GoldwingRc 91" Slick540 60cc Observations

[Peter Jenkins]

Thanks for the photos. Is there room for pack either side of the wing tube?

[Adrian Smith 1]

I will have a look Peter when I go to the work shop. From memory I think the width of the fuselage wouldn't allow for the 6000 mAh lipos to be put crossways, I will investigate anyway. Furthermore, when I do that rather than messing about I will put her back up on my CoG ceiling rig to find out where the weight really needs to be to get a neutral CoG and report back. 

[Philip Lewis 3]

Sorry when you said "I could use the extra weight from 2x 7S lipos (rather than 2 x 6S) for more power as this is within the motor specification. At least then it would be "useful weight". I took that to mean you wanted more power as well as having a C of G issue.

 

Is the fuselage made with an option to install the rudder servo in the tail using a push rod or is it only made for a pull pull arrangement? If the former then that would shift the C of G back quite a lot.

 

Stick on weights (tyre ballance weights) are easily removable but would tell you where you need to be without permanently altering anything.

[Adrian Smith 1]

After sleeping on the problem the answer is staring at me in the face. The only thing was Philip was a lot quicker off the mark than me! I must sharpen up. Thanks Philip. There is indeed the option to use a direct drive system for the rudder shown in manual (I must take a bit more notice, but I must have thought I know better!)

 

 

 

There is indeed a slot for a rudder servo in the tail end. This clearly would free up all that space to the rear of the main wing tube and if need be I can add a false floor with light ply. Anyway as I say, I will put here up on the CoG jig to find out where the weight show actually be to balance where I want it to be and them effect the modifications. I am sure this will solve the problem. Back to the work shop this weekend then!

[Peter Jenkins]

Adrian

 

At the risk of teaching you to suck eggs, if you remove the rudder servo and tape it to the rear position you can have your CG rig set up to see if that fixes the problem.  50 g a long way aft can shift the CG a visible amount.  Fly it with the rear mounted rudder servo and see if that has had a noticeable effect on the flight characteristics.

 

The other issue is, does the tailplane have an adjustable incidence?  Indeed what is the TP incidence vs the wing incidence.  Typically, after levelling the fuselage to datum, I would look for main wing incidence to be between 0.5 to 0.7 deg and TP at 0 deg.  If the TP isn't adjustable, is the wing incidence adjustable?  If yes then increase wing incidence by 0.3 deg and try that.  That will reduce the amount of up elevator trim needed since at the same fuselage sit the wing will have more incidence and therefore more lift.

 

Cheers

 

Peter

[Adrian Smith 1]

No worries about sucking eggs, Peter as sometimes things need re-stating not least to me!

Dealing with your second issue. The tailplane doesn't have adjustable incidence. Same for the main wing. Out of interest I will measure the TP vs wing incidence as I have a gauge and level to do this job. 

However, on to the CoG testing exercise.

Surprisingly the lipos will just about fit sideways BEHIND the wing tube snuggly and fortunately the ESC cables are long enough.

 

 

 

Low and behold the plane balances level where it should do and where I want it to start with like so.

 

 

No need to move the rudder servo at this point. All I have to do is move the RX, switch and RX lipo forward in front of the wing tube and alter the wiring.

 

 

All tidied up. All I need is to buy a bit more sticky backed velcro to finish the job. I have zeroed the elevator trim so I am starting from scratch for the next flight. When I have measured the incidences I will post them here.

Incidentally, I still have the factory measured incidences from my Extreme Flight 95" Extra 330-E before I pranged it last year.

The kit spec is left wing to tip 0.1 to 0.3 respectively and right wing to tip  0.2 to 0.1 respectively. 

my left stabiliser to tip was 0.3 to 0.3 and the the right 0.2 to 0.1.  See chart below.

 

Edited February 7, 2023 by Adrian Smith 1

[Adrian Smith 1]

Still doesn't tell me the incidences in relation to the main wing and tail plane. But can't have everything.

 

 

 

[Peter Jenkins]

I did wonder if you could fit the LiPos across the fuselage in your airframe.  2 m F3A machines are too narrow to allow that.

