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Old Feb 17, 2013, 05:02 AM
Can't fly 3D for toffee ...
United Kingdom, Taunton
Joined Dec 2012
1,122 Posts
Thanks all for the speed advice on Phoenix. I set it to 100% at the start and never touched it again. With Tom's hint of 50% perhaps I can slow my befuddled fingers down enough to learn this stuff!
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Old Feb 17, 2013, 06:55 AM
Diverted by planks
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South Florida
Joined Dec 2010
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Originally Posted by Watdazit View Post
I use the APP crimper. I always prefer to use the manufacturers tools where possible and then generally price does not come into my equation. My pension can stretch to those things.
I was lucky enough to get the official APP 3-die crimper myself as part of an on-line deal. I almost had a cow when I saw how much it would have cost to purchase retail. While in my life, like others I've often had to improvise or 'get by' with less, there is just nothing is like using the proper, full-sized, well made tool for the job.

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Old Feb 17, 2013, 11:28 AM
Gopher huntin' stick jockey
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East Bethel, MN USA
Joined Jul 2009
11,533 Posts
Flight-trimming purpose-built aerobatic planes

Regarding KE flight - if the plane pulls to the canopy, it's nose-heavy. If it tucks toward the gear, it's tail-heavy. (Assuming that the plane is built straight & true, and that there are no alignment problems.) Flight-testing is used for determining the proper CG for neutral handling. The number in the manual is simply a starting point.

For those who are new to the world of purpose-built aerobatic planes, I decided to put together a flight-trimming guide. I posted this in my blog a couple years ago, but I think it's worth re-posting here:

Aside from creating an unflyable condition, CG settings are largely a matter of preference. However, many pilots find that with purpose-built aerobatic ships, adjusting the CG for neutral or near-neutral handling usually works best for all-around aerobatics & precision flight, while a slightly aft CG usually works better for 3D, and a slightly forward CG typically improves stability & tracking - which may be desirable when flying in turbulent air. Understanding the effects of flight-trimming & CG placement, plus experimenting to find the settings that work best for a given airframe and flight condition, will allow the pilot to optimize most any airframe to suit one's purpose and flying style.

The neutral handling point, or CG 'sweet spot' as it is called by some, is the balance point which provides neutral pitch stability. No pitch change with changes in throttle or airspeed. No pitch change when rolled to knife-edge or when rolled inverted. When balanced at this point, an aerobatic plane simply goes where it's pointed until commanded to do something else. Pattern planes are usually balanced at or slightly forward of the sweet spot. 3D planes are usually balanced at or slightly aft of the sweet spot. The manufacturer's recommended CG range for most trainers & sport planes is typically well-forward of the sweet spot. Assuming that the airframe is straight & true, adjusting the CG in small increments will allow one to tune the plane's behavior.

I will attempt to explain what's going on in non-technical terms.

First off - my comparisons below assume we are talking about a purpose-built aerobatic plane or aerobatic sport-plane with a symmetrical or semi-symmetrical airfoil (not a Cub). One that is properly built - correct thrust-line, wing incidence, tail alignment, etc.

Nose-heavy:

All else being equal, the slightly nose-heavy plane will be less sensitive in pitch & yaw than a neutrally-balanced or slightly tail-heavy plane. The nose-heavy plane will also have to fly faster & land faster to prevent stalling. These two factors are largely responsible for the improved wind penetration vs. the neutrally-balanced or slightly tail-heavy plane. Unfortunately, they are also detrimental to slow-speed flight. The nose-heavy plane will have more drag in level flight at a given airspeed, and will therefore require more power to maintain cruise speed. Additionally, the nose-heavy plane will usually have a lot more throttle/pitch coupling. If it's extremely nose-heavy, the nose will drop dramatically during turns, or when power is reduced. There may not be enough elevator authority to establish a power-off glide. It may also be impossible to flare during a power-off landing. Conversely - when power is applied, the nose-heavy plane will tend to pitch up. During knife-edge, the nose-heavy plane will tend to pull to the canopy, unless down-elevator is used. These things happen because the nose-heavy plane requires a certain amount of up-elevator trim for level flight at a given airspeed.

Compensating for a forward CG with elevator trim causes the plane's behavior to change as the power setting or flight-attitude changes, because the trim required is dependent on airspeed and flight-attitude. For instance, if up-trim is required for level flight, when rolled inverted, the up-trim becomes down-trim, which is the opposite of what is needed, so the plane dives. In KE flight, that up-trim turns into "side-trim" which makes the plane pull towards the canopy. The extra nose-weight is now acting on the yaw axis, and is being compensated with 'top rudder', so the up-elevator trim now pulls the plane toward the canopy. A change in speed will change the effectiveness of the up-trim, which will make the plane pitch up as power is added, and pitch down as power is reduced. (Note: most trainers and many sport & scale general aviation planes will also tend to climb/dive when power is added/cut, but in these cases, the behavior is to be expected.)

