDS limitations.

[Bruce Fenstermacher]

It is my opnion that the rpm limits stated in the TCDS for a given prop are the limits to which that model of prop can be used and be approved by the TCDS.

In other words if you have a McCauley 1A170 if you can't meet the minimum or you can exceed the maximum static RPM then the installation is not approved.

You would not be able without another basis of approval than the TCDS to take a McCauley 1A170 and pitch it so that you can achive 2700 rpm on takeoff unless it does not exceed the 2330 limit static per the TCDS.

Other approvals of course could be held by either 337 or STC.

[CF-HEW]

Had mine repitched to 7647. It comes out of the water nicely on edo 2000s, but gives about 80 mph cruise at 2500 rpm. I think it's a little too fine and will probably repitch to 49.

[Bruce Fenstermacher]

A seaplane is allowed higher static RPM.

(a) McCauley 1A170...

Seaplane (Models 170A and 170B): Not
over 2525, not under 2300.
No additional tolerance permitted.

[N419A]

I will echo Bruce (N3243) on the 8042. If you don't mind 100 mph cruise (at 2450 for me) then you will like the take off and climb performance of the 8042. It was night and day when I changed mine from the 7653. I think that most of the 145 hp 170 drivers in AK that are operating in the backcountry are probably running 80in. props. I don't know how the flat 76in. props compare to the 80's. As for a used one you gota be quick they go fast.

Good luck, Paul

[buzzlatka]

Most of the prop shops laugh at me when I ask them about used 80 inch props. They do go fast. I can't even find a used 76 inch to repitch.
Sounds like I just need to stick with the 80 inch. Anyway it will be nice to have two props.
Instead of trying to make this 145 horse engine go fast and climb, I need to accept the fact that if I want to climb I am going to slow the cruise to 100mph and be happy.

[AR Dave]

At 2450 rpm's my cruise is only 100 mph with the 8043. It's worth having the 80" prop just because all the calculations, eta's (1hr/100miles), mpg (8gal/100mls), etc., are so much easier to figure. I believe it was the owner or N4387B, between BVRAIR and I, that had my prop repitched from 8042 to 44 and back to 43. Wish I knew what he found. Probably went to 44 and and then started retreating. Bruce, Joe, Paul, did you record any Data?

Jeff Helmerick used to change his 80" prop back to 76" when he'd fly the Artic Tern back to America.

[simon]

Just thought I would say a few words about the subject. When I bought my airplane, it had the 80" prop on it. As far I could tell, it was pitched to 43. The only paperwork I had for the STC was the original revision, which specified a 1A175DM 8040 prop. The original STC also called out min/max static rpm of 2380/2480, respectively. Upon further investigation, I found that my airplane had been used by Kenmore to get the STC, kind of interesting. I also found that the STC had been revised, in part, to delete the specified pitch and also the min/max static rpm. I went to Kenmore and they graciously gave me the new paperwork, specific to my airplane, last amended Feb 23rd, 1979. Now the STC, SA111NW, specifies the C-145 and O-300 A and B series engines and the only RPM limitation states; RATED RPM:2700 for all operations. There is no mention of pitch or static rpm. It just specifies min/max diameters. Also, it applies to the 170A or B.

As for performance, I have not flown my airplane with the stock prop, but I can echo what the others are saying. About 100mph indicated at 2450. As for climb performance, I have no complaints, It lets you use all 145 horsepower.

Another interesting side note, the original engine in my airplane, the O-300A, threw a rod in 1955. It was replaced by an O-300B. I guess it was not a big deal back then. However when the application for the STC was originally done by Kenmore, it specified my airplane serial number and the O-300B. It was signed by the acting chief of engineering and manufacturing branch of the Seatte FSDO in 1974. I guess that the feds overlooked that technicality also. Thats my story.


Here's a question for you other guys using the 80 inch. Mine runs smooth as glass above 2400. It gets rough to varying intensity below that down to about 1700. Any similar experiences?

[AR Dave]

I've always thought mine was very smooth from start to stop! My first instructor told me to cruise at 2300 rpm's, so that's the way I flew for a few years.