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1. 12:47 PM - Re: Attention Corvair Builders (Brady)
2. 01:40 PM - Re: Attention Corvair Builders (FlyGuyTililDie)
3. 04:17 PM - Re: Re: Attention Corvair Builders (Joemotis@aol.com)
4. 05:59 PM - Re: Attention Corvair Builders (Brady)
Message 1
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| Subject: | Re: Attention Corvair Builders |
James,
I will try to answer your questions in order and in enough detail without being
too long winded.
This may be difficult for me, but I will give it a shot. :)
The shortest stroke crankshaft I offer is a 3". this is only slightly stroked from
the original dimension of 2.9375.
This crankshaft and a 3.622" (92mm) bore will net 185.4 CID.
(3.038 liters)
The 3.125" stroke crankshaft and the 92mm bore will net 193.1 CID.
(or 3.164 L)
The power gains are not dependent on displacement alone.
their are several other factors involved and this can become a very in depth conversation,
But suffice it to say that the power gains can far exceed 10 "Ponies".
In addition, to our application the torque rating is far more important.
I have heard it said that horse power is what sells engines and torque is what
fly's the airplane.
When I plan an engine build; I look for what will produce the most power in the
intended rpm range. I assume you don't intend to spin your propeller faster than
3500 RPM so an engine with loads of torque in that rpm range is what we are
after.
Stroke improves torque.
Displacement improves torque.
Cam profile plays a large part.
Intake velocity is important. (small valves)
Intake volume is less important.(big valves)
whether the gains justifies the cost is entirely your decision. :)
another colorful saying in this industry is:
"Power costs money, how much do you want?" :)
Aluminum Cylinders:
Ah yes, the "diametric opinions".
Please remember that most of these are just opinions from people who have never
run a Corvair with aluminum cylinders much less held aluminum cylinders in their
hands.
However they do have a friends, sisters, boyfriend who had an uncle who knew this
guy once. :)
The key thing to remember is that this is by no means new technology and the list
of successful applications these days is nearly endless.
I have heard all these stories and most of them are misinterpreted and or missing
critical details.
For instance the Porsche example; the studs only pulled out of the magnesium cases
and so they went back to the aluminum cases.
Also these engines were producing substantial amounts of horse power far beyond
what we are after and power = heat.
Excessive Heat is what causes the problems and the cars ability to cool the engine
is far less than that of the aircraft application.
The Coefficient of thermal expansion is measured in millionths of an inch per degree,
per inch of material.
356 T-6 Aluminum's Coefficient is about 12
The length of cylinder between the case and the head of the Corvair is 4".
So lets assume our engine will never see 500 degrees F and use that as our worst
case scenario.
With this we get 0.000012 x 4" x 500* = 0.024"
Now, this may sound like a lot but remember our studs are expanding also.
Steel has a coefficient of about 6.
so we get 0.000006 x 4" x 500* = 0.012"
So what we end up with is only a 0.012" difference.
Let me say at this point that if your engine sees 500* we have other serious problems.
So, if we keep the engine running in its normal temperature range we can expect
to see far less movement. I don't expect to see any problems but without actually
testing the set up I can not definitively say. That is why we are building
the engine to test.
I have 2 sets of aluminum cylinders for the Corvair and I have yet to run them
my self. However we do have a set of 94mm running in a customers sand rail with
no problems as of yet. I have not seen this engine and I don't know how many
hours are on it but so far so good.
I will have my engine with the aluminum cylinders running shortly and then I will
have all the test data in my shop.
Only time will tell.
The hybrid cylinders you mentioned have already been done and there are flying
examples.
They do not offer the weight savings and are approximately the same price.
William invited me to the last Corvair College #13 held in Livermore, CA.
He got to see the Aluminum cylinders in person.
He of course reserved comment until they are running and tested, but he did not
express any immediate concerns to me at that time. He is not one to withhold
an opinion if he sees anything that concerns him. He has always been very open
and forth coming with me in the past.
140 Heads:
There are several examples of 3100 engines running 140 heads and I believe a few
are even flying.
The 140 heads are very popular with the hot rod and sand rail guys and so they
are very hard to find and very expensive when you can find them.
The bigger valves in the 140 heads have less aluminum around them and are known
to drop valve seats.
I do not fee that the increased valve size is much advantage at the lower rpm range
and so I do not consider them a must have.
I actually prefer the 95 horse power heads because they also have the open combustion
chamber and can be modified to maximize the quench height with out diving
the compression ratio through the roof.
