HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 27, 2012, 10:23 PM
Registered User
United States, OR, Canby
Joined Aug 2011
2,249 Posts
3/4 oz of weight on the tail. 2200mah are my smallest battery. I flew it without the tail weight and it was nose heavy, it pitched the same then too unless I was flying too slow? Elevator is neutral, i.e. in line with the Stab.
600Bob is online now Find More Posts by 600Bob
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 27, 2012, 10:30 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
2,296 Posts
Quote:
Originally Posted by 600Bob View Post
3/4 oz of weight on the tail. 2200mah are my smallest battery.
Hmm, that's not so much tail weight. I have .5oz just to balance out my tiny gps unit. The planes tail weight varies a good bit from the factory (depending on how much glue they used) according to reports. The heavy battery is good for windy days, but it will slow down more, and probably thermal better, with a lighter battery.

It may be that you just need to fly the plane a while longer and get familiar with its character. I think most folks start out at 70 mm (recommended stock cg) and move it back as they get to know the plane. Most end up at 77mm but that's about as far back as anyone goes.
JumpySticks is offline Find More Posts by JumpySticks
Reply With Quote
Old Dec 27, 2012, 10:36 PM
Drifting off the reservation..
JumpySticks's Avatar
USA, LA, Broussard
Joined Jan 2011
2,296 Posts
A sudden pitch up seems kind of odd. Can't recall that happening with mine. It does pitch up when I drop the flaps without elevator compensation. Sudden throttle also will pitch up, but not in a glide that I can recall.

If it's low it can hit turbulence from trees & such, but I expect you know that.
JumpySticks is offline Find More Posts by JumpySticks
Reply With Quote
Old Dec 27, 2012, 11:52 PM
Registered User
United States, OR, Canby
Joined Aug 2011
2,249 Posts
Yes, I've flown my powered planes in turbulence and know how they respond. i have never seen any of my planes get pitchy though. And it seems odd that the RP would start to porpoise randomly in a glide yet fly straight in a dive test indicating the CG is OK.

I read someplace, maybe in this thread that some people fly it with the CG as far back as 80mm, the aft CG shows the thermals quicker. I would think that if the CG is too far aft then the plane would be a hand full to fly at all times, mine seems to fly nice when I'm low coming in for a landing, no pitching issues and the elevator doesn't seem too sensitive, but I am using about 45% expo but I run that much on all my planes, elev. only.
600Bob is online now Find More Posts by 600Bob
Reply With Quote
Old Dec 27, 2012, 11:58 PM
Registered User
United States, TN, Columbia
Joined Mar 2006
739 Posts
Saiplanes are different then prop aerobats.... and 80mm is definately to far back. Put it on 75mm and you will love it. And buy a 1300mah 45c... 11x8 prop.
sdstick is offline Find More Posts by sdstick
Reply With Quote
Old Dec 28, 2012, 12:16 AM
Tossing planes into the snow
Canada, BC, Smithers
Joined Nov 2011
2,991 Posts
Quote:
Originally Posted by 600Bob View Post
... it seems odd that the RP would start to porpoise randomly in a glide yet fly straight in a dive test indicating the CG is OK.
I'm not sure exactly what you mean by porpoising randomly. The first step (before you do the dive test) is to trim it so it will glide hands-free without porpoising. After you have done that, what could cause it to "randomly" start to porpoise again? Once it is trimmed to glide properly, it should just do that, day after day.
Jovanx is offline Find More Posts by Jovanx
Reply With Quote
Old Dec 28, 2012, 04:08 AM
Kit Manufacturer
coreman's Avatar
United States, MA, Southbridge
Joined Feb 2010
3,518 Posts
Quote:
Originally Posted by 600Bob View Post
Yes, I've flown my powered planes in turbulence and know how they respond. i have never seen any of my planes get pitchy though. And it seems odd that the RP would start to porpoise randomly in a glide yet fly straight in a dive test indicating the CG is OK.

