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Author Topic: DT Timers?  (Read 1227 times)
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High Point
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« on: January 05, 2011, 08:56:18 PM »

I'm getting to a point to where some of my gliders are getting some altitude and gliding awhile. What is your choice of DT methods on smaller CLG's? I know about setting up the fuse type, but can someone tell me about the plastic round button timers; I have some to use, but no experience. Pictures would be great too.

Thanks,
Curtis
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #1 on: January 05, 2011, 11:05:25 PM »

Hello Curtis,

I simply went to search box, typed in "DT" and got a myriad of info. For example: http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=2214.0

That one refs to viscous timers in certain size models, but you can find all you need by doing the search thing on your own.

Ciao,
Leeper
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Leeper
Zack
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« Reply #2 on: January 06, 2011, 06:45:46 AM »

I've used button timers on 14" and larger gliders, but I think beer can dts with silly putty tube timers work better on 8 and 12 inch gliders. My Sampson the Cat build shows to how build a pop stab dt with a button timer.
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julio
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« Reply #3 on: January 08, 2011, 11:41:59 AM »

High Point-Curtis

Probably you have already received some PMs with good help from many members. Or maybe you found the info by yourself. But just in case, I recall some technical approaches posted at this forum. I did a search for those I recall and came out with the following posts by member Tmat with a full graphic sequence posted by him in his Picasa gallery.

http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=2454.msg25434#msg25434

http://picasaweb.google.ca/tmathews180/MicroTubeDTTimer#

http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=1974.msg32864#msg32864

http://picasaweb.google.ca/tmathews180/A2ZMatcatBuild#

Two other links to Ramon Alban's site.

http://vintagemodelairplane.com/pages/Downloads/CRB_Tasters/SillyPutty01.html

http://vintagemodelairplane.com/pages/Downloads/CRB_PDFs/SillyPutty01.pdf

Don't now if the last link will work here as it is a .pdf file, but it's available at the first Ramon Alban's link by clickling in the word "here" in red fonts.

Regards
Julio
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Tmat
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« Reply #4 on: January 08, 2011, 02:13:36 PM »

Thanks Julio,
I was about to post most of the same links. Grin

The little Silly Putty timers are well suited for 6" to 8" clg's and may also be fine for 12" gliders. I still like the tiny viscous dampers such as those that Alan Cohen sells for 12" and larger gliders as they are less affected by temperature and are more consistent. http://hobbyspecialties.com/product_info.php?products_id=39&osCsid=b74a85c66968627c4ccb7ee7f1db78f5

The dampers can also be used to activate a flap type DT or a pop-up boom or wing.

Tmat
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Zack
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« Reply #5 on: January 08, 2011, 03:11:57 PM »

I wonder what the forum thinks about using Hoerner tips with beercan dts? These are the thick curved tips with the sharp edge at the top to increase the effective span of the wing--they might be less likely to break than wings tapered to a very thin edge--not likely with tiny gliders but will be an issue with larger ones.
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Tmat
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« Reply #6 on: January 08, 2011, 10:39:19 PM »

Hoerner tips are not proven to be effective for our Reynolds number as far as I've seen. And they add extra work for no apparent gain. But they do look pretty cool!

So go nuts! Grin

Tony
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Zack
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« Reply #7 on: January 09, 2011, 06:40:03 PM »

I built a pair of 12" Pathfinders, one with a beer can DT and the other with one of the little viscous timers releasing a pop up boom. The beer can version is a couple grams lighter--so it will probably be better in dead air. But, the pop up boom can be adjusted more precisely. But, I've been building my Vartanians with Silly Putty timers--so I can preserve the profile of the original design.
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Kit
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« Reply #8 on: January 09, 2011, 08:52:06 PM »

For the last couple of years I've been sanding a slight upturn to the tips of my gliders with a straight trailing edge, in addition to a bit of washout in each tip. Not exactly a Hoerner tip but the idea was to try get the airflow off the tip with a minimum of turbulence. Tmat is right though, I cannot testify that it makes a great deal of difference in the outdoor environment in which I usually fly. Putting tip configuration to the test would require building several gliders identical except for tip design and testing them repeatedly in a large indoor venue, which is very scarce these days unless you have access to a Romanian salt mine.

