Consequences of replacing heavy alluminum Prop with lite weight wooden prop?

[1600vw]

This is on a hand propped a-65 with impulse coupler mag. Airplane came from a higher elevation and needed a prop change. Because of cost I went with a wooden prop. What will the effects be on the engine. Now understand this wooden prop is not pitched the same as the one removed. The one removed was pitch around 40 this new prop is pitched and 60. Its a Sterba Prop and Ed said this was the prop to start with for my setup.
But how will this lite weight prop effect engine performance and running? Or will it? I would say it would in some way. Thoughts...

Tony

[Bob Dingley]

Best bet is stay in contact with Ed Sterba and follow his advice. I found a link to his site on the Great Plains engine site. Its a neat site and even has a prop calculator. I don't see any way that a lighter prop will hurt an engine. Are diameters the same or is the new one much smaller?


http://www.greatplainsas.com/edrules.html


A wood prop is generaly a little smoother than a metal prop. Going from a 40 inch pitch to a 60 is a fairly big leap. I'm guessing that the engine will never get up to a meaningful RPM range if the 40 was any way close. Example: Grumman American AA-1, AA-1A and AA-1B use 53 inch or 54 inch pitch. These are good combinations for t.o. & cruise. A 57 inch cruise prop is also approved. However, using that prop on a hot day or high altitude gives owners a real disappointing t.o & climb performance. If any.


Wood props are not my favorite down here on the Gulf coast where rain is a fact of life. The finish suffers. I had one a couple of airplanes ago and it looked like it had been dragged behind a pickup truck.


Good luck, Bob

[1600vw]

Bob the airplane came from an elevation of 5000'. It had to have this prop to reach rpm at this altitude. Ed said this should be really close to what I need if not right on for my elevation of 600'. This is going on a Sonerai with an a-65 engine on her. She is the sonerai 2 stretch built as a single seat because of the extra weight of the a-65.

Tony

[Bob Dingley]

I used to know O-145s, A-65s and A-75s because I learned in Cubs. Wow. Talk about apples and oranges. An airplane designed for a 80 HP 3300 RPM VW now has a 65 HP 2300 RPM Cont. Diameter has to be, what, about 65 inch or so. If you kept the original 71 in dia, you would dig divots down the RW. I bet this is not the only Cont Sonerai ever built. Have you contacted the Sonerai users for a starting point?. Trying props, one after another could add up.
A small change in pitch makes a big change in RPM. I used to have a Luscombe 8A with an A-65. It had a Beech R-003 prop for which it was STCed. It was controlled in pitch with a hand crank on the panel. This crank looked somewhat like late 40s DeSoto. I rebuilt her from a wreck. The metal prop was no longer airworthy and the extra Beech prop went with the plane. I had previous experience with the R-003 prop and had no reservations about it when I trained on the Piper J-3 instrument trainer. ( I won't cloud your mind with those details)
After I had the hung the prop, I just had to fiddle with it. I marked the blade shank and the prop hub and ran it from high to low pitch. There was very little apparent change. After she was returned to service by my AI, the prop seemed to function well. I had a few pilot error incidents when I neglected to go into low pitch on final. Full throttle on climb out resulted less than full RPM. I just cranked real fast and the 65 started to howl and dug out.
I'm just trying to say that just a little change in a prop has a huge effect on RPM. I hope you don't have to go through too many props before you find the right combination. Ed Sterba has a good rep.


Bob

[1600vw]

I am a member of the Sonerai site. They build to plans and do not like it when others build different or stray from the plans. Saying this we do have a few flying the sonerai with other engines besides a VW but they keep to themselves. There have been a few built using the a-65 but these people are gone today. One needs to remember the sonerai has been around since the 70's. Some have changed hands many times over all the years.

Ed told me if its not correct send it back and he would make it right, but he believes it will be real close. I want a static run up of around 2200-2250. In cruise I am looking for 2300-2350. Ed said he has used this same prop on another sonerai with an a-65. I trust him. I was wondering how the effect of the lite weight would be compared to the heavy aluminum prop. But if its not correct it will go back to ED. What a very nice man Ed Sterba is.

If I remember correctly someone from the sonerai site mentioned the Harmony Rock is a Modified Sonerai and the man would not call it a Sonerai out of respect for the designer of the sonerai. I would like to call mine something else to, but its already registered as a Sonerai IILS with an A-65.
The new prop is a 60x60.
Tony

[cub builder]

So why not have a prop shop put some pitch into the metal prop? That usually costs around $100 if you aren't asking for paperwork and log book entries.

