Monday 14 January 2019

Mitsubishi Ki-46 "Dinah" & more by Doug Beardsworth

Here's the Mitsubishi Ki-46 "Dinah" that I designed and built. Twin rubber power ships are a bit trickier to fly, but when they are "on song", they are gorgeous in the air. This one is built to a 44" span, and competes in the Giant Scale class. It also uses traditional stick and tissue construction.  I drew up these plans using some very detailed 1/72 scale drawings as the basis. I draw my plans in the "old school" manner, using a pencil, straightedge, French curves ...and lots of eraser  (smile).
Taking the 1/72 drawings to a commercial copy center, I then enlarge them to the span of the model I want to build, in order to establish the correct outlines. I then lay transparent vellum over these enlarged drawings, and then begin drawing  in the structure for the outlines and other structural elements. Wings and stabilizers get an outline, then spars and ribs are sketched in. Often the 1/72 drawings have accurate fuselage cross sections from which fuselage formers can be drawn, and then stringers placed running nose to tail.
Canopies are made from clear heat shrink tubing stock- the same material used to make tamper evident seals on vitamin bottles and similar. First, full size balsa patterns are  carved and sanded to shape. I don't find the need to seal the balsa at all like a vacuum-formed pattern would need. The plastic is drawn over the shaped balsa patterns using a hair dryer to heat the plastic, and pull it into shape by hand over that pattern. Finished thickness of a typical canopy is approximately .005 inches. 
Anyway, I find the entire process very gratifying and challenging at the same time. 
My good friend Mike Stuart shot the video below (link HERE) this past July of a nice flight, with a few thermalistic bumps adding to the duration:
Best wishes for 2019!
Doug also send over two videos featuring his brilliant Kawanishi "Kyofu" he took part in our latest contest with (HERE). In the first video below the "Kyofu" is flying under rubber power (link here)
In the second video (link here) is flying with electric power.
I hope you enjoy this fantastic post as much as I do. Thank you so much Doug!


carlo said...

That is a great work.
A rubber twin is a feat in itself and not only it looks magnificent but it glides beautifully. Not a small feat for a scale model. Now, where did I put that Guillows Zero thirty years ago ? :-)


George Bryant said...

What a beautiful model. I admire your craftsmanship. Thanks so much for sharing.

D. Chouinard said...

brilliant! The fact that you have to build light and yet strong enough to take the tension of the rubber bands. I know these types of models have to be very stable in order to fly "hands off".
I like seeing the construction and methods. Laminated balsa to form the the engine nacelle?

doug B said...

Thanks for your comments, Gents.

Carlo, yes the glide is nice in the video. early in the flight trimming process, one is often adding or removing bits of plasticine clay ballast to the tail or nose to improve the glide. I believe I built most of the planes in the Guillows catalog as a kid- and the Zero was one of them!

D. C.: yes it is a balancing act for strenght to weight. the airplanes are nver loaded much beyond 1.5 g's in flight, and consequently the structure can be much less substantial than a comparable radio-controlled ship.
And yes, Stability is your friend. One trick is to enlarge the stabilizer area slightly over scale- which I did by about 8% with the Dinah. that added area increases pitch stability. The prototype Dinah had adequate dihedral for free flight scale.
Yes the Nacelle formers are laminations, which are light and strong and fast to make. the Leading Edge, and front and rear spars are cut away through the center of the nacelle in order to give lots of room for long rubber motors, and not have them foul on the internal structure while unwinding in flight.

D. Chouinard said...

Hi, Doug! Thank you!

I like the thought of using the nacelle formers as a carry though for the spars. I dabble a bit in radio control (electric), although I haven't had time to really get into it lately. In my mind, a light plane is always going to fly better, provided it has enough structure to cope with the stresses of flight. (And the occasional hard landing) So, I always like to look at structures, and I find what you did on the Dinah very interesting. Look forward to seeing more!

Danilo said...

Fantastic Flying Model! My congrats - I have never built flying models but I find them pretty fascinating.