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Sig Riser

#1
Soon Ill be building the Sig Riser and I am planning on electrifying it but am at a loss as to what motor and battery I should use. If any of you could recommend a good set up I would appreciate it.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#2
What size gas motor does it normally take?

The simple rule is to multiply the engine capacity , (in cu in), by 2000 and the answer is the wattage required. Next step is to find out what prop is normally required as well as the motor speed range. then look for a motor of the appropriate wattage that has a KV figure multiplied by the Battery voltage that gives the correct RPMs.

Quite simple when you know how!

Have fun!
 

FAI-F1D

Free Flight Indoorist
#3
Soon Ill be building the Sig Riser and I am planning on electrifying it but am at a loss as to what motor and battery I should use. If any of you could recommend a good set up I would appreciate it.
Which size, the 2 meter or the 100?

For what it's worth, here are two power systems (one for each version) which should work very satisfyingly. Ignore the dire warnings of motor run length and overheating. You only need about 90 seconds of WOT capacity to have a very good glider powerplant. You only use two throttle settings: Wide Open and OFF. Anytime it's at WOT, the nose should be at least 45 degrees nose up.

2018-10-10 09_16_58-SIG Riser - eCalc - propCalc.png

2018-10-10 09_23_44-SIG Riser 100 - eCalc - propCalc.png
 

Merv

Active member
#4
What size gas motor does it normally take?

The simple rule is to multiply the engine capacity , (in cu in), by 2000 and the answer is the wattage required. Next step is to find out what prop is normally required as well as the motor speed range. then look for a motor of the appropriate wattage that has a KV figure multiplied by the Battery voltage that gives the correct RPMs.

Quite simple when you know how!

Have fun!

Great idea, thanks for sharing
 

FAI-F1D

Free Flight Indoorist
#5
What size gas motor does it normally take?

The simple rule is to multiply the engine capacity , (in cu in), by 2000 and the answer is the wattage required. Next step is to find out what prop is normally required as well as the motor speed range. then look for a motor of the appropriate wattage that has a KV figure multiplied by the Battery voltage that gives the correct RPMs.

Quite simple when you know how!

Have fun!
Great idea, thanks for sharing
Well it's a great idea for powered models, but the Riser, being a sailplane, isn't engine powered, so there's no data to start with there.
 
#6
Well it's a great idea for powered models, but the Riser, being a sailplane, isn't engine powered, so there's no data to start with there.

Didn’t know it was a sailplane. I’d go with another rule of thumb, watts per pound. My guess, something in the 50-100 watts per pound range. An internet search will turn up many articles to explain the concept, it comes down to how do you want to fly, fast or slow.

https://www.rc-airplane-world.com/watts-per-pound.html
 

FAI-F1D

Free Flight Indoorist
#7
Didn’t know it was a sailplane. I’d go with another rule of thumb, watts per pound. My guess, something in the 50-100 watts per pound range. An internet search will turn up many articles to explain the concept, it comes down to how do you want to fly, fast or slow.

https://www.rc-airplane-world.com/watts-per-pound.html
Much too low for a sailplane. The entire goal is to use the motor as little as possible, and that generally implies a minimum 1.5:1 thrust:weight ratio so you can get it up there quick. You run a light battery so there's usually only capacity for about 90 seconds of wide open throttle. And that's mild compared to free flight electrics where the low end is 300 W/lb.

I would also say whoever wrote that guide on R/C Airplane World seriously never consulted people who actually fly some of the classes he mentioned. Most SAM folks (you know, the purists of old-timers) would laugh in his face at the suggestion of 50-80 W/lb. Yeah...they start around 200.