Billet Aluminum Rotors

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gofastclint

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Dec 17, 2008
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Sydney, NSW, Australia
Here is a link i found interesting, Performance auto parts, turbochargers,Central Florida

Second product from the bottom of the page.

I can see a few good benefits in using aluminum rotors as opposed to the standard iron rotors from the Mazda factory.

1. Less weight is always better in an aircraft of any kind.

2. If you retain the same rpm that you are currently using in you standard rotor motor, the engine will vibrate a lot less, adding to the durability of the entire aircraft.
:)

3. The excellent heat properties of aluminum over iron (I think the oil system would play a much larger roll in the cooling of the motor and probably need a greater size cooler)

One issue I see is the greater expansion of aluminum will give minor wear issues during warm up due to clearances, though this is easily solved by using aluminum with a higher silicone content.

You will also need to replace or balance the counter weights.

There are so many pros and cons of using Aluminum rotor and i am looking forward to your input.
 

addaon

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Feb 24, 2008
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1,686
Location
San Jose, CA
What are the critical temperatures of 6061? How does this compare to the operating temperatures of the rotor?
 

Jman

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Oct 22, 2002
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Pacific NW, USA!
Here are two Youtube videos of those billet rotors in operation. Doesn't prove they will hold up for any lenth of time though. Be sure to turn down the volume on your computer!! I didn't....


 
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orion

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Mar 2, 2003
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Western Washington
As I understand it, the new aluminum rotors are primarily for racing where the reduced mass provides a fairly significant acceleration benefit. But due to the high expansion and tolerancing issues, their longer term application to aircraft might not be as feasible.
 

BBerson

Light Plane Philosopher
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Dec 16, 2007
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Port Townsend WA
The tensile strength of 6061-T6 aluminum is reduced at elevated temperatures starting at 300 degrees F (82% of original) to 500 degrees F (38%)*. The yield numbers are lower.
It just depends on the actual stress involved.

*from Alcoa Structural Manual after 10,000 hours at various temperatures chart.
 

Midniteoyl

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Sep 3, 2003
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Indiana
I think it has more to do with the changes in clearances from the hot side to the cool and the resulting effect on the lip seals.
 

pepsi71ocean

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Jan 31, 2009
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South New Jersey
If you can't decide, i would say build it and let it run till it dies. We have done that with an engine or two just for S&G. Always interesting to see what causes it to go, and i don't think the cylinder temp should get that hot that it would melt the rotary(Unless, read below). I agree having played with Rotarys before i wouldn't really play with the end housing. Just remember that you are taking the engine and puting into a confined space, and so you have to watch your manifold and exhaust header tempts. Unless the engine will be in the open or have good passive cooling. The main issue with heat is the Rotary piston, that does reach hot temperatures.

Having raced with Mazda cars, and their crappy rotarys, the reason that Mazda sticks with iron for the piston is because the rotars hit a huge tempterature barrier, and that unless your on top of the temperature it will melt with horiable consequences. Infact my buddy had a Rotary weith aluminum rotors it melted in a race snapped the drive shaft when she went. I think the engine temp gague hit 220 (not sure though) but the internal temp must have been a whole lot higher then that. Since then we got a LT-1 block for his Mazda. You have to keep the rotarys cool, There are solutions to the fix, i believe running cool gas into the system seems to help, however i think the engines aren't designed to handle that range for the RPM's that he was running. But unless your running low RPM then ide stay away from aluminum rotors, yea he had a fast car, however the engine time was under 100 hours before it went.

Alternatively, I would say why risk lightening up the engine if it will cross any safety threshold, what price does one put on their life to save 50 or 100 lbs. but that is my thought on it.
 

lehanover

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Jul 12, 2005
Messages
10
Location
Hebron Ohio in summer. Zephyrhills Florida in wint
There are two down sides. The expense, and the loss of mass. The stock rotors are cheap and weigh about 9 pounds each. That provides a considerable
flywheel effect. For a smooth low RPM idle you will need a heavier flywheel.

Cast iron rotors are nearly indestructible. Are available in every junk engine you buy. Where are we to buy aluminum rotors? Let the racers sort this out
Mazda has no such rotors even in their racing parts catalogue.

As you remove weight from front engined designs, you move the engine foward to maintain balance. Lengthening the mount and cowl, and adding side area ahead of the center of mass. This suggests a bigger fin and rudder. With no aluminum after market parts the Mazda weighs about the same as a Lycoming, so the design stays the same.

Lynn E. Hanover
 
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