FWIW, I find about 150 RPM difference in my planes (one slow plane and one fast plane) between operating from airports at 7000' vs airports at sea level (I am based at over 7000'). That can be made up by a pitch change of roughly 4". A pitch change of 20" is huge. They do measure them differently from manufacturer to manufacturer, but I have flown behind Sterba props before and his pitch measurements aren't that different from the rest of the world. On the other hand, Ed has been in the business a long time and will work with you to get the prop right for your plane.

FWIW, based on my experience with a number props from a number of manufacturers on various planes and engines over the years, I'm guessing the 60x60 will have a bit more bite than desirable for an A-65 on a Sonerii, but should be close. It would be a lot closer than a 40" pitched prop. I suspect the 40" number may have been misread or otherwise incorrect (as in the prop was repitched, but not restamped) That's significantly less bite than you'll find on a 75 mph Cub with an A-65, typically swinging a 68x44 prop.

As for effects on the plane? Metal props generally turn smoother due to the weight acting like a fly wheel. But the wood prop is smoother in that it doesn't have any harmonics. If you hit the prop it just shatters, so you don't need to tear your engine down. Sterba uses a tough polyurethane leading edge that will protect the prop from rocks and rain damage, but keep it varnished to protect while sitting. The airfoil on a wood prop is typically thicker, so isn't as efficient as a metal prop. However, Sterba has been working with the KR crowd for a long time and has his props dialed in nicely for planes in that class.

The #1 thing it will affect is your W&B. Make sure you check it.:)

-CubBuilder

[RetroAcro]

All things being equal, the switch to the wood prop will give you a little less performance, less vibration, much less stress on the crank flange (if you're into acro), less flywheel effect (may need to bump up your idle), and less weight on the nose, obviously. The prop is also more prone to complete stoppage should your idle be set too low, and you are doing spins. This again, is the much lower flywheel effect. They are nicer on the fingers to prop, though.

[1600vw]

So why not have a prop shop put some pitch into the metal prop? That usually costs around $100 if you aren't asking for paperwork and log book entries.

FWIW, I find about 150 RPM difference in my planes (one slow plane and one fast plane) between operating from airports at 7000' vs airports at sea level (I am based at over 7000'). That can be made up by a pitch change of roughly 4". A pitch change of 20" is huge. They do measure them differently from manufacturer to manufacturer, but I have flown behind Sterba props before and his pitch measurements aren't that different from the rest of the world. On the other hand, Ed has been in the business a long time and will work with you to get the prop right for your plane.

FWIW, based on my experience with a number props from a number of manufacturers on various planes and engines over the years, I'm guessing the 60x60 will have a bit more bite than desirable for an A-65 on a Sonerii, but should be close. It would be a lot closer than a 40" pitched prop. I suspect the 40" number may have been misread or otherwise incorrect (as in the prop was repitched, but not restamped) That's significantly less bite than you'll find on a 75 mph Cub with an A-65, typically swinging a 68x44 prop.

As for effects on the plane? Metal props generally turn smoother due to the weight acting like a fly wheel. But the wood prop is smoother in that it doesn't have any harmonics. If you hit the prop it just shatters, so you don't need to tear your engine down. Sterba uses a tough polyurethane leading edge that will protect the prop from rocks and rain damage, but keep it varnished to protect while sitting. The airfoil on a wood prop is typically thicker, so isn't as efficient as a metal prop. However, Sterba has been working with the KR crowd for a long time and has his props dialed in nicely for planes in that class.

The #1 thing it will affect is your W&B. Make sure you check it.:)

-CubBuilder

I called the company who makes this aluminum prop. They told me they never cut their prop to 60 inches. They said this is wall art, they told me not to use it. They said they tested their props and not to make it shorted then 67 inches. Because of this I did not want to have this prop repitched.

This man also told me he does not like dealing with Experimentals or homebuilts because those who fly them do not listen to what others tell them. I told him not to worry, this prop was not going back into service or use. His attitude changed when I said this and he started to talk to me a little more. Before hanging up I reassured him this prop was not being used again.

I am all over the WB. This airplane will not be flown until its all worked out and recorded in the logs. I thought about adding another fuel tank but as I use fuel I will lose the benefit of the fuel or weight so that won't work. I then thought about adding a starter, but with the cowl it has, that won't work not without a lot of mods to the cowl. So it looks like weight will be added in the forum of ballast. I will first check to see is any ballast can be removed from the tail.
Tony
P.S. I do not fly acrobatics.

