Prop swap questions and value of Sensenich?

[punkin]

Some ignorant questions from a newbie..

I bought a flying early RV6 with O-320 150hp and fixed pitch Sensenich. The early model has the 4" spacer (actually two 2" spacers) to clear the cowl.

If I replace the prop, can the existing spacers be used? I'm assuming that spinners are largely prop-specific, or have been trimmed to be such... but are the spacers special, or can they be reused with, say, a Whirlwind GA prop?

Related question: Previous owner bought it from Sensenich as a 79 pitch, then had it repitched to 77. That seems to be a popular setup for guys that start out down low...my field elevation is about 5k ft, and DA of 8k or so is not unusual...I want something that will rev and get off the ground, even I have to sacrifice some speed!

My prop is low time, I don't have the numbers in front of me, but probably less than 100 hrs...what would it be worth in the classifieds forum?

My dilemma is that if I repitch the sensenich, I still have a 2600 rpm limitation, and I probably have a prop that nobody else would ever want. If I sell it like it is, it's "normal" and fairly unmolested, so buying what I want instead of creating it might make more sense.

Oh, and my money tree in the backyard is looking fairly sparse, so I'm trying to balance $$ too!

Thanks for the tips!
Scott

 

[Christopher Murphy]

Why?

If it performs well why change it?

Cm

 

[punkin]

Because it doesn't! At least not for my purposes!

I'm not sure if I was clear in my original post, but this prop is essentially like trying to take off in extreme overdrive. Yes, it is functional, and when I am finally up to speed, it's fast; however, I want to be able to get off the ground quickly, particularly on short dirt strips with obstacles.

Scott

 

[Raymo]

A Catto prop, for example, should give you better performance all around. If you are relatively happy with the Sensenich and want to conserve cash, have it re-pitched for your needs.

What is the 2600 RPM you mention? Is that static RPM or take-off RPM or is there some other limit imposed on the prop?

 

[rightrudder]

A Catto prop, for example, should give you better performance all around. If you are relatively happy with the Sensenich and want to conserve cash, have it re-pitched for your needs.

What is the 2600 RPM you mention? Is that static RPM or take-off RPM or is there some other limit imposed on the prop?

I believe that restriction relates to a harmonic imbalance problem that affects the prop and/or crank if 2600 rpm is exceeded. I'm absolutely sure someone will correct me if I'm wrong.

 

[punkin]

Doug is correct, the prop itself is limited to 2600, I believe that is an absolute strict limit imposed by Sensenich, not a recommendation or advisory. It is enough to me to accept the limit, but again, to try to track my questions and point:

1.) If I repitch the Sensenich, it's gonna be mine forever, because I doubt if there is much resale value in a twice repitched 75 pitch Sensenich prop. I *hate* the idea of the limitation, knowing that I'm giving up potential top end AND I feel like I'll be constantly watching that if I pitch the prop properly to get off the ground, I'll be likely to be trying to over-rev the prop.
2.) If I sell the prop as-is, I'm sure there is a flatlander out there who will think it is great, or even a high elevation guy who just wants to go fast.
3.) Can i use my Sensenich 4" spacer with a Catto or Whirlwind prop?
4.) What's the Sensenich worth, roughly?

 

[Raymo]

Call Sensenich on 1 and 4 but I do not believe there is a limit on how often a propeller is pitched. There are limits to how many times it can be ground down due to metal loss during grinding.

EDIT: There apparently is a limit to how often a prop can be pitched. Thanks, Gil.

On 2, your best bet would be to sell to an owner of a similar airplane/engine. My Cherokee 140 had a Sensenich prop but the pitch was in the 58 or so due to much lower HP. The new buyer could, of course, have it re-pitched for a few hundred dollars.

On 3, composite propellers require a larger diameter crush plate than aluminium so your spacers may not work. Call either Catto or WW for to confirm. They are always happy to help a prospective buyer.

1.) If I repitch the Sensenich, it's gonna be mine forever, because I doubt if there is much resale value in a twice repitched 75 pitch Sensenich prop. I *hate* the idea of the limitation, knowing that I'm giving up potential top end AND I feel like I'll be constantly watching that if I pitch the prop properly to get off the ground, I'll be likely to be trying to over-rev the prop.
2.) If I sell the prop as-is, I'm sure there is a flatlander out there who will think it is great, or even a high elevation guy who just wants to go fast.
3.) Can i use my Sensenich 4" spacer with a Catto or Whirlwind prop?
4.) What's the Sensenich worth, roughly?

 

[az_gila]

Call Sensenich on 1 and 4 but I do not believe there is a limit on how often a propeller is pitched. There are limits to how many times it can be ground down due to metal loss during grinding.

....

There are limits to repitching a prop. and they are well defined.

http://www.sensenich.com/files/documents/Repairs_Trouble_Shooting_Repitch_Limits_1303228075.pdf

However in this case I think if the OP does a second pitch change it will still be well within the limits above and should not really reduce it's present value.

