surf

I have almost finished a GP Super Skybolt and now into the final balancing. I built per plans and sanded the heck out of the fus. knowing it was a heavy plane. I have a Magnum 120 up front. Problem is I need about a pound up front to balance it[]. Am I missing something here?? Have checked CG measurements many times, even with observers so I'm pretty confident about correct CG.

Any help and ideas would greatly be appreciated. Who knows how it will fly that heavy.

Thanks

WYDAH

Hi surf,

The Skybolt tends to build tail heavy. My GP Skybolt weighs in at just over 10#. I'm using a GMS .76 engine with Jtec Pitts muffler which together weigh 2 lbs 1oz. I put the 1000mAh RX battery against the firewall under the fuel tank. I moved the servo mounting tray forward probably 2" as well. I still added a 2 oz spinner weight to get an acceptable balance at the recommended location. I do have a Sullivan tailwheel brackett setup instead of the kit method, but everything else is stock.
Even with the necessary weight the plane flies very nice. I keep a bit of speed up on the landings, but other than that she does great. I would just make sure you have everything you possibly can moved forward, such as the battery and radio, then add what you must to bring the balance in.

Any Pics??

Have fun.

MinnFlyer

My Feedback: (4)

Something's not right here - There is no way you should need to add that much nose weight with a 120 4-stroke.

I put a YS 91 in mine and had to move the battery pack back into the rear of the fuse to balance it

(And before anyone asks - That was BEFORE adding the smoker)

Where are you balancing it?

rc-sport

My Feedback: (12)

Something is definitely not right. I have a Saito 120 in mine and it balanced dead on with the battery on the CG. Double check the CG placement on the plans. Let us know.

Deadeye

Guys,
Had I not done my lattice work on mine, I'm betting I would've been in the same boat. surf, check out [link=http://www.rcuniverse.com/forum/Lightening_the_GP_Skybolt/m_2496934/tm.htm]this thread[/link] I started when I was building my Skybolt. I am also going with a Magnum 120 up front, and just started covering two nights ago. I managed to take 3.9 oz out of the tail, which translates into roughly a pound up front. With my RX and battery over CG, I need no added nose weight. It balances perfectly. However, I do have to add 1 oz in the right top wingtip (on CG) in order to balance the Skybolt laterally. My Magnum is inverted, and I guess I need to compensate for the off center engine, and the exhaust. I think a sideways mount would've been even worse, just on the opposite wing.

Now I just need to figure out my ground clearance...but that's another thread.

surf

Thanks for all of the replies. I have put the battery pack under the fuel tank. CG is measured from the leading edge on the TOP wing at the ribs where the wing pylons go (2.75" in from the LE). This puts the CG straight vertically above the bulkhead that is the BOTTOM wing leading edge.

Unfortunately I did check out all of the threads on lighting the fus., but after construction (doh). Have built many planes but could still be screwing up somewhere CG wise.

I thought about removing the covering and adding lighting holes but did a killer job on covering so would hate to do this.

Deadeye

My plans show the CG just in front of the LE on the bottom wing. The lightening could still be done, just start out with small holes. I used the inner fuse doubler as a guide when I did mine. The fuse was built, but the turtledeck and the bottom corner pieces were already in place. Once you get one side opened a little, just use a long pin or something to poke through the other side to mark your holes. It's time consuming, but it will save you a pound. A whole pound, man!

EDIT: I neglected to see that yours was covered already.

surf

Deadeye,
Yes the plans show the CG in front of the leading edge (bottom wing). The instructions say to measure in from the TOP wing and balance using the TOP wing. If you shoot the CG straight up on the plans it will be slightly forward of the aft top wing brace (hope I said all of that right???).

Last night I removed the Sullivan tail wheel and the "pull pull" rudder connections which really helped after rechecking CG. Now searching for smaller lighter tail wheel and will stick with the pull pull since I have it set up already.

rc-sport

My Feedback: (12)

Did you try holding the plane where the manual states, at the struts? Where is your battery pack?

moodier

My Feedback: (1)

Hi;Those are a heavy plane mine weighed 11lb10oz friend built one was at 12 Lbs.all required huge amounts of nose weight.Just don't try to many slow landings!!Keep in mind the weight when flying it!

rc-sport

My Feedback: (12)

I must have done something right, mine came in at just under 9lbs.

surf

RC-Sport, interesting idea to try to hold it at the struts. I measured at the struts then stretched a string between them and marked the CG locations above the fus. so I could use the balancer. But I will try at the struts. Battery is under the tank.

I just finished gutting the radio out and remounting as far forward as possible. Went for a lighter tail wheel also. When all said and done, it looks like around 10 lbs. So from the above comments it sounds typical.

Enough is enough, I will final balance tomorrow and start measuring the control throws. It's snowing today in Ohio so it's not like I'm in a rush.

Thanks for all the comments and help.

rc-sport

My Feedback: (12)

surf, once you get this bird in the air, you're going to love it. By the way, cool covering scheme.

krossk

My Feedback: (27)

Looks great! Can we see a pic of the top too?

surf

I don't have a picture of the top right now but the wing tops are the cub yellow, tail feathers all checked (matching checks by the way, I'll never do that again). If I get time I will take a shot from the top and post.

surf

Pictures of the top.