Santa brought me a B-USA 1/4 scale Nieuport 17 kit. I am strongly considering going with a gas engine, but I need one that will swing a 22"-24" prop, which is in the scale range of props for this size plane. Actually I think 25+" is scale, but...

B-USA recommends a Zenoah 23cc motor, but I don't think it will swing such a prop size. Will it?

I thought about the RCV 120 SP, but I'm sure I'll need the weight of a gas motor to balance this model out.

The firewall to cowling front distance is 5.5", so something with a max of 5.75" from rear of engine/mount to thrust plate is needed. Any ideas or success stories?

Thanks... Merry Christmas!

Dave

rarely do the planes we fly these days have scale props on them,the motors we use are used to fly them not run the scale props.That is why display props are made,not for flying but for display.If we were to run motors that were able to run scale props chances are that the motor would be too big for the airframe and too high of a wing loading

Thanks fryfly.

I'm aware of the scale display prop/operational prop situation. It just won't do for me though. I'm pretty analretentive in that area.

You could try something in the 3.2 size class, like a Brison or a Fox. These should be able to swing a 24 X 8 prop. Normally they are happy with a 22X10, so a 24 X 8 should not be too much of a stretch.

I would expect about 6500-6800 rpm.

The extra weight will not be a problem.

How the plane will fly with an 8 inch pitch prop at 6500 rpm, I do not know, but I think it will be OK since this is a slow flying plane anyway. With a 100% efficient prop you would get 49 mph flight speed with an 8 inch pitch prop. Figure 85% efficiency and you end up with 42 mph.

You will probably want to reinforce the structure somewhat for the larger engine.

The 24x8 prop I believe is way too big,you'll not get any performance or the engine will run a little too hot.

If you really want to swing the big lumber - consider using a reduction drive like the old byron kits.
Try this web page:
http://www.mrmodels.fsnet.co.uk/p5kits.htm

Dave

Tommy, will the 3.2 class fit the size constraints I have as far as firewall to thrust washer distance?

If I need to run a 22" prop, I'm sure I could live with that. I just don't want to have a prop that's barely larger than the cowling, as that looks majorly silly to me. Even a 20" might be okay.

fryfly, I certainly don't want to damage or overheat the motor... I'm just thinking that there's got to be a happy medium for this plane.

canman, the reduction drives look good, but I think it would be way too long for my application.

Thanks for the ideas.

the 22x10 is a good all around prop size for the 3.2 especially if you fly a mejzlik.The new zdz 40 would probably be a good size motor for this application,but if you went with the 3.2 size motor you would have something that would be more veristale in the future, something to think about.

3W-42 will swing a 22x10 in the 6500 range. The 3W-50 will swing the 22 x 10 in the 7500 range. If you want smoothness, try the 3W-48 twin which will swing the 22 x 10 around 7000 rpms

Elson

Thanks Elson, fryfly...

Any idea where I can find dimensions on the 3W and ZDZ motors?

cactusaviation.com--------- for 3w

rcshowcase.com----------for zdz

The 3W42 looks like it might fit. I might have to recess a box into the firewall for the carb. I'm just wondering how the airframe would handle 4 HP...

Now, do these motors have magnetos, or do they run off of a battery pack?

Sorry for being so ill educated in the gas engine department.

I just spoke to Dave at Balsa USA, and he's suggesting I NOT go with a 4 horse motor. I was thinking the same thing.

I think I'll go with the RCV 120 SP, as the specs say it'll spin a 20/12 prop at 6000, so I'm thinking it might not have a problem with a 22/8.

Thanks for the help!

Dave

Since you've decided not to use the larger engine, this information is kinda moot, but nevertheless here it is. The Brison 3.2 is 5.359 inches from the rear mount face to the prop hub face. Height is 5.5 inches above the crank center to the top of the spark plug and width across the cylinder fins is 3.6 inches. The carb sticks out from the centerline 3.5 inches. The mount is a rectangular plate 2.5 inches high by 3.5 inches wide, on the centerline of the crank.

If you go to http://www.brisonaircraft.com you can view and download front and side views of their engines. You can print these and then take them to a print place and Xerox them to 100% and use them when laying out the engine on the plans.

If I were Balsa USA I would not recommend this size engine on the plane, because I would not want someone to get pissed at me if it had a structural problem, or even worse, sueing me. Better safe than sorry. But I am certain that I could reinforce the airframe to make it acceptable at a low cost and little added weight.

Thanks Tommy, I appreciate the information. I also think I could reinforce the airframe to run the higher horsepower motor, but I'm just considering the flight characteristics of a heavier plane.

I'm planning on installing DuBro pull-pull on the rudder and elevator. Along with the associated bellcranks, etc. plus flying and landing rigging I think the model will be approaching the upper end of the weight spectrum with these modifications.

I think the RCV will be a good choice. The plane has a lot of wing area (1575 sq.in.) so the lower power motor should fly it in a scale manner even if it ends up at 13-14 pounds. Of course with the relatively small diameter of the RCV, I'll be able to locate the battery near or on the firewall, which will lessen the amount of dead weight to balance the model, especially if I go with a high MAH pack.

By the way, those are some great looking models on your website!