Hi all,

We are considering to use one of 3W engines in a custom aircraft application.
I guess the power output of 3W 157 will be ok for us.

My question is about the RPM-power matching of 3W engines. They are giving the working RPM range as 1100-8500 in the 3w site. We will need to run the engine almost all the time at 8500 RPM.

In this case the vital question is: Can the engines run at this maximum 8500 RPM continuosly?

The second question is: Does anybody have some estimate for the ratio of power available at 8500 RPM to the maximum power?
I mean I know that these engines are designed for low RPM high torque applications (written in the manuals), but I can't know what they mean exactly with low RPM range and high torque values.

So for example what would be the continuous power output of a 17 HP 3W 157 engine at 8500 RPM exactly?

Thanks all for your help...
RIHA

To start off .....welcome to the Flying Giants, if any place here is the place where you"ll get answers unfortunatly I will not be the one giving them

A simple answer to the first question is NO ! rated values are max and min. and are usually not even obtainable specially in the max. area. Can you drive your car with the RPM meter deflected all the way in the red......simple answer is no cause you'll burn the engine out or dramatically shorten its lifetime.

I have yet to see a 3W 157 running at 8500 so I think what would be better for your application is you go a size bigger in engines and then you'll get exactly what you need.

Just my 2 cents worth.

Compared to other 2 stroke engines in the 150 to 175 cc range... 8500 rpm's is low.... (The motorcyle engines and gokart engines are over 10 or 12k rpms)...but typically we fly'em with props that turn in the 5700 to 6000 rpm range...

I think if you can keep the temps reasonable, and the torque demand low, they might run 8500 rpm's... but I don't have personal experiance with that. Maybe call/email AI or 3W?

The 8500 rpm figure would be attainable only with a small prop, (very small for this engine, and I can't guess what it would be) or with the engine unloaded. Typical peak rpm's with this engine are 5600-6100rpm depending on prop, field elevation, weather conditions, and exhaust system used. Look in the section under "Real world RPM's" here and you can get an idea of what to expect.

Use a Gear box to run at a good constant speed

DA 170s in our race planes turn 10,000 with a small diameter(22?) but high pitch(26?) prop...Don't know for how long, a heat race lasts only about 3 minutes at WOT,around 220 mph
usrainfo.org

Many thanks for these fast replies.

We are thinking about replacing our lousy home made (or converted) engine with this 3W engine and don't want to throw away 1500-2000$ in case of not fitting into our aircraft. We already have a gearbox and re-manufacturing it can be a nightmare for us.

According to my calculations our torque requirement at 8500 RPM will be like 9 Nm
(or say 6.5 ft.lbf). That gives us a power output of 10.7 HP .

So, if a 3W 157 engine, supposed to give its maximum power output (17.5 HP) at 5700-6000 RPM, can give us at 8500 RPM without overheating problems a power output of 10-11 HP, this engine will be a nice shot for us.

I guess I'm going to take this shot

I don't know about the rest of these guys but you are makin' me crazy not knowing what this plane is !

Pic's please !

I also get the feeling you need the 8500 to run a generator of some kind ?

there's a nice competition series 157 on RCU and they only want $1000 for it.... just so you know!

Maybe there's a reason that there's no pictures here.

That's something like a student project in our univeristy.

We have been working on it for almost 1 year now.

It is a rotorcraft actually. As I mentioned before we were using a converted engine but I think now it is a big mess. We don't want to go into the gearbox manufacturing business again, so we need an engine at 8000-9000 RPM range to use with our current gearbox.

That's why I'm seeking for some ideas here. The 3W guys say that they take no responsibility for improper or custom usage of their engines, so I think they won't help us.

That's all.

By the way, I tried to put our vehicle's image here, but I'm not sure i'm successful in that. If not I will try it again.

You can see it on my user page in albums...

Also... Consider a Hacker A1100 or A200 electric outrunner.... the technology is getting very good.
http://www.hackerbrushless.com/motor...eries=A100/200

If this is a university project, possibly there can be some donations/price discounts.