The X-Flyers are BT-20-based, minimum diameter birds that even with their full-length tube wraps, weigh practically nothing. Both employ the plastic fin can of the Nike Arrow resulting in relatively low drag.
Recovery system and engine mount, as detailed below.
Specifications given are for X-flyer #1. X-flyer #2 differs very little, both in parts content and flight performance.
Why Estes hangs these high flyers under a 12 inch canopy is beyond me; any wind at all, and the recommended C6 will sail them away. I replaced the prebuilt 'chutes with Custom LDPE streamer material so I might get them back after their flights on those motors.
Without a thrust ring, these birds would suffer the same motor hook failure mode as the Gnome, so I added one to each model. I used a "yellow tube" to place the engine blocks 2¼ inch from the rear, a slight modification of Estes' recommended 2½ inch, and secured them with wood glue. I used PolyZap CA for the rest of the assembly.
Shock cord mounting is done at the tube coupler through a "cavity" with a cap. My set was missing the blue "cavity cap", though I really didn't care. I added a 12 inch length of 300# Kevlar® to each bird to prevent shock cord scorch, another failure mode common to Estes E2X/RTF birds (which has earned them the sobriquets "Easy to eXplode" and "Ready To Fail" in my club).
Along with changing these things to improve flyability, I had a few other issues with the X-Flyers. Firstly, could we come up with a little better names for these birds than "#1" and "#2"? Some sort of "alien robot weapon" motif is suggested by their design; could the blue and yellow one have been a "hyperwarp interdiction missile", and black and indigo one a "transdimensional sensor probe"? It's obvious that somebody at Estes spent a fair amount of time on these birds' looks. It seems a pity to curse that effort with such penurious designations.
X-Flyer #2's transition (called a "tube adapter" in the instructions, a departure from standard nomenclature) has the attachment "eyelet" at the small (BT-5) end. I thought a BT-20 nose cone cap like that supplied with X-Flyer #1 would allow the upper tube to be used as a payload bay, though other than insects, I can think of nothing worthwhile that would fit in such a small space. I tried fitting one just the same, but the transition's large ID is too small for it.
The motor hooks are too big to fit in the slot in the fin cans, and these must be widened. Without a bigger opening, the hooks don't move out of the way far enough to insert a motor. On the other hand, a motor hook on a minimum diameter model is generally not done, though it is often needed. I was glad the X-Flyers have them, and once modified, the fin cans make a good retaining sleeve.
The fin cans glue to the exterior of the body tubes, and these have a glossy surface that would prevent a good joint with almost any adhesive, especially the recommended plastic model cement. As the fin cans were tight on the tubes, especially with the motor hooks installed, I peeled off the glossy covering up to the decal wraps to expose the paper underneath. This gave me an adhesive-friendly surface and made assembly easier.
The fins had a fair amount of flash at the mold joint and required a bit of work to get smooth. My scrape and sand job left a few marks and a dull finish, so I tried to paint the fin cans with spray enamel to cover this up. The black one I painted with a store brand gloss black, and the blue one I just clear-coated. Both paints reacted with the plastic, so they took a while to dry and neither came back glossy, but they are at least of uniform color. Luckily, neither nose cone required any work, both were flashless and smooth.
Care is required during assembly to get the body wraps to align in the manner shown on the box art. The tube wraps are sharp and clean, but their edges keep peeling up where they overlap, apparently they don't stick well to themselves. While I didn't do so initially, I'll probably trim these back to stop this.
Construction Rating: 3 out of 5
Estes' claim of flights to "over 1200 feet" is indeed possible with the C6 motor, though the five second delay is closer to apogee than the recommended seven second one. The recommended ½A6-2 only takes them to about 120 feet AGL, though the ejection timing is good. The Quest A6-4 is perfect for the X-Flyers, the Estes motors all ejecting pretty early or late, i.e., ~20-25 ft/sec either way. With a 13-18 mm adapter, the A10-3 and A3-4 motors would also be good choices for these birds.
Their first flights were on the A6-4, though, and in moderate, gusty winds. Both performed flawlessly, ejecting just past apogee and recovering without damage. Neither achieved the altitude they should have, for while they didn't weathercock into the wind, they were pointed almost vertical at deployment. Their second flights were on B6-6 motors, both ejecting just before apogee. High and fast, these motors are probably the biggest that should be used without a large recovery area or conversion to streamer. #2 was lost in tall grass for about ten minutes, its dark colors blending into the ground cover quite well. It was found with a small bend in the lip of the lower body tube that I initially thought was a classic "Estes dent", but on closer examination I think was probably due to someone stepping on it during the search.
My extended shock cord wrapped around a fin on #2's second flight, but the bird recovered with a fully deployed streamer. I couldn't say that a parachute would have behaved as well in this situation, so I think switching to that type of recovery has another advantage. The fin cans are tough and showed no signs of damage from the faster descent, and I'd recommend streamers to all who build these birds.
Flight Rating: 4 out of 5
With a few changes to the design born of experience and a little work on the parts, the X-flyers can be robust birds that fly quite well. Getting two birds for the price of one, especially a pair with such good looks, is nice. Assembly is a bit more difficult that the typical E2X, but minimum diameter birds always are that way, and there's enough here to make a mediocre bird shine in flight. More careful, experienced modelers will find the X-flyers a nice addition to their fleet.
Overall Rating: 4 out of 5