Tipsy Nipper

Just checking out the nipper and I've noticed a small amount of play at the trailing edge of each aileron. They can be moved up/down about 5 mm in total without the stick moving. The 'play' seems to be at each end of the aileron push rod (i.e. between the bell crank and the aileron horn). I suspect the holes in the push rod have 'ovalled' over time, and the bolts are 'sliding' a bit before the aileron moves.

But:

1) Is this amount of play excessive? It isn't noticable in flight, presumably because the ailerons are under load.

2) What can I do about it - are new push-rod tubes a stock item or is it a case of finding some suitable tube and making my own? On that point, I don't have and have never seen plans or a part list for the Nipper. Are these available?

Thanks,
Rob

Hello Rob,
I don’t like to be outspoken on the web but if you can feel this much ‘play’ in the control circuit then in my view this is seriously wrong and should be remedied straight away. I have experienced aileron flutter in a Nipper (caused by slack aileron cables) and it is not an experience to be repeated!
Regarding your observations I would check cable tension, the aileron horn and all the bolts in the system for security and wear in the first instance and replace these as necessary. The push rod is bushed at one end, is quite heavey duty and therefore unlikely to be the culprit .
Drawing shows all nuts to be castellated and secured with split pins (not self- locking).
Tension in the aileron cables will be adjusted to 35 + or – 5lbs (17 + or – 2Kg) see Nipper hand book.
Remember if you dis-assemble the controls they must be re-inspected By LAA before you fly again.
All the information you require is in the Nipper owner's handbook and assembly drawings numbered 1 -12 which I believe are still available from Nipper Kits & Components Ltd.
Hope you see this as being helpful.
David G-ARBG

Thanks David - I'll go in search of the drawings etc to which you refer. My handbook says cables must be correct tension but doesn't give any more clues.
I'm certain though that the play is the push-rods, as even with the horn held fixed it's possible to move the ailerons a little. I'll add it to my to-do list (fairly close to the top)!
Regards, Rob

Hi Rob,
In addition and just in case you are wondering... "if excessive looseness is found in the hinge pins of ailerons, elevator or rudder, these pivot pins (ref. SP/4Z/B14-0 3/16" ) must be replaced by pivot pins of the same specification but of a larger diameter, which should not exceed 7/32". Holes may be reamed out to suit these oversize pins." (Nipper handbook)

David G-ARBG

Pretty sure that there's a little play in the hinges, but this isn't the major factor. In fact the ailerons are attached to the wing by a doped painted piece of ceconite (as well as the hinges!!), so removal of the ailerons to check/ream the pins is going to be fun! Hoping not to have to do this if I can address the play in the push rods. Will keep you posted!
Regards,
Rob

Hi Rob,

Aileron cable tension must not be over-done, there is an AD for deformation of the aileron belcranks due to over-tension of the cables. Also the wing is a living thing as far as size goes: ie damp=longer=more tension, so err on the slack side.

I would be inclined to check the vertical bolt that attaches the push/pull rod, it is most likely to be worn, but whilst the rod is out it is an opportunity to check it and make good any wear........if you want them welded send them to me and I will get them done.

Aileron pivots is on my menu of "to dos", does anyone have a supplier of quality "oversize"?

David is quite right, any disturbance of the aileron circuit needs a second inspection by a LAA eng'.

Neil

I've traced the majority of play in my system to wear in the bolts connecting the pushrods at each end. There's wear in the 'universal joint' bolts at the aileron end, but most significantly to the 3/16" bolt connecting the bell crank to the aileron push rod. The bolt there had worn a nice 'shoulder' so the push rod could slide about 1mm fore-aft (I have photos!) . The hole in the push rod wasn't worn, so I plan to replace all bolts in the system to see if that cures my problem. I measured in total 5-6mm 'play' at each aieron trailing edge, without movement of the cables.

Quick question though - I don't have any plans / drawings for the nipper - are these bolts standard 'AN' hardware (i.e. AN3-11 or AN3-12) or are they something special such as 'Close tolerance' bolts? The existing bolts seem to be a mix of types with 'X' on the heads, but one or two have an 'X' in a triangle (close tolerance) - should these be used throughout??

Thanks, Rob

Hi Rob


All the bolts on a Nipper are AGS (or should be ) and are BA or BSF. Bolts are available from Light Aero Spares ordered by size and grip length. If my memory serves me right the bolts are 2BA but I have drawings of the assemblies and will check. Will try to PDF the drawings and send you a copy. PM me you email address.

Cheers

Stuart