Jump to content
Kent Ashton

Catto prop shop pics

Recommended Posts

Pics here of what I presume is Catto's prop shop.  He seems to be doing a good business

http://www.vansairforce.com/community/showpost.php?p=944550&postcount=6

 

I have been reading a book on props by Jack Norris.  Interesting.  He tries to explain props without getting too far into the math and has some good discussion but not enough to really design a prop.  Ultimately he says "use our prop computer program."  I learned how pitch determines how fast a prop will push the airplane.  The prop is screwing it's way through the air and a shallow pitch just won't advance enough.  I am seeing that with my second-hand Long-EZ prop.  It accelerates well but doesn't have the pitch or diameter to to take full advantage of the horsepower.

http://www.propellersexplained.com

 

  • Like 1

Share this post


Link to post
Share on other sites

Looks like Catto has it down.

 

I bookmarked that book.  It might be fun to build a prop someday, or at least understand more about the relationship between pitch and horsepower.  Constant Speed props are still a bit of a mystery to me as well, although I know how they change pitch I am just not in tune with the impact those changes have on RPM and fuel consumption.  Same issues as a fixed pitch.  I'll have to get that book.

 

Thanks... this also prompted me to do a quick follow-up on why HP = Torque @ 5252 RPM  :)

Share this post


Link to post
Share on other sites

This fellow, Jan Carlson, posts a lot on HBA and will design a custom prop for a reasonable fee.  I have read most of his old posts and they're pretty good.  The challenge is not so much in the building but to come up with a good design (or copy one).

http://www.jcpropellerdesign.com

 

One of my next projects is to build a prop-duplicator machine (pic).  The Cozygirrls have a good page showing one in use.  The machine is pretty simple but to buy one, they are $1600-$2500.  I already own a router so that's a plus.   :)

http://www.cozygirrrl.com/propellers.htm

 

Norris says it's very critical to get the air inflow angles and pitch correct which you can only do practically with a computer program.  He talks about correctly calculating "slowdown":  on a tractor airplane, the flow in front of the cowl is slowed down by the shape of the cowl and the prop pitch has to be adjusted for it, as well as for the slower rotation speed near the hub.  Something similar happens with a pusher, I suppose.

post-126542-0-00966700-1420641474_thumb.jpg

Share this post


Link to post
Share on other sites

Impressive goals Kent! Those machines are definitely simple, relatively speaking, but you know how straight and true everything needs to be.

 

The Cozygirrls have a good page showing one in use.

They continue to amaze me. That one picture there shows Chrissi working the belt sander with 1/3 of a custom prop. Impressive.

 

The machine is pretty simple but to buy one, they are $1600-$2500.

Or more!

 

Something similar happens with a pusher, I suppose.

I'll speak out of turn, but I suspect the pitch near the hub matters less with a pusher considering that is where most all of the turbulent air is anyway. Aside from that I would not expect for there to be as much "slowdown" (air compression?), if any, at the tail end and so the prop designs for pushers may actually require less adjustment and modification (assuming the "slowdown" factor is valid).

 

(That is possibly enough half-baked theory to get Marc out of the woods to comment). :)

Share this post


Link to post
Share on other sites

That one picture there shows Chrissi working the belt sander with 1/3 of a custom prop. Impressive.

From a zillion years ago, I believe.

I'll speak out of turn, but I suspect the pitch near the hub matters less with a pusher considering that is where most all of the turbulent air is anyway. Aside from that I would not expect for there to be as much "slowdown" (air compression?), if any, at the tail end and so the prop designs for pushers may actually require less adjustment and modification (assuming the "slowdown" factor is valid).

Hard to say. Without a LOT of computer modeling (which wouldn't be particularly accurate in any case) and then a lot of testing of different props, it's unknown exactly what's going on, and since people do all sorts of different things with their cowls and exhaust systems, analysis and testing on one aircraft may or may not apply to a second aircraft. The flow field back there is very nasty and hard to model and/or visualize.

(That is possibly enough half-baked theory to get Marc out of the woods to comment). :)

I am very quickly coming to the conclusion (as most people far more knowledgeable than I am who monitor the mailing lists and fora have before me - obviously I'm slower than they in recognizing reality) that commenting publicly, at least in canard specific fora, is mostly a losing proposition for folks that know what they're talking about. Sometimes I know what I'm talking about, and sometimes I don't, but I have largely found that dealing with people on a one-to-one basis (my customers, or phone/email) is far more likely to result in positive outcomes for everyone.

