

 PLEASE NOTE.....I'm a serious electric flyer and most of my designs are
for e-planes.  However, do not hesitate to adapt these to glow engines.  As
a matter of fact my son is a glow flyer and he builds a lot of my designs as glow
ships.  This one in particular has proven to be a great .20-.25 powered machine.

  If you build it glow powered, do not get fooled into beefing up the design.  Simply make
a firewall to mount your glow engine upside down, at about a 45 degree angle to 
allow the muffler to clear the fuselage.

  Take advantage of the light weight design and you'll have a very light, very aerobatic
airframe.  Don't be put off by the clark Y airfoil...this plane flies very very well, both
electric and glow powered.





The AmpMaster

By Al Eastman


	This design came about after I took a look at an advertisement
for Stream Inc's small 25E electric plane.  I immediately thought why not 
do something along that line, and make it larger for easier gear
installation and yet finish lighter than their advertised four pounds.
	
	Turns out it wasn't that much of a challenge, the lighter part at
least, and I had the drawings done in a couple of evenings.  Building went
pretty quickly as well, and I had it framed up and ready for covering in a 
few days. Should have hidden it away though, as my son dropped in for a 
visit and seeing the uncovered airframe decided he'd have to have one as well.

	Since he's a glow flyer, that meant back to the cad program for some
slight mods for a slimer engine.  The next day he had an almost framed up 
airplane and a big smile as he left for his own workshop.

	I like simplicity, and this plane was designed easy to build and 
easy to use.  Turns out it is a pretty easy flyer as well, and thoroughly
aerobatic, in fact the most aerobatic electric I've done to date with the
exception of my e-streak.  It will do anything you ask of it except for 
extended verticals.  Not that it's any slouch in the climb, as there is 
plenty there for loops, Cuban eights, stall turns etc.

	I used all contest balsa except for the 1/4 square stock.  You will
need eight sheets of 1/16th by 4 by 48 and 2.5 sheets of 1/4 by 4 by 48
balsa, as well as oodles of 1/4 square and some 1/4 triangle stock.  A 
small amount of 1/8th and 1/16th aircraft ply is needed as well.


	Glow versions can use regular balsa, but pick light stock.  Jon's
.25 powered version was about 2.75 lbs ready to fly.

	I like to have ships which are compatible with my existing battery 
packs, so most every design is either for ten or twenty cells.  I've
learned to use the standard astro 05 as if it were an FAI 15.  If you 
look at the winds for these two motors, you'll see they are the same, 
except for the wire gauge. Consequently the 05 works just fine on ten 
cells, provided you prop the motor correctly, or use a gearbox which 
allows pinion change so you can gear for a certain amp draw.  I find 
somewhere around the 25 amp range works well and this means using a 10/8 
master airscrew electric prop on the ten cells.

	I used the MEC gearbox and tested a number of pinions before finding
one with 24 teeth which gave me the best combination of amp draw and rpm
with the 10/8 prop and MEC's standard 60 tooth spur.  You can find many
pinions for this gearbox at any shop which sells rc car racing supplies. 
The box is standard 48 pitch, but you will have to drill the pinions to 
fit the astro shaft.

	So let's get down to the building.  I built my wing on an adjusto-jig,
but realizing everyone won't have one of these I've provided drawings of
the ribs with tabs.  Tabs on the top?   Well, this wing is one piece with
NO dihedral, so the wing is built upside down on the plans.  The tabs allow
for alignment. There is a bit of natural dihedral on the wing bottom due to 
the wing taper.

	Print out the wing ribs and glue or tape to balsa blanks and run
them through the hacker of your choice. If you have an adjusto-jig
I have provided alignment hole locations.  The airfoil is the "real" 
Clark Y generated in Compufoil.	 NOTE that there is NO center rib used, 
although I have provided a drawing of one in case you want to place one
there.  I used two sub ribs about a half inch from the wing center to
allow a servo to be mounted between them.

	I said I like simplicity, so this plane is designed around 48 inch 
balsa.  The one piece wing allows full span sheeting without cutting
any of the sheeting.

