Washout included in Flight mode trim?

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Phill Tadman
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Joined: 18 Aug 2015, 20:38

Washout included in Flight mode trim?

Postby Phill Tadman » 19 Mar 2017, 08:19

Hi all,

I'm trying to set the flight mode trim on my Baudis Antares but am not sure whether to correct for what I believe is washout in the wing towards the tips.

If for example a recommended thermal setting is 3mm down on the entire wing, setting 3mm at the wing root and keeping the surfaces aligned results in about 1mm at the tip.

Is this is how it is meant to be or should I have steps between the flaps, inner ailerons and outer ailerons to achieve 3mm down at the tips?

Thanks,

Phill

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jimbo
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Location: Cornwall

Re: Washout included in Flight mode trim?

Postby jimbo » 19 Mar 2017, 18:23

I usually set the inner flap to 3mm and align it as you suggest. Interesting point about it not being 3mm at the aileron end, never really thought about it until now, I'm pretty sure my thermal mode is less droop at the aileron too on both my alpina and big asw20.
I may try setting 3mm through out and see what happens. Suffice to say thermal model is effective as I fly with how you have it set up at the mo.

Ian Stromberg
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Location: Cheshire

Re: Washout included in Flight mode trim?

Postby Ian Stromberg » 19 Mar 2017, 18:27

A thermal flap setting of 3 mm down usually means 3 mm down measured at the wing root and the surfaces are kept aligned across the wing. 3 mm down at the tip would give considerable washin due to the much reduced aileron chord at the tip.

Phill Tadman
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Joined: 18 Aug 2015, 20:38

Re: Washout included in Flight mode trim?

Postby Phill Tadman » 19 Mar 2017, 20:24

Thanks for your input gents.

Thinking about it, with the surfaces aligned, washout (leading edge down, trailing edge up) at the wing tip should result in a bigger aileron droop not smaller.

Does that mean the wing has washin?

Perhaps tip stall is reduced by having winglets?

Phill

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B Sharp
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Location: Perthshire

Re: Washout included in Flight mode trim?

Postby B Sharp » 19 Mar 2017, 21:27

Phil, as Ian mentioned, it all depends on the chord. If you continued your 3mm all the way to the tip you would have effectively aerodynamic wash-in. Not so much of a problem in straight and level flight but potentially lethal in thermal turns or low level manoeuvres. I learned this painfully a long time ago with glass thermal soarers.
With my flappy models like the 5 metre Alpina and ASW20 the flap setting starts out at about 3 or 4 degrees at the root and is reduced to 1 or 0.5 degrees at the very tip. This gives essentially a slight aerodynamic washout at the tip.
However when you come to set up your distance or speed trim you will find that having the whole flap/aileron set to exactly the same angle of reflex along the trailing edge (say 2 degrees) will give you the best results.
Brian. :)

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terry white
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Location: wareham,dorset.england

Re: Washout included in Flight mode trim?

Postby terry white » 20 Mar 2017, 13:35

Phill, You have one super model there, I am quite envious.

Please be very wary of adding washout to a wing that has such a tapered plan form. An inspection of the aerofoil at the tip would show the aileron width to be a wider percentage when compared to the rest of the wing section.. This along with other alterations is the modification that the manufacturers speak of in their blurb.. If they used the true width of aileron it would be too narrow to produce lift when required in the roll axis. Only creating drag which is the last thing you want when requiring lift. Bauldis has used the F3B favored section P DIRK Mod. on this model, An excellent section which for general use does not need any alteration to perform at its Maximum efficiency. By altering any section with flappy bits on the trailing edge, you spoil the section not enhance it thus altering its designed parameters. I would advise only to consider altering the section by positive or negative flap when the drag it creates is also a bonus such as on landing approach or in minimum thermal .

The modern sections for glass ships which have been designed and tested in wind tunnels and further tested by professional flyers are already at their best.t
Also a properly designed wing incorporating built in washout will be built with a twist to the wing with the wing tip angle of attack being less then the roots. When the aircraft is in a position of stall the inner part of the wing will stall first allowing the aircraft to nod to regain speed instead of dropping a wing should the tip stall first, then enter a spin. If washout is programmed in at the transmitter on ailerons it is quite feasible that one of the ailerons will be at reflex ( say on the last leg before finals) this will create drag to that one aileron and possibly do the reverse of you good intentions.

