Acrolite® 1B


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Information update on the Acrolite Biplane

   It is expected that all builders should have the latest version of the plans, the latest version is dated 08/08/98 this info is contained in the title block in the lower right corner of each plans sheet.  Information related to the old plans set has been removed from this website.  If you do not have the latest version contact Aircraft Spruce at info@aircraft-spruce or by phone at   1-800-861-3192 or Ron Wilson through this web site by Email at or by Fax (Voice) at: 1-807-935-2587.

Here's a list of a few of the changes that we have made during the construction of the latest Acrolite.

Aileron Spars

   The plans show a short length of half round lead weight riveted in the ends of the aileron tube spar.  By using spar tube with a wall thickness of .120 the ailerons will balance with little or no lead weight.  Some builders may find 1 1/4 x .125 6061-T6 tube difficult to find as it is not very popular for aircraft use.  It may however be available from some industrial suppliers.  Using the heavier tube will save the builder the work of building and fitting in the aileron balance weights.

Fuselage Contour

   The plans show the aft half of the fuselage as a gradual curve from the cockpit to the tail post and alternately a straight line is shown.  Builders may find that the back of the fuselage is easier to build as a straight line as the curvature is difficult to maintain after welding.  Just heat the longerons at Sta. 5 and pull them straight to the tail post.  Note that this will effect the size of the turtle-deck bulkheads.  The straight line has the effect of giving the fuselage a longer sleeker look.  The curved line gives the aircraft a shorter stubby look.

Cabane Structure

   On the second Acrolite the top cabane was bolted to bushings welded to the top longerons.  The fitting of the top cowl around the top wing cabane structure was difficult and time consuming, also it prevented the top cowl and windshield from being located as far back as it should be.  By bringing the top cowl back and fitting it around the cockpit to the turtle deck it will close the cockpit in better and will allow the windshield to be installed back as far as possible and for the future fitting of a canopy.  Some of the pictures show how this is done.


   To achieve the optimum performance it is essential that the propeller be perfectly matched to the aircraft/engine/gearbox combination.  This is true of most aircraft and especially so with the  Acrolite.  A number of different wood props were tried with a 68 x 48 being best for climb and a 68 x 50 being best for  cruise on the 912 and a 66 x 48 with narrow blades was best on the 618.  Since building one propeller is a substantial job never mind couple of extra ones to try, the builder may want to try one of the ground adjustable carbon fibre props.  We have had good result with the Warp Drive prop using 70" blades then cutting the blades down and adjusting the pitch until optimum performance is obtained.  Of course the pitch and diameter will depend on the gearbox ratio used.

Bushing Material

   The bushing material shown in the materials list and supplied by Aircraft Spruce in the kits are not as specified in the latest revision of the plans.  Rather than use bushing material we found it easier to use heavy wall 4130 tubing.  This makes it easier to drill out the bushings and the wall thickness is a little thicker making it easier to weld.  Use 1/2" OD x .095 for the 7/16 x 5/16 stock and 3/8" OD x .065 for the 5/16 x 1/4 stock and 5/16" OD x .065 for the 1/4 x 3/16 stock.  The material will shrink a little after welding and may have to be reamed for proper fit

Aluminum Wing

   The aluminum wing is built with .025 thick aluminum skin on the leading edge and .020 on the trailing edge. When building the wing it is sometimes difficult to keep the .020 material taunt enough to keep it from oil canning between the ribs.  If appearance is a concern builders may want to use .025 on the trailing edge as well.  This will add over two pounds to each wing panel or close to ten pounds to the total weight of the aircraft.

2 Cylinder Rotax Engine Mount

   The latest version of the plans shows a change in the way the engine is mounted.  The change was made to try to have the mounts close to the engine thrust line.  The materials for this are not supplied in the materials package from Aircraft Spruce so they will have to be obtained separately.  A 12" square piece of 1/4" thick 2024-T3 aluminium plate and the necessary bolts to attach these plates to the engine will be needed.  Also four 61036 Lord plate holder mounts will be required.  The mounts are 3" square with a 2 1/2" bolt hole pattern and have an axial spring rate of 720 lbs./in.  These mounts are typically used on some Eipper and Quicksilver ultralight aircraft.  Note that all mount tubing is .625 x .058 4130 tube, not .049 as shown on the old plans set.

