Brooks
Sep 07, 2003, 05:19 PM
I made floats for my GWS Tiger Moth. I live at 4600 feet in Bozeman, Montana. This forum has been extremely helpful to me. Thanks for all the great suggestions.
Motor/cup cowl:
The original motor did not have enough power to lift the TM from the water at this altitude (4600 feet, density altitude up to 7500 feet). I substituted a GWS dual motor unit, IPS-D RXC (A gearing, 5.9:1), with an APC 10x7 inch Slow Flyer prop. Note that the dual motor is mounted on the original TM motor mount stick, making the prop off-center. By positioning the prop to the port side, I get a useful right thrust effect. I used a servo mount screw to secure the motor to the stick. Because the drive shaft is now off-center, the original cowl would no longer fit. I substituted a plastic cup: “Solo TP10, 10 oz." I cut off the bottom and the rim of the cup. It fit so well, I wonder if the model designer used one :-).
Battery:
1020mah 2S1P Li-poly from Radical RC. I secure the battery with Velcro to the passenger cockpit. The ESC wire leads out the gap between the fuselage and the lower wing. Changing batteries is very easy, but watch you don't bump the throttle stick; I put a rubberband on the transmitter that holds the throttle closed when I am fooling with the battery/ESC wires.
http://radicalrc.secure-mall.com/shop/index.php?shop=1&cart=63354&cat=1&
Float design: I designed mine using the suggestions in Cunningham's 1997 RCM article. His 1993 article is available online. The only changes from '93 to '97 that I see are: 1) he increased the angle of the bottom of the aft portion of the float
from 3 to 5 degrees 2) he uses a flat surface instead of a curved one on the bottom of the nose of the floats.
To save weight, my floats are not as deep as his. I used 1 inch pink foam insulation. For a strongback, I inlet a 1/4 inch square strip of hardwood into the top of the float. The inlet was just picked out with a #11 blade. 5min epoxy secures the strongback.
I have not put Cunningham's suggested vertical supports in the strongback. So far, the floats have survived numerous pond and land crashes. In fact, I recommend floats as training skids for anyone landing in tall grass. When not at the pond, I fly over an uncut hayfield, so all my landings are crash-like. The floats cushion my arrivals, and also protect the prop ( I do use a prop saver). Remove the spreader dowels to allow the wire struts to spread to absorb shock when flying over land.
RCM Sept 1997 pg.144 Chuck Cunningham article
RCM April 1993 similar Cunningham article online
http://flyinglindy.homestead.com/skisandfloats.html
Float dimensions: 40cm long, 4.5cm wide, 2.6cm deep. Step is 24cm from the nose. Step depth 8mm. Slope at nose 4cm long. Total spread of floats 22.6cm outside to outside edge.
Mine came out 40cm long, but adding another 2.5cm to the stern would make a better float. Floats are covered, bottom and sides, with clear packing tape. 3M77 spray-on adhesive may be used before taping if *Lightly* applied. Allow the toluene in the glue to evaporate before applying the tape, or you risk melting holes in your foam. I airbrushed water-based acrylic enamel (mixed 50:50 with water) on the floats. I did not scuff the tape with steel wool before painting, and got poor adhesion.
Strut wires and spreader dowels:
Wire diameter 0.055 inch for struts and 0.039 inch for the brace. Distance from float top to wing leading edge about 10cm. Spreaders are 1/8 inch dowels held to the floats with duct tape.
Float mounting:
I use rubberbands hooked to the wing hold dowels. I added 1/32 inch ply reinforcement tabs to the fuselage to support the dowels. To make a positive angle of attack between the bottom wing and the top of the floats, I duct-taped a small piece of pink foam to the fuselage where the forward float strut wire rests. This gives me a 5 mm greater distance from float top to wing at the leading edge than from float top to wing at trailing edge. You could, of course, simply make your forward wire mount longer to achieve the same effect. I used a foam spacer figuring it would make it easier to modify the angle than rebending the wire struts.