Most full-scale general aviation planes are balanced somewhat forward of the neutral point for safety/stability. RC trainers & sport-planes are also designed to be very stable, and usually specify a forward CG.

Neutral CG:

The neutrally-balanced plane will usually have very little, if any throttle/pitch coupling. The nose will stay put when power is increased/decreased. The nose will not drop much (if at all) during turns. The plane will also stay level in knife-edge - even without rudder (of course, top-rudder will still be required to maintain altitude). Also - there will be little, if any rudder/pitch coupling during knife-edge. Slow-flight will be much improved, and establishing a shallow power-off glide will be much easier - as compared to the same plane in nose-heavy trim. Very short landings are also easier, as there will be plenty of elevator authority to come in a bit nose-high, and then flare at touchdown. Aerobatic maneuvers become much easier, as the neutrally-balanced plane has no tendency to self-recover. Put it into a climb or dive, and it will stay on track until commanded to do something else. The nose will stay put regardless of power setting. When trimmed for level flight, the neutrally-balanced aerobatic plane will fly level inverted with little, if any elevator input, and should fly a knife-edge pass with no tendency to pitch toward the canopy or tuck toward the belly.

A plane that is balanced at or very slightly forward of the neutral point will typically be well-suited for precision aerobatics. This is where pattern planes are usually balanced. Purpose-built full-scale aerobatic planes may also be balanced close to the neutral point. For less-experienced RC pilots, the neutrally-balanced plane can be challenging to fly. For instance, the nose doesn't drop as the plane slows down; the plane usually descends in a level attitude, and may stay level after it stalls - or it may suddenly drop a wing if aileron input is given. Hence, there are typically few, if any visual clues of an impending stall. When put into a dive, the neutrally-balanced plane will not self-recover; it will continue on the path until the pilot gives some stick input. Same is true for climbs.

Note: With flat-plate and symmetrical airfoils, a certain amount of trim is required for level flight because they must fly at a positive angle of attack to generate lift (unlike semi-symmetrical, flat-bottom, or under-cambered airfoils). Therefore, when trimmed for level flight & rolled inverted, they will require a hint of down-elevator for level inverted flight - even though the CG is set at the sweet spot.

Tail-heavy:

The slightly tail-heavy plane will excel in 3D maneuvers - especially harriers, elevators, flat-spins, hovering, tail-slides, and tumbling maneuvers. Precision flying usually suffers due to the effects of negative pitch stability. Pitch-instability will cause the tail-heavy plane to become extremely sensitive to elevator input. Throttle/pitch coupling will also return, but the effects will be reversed as compared to the nose-heavy scenario: When trimmed for level flight, the slightly tail-heavy plane may have a tendency to tuck its nose when power is applied, and will tend to balloon when power is cut. It will also have a tendency to tuck toward the belly during knife-edge. When trimmed for level flight and then rolled inverted, the tail-heavy plane will usually climb. These things happen because the tail-heavy plane requires a certain amount of down-elevator trim for level flight at a given airspeed.

Compensating for an aft CG with elevator trim causes the plane's behavior to change as the power setting or flight-attitude changes, because the amount of trim required is dependent on speed and flight-attitude. For instance, if down-trim is required for level flight, when rolled inverted, the down-trim becomes up-trim, which is the opposite of what is needed, so the plane climbs. In KE flight, that down-trim turns into "side-trim" which makes the plane tuck towards the belly. The extra nose-weight is now acting on the yaw axis, and is being compensated with 'top rudder', so the down-elevator trim now pulls the plane toward the belly. A change in speed will change the effectiveness of the down-trim, which will make the plane drop the nose when power is added, and pitch up when power is cut.

A bit more tail-heavy, and the plane may become so unstable in pitch that it is impossible to fly. Some airframes are more forgiving than others in this respect. For instance, the UM Sukhoi has a very wide flyable CG range. It will fly with the CG anywhere from 25mm (extremely nose-heavy - very poor flight performance), to 42mm (definitely tail-heavy - wild 3D, but a real handful to fly). Some airframes are not at all forgiving with CG placement. Some may immediately crash after take-off when they're even moderately tail-heavy. Others may remain flyable until they're put into certain situations, such as a spin - and then become completely unrecoverable.

Although full-scale planes are usually designed to be balanced for positive pitch-stability - or in the case of purpose-built aerobatic planes, near-neutral pitch-stability, there are exceptions. Many fly-by-wire fighters and most, if not all of the thrust-vectoring fighters are purposely designed to be aerodynamically unstable so they can do wild, uncoupled flight maneuvers. The flight-control computer(s) sort it all out for the pilot.

