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Oct 07, 2019, 04:33 AM
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Yenya's Avatar
> I trim doing aileron only rolls.. the more axial the better the COG...

How does this tell you which way to move the CoG? Also, on one of my previous builds, I discovereded that left rolls were way less axial than right ones. It was strange because I was not able to find any imbalance or whatever. Only after some time I found out that my thumb is too short/the aileron stick is too long, and when I think I am doing full left aileron, I instead pull the elevator a bit as well. So I don't think with my hands the roll-based trimming would be exact, as I am apparently unable to do full aileron without touching the elevator without looking at the sticks :-). I'll try inverted.

I also tend to make the hinge on the opposite side of the servo horn (for elevons, I have hinges on the bottom of the wing), but having made the fuselage and rudder from two layers of 3mm foam, I decided to put the rudder hinge in the middle, and embed it between the foam layers of the fuselage.

As for the time, is it indoors? Yesterday I flew outdoors in about 2-3 m/s wind.
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Oct 08, 2019, 12:23 AM
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davereap's Avatar
If the COG is too far forward and your model is trimmed for a mid power level cruise, you get more of a barrel roll... you get bigger loops.. your nose will drop when inverted.. you will likely climb when you throttle up... you may lack a nice flare when landing..

too far back gets the model over sensitive....it can become un-flyable.

A dive test is another way to check COG...just point the nose down at 45 degrees ..the model will gain speed, dont adjust the power ..if the model pulls up by itself the COG is too far forward... If it increases the dive angle then its too far back...
It should just keep going at the original angle..

However, a lot of flyers, myself included, like their model just a touch nose heavy... it makes for a more stable flight..

With the quasars the COG has a very wide band where they are nicely flyable.. even to being stable when put inverted, or climbing by itself...
Last edited by davereap; Oct 08, 2019 at 12:34 AM.
Oct 08, 2019, 04:35 AM
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Yenya's Avatar
Morning mist flight session: replaced the 30g 2300KV motor with 43g 1800KV RaceStar (waiting for 2204 1800KV Gartt to be delivered), and the orange 8x4 Gemfan with black 8x4.3 SF, and used new 2S 850mAh batteries: Heavier motor makes it harder to balance the plane even more. Moved the battery 10 cm to the rear and added several grams of ballast to the tail, the CG was still 1 cm in front of the front spar. Handling was a bit better (or I am getting used to this plane). When inverted, it requred a moderate push to stay level (definitely bigger than what my plank wing needs). But rolls were pretty axial, as far as I can tell and as far as I can move the stick w/o touching the elevator. Moved the rudder control rod to from the outermost hole to the middle one, the rudder authority is much better now. I will probably do the same on elevons. Flight time with new batteries is over 7 minutes. I will probably move the elevon servos to the wing to both aid the plane balance and to shorten the rods.

Knife edge is almost impossible for me - I wonder how r/cdawg did it in the video in the first post of this thread. She really wants to have the wings level.

I wonder how to make this plane climb - when I add the throttle, she just enters the high-alpha, and almost stops in the air (which is definitely cool, no signs of tip stall or anything, but sometimes I do need her to climb nevertheless).

Tail chasing/flat spins are still not good: when I add full rudder and try to conterbalance it with the opposite ailerons, I either over- or undercontrol it - she won't stay level. I might have wrong expo, but I have not decided whether to increase or decrease it.

The motor really needs right-thrust, and maybe also a bit of down thrust.

I used the rubber band prop saver for the first time (https://www.banggood.com/Racerstar-3...p-1545060.html), but the prop went off it on several ocasions, usually when working the throttle during hover. Does this thing work for you? I will probably go back to the bullet shaped propeller holders: https://www.banggood.com/Racerstar-3...p-1524404.html
Last edited by Yenya; Oct 08, 2019 at 04:40 AM.
Oct 08, 2019, 09:38 AM
pull up -- PULL UP!!!
You may have to try different O-rings or multiple O-rings or alternative bands until you figure something out. In the meanwhile you can get by just using several turns of common button thread on each post to secure the prop. Or a pair of small nylon cable ties.
Oct 09, 2019, 04:05 AM
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davereap's Avatar
I have thinner o-rings so use two ...

If you have the model trimmed for a level cruise... then Going nose up when you add power is a sign that you are still too nose heavy...

I get mine trimmed so that the nose only goes up slightly when I give full power... which means I have a slightly forward COG..
Last edited by davereap; Oct 09, 2019 at 04:17 AM.
Oct 09, 2019, 12:58 PM
Don't hate bro
I would lose a prop every time if using only 1 o-ring. I would sometimes lose a prop even when using 2 rubber o-rings. Then I tried using 2 silicone o-rings and I haven't lost a prop yet with them.

The orange color band was installed first, then the black.

