wilerbee2

I have a OS 46 VX-DF engine and I plan to fly it with a prop instead of duct fan unit. I will be using a weston uk genesis mini pipe with it. Can anyone suggest a prop size and the amount of nitro fuel and lubricant mix ? Any help will be most appreciated.

Wilerbee

bob27s

My Feedback: (19)

What aircraft do you intend to use the engine on. That will have some factor in the prop selection.

wilerbee2

I am planning to build a F-8 cruasder for the engine. If successful might consider producing kits. My aim is to get it to go fast. I hear that if the prop is too large it'll seize the engine so I am treading carefully here.

Mike Connor

My Feedback: (5)

O.S. claims 2.5 hp @ 23,000 rpm. That would suggest an 8x7 as a starting point.

AlexF

For the .90 size ducted fan engines, lots of folks used wildcat 5% nitro 23% oil ducted fan fuel in my area. I never used anything else in fan engines, and it turns out a lot of prop 2 strokes like it too. I think the oil in the wildcat fan fuel is supposed to be lower viscosity than normal so that's why there's so much of it.

for the high reving engines that I've had too much prop on, it's fairly obvious that something is wrong when you try to set the top end needle. You can get it way too rich or slightly too lean, and nothing in between. The needle acts inconsistently at that point. As long as you recognize that this means not to fly it, you won't blow up your engine : ) Check that it tachs at a reasonable rpm, if you don't use the tach to set the mixture anyway

Rudeboy

If you want to run it in its intended rpm band, try something like an APC 7.4x8 or 7.4x8.25... but these are not really suited for prop jets though...

wilerbee2

Do any of you guys think that the F-8 is a good subject for a kit ? I'm thinking that with the layout of the plane,especially with the intake, the reverse mounted engine will be hidden. The reason for a ducet fan engine is also to hide the tune pipe inside the fuse, so only the prop is visible. I'll build an exhaust tube that runs through the fuse and exits at the rear, just like a duct fan.
If anyone has any comments and suggestions they are most welcome.

Thanks for the help and keep them coming.

Willis

Mike Connor

My Feedback: (5)

Nothing wrong with a F-8 but I have to agree with Rudeboy that a DF engine would not be the best choice. I would put the DF engine on something light and clean.

Flyer95

My Feedback: (1)

Wilerbee2,
Are you gonna use that engine as a puller or pusher?
IMO as long as you are careful with your prop selection, settings and the fuel you use then you are on the safe side. 5-10% nitro should be enough but use at least 20% oil (more is better) castor/syntetic blend, as a wrong setting would heat up the engine rapidly. If you can lengthen the header on your DF-pipe then you would probably be able to use slightly bigger props at lower rpms and get a more stable high speed setting. Check the props to be healthy before every flight. Wooden props are good and light, but loud. CF-props are the best but expensive[].

I would not use APC:s on the 90sized DF-engines but maybe on a 46 it is slightly safer.
If you use APC:s then check the props after every running and if you see a new white line (usually near the hub) then trash them[], or the prop might explode on the next run[X(]. Good luck, Amir

bob27s

My Feedback: (19)

Ditto

F-8 would be a welcome addition to any fleet.

But the DF engine could best be used elsewhere. Best prop choice as noted would be the APC QM40 carbon 7.4x8 prop. You can turn more prop with the fan engine, but you have to lengthen the pipe far beyond what it is set at for use with a fan.

wilerbee2

Thanks for the input guys!! I am using the engine as a puller and the idea of a duct fan engine is that with rear carbs and rear exhaust the only thing sticking out is the prop and you won't see that in flight. I'll have a fibreglass tube running from the exhaust to the jetpipe so the smoke will come out the rear !! Just trying to get that scale look. I'll probably test fly with a normal OS 50 sx first then move on to the duct fan engine after learning the characteristic of the fan. The plane will be as close to scale as I can get it. I am trying to make it LOOK like a small jet turbine. I will be building a prototype with boxy fuselage first before moving on to a scale looking one.

wilerbee2

OOPS ! Just remember that Jett has a front carb rear exhauxt engine !! That is a better choice ? Bob27s I think you'll be getting an order from me soon !! I haven't decided on the 46 or the 50 any suggestions ? Thanks

bob27s

My Feedback: (19)

Wilerbee.....

The fan engine you have will work pretty well as long as it is set up properly. Using a standard sport engine for test flights is probably a good idea... gives you more of a range for prop selection, and just is 'simple'.

The Jett FIRE .50 or FIRE 60LX would be good choices. Either BSE or cast case. Either gives you the capability to pull a full size 10" prop if desired. If you were going to run the pipe through the fuselage, you would might want to consider the welded straight-header and pipe assembly (similar setup used on a diamond dust). Riser header is also available.

When you build the pipe tunnel, allow some room around the pipe for cooling air flow.... about 4mm clear of the pipe OD.

Bob

cwrr5

My Feedback: (32)

Why not just make it a ducted fan model? If I understand it correctly, you plan to run a tube to the back anyway, just add a fan unit. [&:]

wilerbee2

cwrr5,

Actually I was thinking of maybe a 6 pound thrust turbine as an option. The size I have decided on is around 1.4 meter span and 1.8 meter length. I am trying to get to be as close to scale as possible so still playing around with numbers. With duct fan not a lot of folks here know enough about it and even less wants to deal with it here. The reason I'm thinking a kit is that quite a few of my fellow flyers would like to buy one if my prototype flies well. They prefer simple prop jets. Who knows I might just get one of the RC plane maunfacturers to make an ARF kit if I can get him to buy the idea !!