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View Full Version : Oshkosh Comet- a blend of Steve Wittman designs


forresterace
10-29-2006, 01:36 AM
I've always enjoyed re-designing rubber-powered designs for electric power. A while ago I discovered Paul McIlrath's very cute rubber power model (24" span) called the Oshkosh Comet. He intended it as a tribute to Steve Wittman's homebuilt aircraft designs. This model appeared in the May 2003 issue of Flying Models. I was instantly drawn to it. This was probably because I currently have a scale Tailwind project underway (if a bit stalled).

Anyway, after some time at the drawing board, I had a set of up-sized drawings to build from. I added ailerons, almost eliminated the dihedral, added a wee bit of wingspan as well as control surfaces and beefed up the structure a touch. The span is now 38" and the area is 237 sq".

With an Axi 2212/20 on 3S 700 mahr lipoly cells the projected AUW is about 14 oz.

Now that all the bits are more or less finished it was possible to pin them together to get a feel for what the model looks like. I quite like it - it sure looks a lot like a Tailwind/Cougar/Buttercup.

Doug Forrester

buzzbomber
10-31-2006, 02:59 PM
You've certainly captured the Wittman 'essence'. It looks very nice in the bones, and I'm sure it will look even better all done up. Looking forward to seeing her finished up.

Dereck
11-02-2006, 03:38 PM
Hi Doug
Lovely job!

Love those cheek cowls - are you going to remove them for covering, then stick them back on atop covering, or what?

Will we see the plans published anywhere? I should imagine any editor would be happy to see something of that quality hit his desk.

Regards

Dereck

forresterace
11-02-2006, 07:08 PM
Hi Dereck

Yeah, as far as the cheek cowl mounting is concerned - I glued in two cross-fuse 1/8" dowel pieces for the cowls to plug onto after the nose is covered. I'm going to use Doculam and then paint it.

Plans are a bit of a problem these days. I'm just not getting much shop or drawing board time lately (I still draw with pencil on paper) - a bit of a dinosaur, I know, but I prefer it. There is a HUGE difference between plans sufficient for me to build from and plans suitable to sell. I know, I've been there and done that.

Anyway, we'll see.

Also, I thought some might like to see the almost complete, scale Tailwind fuse. It, unfortunately resides on a shelf at the moment awaiting renewed inspiration from me.


Doug

Dereck
11-03-2006, 12:36 AM
Hi Doug
Doculam should do you fine - I messed with painting some way back, was tricky to remove the paint afterwards! I recall it was ordinary Krylon from a spray can and that I only washed the Doculam down with soapy water before spraying.

Ever seen that technique of clear doping coloured tissue atop Doculam? One guy in England did it years ago, I used to have his mag article but suspect it may have rotted away by now. Looked really good, but alas, my dear Sue is very allergic to dope fumes (though house paint doesn't seem to be a problem ;) ) so any kind of 'real' covering is out for me.

Plans - I've published a fair number with various magazines, UK and US. Some can still handle hand-drawn plans too. When you sell a magazine a plan, all distribution and so on becomes their problem, you just go cash the commission cheque and spend it on new toys for the next project. It also puts a big filter between you and those who think the plan price includes unlimited access to the designer...

Mind you, I was hanging out at one of the big UK hobby mag publishers one day - it was on my way home and I knew all the staff through aeromodelling - when someone who'd bought one of my plans called to ask the editor a question about it. I'd have loved to have seen the guy's face on the other end of the phone line when the editor said "hold on, here's the designer - ask him".

What stripwood size did you use for your fuselage structure? I've got a teensy-weensy outrunner - Eflite Park 450 - that needs a new home and I'm working on scaling down one of my old slimer aerobatic hotrods for it.

Regards

Dereck

forresterace
11-03-2006, 10:18 PM
Hi Dereck

Yes, I also lean towards the use of Krylon spray paint on Doculam. The use of coloured tissue doped on does sound intriguing - I must try it.

I have to be very careful with fumes eminating from my workshop into the rest of the house. Thirty seconds after opening a bottle of something useful, I hear "what's that smell?". Usually I put an exhaust fan in the shop window and that does the trick. My situation isn't allergies, it's a house full of "real" flying machines (birds).