 

[smokyray]

Prop me up!

Some ignorant questions from a newbie..

I bought a flying early RV6 with O-320 150hp and fixed pitch Sensenich. The early model has the 4" spacer (actually two 2" spacers) to clear the cowl.

If I replace the prop, can the existing spacers be used? I'm assuming that spinners are largely prop-specific, or have been trimmed to be such... but are the spacers special, or can they be reused with, say, a Whirlwind GA prop?

Related question: Previous owner bought it from Sensenich as a 79 pitch, then had it repitched to 77. That seems to be a popular setup for guys that start out down low...my field elevation is about 5k ft, and DA of 8k or so is not unusual...I want something that will rev and get off the ground, even I have to sacrifice some speed!

My prop is low time, I don't have the numbers in front of me, but probably less than 100 hrs...what would it be worth in the classifieds forum?

My dilemma is that if I repitch the sensenich, I still have a 2600 rpm limitation, and I probably have a prop that nobody else would ever want. If I sell it like it is, it's "normal" and fairly unmolested, so buying what I want instead of creating it might make more sense.

Oh, and my money tree in the backyard is looking fairly sparse, so I'm trying to balance $$ too!

Thanks for the tips!
Scott

Scott,
There are no ignorant questions. Simple answers, no, no, about 2 grand, maybe. Having flown NINE different props on my RV4 over the years, here's my Dos Centavos...

The Sensy FP metal prop for the 0-320 was introduced many years ago when all of us Jurassic RV builders were running the "wood of the month." Back then Van didn't approve of builders using cut down metal Cessna props as they tended to shear blades inflight. (not good) Constant Speed props were considered heavy and expensive and the majority of builders didn't consider them.

The Sensy metal FP for the 0-320 was introduced as the first "approved" FP metal prop for experimental RV aircraft (0-360 prop came much later). It became famous when Jon Johansen attached one to his "World Rounder" RV4 back in the 90s' and flew around the globe, twice. I bought one (70/77) and flew it for 100 hours. I removed and sold it for the following reasons which by no means reflect on your mission statement.

1. Heavy. Noticeable heavier nose and flywheel effect which some people like. I didn't.
2. 2600 Max RPM restriction (0-320 prop) due to harmonics. (a well balanced 0-320 develops another 12% power between 2600 and 2700) Also, I take notice of metal harmonics being an issue having flown Citabrias with similar restrictions.
3. Performance. My wood prop outperformed the Sensy across the board with equal numbers in cruise.
4. No Acro. Sensy doesn't recommend aerobatics with the prop although many people perform them.
5. STOL. My wood prop worked better off my home "short" turf strip and in the ID backcountry. The Sensy, not so much.

I sold my Sensy FP and two weeks later met a audacious (crazy) prop maker nearby named Craig Catto. He was already famous in the Reno and EZ crowd but didn't have any RV props, yet...I helped solve the dilemma by installing a beta test prop on my RV4 and the rest as they say is history.

If you like acro, want to get rated horsepower out of your engine, get off the ground quicker and want to lighten your airframe by at least 10 lbs, remove the Sensy prop, ext, spinner and all. (they're not compatible with anything else) Sell it (2K) and buy either a Ground adjustable prop, (Sensy, Whirlwind are both excellent) or Catto. (Use an extension from Saber Mfg with the factory spinners).

If you like what you have as mentioned above, re pitch and maintain status quo. Realize the 77 pitch will easily exceed the 2600 restriction in a descent without attention. Re-pitching the Sensy metal prop doesn't change the props major drawbacks (for me) or remove the RPM restriction.

V/R
Smokey

PS: A third potentially cheaper $$$ option would be to peruse the VAF classifieds for a used Wood prop (Sterba, Performance, Warnke) with all accessories included, try it, fly it and keep the Sensy or sell it in lieu of something else later...crazy talk!

 

[punkin]

Thanks Smokey...I've read a lot of your experimentation, and I'm kind of in between your last option and the ones just above...

I bought a wood prop here used; I'll give it a whirl, and baseline my desires, maybe I can fly it while selling the Sensi and get a GA prop for long term once I sell it...

Thank you for your descriptive insight!

 

[AX-O]

you cannot use the sensenich spacer on the other props. That spacer has two pins that stick out and line-up with the metal prop.

Do a search for the Catto prop post that I have posted. A lot of potentially helpful stuff there.

I just changed the prop on my bud's RV-6 (and my old -4) because the 2600 rpm limit. He picked up 6 kts in cruise by getting rid off the RPM limit. I picked up 4kts.

Craig is experimenting with another prop for my fastback right now. He is cutting the cord down in order to increase the rpm on the ground (to 2300ish) but increasing the pitch to keep it from over speeding in flight. I am going from a 70X76 to a 68X84. He can make whatever you want. Just tell him you want to get off the ground faster.

 

[punkin]

Excellent, Ax thx. I'll read the past stuff and I'll stalk your future posts too...I like the sound of the test prop!