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Ford Crankshaft Choice

 
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John Black



Joined: 23 May 2016
Posts: 9

PostPosted: Fri Jul 13, 2018 6:59 am    Post subject: Ford Crankshaft Choice Reply with quote

I am building a Ford Model B engine for my Piet. I want to know what RPMs the engine will usually run at ??

I have an early 1932 crankshaft that looks like a Model A crank with bigger main bearings… no counterweights. I also have a 1934 crankshaft that has cast counterweights. It weighs about 12 pounds more. Which should I use ?

I think the engine needs to run smooth… minimum vibration. The counterweighted crank would be smoothest. The 1932 crank without counterweights will vibrate a bit, but there will be RPMs at which a harmonic vibration will be greater.

I have a model A car with a crank without counterweights. I think a good test would be to run its engine at the RPMs that are commonly used in flying a Piet. If it is smooth, I think it is a good indication the harmonic vibration will not be serious at the required RPMs…. and I’ll probably use the 1932 crank without counterweights. Bernard Pietenpol preferred engines with this crank.

What RPMs do Model A Piets mostly use when flying ?

John


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taildrags



Joined: 29 Dec 2009
Posts: 1607
Location: Medford, OR

PostPosted: Wed Jul 18, 2018 12:29 pm    Post subject: Re: Ford Crankshaft Choice Reply with quote

John; I'm really surprised that no one has replied to your query about the crank, since there are quite a number of those engines out there and plenty of hands-on engine rebuilders too. I know Ernie Moreno up here in Independence is building up a Ford to put on his Piet to replace the Franklin that he's got on it now. The extra weight up front will help Ernie's airplane with tail-heaviness.

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Oscar Zuniga
Medford, OR
Air Camper NX41CC "Scout"
A75 power, 72x36 Culver prop
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glen



Joined: 17 Sep 2013
Posts: 166
Location: Oregon Coast

PostPosted: Wed Jul 18, 2018 1:04 pm    Post subject: Ford Crankshaft Choice Reply with quote

Ernie’s at Oshkosh

Quote:
On Jul 18, 2018, at 1:29 PM, taildrags <taildrags(at)hotmail.com> wrote:



John; I'm really surprised that no one has replied to your query about the crank, since there are quite a number of those engines out there and plenty of hands-on engine rebuilders too. I know Ernie Moreno up here in Independence is building up a Ford to put on his Piet to replace the Franklin that he's got on it now. The extra weight up front will help Ernie's airplane with tail-heaviness.

--------
Oscar Zuniga
Medford, OR
Air Camper NX41CC &quot;Scout&quot;
A75 power, 72x36 Culver prop




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=481734#481734











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John Black



Joined: 23 May 2016
Posts: 9

PostPosted: Wed Jul 18, 2018 1:43 pm    Post subject: Ford Crankshaft Choice Reply with quote

I have heard from 2 guys off list.
I learned that using a 76x44 prop or a 78x42 prop…. Model A engine turns 2100 RPM on takeoff, cruises at 1700-1800 RPM, probably never exceeds 2200 RPM.

I took my model A Ford car (pic Below) out and ran the engine at 1700-2200 RPM and drove at those RPMs. The Model A engine in the car has no counterweights on the crank. The engine has been balanced. I did not experience any harmonic vibration. My rearview mirror amplifies the vibration and serves as a great observable indicator.

Based on this test, I am leaning toward using the 1932 Model B crank without counterweights. I figure saving 12-14 pounds is a big deal.

John

[img]cid:F4920A52-E779-4CCC-A478-FF64AB22990E(at)wavecable.com[/img]

On Jul 18, 2018, at 1:29 PM, taildrags <taildrags(at)hotmail.com (taildrags(at)hotmail.com)> wrote:
--> Pietenpol-List message posted by: "taildrags" <taildrags(at)hotmail.com (taildrags(at)hotmail.com)>John; I'm really surprised that no one has replied to your query about the crank, since there are quite a number of those engines out there and plenty of hands-on engine rebuilders too. I know Ernie Moreno up here in Independence is building up a Ford to put on his Piet to replace the Franklin that he's got on it now. The extra weight up front will help Ernie's airplane with tail-heaviness.--------Oscar ZunigaMedford, ORAir Camper NX41CC &quot;Scout&quot;A75 power, 72x36 Culver propRead this topic online here:http://forums.matronics.com/viewtopic.php?p=481734#481734


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taildrags



Joined: 29 Dec 2009
Posts: 1607
Location: Medford, OR

PostPosted: Wed Jul 18, 2018 8:55 pm    Post subject: Re: Ford Crankshaft Choice Reply with quote

John; in the larger scheme of things, saving 12-14 lbs is certainly worth pursuing since lower gross weight means reduced lift required to climb, and thus reduced engine thrust to produce the lift. However, many Piets end up tail heavy and have to shift weight forward somehow, or else shift the wing aft to adjust the CG. Additional weight up near the prop can help balance the airplane. It sounds like you're performing your due diligence in making the decision on which way to go on the crank though.

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Oscar Zuniga
Medford, OR
Air Camper NX41CC "Scout"
A75 power, 72x36 Culver prop
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skipgadd(at)earthlink.net
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PostPosted: Mon Jul 23, 2018 4:00 am    Post subject: Ford Crankshaft Choice Reply with quote

John, Just back from Brodhead, so the late reply.
The thing about Piets is they will almost always be tail heavy. My personal building philosophy is not to worry about weight ahead of cg, but I will have an A65 that is lighter than your Ford A.
The other thing is your personal weight, the bigger you are the more weight you will need up front.
Skip

--


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braywood



Joined: 29 Sep 2012
Posts: 17
Location: Northern Ireland

PostPosted: Mon Jul 23, 2018 6:44 am    Post subject: Re: Ford Crankshaft Choice Reply with quote

Hello Oscar - I am still struggling with the theoretical weight and balance for my aircraft; so I am not pretending to be an expert or suggest others are incorrect.

For me, the issue of CofG is a question of where you locate the wing - if the aircraft is tail heavy (or like me, the pilot is tail heavy....), the wing needs to go back.
If you are changing the engine in an aircraft, then does not the W&B needs to be a clean sheet? I would think that every pound or Kg we add, is detrimental to performance. Opting for a heavier solution for a part of the aircraft seems counterproductive. Is it not better to relocate the wing to provide the correct CofG location for the lowest aircraft weight? I can understand wanting to have the cabane struts vertical, but not at the expense of the safety or performance of the aircraft.
What am I missing??

Mark Bowler


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taildrags



Joined: 29 Dec 2009
Posts: 1607
Location: Medford, OR

PostPosted: Mon Jul 23, 2018 7:13 am    Post subject: Re: Ford Crankshaft Choice Reply with quote

Mark; you are not missing anything. Your comments are correct, and the wing can be repositioned to adjust the CG. One negative to shifting the wing aft is that it makes getting into the cockpit just a bit more challenging, but a hinged flop or a cutout takes care of that.

It's the builder's choice, like so many things about experimental aviation. "Ya pays yer money, ya takes yer choice".


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Oscar Zuniga
Medford, OR
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A75 power, 72x36 Culver prop
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