RCU Review: FunKey Extra 300S I first spotted the

RCU Review: FunKey Extra 300S I first spotted the
 RCU Review: FunKey Extra 300S More On This Product
Show user ratings Check for Retailers Contributed by: Greg Covey | Published: October 2003 | Views: 22556 |
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Review by: Greg Covey Introduction
Posing Time
Flight Report
Manufacturer Information
Manufacturer: Fun-Key
I first spotted the Extra 300S ARF in a magazine
advertisement by Yellow Aircraft and I immediately
noticed its classic sport plane looks. I then discovered
that it was a 30-size scale ARF from Fun-Key Models
and decided it would make a great conversion to electric
power using an Astro Flight Cobalt motor. The attention
to detail and degree of pre-fabricated work are
impressive. All major components are pre-covered with
Monokote. The fiberglass cowl is pre-cut, painted, and
decaled. The plastic wheel pants are colored red to
match the covering scheme. The undercarriage gear
has been pre-painted and the control surfaces are all
pre-slotted and hinged but not glued. The hardware set
is complete with spinner, motor mount, fuel tank,
wheels, and linkage parts.
Distributed by:
Yellow Aircraft International
203 MASS Ave.
Lexington, MA 02420
(781) 674-9898
Kit Name:
Wing Area:
RTF weight:
30-size Extra 300S Aerobatic airplane
$139 from Yellow Aircraft
1370 mm (53.9”)
31.7 dm2 (491 sq. in.)
1100 mm (43.3”)
90 oz. (5.6 lbs.) on 18-cells
Astro Flight 625G Cobalt motor
(geared 1.68:1)
Motor Controller:Jeti 450
18-cells of CP1700SCR
Prop Used:
APC 13x6.5 e-prop
Motor Used:
When I first unpacked the plane, I measured the weight of some key components. They appeared to be both strong and
relatively light for a glow-powered sport model.
The manual looked very nice. It was a complete re-write from Yellow Aircraft about 20 pages long with 40-50 diagrams that
showed key photos of the assembly process.
The kit also includes a strip of matching red and blue shrink film covering for repairs. A roll of fiberglass mesh is included to
reinforce the bottom wing joint after gluing the halves together.
The finished wing is very solid yet reasonably light. The wing fits into plywood slots and is anchored at the trailing edge by
two nylon bolts. The horizontal and vertical stabilizers are glued into place. The resulting assembly is very solid.
I replaced the stock 2" wheels with 2-7/8" LYT73 wheels from Hobby Lobby for better grass takeoffs. This forced me to
eliminate the pre-cut pants.
The bottom view shows the nylon bolts and my Hitec HS-81MG (metal gear) servos. The rudder and elevator will get
stronger HS-85MG (metal gear) servos. The HS-85MG servos would also work well for aileron controls.
Fuselage = 11.0oz
Fiberglass cowl = 2.0oz
Painted canopy = 1.3oz
My AF625G Cobalt motor will fit nicely onto the
firewall. The cowl is pre-cut, trimmed, and
pre-painted. It is the best I've seen yet!
I replaced the stock 2" wheels
3" LYT wheels for better grass
This forced me to eliminate the
pre-cut pants.
Stabilizers, rudder,
elevator total = 2.6oz
Alum landing gear = 2.7oz
Each wing half = 6.7oz
The bottom view shows the nylon bolts and my HS-81MG (metal gear) servos.
The rudder and elevator will get HS-85MG servos.
By inspecting the inside of the fuselage, it was obvious that the construction quality was excellent. The turtle decks have
balsa-wrapped covering over the struts and are then covered with 3 colors of shrink film. A very nice touch! The pre-painted
landing gear is mounted to the fuselage with 4 bolts and captive nuts through light plywood blocks inside. It is very solid.
The finished plane weighs 60oz with everything but battery cells. My 18 cells of CP1700 weigh 30oz and the all up weight is
90oz (or 5.6lbs).
The Extra 300S has a 54" wingspan with a thin airfoil for low drag and high performance aerobatics.
Mounting the Motor:
MotoCalc Static Analysis
The Astro Flight (AF) 625G Cobalt motor fit perfectly using the Sonic-Tronic
#160 motor mount. This motor mount is both light and strong. In previous
applications, I have used only tywraps to secure the AF625G motor to the
Sonic Tronic mount. After a good hard run, the Cobalt motor becomes
sufficiently hot to soften the tywraps and allow the motor thrust angle to
change. To prevent this from happening, I used a stainless steel hose
clamp (range 3/4" - 1 3/4") to secure the motor. I also added a balsa block
between each brush holder and the firewall. This helps add motor support
in the up and down directions. I was curioius to see what kind of power the
motor was putting out, so I wipped out my Tac and measured 7600 RPMs
at 31amps using 18-cells and an APC 12x8 e-prop.
The additional .5oz in weight will be worth the security of keeping the motor in place. I also added two tywraps on either
side of the hose clamp. The tywraps fit into the motor mount grooves per the original design and will keep the hose clamp
from possibly sliding. The result is a very confident mount.
