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This all started when I began looking for a low budget tow plane for ¼ scale gliders that could be used on weekends when a few guys occasionally show up with their gliders and need a tow. There is a good selection of large tow planes available in kit and ARF form for 100cc and larger gasoline engines, but those offer much more performance than I needed. Not to mention the big gassers require a larger investment than my current modeling budget allows.
Some folks have had success converting models like the Telemaster and Sig Rascal 110, but to me those models have some drawbacks - such as a high mounted wing which results in mediocre/poor ground handing, especially in a cross wind; a horizontal tail which is not removable for transport; and a structure that wasn’t originally designed to accommodate a tow line attach/release. And if electric powered, significant modifications have to be made to allow battery packs to be easily removed and replaced.
Since I enjoy designing and building, I decided to construct my own tow plane to get what I wanted. A 3 View of the Pulldog is attached below, along with some photos. The Pulldog was designed from the outset for towing, and is also a good sport aerobatic model which can provide a lot of fun flying when not towing gliders. Some of the features are:
• Low wing position for improved handing, especially on the ground
• Removable wing panels with automatic servo connector hookup
• Removable horizontal tail (only one bolt) to allow transport in small cars like my Honda Fit
• Large fuselage hatch for easy battery and radio access
• Taildragger landing gear for simplicity and low maintenance
• Spoilers instead of flaps - results in easy, no-float landings
• Electric power for low vibration and low noise
• Simple structure and easy to build
• Large enough wing for reasonably good visibility at tow release altitude
• No plastic canopy, so no cracks to worry about
• E-Flite Power 160 Outrunner motor; APC 20 X 8 prop; Castle Creations Phoenix Edge HV 80 ESC; 10S 5000 mah 25C LiPo (two 5S packs in series)
• Fuselage mounted Digital Readout Voltage indicator to keep track of the battery’s remaining capacity
Here are the specs:
Span 100 in
Area 1440 sq in
Length 70 in
Weight 14.6 lbs
E-Flite 160 outrunner motor
Castle Creations Phoenix Edge HV80 ESC
APC 20 X 8 electric prop
10S 5000 mah 25C LiPo battery (two 5S in series)
To date I have tested the Pulldog by towing Andy Grose’s ¼ scale Schweizer 1-26 and Scott Smith’s ¼ scale Aviation Concepts (Gunny’s) Schweizer 2-33. The day we flew the heat index was 104 degrees, so the density altitude was fairly high. All releases were at 1000 – 1100 AGL. It took just under 1 minute to get the 1-26 to 1000’; the Pulldog pulls this glider easily. 4 tows can be made before the battery pack is depleted. I have 4 battery packs, so I can have one on charge while the others are cooling off if need be. Towing the big Gunny 2-33, which weighs 13.4 lbs, takes a lot more power, and runs the battery down a lot quicker. It took 1 minute and 20 seconds to get to 1000’. After 2 tows, I wasn’t sure if I had enough battery capacity left to make a 3rd tow. I think it would be worth experimenting with a different prop, like an 18 X 10, because the towing speed might have been just a little slow for the 2-33 using the 20 X 8 APC prop. The first tows with the 2-33 went OK, but later we had a couple of tows where the 2-33 got too far below the Pulldog and had to release, and I can’t say if it was due to pilot technique (tow pilot or glider pilot) or lack of speed. I plan to do more testing, but it’s just been too darned hot here to do any serious aerotowing, so that will have to wait a couple months.
Bottom line, I believe the Pulldog is a very good tug for 10 lb and under gliders. It can also tow heavier gliders if both pilots are experienced and you can live with the shorter battery life. I can’t really say what the weight limit is yet, as more testing is needed, and also I think it depends upon the type of glider (e.g., glass slipper, vintage, etc.).
I will try to make this build thread a bit light on narrative and use photos to show a lot of the information, since most folks who would build this are likely to be fairly experienced modelers who don’t need a step-by-step explanation. To encourage building I am posting the plans here for free. Also, Marcs Laser Shop http://www.scalesailplanekits.com/ will be offering short kits for the Pulldog. Contact Marc for details. That’s it for now. The next posting will start the build thread.
