Wood prop

[PA1195]

I've applied to the local FSDO for clarification regarding installing a wood prop (Catto). CAR 04 doesn't require certification of wood props and TCDS A-696 only calls for an "Approved wood" but lists none. So we'll see what happens.

Gary

[NC36061]

Re: Wood prop

But engine manufacturers do list approved propellers, no? If you went only by the airframe type certificate, would you be limited to a wood prop, as metal props for small engines were not (commonly) available at the time the original type certificate was issued?

[PA1195]

Re: Wood prop

Propeller manufacturers list products that they've approved on various engines to make it simple for consumers. They are primarily metal props and some newer composites. Engine manufacturers? The TCDS for the small Continentals E-233 doesn't address propellers. There may be other documents that do.

My point and question is stated above regarding wood propellers. CAR 04 addresses propellers in Section 04-61 and 611. Wood props don't require certification. TCDS A-696 notes wood prop is approved under Item 1 (1) formerly 103a on the original equipment list. I merely asked for further clarification regarding the potential installation of a Catto wood prop on a Taylorcraft. Nothing mysterious here.

Gary

[Ragwing nut]

Re: Wood prop

Car4 states wood propeller certification no required on light aircraft. light aircraft as defined in car4 i believe refers to aircraft with gross weight under 1000lbs. I used to think the same thing as well. Your issue is not approval on the airplane. your issue is installation of wood propeller on the o-200 on your airplane. It will require either a field approval which in alaska maybe easy peasy or worst case scenario require an stc

[PA1195]

Re: Wood prop

Yes that was part of the original discussion for a wood prop on my C-85. So I asked for clarification before proceeding like many have done with other CAR 04 planes like early Cubs and Champs. I'm happy with my approved Sen M76AK-2-40 but thought a wood replacement might be a cost effective alternative. Thanks for the comments and I'll repost if I hear anything yea or nay.

A STC isn't an option as it ties up the approval system for others while it's being generated, plus the cost is prohibitive or Catto would have done so already. A Field Approval may be an option. The FAA checked and made sure my prop wasn't already a wood model...pays to be honest with those folks.

Gary

[NC36061]

Re: Wood prop

Propeller manufacturers list products that they've approved on various engines to make it simple for consumers. They are primarily metal props and some newer composites. Engine manufacturers? The TCDS for the small Continentals E-233 doesn't address propellers. There may be other documents that do.

Ah, I see, I thought engine builders had an approved list. Interesting avenue of inquiry, good luck!

[PA1195]

Re: Wood prop

I'm not any expert and Ragwing Nut knows propellers. Let's see what happens and what the FSDO folks generate? Sometimes a "no" or "yes" is better than rampant speculation on our part. It's a two way street as far as I'm concerned.

Gary

[N96337]

Re: Wood prop

A STC isn't an option as it ties up the approval system for others while it's being generated, plus the cost is prohibitive or Catto would have done so already. A Field Approval may be an option.
Gary

It would be a "one time STC", not a multiple...and that's probably what they'd want instead of a field approval. It's just a bit more paperwork and it takes the responsibility off the PMI. A multiple STC would be pretty expensive anymore, thus a main reason Catto doesn't waste their time doing it.
John

[PA1195]

Re: Wood prop

You've followed the Super Cub threads on this subject and the various opinions offered were the reason I thought I'd ask up front about the installation. Initially it was verbally suggested I write up and submit a proposal for consideration given the constraints of CAR 4 and the somewhat ambiguous A-696 specs.

These wood props are not scarce up here so someone must either be just putting them on for decoration or ??? I'm not one to compromise a PMI or I/A so will follow through as a learning process.

The unknown is potential performance vs my metal prop which works well. What compromises are inherent in Catto's design versus mine? I talked with the prop folks months ago and they offered suggested designs based upon their sales experience. Unlike a metal prop once installed there's no option for pitch adjustment and the owner has to live with either a good prop or an expensive wall mount.

Years ago when I was experimenting with fixed pitch props on a Cub we did pull tests on a scale to compare diameter and pitch. We settled on an Mac 80/40 with a hub spacer off a Citabria as the best compromise for a 150 Lyc. Flew that for years and never regretted the performance. But the Cub was airframe and configuration speed limited so T/O and climb were emphasized.

