I ordered a set of B&D retracts for my Twin-Air. Tower won't have them in stock for a couple of weeks, so I was wondering if any of you would have the measurements of the retracts. With the measurements I can get going on my wing, otherwise it will be set back about 3 weeks.
Tower only shows the mounting hole locations.

Thanks in advance,
Greg

Here are some measurements:

I don't know the names of the gear parts. I imagine the gear consisting of a mounting plate with a cylinder box mount to it (event though it is one plastic piece).


Mounting plate:

height (parallel with cylinder): 47,2 mm
width: 44,4 mm
thickness: 3,1 mm


Cylinder box:
width: 19,0 mm

Where the box rests on the plate its rounded so the mounting rails have to be futher apart than 19 mm. I have mine 25,5mm apart.


What other measurements do you need?


Regards
RCer.

RCer,

Thanks for the reply.
If you are looking at the retract from the end it would resemble a top hat.
From the dimensions that you gave me, the hat part would be 19.0 MM wide X 44.4 MM high. The hat brim would be 3.1 MM thick and the radius between the brim and the hat part would be approximately 3.1 MM. Is this right?

Looking ar the retract from the bottom it would be 47.2 high X ? wide?

Tower shows the mounting holes at 30.1MM X 38.1 MM. Is this right?

I hope this isn't too confusing.

When you mounted your retracts, did you use screws or bolts and blind nuts?
Did you recess the plywood mounts so the retracts were flush with the 1/16" bottom sheeting? If the mounting flange is 3.1 MM thick it would stick up 1.5 MM above the sheeting.
It looks as if the retract unit just fits between the ribs. Did you have to reposition any ribs?

Thanks in advance,
Greg

Ok. To make it less confusing I have made some crude drawings with measurements. Hope it helps. I considered removing the decimal point since the retracts are plastic the measurements vary a bit depending where you measure but I didn't want to redo the drawing.

I had to move one of the ribs to make the retract fit. Also the outboard rib needs a hole in it to allow for the wire attached to the piston to extend out throught the hole.

I have my rails spaced 25.5 mm apart and they are 15 mm wide. If I should do it again I might make the slightly wider - maybe 17.5 mm. 15 mm is enough but wider would make the glue joints bigger.

The mounting hole locations was difficult to measure accurately. There was a small difference from side to side. If I where you I would wait to drill the guide holes for the mounting screws until you get the retracts. Can be done after building the wing so should not set you back. With the gear wire attached to the retracts system its easy to align the wire and then drill the holes. NOTICE my measurements are 2 mm off in one of the dimensions compared to what towers says!!

I did not recess the mounting rails. I considered it but in the end did not bother. My idea was simply to add a sheed of balse on the inside before gluing the rails on. As I said I ended up not doing it. Also I considered tilting the rails to accomodate for the wing dihedral when the gear is extended. However, I figured it would be a very tight fit between the wheel and the top sheeting so I did not do that either. I think keeping it simple will make the mount stronger.


Regards
RCer.

RCer,

Thanks a lot for the drawing. That cleared up all the size issues.
Did you get your Twin Air finished yet?

Thanks for the help,
Greg

RCer,

How far apart are the ribs that the retracts are between?
Would 3-1/2" (89 MM) be far enough apart?
Did you move the rib closest to the center of the wing the full amount, or move both?

Thanks in advance,
Greg

Hi.

I have mine spaced about 87mm apart. I use the plywood ribs with the plywood doubler on the outside of the bay. I only moved the inboard rib (as far as I remember). I dont think the sheet extends far enough to allow both ribs to be moved.

If you haven't allready done so you should read the thread "Another twin-air .45 build thread" by Stevetrofemuk. It is on page 2 of this forum. I am following in his footsteps and so far it has workd fine. In this thread there is a comment about extending the sheeting outward in order to make it easier to appply the covering material around the narcells.

I will see if I get the time to make a photo of my gear bay of the wing later today.


I have not progressed very far with my build. Have had a ton of work to do plus I am a slow builder. A stick glued a day makes me happy. I have the wings almost finished. Still needs to cover up gear well, join the two halfs and add the top center sheeting. I have only drilled the firewall for the narcells and will start on them soon. The fuse is 1/3 build. Yesterday I added the mounting plate for the front gear. Will upload a photo of that as well. The tail is done. So as you can see I still have plenty of work to do. Hopefully I will finish it before the flying season starts but I start to have my doubts. Besides a fulltime job I am studying at business school at night and have a lot of exams coming up in 3 month time plus I will become a father in about 2 month time. .


Regards
RCer.

RCer,

Thanks again for the fast response.
Your gear drawing has helped quite a bit. I wasn't sure on the rib spacing because of the rod that extends 24MM when the gear is up. It must retract completely when down. Seeing as the gear is 84MM it must just drop in at 87MM spacing.
I have read all of the threads, and have most memorized. Extending the sheeting was one of the changes I planned on doing. I had some 1/16" balsa sheet in my stock pile and used them to make the wider center sheeting to allow for ease of covering. This would also allow me to move the rib if necessary for retract installation.
I started a post in the pattern forum on the preferred method of securing the gear to the wooden gear mounts. I figured these guys would be the best to ask as they all use retracts. From the responses I got screws are not used to mount gear. Surprisingly 4-40 nylon bolts with T-nuts were the attachment method of choice. I may go with the nylon bolts.
Congratulations on becoming a new dad soon. Sounds like you are going to have your hands full literally.

Thanks again,
Greg

I have mounted my gear using the self tapering screws that came with the gears. I predrilled guide holes and after that mounted the gear. I then droped some thin CA into the holes made by the screws. I can propably still change it adding a T-nut on the back and use nylong bolts. Will stringly consider it. What size nuts will you use? 3 mm (a bit less than 1/8 inch)? Not much room for the T-Nut but with a little of filing it might work.

This is my first retract installation so I am curious about the best mounting method too.

Regards
RCer.

The 4-40 bolt is .108 aprox. 2.7mm
The 6-32 bolt is .135 aprox 3.4mm

I see you found the thread in the "Classic Pattern" area. Here is a shortcut http://www.rcuniverse.com/forum/m_3735205/tm.htm

It occourred to me that these guys grease the majority of their landings. I would choose bolt size accordingly.

Greg