Lazair Ultralight Aircraft News Number 6  September 1982

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Lazair Ultralight Newsletter

The recommendations in these updates must be acted upon before they can be or any benefit.  For your own safety as well as the safety or those around you, please take the time to make the recommended changes to your aircraft.  In the past six weeks we have had three engines sent  to us for service.  Not one or them had the propeller bolts installed as recommended in update S, item 5.4.  Please read these updates carefully and make the recommended inspections  and/or  changes which apply to your Lazair. 

6.1          D-CELL SPLICE 

As you are probably aware, the D-cell skin is comprised of two sections - a main skin and a tip skin.   During final  inspection  of  a batch of D-cells recently. We discovered one which did not have sufficient overlap at the junction of the main skin and the tip skin to allow the proper edge distance for the rivets.  Although  it is  unlikely that any D-cells were shipped with this defect, please check yours as described below.  Since the outboard end of the main skin is covered by the tip skin, if the problem does exist, it will  not  be  obvious and must be checked carefully. 

To check the edge distance for the rivets, it is necessary to know the position of the outboard edge of  the main  skin.   To locate this edge, look at the trailing edge or the bottom or the D-cell.  By looking inside, you should be able to see the outboard edge or the main skin.  Put a mark on the outside of the  tip  skin  at this point  and measure  the  distance  from this mark to the inboard edge of the main skin (so you know the exact length of the main skin).  Then transfer this measurement to the leading edge of the  D-Cell.   You  can now  draw a  line  on  the  tip skin showing the exact location of the edge of the main skin.  To achieve the correct edge distance, the rivets should be located so that the centre of the rivet hole is at  least  I/4  of an  inch from the edge of the skin.  If necessary, install additional rivets (with the required edge distance) between the existing rivets. 

If the overlap on your D-cell is insufficient to permit  the  required edge  distance,  please  contact  your dealer  or  the factory and w6.1.jpg (11019 bytes)e will make up a special splicing kit for your D-cell(s) and ship it to you.

6.2          KEEP YOUR ASI COOL 

Although the Hall brothers airspeed indicators are surviving quite well on  the  aircraft,  we  have  had  two reports  of ASI's becoming so hot that they actually bent slightly and were no longer useable after being left in the rear window of a car.  


In Update 5.8 we reported on a potential problem of carburetors working loose  and suggested that the nuts  be checked  and  retightened periodically.   Since  then  we  have  determined  that the self-locking nuts work properly. but the studs work loose in the crankcase.  To prevent this from happening, we  are  now  lock wiring the  nuts  and  studs after installation of the carburetors at the factory. and it is recommended that this be done on all Rotax engines.  To install the lockwire. Make sure the nuts are tight. then  drill  a  small  hole through  each  nut (and the end or the stud).  Feed a single piece or lockwire through both nuts and twist the ends together. 


Although as stated earlier. we do not supply a conversion kit for the new 20 Litre (5 U.S.  Gal.)  fuel  tank. many  owners have installed the larger tank and now that the new FAA rule specifically allows a 5 gallon tank. many core owners may wish to make the conversion.  As stated previously. these  changes  are  not  recommended unless  you have had experience and have access to the equipment required for bending thin wall aluminum alloy tubing.  However. for anyone who is qualified to do the job. the following guidelines are provided: 

1.       To achieve the proper centre-of-gravity. it is necessary  to move both  the fuel tank and the pilot forward.  This involves rebending and repositioning the seat tube (T44) as shown (or replacing the  T44  with the new T60 seat tube).

2.       Make a saddle for the new tank so that the weight  is  carried by the  T22's  at  the  rear  and by  the seat tube at the front.  Do not attempt to support the weight of 5 gallons  of gasoline  (about  140 pounds at 4 g's) entirely by the T22's.  
6.4.jpg (31637 bytes)


6.5       RIVETS IN P3 PLUGS

 Although calculations and testing have shown that one rivet would be sufficient to hold the P3 plugs into  the control  pushrods.  we use two rivets in each to provide a safety factor in the order of ten-to-one for normal control surface loading.  However. it may be possible in the event of a mishap  (such  as  an  aircraft  being blown  over  by  severe  winds  while tied down) to apply stresses beyond the strength of the rivets and shear them off.  If your aircraft is ever involved in any type of incident which could put abnormal loading on the control  pushrods  they  should be inspected very carefully before the next flight.  Pushrods should also be inspected very carefully if you buy a used aircraft - especially if it has  been  damaged.   if  there  is  any indication that a pushrod could have been overstressed. install an extra rivet in the P3's for security.


