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        Question Slow-G / Slow Stick angles?

#1 del Jan 19, 2007 09:37 PM

Slow-G / Slow Stick angles?
 
A couple of nights ago I got Ari's Slow-G rotor system built.
(Great design...)

Then I started trying to come up with a fuselage and tail
of my own design. That's when I hit the wall of my own ignorance.

I don't own a Slow Stick, and even though they are relatively
inexpensive, I have little desire to buy one. And, so, the questions...

In email, Ari mentioned the need for a bit of down thrust.
That's easy if you're scratch building. But what I still don't know
is what the angles of incidence between the wing and stab, and
the Slow Stick fuselage are.. Are they 0 / 0? Or is there
some positive incedence built in?

--del

#2 iter Jan 20, 2007 02:31 AM

Del, glad you built the kit, and thak you for moving the discussion here. I hope other member will benefit from your questions.

The Slow Stick has 0 downthrust and the stab is set at 0 incidence, but the wing has a positive AoA (front wing support is higher than the rear). The wing also has a single-surface airfoil--this increases the efective AoA further, but I don't know how much because I don't know the airfoil's polar.

The 0/x/0 setup on the Slow Stick is related more to the manufacturing process and ease of assembly than aerodynamics. Let your fixed-wing experience be your guide in choosing angles on your scratch-built model, and then multiply them by a factor of 1.5 as a starting point. The reason is the slower airspeed and higher drag of a gyro compared to an airplane.

#3 StephanB Jan 20, 2007 03:09 AM

Quote:

Originally Posted by del
A couple of nights ago I got Ari's Slow-G rotor system built.
(Great design...)

Then I started trying to come up with a fuselage and tail
of my own design. That's when I hit the wall of my own ignorance.

I don't own a Slow Stick, and even though they are relatively
inexpensive, I have little desire to buy one. And, so, the questions...

In email, Ari mentioned the need for a bit of down thrust.
That's easy if you're scratch building. But what I still don't know
is what the angles of incidence between the wing and stab, and
the Slow Stick fuselage are.. Are they 0 / 0? Or is there
some positive incedence built in?

--del

Del,
the front wingpost is 1 centimetre higher than the rear wingpost and they are about 30 centimetre apart. Downthrust is 0, which leads to nose up under full throttle. I changed that.
Stephan :)

#4 iter Jan 20, 2007 05:18 AM

Stephan, did you change it on your Slow Stick, or do you fly a Slow-G?

Ari.

#5 del Jan 20, 2007 07:10 PM

Quote:

Originally Posted by StephanB
Del,
the front wingpost is 1 centimetre higher than the rear wingpost and they are about 30 centimetre apart. Downthrust is 0, which leads to nose up under full throttle. I changed that.
Stephan :)

Good info, Stephan, Thanks!

Some quick math turned that into an incidence angle relative
to the fuselage of around 2 degrees. Does that seem about right?

So, Ari, are you saying that should be increased to around 3 degrees?

--del

#6 iter Jan 20, 2007 07:45 PM

Probably. What are you using as a reference line? I assume you'll have a built-up fuse, not a stick like the stock Slow-G?

Ari.

#7 del Jan 20, 2007 08:11 PM

Nope, Aei..

As a starting point I'm gonna make a profile fuselage.
The reference line will be 0 degrees to the stab.

--del

#8 StephanB Jan 20, 2007 08:19 PM

Ari, Del,
sorry for late answer and unclear initial post: I changed the thrustline of the motor on my Slow-Stick. Reference line for my measurement was the stick. The stab is glued flat onto the stick. I do not have a Slow-G, but i am sure, that Aris kit is a very good and easy way to get a working autogyro based on the trusty Slow-Stick. Somewhere i saw a picture of a SS based float- autogyro flying over water. That was brilliant! Can't find it now..
Stephan :)

#9 iter Jan 20, 2007 08:49 PM

Del, 3 between thrustline and stab sound like a good conservative starting point.

Stephan, Stacy Gillmore's flying boat Slow-G is here: http://www.rcgroups.com/forums/showthread.php?t=526504

Ari.

#10 del Jan 23, 2007 06:41 PM

1 Attachment(s)
Friends, I love this stuff...

Everybody seems to know what "incidence" and "downthrust"
are. That is until you get into the details...

So, do I have this right? Given the attached drawing, should I
start off with 3 degrees of positive incidence for Ari's "wing"
saddle relative to the reference line, and 3 degrees of downthrust
relative to the same reference line?

In other news:
With two other models on the bench, progress on my hack of
the Slow G has been a bit slow. Last night I hand wound a motor
from GoBrushless and got it running. This afternoon I did a bit
of research and did some more sketches. At last, I think I "see"
the model I want to build.

But, we'll see..