	Pin a 48 inch 1/4 sq. spar on the plans.  Align all ribs, and install
the top (bottom) spar, either cutting it in two, or scoring it a bit to 
allow the minor dihedral bend. Strip 1/4 inch balsa strips from your 1/4 
sheet for the trailing edge, and also a set for the leading edge. If you
want to get extra jazzy, use some carbon fibre strip along the top of the
spars.

	Install wing webbing full span using 1/16th sheet with the grain
vertical.  A 1/16th piece of aircraft ply is used as a dihedral brace as 
per the plans. I cut through the center ribs to install the dihedral brace.
Place this brace on the rear side of the spars. The wing webbing goes
on the leading edge side.

	I used scrap 1/4 balsa to make up a dihedral brace at the trailing
edge, and also to fill out the airfoil to the sheeting line to prevent
the wing mounting bolts from crushing the wing sheeting.

	Note that the leading edge is made up of two pieces of 1/4 to form
a half inch.  The sheeting is glued on over the first piece, and the final
leading edge strip is made wide enough to be rounded off flush with the
sheeting.  I fully sheeted the whole wing as I felt that the weight saving
from the small amount of open area would be minimal. 

	You can now pull the wing off your board and pin it back right side
up.  Pin one side back to the board, using a piece of scrap for dihedral
alignment.  Remove the alignment tabs, and before sheeting fully, install
1/4 spruce rails for the aileron servo (I used micro servos) making sure 
that it is installed so as to allow the servo to bottom out on the bottom 
sheeting. There is not a lot of room under the battery plate for control 
horns.

	1/4 balsa sheet makes up the wing tips, and pieces of aileron stock
make up the trailing edge at the wing center.  I used short standard
wire horns glued into these pieces.  

	Note that the ailerons may seem large, but e-models fly slower than
their slimer counterparts and I find larger ailerons work best.  This plane
rolls very well, but not super quickly, even with these large ailerons. I
increased my throw to max on the computer radio and sealed the hinge lines
before I was satisfied with the roll rate.

	The glow version used the same aileron stock size which resulted in
a very positive roll rate.  

	The fuse is totally built up, both sides being made from a 1/4 
contest balsa "Keel" which houses the wing saddle.  Note the 1/4 stiffener
balsa doubler in the firewall area.  The rest is 1/4 square and 1/8th by
1/4 stick construction.  The complete side is then skinned with 1/16th
contest balsa.

	The landing gear plate and the forward wing saddle former are both
1/8th aircraft ply.  The rear wing former is simply two cross pieces of
1/4 sq balsa.  Pick a bit harder stick for this area.

	Fuselages formers themselves are simply 1/4 stick cross sections
at the appropriate spot, along with the firewall, and the wing leading edge
former.

	The firewall shown is 1/8th ply, and is marked for the MEC gearbox.
Simply print it out and tape the drawing to the plywood, cutting and 
drilling the appropriate holes.  Note the oval cooling hole in the lower
section.  Another cooling exit hole is cut in the 1/16th cross grain 
sheeting under the fuse nose section. I did not sheet he lower rear 
fuselage, just covered it, and this has caused no structural problems.

	Print out a top view of the fuselage and use it for alignment of
the sides.  Without the turtledeck formers, the fuse has a straight top
which allows easy alignment as you build it upside down.  

	Triangle stock reinforces the firewall installation, and a strip
along the inside lower edge of the balsa keel allows rounding of the lower
fuse sides.

	The turtledeck formers shown on the plan may present a problem, as 
I built mine with more of a trial and error effort rather than using the
plan as a guide.  I used the standard sig 12 inch bubble canopy, cutting
it off where indicated.  I jigged the formers to fit.

	The front fuse top hatch is made up of two side pieces of 1/4 square
stock with a contest 1/4 balsa sheet top.  Triangle stock here also allows
for rounding.  A dowel through the rear formers behind the canopy, and a 
4-40 bolt and blind nut on the fuse front top lock things in place.  The 
rather large hatch presents no problem with structural strength and 
allows easy access to everything inside the fuse.  Battery placement 
and removal is a breeze.

