Jump to content

How to choose a prop for my EZ?


britguy59

Recommended Posts

Time to order a prop. Ed Sterba is close to me here in Florida and has a good rep from what I hear. He needs me to choose a hub thickness but I need to choose a spinner first. I'm looking for info on the type of spinner that is best, and/or any input on Sterba props and the hub thickness typically in use. He won't start a prop till the hub size is chosen and I have no spinner yet. Hmmm, catch 22? I may go without spinner and worry about it later.

Link to comment
Share on other sites

Although this seems like a nice option, especially if you already have a spinner, crush plate, and bolts. But it also seems back wards. I would suspect I would want the thinest prop possible (weight savings)

 

I couldn't even give you an intelligent guess as to what the thickness would be. Have you contacted other prop people and ask them for a quote on a prop?

 

Waiter

F16 performance on a Piper Cub budget

LongEZ, 160hp, MT CS Prop, Downdraft cooling, Full retract

visit: www.iflyez.com

Link to comment
Share on other sites

  • 8 years later...

I made an Aeromatic prop for a guy here on the airport, Fallon, NV.  He loves it.  Cut his TO almost in half.  It out climbs and out cruises me in my 0-360 powered Cruisair.

 

I got a couple of pics if anyone would like to see what it looks like.  He has a Veri-EZ with C-90.

 

www.aeromatic.com

 

Kent

Edited by Kent
Link to comment
Share on other sites

  • 3 weeks later...

Sure!  Post the pics here, it would be interesting to see this.

Let us know how this pusher application of your product does.  Is this the first pusher installation for an Aeromatic prop?

Andrew Anunson

I work underground and I play in the sky... no problem

Link to comment
Share on other sites

No, the original Koppers company made some for a Goodyear GA-2, the Republic SeaBee and a foreign plane of some kind, don't have the data on it here at home.

 

I have a couple of photos I was going to post but they are as big a couch.  I'm computer dummy but will work on it tomorrow at the office. kt

Link to comment
Share on other sites

How many hours do you have on these props behind rutan pushers?  It's a nice looking prop for sure but you know, of course, that Rutan did not recommend constant speed props behind his designs because of their weight and vibration passing in and out of the wake.    And at $5300, it's a pricey prop for a scratch-builder.  I suppose you are posting here because you lost your certified prop business.  http://www.aeromatic.com      Really sorry to hear that but without a lot of test hours behind a Rutan pusher . . .

 

"Burt has been . . . adamant about the use of variable speed/constant speed props on our experimental airplanes. To use any manufacturers variable or constant speed prop without conducting a full, in-flight, strain gauged vibration survey is probably courting disaster. Second, anyone who may still insist on doing some of this kind of testing should, at the very least, install a 3/16" diameter safety cable to retain the engine in the event of a failed engine mount - it could save your life. RAF categorically does not recommend any variable or constant speed props on any RAF designed airplane."

http://www.ez.org/t/cpc-050

 

You know how to make props.  How about making some nice fixed-pitch composite props?  Those might find a market with the rutan pusher folks.  Good luck.

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

Link to comment
Share on other sites

Thanks for the good data.  After reading the failure report it seems clear to me that the failure was the front prop.  Then the vibration adversely affected the rear engine/prop.  Also if I interpret it correctly it was the engine mount that started the chain reaction, not necessarily the prop. 

 

Didn't he say that they redesigned the engine mounts?  The plane then flew around the world with a pusher and a tractor.  Though it cruised with only the rear engine if I remember correctly.

 

And, he said that he doesn't recommend an CS prop on any experimental airplane, I assume front or rear.  There are a lot of other canards with all kinds of variable pitch props tacked on the rear.

 

Also, the CAA/FAA approved method of testing a new prop design is known as a "Whirl Test".  I don't have the details in front of me at this time but I think it calls for some number of  hours of flight test.  Other test says that the propeller/blade retention, etc., shall be tested to twice the calculated stress and it shall not fail.  I don't think it says how much above twice the stress it is allowed to break.  But the retention system on my props works out to be way above that.

 

I did calculations on how much force was created with a typical blade weighing 6,5#, turning at 2800 rpm.  The numbers are something like this.  Centrifugal for 20,000#.  There are 15 screws holding the blade in the hub.  Extensive pull tests, destruct test, shows that with the old original screws made of SAE 3035 carbon steel, the screw would break at about 6000# of pull stress.  My new steel screws break at about 8000# of pull stress.  That works out to about 120,000#.  A very good safety of margin over the FAR requirements. 

