View Full Version : Grigorovich DI-3

12-05-2005, 08:33 PM
Hi gang,

This will be my first design/build thread on wattflyer, so thanks for having me! I've been drawing up, and have nearly completed, a Grigorovich DI-3. It's a Russian fighter that never made it past prototype stage back in the 30s but is unique in that it's the only biplane I've ever seen with twin tails. The specs will be as follows:

Wingspan: 35.7"
Wing area: 185.7 top, 129.8 bottom, 315.5 total
Weight: 9 oz RTF
Wing loading: 4 oz / sq ft.
Motor: GWS IPS or equivalent brushless
Battery: 2s 700 to 1000 lipo
Controls: R/E/T

Here are a few pics of the prototype full scale along with my design progression thus far. There's a possibility of this going ahead to short kit form so I'm taking my time on the plans.


12-05-2005, 08:57 PM
Hi Martin

Good luck with the new project, great to see someone doing something different.

Having done a twin fin jobber in the distant past, albeit a sports model, can I suggest that you watch the weight back there real closely. Many scale bipes tend to tail-heaviness to some degree, though yours doesn't look too prone, but with having to stress the tailplane to hang those fins on its end, things could get weighty.

Mine had pushrods inside the tailplane, which was made thicker in section to accomodate them, but you might be better off with light external rudder pushrods. It is really neat to see folk trying to figure out how you waggle the rudders though, not to mention that these days, there's too much radio on the outside of models at best.

Prototype looks 'right' though - good moments, ample tail surface areas, no wild ideas on design.



12-05-2005, 10:28 PM
Thanks, Dereck. I was indeed planning on doing a light bellcrank / pushrod setup for the rudders. The pushrods will route underneath the stab so as not to add too much weight. I'm counting on the long nose giving me the room I need to attain a proper CG. The servo position as shown on the plans is only tentative and may be modified depending on how things balance once I actually put glue to wood. Speaking of which, last week I did cut out about 2/3 of the to-be-laser-cut pieces by hand so I'm about ready to start some basic construction.

I thought the same thing about the full scale design - it just looks "right" to transfer to model form. I'm keeping the moments, tail feathers, and all other measurements to scale so as to avoid the possibility of ruining the unique look.


12-06-2005, 06:11 AM
LOL--sorry about the rude intro--i Love the new project--everytime i see it i like it more..

those twin rudders and the 2 seat version look great.

i am thinking maybe you are involved in a secret plot to deplete the world supply of balsa wood.!!! :D can i help?


12-06-2005, 07:13 PM
Hi Martin
RE-reading this took me back to my first ever own design RC model. As this is a complex and technical subject, mine was a Hannover CLIIIa - a German WW1 two seat biplane with twin tailplanes and elevators!

I figured that the real one was a decent flier, so if I did mine the same shape, it ought to fly.

And it did.

Though I had to be shown the video of flight one - the entire club was standing behind me 'encouraging' me to get on with it - to convince me that I really did say "[email protected]@&y H#!! - it flies" as the model serenely climbed out from a straight take off run.

You also deserve a special accolade for finding a biplane that King Peter 1st (Peter Rake) hasn't :O

12-10-2005, 05:55 AM
it will be interesting to see how those rudders work martin. on the only H tail plane i flew, they were not too effective and to do a crosswind landing you really had to split the throttles.

does the aft cockpit have a gunner there?

01-24-2006, 10:36 PM
why do you think they used twin rudders on those Martin? any ideas??


01-28-2006, 03:28 PM
My guess would be to give the gunner a clearer field of fire, since dead aft is where enemies are likely to be coming from. (In the minds of design engineers, at least!)

01-28-2006, 04:56 PM
i can understand it on a plane like the constellattion because the tail would have to be so tall it wouldnt fit in a hangar., there was a conversion for beech 18's called the Tradewind conversion that made it into a single vertical stab and rudder.. maybe the idea was to make the vertical stabs right behind the prop bast in the twins..

the centrally intersecting tail sufaces are sure to create higher drag with the propwash i suppose, it would be interesting to read sales information sheets that advertised the older planes with this kind of tail to see what they claimed the benfits to be. I used to fly these old twin beech 18's and i loved them dearly --i dont want to bore all with my stories, but lets say once you have 500 or 1000 hours in them, they seduce you. i had to use a lot of finesse on the ground and used differntial power on landing in crosswinds, a very satisfying experience to say the least.

after some searching on google i have found a few articles on this subject, its a good refresher on aerodynamics. very interesting.

it will be nice to see your fighter in flight martin, i will certainly like to make one too if the idea goes that far.

the gunnery idea sounds right too.

please keep up us to date Martin! you are our resident genius!!

01-31-2006, 04:29 PM
Yeah, I'm sure the twin tail deal was for the gunner as well. Since my last post I've built the fuselage sides but that was a month ago and I haven't done much building since then. The 126" ANT-20 is back on the bench for debugging and detailing so the DI-3 is pushed to "next" status.


02-11-2006, 06:27 PM
hey martin--any new pictures of the gorky ??

nothing too intersting going on here right now, waiting for nicer weather to get the flying bug again..