Lazair Ultralight Aircraft News Number  8   

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Lazair Newsletter volume 8.

8.1     SPINNER MOUNTING FLANGES 

We have had several reports of fatigue failures in the spun aluminum flange (F81) used for mounting  spinners. Although  this  may not be a serious problem if it is noticed on a preflight inspection and corrected, we have. had a report of a pilot receiving a foot Injury when the whole spinner broke loose and flew off.   While  part of  the  problem  may  be  due  to  an absence of loctite on the screws securing the spinner, or an ~mproperly centered spinner, these are not likely the sole causes.  Mounting flanges which  have  a  larger  bend  radius appear  to  be  better  but not totally immune to fatigue problems.  Newer propellers have a large area on the rear surface machined to fit onto the mounting flange, but some of the older propellers may have  some  slight interference  with  the  flange  from  the trailing edge of the blade and this should be filed as necessary to avoid distorting the flange.  We are presently running endurance tests with a new design of flange.  When  the testing  is  complete,  the  new  flanges  will  be  made  available at no charge to all owners who return the original ones.  In the meantime, It Is  strongly  recommended  that  all  spinners  and  mounting  flanges  be removed.   Until  new flanges are available, you can fly without spinners --- it doesn't look as good, but the difference in performance isn't noticeable.

 

8.2    TAPE ADHESION

In the past five months we have had four reports of loosening of Tedlar covering, apparently due to poor  tape adhesion.   As  the reports are all quite different, there is no indication of any one particular problem, and therefore determining the cause (and remedy)  is  not  easy.   However,  based  on  the  information  we  have available, we can make the following suggestions. 

(a)     Avoid overheating the tape (and  the  Tedlar)  when  heat  shrinking.   As  stated  in  the  manual, overheating  the tape will cause it to shrink excessively and will lift it at the edges.  It is also probable that excessive heat will have an adverse effect on the adhesive.   Overheating  the  Tedlar will cause it to shrink excessively and could tend to pull it away from the tape. 

(b)     When cleaning the aluminum prior to the application of the tape (whether on a new aircraft  or  when recovering)  use only lacquer thinner as suggested in the assembly manual.  There is some indication (but no proof) that the use of acetone for cleaning the aluminum may effect the acrylic adhesive  on the  tape.   Do  not  use  metal cleaners (such as Met-All, Nev-R-Dull, Flitz etc.) as many of these are designed to apply a protective coating as well as clearnthe metal.  These  coatings  (especially the ones which contain silicones) can severely impede tape adhesion. 

(c)     Make sure there Is sufficient overlap of  tape  on  the  aluminum  (as  described  in  the  assembly manual),  especially  along  the D-cell and along the root rib.  If in doubt, additional tape should be applied with at least 3/4 of an inch in contact with the aluminum. 

(d)     If there is any indication of Inadequate adhesion around the perimeter of the Tedlar,  some  of  the wide single face tape could be removed and replaced, or additional tape could be applied as  In  Cc) above.

(e)    Lack of adhesion of the foam tape on the ribs, while not a common problem, could be a bit  more difficult  to  fix.  We have only seen this problem once, and the effected area was so small, it was just left (though watched closely) and the condition has  not  worsened.    If   you   should   ever encounter  this  situation  (and  assuming  you  don't wish to recover the wing), you could rivet an additional aluminum capstrip to the effected ribs on the outside of the covering (similar to  C4  on the  wingtip').  However, if you do this, be sure to put at least one layer of 1 1/2" or 2" tape over the Tedlar before the capstrip Is put on and use double face tape under the capstrip.   Be  sure  to file  or  sand  the edges of the capstrip so they do not cut Into the covering.  In any case, do not (as one customer suggested) attempt to rib stitch the  Tedlar.   Rib  stitching  a  non  rip-stopped material  could  potentially  create  many  more  problems than it could cure.  While the additional capstrip suggested above does necessitate drilling rivet holes through the covering, the  stress  on the  covering  is  distributed  by the relatively large area of the capstrip.  If rib stitching were used, the stress would be much higher due to the small diameter of the rib cord.  

(f)        If you paint your Tedlar and/or tape, use a light colour.  There is some indication that painted  a  dark colour. and left in direct sunlight for a prolonged period, the covering creep under the tape due to the extremely high temperature developed.  

 It  is may tend to  

(g)       To check for overshrinkage on your wings, put a straightedge on the trailing edge  and  measure  the deflection of the T25 trailing edge tub& between each pair of ribs.  A deflection of one sixteenth of  an inch is about right.  An eighth of an inch is excessive but acceptable.  A quarter of an inch deflection indicates that the particular panel has been overshrunk.  The covering and tape  on  that particular panel should be inspected and watched very carefully or replaced.  

(h)       An inspection of the covering and tape should be included in every preflight.  