Also pictured is a neat thing I do for hanging my profile foamies. I bent a paperclip so that it holds the metal hub of the motor instead of hanging the plane by the prop.
Oct 09, 2019, 01:17 PM
pull up -- PULL UP!!!
Quote:
Originally Posted by davereap
If you have the model trimmed for a level cruise... then Going nose up when you add power is a sign that you are still too nose heavy...

I get mine trimmed so that the nose only goes up slightly when I give full power... which means I have a slightly forward COG..
Thrust angle can also produce that behavior.
Oct 09, 2019, 01:59 PM
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r/cdawg's Avatar
Thread OP
Quote:
Originally Posted by hard line
Thrust angle can also produce that behavior.
Air temperature can also influence the trim on foam airplanes quite significantly. I've had planes go out of trim during an evening flying session as the sun is setting and the outside air temperature cools. If I plan to do any outdoor flying during the winter I will set my planes outside for a few minutes before flying to let the foam acclimate to the cold temps. I always use one servo per control surface so that I can independently trim each surface to neutral before flying.
Oct 10, 2019, 01:45 AM
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Yenya's Avatar
r/cdawg, do you really trim the plane to be neutral, i.e. on a symmetrical airfoil such as the flat one, to provide no lift? I heard some 3D pilots do this, and I have tried such a plane on a simulator - the elevator has to be constantly pulled to fly level (and equally pushed to fly level inverted). So far I have trimmed my planes to fly level at low to middle throttle (for the flat airfoil this means a tiny bit of reflex on the elevons). Thanks!
Oct 10, 2019, 03:37 AM
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davereap's Avatar
The noses on mine are all cut square, the motors mounted with their legs in line with the wings and in line with the fuzz.. They are then given a touch of down thrust, a bit of 1/16" ply put under at the top.. also a touch of right thrust..
The quasars are not trimmed perfectly neutral, they have the slightest amount of reflex..perhaps again about 1/16"..
First flights have the lipo position making it well nose heavy... I then move the lipo to get the size of loops I like.. about 6ft.. and as said before axial rolls ,easy hover.. lots of flare for slow landing..
For me I dont like the flip over tight loops that can be made when the COG is back too far ... others have their own preferences..
Last edited by davereap; Oct 10, 2019 at 03:51 AM.
Oct 10, 2019, 02:31 PM
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r/cdawg's Avatar
Thread OP
Quote:
Originally Posted by Yenya
r/cdawg, do you really trim the plane to be neutral, i.e. on a symmetrical airfoil such as the flat one, to provide no lift? I heard some 3D pilots do this, and I have tried such a plane on a simulator - the elevator has to be constantly pulled to fly level (and equally pushed to fly level inverted). So far I have trimmed my planes to fly level at low to middle throttle (for the flat airfoil this means a tiny bit of reflex on the elevons). Thanks!
I always prefer the CG on my foamies to be slightly slightly forward of neutral. I will trim the plane to fly level which means I typically need a little down elevator while inverted. This is my preferred set up but your preferred set up might be different.
Oct 10, 2019, 03:24 PM
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Yenya's Avatar
Quote:
Originally Posted by r/cdawg
I always prefer the CG on my foamies to be slightly slightly forward of neutral. I will trim the plane to fly level which means I typically need a little down elevator while inverted. This is my preferred set up but your preferred set up might be different.
r/cdawg, thaks! Anyway, I moved the elevon servos from the fuselage to the wing, shortening the pushrods significantly. Today it was too windy, but I think adding the right thrust helped a bit. But I was not able to determine the CoG - upwind she tried to pull the tip up regardless of being upright or inverted. A friend of mine took a video from his DJI Mavic, I'll post it as soon as he publishes it. Rolls upwind were fast and axial, rolls tangential to the wind were slow and somewhat random.
Last edited by Yenya; Oct 11, 2019 at 07:21 AM.
Oct 11, 2019, 02:42 AM
Registered User
davereap's Avatar
having fun... more videos at https://www.rcgroups.com/forums/show...-trials/page14 post 206 on
.
Qv3 10 10 2019 session2 flight3 hover meeting (3 min 8 sec)
Oct 11, 2019, 03:29 AM
Registered User
Yenya's Avatar
Video:

Quasar ve větru (2 min 17 sec)


The wind was pretty strong (5-6 m/s) and turbulent, blowing approximately from the same direction as Sun was. The Q was sometimes flying with negative groundspeed. Do the rolls look axial to you?
Last edited by Yenya; Oct 11, 2019 at 03:44 AM.
Oct 11, 2019, 10:42 AM
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r/cdawg's Avatar
Thread OP
Quote:
Originally Posted by Yenya
Video:

https://www.youtube.com/watch?v=4fybCnDRL4w

The wind was pretty strong (5-6 m/s) and turbulent, blowing approximately from the same direction as Sun was. The Q was sometimes flying with negative groundspeed. Do the rolls look axial to you?
The rolls look exactly like mine! Well done Yenya!

When the wind picks up a ot of guys from my club still enjoy flying the Quasar as it handles wind extremely well. One of these days I need to build a bigger version.


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