[Bob Dingley]

Be careful regarding RPM Tony. When A-65s were everywhere, the Continetal crowd used 2300 as the red line and cruised at 2150. Of course, tachometers are notorious for being dead right all the time. BTW, I have an old one somewhare that that was working when removed from my Luscombe. I upgraded to a C-85 and the Tachs turn the other way. If you need it, its free for the postage.


ACS has one manual that covers operators, parts and overhaul.


Not going to do aerobatics in a Sonerai? Yeah they all say that at first.


Good luck, Bob

[1600vw]

Bob I will take that tach. Let me know what you need for the postage. The prop that was on it, I could have hit over 3000 rpm. I never wanted to do that so it was replaced.

The only way I will ever do aerobatics is with some training. I doubt I will try to teach myself this.

Thanks Bob

Tony

[1600vw]

Bob after thinking about this I do believe Ed said something about 2150 in cruise. I am going to run it and see what I get then get back with Ed with the numbers. I will not let her go over 2300 static but from the post I doubt I will need to worry about this.
Should I see 2300 for take off or 2150 - 2200 ?

Tony

[Bob Dingley]

Tony, A little info that may be helpful. This is a link to the FAA's Type Certificate Data Sheet (TCDS) for the A-65 series. The TCDS number is E-205 and its free from the feds.


http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/3FDEA75FFAD2128E86257950006E9E94?OpenDocument


I don't recall T.O. RPM. Sorry. If you need to ever do a valve job consider the STELLITE (sp) valves. They allow you to use 2500 as a limit and you have an A-75. I belive that there are carb jets to be changed too.


Bob (The search begins for the tach)

[1600vw]

Bob again I thank you for this info.

Tony

[1600vw]

I made that tool the 4 inch one cut down to 1.55 with a shank of .600 This comes no where close to taking this off. The shank of .600 needs to be at least double this. I was wondering if I could use a socket to take up the slack in side this hub or do I need to have this tool reworked?
They said something about not getting into the threads. First I do not see threads, but could I not use something that rests against the middle of the crank and then using this tool? If I explained this to were everyone understands what I mean.
Thanks
Tony

[cub builder]

I don't recall T.O. RPM. Sorry. If you need to ever do a valve job consider the STELLITE (sp) valves. They allow you to use 2500 as a limit and you have an A-75. I belive that there are carb jets to be changed too.


Well, kind of. Any A-65 that has been overhauled in the last 30 years should have modern valves, so that shouldn't be an issue. Additionally, the A-65s need to have the rod caps drilled before turning them up to more RPM. I haven't found one yet that doesn't have them drilled, but there may still be a few out there. (The oil port drilled into the bottom of the rod cap lines up with the oil port in the crank to squirt oil into the opposing cylinder at Bottom Dead Center to help cool the piston crown & lubricate the cylinder better). The actual A-75 pistons have a waffle pattern cast into the bottom side of the piston head to give more surface area for cooling with the oil squirting into it as previously mentioned.

However, in an Experimental Application, I would just ensure that the rods are drilled to assist with piston head cooling, and that you have modern exhaust valves. The A-65 piston is a cam ground piston vs the older A-75 piston being a round piston. The newer A-65 piston is a better piece of equipment.

IMHO, it's always a good idea to become intimately familiar with the insides of your engine before you fly behind it. Whether you do it, or have someone knowledgeable do so, I have found over the years, that what's in the logs usually isn't the real story and often times does not reflect the actual condition of the engine. I never buy an engine, then bolt it on an fly. Did that once and very nearly paid the ultimate price with a night time failure 80 hours later.

-CubBuilder

[1600vw]

After fighting with this hub for days today it comes right off. I believe the PB Blaster finally worked. The aluminum prop came in at 20lbs. The wooden prop came in at 5 lbs.

This is or was a flying airplane. Very few logs came with it. It does have an engine log that says its been rebuilt but that is about all it says besides hrs and it has 45 hrs on it since OH. I do see some oil dripping from the jugs, not a lot but the bottom bolts are a little wet. Everything looks like its relatively new but who knows.

This airplane will be used to bore holes in the sky above my airfield and not going far in it. For the first 20 hrs she is staying close to the home runway. I really hate to pull the engine apart, I will do a cylinder leak down after I static run her for a couple hrs. Then the next day do some testing on the engine after she sits all night. If I was using this airplane to transfer or fly family or friends in I would be sending this engine off to an engine shop. To fly me above corn fields close to my airstrip I will not do this.

I only fly 40-60 min's at a time. I can not sit in these seats any longer then this. Most my flight are 45 min's. Some longer some shorter but never have I flown over an hr.

