Lavcohkin La7, Russian Fighter Project

[Dutkoski]

Hi Guys,
Just started my first serious stab at designing a prop plane for production. I always liked the La-7, it's different yet has good moments to the design, big cowl yet streamlined.
Has a 38" wingspan, 33.25" long, a Clark YM 15% airfoil which makes the wing thick enough for retracts if desired. I'm going to use a Aero-naut power system for the first copy, it's a speed 600 geared 1.94 to 1. I might even get a higher gear ratio if the amp draw is too much for the prop I want to spin.
Generally, it's pink foam construction for the fuse and wings, I have the 5" fiberglass cowl already moulded for it. I have to still carve out a canopy plug but that's not really a hard thing to do. The whole plane will get covered in fibreglass cloth, no balsa covering, and finished with water based poly-urethane.
Anyway, I'll keep all advised as I go along. Any constructive suggestions are always welcomed of cousre.

[Dutkoski]

I cannot seem to add more than one pic per post so here is what the plane looks like finished.

[RT Models]

John, all I can say is Sweet!!! I will keep an eye on this one :wink:


Thanks,
Mark
RT Models

[Dutkoski]

Well, the model is advancing quickly. All that really has to be hacked out is a plug for the canopy. Yep, I re-did the wings already. I had a really neat set made on a CNC foam cutter by a good friend, but I wanted a balsa leading and trailing edge for some toughness to dings. Also, there is a bend in the leading edge near the wing root for the wheel well and to get it scale, a extra piece has to be added to the leading edge. With a pure foam leading edge, it would have been a pain, but with the balsa version, just glue on to pice and fair it in with some scrap strips and filler to retain the smooth airfoil. Also, I thicken up the airfoil to 15%. This brings the wing up to a scale thickness, and provided extra thickness if retracts are installed.
The rudder is quite large and thick due to the style of the vertical fin. Gluing on a thin vertical fin to have the lightness just ruins the shape of the tail. If I made a solid rudder out of balsa, it would be heavy. So the built up one turned out just right, very rigid and very light.
Now to start the process of lightening up the airframe, cutting out foam from within.....

[Dutkoski]

Here is a close up of the rudder and fin. The plug for the Avro Arrow is in the background. It too is coming along.

[Dutkoski]

Well guy's, it's been a few days, but the plane is progressing well. Made the wooden plug for the canopy, gun blisters and the exhaust fairings. I'll next tackle a scale spinner, just trying to figure out a simple, yet accurate way of attaching the spinner to the shaft and prop.
But that'll be next week, have lots to do this week, including the Arrow. But its really taking on the appearance of the Lag-7 now.

[Dutkoski]

I stopped working on the Lag as a foam plane. I put on a few coats of urethane with the light cloth. It's up to 26 oz and thats with only the motor installed. Something went wrong somewhere, too heavy. I'm fairly sure it'll fly, but so will a brick with enough thrust.
So it's back to the drawing board. Most likely will make a wooden plug over the winter months and see how well I can do with a fiberglass fuselage. Look at the bright side, more room for batteries and the fuse will be somewhat more resistant to hot landings over the foam.
If I do another one out of foam, I think I'll have to hollow out the foam alot more than what I did.
I'll let ya know how things go,