As is true in the full-scale world, RC planes with 3-axis stability augmentation systems such as AS3X are usually able to fly even when the CG is far enough aft to render the plane completely unflyable without stabilization.

Trimming aerobatic RC planes:

It has been said that a nose-heavy model may fly poorly; however a tail-heavy model may fly only once. For the most part, it's true. It's best to start out toward the nose-heavy side of the manufacturer's recommended CG range, and then sneak up on the neutral point.

The main problem with tuning RC airframes for one's desired flight characteristics is that many of the adjustments are interactive, and some parameters have similar symptoms when they're out of adjustment. Things must be checked/adjusted in the proper order - otherwise the process can become quite frustrating. The guide below will allow the pilot to sort out various handling issues in a scientific manner. Courtesy of the NSRCA (National Society of Radio Controlled Aerobatics):

http://nsrca.us/index.php?option=com_content&view=article&id=177:t rimchart&catid=114:flying&Itemid=187


See the attachment for a downloadable version.

Joel
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Last edited by turboparker; Feb 17, 2013 at 05:09 PM. Reason: Corrected terminology
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Old Feb 17, 2013, 03:39 PM
Beast 60E Maniac
SLK Count's Avatar
Hamburg, Germany
Joined Feb 2010
874 Posts
Joel, thanks for posting- very interesting.
-
Was out again after repaired my Rudder after crash. Didn't figured out a wire connection problem- motor runs without problem -don't know why the motor/ESC occured a "cut off" while I was in a Hover
3 lipo packs today- this plane is awesome and when I fly 3D with moderate power management it shows like "slowmotion"
Power is enough but maybe a little bit more would be better- when I fly the VA after flown the Edge 50QQ it feels I have a "truck" at my sticks
But it's o.k- I like this VA, can fly in difficult conditions like short takeoff and landing strips, wind aso.
-
I use the Turnigy 3S/2200mAh packs in full backwards position- think this is the best CG position- what do you prefer ?
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Old Feb 17, 2013, 03:59 PM
Beast 60E Maniac
SLK Count's Avatar
Hamburg, Germany
Joined Feb 2010
874 Posts
Flat spin

....currently I have little problems with flat spins with VA.
How is your stickmanagement and how to start ? which flightlevel ?
My lipo is complete in the back.
Thanks
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Old Feb 17, 2013, 04:34 PM
Can't fly 3D for toffee ...
United Kingdom, Taunton
Joined Dec 2012
1,122 Posts
Joel, Thanks very much for all this. Sounds like my CG may be a bit far forward. I have been setting it as per the manual and this needs a bit of forward pressure when inverted and you have explained why it pulls to the canopy. I have the rear of the lipo abeam the screws in the battery plate and the two posters above have it at the rear .... this tells me something!!
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Old Feb 17, 2013, 04:35 PM
Gone Huckin'
turnerm's Avatar
Charlotte, NC
Joined Jan 2011
9,259 Posts
Quote:
Originally Posted by SLK Count View Post
....currently I have little problems with flat spins with VA.
How is your stickmanagement and how to start ? which flightlevel ?
My lipo is complete in the back.
Thanks
I haven't tried a traditional flat spin yet. I did a blender on my first and second flights and it doesn't spin like crazy but it does spin slowly.

From a vertical upline do a stall turn and then put both stick in the lower left corner. Slowly add throttle but keeping full left rudder and then gradually move the right stick to the 6 o'clock position. You should end up in an upright flat spin.

