Control Line JET airplane

I have found a set of plans for a control line jet airplane. The engine is mounted pointing straight up inside the center of the wing. The propeller is inside the top edge of the wing too. The built up fuselage has things on the side that look like jet engines that are really air intakes for the propeller. The air comes in the intakes on the front of the fuselage then through the propeller then out the back part of the jet engine on the back part of the airlane. Its basically a propeller powered jet engine. It looks like an interesting idea. Plans do not show any detail on how to get then engine started. Maybe the crankshaft can be extended out the top of the fuselage or the canopy can be removed to get it started. Seems like it will work as long as the area of the jet engine intake and exhaust are the same as the area of the propeller. Has anyone ever seen an airplane built like this?

Hi Gary,

I suspect what you're looking at is a "ducted fan" plane. Very popular "jet" design for RC. Be interesting for control line.

It is not a ducted fan. The sheeting on the bottom side of the wing is plywood. The engine mounts are hard wood glued sticking straight up from the plywood wing sheeting. The engine is mounted on the hard wood inside the wing and fuselage. The motor sticks straight up. The propeller is about flush with the top part of the wing with a circle shape hole cut in the wing sheeting on the top side of the wing. The jet engines are built wide enough on the fuselage to cover the entire propeller. The air blows out the back of the wing then out through the back part of the jet engine. This is not a ducted fan.

Gary,

It's still a ducted fan (sounds like). The method of ducting, the layout or the purpose doesn't change the type. It does sound like an interesting project, though. What is the theory behind this method? What's the intent?

edit: typos

>It is not a ducted fan. The sheeting on the bottom side of
>the wing is plywood. The engine mounts are hard wood glued
>sticking straight up from the plywood wing sheeting. The
>engine is mounted on the hard wood inside the wing and
>fuselage. The motor sticks straight up. The propeller is
>about flush with the top part of the wing with a circle
>shape hole cut in the wing sheeting on the top side of the
>wing. The jet engines are built wide enough on the fuselage
>to cover the entire propeller. The air blows out the back
>of the wing then out through the back part of the jet
>engine. This is not a ducted fan.
>
Gary,

FWIW, what you describe is not a *conventional* ducted fan, but it is still a ducted fan of sorts. It uses ducts to re-direct at least part of the output of a propeller (fan). If *all* the airflow passes out of the ducts, it is a ducted fan with a 90 degree bend in the ducting (inefficient I would think). If air can pass through the bottom of the model so the propeller produces thrust in the vertical direction (aka lift), then it is a *helicopter*. From your description, it sounds like all the air goes out the ducts. So I vote for calling it a 90 degree ducted fan arrangement. Having access to the prop makes it possible to hand start it...
This sounds like a real oddball--a one-off. Typical of the many innovative novelty designs from the 1950s which I find so interesting and fun. Any chance you could post some sort of picture to help us better understand this beast?

You are right on both counts. It is not a conventional ducted fan but it does direct the air through ducts. I can see it will need an extension on the needle valve so it can be adjusted. The canopy will have to hinge up or come off to get the engine started. I found the plans Sunday I spent about an hour looking through my pile of old plans. I don't recall who the plans were by, Hobby Helper, Model Airplane New, or some other. Many of these plans have no name. I will look for the plans again and post a pic.

There is another set of plans that looks like a large donut built into the spar section of the wing. The engine mounts in the center of the donut and the propeller turns inside the donut. The propeller pulls air in the front and blows out the back along the length of the fuselage like a normal airplane would. This is a realy stupid looking contraption I would never build anything that looks this goofy. If the donut thing were changed to look like a 10" diameter jet engine body about 24" long with wings and a tail built right on the jet engine body it would look sorta like a flying jet engine. It would still be goofy looking. Most of these plans are dated from about 1952 to the late 1960's.

There is a whole body of literature on ducted fan design.

It turns out there are a lot of subtle relationships between the ratios and proportion of the air intakes, the fan, the duct dimensions, the fan placement, the flow straightening fins, and so forth that can make as much as a couple of orders of magnitude difference in the amount of actual thrust coming out the back end of the "jet" exhaust.

Be prepared to do a lot of experimentation and rework to get fan that works well with a long duct.

