Lazair Ultralight Aircraft Newsletter Number  5        June '82

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5.1 Lower strut plug installation

Early Lazairs (the ones with the spoked wheels) were designed so that the P16 strut plug extended beyond the end or  the  T27 strut  tube.   Later models  (with  the "Tundra Tires") have a larger diameter axle (i~)ich increases the spacing between the F6 gussets to 1 1/4 inches) and therefore the P16 must be installed so  that it is  flush  with  the  end or the T46 strut tube.  If you have one or the first few kits shipped after the changeover, your assembly instructions regarding the position or the P16 may have been somewhat ambiguous. Please check to make sure  that ~our P16's are installed as shown below, and there are two 315 bolts in each strut plug (P17's as well as P16's).  As a secondary check. you can measure5.1.jpg (23247 bytes) the  Dihedral  by stretching a string between  the top or the D-cells at the tips.  The distance from the string to the too or the 0-cell at the root should be between 8 and 12 inches. 

If it is necessary to reposition your P16 plugs, it should be possible to do so without having  to scrap either  the strut or the plug.  ~whenever possible. use existing holes in the strut.  Rotate the~Pl6 and drill new holes in it as necessary.  Make sure the center or the lower strut hole is at least 1/2 inch from the  end or the strut.


5.2  TINY Bubbles IN THE LINE  

Now that we have eliminated the primer bulb. the in-line filter, and the tee fitting. the problem or bubbles in  the  fuel  line should be gone forever - but now we have round a new source or bubbles - this one even more intriguing than the others. 

After one or our factory demonstrators displayed some noticeable bubbles. we checked the fuel line  for  leaks and determined that there wass no place where air could get into the line - this is the main advantage or the submersible fuel filter.  Since the bubbles appear to emanate  from within  the  fuel  itself,  it  has  been determined that  the bubbles are not air, but vaporized fuel.  The exact cause or these bubbles is difficult to determine, but it is believed that water in the fuel effectively plugs the filter.   Then each time  the diaphragm in  the  fuel pump is pulsed  there is a momentary reduction in pressure in the fuel line.  This reduction in pressure lasts for only a  fraction or a second, but it is sufficient to cause a small amount  of fuel  to vaporize and form a tiny (almost invisible) bubble.  These gradually merge to form larger bubbles as they migrate toward the carburetor.

This theory has not been proven, but it has gained credibility when the fact that any time  the problem has occurred,  it has been eliminated (completely) by removing the felt from the fuel filter and rolling and stretching it to get rid or the water. 

We are now investigating the use or other materials (such as a brass screen) to eliminate  the  felt  filter. In the meantime, check your fuel lines for bubbles frequently while flying.  Check your filter periodically (especially if you suspect there may be water in the fuel).  Roll the felt between your hands,  stretch it, compress it and then put it back on. 


To prevent possible damage to the starter pulley on the rotax engine, it is essential that  the starter pawl assembly be centered properly.   If you remove  the starter assembly from the engine or if the engine is removed from the engine mounting assembly, the starter assembly position should be checked after re-assembly as follows:

First, make a measuring gauge  from thin sheet metal as shown.   Use this gauge  to check the radial spacing between  the starter housing and the magneto ring.  Check the spacing at four places (approximately equally spaced) around the5.3.jpg (41229 bytes) circumference and make sure it does not vary mare than plus or minus 1/32  or an inch.  If necessary, loosen the 5/16 inch mounting bolts and re-position the engine on the mounts.



Since the introduction or the rotax engine in November '81 we have had three reports or broken propeller bolts.  After examination, it was determined that one or these failures was a result or the engine being run for a considerable length or time with the propeller bolts loose.  The other two resulted Prom the propeller bottoming on the crankshaft nut rather than seating properly on the hub.  A special notice regarding this potential problem and a suggested method or checking the depth or the counter bore in the propeller was mailed to all owners or kits shipped prior to January '82 (those who we thought could have experienced this problem) but it appears that some or the notices either did not reach  their destination or  were ignored by their recipients.  

Please check the installation or your propellers and ensure that they are properly seated on the propeller hub.   The depth  or the counter bore may  be increased slightly if necessary to allow the propeller to fit properly against the hub.  

To reduce the possibility or a bolt failure (even if a propeller is improperly installed) all kits shipped after May 17, 1982 have the bolts inserted through the hub in the opposite direction to that in5.4.jpg (49411 bytes) the original configuration.  To increase the margin or safety, it is recommended that owners or Lazairs shipped prior  to May 17, 1982 reverse their propeller bolts as shown here.                                      


 This requires drilling out bolt  which goes  through configured, the bolts were the holes in the propeller hub to 5/16 inches diameter, and allows the part of the hub  (where  the stress is highest) to be the full diameter.  As originally threaded into the propeller nub.  