Tony

[Bob Dingley]

Tony,
I'll get the tach headed your way. Just need an address. PM me. Good info from Cubbuilder. However, my eng log showed stock valves. And you don't have logs.
Bob

[1600vw]

Tony,
I'll get the tach headed your way. Just need an address. PM me. Good info from Cubbuilder. However, my eng log showed stock valves. And you don't have logs.
Bob

Buying an A-65 With No Logs I usually don't worry too much about lack of logbook information as the "current state condition" is really what counts. As long as compression is in limits, oil temps, pressure, and consumption are in line, you should be good to go.

From Harry Fenton

Tony

[1600vw]

Thanks Bob.....

[Neil]

This is on a hand propped a-65 with impulse coupler mag. Airplane came from a higher elevation and needed a prop change. Because of cost I went with a wooden prop. What will the effects be on the engine. Now understand this wooden prop is not pitched the same as the one removed. The one removed was pitch around 40 this new prop is pitched and 60. Its a Sterba Prop and Ed said this was the prop to start with for my setup.
But how will this lite weight prop effect engine performance and running? Or will it? I would say it would in some way. Thoughts...

Tony

Getting back to your original question, you need to understand that prop pitch is usually measured at a certain percentage of the blade length and the pitch (blade angle)changes continually through it's length. If your aluminum prop was shortened then the original blade angle at a percentage of blade length is no longer accurate. Some prop makers measure pitch on the rear face of the blade and some use the cord line of the blade airfoil. different prop makers may use different blade airfoils so this is another area for pitch measurement to differ for the same affective pitch.
Ed Sterba built me a couple of props over 30 years ago when I was flying a Sonerai and as good as he was then he can only be better now. Personally, I would consider asking anyone else for advice concerning a Sterba prop a waste of time. I don't mean any disrespect toward the posters here, but no one knows props on Sonerais' any better than Ed.
I would agree that the clipped metal prop is a wall hanger.
The change will have an affect on your weight and balance so adjust accordingly.
Neil

[1600vw]

Getting back to your original question, you need to understand that prop pitch is usually measured at a certain percentage of the blade length and the pitch (blade angle)changes continually through it's length. If your aluminum prop was shortened then the original blade angle at a percentage of blade length is no longer accurate. Some prop makers measure pitch on the rear face of the blade and some use the cord line of the blade airfoil. different prop makers may use different blade airfoils so this is another area for pitch measurement to differ for the same affective pitch.
Ed Sterba built me a couple of props over 30 years ago when I was flying a Sonerai and as good as he was then he can only be better now. Personally, I would consider asking anyone else for advice concerning a Sterba prop a waste of time. I don't mean any disrespect toward the posters here, but no one knows props on Sonerais' any better than Ed.
I would agree that the clipped metal prop is a wall hanger.
The change will have an affect on your weight and balance so adjust accordingly.
Neil


As I stated before this post is not about the Sterba prop but about what the reduction in weight will have on the engine.

As for W/B I post this will be done and ballast add or removed as needed.

This old prop was sent to a prop shop. They cut and repitched this prop. They put the length on the hub but not the pitch. They also put on this hub this prop has been reconditioned.

3769
Tony

[Neil]

Suppose I should have read your post a bit more thoroughly. One thing you will notice is that you will have much less flywheel effect since the wood prop is much lighter. The engine may not idle as slowly and you may notice that hand propping requires a bit more effort. The gyroscopic loads on the crankshaft will be lower and you may even notice that you need less rudder input on take off with the lighter prop. Generally speaking the wood prop is easier on the engine, particularly the propeller flange and front main bearing, but since the lighter weight allows the engine to respond to the throttle quicker is is wise to advance and retard the throttle a bit slower than one might with a metal prop.

[1600vw]

Suppose I should have read your post a bit more thoroughly. One thing you will notice is that you will have much less flywheel effect since the wood prop is much lighter. The engine may not idle as slowly and you may notice that hand propping requires a bit more effort. The gyroscopic loads on the crankshaft will be lower and you may even notice that you need less rudder input on take off with the lighter prop. Generally speaking the wood prop is easier on the engine, particularly the propeller flange and front main bearing, but since the lighter weight allows the engine to respond to the throttle quicker is is wise to advance and retard the throttle a bit slower than one might with a metal prop.

I like this, thanks Neil. I was wondering about the hand propping part. If I do not keep this airplane it will be because of this. I hope its not a issue but we will see.

Tony

[Bob Dingley]

Shucks Tony, your A65 was "born" with a wood prop three quarters of a century ago. No problem.

Bob