 

But even that doesn't mean that you can't destroy a prop.  I have one customer that called in a guy to dynamically balance his prop.  He brought the prop to me along with a disc about 10" diameter with over 4 oz of weight added to one side, said it vibrates like hell.  I put the prop on my balance stand, sans the added weight his prop balance guy put on it  and found it to be in balance.  I opened the prop up and found 5 broken screws.  The four plus oz of weights the guy put on the prop almost destroyed it. 

 

Static balance is a valid balance.  You can't unbalance a prop to balance an engine.  You can usually get by doing that with a fixed pitch prop but not with a variable pitch prop simply because the variable pitch hub can't be made as strong as solid metal or wood for that matter.  But even then I often hear of a guy slinging the metal tip off his prop.

 

If someone starts stacking weights on one of my props, he has voided any warrantee, written or implied.

 

Prop clocking on the crankshaft is important.  I think I sent an article I  picked up from the journal "Coupe Capers", to one of your canard folks a publication of the Ercoupe folks.  It has a very good article on vibration problems as a result of clocking of the prop in relation to crank throw. especially for four cylinder engines.  You will notice that Hartzell, McCauly  and others, in conjunction with the engine folks, makes it such that their prop can be installed in only a certain way.  The Aeromatic can be installed at any one of several clockings.   

 

 

My new screw design is made of a newer steel, SAE 8720.  They break at 8,000# +/- 10%. I have to check that my memory about the steel is correct.  The old steel Rockwelled out at about 6000PSI, the new steel Rockwells out at about 8000PSI.

 

I think it is FAR part 35 that details this information.  I think the old CAR part was part 17, I'll check it at work, I can't get into my IA library here at home for some reason. 

Link to comment
Share on other sites

How many hours do you have on these props behind rutan pushers?  It's a nice looking prop for sure but you know, of course, that Rutan did not recommend constant speed props behind his designs because of their weight and vibration passing in and out of the wake.    And at $5300, it's a pricey prop for a scratch-builder.  I suppose you are posting here because you lost your certified prop business.  http://www.aeromatic.com      Really sorry to hear that but without a lot of test hours behind a Rutan pusher . . .

 

"Burt has been . . . adamant about the use of variable speed/constant speed props on our experimental airplanes. To use any manufacturers variable or constant speed prop without conducting a full, in-flight, strain gauged vibration survey is probably courting disaster. Second, anyone who may still insist on doing some of this kind of testing should, at the very least, install a 3/16" diameter safety cable to retain the engine in the event of a failed engine mount - it could save your life. RAF categorically does not recommend any variable or constant speed props on any RAF designed airplane."

http://www.ez.org/t/cpc-050

 

You know how to make props.  How about making some nice fixed-pitch composite props?  Those might find a market with the rutan pusher folks.  Good luck.

I have great respect for Burt.  But I think it is clear that Burt has not come up to speed on the Aeroamtic prop.  Anyway we are doing extensive flight testing on the EZ with the Aeromatic prop.  Will be posting it as we get useful data.  But we see no adverse problems so far.  It is just as smooth as the fixed pitch wood prop that we took off the EZ.  It's a wood prop folks.  And it has the reputation of being a very smooth prop.

 

We did some flight testing today.  Step climbing.  The Aeromatic, in the fully automatic version, looses about 20 rpm per thousand feet.  The numbers we got pretty well confirmed that.  Started at 5K and went up to 12K.  I forgot to bring the data home, dangit.

Link to comment
Share on other sites

Fixed pitch props,  I sold most of the machinery that supported making fixed pitch.  I sold it to Bob Hunt 228 563 0927.  I don't know what he is doing with it but I think he told me a year ago or so that he was making props for EAB planes.

 

I have flight date on the EZ,  The conditions were gusty and I don't put much stock in the numbers unless you average them, I will post the for the testing we did from 5K to 11K.  Later. Kent

Link to comment
Share on other sites

  • 3 weeks later...

Here is the certification requirements for prop cert from the original Civil Aeronautic Admin.   The Aeromatic was certified under these rules.

 

(1) A 100-hour endurance test shall be conducted on an engine of the same power and rotational speed characteristics as the engine or engines with which the propeller is intended to be used. The endurance test shall be conducted at the maximum continuous rotational speed and power rating of the propeller, except that, in the event a rotational speed(s) and power condition(s) is found to be critical on the basis of the vibration test prescribed in § 14.152, such portion of the 100 hours as the Administrator

finds necessary, but not in excess of 50 hours, shall be conducted at the critical rotational speed(s) and power condition(s). If a take-off rating greater than the maximum continuous rating is to be established, a 10-hour block test in addition to the 100 hours shall be conducted at the maximum power and rotational speed for the take-off

rating.

 

(2) The propeller shall be operated throouugth the engine endurance tests prescribed in Part 13 of this subchapter.

