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Author Topic: Setting up a D/T  (Read 822 times)
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Pete Fardell
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« on: June 19, 2018, 05:14:33 AM »

 I want a dethermaliser on my FROG Petrel but have never made one and know nothing, so could really do with some very basic advice. Better still, a simple diagram showing me how to set it up. Can anyone provide or direct me to one, or perhaps there's a duffer's guide in a back issue of Aeromodeller somewhere?
(I've already got a Tomy timer thanks to Bill.)

Thanks in advance!
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LASTWOODSMAN
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« Reply #1 on: June 19, 2018, 06:29:43 AM »

Hi Pete.       This really great 12 min video, by Joshua Finn, demonstrates not just one, but several different models working, and discusses Fuse Timers, Clockwork Timers, Viscous Fluid Timers, and Electric timers.  He demonstrates 5 different Fuse Timer models where the whole tail (rudder and stab) tilts up, another where the main wing pops up, another where the main wing completely separates, but is attached by a line to the tail, and follows the fuse back to the ground, and another where the main wing tilts forward.  He also demonstrates clockwork timers where the whole tail tilts up, and he demonstrates viscous fluid timers where the stab only pops up.   I really do recommend this video.
VIDEO HERE
https://www.bing.com/videos/search?q=MODEL+AIRPLANE+DETHERMALIZER&&view=detail&mid=3D75F31716E1C37593353D75F31716E1C3759335&&FORM=VRDGAR

LASTWOODSMAN
Richard
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USch
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« Reply #2 on: June 19, 2018, 08:17:16 AM »

Hi Pete,
show us a pic or drawing of the tail feather's of the Frog Petrel. They are thousand and one solution to the problem, but most depends on how tailplane, fin and fuselage meet.

Urs
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« Reply #3 on: June 19, 2018, 08:44:43 AM »

Do you want to use auto-rudder Pete? (Or at least keep the option open?) If so that may be a factor in how you set up a d/t.

You could make the whole tail and fin pop up quite easily, just use rubber band attachments at the front and have the d/t line hold down the rear. A small angled aluminium tube at the rear is useful to turn the line. This would allow you to use the sub fin for the autorudder tab.

Have a look at the d/t bit in pic 3 on this Lulu set up:

http://www.theplanpage.com/things/Lulu/Mods.jpg


Alternatively you could have the wing pop up, but I would suggest that it pops forward (TE up) rather than backwards as shown on Josh's video.


Jon
Setting up a D/T
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D/T
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« Reply #4 on: June 19, 2018, 09:58:47 AM »

I would keep clear of the wing TE up d/t, otherwise known as the Tumbling Pigeon d/t - likely to take off the wing tips on landing!
Regards
Don
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billdennis747
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« Reply #5 on: June 19, 2018, 11:14:30 AM »

Pete
Have a good look around at Oxford - there'll be as many variations as models. Here's my scruffy Dolphin.
Timer - drill a fine hole for a pin to interfere with the waggler - withdraw to start. Small balsa block to stabilise it. No need for auto-start here; add a bit of time on and pull the pin on release
Run the cable through little wire guides. At the back, a curved piece of ally tube is best. The small piece of tube crimped on acts as a stop for the angle - 45 degrees.
Autorudder essential
Bend the hook down a bit for easy release or it will stay up there all day
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Pete Fardell
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« Reply #6 on: June 19, 2018, 11:57:37 AM »

Thank you all- I'm perusing and absorbing. Pictures are really helpful, and I'll check out the video too. Yes, was going to ask about auto-rudder next. Urs, drawing of Petrel tail attached.
(Bill, I do intend to have a good look at Oxford, but meantime I'm hoping to get this built in time for that very event!)
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« Reply #7 on: June 19, 2018, 12:10:18 PM »

Having got the Dolphin out of the depths, I might fly it at Oxford too
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Pete Fardell
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« Reply #8 on: June 19, 2018, 01:12:52 PM »

Richard, thanks for the link to Maxout's very enjoyable and informative video. I love watching films of people doing stuff they know about.

Slowly getting my head around it. I think then I'm going with a tail which pops up at the back and an auto rudder on the underfin, much as Bill's Dolphin. I  know this stuff is obvious to most on here, but can I just check I've got things straight...


The DT works by means of a line holding the back of the tailplane down. The other end of the line hooks over the pin on the timer. When the pin turns back round to its original position, the line slips off the pin and the tail pops up.


The AR works by means of another line which holds the rudder staight against the tension of a piece of elastic on its opposite side. The rudder line's other end  is hooked over a pin in a vertical tube. The bottom of this pin is linked (by its own line) to the towline. As the towline is released the pin is pulled down, leaving the rudder to snap over again so that the glider will circle.