All new Lazair's and many older ones are now being covered in Tedlar.  while the operating life or  the  Tedlar is  expected  to  be many  times  that  or  Mylar  the  life or the adhesives used and the tapes has not been precisely determined.  To obtain the maximum life  from  the  tapes,  it  is  recommended  that  all  tape  be protected from ultraviolet exposure.  This can be done in several ways.  If you intend to paint your Tedlar then the paint will afford some ultraviolet protection but the degree of that protection will  depend on  the particular  type of pigment used in the paint.  Aluminum paint works best and it is therefore recommended that the tapes be painted over with aluminum paint (regardless of whether or not  the  balance  of the  Tedlar  is painted).   As  an alternative, the tapes holding the Tedlar in place may be covered by a metalized tape (such as type 85O PAU. available from your local 3M distributor).  In addition to providing ultraviolet  protection, this tape creates a very neat, clean appearance. especially when used over the foam tape on the ribs.


In Update 5, item 5.7 we stated that the use of Rotax engines on Lazair's with .016 inch  leading edge  skins was not  recommended.   This  statement  was not based on any particular experience, but rather on a lack of experience.  At that time, we had one demonstrator  flying  with  this combination,  but  we did not  have sufficient  time on it to evaluate the results.  Since then, our demonstrator has continued to perform well. however, one dealer "who installed Rotax engines on  .016 inch D cell  reported that  one of his  D-Cells acquired a slight buckle just inboard of the Nacelle when he shut down the engines and one of them backfired. Based on this, we are obviously not recommending the installation of the  larger engines on  the  lighter D-cells.

However, for those "who have already made the  conversion  and  those  who probably  will  (in  spite  of our recommendations),  we 6.7.jpg (16405 bytes) suggest  that,  as  a minimum,  you  rivet  on a two root wide doubler of .020 - 2024-T3 aluminum alloy over the leading edge of the D-Cells under the Nacelles.


In the assembly manual for the rudder pedal kit, there is a reminder that when one  rudder pedal  is pushed down,  the other one must come up, and therefore you should not attempt to push on both pedals simultaneously. However, for whatever reason, people do occasionally push down on both pedals.   While  reasonable pedal pressure does not cause a problem. excessive force will bend the two 323 bolts which hold the nosewheel axle to the side tubes.  To alleviate this problem, we are now including with  the  rudder pedal  kits  two small gussets  (G76J  to help  support  the axle.   If you have an earlier rudder pedal kit and6.8.jpg (11553 bytes) wish to add these gussets, you can make them yourself from two strips of aluminum alloy .040 to  .080 inches  thick.  1/2 inch wide and 6 inches long.  Bend and install the gussets as shown.

6.9        Muffler Outlet Angle 

Although the velocity stacks reduce the amount or oil buildup on the wings considerably, you may still  get  a bit  or  residue  on  the  wings  from  the exhaust if you have the new Nacelle mounted mufflers.  This can be greatly reduced by bending the exhaust exit tube in the muffler upward about 15 degrees.  To do  this.  simply fit a 3/4 inch diameter rod or pipe into the exhaust exit tube and pull it upward to the desired angle. 

6.10   Front Fitting Radius 

A few kits were shipped recently with front fittings shaped as shown at  left  below,   If you  assemble  the control  system with the fitting6.10.jpg (8591 bytes) as shown, you will probably rind that it interferes with the pushrod when you move the control stick to deflect the ailerons. 

To work properly the fitting should be cut, filed or sanded as shown at right above. 


If you recently covered your Lazair  in Mylar and you don't relish the  thought  or  tearing  it  all  off  to recover  in  Tedlar,  you may be interested in the following:  in spite or the fact that paint will not adhere well to Mylar, a couple or owners have had relatively good success with it.  The testing which we did a  year ago  indicated that  initial  adhesion  was  extremely poor after a 48 hour cure.  The same test samples were re-tested about a week ago and while the adhesion was not as good as we might like. it was acceptable.

If you wish to experiment with paint on Mylar, we suggest that you let the Mylar  weather  for  a couple  or weeks.  then degrease  it with Lacquer thinner and paint it with a pigmented urethane (this appears to be the best or any or the paints we tested).  Although the paint should offer  some  protection  against  ultraviolet radiation,  for  maximum Mylar  life  it is recommended that you still follow the guidelines in update 3 item - 3.11.