But I haven't tried it on this plane. I'll do that next time and let you know what I find.
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Old Feb 17, 2013, 04:41 PM
Can't fly 3D for toffee ...
United Kingdom, Taunton
Joined Dec 2012
1,122 Posts
I have tried it and it flattens out nicely either way up. IIRC, I ended up with approx full opposite aileron when upright for a very flat spin. If I try that on aircraft in the sim, they tend to stop spinning once you get much opposite aileron and some even flick in a strange manner. The Visionaire just sat peacefully in the flat spin. Same deal inverted but I can't remember how much opposite aileron I needed.
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Old Feb 17, 2013, 04:55 PM
Gone Huckin'
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Charlotte, NC
Joined Jan 2011
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Quote:
Originally Posted by GoAround View Post
I have tried it and it flattens out nicely either way up. IIRC, I ended up with approx full opposite aileron when upright for a very flat spin. If I try that on aircraft in the sim, they tend to stop spinning once you get much opposite aileron and some even flick in a strange manner. The Visionaire just sat peacefully in the flat spin. Same deal inverted but I can't remember how much opposite aileron I needed.
Yea... Some planes like a different aileron input during flat spins for sure. Some don't like any aileron and some like one side or the other.
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Old Feb 17, 2013, 06:50 PM
Cats can fly!
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Joined Jun 2012
148 Posts
Joel...thanks for that trimming chart. I printed it out...excellent reference!
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Old Feb 17, 2013, 08:16 PM
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Joined Jan 2013
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If CG is correctly the VA should experience no coupling during knife edge. No roll and not pitch coupling. If you are experiencing pitch up (canopy) during knife edge (Applying rudder pressure) means your plane is nose heavy.
Every plane "owns" a CG where "all" is built around. Wing location, stab position, wing angle, stab angle, motor angle, shape of fuse and on and on....it is built around CG. So every plane has a CG where the airplane delivery all it potential. If you change CG then you start to see few things like some people observe (canopy in Knife edge when rudder apply or roll coupling). Also when is nose heavy the VA will pull to the canopy on extended vertical up lines.
CG with E power is very easy to change!......so I suggest you to follow what we say in the manual. Place the battery to reach the static balancing point. And follow the tip we gave you, to double check it is exact.
First trim the airplane to fly "hands free" so no climb or descend when you fly 3/4 throttle or full in upright position and level flight. Then roll the airplane inverted at same airspeed and if CG it is right you should not apply pressure to elevator (Hands free)across the field or VERY small pressure after long and extended lines. Do this up wind and down wind. Move battery till you reach that kind of flight. In general the battery would be placed center with the hatch (not with the battery cavity).
Once you get that correct CG you should experience no coupling with your VA.
I also want to add that if nose heavy you will experience problems trying to get the plane flat during flat spins, lazy knife edge spins and lazy waterfalls, weaker knife edge and overall less agile airplane.
One thing I love on the VA that even with that traditionally known as aft CG (hands free/no push inverted) the airplane still very docile and pitch friendly.

Finally I am glad to see you guys having fun with it....I have seen terrific videos and excitement!!.....I am just like you I cannot wait to have decent temperatures to go out an fly my VisionAire till my thumbs hurts! .
Thank you all for your great passion for our hobby.

PS: Thank you Joel for sharing your trimming experience!.....

Quique Somenzini
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Old Feb 17, 2013, 08:17 PM
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Katy Tx
Joined Nov 2007
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Anyone tried it with an OrangeRX T-Six transmitter?

I did a search, but didn't find any results indicating anyone has tried the Visionaire with an OrangeRX T-Six transmitter. I picked one up about a month ago, and like it a lot so far (hanging a 2S lipo out the back rather than dealing with AA batteries, lol). Really not bad at all for $60ish!

I had no problem binding my Orange TX to the UMX Sbach, and all the channels line up the way they should. I presume the same would be true for the Visionaire, but would like to hear if anyone else on the entire planet has tried it, or it's up to me to be the first. I read that the OrangeRX module that plugged into the Turnigy 9X didn't have the channels line up correctly with the UMX models, and required flashing a new firmware to correct - which in turn, required some programming boards and additional supplies. That's what I call a dealbreaker. However, the T-six had no such issue that I'm aware of. BNF worked great on the Sbach.

Basically, I'm strongly considering adding the Visionaire to my stable of planes. I'm just starting to try 3D flying, and I currently have a freshly built Crack Sbach awaiting maiden, so I don't feel like I HAVE to get a Visionaire. If I have to buy a Spectrum TX to do it, I'm not going to. Works with my Orange TX? Just might buy one.

Anyone? Bueller? Bueller?
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Old Feb 17, 2013, 08:38 PM
Gone Huckin'
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Charlotte, NC
Joined Jan 2011
9,259 Posts
Would am external BEC work with this receiver/ESC? It felt to me that a few times the servos were struggling to hold so I'm thinking of adding a castle BEC. Seems like there wouldn't be an issue but just thought I'd check.
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Old Feb 17, 2013, 08:46 PM
Team Aztech Aeromodels!
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United States, PA, Allentown
Joined May 2011
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Quote:
Originally Posted by turnerm View Post
Would am external BEC work with this receiver/ESC? It felt to me that a few times the servos were struggling to hold so I'm thinking of adding a castle BEC. Seems like there wouldn't be an issue but just thought I'd check.
I don't see why there would be an issue! Go for it!
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Old Feb 18, 2013, 03:03 AM
Can't fly 3D for toffee ...
United Kingdom, Taunton
Joined Dec 2012
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Quote:
Originally Posted by Quique Somenzini View Post
.... If you are experiencing pitch up (canopy) during knife edge (Applying rudder pressure) means your plane is nose heavy ....
Quique. Thanks very much for all the advice. I was sure I had achieved the static balance point but I was only using fingers. I have put some strong tape on the underside with the CG marked so will try the balance on something sharper.

Like you say, flight testing will be the ultimate test. Next time I get chance to go to the flying club, I will concentrate first on getting the perfect CG in flight before having my fun!
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