My quick comparison - Prince climb prop vs Sensenich

[Bryan Cotton]

As I reported in another thread, our top cowl pin came forward and damaged our prop. I had retention built in but it was missed when we closed the fuel door. Had a generous offer to borrow a Sensenich prop while Lonnie fixes my P-Tip:

I bought the P-tip from Mike Farley when he put the turbo on his Waiex. It is more of a climb prop. I had typically been cruising at 100kts turning 3000 RPM. With the Sensenich I'm seeing more like 110 kts. Here is a little table for comparison:

Prop/ Static RPM/ Climb RPM/ Cruise at 3000' / WOT
Prince/ 3000+/ 3150/ 100kts/ 118kts
Sensenich/ 3000+/ <3000/ 110kts/ 120kts

I hope that aligns good enough. I don't have any comparison for takeoff distance at heavy weights. Solo it was great and I was climbing 800-1000fpm although I was turning less than 3000 RPM even at 90kts.

Edit: added slashes for delimiters.

[MichaelFarley56]

Glad you’re back in the air Bryan! It looks like both props are fairly closely matched overall.

I know this is subjective, but do you think one is smoother than the other?

Hopefully you’re still on track for the Tennessee trip!

[Bryan Cotton]

Mike,
I can't say if one is really smoother or not. I'll get Adam's take when we fly together. Plus I'll try and consider the smoothness when we swap back.

We are on for Tennessee, if the weather cooperates. Right now the long range forecast looks bleak. Of course that could mean it will be good.

[DCASonex]

Had not noticed your comment about prop being damaged by cowl pin, but common sense to install the pins from the rear only. That little piece of metal can saw right through a wood prop very quickly at 3,000 RPM. I have a bit of a reversed hook shape on end of mine that buts against a small metal tab when installed, Just grab the end with any small pliers and pull out and back, nothing else to remove and forget to install.

David A.

[builderflyer]

Hi Bryan,

Joe Norris may be better equipped to respond and/or clarify my remarks but here goes........did you put your Waiex back in Phase 1 for testing the different prop? I ask because, depending on the prop used, this change has the potential to have an appreciable effect on the operational characteristics of the aircraft, in which case it would be considered a "major" change. And, also, Vx and Vy could likely change and they have been previously documented in the Operating Limitations for your aircraft.

I ran into this issue when I changed the prop on my Sonex. I had moved so it was necessary to go back to the FAA to obtain approval for a new test area. In the FAA's approval they also indicated that my Sonex would need to be placed back in Phase 1 for a minimum of 5 hours. Then, too, upon completion of the testing a statement similar to the one in the Operating Limitations regarding Vx and Vy for the new prop would need to be recorded in the aircraft logbook. If that wasn't enough, going back and reading my insurance policy, I also found that the insurance policy would be null and void during the time my Sonex was back in Phase 1.

One other thing.........with my new prop my Sonex picked up an increase of 5 mph at the usual cruise RPM. But that was with a penalty in fuel consumption. Unless the new prop happens to be more efficient than the old prop, there will be a noticeable increase in fuel usage. Disappointing, but true just the same.

Testing a different prop sounds like a simple matter but it turned out, it wasn't for me.

Art,,,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[13brv3]

In my personal opinion, changing between two very similar props is a "minor change", and would not require any additional test period. It's very unlikely that most people will even be able to accurately measure a change in Vx or Vy between those two props, and I wouldn't consider any slight change an "appreciable effect". Just my opinion of course.

My operating limitations refer to 21.93:

According to 14 CFR 21.93, “A ‘minor change’ is one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the product. All other changes are ‘major changes’ (except as provided in paragraph (b) of this section).”

Rusty

[builderflyer]

In my personal opinion, changing between two very similar props is a "minor change", and would not require any additional test period.

Rusty

You're probably correct, Rusty. I think the key is what constitutes "very similar props". If Sonex LLC has tested both props and has reported similar results with each, then who would argue with that as being a "minor change". In my case I went from a Sonex LLC tested and recommended Sensenich all wood prop to a Prince composite elliptical prop. To my knowledge, Sonex LLC had never tested the elliptical prop or if they had, they didn't publish the results. So, at least in my case, there was an argument to be made that changing props was a potential "major change". Unfortunately, until one actually tests a different prop on a particular airframe/engine combination, there really is no way to know for sure how Vx, Vy, fuel consumption, etc. may have altered the operational characteristics of the aircraft, or in other words, if any of the measured changes are actually significant. We are at least initially obligated to test our unique aircraft and not merely accept the factory tested results. So one could argue that even if we change from one factory approved prop to another factory approved prop that all of the related initial testing we accomplished should be repeated for the new prop, whether it's considered to be a "major change" to be done under a "Phase 1" designation, or not.

Art,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,Jabiru 3300 #261

[GraemeSmith]

In my personal opinion, changing between two very similar props is a "minor change",

And while I respect an "opinion".......

It's a bit of a Catch 22....... Bryan could not know that it was a minor change to his aircraft until he had tested it. So that implies back to Phase 1 to find out the prop change was not major. Perhaps we should ask Major Major.......

[13brv3]

It's a bit of a Catch 22....... Bryan could not know that it was a minor change to his aircraft until he had tested it. So that implies back to Phase 1 to find out the prop change was not major. Perhaps we should ask Major Major.......

At some point you've got to apply some common sense. If I called the FAA every time I changed pitch on my ground adjustable prop, they'd start blocking my calls :-)

[MichaelFarley56]

Unfortunately, this is a perfect example of each FSDO and each POI having their own thoughts on what constitutes a “major change”.

Not that I want to muddy the water, but just to throw in a humorous frame of reference, when I added the turbo to my AeroVee all those years ago, the inspector at my local FSDO told me he “didn’t consider that a major change”. I even tried to convince him that adding a turbocharger would change performance enough to constitute a major change but he wouldn’t waiver.

So long story short…Bryan, you could consider talking to the FSDO if you want, but at the end of the day, I’d say it’s your call