 

§ 14.154 Functional test. Variable-pitch propellers shall be subjected to the following functional tests as applicable. The same propeller as used in the endurance test shall be used in the functional tests and shall be driven by an engine mounted on a test stand or on an aircraft.  (a) Manually controllable propellers. 500 complete cycles of control shall be applied throughout the pitch and rotational speed ranges.

 

(b) Automatically controllable propellers. 1,500 complete cycles of control by means of automatic control mechanism shall be applied throughout the pitch and rotational speed ranges.

 

© Feathering propellers. 50 cycles of feathering operation shall be applied.

 

(d) Reversible-pitch propellers. 200 complete cycles of control shall be applied from the lowest normal pitch to the maximum reverse pitch. At the end of each cycle the propeller shall be operated in reverse pitch for a period of one minute at the reverse pitch maximum rotational speed and power.

 

§ 14.155 Special tests. Such tests shall be conducted as the Administrator finds necessary to substantiate the use of any unconventional features of design, material, or construction.

 

§ 14.156 Teardown inspection. After completion of the tests, the propeller shall be completely disassembled and a detailed inspection shall be made of the propeller parts to check for fatigue, wear, and distortion.

 

§ 14.157 Propeller adjustments and parts replacements. During the tests servicing and minor repairs of the propeller shall be permissible. If major repairs or replacement of parts are found necessary during the tests or in the teardown inspection, the parts in question shall be subjected to such additional tests as are found by the Administrator to be necessary.

 

[F.R. Doc. 56-10369: Filed, Dec. 19, 1956; 8:50 a.m

Edited by Kent
Link to comment
Share on other sites

I would bet that all you guys are members of EAA.  And you look forward each month to Barnaby’s articles on airplanes and aerodynamics.

 

In the Feb issue he writes about Propeller Momentum Theory.  There is no question that Barnaby knows his stuff.

 

He explained how the velocity change across the propeller disc is a measure of efficiency.  To visualize this, think of your airplane sitting on the ground with the brakes locked and full power on the engine.  This is the case where the airplane is standing still and the air is moving through the propeller disc really fast.  Here you have zero propulsion efficiency if we are talking about the speed of the air against the forward speed of the airplane.

 

Now, after you are in cruise flight you airplane is moving really fast and the air is virtually not moving at all.  And if the air is not moving at all this is where, as Barnaby explains, that your propulsion efficiency is 100%.

 

That is a mental picture of the of his formulae, T=2Apv(V+v).  The P in the formulae is supposed to be the symbol rho, (air density).  My keyboard doesn’t have rho.  :-)

Edited by Kent
Link to comment
Share on other sites

  • 2 weeks later...

I thought I posted some flight data on this site but I don't see it.

 

To answer Ashtons' comments.  The reason I surrendered my repair station certs and PMAs is because Seattle MIDO threatened a witch hunt because I disagreed with one of their invented rules.  My entire facility for making props is less than 2000 sq/ft.  They got pissed at me and said they were going to send auditors down here and spend two days auditing me.  Then after that they said they were going to come down three weeks later and do it all over a gain.   That amounts to a witch hunt and after that the burning at the stake.

Link to comment
Share on other sites

To answer Ashtons' comments.  The reason I surrendered my repair station certs and PMAs is because Seattle MIDO threatened a witch hunt

 

 

Believe me, I know how arbitrary and capricious the FAA can be so I don't take anything they say at face-value.  However, it's probably best to publish the FAA's objections and say your side of it.   Just saying they're on a witch hunt does not give buyers enough info.  If I was going to buy one of your props, I would call the MIDO and ask what they objected to.  It would be dumb not to do that.  

 

Really, I wish you good luck with your business but that's how I'd look at it.

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

Link to comment
Share on other sites

  • 2 weeks later...

They don't object to the prop, they object to me.  I got into an argument with Seattle MIDO about my supposed oversight and auditing of my paint supplier.  The rules say that I shall have oversight and audit any supplier that makes anything or does anything to my drawing, specifications or procedures.  I was buying paint from NAPA.  NAPA doesn't make anything to my spec.  I buy the paint made to their spec.  Then the SEA MIDO idiot told me,  "OK from now own you have to get a signed statement from the store owner or the store manages that says, 'The paint you have in you hand is the paint that is on the sales slip". 

 

I told him how I was handling the situation when I was under Van Nuys MIDO.  He said words to this effect,  "Well, we don't run the Van Nuys MIDO, this is what you will have to do from now on".

 

This is about 2% of the sh*t the FAA has put on me.  These people are drunk on Power of The FAAA.