Tmat is also right, however, that they look really cool. That might even be worth the extra effort.

Kit
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Stan
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« Reply #9 on: January 12, 2011, 07:35:11 PM »

Tony, you are perhaps the only one that has ever agreed with me about the hoerner tips and our models. At least until they beat their head against that wall for a while. Nice to hear someone as sharp as you on my side!
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #10 on: January 12, 2011, 08:55:51 PM »

We all pretty much agree that fancy Hoerner tips are of no apparent use to we FFers. Stan & I have talked on this subject at length. He may recall that I mentioned an early 70s A2 of mine had downswept Hoerner tips. Then I saw some RC sailplanes with slightly upturned tips which seemed to work well, so cut off & replaced the tips with curled up Hoerners. It did fly better. My thinking being the vortex was smaller and cleaner. In addition, they seemed to ADD slight dihedral effect, whilst the downswept Hoerners seemed to 'dig in' on crosswind turns, & not to act well when needing to correct yaw. This leads me to believe they LESSENED the dihedral effect enuf to hurt performance. That A2 became better in all respects, with about 5 more seconds more still air time on average. Shortly after that and to this day, I normally round up the bottom of A2 tip blocks to meet the top surface. Of course, CLGs & HLGs with rounded tip planforms do not necessarily fit this scenario.

Leeper
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Leeper
Olbill
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« Reply #11 on: January 12, 2011, 09:06:45 PM »

My Cat 2 catapult glider has tip plates. It flies really well.

I think the prevailing logic about tip plates is that if you don't know how to design them it's best not to try. I guess I got lucky.
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Tapio Linkosalo
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« Reply #12 on: July 08, 2019, 08:02:21 AM »

Trying to set up the DT for my new CLG, I was wondering about the best type of spring. My button timer seems to run pretty fast to start with, then considerably slows down towards the end of the rotation. An optimal spring for the motive power would have constant power as it stretches, but normal spiral springs have a force that linearly increases as the stretch increases. So I would conclude that as long a spring as possible would be best, so that the force increase is as small as possible. But are there other means to make the force constant?

Also, would it be ideal to have the button "drum" diameter small or large? the latter would need weaker spring to rotate (as the radius is increased), but at the same time has larger travel and thus need a longer spring.

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Skymon
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« Reply #13 on: July 08, 2019, 11:30:19 AM »

use rubber.
It's lighter and you can easily adjust the 'pull' with cross section.
You fly indoor, so you will probably have a rubber stripper, or some offcuts of pre-stripped stuff.
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Stan
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« Reply #14 on: July 08, 2019, 02:40:42 PM »

If you want to be very consistent on a given day then rubber is not the ideal. You know that if you stretch rubber a bit more one time then it remains a bit longer for a time and thus your dt time will change. Also rubber wears out due to environment, like exposure to sunlight, and your dt time will change. There are already enough issues with a viscous timers that cause inconsistencies that using rubber is not a good option. However, if you are not particularly interested in getting close to 2 min then rubber can work fine, especially for very short test flying.

You are right, longer springs can help.

My timers use a "cam" so that as the rotation approaches its release point the leverage on the drive pin increases and the timer rotates faster even as the spring force weakens. This also helps overcome problems the timer might have due to inconsistent friction near the end of the rotation.
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Tapio Linkosalo
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« Reply #15 on: July 08, 2019, 03:01:39 PM »

My timers use a "cam" so that as the rotation approaches its release point the leverage on the drive pin increases and the timer rotates faster even as the spring force weakens. This also helps overcome problems the timer might have due to inconsistent friction near the end of the rotation.

Excellent idea! And as the viscous button has the shaft that is formed to accommodate the gear anyway, it should be straight-forward to 3D print a cam dropping into that place.

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lincoln
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« Reply #16 on: July 08, 2019, 03:54:11 PM »

If you're going to use a beer can DT, I suggest you replace the metal tab often. Nothing like seeing a little flashing thing separate from your glider as it rises in a strong thermal. Or maybe use a different material.
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