Timo44

..just had a couple of flights with my 5 meter Krause Salto - and it seems
(that's my "feeling") this glider is a little bit to fast on the ground after
releasing the rope of the pulling bird.
Nevertheless I'm just getting about 3,5 minutes of flight not more above
600meters groundlevel.

Have also the info that the Salto weights about 12kg - seems a little bit to much -
but I can't reduce the weight.
Does anybody of you have any suggestions what to optimize to make this glider
"run" more stabel through aerobatic manuvers ?

anyway I also fitted some "turbulators" at elevator.

Perhaps the evaluation of the vid can give some hints how the bird behaves -
have a look at the "heavy" aileron rolls.
...may it even be to much tail heavy ?

[youtube]http://www.youtube.com/watch?v=3A7HA5cuKRw[/youtube]

rhall999

Well, to be honest, after watching your video, I was thinking that the performance was pretty dang nice. It seemed to me as though for the amount of fairly agressive aerobatics you did, it stayed up for quite a while. Now, that being said,I do not know that glider at all so I could be wrong. The biggest thing I noticed, is that other than the faster than "scale" roll rate, it was almost exactly the same as watching Manfred Radius fly his full scale Salto at airshows. Perhaps a lighter weight would be nicer and provide a bit better performance, but as you said, there is not much you can do about that.

Here is a video of Manfred for comparison.

[youtube]http://www.youtube.com/watch?v=_vVkaIdfwb0[/youtube]

BMatthews

First off I'd have to agree that with that sort of aerobatics show you're not doing badly at all. There's no doubt that at 12 kg that it's at the upper end of the weight range for such models. But it's far from being the worst example I've seen. It actually seems to be flying quite well. How well does it thermal? Is the slow speed side of the flight envelope a bit sinky? Maybe try some turbulators on the wing to aid the higher lift coefficient side of things?

I think the altitude comes into it as well. You're flying roughly a 1/3 size model and being released at around 600 feet. Seems to me that when the aerobatic gliders do their routines at the air shows that they start up more at around 4000 to 5000 feet. They also lead into their routine with a dive from a little higher to begin the routine with some extra speed and momentum. Something that you can't do when you're starting with just 600 feet. Starting your own show at 600 is roughly equivalent to them starting their show at 1800 feet. An altitude that they don't reach until half way into the show. So to get about 3.5 minutes isn't a bad performance at all.

Stability of the glider looks fine. And I noted that the yaw in the rolls is a proverse yaw rather than adverse yaw. It makes me suspect that you've got the aileron coupled with the rudder function. If so I'd turn off that mix and fly with all the controls independent.

One thing that could aid your model if it has plain flaps and ailerons that run for a total of the whole span is to couple the flaps and ailerons to the elevator. The idea being that hard up will deflect the flaps and ailerons a few degrees down to increase the camber and allow reaching a higher lift coefficient more efficiently during the high G pullups and loops. And when you go inverted the down you need to hold the nose level would force the flaps and ailerons to reflex to remove some of the camber or even add a bit of negative camber to make the airfoil more efficient in the "dirty" inverted mode. You'd only need maybe a total of 4 to 5 degrees of up flap for full down and likely only about 3 to 4 down flap for full up. Otherwise the distortion of the airfoil will cause more harm than good.

Drag in such models is the enemy. Drag comes from creating lift. And drag comes from deflecting control surfaces. So using the minimum control deflections possible will help. And there's no point in trying to use rudder for some knife edge help with such a slender and slippery fuselage. Instead all you'll get is drag. Some canopy like fairings over the smoke bombs would not be out of place either. It would give a smoother and less draggy flow around the wing tips.

Timo44

...unfortunately I ment I started with 600 meters above ground level that means - rope release of 1800 feet ! - so I catually started my aerobatics program
at 1800 = 600 meters and ended up at 3.5 minutes...
Anyway the salto has no flaps - so I have not the possibility to mix flaps to aileron .(....

so what I will go on with turbulators at the wings...

UStik

Don't have any experiences with such models, just a comment on impulse:

That thing must be on the heavy side, assuming it's 1:3 of the 15m original. Would have 125 g/dm2 wing loading (like a jet airliner model) and much momentum. It can be flown but you have to fly it really fast to avoid higher lift coefficients and induced drag. An egg-shaped loop and a steep turn (as in the video) just show that the model had to produce much lift and much energy was dissipated (wasted) by induced drag.

As BMatthews said, more speed and small (minimal) control deflections should do the trick, I'd guess. (Energy conservation, avoid drag, just exchange potential and kinetic.) Those steep turns are just what I did in the paradropper airplane to descent faster.

BMatthews

My mistake on the 600 feet vs 600meters issue.

There's no doubt that 3.5 minutes from such a height isn't all that great in that case. With some changes in how you fly the model you'll likely work it out to be more like a 4 to 4.5 minute program. But in the end if you're doing these sort of aerobatics it takes a good amount of energy to perform them. You just won't get times up over 4.5 to 5 minutes when flying such a routine.

I'd suggest you spend some time actually soaring with the model and time your flights to get more feel for the speed where it flies the most efficiently and how fast and slow you can go from that point without losing altitude too fast. From there you'll want to learn to fly the model so that it stays in the lower drag/ more efficient speed range for more of the aerobatic performance. In other words fit your flying to suit the plane so you emphasize what it's good at and avoid what makes the flight suffer. Dive for speed then trade that speed for regained height using big open graceful maneuvers that don't slow the model down more than required.

Doing a quick check of some of the 4 to 6 meter scale gliders there's no doubt that at 12 kg that your own Salto is definetly on the heavy side. Most models are down more around 7 to 9 Kg. The higher weight is going to both hurt and help. It'll hurt every time you try to change direction in a hurry. It'll help with momentum and speed. So I'd suggest that you concentrate on learning to fly the model in a style which rewards the high speed, open and graceful maneuvers over the sharp and quick ones. Doing so will generate less drag and lose less speed and extend your flight times.

Using turbulators on the wings may or may not help. But you won't know until you try them. The optimum position for them depends on where and if the airflow is separating from the surface to form a big and draggy bubble. I'd suggest you try strips made from 3 layers of 4 or 6 mm wide automotive masking tape and start with them at about 20% of the wing chord. Take the model up and try flying a bit more slowly at a minimum sink like speed. If the model flies in a flatter slope with the turbulators than without then they are helping. If the turbulators work try moving them back to 30, 35, 40, 45% of the wing chord and see where they stop working as well. At that point install permanent strips made from 3 layers of automotive trim stripe tape at the last known best position. Also compare the high speed with and without the turbulators. In my case the two times I've used turbulators they aided the slow speed without hurting the high speed to any noticable degree. But each case is special so you need to try this yourself. It may well be that they make no difference at all. If so it shows that the airfoil is efficient right down to the slow speed range.

tobuy3003

The Cg can be at a place other than what most people say it is for best energy retention. Iknow this from exp. Moving it way back is not always faster and more agressive. You can see the difference with your eyes its so much.