The threads on the bolt not only reduce the cross sectional area of the bolt by approximately  forty percent, but  they also introduce a stress concentration, which, under fatigue loads, can be as high as 2.7 to I.  By reversing the bolts, the threaded part of the bolt is moved from the area of maximum stress  to  the area of minimum stress.


To insert the bolts as recommended, it will be necessary to remove the propeller hub from the crankshaft.   If you don1t have a gear puller, the following method may be used: First, loosen the crankshaft nut and screw it off until it protrudes about 1/16 of an inch past the end of the crankshaft, then remove the propeller hub using a puller made from 1/4 inch steel and the two propeller bolts as shown.  If you don't have a piece of steel handy, you can use one of your nacelle weights and drill a couple of 3/8 inch holes in it.  Tighten  the two bolts alternately,  slowly5.4a.jpg (28588 bytes) and evenly until  the hub breaks loose from the crankshaft.  Tapping the puller where it fits over the end of the crankshaft, while you tighten the bolts, may help to loosen the hub.

When drilling the holes to 5/16" diameter, make sure the drill is perpendicular to the race or the hub.  Make sure you put the bolts in the hub before you install the hub on the crankshaft. 

To reinstall the propeller hub, make sure the taper on the crankshaft and the hole in the hub are absolutely clean and  free of grease. Apply a small amount of Loctite 242 or similar locking compound, fit the hub onto the shaft and tighten the nut to a torque of 35 root pounds.  After the propellers are installed,  the NSC propeller nuts should be tightened to a torque of 15 foot pounds. 


In update number 2 we discussed the problems of catching long grass in the cables.  To alleviate this problem,  all new Lazairs have the cables attached to the stabilizer at the end of the spreader (TlI or TilS) rather than at the lower (outboard) corner as was done originally.  If you wish to modify your Lazair to move the cables uo~ it is a relatively easy change provided that you have access to a Nicopress tool and sleeves, since the cables must be shortened.  If you can't locate a tool readily, check with your local EM chapter. 


In a previous update (item 4.4, December '81) we reported on a potential wearing of the T26 pushrods where they pass through the F32 pushrod guides.  To alleviate this situation, kits shipped in May and 3une of 1982 included a roll of 5421 or 5423 abrasion resistant tape.  We have been flying factory demonstrators  with this tape installed for over four months and have not encountered any difficulties.  However, if the tape is not properly installed, or if it becomes damaged (by mishandling while assembling or trailering the aircraft) there is a possibility that it could come loose and get wedged in the F32 making it difficult to move the ruddervator pushrods. Although this has not happened, the possibility does exist.   Therefore,  if you have the  tape on your aircraft, it is recoemended that the tape be recoved from the pushrods and discarded.  If you received the tape with your kit, but nave not installed it yet, don't.  

5.7        D-CELL NOSEERIBS 

The owner of a highly modified Lazair reported recently that several of the foam noseribs inside his D~el1 had moved out of position.  This was one of the earlier kits with the .016 inch D~ell skin, (kits A192 and subsequent have a .020 inch D-cell skin) and was fitted with relatively heavy reduction units and very large propellers.  

Although this is believed to be an isolated case, it is recommended that all  owners check the position or their nose ribs occasionally (especially in the area or the engine nacelles).  This can be done easily by tapping along the top or the D-cell (about 4 inches ahead or the main soar) and listening  for  the ribs. There should be a rib every 4 inches.  if you should ever get an indication that two or more adjacent ribs are out or position, drill out a few rivets so that the D-cell skin may be lifted sufficiently to look inside (with  the aid or a flashlight). Any displaced ribs should be repositioned and bonded in place with panel adhesive.  To avoid loosening the D-cell skin, remove only as 'many rivets as necessary and use  tools made from coat hangers to fish the ribs into position.  

It should be noted that because of this possible problem, the use of Rotax engines on a Lazair with .016 inch leading edge skin is not recommended.  


In spite of the fact that carburetor studs are installed with Loctite and the carburetors are attached with metal to metal shake proof nuts,  we have had three reports of carburetor studs or nuts working loose on the Rotax engines.  while it is unlikely that this would ever cause a carburetor to  fall off ,  it could become loose enough  to cause an engine to stop.   To lessen the chance of studs becoming loose, make sure the carburetor nuts are tight.  They should be retightened after the  first  few taxi runs,  before  the  first flight,  and at least once every 20 flight hours thereafter.  Tightening the carburetor nuts can be made much easier if you modify a 10 mm wrench by making a 45 degree bend in it about 1 1/2 inches from the (open) end.  


As with any engine, the head nuts on the Rotax recommended that  this be done after taxiing nuts should be tightened in the sequence shown engine should be re-torqued after the break-in period.   It is and before the first flight.  To avoid distorting the head, the in the figure below.  