The nose of the floats is 20cm forward from the lower wing's L.E. at the fuselage. This gives approximately 5.5cm of float extension forward of the prop. My original design did not allow enough forward extension, and the nose would bury when I applied power. To correct, I merely glued pink foam to the float aft of the step, and re-positioned the strut mounting blocks (pieces of 1/4 hardwood left over from the strongback). Both the correction foam and the mounting blocks are attached with foam-safe CA. Sanding the new foam to match the existing slope of the bottom resulted in a total float depth of slightly more than the 1 inch foam I started with.
Flying experience:
When landing, have patience: set up your descent with power and elevator, then let the plane do the work; don't rush it by fiddling with the stick, or you risk flaring too high and dunking. Been there, swum that.. It is much easier for me to
judge my flare when the plane is passing right to left in front of me than when it is traveling away from me. Traveling away during landing makes it much easier to discern if wings are level, but much harder to detect distance from the water.
The dual motor makes the plane nose heavy. You can add enough lead to the tail to balance to the same specs as with the original motor: but the floats themselves will cause a pitch-up moment when you take off (they act like wings with a center of lift forward of your regular wings). So, a little nose heavy is not a bad thing in this circumstance.
The increase in weight (dual motor and some counter-balancing lead) leads to a faster glide, changing the timing you are used to. Practice some landings over a hayfield before you go to the water...unless you like swimming for your plane. Well I needed a bath anyway.... In my water crashes, the plane floats nose down, but very high out of the water. The electronics (encased in Trojans, non-lubricated, the end tied with rubber band) don't even get soaked, just splashed by whatever gets past the wing/fuselage gap. I used tape to seal the old battery slot into the fuselage.
When retrieving your plane, which I do by swimming, hold it vertical, just like it was floating, and you may keep water out of the electronics compartment. Once back on land, I gently tip the plane to it's side to release any sloshing water from the fuselage. So far, I've been able to relaunch without moisture problems.
The Tiger Moth on floats looks beautiful. At sunset, with the red light glinting on the wings, you are living Out of Africa. I'd encourage anyone with access to water to try floats.
Brooks
Motor/cup cowl:
The original motor did not have enough power to lift the TM from the water at this altitude (4600 feet, density altitude up to 7500 feet). I substituted a GWS dual motor unit, IPS-D RXC (A gearing, 5.9:1), with an APC 10x7 inch Slow Flyer prop. Note that the dual motor is mounted on the original TM motor mount stick, making the prop off-center. By positioning the prop to the port side, I get a useful right thrust effect. I used a servo mount screw to secure the motor to the stick. Because the drive shaft is now off-center, the original cowl would no longer fit. I substituted a plastic cup: “Solo TP10, 10 oz." I cut off the bottom and the rim of the cup. It fit so well, I wonder if the model designer used one :-).
Battery:
1020mah 2S1P Li-poly from Radical RC. I secure the battery with Velcro to the passenger cockpit. The ESC wire leads out the gap between the fuselage and the lower wing. Changing batteries is very easy, but watch you don't bump the throttle stick; I put a rubberband on the transmitter that holds the throttle closed when I am fooling with the battery/ESC wires.
http://radicalrc.secure-mall.com/shop/index.php?shop=1&cart=63354&cat=1&
Float design: I designed mine using the suggestions in Cunningham's 1997 RCM article. His 1993 article is available online. The only changes from '93 to '97 that I see are: 1) he increased the angle of the bottom of the aft portion of the float
from 3 to 5 degrees 2) he uses a flat surface instead of a curved one on the bottom of the nose of the floats.
To save weight, my floats are not as deep as his. I used 1 inch pink foam insulation. For a strongback, I inlet a 1/4 inch square strip of hardwood into the top of the float. The inlet was just picked out with a #11 blade. 5min epoxy secures the strongback.
