1/2A Ducted Fan - Project Skyray - RC Groups
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Mar 01, 2002, 11:10 PM
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1/2A Ducted Fan - Project Skyray

1957 Berkeley Models - 1/2A Ducted Fan - Douglas F4D-1 Skyray

This is a stick and tissue kit of the Douglas F4D-1 Skyray. It has a 25" wingspan with 250 sq. in. of wing area and a FF weight of 10 oz. an was designed for Cox .049 Thermal Hopper or .049S OK Cub engine. The Stanzel Monoline option weight is 11 oz.

I purchased this kit complete and plan to copy it and convert it to micro r/c use. The kit supplied impeller is a soft stamped aluminum piece that I would like to replace with a modern blade, as well as the powerplant.

The remainder of the design will be left as close to the original with the exception of film covering and radio installation.

Due to the pusher configuration of the design, the only motor option is a reed-valve, as this is the only modern .049 that can be run clockwise that I am aware of.

Reports from other modelers recommend the replacement of the aluminum impeller, as this only had enough thrust and efflux to only carry the glide of the model and would self destruct after a few uses.

I have found a temporary replacement impeller to experiment with, it is a Veron Type C nylon unit that out of production (I have heard) that is specified for .061-.074 engines, but the diameter closely matches the 3.625 inner thrust tube diameter, which the kit is designed around.

My experience with Cox engines as a controline flyer tells me a Killer Bee engine will have enough power to turn the blade respectible rpm. The packaging supplied with the blade indicates the rated engine size was given with older type engines that are not even produced anymore, such as "AM10", E.D."Bee" and "Racing Diesels". There is no date anywhere to be found on the packaging, but it looks quite old to me.

The impeller has 9 blades pitched at an approximate 35-40 degrees, and each have a slight cup and are .687" blade width. The hub diameter is 1.750" with a 3.625" overall diameter at the blade tips. The stock kit blade is a six blade with an approximate 15 degree pitch and by the looks of it, it would not survive one run on a Cox Killer Bee.

Any suggestions on the build-up of this kit are more than welcome, especially as far as experimental blades and powerplants. My research for other suitable blades of this diameter produced no results with the electric D/F crowd.

There were many suggestions to drop the .049 and convert it to electric D/F, but this goes against my desire to keep it gas powered for longer flight times and the shear enjoyment of hearing a 1/2A motor scream agian as I did when used to flying controline.

With a modern powerplant, impeller and a micro two-channel R/C unit, this elevon controlled delta wing should be an outstanding flyer at a reletively low cost initial investment and operating costs, with lots of fun building involved.

Anyone with 1/2A D/F experience, or anyone really, that has any thoughts as to how I should proceed with this project is welcome to add any comments or suggestions to help my lack of knowlege with D/F planes, as this is my first attempt in this area of design. I am only going on the study of the plans as I go about this conversion to R/C and the update on the powerplant.
Last edited by jetpack; Mar 01, 2002 at 11:25 PM.
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Mar 26, 2002, 06:23 PM
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dave morris's Avatar

This is what I was working on
Mar 26, 2002, 08:25 PM
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Double D's Avatar
I remember reading the ads in RCM years ago for .049 fan units.
Try a web search for RK 709 or (RK 049?), Kressjets maybe? I do remember the ad stated 16 oz. thrust with a TD .049. Good luck.

Dave, very cool! Need more info on that unit.

Mar 27, 2002, 12:26 PM
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dave morris's Avatar
all home made using 1/32 and 1/64 ply. AME 061 rc enging on 35% norvel fuel. rotor dia 2.4 inch, 1oz integral tank, about 12oz thrust. I have flown it on a small pylonest type plane, (mounted on a pylon) and also fitted it into a syrofoam F-16 made by robart. Both flew but the F-16 gave up a lot of thrust due to the poor ducting arangement I had (ended up with about 5oz). Noisy as all get out, but reliable and throttle worked very well. All up weight of the unit dry was about 5.5 oz. It could be made lighter but I got out of the project to pursue electric power. The biggest problem was getting it started, would frequently spin the rotor off and the mess was awful. The eletric versions look alot better as far as less fuel proofing, and the use of the power pack as the Rx pack. I would try it again if I could get a rear exhaust engine that would allow for a tuned pipe. I saw the Toki unit up close and it looked pretty good but was a bit larger that I wanted at the time.
Jun 13, 2002, 05:37 PM
Stefano Spalding Baron
A cutted prop wouldn´t do the job ?
Oct 22, 2008, 04:15 PM
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Here's an .09 that has rear exhaust. It might be a little big for your project though.