 

I can't tell you the number of folks that monitor these lists that know WAY more than I do and never say a word - they just don't want to deal with the crap.

Share this post


Link to post
Share on other sites

The flow field back there is very nasty and hard to model and/or visualize.

 

One time I had fuel stream out of top vents.  It was blown back along the cowl, then under the cowl, and left fuel stains inside the top of the cowl as much as 8" forward of the exit!

 

I can't tell you the number of folks that monitor these lists that know WAY more than I do and never say a word - they just don't want to deal with the crap.

 

Well, that is too bad.  I think Jon is determined to control the crap and maintain a friendly tone so if people are reading and staying silent, maybe they are just "aging out".  Not me!    I post my little canard threads and pics here because (1)  I enjoy it and (2) Jon controls the crap--so far. :P

  • Like 1

Share this post


Link to post
Share on other sites

The flow field back there is very nasty and hard to model and/or visualize.

And thus the desire to use the longest prop extension possible.

 

BTW, talking to Sabre a while back, the rep pointed out that someone at Reno was racing with two 8" extensions bolted together.  Is that  :yikes:  or  :cool2: ?  To me, that seems comparable to an athlete using performance enhancing drugs. Instant gratification, but with potential near- and long-term consequences.

 

I created a new topic for the other discussion regarding "community" into its own thread here.  Back to Catto props here...

 

Share this post


Link to post
Share on other sites

BTW, talking to Sabre

Saber

 

a while back, the rep pointed out that someone at Reno was racing with two 8" extensions bolted together.  Is that  :yikes:  or  :cool2: ?

The issue with long prop extensions is two-fold - runout, leading to vibration, and gyroscopic loads on the crank due to excessive yaw or pitch rates.

 

If you dial-indicate the prop end of the extension and it has an arbitrarily small runout (Sam at Saber can tell you what that maximum amount should be - IIRC, its a small # of thousandths of an inch) then you'll be OK from a vibration standpoint (but a dynamic balance would be a good thing).

 

As long as you don't do aerobatics, your yaw and pitch rates will be OK (and I don't think we can create excessive yaw/pitch rates in canard aircraft anyway).

 

Obviously some calculations would be in order, and it's unusual to have a 16" extension, but it's not prima-facie insane.

Edited by Marc Zeitlin

Share this post


Link to post
Share on other sites

As long as you don't do aerobatics, your yaw and pitch rates will be OK (and I don't think we can create excessive yaw/pitch rates in canard aircraft anyway).

 

Obviously some calculations would be in order, and it's unusual to have a 16" extension, but it's not prima-facie insane.

 

Interesting.  I'd still be leery about bolting 2 together as the balancing is more likely to change over time vs. a single piece extension.  Excellent points about the yaw/pitch rates on canards, which is also a reminder to what EZs have been designed for (efficient cross-country aircraft).  

 

The other issue with long extensions are prop strikes on landing and takeoff.  Do you know the typical size of prop extensions the Long-EZ and Cozy people are using today?

Share this post


Link to post
Share on other sites

Interesting.  I'd still be leery about bolting 2 together as the balancing is more likely to change over time vs. a single piece extension.

I doubt it. They're metal, and made with better lugs than the prop flange itself. there's no movement whatsoever on a bolted extension. If the runout is OK, it'll stay OK.

The other issue with long extensions are prop strikes on landing and takeoff.  Do you know the typical size of prop extensions the Long-EZ and Cozy people are using today?

Most COZY MKIV's use 8" extensions. LE's/VE's are generally 4" - 6", but some have 8". I wouldn't use more than 8" for the reason you state. Edited by Marc Zeitlin

Share this post


Link to post
Share on other sites

Just to be clear, we're talking about bolting 2 prop extensions together.

 

there's no movement whatsoever on a bolted extension.

 

You're assuming the bolts have been properly tightened.  I was just pointing out the additional points of failure.  Regardless, I appreciate hearing of the confidence in a properly bolted double-extension setup.