The following two paragraphs have been added to the assembly manual, and should be  observed  if  you  recover your Lazair':  

"As with most acrylic adhesives, the initial tack with this tape is only moderate, but the  adhesion  improves as  it  ages.  For this reason, it is essential that the tape be firmly pressed down to make sure there is 100 percent initial contact.  Then, as the adhesive cures, a proper bond will develop."  

"Unlike Mylar and most other heat shrinkable covering materials, Teldar will continue to shrink  significantly after  the heat source has been removed.  Therefore, to avoid overheating the Tedlar, apply the heat for a few seconds, then remove it and check for signs of shrinkage.  If there is no indication, heat it  a  bit  longer, then  remove  the  heat  and check again for shrinkage.  As the heating period is Increased, you will find the correct exposure so most of the shrinkage will occur after the heat source has  been  removed.   If  the  heat is  maintained  on  the  Tedlar  for a significant period of time after it begins to shrink, it is possible to overheat the material and reduce the adhesion of the tape."  

8.3  ENGINE INSPECTIONS  

We have received one report of a Rotax engine stoppage becausd the small wire between  the  magneto  coil  and the  condenser  was  routed  improperly  and  contacted  the  rotating flywheel.  Although this is an unlikely

situation, we will be checking all engines before they  are  shipped  to  ensure  that  the  wire  routing  is correct.   Engines  in  the  field can be checked quite easily if the engine is removed from the nacelle.  The flywheel does not have to be removed since it has cutouts through which the wiring may be inspected. 

We also know of two engines which made rather ominous noises when  the  crankshaft  was  rotated  because  the polefaces  on  the  lighting coil were rubbing on the flywheel, so it might be wise to also check that the two screws securing the lighting coil are tight.  This can also be done without removing the flywheel.

8.4  COMPRESSION RELEASE 

We recently received the second report of an engine being damaged because it ingested the valve stem from  the compression  release.   To  preclude  the possibility of this happening on one of your engines, we suggest you pry off the little green plastic cap and inspect the quality of the riveting which holds the  aluminum  button onto  the  valve  stem.   If there Is any sign of weakening or bad riveting, the compression release should be replaced.  The plastic cap is not required and may be left off to permit a check of  the  compression  release in every preflight inspection. 

8.5  RUDDERVATOR PUSHROO ROTATION 

Item 6.16 in an earlier Tech Update described a problem where the BE rodends tend to rotate in  the  P3  plugs during  cross  control  of  rudder and aileron.  This problem has been eliminated on the Series III Lazair~ by the use of a totally different control linkage, but if you have one of the earlier models with rudder  pedals, you  can make two relatively simple changes.  First, replace the large diameter S675 spacers supplied with the earlier kits with the small diameter S344 spacers used on the Series III kits (with W3H washers added to  make up the required length). 

Secondly, the allowable rotation of the ball can be increased  by inserting  a 3/16 inch diameter chainsaw file through the pinhole in the ball and carefully filing out a small section of the  ball retainer  as  shown.   Only a very small amount of metal needs to be removed, so don't file away any more than necessary. 

8.6  FUEL FILTERS

That little white plastic cover on the bottom of the carburetor on the Rotax engines contains a  small  filter screen.   This  should be removed and inspected (and cleaned if necessary) after the first few hours and every 50 hours thereafter to verify that the fuel filter in the tank is doing its job. 

The problem with the felt fuel filters described in Tech Update Item 5.2 appears to have  been  eliminated  by the elimination of the felt fuel filters.  The newer kits are supplied with an all metal screen-type filter. 

8.7  AXLE WEAR 

If you're still flying one of the very early Lazair's (the ones with the spoked wheels) you  should  pull  the wheels  off  at least once every 50 hours and check the 4130 steel axle tubes for any indication of rust, wear or any other condition which could lead to failure.  We have had two reports of axle breakage resulting  in  a sudden  and  extreme  Increase  in dihedral.  In one case, the airframe had been highly modified by a previous owner and the steel axle had been replaced by a small diameter aluminum rod with a cross-drilled  hole  in  it  prior to the failure.  The other one, however, appears to be a failure of the original  axle  tube  caused  by wear  as  a  result  of a wheel bearing seizure.  In lieu of the frequent disassembly and inspectl9n. the axle could be replaced by the later double wall large diameter aluminum one with the tundra wheels1 or a  1/8  inch stainless steel cable could be installed to keep the A-frame from spreading in the event of an axle failure.

8.8     ROTAX HEAD GASKETS 

There is an indication that the head gaskets on the Rotax engines may compress unevenly if the head  nuts  are repeatedly  retorqued1 and this could eventually result in a cracked cylinder head.  Retorquing the heads once or twice during the first few hours of operation is not uncommon, but if you find  it  necessary  to  retorque the  head  3  or  4  times,  It  is  strongly  recommended  that you replace the head gasket.  The recommended tightening sequence and torque value are given in Tech Update Item 5.9. 

