I have used retract gear in quite a number of R/C aircraft and noted they generally would improve the aircrafts performance due to the reduced drag when the gear is retracted.  I wasn't sure how this would relate to control-line stunt world where the aircraft is tethered, but surely it would be impressive for judges and spectators alike.

Since I am now flying a few electric stunt ships, I saw an advantage to electric retracts because they would require no further power source than the one I am already carrying. I went to the Top Gun giant scale invitational one year down in Ft. Lauderdale and had the opportunity to speak with Dave Platt for a bit. Dave showed me his really nice electric retracts in his fabulous scale model and told me they were made by Lado.

When I decided to try this project, I searched high and wide but could find no electric retracts in the size I needed. Was out at one of the clubs and talked to an old friend, Art Werner, who let me check out his R/C T-28 Trojan with electric retracts. That set me on the course to E-Flite to see what else they offered.

Found the .10 - .15 size which looked just about the right size to me. Here is a picture:



Here are some specs on this gear:

10 to 15 - Size Main Electric Retracts EFLG100

Key Features
   •   Robust landing gear strut and mounting bracket
   •   Integrated electric motor with a micro PCB
   •   Built-in overcurrent protection
   •   Aircraft Weight: 2.00 - 4.50 lb (0.90 - 2.00kg)
   •   Strut Diameter .118 inch (3mm)

Overview
10 to 15 - Size Main Electric Retracts [EFLG100]
You don’t have to be a master modeler to add the realism of functioning retracts to your airplane. E-flite’s completely self-contained retract system requires no air tank, complex linkages or extra servo. It can simply be bolted into place and plugged into the receiver. A specially designed Y-harness is included that allows for the use of a single receiver channel to control all retract units.

Product Specifications
Application:
Aircraft 10–15 size
Speed: 4.8V (1.25 seconds), 6.0V (1.0 seconds), 7.4V (.80 seconds)
Weight: 3.1 oz (complete set)
Motor Type: Electric brushed can
Connector Type: JR, universal
Gear Type: Metal
Current Draw Idle: 5mA
Current Draw Stall: 200mA
Voltage: 4.8–7.4

Ordered up a few and proceeded to bash up my T-Bolt for the retracts. This aircraft had already been bashed, started out as a Brodak T-Rex ARC I converted to electric and made to look like a P-47. Here is what it looked like:



Stripped off the bottom wing covering of polyspan and auto urethane to reveal the structure and proceeded to modify the spar area to accept the retracts. My brother Wayne and I did the re-design and to date no problems. Each retract has a connector which plugs into each end of the y-harness furnished with the gear. We needed to use a 12 inch extension to route things far enough into the fuselage to reach the retract channel of the timer Will Hubin kindly made for us.

Here is the completed bottom wing structure after covering things back up with some Park-Lite heat shrink covering.


Here is a closer look:



Here is a closer look at the timer Will made for us:



The two white leads go to the start switch for powering up the system. You'll also notice some markings and connectors for "servo" (retracts), "ESC" (speed controller), "Prog" (remove ESC connector and plug Will's programmer onto these six pins) and "BEC" (battery eliminator circuit). You'll also notice several "G's" printed on the board to make sure you connect things just right.

Here is an overall view of everything connected:



I won't go into the entire adventure of getting these retracts to work, but the above set-up works perfectly. The big mystery was trying to power these retracts with the very nice Z.4 Z-tron timer. Though this timer has a retract channel, it was designed to work with a separate retract servo powering mechanical retracts. The included BEC for this Z-Tron timer does not have enough punch to make these go. Once I switched to the Hubin retract timer and added a separate Castle 10 amp BEC, it was like magic. Here is  picture of the BEC:



Some speed controllers have their own internal BEC, so one must use care when deciding how to power these retracts. 10 amps works, but I do not know the minimum amount required.

Sam, Wayne and I all got to fly it with the retracts functioning and it was very cool though the first flight was pretty exciting at takeoff. This timer is programmed to retract the gear 10 seconds after you punch the start-up button. This is perfect with the gear retracting about 3/4 to 1 lap into the flight. We decided to get a tach reading which put us a bit behind the curve and the gear starting to retract about two foot into the takeoff run while still on the ground. I held a lot of up elevator and got her up without so much as a nick the the APC propellor. Will's newest timer allows you to set this time delay yourself. Will also programmed the three bleep warning I liked so much on the Z.4 timer.

Was going to get some flight photos last weekend, but the weather and Santa decided to intervene. I'll try to post some if the weather looks better this weekend. I was very surprised at the difference these retracts made in the flight performance of this particularly heavy aircraft (a svelte 77 ounces). I knew it would look good, but the flight performance difference was very noticeable.

I've promised this aircraft to a good friend of mine once I am done with this experiment. I'll yank all the gear out and he will put in a nice .60 glow. Should fly very nice then, will lose about a pound of weight converting back to glow. Here is an outline of the gear I use in this ship:

Motor: the mighty Plettenberg 25/12 (we have since switched to the 20/16).
ESC: Schulze 18.61K F2B (originally used an 18.46K, F2B but this was marginal with the 25/12)
Prop: APC 13X4.5P Electric
Timer: Hubin FM-9 retract (there is a brand new one available with more programming options)
BEC: Castle 10amp

I love the 25/12, about the smoothest running thing I have ever heard. Weighs a couple of ounces more than a 20/16 which is more than enough power for ships of our size. Run the same prop on both. All Plettenbergs and Schulze ESC are hard to get. The only source I know is I-Care (http://www.icare-rc.com/). Seems the Euro's in these factories get to take off 12 weeks or so for siesta time during the summer, so who knows what other time they get off. Probably off for a month for Christmas Expect to wait for these items if you want one.

Getting ready for KOI in a few weeks, converted my old Tracer  to electric a while back and have it flying sweet right now. Looking forward to that event as it will be held at a new facility this year. Hopefully Mother Nature can conjure up some warm and friendly weather for us. Here is a picutre of my electric Tracer:



Hope I attached the photos OK.

Happy Holidays

Jim Smith

Jim:

THANKS for sharing your set-up  It looks like a real clean installation - quite a feat considering you started with an ARF.  Do you know how much weight you added with your installation?  I see the retracts spec out at 3.1 oz (not bad at all!) and it seems with some TLC the anchorages and wheel houses should not be too much worse than a fixed installation.

Not sure I'm ready to bite this bullet yet, but it looks like it will be a pretty exciting year for new birds with vanishing feet!

In regards to the .10 to .15 size of these retracts, the landing gear wire appears to be 3.0mm, very close to our standard 1/8 wire for wing mounted gear on our .60 size aircraft. The T-Bolt was a good test bed and probably has about 10 retract flights with no issue. We will replace the soft coiled wire struts with 1/8 music wire for our new birds. Heard Bob Hunt is going with titanium struts - might need to get my hands on some of that stuff.

The T-Bolt weighs a hefty 79 ounces, so if these retracts can handle this weight without issue so far, I am confident they will hold up fine in a lighter ship. My nephew even gave it a very good bounce test on a windy day at the field. Longevity may be more of an issue, but so far, looks good, no problems - works flawlessly.

Thanks,

Jim S.