 Wing Incidence

   The plans and the builders manual show the wing incidence as + .5   degrees. top and 0   degrees. bottom this should be changed to -1  degree top and -1.5 degree bottom.  The reason for this was that with the old setting there was still too much trim drag at cruise speed.  The top wing has more incidence than the bottom so the top wing will stall first and drop the nose for a quick recovery.  This works very well the Acrolite has a very gentle stall and holding the stick full back just results in the aircraft stair stepping down under full control.  If the aircraft is built very light the builder may find that there is still too much incidence in the wings.  This is noticed when with full nose down trim and the throttle at cruise setting some forward pressure is needed to keep the aircraft from climbing.  Drilling a new set of holes on the main spar plates 3/8" above the old ones will be required.  Remove the wings, drill the new holes then re-attach the wings using the new hole locations. This will reduce the lift and correct the condition. A Jig block cut to the pattern of the front half of the wing section and the proper incidence angle cut on the top will make it easier to measure.  An example is shown in one of the attached drawings.  The jig is cut out of a piece of 3/4" thick particle board or plywood.  A separate jig is required for the top and bottom wing.  Just hold the block on the wing and use a carpenters level to check it.  Be sure the fuselage is blocked up level first.

Struts & Gear

   Some builders have had difficulty getting the proper strut material from Aircraft Spruce as they do not stock it and are not supplying it in the kits.  If the aircraft is to be stressed to the full 6 g. loading it is imperative that the lift struts be built from the 3" x 1 1/4" aluminum strut material specified in the plans.  The interplane struts can be built from the smaller  2 1/2" x 1" material that is easier to obtain, if desired.  Using the smaller interplane strut material will require modifying the S1B and S1C strut fittings. Strut material for the Acrolite will have to be ordered from SKYTEK, they are the distributors of the struts that are manufactured by

Carlson Aircraft Inc.

It can be obtained on the web at

They claim to have it in stock at $41.50 U.S. per 10'6" length. (good price!)

To Contact Sky-Tek:

Voice 1-330-426-3934          Fax 1-330-426-1144

The mailing address is

SKYTEK Light Aircraft Kits and Components.
Carlson Aircraft Inc.
50643 S.R. 14 - P.O. Box 88
East Palestine, Ohio 44413 USA

   The part number is A2681 and it comes in 10 ft. 6 in. lengths. If one is careful it is possible to get a lift and interplane strut out of one length. The 6" x 6' x 5/8" bar for the landing gear is also not being supplied by Aircraft Spruce in the kits.  We obtained the material from a large industrial metal supplier.  You may want to look for one in your area.  Since bending it takes a lot of care and a 30 ton press most builders may want to look at having one of the landing gear suppliers that advertise in Sport Aviation or Homebuilt Aircraft magazines make it up.

Rudder Pedals

   The rudder cable guide bushing mounts are shown as being welded to the upright tubes at sta.2.  Builders with short legs that have mounted the pedals further back or in a more upright position have noted that there is binding between the cables and the cable guide.  To alleviate this condition the cable guide bushing mount should be welded to the diagonal tube that runs from the aft side if the gear to the top of sta.3.  Lowering it slightly to line up with the cable attach point on the rudder pedal will help also.

Control Column

  The distance between the pivot points on the C4A idler arm and the C3 arm on the control stick should be 3.25 inches.  Builders should check that this correct on their plans set.

Aileron Linkage Arms

   The proper horizontal distance from the center of the aileron spar to the center of the pushrod attach bolt hole is 1.875 inches.  Builders should check that this correct on their plans set.  This will allow the ailerons to deflect to their full travel without the push rod hitting the lower wing rear spar at full deflection.  It is recommended that the amount of aileron travel be adjusted by varying the location of the push rods in the C2 torque tube arms and the A4 idler arms.