Hints & Tips for building a successful flying model autogyro, from the modelers who have been there, done that, and were successful!

From Mark Nienhaus:  "An inexpensive source for Rotor Blade shims..."

I believe I have found another source for  [rotor blade] shims.   I work for Eagle Hardware and Garden.   I was over in the lumber dept. where wallboard tools are located.   I found some cheap throwaway plastic putty knives made by Walbro they cost about  .89  and you can make about two shims out of one blade.   I hope this will help those having trouble getting the Ernst shims.    I believe the blades are tapered 2 degrees.

From Jim Baxter:  "Standardize... and save time and effort"

Blades require probably the most painsaking effort when building autogyros... So as a suggestion, I recommend you try to standardize many as many items as possible between models of similar size, especially your blade mountings..
As an example, use the identical blade mounting bolt(s) spacing on as many of your blade tangs as possible. The vast majority of my blades have the sheer bolt/stick hole drilled 3/8" in from the root of the blade and the hard mounting bolt hole is spaced 3/4" outward from that.   I try to use the 3/4" spacing even on larger blades where possible...
Why bother?  Well, you -will- break/bend a blade or two, and thus it is easier to switch blades between models, etc.  You can even take a damaged set of larger blades, trim off the tips (check balance), and use them on another model.... since the blade mountings are the same..


From Rick Anderson:  "Useful Materials & Parts...."
(1)  An excellent rotor shft/axle is the Klett wheel axles with the grey nylon wheel sleeves.  The sleeves function very well as a substitute for metal bearings in rotor hubs.
(2)  Don`t hesitate to use your covering film/fabric for hinges on the tail surfaces... this saves weight and if ironed on properly they are just as strong as the standard hinges, and they eliminate the air-gap..

From Steve Tillson:    "Heat  Shrink   blade  covering"

(1) Cut "sleeves" oversize (an inch or so overhang on blade tip & root)
(2) Center blade inside heat shrink.
(3) Beginning on the underside of blade, apply heat from center working towards one end.
(4) One technique for smooth tips is to weight down the opposite end of blade with a phone book, then by gripping that 1" of oversize with a pair of pliers, heat and pull downward & stretch simultaneously, stretching out wrinkles.
(5) Allow to cool slightly as a bead of CA is a applied between "shrink" and wood blade, spritzing quickly with "kicker"
(6) Finish the rest of blade as above.
(7) Sand any remaining "overhang" and wrinkles smooth both at tip and root end
(8) Double check that all "shrink" is bonded to the wood at tip and root
(9) I should mention that I then trim the excess heat shrink off and apply medium CA, with kicker, to fill the gap in the sleeving.   When it's good and dry,  I use my sander to really smooth the root and tip.

Editorial note:   The most efficient rotor blade is one which is not only  balanced, but as  smooth as possible.

Heat shrink not only provides a smooth finish, but adds to the overall strength of the blade.