It's now almost a year since we started flying with Rotax 185 cc engines,   in general,  the  reliability  or this  engine has  been  very good, but the operating life of the recoil starters has been less than we would like.  The most common problem we have seen is premature wearing of the starting pulley  (this  is  the  cast aluminum device  which mates  with the pawls  - not the sheave on which the rope is wound).  The shape and location or the wear pattern indicates that the pawls are vibrating in synch with the  engine.  but  vibration testing  with  an  amplitude or l0g's over a frequency range o 10 to 100 Hz. failed to detect any resonances. Changing the rate or the pawl springs and adding rubber damping seems to reduce the problem a bit, but not  to an  acceptable level.   Evaluating  a potential  5olution to this type or a problem Is very time consuming because although we have had a few starters show signs of wear In the first 20 hours. Most  will  last  80 to 100 hours  before exhibiting any indication or a problem. and It can take this much running time to determine if any improvement has been made.

 After several weeks or changing, testing, and evaluating we have reached the conclusion that the only  way  to get  rid of  the problems in the Rotax starter is to get rid of the Rotax starter.  A survey of manufacturers and small engine mechanics indicated that the most reliable recoil starter  in  common use  Is  a  relatively cheap  and simple unit made by Tecumseh.  We have several of these starters undergoing testing at present. and so far the results have been excellent.  if this starter proves to have the reliability we  expect.  it  will soon become  standard on  all  of our Rotax engines.  In addition to improved reliability. this starter also provides a couple or other advantages:  It has a larger sheave  which makes  it  much  easier  to pull  when starting  the engine, and the overall size is smaller than the Rotax.  This allows us to use a  smaller engine mount which will accept a close fitting molded engine cowl to reduce drag and improve  the  appearance. The proposed mounting system will use the same rubber mounts and mounting pattern as we have used since late January 1982 (four mounts on top and two on the bottom) so retrofitting the new starters should be  relatively easy.

For those who wish to repair the Rotax starters when necessary. we will be  stocking  parts.   For  those  who would  like  to convert to the new starter. we will make a retrofit kit available as soon as the test program is complete and the necessary parts are made.  All dealers and distributors will be notified as soon as  these retrofit  kits  are  available.  As a service to customers, these kits will be sold at our cost. and the usual manufacturer and dealer markup will not be applied (when the kits are purchased to replace Rotax starters).

 6. Engine Mount Angles 

We have received two reports of broken G42 engine mount angles (these are the large brackets which are  bolted directly  to  the  crankcase).   Although  this  represents less than 0.2 of the mounting brackets in use and therefore does not indicate a trend. a careful inspection of these brackets should be included in your  normal pre-flight.   Since we will probably be changing to a different type of mount to accommodate the new recoil starter, we expect to have a few surplus mount angles which we could supply at no charge to anyone  who returns a broken one.

6.I5  Stabilizer Attachment 

Approximately a year ago we investigated a potential problem of broken F32 pushrod guides causing the  leading edge  of  the  stabilizer  to become detached from the boom.  At that time, it was determined that it would be necessary to break two F32 fittings to cause a problem. and even if this  did happen,  the  stabilizer  would be  held  in position by  the  T26 pushrods  to permit  a  safe  emergency  landing.   This conclusion was substantiated by structural testing on the ground. flight testing. and field reports.

However. we have since received one report or F32 breakage. believed to be caused by  severe  lateral  loading on  the  tail  caused by  side-slipping  - this  was not possible before the rudder pedals were incorporated). Fortunately. this did not cause a serious problem and the aircraft made a normal landing, but  it  does  renew our  concern.  This situation is not relevant to the newer kits which incorporate the folding tail because the stabilizer is secured to the boom by the hinge brackets. 6.15.jpg (30214 bytes) However. if you have one  of  the  earlier  Lazair's and you  intend  to execute some of the higher stress maneuvers possible with the rudder pedal conversion, we suggest the use of a small safety cable wrapped around the boom and T9 as an added precaution.  

6.16 Pushrod Rotation: 

If you have rudder pedals on your Lazair; you may have noticed that if you push the stick as far as  it  will go in  one  direction.  and push the rudder pedals as far as possible in the opposite direction, then reverse both to get full cross control the other way, the BE rodend on one end of the T18 pushrod will rotate  on  its threads  about twenty degrees.  Since this will happen only infrequently in service, the amount of thread-wear In the P3 will not be appreciable.  However. you should be aware of this situation  and ensure  that  the  BE which  rotates  is  threaded into the P3 at least half an inch.  Check the quality of the threads occasionally and replace the P3 if there is any indication that the threads are worn.


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