I read someplace, maybe in this thread that some people fly it with the CG as far back as 80mm, the aft CG shows the thermals quicker. I would think that if the CG is too far aft then the plane would be a hand full to fly at all times, mine seems to fly nice when I'm low coming in for a landing, no pitching issues and the elevator doesn't seem too sensitive, but I am using about 45% expo but I run that much on all my planes, elev. only.
people have gone as far back as 94mm but then you need to fly it. It does indicate thermals much better. I will probably end up back more. I'm in the low 80s now but I competed in thermal duration so I like being on that edge

It seems odd behavior as stalling it would cause the nose to drop and then porpoise. My thought was you might have slowed down too much and you are getting some headwind and slowing enough to stall. Could it be a glitchy elevator servo? Are you hearing any hunting when you are on the ground?
coreman is offline Find More Posts by coreman
RCG Plus Member
Latest blog entry: Heading to the NEAT Fair
Reply With Quote
Old Dec 28, 2012, 09:56 AM
Old Bold Pilot
got-one's Avatar
USA, MI, Rochester
Joined Nov 2008
699 Posts
Quote:
Originally Posted by 600Bob View Post
I have a flying characteristics question. I mostly fly glow and gas planes, the RP is my first glider and I have a few flights on it now. I have a 2200mah battery and the CG is set at about 80mm best I can tell on my fingertips. When I do a dive test it doesn't pull up or down but flys straight until I pull out.
Did you do the decalage modification to the horizontal stabilizer for getting zero decalage?
Compitition saillplane pilots have discovered they can see distinctive visual changes in pitch which is evidence that their plane enters or exits a thermal and that is good.
They found that moving the CG aft increases the authority of the elevator/stabilizer meaning the plane needs less elevator movement. They also found that an up draft or down draft could kick the tail around and make the tail twitchy, giving them the visual indication they wanted. However, moving the CG back exposed some other problems.
As the CG goes back, a horizontal stabilizer with positive decalage also has more authority as a up stabilizer even though the elevator has no deflection. And the plane flys slower, leading to a stall and porposing. The fix is to modify the horizontal stabilizer to zero decalage. You can check your decalage with two straight edges, one under the wing root at the fuselage and one on the stabilizer. Both edges should be parallel.
The ideal state to be in for a glider is zero decalage for the stabilizer, the elevator lined up with the stabilizer, and with the CG just forward of being unstable. This set up will make the sailplane give distinctive pitch changes when a thermal pushes the tail up or a down draft pushes the tail down. Pitch will get real twitchy (which you can see), give it a few clicks of down elevator and circle in the thermal until it is out of sight.
Dave F
>< *>
got-one is online now Find More Posts by got-one
RCG Plus Member
Last edited by got-one; Dec 28, 2012 at 02:03 PM.
Reply With Quote
Old Dec 28, 2012, 01:41 PM
Registered User
United States, OR, Canby
Joined Aug 2011
2,249 Posts
I bought it slightly used, I have done no mods to it. It had the battery compartment enlarged and carbon rod braces on the underside of the horz stab.

I have not seen any servo issues on the ground. On the first flights with the CG forward I might have flown too slow and stalled it.

I am used to trimming a fuel plane by power setting and level flight. With the RP I would be trimming with no power so what am I looking for, a level pitch attitude or slightly nose down?

@Jovanx, it does fly hands off most of the time, my landing approaches are nice and smooth. I'm thinking I must be hitting some thermal or light gust at altitude that effects the pitch attitude.

It has been very wet lately and I was flying on a rare day with a little sun. After finishing for the day and looking at the ground instead of the sky I noticed that I seemed to stay up longest when I was over a patch of ground where cattle are being fed., it was very muddy and surrounded by green grass. Maybe I was getting a little lift there? After a 30sec run my longest flight to landing was almost 5 min., not sure how good that is for a day in the low 40's and calm conditions.
600Bob is online now Find More Posts by 600Bob
Reply With Quote
Old Dec 28, 2012, 02:09 PM
Tossing planes into the snow
Canada, BC, Smithers
Joined Nov 2011
2,991 Posts
600Bob

A 2200 is too heavy for everyday flying. It is ok once in a while to cut through big winds or if you plan on flying with the motor on all the time and packing extra weight like the fpv guys do. It was designed to fly with a 1300, and that would allow you to remove the tail weight and the plane will thank you for lightening it's load.
Jovanx is offline Find More Posts by Jovanx
Reply With Quote
Old Dec 28, 2012, 02:19 PM
Registered User
United States, OR, Canby
Joined Aug 2011
2,249 Posts
How many launches can you get out of a 1300mah battery? I wasn't counting but I would guess I made 6 launches and ran my battery down to about 3.7v per cell.

