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Old Jul 21, 2012, 08:27 AM
Zor
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Ontario,Canada
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Zor's comments in green

Hello WimH

I am expecting some response from "dawsonh" with explanations for his claim of much more sensitivity of control as the CG is moved toward the tail.

I am not surprised of your post from overseas Belgium.
That may give a reason for dawsonh to avoid responding.

I still hope he will respond.

I also notice that your posting does not reflect your personal explanation. You are using a link and some copied quotes from other sources. I am not objecting to that; there is no point in re-inventing the wheel but it would have been nice to read your outlook in your personal words.

Quote:
Originally Posted by WimH View Post
Sorry, no. With a more backward CG the forces needed to counteract the wing's pitching moment are smaller, hence less elevator throw needed... look here , especially the drawing:
http://en.wikipedia.org/wiki/Longitu...atic_stability
Studying the formulas in the Wikipedia article any torque difference in the hoizontal tail surfaces would vary due to the small changes in the factor "h" that would change the moment arm. That variation compared to the moment arm of the tail surfaces is a very small percentage. It just does not justify to declare a very significant difference in sensitivity of control.

I think it is exageration trying to prove a point.

I remain convinced that the difference is not noticeable by the pilot. I am not claiming that a small difference does not exist; I originally wrote in terms of what would be evident.

Quote:
and this :

CG remains a matter of preference as is well explained in the Polecat/Drela link. A different CG goes with different decalage. This can be achieved by trimming the elevator and /or changing it's incidence relative to the wing (which is the same for an all moving stab). Only a really huge trim adjustment would "need" the "decalage mod" IMHO. So that mod is only a minor thing, it does not instantly and by itself transform the Radian into a contest winning machine like some people here seem to believe.It's just the "final touch" See also this quote from Mark Drela:
In my own words, a change in the decalage setting would benefit from a small change in the CG location.
However there is no valid reason to change that decalage which should be the decalage that offers the best Lift to Drag L/D ratio.

Quote:
FWIW more F5J contests have been won with Radians without the decalage mod than with it...,yes, against high end F5J machines ,only proves good pilots can win with any plane (The F5J rules are very well made IMHO)
It is interesting that the above paragraph is backing up what I have written all along.
Contests are won by pilots dexterity in an often varying weather conditions (atmospheric conditins at the time of the particpant flying).
His best chances are with a model having the proper decalge angle which is very close to 3 degrees for a Radian or Radian pro.

I did not miss who claimed having a zero degree decalage and attached pictures clearly showing about 2 degrees of decalge. He was not measuring the decalage correctly.

I think we have beaten the subject to depth.
Let us leave the participants continue to enjoy this thread their own way.

Zor
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Old Jul 21, 2012, 08:33 AM
Zor
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[QUOTE=geoffrich;22224245]
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Originally Posted by Raften View Post

+1 Geoff
Geoff

Apparently you did not read post 12622.

Zor
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Old Jul 21, 2012, 08:45 AM
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USA, CA, Pismo Beach
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Quote:
Originally Posted by WimH View Post
Still too small, and heavy. My Reisenauer 54.5mm fits perfectly and is a lot lighter. It is a bit expensive though... :
What is the weight of this spinner and yoke assembly? In pictures from the vendor, the spinner looks light but the yoke appears pretty substantial.
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Old Jul 21, 2012, 08:51 AM
Flagstaff, AZ
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USA, AZ, Flagstaff
Joined Mar 2003
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Quote:
Originally Posted by Zor View Post
Hello dawsonh
Does not the above make good sense ?
Howdy ZOR:

I don't know if your comments make sense; but they don't explain what I am experiencing when I fly.

I wonder if you looked at the Drela article at all. That one article, written a while ago, gave me much insight as to how I wanted to set up my gliders... slope aerobatic and thermal.

With my Radian I choose to fly with the CG further back. I like how it feels. The elevator feels more sensitive (to me) and as a result I have dialed back the throws for normal flying. The rearward CG and associated pitch sensitivity allows me to see indications of lift more easily... i.e. tail up/down. It does take a bit more work to fly (more prone to stall); but that is OK with me. When I want to speed up (to get out of sink), it takes only a click or two of down trim and I am speeding along. When I hit the throttle the Radian does not pitch up dramatically (this is also the main reason for the decalage mod).