Please let me know if any of that is wrong. Also, at events, is the autorudder release line usually a communal thing permanently attached to the towline for everyone to use? Or do you clip on your own as you launch and retrieve it later?
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« Reply #9 on: June 19, 2018, 01:41:45 PM »

Pete
You've got the DT right. One turn on that timer will be about a minute. Key the tailplane so it always goes back the same way.
I would consider a different method for autorudder because the line won't have a pin. Also, there is some tension involved and if it hangs up, you aren't on the end of the line to give it a tug. Consider the swinging arm, which is very simple and needs no setting up. An example here on Ray Monks' Quickie:
https://outerzone.co.uk/plan_files_03/3444/Quickie_BW_Print_oz3444.pdf
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« Reply #10 on: June 19, 2018, 02:46:24 PM »

Bill, I use a pin a/r release on my 36" 'Walkin' Shoes'  and so far there's never been a hang up.     So far....        Rudder requires very little tension.
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« Reply #11 on: June 19, 2018, 02:56:16 PM »

Hello Jim
In that case I think the main drawback is that a bungee provided in a contest will not have a pin attached
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Pete Fardell
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« Reply #12 on: June 19, 2018, 03:53:28 PM »

The swinging arm looks like a nice simple solution, but won't it be a problem if I have to move the tow hook? I've already given myself the option to do that by using the screw-in cup hook idea suggested by John on the other thread...
I would also recommend using 1.5mm dia. screw in cup hooks (straighten to a normal hook ) and screw them into a piece of ply(1.5mm should be enough) along the bottom instead of binding wire hooks to the fuse. This makes it very easy to adjust the position for the best tow by just having  series of drilled holes.

Pic shows what it looks like at the moment. What would happen if I just had a ring on the AR line and put it onto the tow hook before the towline went on?
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« Reply #13 on: June 19, 2018, 04:02:43 PM »

I'm sure that works too. Or there is the Caprice method; bend the end of the towhook down just enough to hold a band on the end of the AR line and the tow ring pulls it off on release.
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« Reply #14 on: June 19, 2018, 05:15:57 PM »

If the bungee has no pin attached you can prepare one at home with a swivel as in the picture (fishing accessory).  That you can simply clip to the ring at the end of the bungee. For the pin dont use a rigid piece of wire but instead a piece of thick (0,8mm) nylon monofilament, this will always come out of the mousetrap even if the model is not straight up on the line.

Urs
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« Reply #15 on: June 19, 2018, 07:07:59 PM »

Pin works for me.     Clip to towline ring, retrieve after flight(s)  and keep in flight box for next contest
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« Reply #16 on: June 19, 2018, 07:25:20 PM »

Simple adjustable towhook with precise adjustment  facility.      1/16" ply frame let into fuselage base.     Lousy photo ... sorry.
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« Reply #17 on: June 20, 2018, 04:50:58 AM »

Hi Pete,

I've done a little drawing that might help with the D/T.

You can see that a stop is needed just forward of the LE to give the tail something to pivot against. This can be a piece of 1.8" balsa just wider than the fuselage and glued down. The rubber bands strap over it and to a small hook in the tailplane spar area. (Or a hole through the fin would work)

The D/T line holds the TE down and runs through the bent ally tube CA'd to the end of the fuselage. A bead on the D/T line can form a stopper that holds the Tail at 45 degrees when the D/T is deployed. This can be a bit fiddly so I use a separate adjustable line to set the tail angle.

You will need to provide some kind of keying so that the tail sits in exactly the same place every time when flying- otherwise you will get inconsistent trim from the misaligned rudder. I use little balsa stops either side but you could have a ply tab slot into the fuselage or something.

It's also good to have a 'turnaround' or 'capstan' somewhere between the D/T and the timer. This can be just a bit of dowel poking out the fuselage that you wrap a turn or two of the D/T line to secure it. This allows you to get plenty of tension holding the tail down but minimum tension on the timer arm. A small rubber band may be handy between the capstan and the timer too.


Jon
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Pete Fardell
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« Reply #18 on: June 21, 2018, 04:27:16 PM »

Thanks again chaps; all very helpful stuff.
Jon, many thanks for taking the trouble. That drawing makes everything much clearer, as do your words. Just exactly the kind of detailed info I need!
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Pete Fardell
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« Reply #19 on: June 22, 2018, 12:45:06 PM »

Is there anything I need to know regarding attaching the timer to the fuselage?
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« Reply #20 on: June 22, 2018, 01:12:10 PM »

Is there anything I need to know regarding attaching the timer to the fuselage?
sheet the bay, make a hole, glue
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Pete Fardell
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« Reply #21 on: June 27, 2018, 04:38:30 PM »

Thanks again for all the excellent helpful input on here. As a result, I've now managed to set up both DT and AR on the Petrel. A few pics attached. The auto-rudder uses the Caprice release method Bill suggested, which is nice and simple. I've also used Bill's holding pin in a balsa block for the DT starter. Everything works quite reliably in the workshop. Let's hope it works in the field as well!
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« Reply #22 on: June 27, 2018, 06:47:52 PM »

Looks great Pete Smiley The model looks lovely in the pics on the other thread.
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« Reply #23 on: June 28, 2018, 09:39:39 AM »

nice job Pete
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