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Synthesis Questions


togsie
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Hi All,

I'm now the proud owner of a Synthesis wing and am busy practicing my ground handling in the hope that I'll be flying sometime soon. I've been reading through the manual and there are a couple of points that I'm not clear about, perhaps Simon or another member of the forum could shed some light:

On page 12 of the manual there is a cautionary note "During take-off it is important to keep the risers under pressure until almost airborne. Reflex profile used has an inherent tendency to increase the angle of attack. In effect, Synthesis can lag behind the pilot when not pulled up appropriately" :?:

I'm not clear what they mean by this, in the training that I have done to date, with a conventional wing (non reflex), the technique that I was taught was to get the wing overhead and then come off of the risers and control with the brakes. Is the technique different with a reflex wing? How do you "keep the risers under pressure until almost airbourne"?

Another point that puzzles me slightly is to do with the trimmers. I understand the principles but in practice when (if ever) would you want to fly with an intermediate setting i.e. somewhere between the '0' and fully opened?

Another point about the trimmers the book says that posistion '0' is best suited for take off, why wouldn't you use the fully closed position for take off "Minimal speed and minimal sink" and when would you use the fully closed position?

Regards

Togsie

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Asquaddie,

OK you win, I'll get on the case this weekend. There really isn't much to report to date but I suppose I should make a start.

Will you be visiting Lambourn at the weekend? I was down to ground crew for the Dartmoor trip but it doesn't look like it will be going ahead so I was thinking of taking the opportunity to practice my ground handling. It would be good to meet up and compare notes.

Now please answer the question. :(

Regards.

Togsie

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All I know is that it is a hell of a lot harder to ground handle when the trims are not set equally. If ever I'm having a hard time getting it to settle right I usually find that one of them has slipped an inch relative to the other.

I'm sure Simon can give us the detail on what they do and why it matters :wink:

Stuart

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Ken, don't worry about it. Just use your normal technique with riser pressure and it comes up just fine. Let the risers come out of your hand in the normal way, works fine for me. Trims set at 0 works just fine for take off and landing. I havn't tried landing with the trims pulled fully in but I gather you don't carry the same energy that gives you such a nice positive flare. For take off I would imagine having the trims pulled fully in could increase the tendency for the wing to lag behind. 0 works just fine.

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During take-off it is important to keep the risers under pressure until almost airborne. Reflex profile used has an inherent tendency to increase the angle of attack. In effect, Synthesis can lag behind the pilot when not pulled up appropriately"

This is written particularly for those who have flown traditional gliders before moving to reflex. The reflex profile means that the wing needs the A risers pressured for longer than a 'normal' wing. Those making the transition from traditional wings often struggle with this, hence the emphasis in the manual. It is possible to launch a reflex glider with pressure still held on the As. On a traditional wing this would be very dangerous and it would probably frontal before you left the ground.

There are various reasons for using trimmers in intermediate positions. In very rough thermals, I sometimes fly with a little speed on so I can benefit from the pitch stability of the reflex profile. Normally I would prefer to thermal on slow. If you are trying to fly economically then you should be using Speed to Fly theory to maximise the distance you can fly on your fuel. This means adjusting your airspeed depending on what the wind is doing. I won't try to go into more detail here as its a much easier concept to have explained in person. I'm sure Simon can talk you through it. For precision maneouvers in competitions, there is a compromise between making it easy to fly (slow) and doing a good time (fast) and so intermediate trimmer settings are often used here.

For interest, when I was testing the first prototype of the Synthesis, my major feedback was that the wing was too responsive and nippy on full slow trim for its target market. I felt it was more suitable (& safer) with about an inch of trimmer. Later versions were calmed down a little. Trimmers do affect many aspects of a wing.

Cheers

Dave

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Dave, is this riser pressure partially to do with being designed to launch from flat ground rather than on a sloping hillside?

It's not directly a result of that - it's really just a common feature of reflex wings. It's also why we don't trim them to full slow when we launch. At full slow they are less happy to come over our heads, although once there the launch can be slower and therefore easier.

Launching down a hill can make a glider more forgiving of a lack of pressure though. On the downside, it also makes the consequence of a failed launch potentially more painful.

Cheers

Dave

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