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Old Jun 24, 2014, 06:22 PM
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United States, UT, Salt Lake City
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launch peg/blade location?

so i am new to this portion of rc and was curious where on the wing tip do you place your peg/blade? more to the front of rear? on the CG? thanks for the info
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Old Jun 24, 2014, 09:57 PM
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I've never really even considered the CG, but some are saying a father aft install helps.......? The problem is, their reasoning was that there was more weight forward, so the side yaw was less, but I don't think one inch (or less) is enough to impact it all that much.

But using the CG as a guide, it (seems) to me that aft of the CG would be " unstable" as compared to forward of CG "pulling" the plane, and thus more stable while in hand ....?

Maybe GT will chime in on this.
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Old Jun 24, 2014, 09:59 PM
Walter Roos
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Canton, Ga.
Joined Aug 2004
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I have always followed the Mark Drela method of " as far back and as near the tip" as you can get the blade (depends on the hinge line, somewhat) . And as your structure allows. I also still prefer the straight Drela type blade for strength and consistent releases.


BTW you need to have clearance for the web of your fingers to clear the back corner of the tip or you can't get a good back swing to your DLG. IMO. ie, your DLG should be able to swivel on your fingers far back behind you.


walt
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Old Jun 24, 2014, 10:58 PM
sticks2sticks
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Quote:
Originally Posted by ROOSWH View Post
I have always followed the Mark Drela method of " as far back and as near the tip" as you can get the blade (depends on the hinge line, somewhat) . And as your structure allows. I also still prefer the straight Drela type blade for strength and consistent releases.


BTW you need to have clearance for the web of your fingers to clear the back corner of the tip or you can't get a good back swing to your DLG. IMO. ie, your DLG should be able to swivel on your fingers far back behind you.


walt
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Old Jun 25, 2014, 06:13 AM
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thanks guys very helpful. now on to finishing my plane
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Old Jun 25, 2014, 08:03 AM
rug
Matt Cook
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Quote:
Originally Posted by Triggerhappy View Post
it (seems) to me that aft of the CG would be " unstable" as compared to forward of CG "pulling" the plane, and thus more stable while in hand ....?
The force will always run directly from the throwing blade to the CG. If the blade is forward, then the nose will be slightly towards the thrower, and if it is aft, then slightly away. Very small differences given the .75m distance to the CG, but it would suggest that aft is probably better, as hooking is a bigger problem (probably due in part to the angular momentum of the plane at launch).

Structure is going to be an issue though, so this ties in with Mark Drela's suggestion - and I'm not going to argue with him on such things.

Matt
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Old Jun 25, 2014, 09:44 AM
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A good topic to revisit

Launch peg location is one of those old topics that has been discussed many times before, but perhaps not much lately. There are a number of different considerations to think about and the final solution will, of course, be a compromise. Below are a couple links that will take you to previous discussions on this topic:

The first link is a search of my posts which include the words "aft" and "peg". I'm not suggesting that I am some sort of ultimate authority on the topic, it's just that I have the unique ability to find my own previous posts on a particular topic because I wrote those posts and can remember unique search terms that will find the desired results. This first link will get you posts that talk about at least three different considerations when talking about peg location:

1) Location for best "comfort", meaning the location that feels the best to your hand and perhaps allows you to throw with the best speed/power.

2) Location for best structural integrity.

3) Location for best aerodynamics and physics that will result in the fewest losses of energy from the initial roll and yaw excursions during the early part of the launch and lead to higher launches.

In my opinion, the three considerations listed above are listed in the correct order of importance. If you are new enough to DLG to be asking the question, then you likely should focus on the three considerations in that order. If you are an elite level competitor, then maybe you can satisfy considerations 1 and 2 well enough that the focus on consideration 3 will produce a net gain in launch height.

http://www.rcgroups.com/forums/searc...uery=aft%20peg

The second link, below, takes you to information from Mark Drela and his launch simulation. It explains the aerodynamics and Physics behind consideration number 3. I had to study it again to remind myself why the aft peg location would be better for launch height. It is quite anti intuitive unless you have a deep understanding of launch dynamics. The main benefit from studying this information would be the opportunity to get such an understanding.

http://www.rcgroups.com/forums/showt...eg#post5660781

It's interesting to note that this second link goes back to a post from eight years ago.
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Old Jun 25, 2014, 09:25 PM
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Quote:
Originally Posted by rug View Post
The force will always run directly from the throwing blade to the CG. If the blade is forward, then the nose will be slightly towards the thrower, and if it is aft, then slightly away. Very small differences given the .75m distance to the CG, but it would suggest that aft is probably better, as hooking is a bigger problem (probably due in part to the angular momentum of the plane at launch).




Structure is going to be an issue though, so this ties in with Mark Drela's suggestion - and I'm not going to argue with him on such things.

Matt


OK, now I see what your saying about the nose tending to point out if you're behind the CG (a good thing), that makes sense.
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Old Jun 26, 2014, 05:30 PM
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Thanks Phil, but the first link
http://www.rcgroups.com/forums/searc...uery=aft%20peg
doesn't work for me.

Neil.
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Old Jun 26, 2014, 06:36 PM
Duane
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RCgroups doesn't appear to have a way to permalink search results. Just search the Hand Launch forum for posts with the words "aft peg" and user name "Phil Barnes"
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