TimJohansen

Hello!
I am considering getting a Sig Four Star 20 EP to run my OS .25 engine.
Has anybody made this switch? If so, were there any critical mods, I.E. firewall placement/reinforcement, LG changes, etc.
Any info would be sincerely appreciated...thank you for your expertise/building wisdom👍

mgnostic

I've built the Four Star 40 and Four Star 60 and recently built a Slim Jim 20, an airplane similar to the Four Star 20. The major changes involve the nose of the airplane. Most of the time when you see an electric version of a gas airplane the nose structure is lightened because it doesn't have to deal with the vibration of a fuel engine. You will want to go the a 1/4 inch thick firewall for mounting the engine. You can probably use the stock firewall as a template for tracing out the new one. Most gas planes of this size use some sort of fuselage doubler to reinforce the fuselage sides. This is usually just a copy of the fuselage side that runs back to the trailing end of the wing saddle. The Four Star may already have this, I just don't have any plans for it handy. If you add doublers just remember to narrow the fuselage formers by the same amount of material so that all of the die cut pieces still line up. Dry fitting will be your friend here. You may have to delete a battery tray to make room for the fuel tank and flight pack battery. A four once fuel tank will be plenty. I seldom burn more than 2 to 2.5 ounces of fuel per flight. You shouldn't need to make any changes to the landing gear and the CG should be in the same place. You can use the location of the flight pack batter to adjust the CG. Don't skimp on servos. I've seen a lot of people using micro servos on similar size electrics but a mini size servo will last a lot better. I've had good luck with Hitec 225bb servos. They are plenty strong for the application and are reasonably priced. If you follow through with this I think you will be pleased. It should be a good flier and is conveniently sized to toss in the back seat of your car.

TimJohansen

Thank you for that excellent info. I called Sig today; that kit, along with the Hog Bipe, are out of stock. I was told that the inventory date for both kits is unknown...What is going on at Sig??

mgnostic

I understand that Sig had a fire in their balsa wood warehouse a while back. I wouldn't be surprised if that cut back on production.

tmaxx1701

I built a 4*20 (EP) last year with a Saito FA-30S (H). At the time I didn't think about moving the firewall back to keep the prop in the same location as stock. I ended up mounting the receiver battery about 1/2 way between the wing and tail to get the CG right. It has been maidened by one of our club instructors but the engine needs a little more tuning.

Here are a few pictures that I took

TimJohansen

Many thanks for your input! Your plane is a beauty! I am looking forward to build this...waiting on Sig...
Happy Landings👍