PRSU

[Riseguy]

What percentage of power do PRSU or redrives eat up?

[DustinD]

About 1% to %15+ depending on the type. Belts are the worst, especially V-belts A simple two gear setup is about as good as it gets. Silent chains are also pretty good.

www.rotaryaviation.com and www.oriontechnologies.net/docs
have lots of good information.

[Riseguy]

I did some looking up too. About the most efficient was the spur gear. 15%
I sure would like to see the 1%. Do you have a sight I see one?

[DustinD]

I thought spur gears where typically 1.5% - 5% per mesh? I doubt the bearings and oil system would eat up much more. Car drive trains (manual not automatic) IIRC could do better than 10% but that was rare, but car drive trains have a lot more gears and parts.

Bill Husa (the owner of Orion Technologies) used 3% as an example in his paper for a 100hp engine.

[Riseguy]

I read his paper. It was theory. His test failed miserably. After doing some more research on Orion I can't except his numbers without question. The engineering books i have say 15% is about the best you can get from a single reduction gearbox. I would like to see no more than 5% energy loss. I don't want to have to put a 175HP engine just to get a 150HP output after the gearbox. On a Canard weight aft is not good.

[Marc Zeitlin]

Originally Posted by Riseguy

..... The engineering books i have say 15% is about the best you can get from a single reduction gearbox. I would like to see no more than 5% energy loss.....

I can't tell you how to design for low losses, but a cursory google search brought up:

http://gltrs.grc.nasa.gov/reports/20...003-212222.pdf

which indicates that efficiencies of gear trains can range from 80% to 98%. So it SHOULD be possible, if correctly designed and tuned for the system in question.

I would think that folks selling PSRU's (not PRSU's) would have performed dyno tests to determine power losses. Also, a PSRU that was absorbing 10-20 HP would get freaking HOT.

[Riseguy]

Thank you Mark for the look up. The information was spot on for what I was looking for.
From my experience with gear reductions they do get real hot.

[rv6ejguy]

Single mesh helical gear sets are typically 98-98.5% efficient. Just think about the heat generated if you are talking about a 15% loss on a 200hp engine setup. About 22,000 watts. To visualize this, focus fourteen 1500 watt electric space heaters on your redrive and see how hot it gets! Obviously not the case.

My Marcotte drive (integral oiling) oil runs well below the coolant temp at all times with no cooler in the system.

[MarbleTurtle]

So what's wrong with belt redrives?

[DustinD]

The belts in belt drives usually need to be replaced often. For ultralights some only last 50 hours, some of the better belt drives for larger airplanes go for 500 hours between replacements. Some may go longer, I am not sure.

I just found out while searching for this post that the giant Poly V belts that are several inches wide can last several thousand hours. They seem to be used on many helicopters that are around a few hundred HP.

There are a few belts that do about as good as gears or silent chains for efficiency, but most loose more hp. Blower belts for example would not work, plus they have low RPM and torque limits for continous use. One possible exception are the metallic belts that are used in CVT (constantly variable transmissions) They can get 98% efficiency. Almost any other belt that runs of friction would not work.

The alignment between the belt and pullies must be nearly perfect or belt and or pulley will not last. I doubt this is a big deal, but something to watch out for.

You also may need to ensure proper airflow so that they do not over heat. They also have to be protected from FOD damage.

If they have to deal with significant torsional feedback issues they will fail very quickly.

If you use two belts and one breaks it is likely to take out the belt(s) next to it. I am not sure if you can realistically use guards to prevent this.

www.homebuiltairplanes.com has a lot of great threads on the subject by engineers and people who have designed reduction drives.

www.epi-eng.com Also has some great information on redrives in general, not so much on belts.

I guess belts can work if it is done right, but I have seen many that where not done right.