BTY.. You seem to be the type of flyer that likes the forward CG and stability associated with it... and that is OK too. This is what you refer to as "neutral CG".

I think it is fine that you like to think and talk about why things are what they appear; but sometimes it is better to just "do it" and see what happens. I challenge you to move your CG back on your Radian Pro and see for yourself if the elevator/pitch becomes more sensitive.

Regards,

Dawson
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Old Jul 21, 2012, 10:56 AM
Tossing planes into the snow
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Hey, Radio.Active

I was looking at your pictures and noticed a couple that showed the receiver located right beside the esc. From what I have read, this should not be a problem with 2.4G, but most people say they are afraid to try it. I am guessing that this setup works well for you. Why did you put it there? Is it so the battery can be moved further back?
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Old Jul 21, 2012, 11:24 AM
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Old Jul 21, 2012, 01:27 PM
LIVE TO FLY, FLY TO LIVE!
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Lighter Canopy

Random weight savings mod.
Is it as cool looking as the original canopy? Not at all.
Is it lighter? Yes, by 20 grams.
As quick to take on and off? No, takes additional 1.9 seconds.


Cut from a 2 liter Sprite bottle. In the pic it doesn't look like it's shaped correctly but once on fits very snugly. (Held on with 2 pieces of packing tape, same method I've seen on $1,000 + gliders so couldn't be all bad)

The lighter canopy is to compensate for the extra weight of a fairly heavy aluminum spinner. The lack of a cooling scoop hasn't been a problem, I've measured the motor and ESC temp after flights in 100 degree weather and it's all within range. I think it probably gets enough airflow from the small scoops in the cowl down to the vents in the belly. And this may be in my head, but it seems noticeably less draggy without the air scoop on top. Thoughts?
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Old Jul 21, 2012, 01:40 PM
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Quote:
Originally Posted by WimH View Post
A different CG goes with different decalage. This can be achieved by trimming the elevator and /or changing it's incidence ...
Agreed. For any value of decalage including zero there are an infinite number of elevator trim / cg combinations that will place the wing angle of attack at whatever point is desired, e.g., best L/D. In my case I achieve it with neutral elevator trim and a more aft cg.

A primary reason for having decalage is that it enhances pitch stability. For an explanation of why that is so look at this link:

http://www.av8n.com/how/htm/aoastab.html

It follows that reducing or removing decalage will result in increased pitch sensitivity. The advantage to the glider pilot is that it makes the glider react more to changes in lift, thereby signaling the presence of thermals. I believe that is goal Paul had in mind.

I have not felt the need to dial back elevator throws but I was flying with reduced throws and a lot of expo before the mod.

Quote:
FWIW more F5J contests have been won with Radians without the decalage mod than with it...,yes, against high end F5J machines ,only proves good pilots can win with any plane (The F5J rules are very well made IMHO)
That is to be expected. I believe there are far more unmodified Radians than modified ones, and there are many factors that determine a win or loss.
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Old Jul 21, 2012, 02:02 PM
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Can you not let anything go? I wasn't even going to pick you up on your original terse "I can't find the photos you said you'd post". Please do us all a favour and chill.
Geoff
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Last edited by geoffrich; Jul 21, 2012 at 02:05 PM. Reason: hit wrong key meant for ZOR re post #12632
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Old Jul 21, 2012, 02:12 PM
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Old Jul 21, 2012, 04:48 PM
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Originally Posted by geoffrich View Post
Can you not let anything go? I wasn't even going to pick you up on your original terse "I can't find the photos you said you'd post". Please do us all a favour and chill.
Geoff
+1. It is beyond ludicrous that the only person that endlessly posts against Paul's mod is someone who has never tried it or even seen a modified Radian. Enough already. Have some respect for those of us who have done it and are pleased with the results.
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Old Jul 21, 2012, 07:31 PM
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Quote:
Originally Posted by got lift? View Post
Random weight savings mod.
Is it as cool looking as the original canopy? Not at all.
Is it lighter? Yes, by 20 grams.
As quick to take on and off? No, takes additional 1.9 seconds.