The stock tailwheel is both steerable and solid.
The split elevator has a "Y" linkage for independent
adjustment of each half.
Battery Removal Design:
I split my 18 cells into 2 packs; one 10-cell and one 8-cell. The bottom 10-cell pack rests on the sturdy wing top. The 8-cell
pack is then placed on top of the 10-cell pack. I attached a thin rubber pad to the wing top using servo tape. This helps to
absorb any shock produced by the battery pack movement during flight. Both packs are then secured by foam blocks.
To eliminate the receiver battery pack, I used the Ultimate BEC from Kool Flight Systems. The Ultimate BEC (UBEC)
eliminates the need for a separate 4-cell Rx. battery pack by powering my receiver and servos right from the main flight
packs. Both 35v and 45v versions are available for systems up to 37 cells. You no longer need to charge receiver packs
and the UBEC is several ounces lighter than a 4-cell receiver pack. I held my UBEC to the top turtle deck struts using
servo tape.
I moved the rudder and elevator servos about 2" aft from the stock position to facilitate the battery placement. This made
the linkage wires very short but they appeared to work just fine.
Overall, it is a simple 1-2-3 insertion of pack1, pack 2, and foam block. The batteries can be swapped easily by removing
only the canopy. There is no need to remove the wing except for traveling or storing the plane. My remaining task is to find
a good way to replace the 4 canopy screws that currently hold it in place.
Placement of the servos and battery pack.
The white foam block is from a GWS R4-P recever
This second picture shows the canopy cutout. The white foam block is from a GWS R4-P recever case. This foam is the
lightest and firmest foam that I have seen. It is great for many R/C applications. I stuff the foam block inside last to hold the
top battery pack.
Overall, it is a simple 1-2-3 insertion of pack1, pack 2, and foam block. My remaining task is to find a good way to replace
the 4 canopy bubble screws that currently hold it on place.
Canopy Removal Design:
My solution to easy canopy removal on the Extra 300S incorporated a combination of wooden dowels and rare earth
magnets. I wanted a secure yet easy to remove solution for swapping battery packs without removing the wing. I used 6
sets of tiny rare earth magnets from Radio Shack.
The tiny rare earth magnets are recessed into the fuselage and a matching set is epoxied onto the inside of the canopy. I
drilled a hole through the canopy plastic to help the epoxy hold and then painted over it.
To help secure the canopy from lifting due to wind forces during flight, I added a double wooden dowel prong to the front
that slides into matching holes on the fuselage dashboard. I used 3 sets of magnets on each side. The combined 6 sets of
magnets and wooden prong hold the canopy secure during rolls, snaps, and high speed runs.
The canopy easily removes by pulling out the sides and sliding it back until the dowel rod has cleared the holes in the
My new Extra 300S was flown for the first time at a local meet on Memorial Day, 2002. We flew it 5 times and it was very stabile in flight! I wasn't expecting it to perform quite that
well myself. The combination of a light and low drag airframe has made it a perfect housing
for my AF 625G Cobalt motor.
For the maiden voyage, I had my friend Lynn Bowerman fly the Extra. Lynn has many years
of experience in flying high performance glow-powered sport models. Additionally, I wanted to
see what the other guys at the field thought when the plane was given a real workout. After a
short 25' takeoff, the plane went straight up into the air like a bullet! Everyone stopped what
they were doing and came over to watch. I'll bet you can guess what the first question
was..."That's electric?"
I don't have power for unlimited vertical flight but the plane goes high enough for a proper
stall turn in the sky where you start to loose perspective because it is so small.
All the flights were with 18 cells of CP1700SCR and I was also surprised that the duration
was longer than I had expected. Since the power level is so high, you can use good throttle
management during the flight to prolong duration.
My 30-size Extra 300S was a great fit with the Astro Flight 625G Cobalt motor. The 5.6lb
sport plane is highly aerobatic and has reasonable flight duration with proper throttle
The quality of the ARF kit was superb and Yellow Aircraft offers replacement plastics and
fiberglass cowls separately. All the parts are pre-painted and covered. The Ultimate BEC
eliminated the need for a receiver battery and reduced weight. Battery packs can be easily
swapped by removing the canopy without having to remove the wing.
This is a true scale design of the championship aerobatic full size model. R/C pilots that
have high performance sport plane experience all know that nothing flies like an Extra! Manufacturer: Fun-Key
Yellow Aircraft International
203 MASS Ave.
Lexington, MA 02420
(781) 674-9898
www.yellowaircraft.com Koolflight Systems
355 Sunderland Circle
Fayetteville, GA 30215
(770) 486-1663
www.koolflightsystems.com/ultimatebec.htm email: jsmeyers@earthlink.net
Astro Flight
13311 Beach Ave.
Marina Del Rey, CA 90292
(310) 821-6242
email: info@astroflight.com
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The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the
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