When re-torquing the nuts, they should be torqued to 17 foot-pounds.  If a head has been removed, or the nuts are very loose,  tighten all  the nuts to 5 foot pounds each (using the sequence above), then to 10 foot pounds, then to 17 foot pounds.  


Note: In 1982 a completely revised Lazair assembly manual  was introduced.  For the benefit of those owners having earlier revisions of the manual,  some selected paragraphs from the new manual are reprinted below.  If you have completed your Lazair, you may wish to check the items listed below,  but note that  this information is provided as a guide only.  If you are satisfied with the way your aircraft riles, it is not necessary to make changes based on  these checks,  however, you might rind the information useful if you plan to make any other changes.


Flight  testing has shown that  the Lazair is very tolerant or changes to  the  position  or  the center-of-gravity.  However,  for comfortable hands -off flying at a reasonable airspeed. and for assurance that there is no gross error effecting the center-of-gravity, the check outlined below is recommended with the center-of-gravity positioned as desired, the Lazair should trim out hands-off at approximately 25 to 28 ~H indicated airspeed. 

With the seat positioned as indicated in the Assembly Instructions,  the pilot sits  very near the center-of-gravity, so reasonable differences in pilot  weight do not have an appreciable effect on the position or the pilot's feet, or even the type or shoes he is wearing. Minor in-night  adjustments  to the position or the centre-of-gravity can be made by just moving the position or your feet.  Also, there will be an effect from the weight or the fuel, so it is recommended that the following check be made with the  fuel tank approximately half full. 

With the aircraft on the ground and the pilot sitting in the seat in the normal (or most comfortable) seating position,  raise the  tail until the boom is level (use a spirit level).  Hold the aircraft in this position with a bathroom scale under the spreader (T115). The reading on the scale should be between I and 5 pounds. If the aircraft meets this requirement it is adequately balanced for the first test fight (If possible the first fight should be made by an experienced Lazair pilot who is capable or recognizing any unusual flight characteristics).  Fine  tuning or the balance is best done by flying the aircraft and adjusting the centre-of-gravity for hands-on trim at the power setting and airspeed preferred by the pilot.  


Move the stick as far as possible to the right, making sure it is neutral  rore and art.   Check that  the aileron deflecti5.10.2.jpg (17028 bytes)on is  within the limits shown in the figure. Move the stick as far as possible to the left and check the aileron deflection. Aileron travel may be adjusted by removing or inserting  washers as described in the Assembly Manual:  


Push the stick forward as far as possible.  The downward deflection or the ruddervators should be such that they almost touch each other. Adjust the length or pushrod T18 as required to achieve the correct downward deflection. 

Pull the stick back as far as possible.  The upward deflec5.10.3.jpg (14575 bytes)tion or the ruddervator (from the neutral position) should be within the limits shown.  Adjust the stop on the control stick as requifed to obtain the correct upward ruddervator deflection if the stop is moved, be sure to recheck the downward travel and readjust if necessary.


Please check the clearance between the 35 bolt holding the EE rod end to your F39 aileron bellcrank (F39) and the spar cap  (reference drawing C in the parts catalog). Although we have seen a problem in this area, a worst case tolerance buildup plus a slight error in locating the bellcrank mount F38 could possibly combine to cause the bolt  to foul on the spar cap. if necessary the spar cap should be bent slightly to provide sufficient clearance. 


When the large (20 litre) fuel tank was introduced  the assembly manual indicated that  the rubber strap holding the tank in position should be routed over the top or the tank and beside the large cap.  As most owners have already realized, an extra measure or safety can be obtained by routing the strap through the handle on the fuel tank before hooking it onto the T22's. 


We have had one report of loose rivets on a fuel tank support angle (where it is riveted to  the  T22's), after a series or hard landings. As a minimum, these rivets should be checked on your walk around, and it is recommended that they be removed and replaced by stainless steel rivets.  on older models the rivets would be those in FY and F30.  on newer models, (with the 20 litre fuel tank) this would be G62.  on newer models, it is also recommended that the bottom three rivets attaching the fuel tank saddle, G63, to the seat back, be replaced by stainless steel as an added precaution. 


After three years of production and hundreds or Lazair flying all over the world there was never a report of nacelle mounting bolts working loose in flight until last  week when we were told or two such instances.  Fortunately,  the renaming bolts held the engines on the wing but the possibility of an engine falling off is obviously somewhat disconcerting.  Since the mounting bolts are threaded into nut plates  with an elastic stop nut  feature.  The bolts should stay in place unless something degrades the gripping action or the stopnut. Although the grip can be reduced slightly with repeated insertion and removal of the  bolt. Other factors such as the presence or grease or oil are probably more significant.  

To make sure your bolts don't work loose, it is recommended that they be lockwired  This may be done by replacing  them with drilled-head bolts (type AN3H5A and AN43HA) or by drilling a small hole through the heads for the lockwire.

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