These heads are easy to find and cheap.
Also the small valves are good for the intake velocity and therefore good for torque.
I have tested 95 HP heads on a flow bench and they will flow about 106CFM @ 28"
of H20 in their stock form which will accommodate up to about 163.7 horse power.
Certainly more than we what to subject our little airplanes to? :)
--------
Brady McCormick
Poulsbo, WA
www.magnificentmachine.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=226917#226917
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| Subject: | Re: Attention Corvair Builders |
Thanks a bunch Brady,
This is the kind of help and information I was hoping to get by joining this forum.
My #1 concern is maintaining reliability. It seems by now that most of the weak
components of the corvair have been exposed, most recently being the crankshaft.
With nitriding and a 5th bearing, the additional stress can be mitigated.
You had mentioned cam application. Are you a fan of the OT-10 or do you recommend
something else?
Also, I see that it has been a popular choice to have the crank milled down to
-.10 I still don't know the reason for this and perhaps you could clarify.
Is this just so they can radius the edge of the journals? If so, do they make
rounded main bearings?
I admit I am a complete novice when it comes to this and I look up to you educated
folk to show me the way. You have been great Brady!
I'll send you another PM on getting my project started.
James
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=226926#226926
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| Subject: | Re: Attention Corvair Builders |
Have you purchased William Wynne's conversion manual yet?
By the way, you turn a crankshaft on a lathe to get rod and main bearing
journals to a standard undersize such as .010 not mill them.
Do not archive
Joe Motis
In a message dated 1/26/2009 1:41:27 P.M. Pacific Standard Time,
flyguytilidie@aol.com writes:
James
**************From Wall Street to Main Street and everywhere in between, stay
up-to-date with the latest news. (http://aol.com?ncid=emlcntaolcom00000023)
Message 4
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| Subject: | Re: Attention Corvair Builders |
James,
The Corvair has flown nearly 45 years (since 1960) without nitriding or the fifth
bearings, with relatively no problems until recently.
The rash of recent crankshaft failures are due to several factors and I think the
most important is an aging crankshaft that is Fatigued.
Some of the Crankshafts were subjected to prop strikes, extra long prop extensions,
propellers that were not indexed properly, excessive RPM and these engines
were producing far more horse power as well as airframes that are much faster
and more nimble. This all adds up to more force exerted on the crankshaft.
In addition to the extra forces all these crankshafts were 45+ years old with unknown
& undocumented Histories. So you never know if the crankshaft has experienced
sever over heating, oil starvation or catastrophic engine failure.
This is why I started to manufacture new crankshafts.
The Nitriding is done to bolster the fatigue strength of the crankshaft.
But it can not erase the previous 45 years of use or abuse.
The fifth bearing concept is to limit the forces exerted on the crankshaft to begin
with. I think this is an excellent idea and there are several to choose from
most of which have flying examples.
I do not however feel this is a substitute for a new crankshaft.
The Magna fluxing can only tell you that the crankshaft is not cracked right now.
It can not tell you when it will crack or that it will not crack tomorrow.
When a crankshaft has worn to the point of increasing the oil clearance beyond
specified limits, the crankshaft is ground on a crank grinding machine to a known
under size and over sized bearings are installed to make up the difference.
Reliability is of the utmost importance and I hope that people will not put budget
before safety.
The new crankshafts are produced with the largest radius's passable yet accommodate
the use of standard width bearings. The main bearing journals are radius-ed
to .125" & the Rod journals are radius-ed to .100". They come completely machined
for the aircraft application (safety shaft) and come with a new Gear.
They are made from high quality 4340 alloy.
The original OEM crankshaft was made from 5140 alloy and has an ultimate strength
of about 86,000 psi.
The 4340 crankshafts have an ultimate strength of about 165,000 psi,
so you can see that in material alone we have increased the strength about 79,000
psi. (almost double)
With the increased radii and heat treating we further increase strength and durability.
Cam Shafts:
The OT-10 camshaft profile is a very popular one.
It works well and is readily available.
Most of the Corvairs flying are probably using this cam.
this camshaft was designed for the automotive application and peaks a bit higher
in the RPM range than what I think is useful to the aircraft application.
I had a cam cut to a profile that we designed to peak a bit lower in the rpm range
and that is intended to focus on torque, it will be tested in our next engine
build shortly.
If this proves to be advantageous we will offer cams in this profile.
--------
Brady McCormick
Poulsbo, WA
www.magnificentmachine.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=226982#226982
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