 

If you wanted to you could always fit incidence adjusters to the wings.  That allows you to set slightly different left and right wing incidences to cater for minor wing variations while removing the need for any aileron trim.

[Adrian Smith 1]

It's fortunate, Peter, that the rear of the fuselage behind the wing tube is wider than in front of the tube due to a double wall in front as can just about be seen from one of the above photos.

[Peter Jenkins]

That was fortunate!

[Adrian Smith 1]

Just an update since I move the lipo packs to directly behind the wing spar. Not perfect day, but good enough with the wind straight down the strip. I put my two heaviest pairs on first of 795g apiece (Overlander 5800mAh 6s x2) followed by Turnigy graphene packs 860g apiece (5000 mAh x2) on the second flight. The result was an improvement, but not how I want. I  am quite surprised as I thought this would have more effect. The elevator improved from 24 clicks of up to 16 clicks of up therefore marginal at best. There is still a bit of space behind the wing spar such that I can move the packs a bit further back. That will be the next move I think. With the CoG where it is it is not possible to effect a flat spin from height which I like to do so more experimentation is needed I think. Other observations are that the motor +prop combination provide plenty of power and good vertical performance seems ok. Will report back. 

[Peter Jenkins]

Sounds like progress Adrian.  I would still use stick on weights to find the right CG position as you can do that between flights and then take the CG far enough back to decide enough is enough before removing the weights to get back to the ideal position.  Then calculate how much you need to move the pack back to get to the same CG and remove the sticky weights.

[Adrian Smith 1]

Yup you are right, Peter stick on weights are on my shopping list.

[Peter Jenkins]

👍

[Adrian Smith 1]

Coming back to what you say, Peter.

After nine flights I think I need to approach the substantial amount (18 clicks) amount of up elevator from a different angle. Despite this she flies very well and performs my aerobatic schedule without complaint with very good vertical speed/power. I do notice that in knife edge the nose position needs correcting slightly using the elevator. I have gone back to basics on my adapted Vanessa Rig and performed a couple of re-checks. The manual CoG measurement pretty well coincides with the wing spar position which makes it an easy starting point. It seems that using the battery configuration as pictured on the thread she actually has a rear-ward  CoG after all. Can't say I noticed any uncontrollability in flight despite this. So my initial thoughts on the original reason for up elevator is unreliable. Both the incidences on the main wing and tail plane are fixed due to alignment pegs and can't easily be altered without major surgery. Not something I will try. I am wondering if the motor thrust lines need attention. Side thrust (built in) seems to be correct as doing the vertical test shows no issues there. It's a long time since I played around with up or down thrust so I am not sure whether this needs correction. The last I checked the side thrust was about 2 degrees. I am not sure about down thrust so I will need to check. I am just wondering if it's best to leave well alone or go into tinkering mode!

 

This is how she sits and the small amount of tail heaviness can be seen.

[Peter Jenkins]

Hi Adrian,

 

If you cannot alter the wing incidence then you are stuck with the tail down attitude.  On my aircraft, I would increase the wing incidence and that would allow the aircraft to sit level at the same speed as the wing incidence is returned to that needed at that speed.

 

My latest F3A design came with no front incidence adjuster but provided a rear adjuster!  Converting to an adjustable incidence is fairly simple provided the front and rear anti rotation pegs are wing mounted and not fuselage mounted.  A little more involved if fuselage mounted!  You can buy an incidence adjuster (link), it's the one I've bought.  They are pretty simple to install but you will need to cut slots in the fuselage to allow the wing pin to travel up and down.  You may need to fabricate a support at the rear that will allow the wing pin to move as it's adjusted and then clamped in place.  I'll post a photo of what I mean later.

 

As regards up/downthrust on the aircraft, I usually check for this by flying at my datum speed and trimmed and then slamming the throttle open.  If the nose pitches up immediately, add down thrust, and vice versa.  As the aircraft accelerates the increased speed will cause the aircraft to climb due to the increase in lift so it will not stay level as it speeds up.  It's the instant reaction that you are looking to fix.  You also throttle back from datum thrust to do this check.  Since you will be flying at essentially the same airspeed but with varying power, fixing any thrust malalignment will help to reduce pilot workload.   

