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Old Mar 25, 2010, 02:36 PM
RIP MC
fnnwizard's Avatar
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Reflex for zoom.

Quote:
Originally Posted by target View Post
I'm flying my 3.5 with the CG @ 110, and like a little less reflex than Tuan recommends, just in case someone wants a differing opinion. I think that in calm air, the CG could be easily pushed back a little further than that as well.
I also run a little differential, and fortunately, my plane still has not plummeted from the sky....


R,
Target
Stuck on a boat and B-O-R-E-D ! ! !

I'm not sure what the best reflex setting is in the various winds, but if my thinking is right, there should only be one best reflex setting for the zoom if the zoom is to be vertical. And that is with polar at zero lift. Since there are no published recommendations from the manufacturer for where zero lift is on Xplorer, we can only go by the method of using a straight edge along bottom which gives about 4mm.

In this reflex setting the ele (h stab) should be at 0 incidence to the wing. This should give the least amount of drag. I extracted this info from the 3 sources I considered most knowledgeable in this area: Joe Wurts, Dr. Drela and Andreas Herrig.

For example, on the Aspire, the zero lift is 2 degrees reflex, which is about 2.2mm. When I put the straight to the bottom test on the Aspire, it is 2.2mm of reflex.

T
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Old Mar 25, 2010, 02:57 PM
Eggcellent...
tewatson's Avatar
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You guys are killing me with the tenths of a millimeter jazz...

Tom
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Old Mar 25, 2010, 03:01 PM
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fnnwizard's Avatar
United States, CA, Midway City
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Also, I concluded that to get the best performance out of the wings, "snap flaps", which is camber or reflex mixed in with ele, should be "contained" between max reflex and max camber in all flight modes, with the mix linear, but I have the mix maxing out with just 1/2 ele throw in each direction.

I think the most important time for this "snap flap" is in the pullout from the dip before the zoom. I have it so that the TE of wing goe from 4mm of reflex to 2mm camber when I pull back 1/2 of ele stick at bottom of bucket.

Try it. I promise you will like it! Also, for those who find it hard to get the timing right when to switch launch mode off and into speed zoom, mix in reflex snap flap in launch mode to give 4mm reflex when you dive. Then just switch off launch after round the top.

This should yield better timing than if one were to switch launch mode off too early or too late.
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Old Mar 25, 2010, 03:05 PM
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Tom I am with you, I use that old fashioned really precise TLAR gauge to measure all my settings. They all end up getting changed once the flying begins anyway. Not saying using Tuan's methods are wrong just seems like a lot of overkill to me. I love following Tuan's build threads since he does have lots of great information.
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Old Mar 25, 2010, 03:11 PM
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Brea, CA
Joined Feb 2007
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Good information

Tuan;
Always good information and your set up tips are very helpfull. Just some food for thought for you.....The zero lift trailing edge setting on a cambered airfoil may or may not be the lowest drag solution.
R,
D
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Old Mar 25, 2010, 03:24 PM
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Quote:
Originally Posted by dlrepp View Post
Tuan;
Always good information and your set up tips are very helpfull. Just some food for thought for you.....The zero lift trailing edge setting on a cambered airfoil may or may not be the lowest drag solution.
R,
D
Don I agree, but until someone posts what it is, I can only go by the method as described above and my recorded data... which actually suggests 4.5-5mm of zoom reflex. So maybe undercambered airfoil needs more reflex than the straight edge method ?

I know that 99% of the time it's the pilot. Of that 99%, 90% is about reading air and getting her to touch the ground on time. The other 10% of that 99 usually is in the landing.

But for all us guys who can't read air that well, and still need work in the landing zone... this "bud's for you" .
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Old Mar 25, 2010, 04:31 PM
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Aileron differential

O.K. one more thing that has been bugging me on several of the threads here on RCG..........Some of the posters I believe have taken some of the "Experts" statements out of context or as a cure-all when they were intended for very specific designs, and or circumstances. Some food for thought:
1. "Adverse" yaw is not the same thing as lack of yaw or zero yaw
2. In a properly "Co-ordinated turn"(full scale or model) you add rudder
because hopefully your aileron input did not create a yaw or pitch change
(+ or -) and you need some yaw to line the fuselage up with your intended turn radius.
3. Don't remember who posted "People carrying sailplanes don't use
differential" but I can assure you, they do (some 2-1 or more). Next time you do your preflight, look at the ailerons when you wiggle the stick The reason is simple: in an ideal world when the pilot initiates a roll input, he wants a roll input, not a pitch or yaw response. If he wants a pitch
response he uses elevator, or a yaw response, rudder. Since the real world is not ideal, Full size sailplanes are not "fly by wire" (yet), the designers choose a mechanical differential that is a compromise over a broad range of airspeeds to reduce pilot work load and optimize efficiency. With our modern radios we have an advantage in that we can set up for several different airspeeds (flight modes).
The point is: while you don't want to create a co-ordinated turn using differential only as Dr. Drela points out, setting up your airplane to have extreme adverse yaw or pitch change with aileron input only, then correcting that with large rudder movement is not efficient either, particularly with v-tails where a large percentage of your rudder input is unwanted opposing elevator.
4. Sometimes our needs are different than optimised full scale practises or even best case aerodynamics because we are remotely piloting our aircraft at long distances and need pilot work load reduction methods that may not be aerodynamically perfect for the airplane but are the best compromise for the pilot/airplane combination under those particular cicumstances.

