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Wednesday, June 1, 2016

GWS P-38 Lightning

Great Wing System (GWS) P-38 Lightning

Model was purchased several years ago without any radio or electronic components.

It was designed to be powered by a pair of GWS geared brush type power units and it was first flown successfully a few times using this power set-up. But we were never completely satisfied with its performance and we spent a lot of time trying to figure out how to attach those beautiful spinners
to the propeller shafts .

 Now it's fitted with a pair of matched brush-less motors turning 5X7 GWS propellers. But still no way to mount those spinners.  I never understand how they rate these motors but, I would estimate each is equivalent to a good 049. Now at the speed these props turn it is impractical to mount large spinners. The Project to make this model into a reliable fun to fly model airplane has been an off-and-on effort for about five years. The first problem to solve was the nosing over and digging in on takeoff caused by the very small fixed nose wheel ( we always fly from grass so this is a big problem). Problem solved by making a stout oversize steerable nose wheel which doesn't look that pretty, but from 20 feet it is not that distracting and the smooth straight takeoff runs go a long way in compensating for the looks of the thing.

There is no rudder control but the rudder channel is used for the steerable nose wheel and the elevator is activated by push pull wires which makes for a simple system.
Lots of room inside the radio compartment for a much larger battery then the 1800 mah 3 cell one used for the initial flight. Cooling air for this compartment is directed through the gun ports in the nose (drilled oversize) and exited through the opening at the back of the canopy. Since my Spektrum mini receiver was being used at the time in another project, we used an old GWS 4 channel park-flyer 72 mhz one for these flights.
ESC's are attached to the wing with Velcro or as the people at the dollar store call it 'hook and loop".
 Under the wings we have mounted a pair of 30 amp brush-less motor controls. The key thing here that is essential to follow is; only one is used to power the control system. This is accomplished by removing the pin for the positive (red wire) and pinning it back out of the way. I tried more times than I care to remember to get both engines running at the same time, without success. I even tried two stand alone battery ESC combinations; It wasn't until I cut the red wire on one ESC was I able to get each engine turning simultaneously. Even now they each stop and start at different throttle setting which makes for lots of excitement on landing.

There is not enough room inside the fuselage for the two ESC's so I opted for mounting outside under the wings where cooling is not a problem. I used a 1800 mah 3 cell battery for the flight shown below but now I have room for a much larger battery in future flights.

As you probably noticed from the video, I need to give some thought into what landing techniques should be used in landing this model. This is because the two motors quit at different low throttle settings (equal thrust at full to about 1/3 throttle) the plane yaws to the dead engine. This situation has to be avoided so, I have to train myself to snap the throttle closed while over the field at half throttle; something to work on the next visit to the field.

GWS specs.
Length853mm (33.6 in.)
Wing Span1200mm (47.2 in.)
Wing Area19.9dm2 (308.5 sq. in.)
Flying Weight720g (25.4oz.)
Wing Loading36.2 g /dm² (11.9oz./sq. ft.)
Power SystemGWS 2208/18T or EPS300C
ServoNARO *4
ReceiverR6NII / RD8SL / R8MSL / R8MSL+
Speed controllerGWESC25A×2/ICS600Li×2
Radio Required4CH Channel radio or above

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