I have not put Cunningham's suggested vertical supports in the strongback. So far, the floats have survived numerous pond and land crashes. In fact, I recommend floats as training skids for anyone landing in tall grass. When not at the pond, I fly over an uncut hayfield, so all my landings are crash-like. The floats cushion my arrivals, and also protect the prop ( I do use a prop saver). Remove the spreader dowels to allow the wire struts to spread to absorb shock when flying over land.
RCM Sept 1997 pg.144 Chuck Cunningham article
RCM April 1993 similar Cunningham article online
http://flyinglindy.homestead.com/skisandfloats.html
Float dimensions: 40cm long, 4.5cm wide, 2.6cm deep. Step is 24cm from the nose. Step depth 8mm. Slope at nose 4cm long. Total spread of floats 22.6cm outside to outside edge.
Mine came out 40cm long, but adding another 2.5cm to the stern would make a better float. Floats are covered, bottom and sides, with clear packing tape. 3M77 spray-on adhesive may be used before taping if *Lightly* applied. Allow the toluene in the glue to evaporate before applying the tape, or you risk melting holes in your foam. I airbrushed water-based acrylic enamel (mixed 50:50 with water) on the floats. I did not scuff the tape with steel wool before painting, and got poor adhesion.
Strut wires and spreader dowels:
Wire diameter 0.055 inch for struts and 0.039 inch for the brace. Distance from float top to wing leading edge about 10cm. Spreaders are 1/8 inch dowels held to the floats with duct tape.
Float mounting:
I use rubberbands hooked to the wing hold dowels. I added 1/32 inch ply reinforcement tabs to the fuselage to support the dowels. To make a positive angle of attack between the bottom wing and the top of the floats, I duct-taped a small piece of pink foam to the fuselage where the forward float strut wire rests. This gives me a 5 mm greater distance from float top to wing at the leading edge than from float top to wing at trailing edge. You could, of course, simply make your forward wire mount longer to achieve the same effect. I used a foam spacer figuring it would make it easier to modify the angle than rebending the wire struts.
The nose of the floats is 20cm forward from the lower wing's L.E. at the fuselage. This gives approximately 5.5cm of float extension forward of the prop. My original design did not allow enough forward extension, and the nose would bury when I applied power. To correct, I merely glued pink foam to the float aft of the step, and re-positioned the strut mounting blocks (pieces of 1/4 hardwood left over from the strongback). Both the correction foam and the mounting blocks are attached with foam-safe CA. Sanding the new foam to match the existing slope of the bottom resulted in a total float depth of slightly more than the 1 inch foam I started with.
Flying experience:
When landing, have patience: set up your descent with power and elevator, then let the plane do the work; don't rush it by fiddling with the stick, or you risk flaring too high and dunking. Been there, swum that.. It is much easier for me to
judge my flare when the plane is passing right to left in front of me than when it is traveling away from me. Traveling away during landing makes it much easier to discern if wings are level, but much harder to detect distance from the water.
The dual motor makes the plane nose heavy. You can add enough lead to the tail to balance to the same specs as with the original motor: but the floats themselves will cause a pitch-up moment when you take off (they act like wings with a center of lift forward of your regular wings). So, a little nose heavy is not a bad thing in this circumstance.
The increase in weight (dual motor and some counter-balancing lead) leads to a faster glide, changing the timing you are used to. Practice some landings over a hayfield before you go to the water...unless you like swimming for your plane. Well I needed a bath anyway.... In my water crashes, the plane floats nose down, but very high out of the water. The electronics (encased in Trojans, non-lubricated, the end tied with rubber band) don't even get soaked, just splashed by whatever gets past the wing/fuselage gap. I used tape to seal the old battery slot into the fuselage.
When retrieving your plane, which I do by swimming, hold it vertical, just like it was floating, and you may keep water out of the electronics compartment. Once back on land, I gently tip the plane to it's side to release any sloshing water from the fuselage. So far, I've been able to relaunch without moisture problems.
The Tiger Moth on floats looks beautiful. At sunset, with the red light glinting on the wings, you are living Out of Africa. I'd encourage anyone with access to water to try floats.
Brooks