It's all fun,

Gary

[Ragwing nut]

Re: Wood prop

Yes that was part of the original discussion for a wood prop on my C-85. So I asked for clarification before proceeding like many have done with other CAR 04 planes like early Cubs and Champs. I'm happy with my approved Sen M76AK-2-40 but thought a wood replacement might be a cost effective alternative. Thanks for the comments and I'll repost if I hear anything yea or nay.

A STC isn't an option as it ties up the approval system for others while it's being generated, plus the cost is prohibitive or Catto would have done so already. A Field Approval may be an option. The FAA checked and made sure my prop wasn't already a wood model...pays to be honest with those folks.

Gary

Catto's market is so large he has the luxury to not worry about STC's for small markets. I have been in the planning stages of a blanket STC regarding this exact thing for several years now, and I can't get anyone to tell me how to approach it. Its a paperwork conundrum and I have talked with countless FAA inspectors, DER's, and other people, and no one has a definitive answer on how to proceed.

[PA1195]

Re: Wood prop

You have experience in these prop matters while I know a few good people in the FAA and maintenance industry but am not a A&P. From what I observe locally the approval process has involved someone like McCauley sending a prop to someone who has an interest in their product, then attaching strain gauges (or whatever) to the assembly, then flying to determine critical parameters...I assume those are vibration, cooling, and whatever else Catto briefly describes on their webpage. After the results are in an application is made for an STC. A quick search for STC bafflegab: https://www.faa.gov/aircraft/air_cer...s/stc/stc_app/

You mentioned DER...that would be my first choice if for no more than merely to determine, at their hourly rate, what needs to be done from their standpoint. Beyond that what they do is a mystery to me but I do know locals that have engaged them for STC's to some success.

The next question (which I mentioned earlier) is whether or not there's a benefit to be achieved as an owner/operator in using an optimized wood prop. You know about that I assume. If the benefit is purely financial to the consumer over performance, then I wonder if sales would justify the expense of certification and production? Catto has claimed that, builders of fast planes claim that, and Cub Crafters has seen fit to use their wood products (and Sensenich) on expensive aircraft. So have others in the Black Ops segment of General Aviation some of who extoll the virtues while others doubt the claims.

A pull test will tell T/O benefit, ROC will tell that aspect, and cruise vs power will tell efficiency in that mode I assume.

So that's why I asked to open the can and see what the local FAA and associated folks have to say about this proposal. How else would we learn and develop our aircraft without violating the FAR's?

Gary

[astjp2]

Re: Wood prop

This is interesting, wood by itself does not require a cert, but the addition of composites adds complexity to the question, keep us informed and good luck. Tim

[PA1195]

Re: Wood prop

I've been pondering the wood's covering versus core relationship. Sensenich applies metal, some protective material in the form of ???, and the use history appears dependable. Now other manufacturers add protective layers, metal, and suggest methods for monitoring continued airworthiness. I don't know what structural or performance deviation from the wood base the covering may create.

Not sure what the FAA response will be but given the documented history of Catto on some seriously high performance aircraft I doubt there's much of a structural concern on a C-85 to O-200 at rated power and established rpm limits. It may just be the meaning of the words used by CAR 04 and A-696 that is the final determinant.

Gary

[PA1195]

Re: Wood prop

Some progress. After internal discussion the FSDO has suggested an engineering coordinated Field Approval may be in order for installing a Catto prop. When I receive a letter of response from them regarding my initial inquiry I'll respond to it by writing up a 337 application describing the change of propellers and CIA document for a mechanic's concurrence. In addition I'll present a discussion as to why I feel the term "composite propeller" in this case compares favorably with existing structural technology such as demonstrated by wood propellers offered and certified by Sensenich and others. Then they can discuss and reply to my request. After all...a base of wood is wood and covering is covering.

I'll also contact Catto and see what they are willing support or substantiate regarding their products. Good winter project.

Gary

[Ragwing nut]

Re: Wood prop

Catto's props are mostly carbon fiber with wood core. Once layed up, the wood core adds no strength to their propeller. They have superior strength over straight wood and better airfoils so they preform better than many metal props. I don't think wood props are being bought for financial reasons. They are being bought mostly for their beauty which outweighs performance for their buyers. The added benefit is no harmonics and no engine teardown if you have a prop strike. In extreme climates wood is not ideal due to major climate shifts in which a wood propeller with expand with heat, contract with cold, and hold moisture when it rains. As far as wood propeller being listed on the taylorcraft tcds, it is irrelevant because there is a specific callout for the metal propeller on the f-19 making any other propeller installation requiring a 337 or stc, even if it is a different brand metal prop.