--- Joacim Persson wrote:
> On Fri, 8 Dec 2006, Stuart Buchanan wrote:
>
> > - There is no trimming for different flight phases. Vertical speed is
> > purely controlled by power.
>
> Many trikes has a trim function, just like all non-trainer hang glider
> has
> nowadays.
Many do, but mine doesn't :)
Even by microlight standards, my aircraft is very basic. My panel has 5
instruments: ASI, Altimeter, Compass, EGT, RPM. Plus a stopwatch stuck on
with velcro...
However, I am talking about a directly controlled pilot-controlled trim
system rather than the side-effects of the wing flexing.
> (I know the Airborne trike we use for aerotowing has it.) This
> trim is usually operated by a line, the trim line, which is drawn to the
> speedbar (on a HG) or on a sidebar (on a trike) and most noticeably it
> adjusts the tension of the cross beam (which is divided in two parts
> connected with a hinge at the centerline). (Compare with the "kick" or
> sheet on a sailboat mainsail.) There are however more functions coupled
> with the trim than cross beam tension. On kingpost HG's (like your
> trike),
> there is something called "luff lines" connected to the trailing edge
> via
> the kingpost, on the newer topless hg's there are "sprogs" at the wing
> tips
> filling the same function. Luff lines and sprogs act like an elevator
> trim
> under certain circumstances, and is primary a safety detail to prevent
> an
> uncontrollable dive. The setting of those are also altered along with
> the
> trim setting.
I believe I can alter the luff lines on the ground, but I doubt it is
something I'll be doing in the near future.
The cross-beam isn't fixed to the keel. When the wing is un-folded a
pulley system is used to pull the crossbeam into position and tie it off
against the keel, but I guess it will still have some lateral movement. I
didn't know that trim affected the cross-beam. I
> So the trim on a HG or trikes changes:
>
> 1. The camber of the whole wing. (cross beam tension) This affects L/D
> ratio,
> stall speed.
> 2. Apex (follows from sail tension) and dihedral (not much).
> 3. The elevator trim function of sprogs or luff lines.
>
> Your trike may have the cross beam fixed to the keel (can't tell by the
> photo) and would then be a bit stiffer in handling (but more course
> stable)
> than a hang glider with the trim fully loose, but with a floating cross
> beam (i.e. not connected to the keel) as all hang gliders have today,
> the
> first effect of moving the weight to one side (shifting the keel
> sideways
> with respect to the cross-beam and wing tubes) is that the wing you move
> away from gets less camber and the other gets more camber. This in turn
> makes the outer wing tip fly a bit faster than the inner wing tip,
> generating some rudder and aileron effect. A hang glider with a
> non-floating cross beam is rather slow in turns.
>
> This difference in camber between the wing halves is less the more the
> pilot tighten the trim. So we can add a fourth function of the HG trim:
>
> 4. Sets the amount of rudder and aileron effect from shifting weight
> sideways -- indirectly by adjusting the cross beam tension and thus the
> difference in tension of the trailing edge on each wing half.
>
> In short: when circling thermals or coming in for landing, you release
> the
> trim, when flying straight between thermals you tighten the trim (fully
> or
> to a wanted trim speed).
>
> But that is perhaps a bit beside the point -- a trike pilot doesn't have
> to
> worry much about L/D ratio, and there is plenty of weight for steering
> with
> pure CG shift on a trike.
>
> > So, should I use YASim or JSBSim for this project?
>
> Or larcsim? The only hang glider model in FG (airwaveXtreme150, a
> larcsim
> model) has an invisible motor+propeller attached to it, so we could call
> it
> "a trike". It doesn't have a trim function anyway. (I'm quite sure the
> original has.)
I did consider using larcsim, but decided not to on the basis that it is
no-longer developed much (if at all).
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