The down side to this is that when one pushes the aircraft at high speed (which the Bauldis Antares is more then capable of) the root angle of attack could now easily be at zero - the wing tips angle will now have a high negative angle of attack. The effect of this is the tip trying to twist the wing, the wing appearing to the onlooker to bounce as the whole wing hunts from positive and negative angles. The long slender wings of the modern glass ship can often be seen doing just that. Although Bauldis say they have designed this problem out with 'special' carbon full length spars.

A number of manufacturers favor (as I did) a change of section throughout the wing, with the tip using a section giving more lift at slower speeds and can sustain higher angles of attack. This way there is no drag created at the trailing edge, no attempt at wing twisting, no wing bounce in hunting.

So Phill , A very controversial subject I know, but for my two penneth,leave your wing exactly as manufactured, only spoiling the section on finals, and as altering the narrow trailing edge of the wing cant possibly give you real washout only drag.. forget it.

I wish you well with your maiden flight and hope to see you and it at M.W. Regards Terry.

.

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Chris Jesshope
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Location: Shropshire

Re: Washout included in Flight mode trim?

Postby Chris Jesshope » 21 Mar 2017, 07:46

Phil,

I agree with a lot of what Terry has said but I wanted to add a couple of points. Firstly there is a difference between washout, usually achieved by reducing the angle of attach at the tip or by changing to a different section, and camber. Setting flaps will add camber to a section and as Terry says, quite rightly, this will induce more drag, however it also increases the section's lift. Unfortunately both go hand in hand, although the relationship is not linear. A section with increased camber will also allow a higher angle of attack and slower stall speed. So I do not think adding camber should be avoided, higher lift combined with slower speed means tighter turns in a thermal. In short different camber settings allow the wing section to be optimal for different aspects of a flight.

As to a practical answer, I tend to align my surfaces when I add camber for thermal mode, although for landing I will add significantly more camber but only on the flaps, leaving the ailerons in the normal position. I have never induced tip stalling doing it this way on any of the models I have flown.

Regards Chris

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Antonia
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Location: Oxfordshire

Re: Washout included in Flight mode trim?

Postby Antonia » 21 Mar 2017, 13:12

Hi Gents,

For my four penny worth I copy the full size control movements with the exception of the thermal mode on the advice of John Greenfield, where I don't have the ailerons droop at the same rate as the flaps, this would give in effect a washout in thermal mode, this does work quite well, if pushed the ASH 25 will drop a tip, which can be interesting if you are flying some distance from yourself!... :?

With regard to the landing phase of the flight again I copy from the full size in the case of the ASH, the inner flaps go down to about 38 degrees and the flaperon function is removed, the outer flaps goes down to about 25 degrees and has approx 30-40% of the flaperon function, the ailerons go up by approx 5-7 degrees.

The flaperon function retains the 100:50 deferential ratio in cruise and thermal modes, in the speed mode the flaperon movement is reduced to approx. 70:50 deferential and movement of the ailerons element reduced by 50% as retaining full movement at speed could be interesting to say the least :shock:

Here's couple shots of the ASH's landing phase, the glider reacts a'la full size, very nose down attitude with no speed build up, very odd in a full size glider where the nose drop would accelerate you up to VNE in no time,... quite surreal!...

Antonia
Attachments
ASH 25 Full FlapLanding2.jpg
ASH 25 Landing_1B_cr4.jpg

Phill Tadman
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Joined: 18 Aug 2015, 20:38

Re: Washout included in Flight mode trim?

Postby Phill Tadman » 21 Mar 2017, 17:02

Wow, thank you all for your input, this is all really useful stuff!

I think I'll keep the control surfaces aligned so that thermal flight mode trim set at the wing root reduces towards the tips as a function of the wing design.

I wont apply trim to add washout or washin to the wing.

I might add a touch of up aileron and down elevator for the landing mode which has 30mm of down flap and neutral flaperons.

Phill

John Vella
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Joined: 20 Mar 2017, 22:09
Location: UK

Re: Washout included in Flight mode trim?

Postby John Vella » 27 Mar 2017, 16:00

Phil, I agree with having the wing trailing edge move together over small changes of angle in the range of thermic , cruise and speed.You are spot on with the "crow" landing settings you describe.
However I was helping rig a full size ASH 31mi last Friday (similar size and planform to your Antares) when I noticed that the flaps and ailerons split slightly (a couple of degrees) in thermal settings. This must be done to give more wash out for better handling at low speeds. So this might be worth trying on your Antares?
Regards John.


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