Syonyk

I think you'll be fine with pushing the prop up through the middle RPM bands to 8500 engine RPM.



One thing you will also want to consider is the water pump and cooling system. 8500 RPM at WOT on a rotary produces massive amounts of heat. I don't know what you're looking at for a radiator, but a stock NA radiator can't hold that kind of power output for long without coolant temperatures going rather high.



The other concern I have with high RPM operation is cavitation. With the stock pulley setup, the water pump begins having issues around 6000-7000 RPM. This isn't normally a problem, because a road vehicle is only at that RPM for a short period of time. However, if you'll be turning 8500 RPM for 10+ minutes (damn, I want to get my pilot's license...), the stock water pump will likely stop pumping efficiently. You'll want to get some racing underdrive pulleys designed for high RPM operation in order to keep the engine properly cooled. You shouldn't have any of the normal low RPM operation problems with the underdrive pulleys because you won't be running at low RPM often.



I'm not sure how you're planning to mount things, but you might want to look into a serpentine belt setup instead of the stock V-belts. Better grip, smoother running, and I know that at least some of the underdrive setups come with the serpentine belt pulleys.



-=Russ=-

j9fd3s

[quote name='Shotgun' date='Jun 23 2005, 10:52 AM']"do not make it a single port at the rotor such as the second pic shows.

it just doesnt work well."



Thanks for the pic. My next question was going to be how to join up the side, but I see you brought the two circles into a bastardized elipse. Can you elaborate on what you mean when you say it doesn't work well?



To give back some of the education I'm getting, and in way of explaing my situation. The typical propeller on a small airplane is limited to somewhere around 2700 RPM. The limiting factor is you want to keep the prop tip from going supersonic (around 650-700mph, give or take), and for a given RPM the longer the prop the faster the tip will go. You want to run the biggest propeller possible without it hitting the ground in order to get the maximum thrust. I have a 3.17 gearbox reduction. So that will allow me to run up to 8500RPM for takeoff. I'd run that level for a maximum of around 10min, then would back off to around 6000RPM for cruise.



The other interesting twist is the 'how do I get there from here' problem. You can't get to 8500RPM if the engine can't push the prop through 4000RPM. Power aborbed by the prop is a cubic relationship. The prop absorbs 1/8th the power at 1/2 the RPM.



So I revisit my original question. Can you elaborate on what you mean when you say it doesn't work well?


[/quote]



so how much power does it take to spin your prop at an engine rpm of 8500?

ColinRX7

[quote name='j9fd3s' date='Jun 24 2005, 08:11 PM']so how much power does it take to spin your prop at an engine rpm of 8500?


[/quote]



Exactly





You'll produce alot of heat pushing 3000 lbs across the road WOT and struggling to work it's way up to 8500, you won't need full open throttle even to spin 8500 RPM with just a prop. Once it hits that high the throttle can back off somewhat and maintain the RPM.





An underdriven eccentric shaft pulley will be sufficient enough, so the pump and alternator aren't stressed





And being in an air plane I don't think he's using an FC3S radiator, he will use something professional.

mazdaspeed7

[quote name='ColinRX7' date='Jun 24 2005, 08:36 PM']Exactly

You'll produce alot of heat pushing 3000 lbs across the road WOT and struggling to work it's way up to 8500, you won't need full open throttle even to spin 8500 RPM with just a prop. Once it hits that high the throttle can back off somewhat and maintain the RPM.

An underdriven eccentric shaft pulley will be sufficient enough, so the pump and alternator aren't stressed

And being in an air plane I don't think he's using an FC3S radiator, he will use something professional.


[/quote]





Actually, the prop pitch will be tailored to the engine, and ideally, it will take close to full power to spin the prop up to speed for take-off.



Radiators will need to be aviation specific, but thats not that difficult. They can be compact and thick, since there will be considerable airflow through them when done properly.



You will definately want underdrive pulleys, as much as possible. The stock pulley diameters were engineered for optimal performance at the average rpm range for normal driving, which will be considerably lower than what you see in an aircraft. The stock water pump will cavitate at 8500 rpm, and flow will be severely compromised.

