I am just finishing up a Goldberg Chipmunk that I bought a while back, and I don't have the instructions. Does anyone know what the recommended CG rang is for this airplane? Also, any advise on the best prop to use? I am using an OS FS-91 II engine. Thanks!

DKflyer
I have this same bird with the OS FS .91 with the pump. I will dig out the plans and let you know what the recommended CG is. I have been running a Master Airscrew 13x8 and 14x6.

Wyo_Flyer,

Thanks for checking on the CG. How does it fly with the OS 91? I bought a Master Airscrew 14 x 6 prop for mine also. Does it fly better with this or with the 13 x 8? Thanks again!

DKflyer
I checked the plans and it shows a CG of 3 11/16" to 4 9/16" back from the leading edge or 1/4" ahead to 1/4" behind the wing spar. I have not had a lot of time on the .91 with the 14x6, but I have not seen a big difference. I comes in nice and slow to land but flys real nice, vertical is limited but flys very scale. I did add 1/2" to the rudder with pull-pull system. I moved the alir. servos out into the wings, one each side. I added flaps but have not played with them much yet. Hope this helps. If you have any other questions, let me know.
Gary

Thanks for the info. I was thinking of going to dual aileron servos also, maybe for a winter project.

When I had a .91 on my chippy, the prop it liked best was the 13x6x10 wood prop. It pulled better than the 13x8 and the 14x6. I have hundreds of flights on my chipmunk.

It DOES have three servos on the wing. One for each aileron and a third for inboard flaps. It's a nice setup.

Chipmunk Picture

-Cheech

I had an OS .91FS on my chipmunk also. It pulled an Graupner 12.5x7 3 blade prop at 8800 rpm. This engine is at the moment giving me a headache because its high end is very bad. But this is another story. I replaced the .91 with a OS FT120II pulling an Graupner 16x8 at 8000 rpm. The biggest problem with this configuration was its weight. The vertical performance was a little bit better, but not much. Also a problem was that the prop was pulling so hard at idle, the plane was rolling away when i let go. At the moment, as an experiment, there is an OS 46 LA pulling it. Now i have to pull 300 gr. of lead because the engine is so light. The engine survived a really bad mid-air collision, so it was just for testing it in flight. Its vertical performace was bad, with very strong winds. The used prop was an APC 11x7 turning at 10000 rpm.
By the way, the cg is about 10 cm (4inch) from the leading edge.

Greetings,
Vince

I also want to add that i installed a servo for the flaps, but i have used it only a couple of times.

Greetings,
Vince

I have a chipmunk with a OS .61 absolutly love the plane.

I use the flaps all the time for landing, helps slow the plane down after coming over the trees at our field. also good for slowing down after a deadstick so you dont run out of field. I use only about 1/2 to 3/4 throw on the flaps (30-40 degs?? )

right now it has a single aileron servo but i might switch to dual soon (i bought it second hand and thats how it was)

here is a pic of mine