[kip51035]

I have a couple of Rossi .81 ducted fan engines. I was wondering how they would run with a prop. Due to the shape of the new cylinder head, I would suspect that there has been a large increase in the stroke. This should mean good torque. These engines look like they are new with very little run time.

[davidmc36]

Not sure what they do to these to make more RPM and HP, bigger carb? since you can alter max RPM by changing the carb throat size?

These have the same bore and stroke.

http://www.mecoa.com/kb/aero/aircraft.htm
http://www.mecoa.com/kb/aero/ductedfan.htm

I was just looking at the 1.00 size.

I would expect you to have a shorter stroke in a higher RPM engine, if all other things were equal.

Hard to say from the photos but that rear mounted carb on the DF version sure looks like it has a bigger intake.

First instinct for me would be to carb it the same as the "aero" version.

[williame3590]

The trouble with DF engines swinging a prop is trying to get a low idle for landing.


Bill

[davidmc36]

Originally Posted by williame3590

The trouble with DF engines swinging a prop is trying to get a low idle for landing.


Bill

Which leads me to think it has a lot to do with the carb size.

[smoknrv4]

I've had some experience with this, and it works awesome for speed applications, with the proper CARBON FIBRE Prop, very clean airframe and patience. DF engines are high timed, usually an exhaust duration period per stroke of 180 degrees or more so you must get them into their "happy" running Rpm by prop trimming a header length. Those DF engines in that size range, .80-1.00 ci, usually like to run about 20-22000 peak rpm on the ground. So you need to aim for that with the prop. Then you have to install it on a clean airframe so the drag isn't too high in the air to allow these engines to unload properly in the air to their "happy" rpm, otherwise they just overheat and run like crap.
These should never be run with regular glass filled nylon props to these rpm's because the tips wil break off and that's dangerous, you can get away with wood props for tuning, that are tight grained, but they are not ideal for actual flight. With the OS 91 VRDf I have played with, I use a home made continuous strand carbon fibre prop moulded after a APC 10x10, with the diameter only 9", so it's a 9x10, other sizes that work good are 8x12, 8.5x 12.5, or there abouts. Needless to say props for these are hard to come by and can be purchased with a little research, people do make them.
There is a photo of a good example of airframes that are clean enough for these engines.
Hope I haven't bored anyone.
Cheers

[smoknrv4]

I've had some experience with this, and it works awesome for speed applications, with the proper CARBON FIBRE Prop, very clean airframe and patience. DF engines are high timed, usually an exhaust duration period per stroke of 180 degrees or more so you must get them into their "happy" running Rpm by prop trimming a header length. Those DF engines in that size range, .80-1.00 ci, usually like to run about 20-22000 peak rpm on the ground. So you need to aim for that with the prop. Then you have to install it on a clean airframe so the drag isn't too high in the air to allow these engines to unload properly in the air to their "happy" rpm, otherwise they just overheat and run like crap.
These should never be run with regular glass filled nylon props to these rpm's because the tips wil break off and that's dangerous, you can get away with wood props for tuning, that are tight grained, but they are not ideal for actual flight. With the OS 91 VRDf I have played with, I use a home made continuous strand carbon fibre prop moulded after a APC 10x10, with the diameter only 9", so it's a 9x10, other sizes that work good are 8x12, 8.5x 12.5, or there abouts. Needless to say props for these are hard to come by and can be purchased with a little research, people do make them.
There is a photo of a good example of airframes that are clean enough for these engines.
Hope I haven't bored anyone.
Cheers

[smoknrv4]

Sorry about the double post.

[pianodude]

Originally Posted by smoknrv4

I've had some experience with this, and it works awesome for speed applications, with the proper CARBON FIBRE Prop, very clean airframe and patience. DF engines are high timed, usually an exhaust duration period per stroke of 180 degrees or more so you must get them into their "happy" running Rpm by prop trimming a header length. Those DF engines in that size range, .80-1.00 ci, usually like to run about 20-22000 peak rpm on the ground. So you need to aim for that with the prop. Then you have to install it on a clean airframe so the drag isn't too high in the air to allow these engines to unload properly in the air to their "happy" rpm, otherwise they just overheat and run like crap.
These should never be run with regular glass filled nylon props to these rpm's because the tips wil break off and that's dangerous, you can get away with wood props for tuning, that are tight grained, but they are not ideal for actual flight. With the OS 91 VRDf I have played with, I use a home made continuous strand carbon fibre prop moulded after a APC 10x10, with the diameter only 9", so it's a 9x10, other sizes that work good are 8x12, 8.5x 12.5, or there abouts. Needless to say props for these are hard to come by and can be purchased with a little research, people do make them.
There is a photo of a good example of airframes that are clean enough for these engines.
Hope I haven't bored anyone.
Cheers

I want one!

[smoknrv4]

You need one John! LOL

[davidmc36]

Originally Posted by smoknrv4

....Hope I haven't bored anyone.
Cheers

Heck no! Not even close to boring. Interesting to see what you have done with a "non-standard" application. Nice to have the advice about props too, may help somebody avoid frustration or worse if they want to use this type of engine.