Shotgun

[quote name='ColinRX7' date='Jun 24 2005, 08:36 PM']Exactly

You'll produce alot of heat pushing 3000 lbs across the road WOT and struggling to work it's way up to 8500, you won't need full open throttle even to spin 8500 RPM with just a prop. Once it hits that high the throttle can back off somewhat and maintain the RPM.

An underdriven eccentric shaft pulley will be sufficient enough, so the pump and alternator aren't stressed

And being in an air plane I don't think he's using an FC3S radiator, he will use something professional.


[/quote]



The airplane's max gross weight is 2000lbs, but the point is well taken.



Actually, if I build the prop correctly, the engine won't be able to push the prop to full speed until the airplane is moving at a fairly high speed. The maximum RPM while sitting still is often used as a crude dyno.(while standing on the brakes to keep the plane from skitting all over the place). We call this 'static RPM', and it is usually somewhere around 80% of the max RPM for a fixed pitch prop.



The most popular 'radiators' for aiplane conversions of the 13B are discarded evaporator cores from late model GM air conditioning systems. Not exactly 'professional', but they are $5 or $10 as scrap, built to withstand 200psi, and just the right size for two of them. My cooling system will have dual electric water pumps, the stock engine pump being removed and replaced with an adapter. Then engine will be up front, and the radiators placed about 7 to 8 ft nearer to the back. Air will enter through a carefully designed duct to maximize airflow. The water will be routed through finned aluminum pipes for most of that distance, so the returning coolant will be much closer to ambient than a typical radiator setup would allow. Still, cooling will be marginal on a warm day if I expect to use all that power (and I can actually get it). The solution is not to use all that power on a warm day 8*). But it is better to have the power available with the caveat that it may stress the engine installation, than to have one less option.



The alternator is being removed, replaced with two Harley Davidson permanent magnet type alternators...one at the front, one at the back. Lighter. All belts and associated pulleys are being eliminated. Smaller profile.

Shotgun

[quote name='j9fd3s' date='Jun 24 2005, 08:11 PM']so how much power does it take to spin your prop at an engine rpm of 8500?


[/quote]



Short answer: All of it.



Long answer: I'll let you know after I build the prop. If I'm able to get over 6500 RPM with the plane tied down, then I'll need to build another prop, one that is:



-longer

-has more blades

-has more 'pitch', ie. angled so that it takes a bigger chunk of air with each pass.



If I can't reach 6500, then I may need to shorten/remove a blade/remove some pitch.



Iterate until the prop and engine like each other.

j9fd3s

[quote name='Shotgun' date='Jun 27 2005, 09:22 AM']Short answer: All of it.



Long answer: I'll let you know after I build the prop. If I'm able to get over 6500 RPM with the plane tied down, then I'll need to build another prop, one that is:



-longer

-has more blades

-has more 'pitch', ie. angled so that it takes a bigger chunk of air with each pass.



If I can't reach 6500, then I may need to shorten/remove a blade/remove some pitch.



Iterate until the prop and engine like each other.


[/quote]



hmm, if we assume, on a non turbo engine, that power = rpms * displacement. displacement is fixed, and we want max power at 8500rpms, what kind of port supports that?



i'm thinking a larger street port and about 220ish hp is close

kahren

[quote name='Shotgun' date='Jun 23 2005, 01:52 PM']"do not make it a single port at the rotor such as the second pic shows.

it just doesnt work well."



Thanks for the pic. My next question was going to be how to join up the side, but I see you brought the two circles into a bastardized elipse. Can you elaborate on what you mean when you say it doesn't work well?




[/quote]





when i say it doesnt work well, i mean that it doesnt make as much power, the flow gets worse as the 2 runners become one at the rotor face. but knifeedging the 2 runners such as the first pic shows does improve teh flow and does add power. hope this makes it clear

diabolical1

[quote name='kahren' date='Jun 21 2005, 09:06 PM']bad pic, but you shoudl get the point.

what i was tryign to say is leave it as two separete ports at the rotor like it is stock. and if you made a custom intake manifold where the secondary port and aux port are one runner on the intake manifold then u can knife edge it at the intake manifold side to have it flow better then just hitting a wall. as the first pic indicates.



do not make it a single port at the rotor such as the second pic shows.

it just doesnt work well.


[/quote]

now i clearly see what you're saying. the pics were a great touch.



thanks, kahren.