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Author Topic: Stabilizer Tilt  (Read 1207 times)
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High Point
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« on: April 27, 2008, 04:50:37 PM »

On a few glider designs, the plan calls for attaching the stabilizer at a tilt (about 1/8") for a left circle. I've done this and it seems to work fine. How do you feel about attaching it with this same tilt for a plan that shows it to be installed with no tilt?

Thank you,
Curtis
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albackstrom
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« Reply #1 on: April 27, 2008, 04:57:54 PM »

It will work fine. The object of stab tilt in HLG and CLG is to have no turn correction during launch but provides the turn when the glider slows after losing the speed from the launch.
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Kev
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« Reply #2 on: May 11, 2008, 05:06:50 PM »

All I would do is make it with the tilt (Sweepette is a noteable aircraft) but leave the stab 1/8 inch sticking out of the back - makes it easier to adjust this for trimming. Up if it dives, down if it loops.

Kev
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Dan G.
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« Reply #3 on: May 12, 2008, 02:17:41 AM »

Yah ... I'm all in favour of tilt.

Dan G.
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crashcaley
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« Reply #4 on: May 28, 2008, 01:50:20 PM »

I was told that if you tilt the stab, to tilt it even with the inner panel of the wing if polyhedral. My Sweepette 12 has it that way. I'm not sure how to do it with just a two piece wing. I would guess that your 1/8" would be fine. I would imagine that the amount of tilt will determine how large or small the circling will be in the glide mode. I'm still learning these little critters, but the more I learn, the more fun they are becoming.

Caley
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Dan G.
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« Reply #5 on: May 28, 2008, 11:26:36 PM »

I don't know how much inner dihedral the Sweepette 12 has ... but when I put my stab even with the inner panel on my Supersweeps (which don't have much), it is twice what is needed and the turn is hurtfully tight. I hasten to point out that turning a glider tightly, really hurts the rate of sink.

I've heard that advice before ... think of it as a popular misconception.

Dan G.
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crashcaley
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« Reply #6 on: May 28, 2008, 11:46:55 PM »

I flew my Sweepette 12 this morning and the tilt gave it a little turn, but not enough as the upper jet stream or whatever took it straight away from me. I got lucky and it didn't go into any yards or on a roof and really lucky that it just stayed out of a yard with two dogs in it, or it would have been instant dog chew.

I'm still experimenting with gliders, trying to learn, so everything that I am told I try. So far things seem to be working for me, but I'm sure that some of it is probably luck so far. I've built six gliders of varying sizes and types and had only two fly well enough to make me happy. But they are fun, and it seems that the ones that I am not happy with provide the neighborhood kids a lot of fun and enjoyment. Smiley I think the key is having fun.

Caley
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What's stall speed?  Undecided
gossie
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« Reply #7 on: June 16, 2008, 02:15:19 AM »

When your a bad 'chucker' like me Caley------it HAS to be strictly for fun. Grin
 
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #8 on: June 17, 2008, 12:51:06 PM »

I eschew tilt.

Only use a bit now and then to vary glide circle size. Yes, it will aid turn on most designs, but the sink rate will be hurt. V dihedral gliders seem most to benefit from tilt [like many Oldtimer HLGs].

Some tip weight, wing offset and maybe skew, a bit of left rudder, balanced with washin wedge just outboard of dihedral joint. That is my trim technique.

No tilt, or just a visible smidge.

Leeper
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Leeper
Dan G.
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« Reply #9 on: June 17, 2008, 08:36:28 PM »

I would point out that when I'm busy trying to keep a class of thirty students flying their Cubs, and they come to me for trimming, I rely very heavily on stab tilt. I will check the wing warps or inconsistencies, and then turn toward the wash-in with rudder and stab tilt.

I've already written on the value of stab tilt in another thread about hand launched gliders, but it bears repeating: in that transitory stage from climb or stall into glide, when the airspeed is next to zero and the plane might actually fall a bit or flop, the rudder will have no effect but the stab tilt might well heel the plane around into a turn and make that stall much less severe or even avoid it altogether -- one of the strong arguments against large fins (or side area in general) on gliders which would prevent that pivoting, stall averting maneuver.

Dan G.
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packardpursuit
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« Reply #10 on: February 24, 2009, 10:46:49 PM »

It's been quite awhile so please forgive the dumb question, but tilting the stab turns the model what direction? Does it turn toward or away from the high side?
I'm about to mount the stab on a couple polyhedral originals.
TIA
charlie
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Rewinged
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« Reply #11 on: February 24, 2009, 10:56:04 PM »

Charlie,

The model will turn toward the high side.

--Bill
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Good air don't care!
Hepcat
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« Reply #12 on: February 25, 2009, 01:14:00 PM »

There always seems to be a bit of mystery associated with tailplane tilt but there is no reason for this if the simple basics are understood. Actually Al Backstrom said most of it very succinctly in the first reply but it may be worth amplifying a bit.

If a tailplane is lifting then the lift force can be represented on a drawing by an arrow (a vector) pointing vertically upwards. If that tailplane is now tilted then the lift force is tilted sideways which pushes the rear of the model towards the low side of the tailplane and, (as Rewinged has already said, #11) the nose of the model is turned towards the high side of the tailplane.

Now it will be seen that for a tilted tailplane to cause a turn the tailplane must be lifting and tailplane lift depends mainly on two things; the position of the centre of gravity and particular trim changes at certain times in the flight. Dealing first with the CG position. It is apparent that the further back the CG is placed then the more the tailplane must lift in relation to the wing therefore aeroplanes with a rearward CG position are responsive to tailplane tilt to give a turn. Conversely as the CG is moved forwards the tailplane lifts less and less until with a very forward CG the tailplane will have to lift downwards for balance and in these circumstances the tailplane tilt will turn the model towards the low side of the tailplane. Now to the matter of trim changes. High powered models use thrust offsets, spiral climbs and perhaps other subtle ways of reducing the lift of the wing and the tailplane during the climb. (This is necessary because the thrust force is lifting the model and if the wing was also lifting the model would loop.) As the tailplane lift is reduced under these condition then the turning effect of any tilt is also reduced.

I think tailplane tilt first came into general use in the gas models of the 1950s. They had huge tailplanes with CGs near the trailing edge and so circled well with tail tilt. The climb trim reduced the angles of attack such that the tilt was not effective and the climb turn could be adjusted with a rudder tab. The rule of thumb that Caley mentioned, of tilting the tail parallel to the inner panel dihedral, started at this time and was quite sensible then because most of the models were so similar in layout and proportions.

Around this time rubber models (and HLGs) also got longer with aft CG positions and the tilted tailplane became common with lots of models for a long time. However more recent designs go with smaller tails and more forward CGs and the tilted tailplane is much less used than it was in the past.

I would also like to support Dan (reply #9) that there does appear to be an effect when near the stall even with forward CGs and small tails. The high angle of attack near the stall does seem to cause a turn. I am sure I have seen this many times on ‘Coot’ style indoor gliders at the top of the climb although I have not noticed it on outdoor CLGs – perhaps no one uses tilt!

John
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John Barker UK - Will be missed by all that knew him.
Jun
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« Reply #13 on: February 27, 2009, 04:18:05 PM »


 Hi John,

I've just discovered the origin of your nom de guerre. In a compilation by Vic Smeed called "Plan Parade" (Nexus Special Interests 1997), there's a reprint from the January 1946 Aeromodeller of a plan for a 30" span rubber model called Hep Cat (two words) by one John Barker (no stab tilt!). Looks like it would make a great P-30 except for the single blade 12" balsa folder. How old were you then? Twelve?

Regards, Jun
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