 

And BTW, the MIDO dingbat was an Ex employee of Cirrus Aircraft Co.  He wrecked a new airplane of theirs, landed it about 20 feet above the runway, retracted the landing gear through the winds and broke the tail cone off.  Now he works for the FAA.  And that ding bat actually displayed joy about screwing up.  Maybe he was joyous about getting a fat paying job with the FAAA. 

 

Seems like the FAAA seeks out the people that can't make it in the filed.

Link to comment
Share on other sites

The other 98% would take the size of a thick book.  But here is another 2%.  First Article Conformity Inspection.

 

Here is how that went down. 

 

FAAA;  "You can't do your own inspection, you have to hire an independent testing laboratory to do the FACI".

 

Me; "OK, give me a list of FAA certified independent testing laboratories". 

 

FAA, "There aren't any, we don't certify them". 

 

Me: "OK, since you are a member of the FAA Manufacturing Inspection District Office, come down here and witness the inspection". 

 

FAA;  "We don't have the budget to go down there and witness an inspection, you have to hire a DER/DAR to do that". 

 

Me;  "According to your certified mail to me, you found budget to send auditors down here and spend two days auditing me in my 1500 sq/ft facility".

 

FAA;  "You have to hire a DAR to witness the FACI.

 

So, I flew down to Lancaster, CA., picked up my DAR.  (He was a retired FAA MIDO inspector}  I flew him up to Carson City, NV.  I had cut a deal with Rick Clemens, owner of Specline.com,  We used his QA laboratory.  My DAR and I spent about 30 minutes inspecting the part.  I flew him back to Lancaster.  He charges $50 per hour from door to door.  He gave me a discount and only charges me $300 for the half hour inspection and his time away from home.  The fuel bill for my Geronimo was over $1000.  So, with all the delays and jerking around that half hour inspection cost me just shy of $3000.

 

I am not going to take up the space and time to write a book on this crap.  I do think I shall get to hell out of the certified propeller business. It just isn't worth it to me.

Link to comment
Share on other sites

If I made a pilot controlled variable pitch propeller that weighs about the same as a fixed pitch wood prop, would any of you guys be interested?

 

It would be similar to the MT controllable  prop which uses a knob on the instrument panel to control pitch.

Link to comment
Share on other sites

I know a few of us (small few) have had/chosen MT and possibly other constant speed and variable pitch props. Some ground adjustable too.

The reasoning is that these planes require more runway than a Cessna 150, and some feel the need. Personally, I might be interested in a lightweight and reliable variable pitch prop. However, my intentions are to keep it simple and use a wooden prop.

I acquired a plane project that had a MT Constant Speed prop on it but had a prop-strike incident that trashed all of it.  $8,000+ to fix and so I am looking forward to using a fixed prop for a fraction of that.

 

So sure... tell us more.  I'll really be interested after a few others have a few hundred hours on theirs.

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

Link to comment
Share on other sites

It doesn't make sense to be asking for a few thousand hours on a propeller before one is comfortable with it.  The regulation I posted on this site is reliable.  You know how long it would take to put 2 or 3K hours on a prop?  The prop we put on the local  Veri-EZ is safe.  It is smooth as silk. It has been disassembles twice and there is no degradation of parts.

 

The problem with pusher props is if they are metal blades.  This prop on the EZ is wood core with carbon fiber coating.  Vibration excitation from the engine along with the disturbed air off the pusher creates excitation frequencies that fall within the resonant modes of metal propeller blades.  Wood blades have resonant frequencies that are mostly outside the excitation frequencies of most engines.

 

Pardon my ignorance but I don't know how to set up my computer to do what Jon suggested.  I will see if I can find a kid to do it for me.  I'm sorry for my low knowledge of computer noise.

Link to comment
Share on other sites

  • 3 weeks later...

It doesn't make sense to be asking for a few thousand hours on a propeller before one is comfortable with it.  The regulation I posted on this site is reliable.  You know how long it would take to put 2 or 3K hours on a prop?  The prop we put on the local  Veri-EZ is safe.  It is smooth as silk. It has been disassembles twice and there is no degradation of parts.

 

The problem with pusher props is if they are metal blades.  This prop on the EZ is wood core with carbon fiber coating.  Vibration excitation from the engine along with the disturbed air off the pusher creates excitation frequencies that fall within the resonant modes of metal propeller blades.  Wood blades have resonant frequencies that are mostly outside the excitation frequencies of most engines.

 

Pardon my ignorance but I don't know how to set up my computer to do what Jon suggested.  I will see if I can find a kid to do it for me.  I'm sorry for my low knowledge of computer noise.

 

I didn't ask for "a few thousand hours..."  I asked, "...I'll really be interested after a few others have a few hundred hours on theirs."

 

Regardless, I've since seen the price of your props (~$5,000) and that's well above my propeller budget.  I get it though...

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information