Cut from a 2 liter Sprite bottle. In the pic it doesn't look like it's shaped correctly but once on fits very snugly. (Held on with 2 pieces of packing tape, same method I've seen on $1,000 + gliders so couldn't be all bad)

The lighter canopy is to compensate for the extra weight of a fairly heavy aluminum spinner. The lack of a cooling scoop hasn't been a problem, I've measured the motor and ESC temp after flights in 100 degree weather and it's all within range. I think it probably gets enough airflow from the small scoops in the cowl down to the vents in the belly. And this may be in my head, but it seems noticeably less draggy without the air scoop on top. Thoughts?
This is also a great solution when you've left the stock canopy at home on the bench, everybody's got an empty water bottle rolling around under the seats
Dave
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Old Jul 21, 2012, 09:25 PM
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Arrrrrrrrg!
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Old Jul 22, 2012, 12:32 AM
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Hooked

Hi All:

Thank you to all who have posted before me on this thread... especially for stuff on how to thermal, and the tip to do a hand launch before your first flight. Everything was spot-on out of the box, but I appreciated the peace of mind knowing so.

Doing RC for years, but this is first sailplane. Had a successful maiden today. First flight was 30 minutes on four motor runs, including amazing speck-ed out flight into outer space. Hooked.

Second flight was 43 minutes on four motor runs. Try as I might, I couldn't get my beginner's luck thermaling speck back again. Need to dial in my CG and trim, though... and looking forward to more practice.

A few "lessons learned" for those lurkers who come after me here:
  • Finger-tight on the pushrod keeper is just fine. I wanted to "just snug 'em down" with the light touch of a screwdriver, and broke off a screw head immediately. (The keeper body is then rather difficult to get off the pushrod...) After wrecking a keeper, or for other reasons...
  • You may want to upgrade to Dubro connectors. If so, it's probably the *MINI* E/Z connectors that ye be wantin'. I couldn't tighten down regular ones to that small wire. (Interesting to me was that the Radian pushrods are a smaller diameter than the ones that come with a Slow Stick. Sorry I had to borrow the Mini Dubro connectors from you, Slow Stick: nothing was going to stop the Radian maiden today. They fit better on the Radian anyway.)
  • Do a hand launch before your maiden. You'll be glad you did. Mine flew more than 40 feet on just that little push.
  • The Radian fits just fine in an Outback, back seat down.
  • Polarized sunglasses work wonders for spotting something tiny in the air. Rolling your head a little changes the sky from white to dark blue... bringing the Radian into sharp relief.
  • A Corona synthesized receiver and old Futaba 72 MHz transmitter worked well for me. I ran the antenna out the bottom hatch, taped it down with blue masking tape on the underside of the right wing, and let about eight inches dangle.
  • Two strips of blue painter's masking tape on the underside of each wing do nothing for visibility when the Radian is at altitude. In fact, I'd hazard that *no* marking or coloring on the wing bottom will do much when you're at altitude. Better to have your plane trimmed correctly, so you know that what it was doing 15 seconds ago is probably what it is still doing now.
  • Finally... the Radian takes a long time to get close to the ground, but the final plop onto the ground was always slow and easy.

Good luck!

(A special shout-out to aeajr, whoever you are... your posts are gold.)
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Old Jul 22, 2012, 01:23 AM
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Belgium, Flemish Region, Oosterzele
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Quote:
Originally Posted by Zor View Post

it would have been nice to read your outlook in your personal words.

Quote:
Originally Posted by WimH
Sorry, no. With a more backward CG the forces needed to counteract the wing's pitching moment are smaller, hence less elevator throw needed... look here , especially the drawing:
http://en.wikipedia.org/wiki/Longitu...atic_stability
You quoted "my own words"??? The link was only to make things clearer. It's just physics. It's your good right remaining convinced that the effect is small, it is in reality much bigger than you believe.
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