Interesting that you should ask about the balsa stick size on the Comet fuselage - it's a bit of a story. Many years ago I built an Astro Flight kit (Viking old timer) and the fuse used 5/32" wood strips. It was the first time I had seen the size and I never forgot it.
About a year ago I happened to be pawing through my local hobbyshop balsa stock and happened upon two 4" x 36" sheets of 5/32" Sig balsa.
I quickly grabbed them (fortunately they were medium weight and relatively straight-grained) and put them away in my balsa supplies box.
When it came to up-sizing the Oshkosh Comet, 1/8" sq seemed too small for the fuselage and the next generally available size of 3/16" sq. was too big. Remembering the two sheets of 5/32' sheet that I had, I quickly stripped about half of both sheets into 5/32" square pieces - and the rest, as they say, is history.
Sig may be the only balsa supplier to cut 5/32" stock as none of the other online suppliers list the size.

To change the subject a bit - Dereck, I happened to run across one of your posts wherein you mentioned that you are a big fan of the Chilton DW1. Me too - it's one of my alltime favourite planes. I have a set of the Brian Peckham-designed 57" span plans that I acquired about ten years ago. Some day I'll build it. In the same genre, I'm also a lover of the Dart Kitten and the Tipsy S2.

Cheers

Dereck
11-04-2006, 03:34 AM
Hi Doug
I have a 54" Chilton DW1 - the early version with the "Train" upright four jug lump - in the RCMW plans range. Flew it on the first OS 40 FS - the open rocker version - the Train's lower thrust line allowed me to draw the model to a scale where an upright engine was completely enclosed.

Despite the highly tapered wings, it was something of a *****cat by scale model standards and I even had to add an ounce or so of weight to the tail to get it to stall and spin at all. I'd rigged it with no down-going aileron at all and it handled just fine, with a very nice looking roll rate - not sure if that was prototypical, but it scored me well in some scale comps so that was fine by me!

It would be an ideal model for the likes of an AXI 2820/10 on 3S flatties...

There is an electric-specific DW1A in the QEFI plans range, but I always feel like it was stretched somewhat... Anything by Brian Peckham will be great though - the guy was a real gentleman and a superb aeromodeller.

The only snag with a Chilton is that it has tiny little wheels that hardly protrude from those deep wheel pants. I made several repairs to my wing undersides before (A) making a 'flying' sets of pants that were somewhat shorter than the "static judging" set and (B) Only flying the little beggar off tarmac or ultra-smooth grass!

Oddly enough, I ran into a guy at a funfly who'd been taken with the then-new 'bigger is better' brainfart and had a 1/4 scale plus version at some obscene weight. He was bemoaning that it snapped off tops of loops and had a killer wingdrop at the stall, so I commiserated but offered that mine had no vices at all. Couldn't resist throwing in that mine was half the span of his and about a third or better of its weight, but that I'd been told that big models fly better than little ones...

At which, I wandered off while he sat under a big think bubble :) ?

5/32" square - ingenious! Have heard of Sig's 5/32", never actually seen any. Having had good experiences crash-testing my many Lazy Bees, I'm inclined to use smaller section spruce or obeche - the Bee uses mostly 1/8" square strip in that huge fus, spruce longerons, balsa uprights (shorterons :confused: ? ). 3/32" square hardwood should do for a 36 - 40" lightweight, I reckon.

The trick to the small corner joints is the neat little 1/16" x 3/16" balsa gussets Andy Clancy developed for the Lazy Bee's structure - you lay the strip across two fuselage members where they meet in a corner, glue to them and cut/sand the strip to match. With CA you do the lot in minutes and they strengthen up the corner joints immensely for very little weight. Makes for a very light and flexible structure that won't suffer from upright to longeron joints coming unglued.

Okay, it's heatshrink plastic, but "SoLite" is my all time favourite for smaller models. I used it on a 500 square inch ten cell aerobatic ship I designed and flew for over four years, with no problems on the covering at all. As my building shop is in the basement with but one door for access, any smelly stuff is right out :mad:. My last venture with ordinary housepaint in a bedroom environment left me feeling none too good for a couple of days, suspect my painting days are about over now.

D