Here are the changes I recommend to the David Boddington plans which are
available from Bob Holman Plans. What these changes will do is give you a
model that will perform much better at lower airspeed than the basic Gyrace is capable of.
(1) Reduce the downthrust from 6 degrees to 4
(2) This model would be easy to build tail heavy... So I allowed
room for a flat battery pack in the nose. This worked very well. BUILD LIGHT... heavy gyros will not fly well at slow speeds at all. An autogyro is SUPPOSED to fly slow..
the real ones did... so if it won`t, it`s not a good one at all.
(3) Install a flat piece of ply for the gear mounting and use
fiberglass gear (klett #256). Keep the wheels well FORWARD as shown.
( Note (Oct 1998): It appears that the Klett glass
gears are no longer available. In this case consider ordering an aluminum gear
of the aproximate size from SIG Manufacturing..)
(4) I thought there were too many "uprights, diagonals, etc., so I
used 1/8 balsa sheet & applyed the longitudinal stringers to
give it that "round look". Personal preference... you decide
for yourself.
(5) Forget about the tail skid. Install a piece of lite ply or hardwood,
about 1/4 x 1/4 x 3"... along the bottom of the sub fin, and use
a tail wheel controlled by the rudder.
(6) My pilot is attached to a hatch plate, and the servos were
installed just below the pilot. The receiver is in the lower
part of the fuselage, between F-3 & F-6 area, accessable thru
a hatch on the bottom. I always "build-in" a area there on
nearly all models, to help when it comes to balancing.
(7) **Balance 1/4" ahead of where the plans show. And certainly
NOT AFT of the plans position.
(8) Note the dihedral braces "slope together" outboard... with no
explanation as to why. Use the TOP line, and make it 1/2" wide
all the way out. In otherwords, keep the dihedral to NO more
than 10 degrees each side, and slope the rotor pylons out about
3 degrees. NOTE of CAUTION: when building the wing...
make sure it is not 'twisted'...
(9) Open bulkhead F-2 to allow install/removing of the tank & battery.
(10) I installed my engine on its side... simply to insure good fuel
flow from the tank... personal preference.
(11) ROTORS & HUBS: I used the 3 blades, and a Clark Y airfoil with a flat
bottom was used. Seems to work exceptionally well. NOTE: My aluminum
blade mount has about 5 degrees of "cone" angle (dihedral) bent in for each
blade... I RECOMMEND THIS HIGHLY! The blades that rach over the inside wing and
fuselage should be level with the horizon. The aluminum blade holder below
is set for the right side rotor and a Clockwise (CW) rotation. Note
the negative incidence bent into the blade mounting tang.
(12) Using the smaller (3/32 bearings & shaft) I went with a light
ply rotor pylon... and it has worked very well. These very
tiny bearings have proven to be remarkably durable. An
alternate Hub assembly could be used, using 1/8" music wire
shaft, & 1/8" ID ball bearings. A bit heavier, but more sturdy.
if you use the 1/8" approach, I`d go with normal ply for the
pylon. NOTE: I extended the "stitching" to include the lower
horizontal portion of that shaft.
(13) Nothing says you can`t go with the brass sleeved hub... except
that with Ball bearings the problem of spining drag, etc., is virtually
eliminated!
(14) I did NOT use the Pull-Pull rudder cables. Use normal
lightweight nyrod.
(15) Due to stability problems on the first couple flights, I added
extra fins, same shape but 1/2 the size, to the outer ends of
the Stabilizer. These replace the carved stab tips.
The extra fins actually weighed less than the carved balsa tips.
ADDITIONAL NOTES:
Bearings used: Model car.. Team Losi # A-6812 XX 3/32 id.
4 for $20, at your model car hobby store.
Set rotor rotation to rotate with the forward moving blades OVER the
fuselage. (CCw left ... Cw right)
When held by the wing at the CG position, the model should tilt nose
down 5 to 10 degrees.
To recover from an unusual attitude... even on T/O... just chop/reduce power
& relax on the sticks.. it will normally right/level itself.
Flys well on a good.40. At or near sea level, an OS .32 would
probably work well. A Thunder Tiger .36 would also work well.
This model has a "lifting stab"... the tail will rise quickly on T/O
roll... so hold the tail down a bit just to get started straight, then
allow the tail to rise & then HOLD the nose down until the rotors accelerate,
followed by a normal T/O as you would do with an airplane. If you attempt
a crosswind T/O the upwind rotor will spin first... so delay lift off until the downwind
rotor accelerates like the other one.
My initial T/O`s were a quick climb to 10 feet, followed by a
roll inverted.. Corrections made were to bend in the 5 degrees cone
angle on the blades, building a new wing with only 10 degrees dihedral,
substituting the extra fins for the carved stab tips, and reversing
the direction of the rotors.. now having the inboard blades moving
forward. It now flys absolutely beautiful...
If the weight is 56 ounces or less, it will easily hover in a breeze
of about 8 to 10 knots.
Enjoy your Gyrace.......... Jim B.
Plans page...
Gyrace model page..
rev..11-2002..jb