Sorry about the thread hijack........I'll return to the Explorer now........Love mine, red 3.5
R,
Don
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Old Mar 25, 2010, 04:42 PM
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This is all very interesting and I hope that someday my piloting skills are up to the task of being able to take advantage of some of the ideas presented here.

For now I'll stumble around the sky hoping to bump into a thermal that is strong enough for me to recognize it and maybe be able to keep the plane in it long enough to make my time.

Then I still have to land, and THAT is a whole other story!!

I did want to add one tip I recently got from Mr. Perkins. He told me: "Fly in lift Dude". Sage advice which I will endeavor to follow.
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Old Mar 25, 2010, 06:21 PM
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Don, have you tried flying the X without differential and a little extra rudder mixed in? Try it .

Here's a thread that most recenty talks about this starting at post 31:
http://www.rcgroups.com/forums/showthread.php?t=1200978

I don't think we took Dr. Drela's analysis out of context .

I
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Old Mar 25, 2010, 07:30 PM
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Don says,

Quote:
"People carrying sailplanes don't use differential"
I think most people carrying sailplanes use one hand and a good plane bag

Clay
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Old Mar 25, 2010, 08:09 PM
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I have read all of the threads pertaining to Differential that I could find including everything written by Dr. Drela and several other Dr's of Aeronautical engineering. I have also flown and worked on the linkages of full size sailplanes.
I have experimented with the set-up on my Xplorer as I do with all my airplanes and will continue to do so and it is to my liking. Having said that, I do have a smart left thumb and use it alot When I ask for "roll" without rudder mix, it rolls with near zero pitch or yaw. When I switch on rudder mixing it makes very nice co-ordinated turns. For me that works.
Not all you read on RCG written by the "experts" is technically correct, and sometimes it doesn't matter because it works for that particular case in the model world.
Opinions differ and different set-ups work well for different pilots for a number of reasons. As I tried to point out in my reply, the easiest to fly or most effective set-up for a given pilot, may or may not be the most aerodynamically efficient or lowest drag. It may however yield the best mix of man machine interface for that pilot for the task at hand and there's nothing wrong with that
One thing I've learned over all the years of being an engineer is this:
The words "always" and "never" don't belong in an engineers vocabulary.
Again, no disrespect meant to anyone, just trying to provide some perspective. Really don't want to start a debate. I'd rather be flying!!
Enjoy all the good information available on RCG.
R,
Don....out
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Old Mar 25, 2010, 08:11 PM
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LOL Clay
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Old Mar 25, 2010, 09:54 PM
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You're killing me, Clay!
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Old Mar 25, 2010, 09:57 PM
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tewatson's Avatar
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Quote:
Originally Posted by fnnwizard View Post
Don, have you tried flying the X without differential and a little extra rudder mixed in?
I, too, read all about the perils of aileron diff and gave the zero diff thing a go when I was flying Perfects. Could not get it to work, regardless of rudder mix, whatever. It sucked.

To quote Angus from 'Summer Rental': "She's a to'al pig..."

Tom
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Old Mar 25, 2010, 10:09 PM
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[QUOTE=dlrepp;14693074]
Opinions differ and different set-ups work well for different pilots for a number of reasons. As I tried to point out in my reply, the easiest to fly or most effective set-up for a given pilot, may or may not be the most aerodynamically efficient or lowest drag. It may however yield the best mix of man machine interface for that pilot for the task at hand and there's nothing wrong with that
One thing I've learned over all the years of being an engineer is this:
The words "always" and "never" don't belong in an engineers vocabulary.

/QUOTE

Truer words have never been spoken..... I always give the advice that the radio program and overall airplane setup is there to yield the easiest setup to fly the plane well (a fantastic burned into my brain from my soaring mentor MS).

I do believe it is important to understand what your mix is really doing, so that you can tune your plane to fly the way you want it too, and adjust it to work better for you.

I recently (last weekend) took some differential out of my F3B speed mode. I was having a hard time safely pulling my last pylon turn 150 meters away and 4ft off the deck without popping up first. My roll command was pushing my plane down into the ground a bit, very subtly, but it was there, and every inch matters in that case.
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