Al Eastman
Aug 01, 1996, 01:00 AM
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<a href="/articles/ezonemag/plans/ampmaster/../../../pages/orderpln.htm">Order Plans</a> </p>
<hr>
<p align="left"><img src="http://static.rcgroups.com/articles/ezonemag/plans/ampmaster/amp1.jpg" alt="ampmaster picture" align="left" hspace="0" width="258" height="136"> 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. </p>
<p align="left">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. </p>
<p align="left">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. </p>
<p align="left">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. </p>
<p><img src="http://static.rcgroups.com/articles/ezonemag/plans/ampmaster/ampmast.gif" alt="plans" align="left" hspace="0" width="449" height="578"> 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. </p>
<p>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. </p>
<p>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. </p>
<hr>
<h2 align="center">The Wing </h2>
<p>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. </p>
<p>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. </p>
<p>I said I like simplicity, so this plane is designed around 48 inch balsa. The wing
piece wing allowa full span sheeting without cutting any of the sheeting. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p>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.
</p>
<p>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. </p>
<p>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. </p>
<hr>
<h2 align="center">Fuselage </h2>
<p>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. </p>
<p>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. </p>
<p>Fuselages formers themselves are simply 1/4 stick cross sections at the appropriate
spot, along with the firewall, and the wing leading edge former. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p><img src="http://static.rcgroups.com/articles/ezonemag/plans/ampmaster/amp2.jpg" alt="battery hatch picture" align="left" hspace="0" width="376" height="216"> 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. </p>
<p>I used scrap 1/4 balsa bits to build up and form the nose, gluing these to the firewall
and then carving. </p>
<p>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. </p>
<p>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. </p>
<p>The stab and fin/rudder are standard built up structure, using some 1/4 sheet and 1/4
square stock. </p>
<hr>
<h2 align="center">Flying </h2>
<p>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. </p>
<p>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. </p>
<p>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! </p>
<p>A standard sport geared 05 would also be an excellent choice for this plane 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. </p>
<p>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. If you can get it any lighter, then you'll really have something! </p>
<p>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. </p>
<p>CG on mine is now right on the spar. </p>
<p>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. </p>
<p>I'd especially like to hear about any other motor combinations which might be used. </p>
<p>If you have any questions don't hesitate to <a href="http://rcgroups.com/shared/nospam.php?u=nstn1183&d=fox.nstn.ca">contact
me via e-mail at nstn1183(at)fox.nstn.ca</a> </p>
<p>cheers </p>
<p>al
<a href="/articles/ezonemag/plans/ampmaster/../../../pages/orderpln.htm">Order Plans</a> </p>
<hr>
<p align="left"><img src="http://static.rcgroups.com/articles/ezonemag/plans/ampmaster/amp1.jpg" alt="ampmaster picture" align="left" hspace="0" width="258" height="136"> 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. </p>
<p align="left">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. </p>
<p align="left">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. </p>
<p align="left">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. </p>
<p><img src="http://static.rcgroups.com/articles/ezonemag/plans/ampmaster/ampmast.gif" alt="plans" align="left" hspace="0" width="449" height="578"> 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. </p>
<p>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. </p>
<p>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. </p>
<hr>
<h2 align="center">The Wing </h2>
<p>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. </p>
<p>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. </p>
<p>I said I like simplicity, so this plane is designed around 48 inch balsa. The wing
piece wing allowa full span sheeting without cutting any of the sheeting. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p>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.
</p>
<p>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. </p>
<p>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. </p>
<hr>
<h2 align="center">Fuselage </h2>
<p>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. </p>
<p>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. </p>
<p>Fuselages formers themselves are simply 1/4 stick cross sections at the appropriate
spot, along with the firewall, and the wing leading edge former. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p>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. </p>
<p><img src="http://static.rcgroups.com/articles/ezonemag/plans/ampmaster/amp2.jpg" alt="battery hatch picture" align="left" hspace="0" width="376" height="216"> 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. </p>
<p>I used scrap 1/4 balsa bits to build up and form the nose, gluing these to the firewall
and then carving. </p>
<p>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. </p>
<p>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. </p>
<p>The stab and fin/rudder are standard built up structure, using some 1/4 sheet and 1/4
square stock. </p>
<hr>
<h2 align="center">Flying </h2>
<p>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. </p>
<p>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. </p>
<p>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! </p>
<p>A standard sport geared 05 would also be an excellent choice for this plane 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. </p>
<p>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. If you can get it any lighter, then you'll really have something! </p>
<p>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. </p>
<p>CG on mine is now right on the spar. </p>
<p>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. </p>
<p>I'd especially like to hear about any other motor combinations which might be used. </p>
<p>If you have any questions don't hesitate to <a href="http://rcgroups.com/shared/nospam.php?u=nstn1183&d=fox.nstn.ca">contact
me via e-mail at nstn1183(at)fox.nstn.ca</a> </p>
<p>cheers </p>
<p>al