I will probably remove some tail weight even with the larger battery because most seem to think my CG is too far back now.
600Bob is online now Find More Posts by 600Bob
Reply With Quote
Old Dec 28, 2012, 02:57 PM
Kit Manufacturer
coreman's Avatar
United States, MA, Southbridge
Joined Feb 2010
3,518 Posts
Quote:
Originally Posted by 600Bob View Post
How many launches can you get out of a 1300mah battery? I wasn't counting but I would guess I made 6 launches and ran my battery down to about 3.7v per cell.

I will probably remove some tail weight even with the larger battery because most seem to think my CG is too far back now.
I get 4-6 solid launches with a 1300mah battery and still have plenty of power if I need to "go around" on landing
coreman is offline Find More Posts by coreman
RCG Plus Member
Latest blog entry: Heading to the NEAT Fair
Reply With Quote
Old Dec 28, 2012, 03:11 PM
Tossing planes into the snow
Canada, BC, Smithers
Joined Nov 2011
2,991 Posts
With this plane, it is not about the number of launches per battery, but about what happens when the motor is turned off. With a 2200 it will come down way too fast and you will never see it fly the way it was intended to fly. Lately I have been using a high-C 1000 and it is even better. Some people use 850's.
Jovanx is offline Find More Posts by Jovanx
Reply With Quote
Old Dec 28, 2012, 03:17 PM
Registered User
Joined Feb 2006
579 Posts
Quote:
Originally Posted by got-one View Post
Did you do the decalage modification to the horizontal stabilizer for getting zero decalage?
As the CG goes back, a horizontal stabilizer with positive decalage also has more authority as a up stabilizer even though the elevator has no deflection. And the plane flys slower, leading to a stall and porposing. The fix is to modify the horizontal stabilizer to zero decalage. You can check your decalage with two straight edges, one under the wing root at the fuselage and one on the stabilizer. Both edges should be parallel.
Dave F
>< *>
One can change the angle of the stab or change the angle of the elevator in order to get the same result. Changing elevator trim is a lot easier. When you have trimmed out the plane, the elevator may not be in line with the stab. The result is a negligible increase in drag. If having the elevator at an angle with respect to the stab offends your sense of cosmetic elegance, change the stab.

You have provided one of at least three possible definitions of zero decalage. A second definition is to have the stab aligned with the chord line (not the bottom surface) of the wing. A third definition is to have the stab aligned with the airflow over the stab. Note that the general airflow is downward aft of the wing.

For a plane to be stable in pitch, the combination of stab and elevator must provide a downward force to offset a CG that is ahead of the neutral point. Also, that downward force offsets the pitching moment of the wing.
williamson is offline Find More Posts by williamson
Reply With Quote
Old Dec 28, 2012, 03:31 PM
Tossing planes into the snow
Canada, BC, Smithers
Joined Nov 2011
2,991 Posts
Quote:
Originally Posted by williamson View Post
You have provided one of at least three possible definitions of zero decalage. A second definition is to have the stab aligned with the chord line (not the bottom surface) of the wing. A third definition is to have the stab aligned with the airflow over the stab. Note that the general airflow is downward aft of the wing.
Good point. On a washed out wing of a Radian Pro, the waters become even more muddy and more options present themselves. If you align the stab with either the underside or the mean chord at the root. you will end up with a negative decalage with respect to the outer half of the wing. Any angle measurement becomes a judgement call, and we have seen where people have gone too far, and ended up with a plane that flies better upside down than right side up.

The measuring of angles method would work for the Radian, but for the Radian Pro, if you must alter the decalage, I think the best method would be the one proposed by cliffkot here..

http://www.rcgroups.com/forums/showp...ostcount=11266
Jovanx is offline Find More Posts by Jovanx
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Rave New Parkzone Radian Pro-discussion thread!!! lightspeeddud Electric Sailplanes 3680 Yesterday 09:37 PM
Discussion Official Radian Pro Thread Magnumb Parkflyers 14 Apr 10, 2011 10:56 PM
Gallery Parkzone Radian Pro Video bakon Electric Sailplanes 6 Mar 11, 2011 05:21 PM
New Product Parkzone Radian Pro bakon Electric Plane Talk 24 Oct 01, 2010 01:39 AM
Discussion Parkzone Radian Pro $229.99 BnF preorder Tekwip Hot Online Deals 10 Sep 29, 2010 04:35 PM