Building & Flying the Speed XP
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Introduction
The Speed XP is a cross between a small pylon racer and a small glider. At 1120mm wingspan its considerably larger than a Sokol or Dynamic and has a high aspect
ratio similar to that of a glider.
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The Wing
The wing build was relatively straight forward, borrowing on techniques used in my gliders. The first step was cut away the covering over the servo wells and then to line the exposed wing
skin with a bit of light weight (0.7oz) glass cloth and epoxy resin. |
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A slot was cut for a fibreglass control horn with a sharp scalpel rather than use the supplied nylon horn. The servo leads were also extended, soldered rather than using an extension lead as it is easier to fit in the slim wing. |
| A 0.8mm hole was drilled in the control horn which was then glued into the aileron with CA. | ;) |
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The servo's used in the wing are GWS Pico+F which at 9mm thick still protruded slightly at the trailing edge. The tabs were cut off the servo and it was then heat shrink ready for gluing into the wing. (This makes it possible to remove if ever the need arises). The pushrod assembly was made from MPJet clevis's and 2mm brass coupler. A short length of 0.8mm piano wire with a Z bend was epoxied into the brass coupler. The extended servo wires were feed through the premade channel using the supplied pull cord with an exit hole cut in the centre of the wing. |
| The Servos were then centered and glued in place. The control surface & servo were held in place with masking tape to keep things as accurate as possible. | ;) |
| The Fuselage | |
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A problem was encountered with the design where there was not enough room for the elevator horn to move with out hitting the rear former fitted to the end of the fuselage. |
| The rear former was removed with a dremel tool and then a balsa block glued in place and the tube glued to that with a blob of epoxy. This allowed the aileron horn to rotate freely around the hinge line. | ;) |
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The supplied nylon horn was not used and instead a slot was cut and I glued in a fibreglass horn (Aeronaut). The pushrod wire (0.8mm) was replaced with a length of 1mm wire which I felt was a better fit.This was secured with a Z bend at the control horn end. This produced an extremely good linkage with no discernible slop. |
| At the other end of the pushrod the servo was fitted (Another GWS Pico). Rather than use the supplied battery tray and servo mount I just glued a ply plate into the fuselage and then glued the servo to that (wrapped in heat shrink). Again MPJet Micro Clevis and brass coupler were used. In retrospect I should have positioned the servo a little further rear ward to give a bit more adjustment of battery position for obtaining the C.G. | ;) |
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Power System
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I chose to install a Mega 16/15/3 Brushless motor with an Airpower 35A ESC turning an APC 4.7x4.2 prop on a 3S 1800XP Lipo. An MPJet 30mm spinner was used to smarten up the appearance.
The canopy had the piano wire holder glued in and was given a quick coat of paint for looks. I used a Hitec HFS05MS receiver as nothing else I had would fit. I was a little concerned that it is only single conversion but these fears were later shown to be unfounded.
A bit of fluro decal was added to the opposite wing tip to aid with visibility (This had interesting consequences as detailed later).
I tested this setup with the watt meter and was quite surprised to see 27A at full throttle. This was a little higher than expected but all components were still well within there specs. |
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| Flying Control throws were set to pretty low rates with plenty of expo and about 50% differential on the ailerons. I also programmed up spoilerons on a slider on my 9cap. The C.G was checked and it was spot on with the battery butting up against the elevator servo tray (pheww). Off to the field we go! My launcher gave a firm toss and she was away, it needed a couple of left clicks and a bit of down elevator to get it tracking well. (The down elevator was later removed a bit after adjusting the motor thrust angle with a washer) Its quite quick and can get pretty small fast, especially on some angles it almost disappears due to that thin wing. I was glad of the bright fluro tip as it really stood out well. I found that most of the flight was performed at half throttle as this was plenty fast enough, with a few blasts of full to see what would happen! I landed after about six minutes as thats about all my nerves could handle. The spoilerons had some effect and it can be slowed up quite well with careful use of the elevator. Not bad I thought, quite pleasantly surprised at how nice it was to fly. The second flight however was a different story..... About 2min into the second flight I pulled a fairly tight turn at the right hand end of the field and then Holy Crap! it spun out on me and seemed out of control. I cut the throttle as I thought I may have seen something flutter and struggled to regain control. I managed to keep the wings level and glided it in to the ground at a long distance away over the fence and into long grass. I was thinking BUGGER I've stuffed it so early in its life before I really got the feel for it. Any way after walking over to where I was expecting to find the wreckage, there was a perfectly intact model, with the nose buried in a cow pat! Not even the prop had broken. But what had happened? On close inspection it was discovered that my fancy fluro sticker had peeled up at the leading edge of the wing, acting like a big spoileron on one wing only. I was very lucky. After several more flights I'm getting more comfortable with it. I suspect it has a small amount of washout built into the wing as the stall is very docile without any tendancy to drop a wing. Speed is fast enough for me, but not as quick as a Sokol. However its wing loading is lower and therefore a bit easier to fly as well as being easier to see with its larger wingspan. Overall after initially being a little disappointed with a few quality aspects its turned out to be a fun little model. Heather Mardon |