8.9     SWITCH CONNECTOR INSULATION 

The following note regarding the terminals on the magneto switches has  been  added  to  Step  8.2.10  in  the latest  revision  of  the  assembly manual.  Please check this on your Lazair'" ahd make the recommended change if necessary.  "Make sure the plastic insulator is properly positioned after crimping.  If it  appears  loose, use  electrical  tape  or plastic sleeving to ensure that the terminal cannot contact the F55 switchplate."  A short piece of fuel line slipped over each terminal  can  provide  additional  protection  against  accidental grounding of the magneto wire. 

8.10   OIL FOR YOUR ROTAX 

In the operating manual provided with Rotax powered Lazair  kits, we recommend the use of  mineral  based  two cycle  oil  mixed  in  a  ratio  of  25  to  1, and do not recommend the use of synthetic lubricants which are usually mixed in much lower concentrations.  This advice is  based  on  information  supplied  by  the  engine manufacturer,  on  our  own testing and experience, and on feedback from customers.  Although some owners have been using synthetics for a considerable length of time with apparently  no  problems,  others  have  reported mysterious power losses and incipient seizures believed to be a result of inadequate lubrication.

 

8.11   GROUND ADJUSTABLE PROPELLERS 

Although  most  Lazair  owners   are   familiar   with situation   regarding   the   ground  adjustable  props, the following is provided for the information of  those  who have heard only half of the story.

Following over a year and a half of  development,  we  finally  began  shipping  our  composite  blade  ground adjustable  propellers in June of 1983.  In mid July we received a call from a customer who described in vivid detail what happened when one of his propeller blades separated in flight.  Because of the  very  real  danger presented  by  this  situation  (and  because  there was nothing obviously different about his propeller which could explain why it failed and the others with hundreds of hours on them did not) the decision  was  made  to initiate  a  100  percent  recall of all the ground adjustable propellers.  This decision was not made easily, but it was made quickly and every Lazair  owner who had been shipped  this  propeller  was  personally  phoned and  asked  to  return  the  propeller  (or part of it) to the factory.  Customers who had received the ground adjustable props in their Series III ktis were sent the proven carbon fibre bi-blade props as replacements,  and customers  who  had  purchased  the  ground  adjustable props for retrofit were offered a cash refund.  As you might imagine, the cost of this decision was substantial. (continued next page)

Including the  development  costs  incurred  during the  past  year  and  a  half, the cost of tooling, the production costs of the propellers which have now been destroyed, the cost of the replacement bi-blade props, and administrative costs  associated  with  the  recall, the  bill  came to over forty three thousand dollars.  While this may seem like a small price to pay if it can avoid a serious accident, it is not an insignificant amount to a company the size  of  Ultraflight  (sometimes we  like  to think big, but we're not exactly General Motors).  It should be noted that the incident mentioned above was the first (and the only) blade separation on one of our  production  ground  adjustable  propellers. The  recall  was  issued  not because we felt there was a high probability of a second occurrence, but because the possible consequences of a failure are so severe.  A failure of a wooden prop or even  a  small  composite prop  like  our  bi-blades  can be frightening and is certainly not without danger, but there is usually enough propeller left after the failure to limit the unbalance to some degree.  However, when the  ground  adjustable blade  separated,  one  whole  blade  came off, resulting in a horrendous unbalance --- sufficient to tear the engine off its mounts, rip off both ground cables (which are rated at 600 pounds each  in  tension)  and  pull out  the  magneto  wire  so the engine could not be switched off.  Only the throttle cable was left to support the engine and thi  served only to  allow  the  engine  to  flail  around  like  a  guillotine  on  a  string. Fortunately,  the  pilot,  who  has  had  many  years  of flying experience, was able to retain his composure, control the aircraft and shut off the engine with the choke, and he was able to land safely.  However, if  you can  visualize  yourself  in  this  situation,  you  might  understand why we took the only action which could positively prevent a recurrence.  The reaction to the recall has, for the most part, been quite good.   Almost every  owner  agreed  to  follow  our  instructions and stop using the propellers.  Many even said "Thanks for telling me".  However, two Individuals have resisted our attempts to dissuade them and are continuing  to  fly with  the  ground  adjustable  props.   We  care  about your safety.  We care enough to spend that forty three thousand dollars to help preserve it. If you don't care, there may not be much we can  do  about  it  ---  but we  will  continue  to  try.   In  the  meantime,  we are investigating other avenues to try to get a bit more efficiency out of the propulsion system.  Many wooden props of various shapes, lengths and pitches  have  been tested  and while some are certainly satisfactory, none has been outstanding, and so far not one has been able to match the thrust-to-noise ratio which was obtained with the ill-fated  ground  adjustable  prop.   However, our efforts are continuing and as improvements are made, you will be notified.  

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