Center of Gravity, Nobler

[Allen Eshleman]

I have a Top Flite Nobler, built from a kit that I purchased 19 years ago or so at a Flea Market.  I haven't flown it much because the old Fox 35 that came with it didn't pull it real well.  I recently put a Brodak 40 in it.  On the first flight my brother noticed that the wings were bowing up.  We got inside the wing and did a repair job.  I'm looking forward to flying it.

However,  I'm wondering what the recommended balance point is.  It currently balances in front of the leading edge.

Allen Eshleman

[Warren Leadbeatter]

From memory the CG is about 2" behind the L.E.

[leoflyboy]

CG is somewhat dep on wgt; light at 38 to 40 ozs can use 2+ from LE, heavier ships may have to go with more rearward cg say 2.5.  based on 1-1 flap ratio as most people fly them. The new 40 size engs have given this craft a new lease on flying, several on west coast are flying competitivly in hands of exp pilots Light ships can use more foreward CG and turn hard with smooth tracking. Hope this helps you,report on results as all can learn from exp pool.  Blu skies , calm winds for your flts, cheers.   Rob F

[Allen Eshleman]

Thanks guys,

      I added some weight to the back and it flew much better, the best it has ever flown.  I now realize that it was very nose heavy.  Last take-off before this thread it ground of the ends of the propeller on take-off.  This time, it took off much better - longer prop but no ground kissing.

However, I then had problems keeping the B-40 running.  It seems to be a needle valve problem.  It has been bent.  I couldn't get it to run slow enough on one flight - It seemed that turning the needle even a turn and  half didn't make any difference.  We tried several things.  No luck!  It blew a glow plug and took a nick out of my right pinky. 

I will have to figure out how to fix the needle valve problem.  How does one adjust its various pieces so the needle stays put in one place?

[john e. holliday]

If any portion of the needle valve assebly is bent, replace the whole thing.  Also is the collet/nut tight enough.  I am hopeing you have checked out the whole fuel system for leaks of any kind.  I had a two peice metalfuel filter that was the culpret for me one time.  Let us know the results.

[Allen Eshleman]

Is the outside nut, a larger one,  is that the collet nut?

[Allen Eshleman]

After a careful inspection, I will be buying a new NVA.   They're only around $10.00 at Brodak.

[john e. holliday]

Is the outside nut, a larger one,  is that the collet nut?

You have hit the nail on the head.  I have even used Teflon tape to seal the needle to the spray bar.

[Allen Eshleman]

I have the CG at two plus inches behind the LE.  However, the controls are very sluggish.  Does that mean I went too far?

With a new NVA I have the engine problems solved.

[Tim Wescott]

I have the CG at two plus inches behind the LE.  However, the controls are very sluggish.  Does that mean I went too far?

All else being equal, the further forward the CG is the more sluggish the plane will be, and the more rearward it is the more it'll react to pilot input.  I'm just learning on a Nobler, and my first few flights were hairy indeed with the CG at or a bit behind the suggested spot.  I'd think "down" and before I got to 'w' the plane would be diving; I'd think 'up' and the plane would be going up.  I removed some tail weight and things got lots better.

Note the "all else being equal" part -- make sure that you don't have some other problem before you go moving the CG back into the totally unstable zone.

Someone on the group mentioned that if the plane really slows down when the engine quits that the CG is probably too far back -- I had that condition with mine at first, and it is much alleviated now with the CG adjustment.

[Neville Legg]

I thought all kit built Noblers had flexing wings? All kit versions I've seen fly, had their wings flex alarmingly! but never saw one break in flight.

Cheers    Neville

[Gene O'Keefe]

Neville -- your comment brought back an old memory. My first full fuselage was a green box Nobler that I didn't
reinforce wing enough at fuselage and the outboard wing folded up during a loop and was totaled. Never made that mistake again.  P.S. I grew up in Green Bay, WI and we were flying on the blacktop parking lot of the Packer Stadium(Lambeau Field)    Pleasant memories.

  Geno

[Brett Buck]

I have the CG at two plus inches behind the LE.  However, the controls are very sluggish.  Does that mean I went too far?

    Two inches behind the LE??  At the root or the tip?

    Moving the CG aft makes it more sensitive. Moving it forward makes it less sensitive.

     Brett

[Garf]

After a careful inspection, I will be buying a new NVA.   They're only around $10.00 at Brodak.

I don't like the Brodak NVA. It is a twin hole type that is tricky to get right. Use either a Super Tigre or a Randy Smith custom unit.