 

Unless you particularly want to measure the CG you arrive at by flying, I see little point in checking where it actually sits provided the aircraft's behaviour in flight is what you desire.  Manufacturing tolerances are always going to mean that CG needs to be tweaked from air frame to air frame of the same model.  Getting coupling free knife edge flight may be difficult with an IMAC design but moving the CG may help to reduce the amount of aileron or elevator needed to fly knife edge without using aileron or elevator. Of course, you can always mix out any unwanted pitch or roll for KE flying - if you put that on a switch you can just use it for KE.  On my current 2 m aircraft, having the CG to the aft of the range gives pure KE with left rudder and a very slight pitch to canopy on right rudder but you have to fly almost the length of the field to see that effect.

 

You mention that you have a rear ward CG.  Is the aircraft neutral in pitch i.e. if you pull up or push down the nose does it stay there or recover?  It's always a balance between stability and having the aircraft hold its attitude that is the trade off.  Provided the aircraft isn't unstable, and they don't get unflyable if you are inching the CG aft, then what ever position you feel gives you the handling you are seeking then that is the right CG.

 

Good luck with further tweaks but if you are happy with what you have then just go and fly.

[Adrian Smith 1]

Plenty to absorb there, Peter. The anti-rotation pegs are in the wing so not too awkward. The incidence adjuster sounds like a great idea. 😊

[Peter Jenkins]

This is what the rear support looks like.  It is made of a piece of ply with a spike nut and a paxolin plate with a slot for a screw to secure the position of the rear peg.  The second photo shows that in my current build, the rear rod is held in the fuselage by the two adjusters.  You slacken off the rears, adjust the front incidence to the required angle and then tighten the rear mounts.  All works very well. 

[Peter Jenkins]

Oh, the set up I'm using is:

 

Tail plane - 0 deg  - basically this is the datum

Wing - 0.7 deg  (somewhere between 0.5 and 1.0 deg is OK.

Down thrust -  minus 1 deg.

 

Might change after flying it but probably not by much.

Edited March 21, 2023 by Peter Jenkins

[Adrian Smith 1]

Very interesting thanks, Peter. Clearly it is easier to fit these during the build. With an ARTF it might be a bit problematical to fit on within the TP part of the fuselage. A bit easier though for the main wing I guess. When I continue testing I will repost if only to provide guidance to anybody else to buys the kit.

[Peter Jenkins]

You are right about TP incidence adjusters

  My current kit has a fixed TP so just the wing to play with.  In reality, provided you can adjust the wing/TP incidence difference then the only need for an adjustable TP is to enable any elevator trim to be removed by adjusting the TP incidence.

[Adrian Smith 1]

👍 Cheers, Peter.

[Adrian Smith 1]

Just a bit of a debrief after flying the GW Slick 91" for 20+hours. Firstly the 26x10 prop works well with the Dualsky GA8000 motor. The vertical performance is excellent with good power. The larger diameter/low pitch allows for better slowing capabilities, not withstanding I need to keep more than my usual throttle on to stop the possible stall.  I am still having to fly it with some up trim on the elevator, but I have just learnt to deal with it and this doesn't affect my overall enjoyment of just "getting out there to fly". 😀

[Peter Jenkins]

Sounds like you've reached the sweet spot.  Good work.

[Adrian Smith 1]

Thanks, Peter. When I get a run of days in the work shop I am toying with the idea to check and see if there is some inadvertent down thrust in the motor which causes the need for up elevator trim. I am a bit dubious about it purely because when I close the throttle on finals there is no ballooning in fact she she keeps a nice line. I am not a one for tinkering too much, but it will be interesting to measure if there is any down thrust at all which I don't think should be present given the pure aerobatic nature of the plane (only side thrust) . As I have noted previously given the ARTF nature of the aircraft altering wing incidences is not a place I wish to go. Additionally, I have noted that the CoG if anything is a bit rearward. I am not going to stress about it too much as she is a treat to fly even given the trim dialled in.