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Apr 28, 2009, 01:38 PM
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Discussion

Sirius and flying with no rudder.


So Bruce Davidson won Poway without a rudder flying the Sirius.The guys won the German open last year with a similar plane.(2008 Sirius).There are some things to note when talking about this plane.I have one and also flew it at Poway.I had only one flight on it before the contest so I used the weekend to learn how the plane flies.

The first thing to note is that you fly with more down than up aileron travel in all modes. I am attaching the recommended throws straight from Momentum.There seems to be some mistakes in the numbers ,which we evened out.

The second thing to note is that the wing is really thick and performs different than the trend to thin wings.

The really difficult but not impossible thing is to catch those really low small thermals.Its going to take me a long time to figure that out. Have to turn my rates down and use super small corrections.


I would love to hear what all you smart guys have to say about this.
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Apr 28, 2009, 01:57 PM
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djklein21's Avatar
I take it that down means that the surface moves up?

Also, what is up with the difference in the right compared to left aileron throw? Is the differential due to an unsymetric vertical stab, or is it a typo, or something else?
Apr 28, 2009, 02:01 PM
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I think thats a typo.Both Bruce and I used the same on each side.

From those settings we used more down travel on the ail than up travel in all modes.I know its counter to the way most normal planes do it.Thats why I want to hear from all you smart guys on why this works.The plane flies great once you learn how it likes to fly.
Apr 28, 2009, 02:07 PM
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djklein21's Avatar
should there be a -.5 in the launch/speed flap setting? Surely you don't run camber rather than reflex?
Apr 28, 2009, 02:09 PM
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Thats how I flew it all weekend..Although I was thinking of taking the RAM 3 and doing some testing on launch height with different settings.
Apr 28, 2009, 02:30 PM
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So, to repeat my statement from the other thread, I'm beginning to question the value of the rudder. Use of rudder to reduce side slip is great in theory, but who has the visual acuity and quick thumbs to utilize it effectively?
Apr 28, 2009, 02:37 PM
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In the early stages of learning this plane I am 50/50 about wanting a rudder or not. The launch benefit is great. But the difficulty in flying flat in weaker thermals might be the weak point.I hope Bruce can chime in as he has a lot more flight time and knowledge.
Apr 28, 2009, 03:08 PM
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I'm no Mark Drela but there's something about the wing section that the drag from the upward deflection of the inside aileron is higher than the outside aileron. What about washout? That may also factor into the equation?
Apr 28, 2009, 03:09 PM
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ClayH's Avatar
I'm trying to decide which way to go with my new Sirius. The boom is so stiff that I am afraid that all the side load on launch would be directed to the rudder, so I can why just having a vertical stab would be beneficial for maximizing the launch. I just wonder how much height one would be giving away by having the rudder, and if the overall thermaling capability of the plane, especially in small thermals, would benefit from rudder control.

It's hard to let go of that left thumb activity after training it for so long!

Clay
Apr 28, 2009, 03:16 PM
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djklein21's Avatar
Quote:
Originally Posted by moto0013
In the early stages of learning this plane I am 50/50 about wanting a rudder or not. The launch benefit is great. But the difficulty in flying flat in weaker thermals might be the weak point.I hope Bruce can chime in as he has a lot more flight time and knowledge.
The lack of rudder might be beneficial to you, especially since you mentioned turning "flat". Most that fly with a rudder, use it to much, and actually screw themselves into the ground. rudder should be used to fight adverse yaw, nothing more. The smaller the span, the less rudder you need.

I think 95% DLG pilots would be done a favor by getting rid of their left thumb.
Apr 28, 2009, 03:17 PM
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djklein21's Avatar
Quote:
Originally Posted by Mr._Mulligan
So, to repeat my statement from the other thread, I'm beginning to question the value of the rudder. Use of rudder to reduce side slip is great in theory, but who has the visual acuity and quick thumbs to utilize it effectively?

Yep, few do.

Most think that they should keep their wings flat, and skid around using their rudder. WRONG.
Apr 28, 2009, 03:22 PM
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I was not flying the Sirius flat at all.In fact its really hard to. Its just those low level saves that might be hard with no rudder. Regular thermals were fine once I dialed in the plane a bit. Sometimes I banked a little too much,but the plane likes that.

Clay
I say go no rudder,you can always change it later.
Apr 28, 2009, 03:36 PM
Registered User
A small clarification about the setting file for the Sirius.
The figures are from a measurement I did last year, actually the first.
The aileron up is when the aileron point up and the opposite for down. Difference between left and right is the way it became after installation. I haven't seen a need to adjust because right and left turns are completely different for my brain.

The flap position is actually right it should be about 0,5mm down because the wing is moulded in a more reflex flap position.

Use the throws as help, they will be different depending on flying style, CG position etc.

Best regards
Mattias Hammarskiöld
Apr 28, 2009, 03:45 PM
Alex Hoekstra's Avatar
I fly Twister but also have similair settings like the sirius. More aileron down then up.
I do fly with rudder so aileron input is mostly against the turn. The hooking effect that occurs helps the plane turn and circles become smaller. My rudder is set with a dynema wire and spring (d47 servo)and launches go with some wind over 70 metres. Important is a very stif boom, a good a-symetrical airfoil(HT23)at the fin and enough surface preferable in a high aspect ratio fin. I also find flying without rudder no problem at some altitude but at low hights a rudder is a must.
Apr 28, 2009, 04:00 PM
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Mattias
I am wondering what your cg is now with the 2009 version.Is it a little more forward?


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