CEF speed contest Design Discussions (2014)

Roddie, did Cox make a jet engine?

Oldenginerod wrote:Roddie, did Cox make a jet engine?

No Rod.. but this wouldn't be the first jet model to be built for the speed contest.

Doug (GUS THE I.A.) built this cool A7 for the first contest.



I had considered an F-20 Tigershark.. but decided on the T-33 instead. There was a fan unit designed for the Tee Dee. I don't think it would work well with control-line though. It also wouldn't qualify for this "profile" event.



I think "Kress" made one too. Here's a model with a Bee powered fan unit.

modelbuilder49 wrote:No Rod.. but this wouldn't be the first jet model to be built for the speed contest.
Doug (GUS THE I.A.) built this cool A7 for the first contest.
I think "Kress" made one too. Here's a model with a Bee powered fan unit.

Man!! Now that's jus' downright KOOL!!   Ya' done good, real good![/quote]

Not mine Jim! I don't know who's model that is with the fan. I save random images that interest me. I really like it though.. because it's Cox powered!

The more I look at it.. the more it looks like a free-flight model..

rogermharris wrote:You know was doing a search yesterday and saw educated fan blades made for cox 049's

"Kress" made fan units for the Tee Dee years ago, having I believe an "RK" designation in the model#. I'll see if I can find a pic.

The "Axiflow" RK-049 was a Kress fan kit that I remember seeing in magazines years ago. I found these images. I don't think it was in production very long.






With all the high performance engine tuning that takes place on this forum.. along with some really skilled builders.. I'd love to see one of these kits utilized. Back when these kits were being made, radio gear was HEAVY.. compared to what it is now.

rogermharris wrote:Now that is cool!  I would like to see it on a set of control lines

I suppose it's possible Rog. It would have to be strictly a roundy-round model.. and have a smooth runway for take-off. There's not enough area for any kind of tight turns in a control line circle. I'd still like to see it though. The Dynajet wasn't a stunter either!

Mike Mulligan wrote:I had one of those RK-049 fans when I was a kid. If you want to try to fly one control line you's better have a smooth lot to fly from and expect a five-lap take off run! Definately 'top gear' only!

Roddie, I'm really looking forward to seeing your T-33 take shape. Your models are always interesting, well thought out and well built. Cool subject too! I had given some thought to an F-94C for a TeeDee, but I should probably just finish what I've already started...

Post lots of pics!

Mike

Thanks Mike! I saved a 3-view of an F-94C when gathering images for the T-33.



I know all about the finishing what I've already started thing.. It's never too late to get back to something that was put on the back-burner.. or should I say; "after-burner"

Ken Cook wrote:The Dynajet will stunt fine if the airframe and tank are correctly built. Unfortunately, while it is a reed engine and this is for Cox engines I just wanted to show that it will stunt. Here's my son https://www.facebook.com/PhillyFliersCL/videos/vb.513140418756097/858020277601441/?type=3&permPage=1 I'm on the spark box and launch. Pete one of our senior members shouldn't of been pumping. Hopefully by next season we have another built as were going to do this 2 up. Dan was quite excited as he was able to increase the run time a bit but still not enough for a pattern. That was 19 oz's of fuel for that flight.  Ken

Nice flying! You guys sure know how to have fun!

The T-33 will be my first Tee Dee powered model. I just took some mount measurements. The case width; I get .650" with .930" O/C; beam to beam and .375" F/R. Back-plate to drive-plate face is 1.700".

My entire fuse is a lamination of ply/balsa/ply.. so there will be no beams. It's thickness is .250" nom. and should be beefy enough for the mount. I'm thinking tonight about bushing the mount holes. I really like those 4-40 threaded inserts that Jim found and used on one of his models. I don't think I'd trust them in my ply/balsa/ply lay-up though. I'll probably go with locknuts.

Here's a cross-section of my lay-up. 2.8mm luan sides with a 1.2mm balsa core.



It's very rigid.. but actually not that heavy. The blank weighs 1.6 oz. but when the fuse is cut and shaped, I expect it to be down close to 1 oz. I designed the fuse this way because of the take-off dolly. The belly engages a cross-pin in the cradle via a vertical slot located close to the airplane's balance point. This area needs to be strong, and I wanted to avoid sheeting around the slot if possible. The nose-to-tail lamination is smooth-sided and doesn't require any doublers.



I hope this take-off dolly works. I have concerns.. but nothing ventured, nothing gained. I've haven't seen any other designs that use an incline.. but I'm counting on that to provide lift and prevent the model from pitching down as it lifts off the pin. The cradle concept has it's limitations. The fuse needs to sit down between the rails deep enough so that the model doesn't "teeter" from side to side. This requires the model's wing to be mounted possibly higher than the scale location.. depending on the design. I'm also not sure if the dolly's main gear is spread wide enough.. and how the dolly will track. I had thought about building a caster-type tail-wheel.. but that could create it's own set of tracking issues. I always seem to over-complicate what should be simple.. but the dolly concept I think is key to getting a successful launch with these little Speed models.. as well as having provision for a pin-stooge in case there's no pit-man.

Ultimately.. I'd like to design a take-off dolly for general 1/2A use.. that supports the wing rather than the fuse.. but staying with the incline principle. A lightweight frame having a wide stance.. widely-spaced gear and large foam tires/wheels that roll easily over grass, like I mentioned a while back.

rogermharris wrote:How about a set of wheels made from a ply and or balsa skeleton skinned with monokote?
Would bee able to make nice wide light weight wheels for grass

That's the idea Rog.. I had thought about making them from 1" thick Styrofoam about 3" diameter.. with the hubs bushed with aluminum tubing epoxied-in for the axles to pass through. The gear is the trick... I think the legs/struts should be two separate vertical pieces having a wide-track for stability. What I have now is an inverted "V".. and I think it's going to be problematic. The dolly frame should have an open center-section to accommodate any width/depth fuse.. and have pads for the wing and tail-plane to rest on. Pegs with padding would hold the leading-edge from moving forward on the frame. It's a tricky thing to design without being to heavy and complex.. or else I'm sure we'd see more of them. I like a challenge.. and I will definitely keep going over design considerations in my head until I come up with something that's not too complicated.. and can be made using common goods.. like paint-stirrers and wooden dowels.