Home › Forums › Free Flight › Construction Tips & Tricks › Building reliable DT pop-up mechanisms
- This topic has 26 replies, 9 voices, and was last updated 13 years, 1 month ago by marauderbomber.
08/06/2009 at 9:08 pm #41168AnonymousInactive
I have had a number of problems with DT pop-up limit mechanisms and have wasted much time in the field hooking them up and tweaking them. I have graduated from tying thread to the fuselage and the stab trailing edge. This was time consuming and upon occasion the fuse would burn through the thread with predictable results.
I have tried monofilament lines but find them difficult to tie particularly in the field. In addition it is difficult to tie them off to achieve a predetermined length. I have yet to devise a good method of attaching the limiter to the stabilizer so the stab is easy to remove and reinstall.
08/07/2009 at 3:19 am #47604BRIAN M PACELLIParticipant
One way is to put the snuffer tube on the side of the fuselage near or under the wing. You can run the DT line around the rear and up the side of the fuse.
I like to use just mono-filament line as apposed to a stiff braided line because of it springiness. You could use a stiff line with a spring on it if you prefer.
To make the line, cut 1/16″ to 1/8 ” pieces of brass tubing and crimp the loops in. If you don’t have crimps, you can use pliers and then lightly “crimp” the tubing in a couple places with wire cutters.
On the end of the line near the snuffer tube attach a split ring or something similar. The rubber band can go on this, around the fuse, and to a hook a couple of inches away.
To limit the length of the pop-up, cut a 1/2″ piece of brass or preferably aluminum tubing. Before you do the second loop in the line thread the line through the tubing. Depending on where you glue the tubing to th fuselage, you can adjust the DT length as the crimped tubing will keep the line from going all the way through.
Hope all this helps, will try to get a picture,
😀08/07/2009 at 5:35 pm #47605AnonymousInactive
Many thanks for your suggestions. Not having to tie knots in monofilament is a huge help.
John Frpthingham08/07/2009 at 8:18 pm #47606
Don’t use monofilament. Use braided dacron line. 20lb test is a good size for all but BIG planes. Way less aggravation. If you’re using the fuse at stab trailing edge, you metal cable for a limit wire.08/08/2009 at 4:18 am #47607Dean McGinnesParticipant
The dacron has the same problem. How do you tie the loops to end up at a precise length? At least with monofilament you can used crimped aluminum tubing.08/08/2009 at 4:21 am #47608
Well, you can use crimps on braided also. 😀
I just re-tie until I’m close. You can shorten a line with overhand knots. I ‘set’ the knots with medium CyA. Don’t use thin, it wicks down the line and kills flexibilty.01/16/2010 at 4:15 am #47609JLorbieckiParticipant
Little stuff- use the dacron line just like Dan stated and a drop of CA does wonders-
Bigger stuff- use thin .010- .012- stranded steel control line- Then you can use the small brass tube to crimp- I have also used a fishing connector- the non swivel type- you squeeze it to open. This also works with the dacron line-
This all works on a rear fuse type-
Another method is to put a loop of dacron under the stab. It hangs loose and when the stab is released it stradles the fuselage- This method works only when the fin is in front of the stab.01/16/2010 at 12:01 pm #47610Dean McGinnesParticipant
John & Dan,
Where do you draw the line at “big stuff”? 😕
I am starting to build B, C, & D ships.01/16/2010 at 1:55 pm #47611
‘Big Stuff’ ?
That’s the stuff that makes me nervous. Anything bigger than a 049.02/18/2010 at 10:32 pm #47612
I have used the method of the .020 Strato-Streak DT system. It’s a piece of wire that is built into the stab LE hold down. It has a pre determined angle bent in the lower part of the wire. Just bend the angle to the amount of deg. you desire. No DT line used at all to worry about. No hanging up or burning thru. You simply install the DT fuse into the tubing, tie it down with #8 rubber band and fly as advertised.
It’s also great for “QUICK” assembly and removal if you need to put the model up in a hurry.
I have used this method on ALL of my models from .020 to my “D” ship. I’m going to be using this method on my towline models when they get done.02/19/2010 at 4:35 pm #47613AnonymousInactive
Kenny – tell us more – ‘Strato-streak system’…not familiar with it, but I’m picturing a wire sorta z-bent to create a spring effect…?
I assume you’re setting it up so it’s constantly trying to cause the stab to pop up, you use the elastic at the TE near the DT tube to burn through. Is that correct?02/20/2010 at 2:54 pm #47614
Well…I’ll do my best to explain a bit more. I have a few photos that I have attached to hopefully express what I’m talking about.
Please don’t shoot me for the poor photos.
The white stab with the orange fluorescent tips is the .020 Strato-Streak tail section.
The yellow Jap-Tissue stab with black fuselage is the 1/2A Starduster tail section.
Look at the side-view of the Strato-Streak tail section where I have placed the stab assembly on the “outside” of the fuselage for clarity and how the wire mechanism will look once installed “inside” the fuselage.
You can see how the wire comes straight down and then I have the 45 deg. bend in the lower part of the wire.
The vertical part of the wire acts as a stop for the .020/ 1/2A (View the “top view” of the .020 and the 1/2A fuselage tail sections without the stabs installed). to show you how the small incision is made.
This is a pretty neat situation. You can pivot the stab side to side for straightness if needed and you don’t have to worry about that pesky “wooden key” in the front that is usually installed.
Use your plans to help set up the DT angle. Make a complete “dummy center rib” out of 1/32 plywood to position on the plans side-view to help set the angle you desire. I use 45 deg.
Once the angle is achieved then draw the rib and then the wire configuration of your choice on the plans and use it as a template to make the DT hold down wire. This is how your stab will be in full DT position.
The incision in the stab plywood hold down will have to be drawn on the side view of the plans and cut accordingly into the stab plywood support.
“This length is critical”.
This is so, that when the stab DT’s it will have the proper amount of travel with no interference and be able to achieve the correct DT angle.
“Don’t make the incision sloppy”. Lightly sand the incision so the wire moves freely with a slightest interference fit.
Always make your stab plywood platform a little longer (LE to TE) to help support the wire when in full DT position. (See 1/2A fuselage photo without stab.)
I used K&S 0.0625 dia. wire for the two models. I use K&S 0.078 dia. wire for my A & B ships and K&S 3/32″ or 0.09375 dia wire for my C & D ships. I have also attached a photo of a sketch that I drew up to help show you the way I make my wire set up. This is not to scale. Reference only.
I hope this info and photos have helped. If you need more explanation, I’ll do my best to answer your question(s).02/20/2010 at 3:00 pm #47615
Just found out that my photos are to big. When I get them smaller I’ll post them.02/20/2010 at 3:38 pm #47616
OK..lets see if the pictures come through….
02/20/2010 at 3:40 pm #47617
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