Al Clark
Some folks have had success converting models like the Telemaster and Sig Rascal 110, but to me those models have some drawbacks - such as a high mounted wing which results in mediocre/poor ground handing, especially in a cross wind; a horizontal tail which is not removable for transport; and a structure that wasn’t originally designed to accommodate a tow line attach/release. And if electric powered, significant modifications have to be made to allow battery packs to be easily removed and replaced.
Since I enjoy designing and building, I decided to construct my own tow plane to get what I wanted. A 3 View of the Pulldog is attached below, along with some photos. The Pulldog was designed from the outset for towing, and is also a good sport aerobatic model which can provide a lot of fun flying when not towing gliders. Some of the features are:
• Low wing position for improved handing, especially on the ground
• Removable wing panels with automatic servo connector hookup
• Removable horizontal tail (only one bolt) to allow transport in small cars like my Honda Fit
• Large fuselage hatch for easy battery and radio access
• Taildragger landing gear for simplicity and low maintenance
• Spoilers instead of flaps - results in easy, no-float landings
• Electric power for low vibration and low noise
• Simple structure and easy to build
• Large enough wing for reasonably good visibility at tow release altitude
• No plastic canopy, so no cracks to worry about
• E-Flite Power 160 Outrunner motor; APC 20 X 8 prop; Castle Creations Phoenix Edge HV 80 ESC; 10S 5000 mah 25C LiPo (two 5S packs in series)
• Fuselage mounted Digital Readout Voltage indicator to keep track of the battery’s remaining capacity
Here are the specs:
Span 100 in
Area 1440 sq in
Length 70 in
Weight 14.6 lbs
E-Flite 160 outrunner motor
Castle Creations Phoenix Edge HV80 ESC
APC 20 X 8 electric prop
10S 5000 mah 25C LiPo battery (two 5S in series)
To date I have tested the Pulldog by towing Andy Grose’s ¼ scale Schweizer 1-26 and Scott Smith’s ¼ scale Aviation Concepts (Gunny’s) Schweizer 2-33. The day we flew the heat index was 104 degrees, so the density altitude was fairly high. All releases were at 1000 – 1100 AGL. It took just under 1 minute to get the 1-26 to 1000’; the Pulldog pulls this glider easily. 4 tows can be made before the battery pack is depleted. I have 4 battery packs, so I can have one on charge while the others are cooling off if need be. Towing the big Gunny 2-33, which weighs 13.4 lbs, takes a lot more power, and runs the battery down a lot quicker. It took 1 minute and 20 seconds to get to 1000’. After 2 tows, I wasn’t sure if I had enough battery capacity left to make a 3rd tow. I think it would be worth experimenting with a different prop, like an 18 X 10, because the towing speed might have been just a little slow for the 2-33 using the 20 X 8 APC prop. The first tows with the 2-33 went OK, but later we had a couple of tows where the 2-33 got too far below the Pulldog and had to release, and I can’t say if it was due to pilot technique (tow pilot or glider pilot) or lack of speed. I plan to do more testing, but it’s just been too darned hot here to do any serious aerotowing, so that will have to wait a couple months.
Bottom line, I believe the Pulldog is a very good tug for 10 lb and under gliders. It can also tow heavier gliders if both pilots are experienced and you can live with the shorter battery life. I can’t really say what the weight limit is yet, as more testing is needed, and also I think it depends upon the type of glider (e.g., glass slipper, vintage, etc.).
I will try to make this build thread a bit light on narrative and use photos to show a lot of the information, since most folks who would build this are likely to be fairly experienced modelers who don’t need a step-by-step explanation. To encourage building I am posting the plans here for free. Also, Marcs Laser Shop http://www.scalesailplanekits.com/ will be offering short kits for the Pulldog. Contact Marc for details. That’s it for now. The next posting will start the build thread.
Al Clark
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