*** Andy Steere's ExtremeFlightRC Yak55SP-E Static Images ***

These are pictures of my Yak 55SP-E from Extreme Flight R/C. Purchased in mid November 2004, assembled and first flown on November 20, 2004. My son had taken his camera to college, and I didn't have access to it until he came home for Thanksgiving. These pictures were taken after I had completed just 2 flights.

Fuselage is made of mainly balsa, with a few pieces of plywood in critical areas. About the same weight as your average Depron flat foam 3D'er. Slightly less wing area, giving slightly higher wing loading... but a real airfoil more than makes up the difference. It's a great flyer! Here is the equipment used (as of November 26th, I may change out motors later):

E-Flite Park 370 5400kv Brushless motor with MPI ACC3921 heatsink (had both laying around not doing anything).
Todd's TM2000 gearbox at 7.6:1 (76-tooth spur, 10-tooth pinion).
Castle Creations Phoenix-25 25amp Brushless Speed controller.
ThunderPower 1320mah 10-12C and Tanic 1500/1550mah 10-12C 3cell lithium polymer Batteries (I need to get some smaller batteries).
APC Thin-E and Slow-Fly props, currently using a 12x6 Thin-E.
JR R610UL micro receiver.
Hitec HS-55 sub-micro servos (four).

This combination draws about 15amps and 6200rpm at full throttle. According to Motocalc, this gives about 34oz of thrust to the 14.5-15oz all up weight. It provides 15-20 minute flight times, depending on throttle, and excellent pullouts from a hover. 15 amps is a little much for this motor, but full throttle is very rarely used and the heatsink helps keep things cool. If I didn't have the motor already, I would suggest something in the 4100kv range is better suited for this model. At full throttle, the 5400kv motor spins just under 50,000rpm and has the potential to go above it's maximum rating of 60,000 if the prop ever came off in flight.

*** UPDATE 12/21/2004 ***

As of 12/17/2004, I have made a couple changes to my Yak. First was to add Carbon Fiber Landing Gear from www.3DFoamy.com. I used the Tall version, and 2" Light Weight Foam Tires (EPW200). These gear come with a carbon fiber tailskid, and laser-cut Depron foam to make wheelpants. I flew the Yak for 5 flights with these gear, but without the wheelpants. Trying to increase visibility in the air, I went ahead and built the wheelpants, glassed them, and painted them with true red Ultra-paint... which is a decent match for the red covering. This added about 12grams to the weight, and required 3-grams of lead in the tail to balance. Flew a couple flights with the wheelpants... and decided to take them back off. They didn't improve visibility enough to make up for the additional 1/2 ounce of weight.

The second modification was to change out the motor for a Razor RZ-350 Brushless Motor. This powerful little motor weighs an ounce less than the Park 370 and is very efficient. Combined with a 12-tooth stainless steel pinion and a 72-tooth spur-gear in the Todd's Gearbox (6.0:1 ratio), and an APC 11x7SF prop... this combo will hover at a click or two above half throttle. About the same as the Park 370, but with fewer amps drawn from the battery. The lighter motor also allowed me to move the battery up to the factory recommended location on the thrust-line. The Yak is lighter now with the landing gear... than it was with the other motor and no gear! This combined with the batteries weight on the thrustline, should improve the flying. See the pictures below.