From Jim Baxter:     "One method of building an efficient,  strong,  yet very light rotor blade"
Important keypoints to remember:   Use quality light weight balsa sheets and constantly form each blade virtually identical to each other during construction,  with a cross check of equal weight of each blade.    If your blades are going to be larger than the small ones discussed below, it is recommended that you purchase the airfoil shaped balsa sheets available from SIG  manufacturing.     The use of the SIG sheets provide you with a uniform preformed airfoil surface to begin with.     This would save you considerable sanding.    However, I also suggest you weigh each (SIG) sheet and construct your blades from ones of equal or near equal weight.   All this effort & caution at the beginning pays off in huge dividends when it comes to the necessary  balancing which will be covered later.
(1)   Select a good quality sheet of light to medium balsa ,  with a uniform grain/weight throughout.    By using a uniform weight sheet,  it will be far easier to complete all blades with a minimum of difficulty in balancing.    If it is going to require more than one sheet of balsa, purchase "matched" sheets if at all possible.   Mark & cut out the blade blanks.
(2)  Select very straight square hardwood strips  (spruce, pine, etc.) for the leading edges.     For rotors of 36" or less  (each blade less than 18")  I use 1/8" square strips.    Cut the strips the length of the blades,   and epoxy to the leading edges of each blade blank, keeping the lower surfaces flush with the table.     I use a very flat surface and weight everything down while the epoxy is curing.     It is important to keep things as flat as possible!
(3)  Make an  airfoil template from a thin card or plastic. File & sand the blade blanks to shape.    It is important to keep all the blades as equal & uniform in shape as possible.   The more uniform the airfoil the higher the efficiency and performance.
(4) Cross check the individual blades thoroughly for uniformity in weight & airfoil .    Once you are satisfied, then "flat" sand a slight flat edge to the hardwood leading edge,  just enough to allow for the glueing (epoxy) of a piece of thin (1/32") music wire,   and still be able to maintain the smooth airfoil curvature of the leading edge.    Cut the wires to the length of the blade, then bend in an "L" hook in each end using aproximately 3/16" of each end.    Hand drill a small hole in the spruce L.E. strip where the "L-hook" will enter,  and using a thin bead of epoxy,  secure the wires in place.   Use some scotch tape strips wrapped laterally across the wire to keep it in place.    Run your fingers along the sides of the wire, to smooth out the glue bead.
(5)  Cut two (1/8" wide) strips of (iron-on) Carbon Fiber for each blade, equal to the length of the blade, less perhaps 1/2".     Mark the strip location at the chord balance line (usually at 25% of the chord) on both the top & bottom of the blade(s).   Tack the CF in place with a covering iron.    Then use thin CA glue to secure the CF strips to the blades on both the top & bottom.    Use a small piece of waxed paper,   to keep the strip smooth to the blade when applying the CA.    Start the strip flush with the root end, and it can be about 1/2" short of the tip when glued in place.     The reason I leave about 1/2" open,   is because you may have to insert some weight at his point during balancing.
(6)  We are now ready to install bolt mounting pads to the root ends of each blade.    These pads go where you will drill & mount the blades to the rotor hub blade holding bars (sometimes called "tangs") . NOTE:  Be sure these pads are centered lengthwise along the chord line (where the CF strips should be).    Cut these rectangular ply mounting pads from 1/64 (bottom) and 1/32 (top) plywood, and epoxy in place,  using clamps to insure the top pad conforms to the airfoil curvature.    For small blades of this size,  the pads will be generally about 3/4" wide,  by 1 1/2" long.    NOTE:  Be sure you glue these pads to the correct ends of the blades!   If the blades rotate CCW when looking down from the top the pads will be on the left.    After the epoxy is dry,  Carefully mark and drill for the mounting bolts & shear pins.    These holes must be aligned lengthwise and spaced properly to fit the mounting holes in the rotor hub tangs.    This careful alignment is necessary to insure the blades radiate at the correct/accurate number of degrees apart when mounted to the Hub.
(7)  Except for balancing, the blade(s) are ready for covering.    Monokote is excellent, as is heat shrink.   The important thing here is that they need to be smooth and the easiest way is to use something light & smooth like Monokote or heat shrink.   NOTE:  It is advisable to completely balance the blades before covering.    Balancing will be explained in the next chapter.
(8)  These specific instructions apply to my method of making the blades for my small MINNIE autogyros.    However I use virtually the same system for larger blades, except that I up-scale the sizes of everything accordingly.

Now   let`s  balance  those  blades!
  It is very important to completely balance the blades.   Each one must balance along the chord line,  a line drawn along the highpoint of the airfoil which is generally between 25% and 33% back from the leading edge,  and running parallel to that leading edge.   Be sure you use the identical line for each blade.  Additionally,  each must be checked for balance along the length of the blade.     It is easier to perform the chord line balance first, the follow up with the lengthwise balancing.    Finally,  mount all the blades on the hub assembly,   and while holding the assembly on a suitable shaft,   spin the rotor a few times to determine if any particular blade seems heavier.
(1)  To begin all this,   insert a thin nail, or piece of wire, in the mounting hole at the root end of the blade, and suspend it vertically in line with a door frame or something else known to be vertical.   If you`ve done your work well in building,  the blade leading edge will align fairly well vertically.    Check and compare each blade using the same procedure.   It`s possible that each blade may require a slight amount of weight between the chord line  (where you placed the Carbon Fiber strip)  and the wire leading edge, at or near the tip of the blade.    If the blades are all equal,  and are within about a degree of vertical, they should be OK.    If any are off,   you can cut a small hole and epoxy in a lead fishing "bb" to bring the blade into balance.
(2)  Now,  the blades must also be balanced spanwise,  along their length.    Using a small dowel,   place a blade perpendicular on the dowel & rotate the dowel to "teeter" the blade to locate the lengthwise balance point of that blade.   Do this with each blade and mark the point of balance.    Ideally, all blades will balance at the identical point along it`s length.   If any mark is more than 1/8" (my personal limit) off from the others,  insert/glue a bit of lead weight at the appropriate end of the blade to bring it into balance.    NOTE:   insert/glue this weight in line with the chord balance line.   This is necessary so that you do not change the chord balance of that blade.
(3)  Once you have balanced the blades, you can now cover them with a material such as Monokote.   I highly recommend you use a bright color on the top, and a very dark contrasting color on the bottom.    You will find this aids considerably in maintaining an orientation on this small model in flight.
Finally,   I might mention that an excellent weight to use for insertion / gluing into such small blades is the tiny "split" lead fishing line weights ( the size of bb`s, with a slit in them).   They are easy to compress / reshape  using pliers  to accomodate a small hole in the thin blades.    I generally use epoxy to hold them in place.


From Steve Tillson:   "Inserting small weights in Blade tips"
Drill a suitable size hole in the blade tip,   and insert/glue a small plastic tube, such as an outer Nyrod sleeve,   and then slip a number of lead bb`s into the tube....  as necessary or desired for balance, etc.

You may want to take a look at our "Frequently Asked Questions"   page for additonal hints on building, as well as flying.


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