	Jon's glow version did not have the removable hatch.  However, we've
just done a new 40 sized design where he DID use the open hatch approach, and 
it makes for some easy maintenance in a glow model.  Fuselage strength is NOT
compromised with the open top hatch. We're flying a ys45 piped model this way.

	I used scrap 1/4 balsa bits to build up and form the nose, gluing 
these to the firewall and then carving.

	My battery plates are made from two layers of 1/16th balsa, ca'd
together cross grained.  Drill 1/16th holes in one piece to allow CA to wick
between the two layers. Two 1/4 square spruce rails glued along the fuse
sides provide a spot to screw the plate into the fuse.  I don't glue the 
plate itself in, as removal makes things more accessible.  I find that the 
two layers of 1/16th tend to separate after you pull out a few velcroed 
battery packs, so I usually place a 1/4 square balsa rail across the fuse 
over the front edge of the battery plate.  However I usually wait until 
after a few flying sessions before doing this as I sometimes move both the 
battery and it's mounting plate for a better CG placement.

	The landing gear just didn't look right sitting ahead of the wing, 
so I used a bit larger piece of 1/8th aircraft ply, allowing some gluing 
area under the front fuse, and at the same time allowing mounting of the 
gear on the fuse, and yet back in the leading edge area of the wing. A 
piece of triangular stock helped fair the mount into the wing underside.
The gear mount is also glued here to the ply former at the leading edge
of the wing saddle.  Triangle stock also reinforces this joint. This has 
proven bulletproof so far, despite some hard landings.  The gear position 
allows for excellent ground handling, with no nose over tendencies.

	The stab and fin/rudder are standard built up structure, using some
1/4 sheet and 1/4 square stock.

	At this time I have over 50 flights without incident.  Although I
have some larger and much more exotic electric twins, this little plane is
the one that always gets the attention.  The twins are neat and fly scale
like, but glow drivers always have an excuse for a successful e-twin.  The
ampmaster-jr. however gets their attention.  Not many of them realize that
it's electric until they listen, and look up close. 

	So if you want something quick, spirited, and lots of fun, consider 
building one of these.  I get 5.5 minute flights routinely on 10 1700 mah 
cells despite a lot of full power use for vertical maneuvers.  Half 
throttle cruise flight should get you quite a bit more.

	The MEC gearbox/astro 05 setup geared at 24/60 and using a wooden
MA electric prop draws 26 amps at 7200 rpm.  My finished airframe covered
minus gear weighed in at less than 20 ounces.  The finished ship is 56 
ounces. At that weight it is a performer!

	A standard sport geared 05 would also be an excellent choice for this
pane and would install with only a small modification to, and relocation
of the firewall.  I use geared sport 05's in my twins with the same
prop/10 cell setup and they work just fine.

	There is room for full size radio gear, at least there is if you 
built it as a slimer.  My son had no problem placing the gear in his, but
the battery pack would change that for electric.  Anyway, the larger 
servos would increase what I feel is an ideal weight for this design as an
electric. If you can get it any lighter, then you'll really have something!

	The ampmaster gets off a grass field very aggressively in about 20
feet. You can tool it around gently as a mild sport ship, or really bend 
the sticks for tail biting turns.  It can be flown in close and personal,
and in fact this is where I enjoy it.  Initially I was a bit disappointed
with it's performance, but traced that down to a too forward CG and not
enough elevator throw.  It now loops tightly and aggressively.  On it's 
first few flights the control throw wasn't enough for a smaller loop and 
it lost momentum going through the large loops it was trying to do.  So 
setup is important, especially to an electric plane.  Get them flying on 
the CG and performance is enhanced considerably.

	CG on mine is now right on the spar.

	In return for this plan, should you decide to build it, I'd appreciate
a note telling me of your decision.  Especially when you get it flying.

	I'd especially like to hear about any other motor combinations which
might be used.
 
	If you have any questions don't hesitate to contact me via e-mail at
nstn1183@fox.nstn.ca

 cheers
al

 