 

Now this... The custom three-lifting-surface CC02 came across the radar today.  Looking at the picture in that link, I am guessing he's using a 18" - 24" extension.  Perhaps there's an additional bearing near the prop?  I suppose there would have to be, at least in more extreme pusher configurations such as with the Mini-Imp (picture attached).

post-126731-0-09895500-1420749784_thumb.jpg

Share this post


Link to post
Share on other sites

Just to be clear, we're talking about bolting 2 prop extensions together.

 

True but the longer the extension, the greater leverage it exerts on the main bearings unless the alignment is absolutely perfect.  From memory, Pushy Galore used a long extension--10-12", as I recall--I suspect that's about the practical limit.

 

BTW, I see that Molt Taylor's original Mini-Imp is available on Barnstormers for $150K.  I used to have some Mini-Imp plans but sold them.  It is not an EZ project.  There is some rather complex machining to do to finish the drive system.

Share this post


Link to post
Share on other sites

BTW, I see that Molt Taylor's original Mini-Imp is available on Barnstormers for $150K.

A bit much, don't you think? It's also disappointing to see the seller NOT use the Mini-Imp category that has been empty since... ever. :)

 

I created a new thread with the pictures here. Nice looking plane for sure.

Share this post


Link to post
Share on other sites

I received the following reply to this topic from Dale Martin, in email, asking me to forward here.
 

It is fun thing to do but it does cost a great deal of money. As you may know I am a contracted to build certain Silver Bullet props and was trained by Gary Hertzler to build his very nice propellers.

The duplicator is only one of the processes used to build a prop and the use of it is a science when it comes to propellers and is only 16% of all that needs to be accomplished. Anyone can make a prop, but without the training your props would be mediocre at best as far as performance.

With all the money you would spend to make your own propeller that has the performance anywhere near an SB you could easily buy 3 or 4 Silver Bullet props. The reason I say this is not to steer you away from building a prop but to insure you realize how much your going to spend.

The other matter is performance. I am willing to bet should you build your own prop it would most like have close to 70 to 80% the performance of the SB prop. I can tell you there are a handful of proprietary procedures that go into Gary's props and I know I would not be happy if I could not get the performance I now enjoy with his props. There is a lot to consider and learn including installing a rain leading edge. Building props is not an easy task. If you choose to go ahead and make one, stay in touch with your progress.

Warm Regards,

Dale
www.long-ez.com

Share this post


Link to post
Share on other sites

Jon, are you encouraging "phoning it in" now?   :P

 

Yes, I admit there are probably a learning curve to building a perfect prop but I have trimmed, glassed, balanced and painted my Performance Prop and was rather pleased with the result.

http://forum.canardaviation.com/showthread.php?t=5170

 

It seems to me that if you copy a wooden prop and it comes out with the same dimensions as a known good prop for that horsepower and speed, well, it's probably going to be close enough to satisfy me, at least.

Share this post


Link to post
Share on other sites

Kent, 

 

Everything you mention is external.  This is hardly qualifies as building your own prop.  But, if your happy with higher fuel burns and less efficiency than I say, Great! 

 

BTW, We (at Owl Eagle) have a 3 blade Catto Prop that is in good shape for sale.  It is for the 160HP LEZ.  Anyone interest please call 208-292-5897.

Edited by niceez

Share this post


Link to post
Share on other sites

But, if your happy with higher fuel burns and less efficiency than I say, Great!

 

Ha!  I will be happy just to not be flying in a crab.   :P

 

I get from Jack Norris's book that the parameters for a prop are pretty critical: pitch in particular, diameter, twist.   So there is where the real expertise lies, it would seem.  But wood is wood, there is probably some expertise in how the glass is applied.  I have seen guys that added routed-out channels of UNI to strengthen the prop.  OK, I can do that.  Give me a hint.  Other than that, what's the secret sauce in a Silver Bullet (without disclosing the recipe) that is much different from anyone elses?  My lips are sealed.

 

Here's how I glassed my Performance Prop:  On the cambered side, BID-UNI-BID with the UNI running lengthwise and the BID overlapping on the flat side.  On the flat side UNI-BID.  After the cambered side had hardened, I  dremeled and chipped out about 3/8" of the wood on the trailing edge and filled that with flox before doing the flat side.  My leading edges are JBWeld, filed to shape.  They will probably want it for the Smithsonian some day.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×