Or just buy an off the shelf R/C ducted fan and embed it in a fat tube fuselage.

Sounds like an early Harrier...Real early.

>Sounds like an early Harrier...Real early.

Actually, this is sort of true. To place this beastie in context, my best guess is that it dates from the early to mid 1950's. The jet age had arrived, jet fighters were the cutting edge (Korean War) and modelers were eager to build "jet" models. This is the simplest approach that would yield something like a "jet" in the form of a crude ducted fan:

(1) Uses a conventional engine and propeller

(2) No special materials

(3) Can be started in the conventional manner by flipping the prop

(4) Novel design. Simplicity is attained by having the fan axis and thrust axis at 90 degrees to each other. Makes (1)-(3) possible.

This pre-dates electric starters, modern ducted fan technology, and turbines. I would argue it is an early first step toward the modern ducted fan, and ultimately toward turbines. Each represents a technology developed to satisfy the model builder's passion to replicate jet flight as realistically as possible. In this context, such a model is a fascinating early step along that road.

JMHO,

Gary-

FWIW. Roy Clough, Jr., that zany designer of all things imaginative and sometimes whimsical, once published a jet FF (ca. 1940's-1950's)that drew air into the fuselage from a hole in the upper surface and directed it rearward through a "Jet" exhaust via a centrifugal blower whose impeller turned the flow 90 degrees. Well, actually, I think it built up pressure in the fuselage cavity that caused the air to be exhausted rearward through the provided passage. Like all of Roy's designs, it had several revisions and optimizations behind it, ensuring that models built from the article would fly.

Is Roy Clough, Jr. still around? Last plane I saw that he published was, I think, called the "Stunt Goat".

I used to marvel at his ideas in the 1950's. If you build some of those designs remember that engines of that period could handle an aluminum or fabricated fan. Today's engines would spin them into missiles. Remember the one that had slats instead of wings.

One problem in using ducted fans for CL is, if I understand correctly, the fan gets more efficient when the velocity of the plane approaches the airspeed inside the duct. This would be great for a scale plane if you just go 'round and 'round, but not for stunt where you make abrupt changes. Anyone know for sure?

Gary, I'm not trying to discourage you from experimenting. I know these type of designs probably picque your interest. You might look up some Roy Clough designs.

Some of Roy's designs were named after planets.

George-

>Is Roy Clough, Jr. still around? Last plane I saw that he published was, I think, called the
>"Stunt Goat".

Yes, he published two or three articles in Flying Models a couple years ago, one on using Design CAD and one of a model with a unique airfoil structure. My favorite was his slotted saucer FF (AT 8/52, I think). Mine flew away with a cox .020. I don't think there ever was another modeler/designer/researcher more imaginitive than Mr. Clough. He was also quite prolific in his published designs, especially considering that some of them required building series of several models each in order to get things balanced and working, since his models often had no previous designs to emulate. Many of them researched some original or offbeat idea. It seems that he has been published over a period exceeding half a century.

A link published here recently accessed at least three Clough designs on a site where CL and FF plans could be downloaded.

You guys have given me an idea. This idea probably is not useful for anything but it might be educational. I know if you have air flowing through a pipe at a certain speed and you funnel the exhaust end of the pipe down smaller an increases the velosity of the air exiting the pipe. If someone were to build a pipe device around the propeller of an airplane and funnel it down a few inches smaller than the diameter of the prop it should increase the air velocity and make the airplane fly faster than before. I know this is not practical and would look stupid on the front of a fuselage but it should work. I think I will experement with this ducted fan airplane engine idea by building an RC car to see how well it works. I built a car design last night with cardboard. I designed it around a norvel 15 engine. It might be best just to build the ducted fan part and make a test stand to see how much air pressure it produces compaired to an engine with a propeller.

We put a leaf blower on a skate board and WOW, it takes off quick. We took it to a large parking lot my son can not keep up with it on a bicycle. I tried to keep up with it in my truck. The skate board can pick up speed faster than my truck at 60 mph it left me like I was parked. The skate board shot off the end of the parking lot into the 3 ft tall weeds and stopped. The leaf blower has a sticker on the side that says 150 mph air. If the weight of this leaf blower could be reduced it would probably power an airplane.

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