Self-launch take-off technique

[Mark B]

In common with other Schempp-Hirth self-launch gliders, the Arcus M dips onto its (essential) nose wheel if full power is applied from a standing start. On our soft grass field, speed has to be built up quite slowly before full power can be applied without the Arcus dipping onto the nose wheel, even with the stick fully back.

 

I cannot decide whether to apply full power earlier, and let the aircraft run on the nose wheel, or to wait a long time before applying full power, and not make the aircraft dip onto the nose wheel.

 

What do others think?

Once you can use full power, to me, it comes naturally to hold the aircraft in a level attitude during the ground run. Tilo Holighaus suggested holding the tail wheel on the ground, presumably so that you lift off sooner, However, I would expect there to be less friction running on the main wheel than on the main and tail wheels. A compromise would be to run level until near lift off speed, and then pull the stick back. Again, what do others think would give the best performance?

 

Now flap settings. The manual suggests generally taking off in flap plus 2 (after starting in negative), but that you may use L on a soft field. If you took off in L, I presume that you would lift off the ground sooner as the stall speed in my experience is significantly lower, but would not climb well due to the extra drag. Has anyone tried it? How soon after coming off the ground,do you think you could change to plus 2 without risking putting the glider back on the ground? (I could try this out at height, but have not yet done so).

 

[Mark B]

I have now found that on a firm surface you can apply full power pretty much straight away without the glider dipping onto the nose wheel. If you take off using flap L, there is no discernible drop when you change to flap plus 2.

[rogd...@bigpond.com]

Mark,

My opinion is that the Arcus M takes off happily in L or +2 based on my limited experience.  There is little difference in stall speed or drag between the two settings such as to warrant fussing over fractional & momentary advantages/disadvantages arising from stall speed or drag differences.  Nevertheless L is better on soft ground and it is very easy to achieve this setting because you just bring the flaps all the way back without the distraction of needing at some point to look at what setting you have achieved.  If you use L then put it to +2 when well away from the ground and when not subject to other distractions.  I personally use L all the time.

 

Also look at the longitudinal balance situation.  Is it dipping onto the nose because you have two heavy pilots and no tail water ballast or tail battery compensation?

 

I personally aim never to accept running on the nosewheel at the start of take-off.  If this happens then there is a later point at which nose up-tail down authority is achieved and this can thump the tailwheel on the ground hard which can be a bit disconcerting.  More than this having the tailwheel on or near the ground keeps the wings providing maximum lift and thus unloads the mainwheel reducing mainwheel drag on soft ground.  This equals shorter take-off run.  More importantly tail down on the ground assists with directional control which may become critical in a strong crosswind.  The Flight Manual advice & Tilo's advice seem to me to be well based.  There will be others with Arcus M and much more familiar with take-off in crosswind issues than I am and they might advise further.

 

Roger Druce

And by the way check out on their website Solo technical note 4600-4 re action to address potential cracking of the blue anodised angle pieces between the two air induction units issued 12 December 2012.  It is frustrating that such documents are not communicated in a timely manner, at least it appears to be not the case from where I sit here in Melbourne Australia.

[Mark B]

I have been starting in Flap -1 and taking off in Flap L - this has been very satisfactory since the ground at my grass airfield has been dry and firm. When it was soft over the winter self launch takeoff was difficult because when you opened the throttle the nose went down and it was difficult to build up speed.

I have always started with one wing on the ground. In a cross wind I have the into wind wing down.

[Simon Waddell]

Initially, I also experienced the 'tipping forward onto the nose wheel' problem - in full flying trim I weigh in at 115kg.  I solved it by always adding ballast in the fin - about 7kg when flying solo, more two-up.  The FM doesn't suggest doing this but after discussion with Tilo he endorsed the idea.  Opening the throttle progressively also helps, but since we only have a 600m runway with trees at the end we can't be too progressive.

 

[cernauta]

I also ended up loading more tailballast than I would do for the soaring flight.
I don't exceed CG limits, but then I start dumping during the take off, either by opening the ballast lever, or by having someone remove an appropriately posotioned red tape from the tailballast level holes (like: holes taped up to 10L, red tape at the 4L position, fill up; remove red tape when ready for takeoff).
This way, on hard surface, I usually can apply full throttle within 2-3 seconds from the release of the brake.

I only tried L flap on take-off once. The ground was soft and wet, and the sailplane didn't lift-off anyways.
If you try, I believe you can just let some more speed build up, then gradually reduce to 2 or 1.

I still don't like the "stick held back" take-off technique, but it's probably for the best, intended to protect the tailwheel assembly from damage. The same applies for landing. Even an un-dramatic, very slow groundloop can badly damage the rudder. Keepeing the tail on the ground helps prevent these mishaps.

best regards

aldo cernezzi
sn 37

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[Mark B]

As mentioned earlier in this thread, my take-off technique has always been to start with the into-wind wing on the ground, and no wing runner. I think this is particularly useful if there is a cross wind, because otherwise it can be difficult to prevent the into-wind wing being lifted up, and also if the ground is soft and you have to start slowly, which is difficult for a wing runner. Most of the self-launching gliders on our site use this technique.

This week I made a failed attempt to take-off from a soft field. The tip wheel of the wing on the ground dug into the ground, the tip wheel broke off, and there was a slow ground loop. There does not seem to be any damage except to the fairing of the tip wheel which is going to be repaired. There is no damage to the wing, and happily there is no sign of damage to the rudder.

With a very soft field I should have used a wing runner instead of starting with the wing on the ground. It is a pity that S-H do not use fatter tip wheels like the ones used by AS and DG.

My earlier posts in this thread were mostly about the problem of the nose going down onto the nose wheel when you open the throttle. I now know that this is not a problem and I can open the throttle quite quickly either if the ground is firm or if I have ballast in the fin. It is a problem in winter when the field is soft and the temperature is rather low to put ballast in the fin. I agree with other posts that it is probably best to try to have the tail on the ground during the ground run.

Mark Burton

Arcus M s/no 24 G-KFVG

London Gliding Club, Dunstable, UK

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