--del

#11 iter Jan 23, 2007 08:09 PM

1 Attachment(s)
Del, first off, and I imagine you figured it out already, you don't need the long 2"x3/16" plank if you're not trying to make the wing interchangeable with the stock slow stick wing. Also, the wing panles themselves are triangular in cross-section (3"/8x2"), so the shafts lean back an extra 10.5, for a total of 12.5. This is a bit lower than optimal--the concensus seems to be around 15. So you want to sit your wings at about +3-5 to the reference line.

Center of pressure is relatively high (at the rotor hubs), so you want to use generous downthrust to avoid a pitching-up moment with throttle. It will depend on how low your motor sits. I'd aim for the thrustline to go somewhere halfway between the vertical CG and the center of pressure.

Hope this helps.

Ari.

#12 del Jan 24, 2007 10:33 PM

1 Attachment(s)
Quote:

Originally Posted by iter
Del, first off, and I imagine you figured it out already, you don't need the long 2"x3/16" plank if you're not trying to make the wing interchangeable with the stock slow stick wing. Also, the wing panles themselves are triangular in cross-section (3"/8x2"), so the shafts lean back an extra 10.5, for a total of 12.5. This is a bit lower than optimal--the concensus seems to be around 15. So you want to sit your wings at about +3-5 to the reference line.

Center of pressure is relatively high (at the rotor hubs), so you want to use generous downthrust to avoid a pitching-up moment with throttle. It will depend on how low your motor sits. I'd aim for the thrustline to go somewhere halfway between the vertical CG and the center of pressure.

Hope this helps.

Ari.

OK, Ari, Good info! The rotor shafts need to be tilted back around
15 degrees. But I'm still a bit unsure about your estimates for
downthrust...

Normally I'm reluctant to show anyone a sketch of a model I'm
working on. It could change as I work on it. It might not fly at all...

But I felt the need to attach the image in order to clarify your
notion of downthrust.

If I start with my sketch, make a guess at the CG location, and
what I think your notion of CP might be, I come up with something
that looks a bit extreme in terms of downthrust.

What do you think?

--del

#13 iter Jan 25, 2007 02:13 AM

1 Attachment(s)
Del, I realize the model may change, but I love this layout! Captures the essence of a period autogyros really belong in.

The downthrust does look extreme, but that was what I suggested. My experience is mostly with stick fuses and not enough downthrust, so perhaps I'm overcompensating. Maybe we can get Mickey to weigh in on this? He's much better than I am at explaining why these things fly the way they do.

Keep in mind that if you mount the wing flat like your sketch suggests (I don't know if that is juat a simplification you made, or you intend to have disks to rotate in a plane parallel to the refence line), your flight attitude will be 15 nose-high, almost the attitude of the model when it sits on its gear. If I rotate your sketch that way, the downthrust doesn't seem as extreme.

Ari.

#14 mnowell129 Jan 25, 2007 05:46 AM

1 Attachment(s)
Quote:

Originally Posted by iter
Del, I realize the model may change, but I love this layout! Captures the essence of a period autogyros really belong in.

The downthrust does look extreme, but that was what I suggested. My experience is mostly with stick fuses and not enough downthrust, so perhaps I'm overcompensating. Maybe we can get Mickey to weigh in on this? He's much better than I am at explaining why these things fly the way they do.

Keep in mind that if you mount the wing flat like your sketch suggests (I don't know if that is juat a simplification you made, or you intend to have disks to rotate in a plane parallel to the refence line), your flight attitude will be 15 nose-high, almost the attitude of the model when it sits on its gear. If I rotate your sketch that way, the downthrust doesn't seem as extreme.

Ari.

I've found that you need about 110 between the thrust line and the rotor. The model flies with the rotor tilted back about 15. It's just then a matter of fitting a fuselage that flies level placed over the rotor/motor arrangement, then selecting landing gear to hold roughly that layout or slightly nose high for takeoff.
If you build the model in the sketch it will probably fly but with the tail very low.
GT17 side view for perspective.
mickey

#15 del Jan 26, 2007 06:11 PM

1 Attachment(s)
Quote:

Originally Posted by iter
Del, I realize the model may change, but I love this layout! Captures the essence of a period autogyros really belong in.

The downthrust does look extreme, but that was what I suggested. My experience is mostly with stick fuses and not enough downthrust, so perhaps I'm overcompensating. Maybe we can get Mickey to weigh in on this? He's much better than I am at explaining why these things fly the way they do.

Keep in mind that if you mount the wing flat like your sketch suggests (I don't know if that is juat a simplification you made, or you intend to have disks to rotate in a plane parallel to the refence line), your flight attitude will be 15 nose-high, almost the attitude of the model when it sits on its gear. If I rotate your sketch that way, the downthrust doesn't seem as extreme.

Ari.


Ari, thanks for the kudo's on the general sketch. It's very loosely
based on the Gee Bee Model B. I like it too...

And yes, it's just a sketch. The rotors will be tilted back at the
"wing" mount to give the rotor shafts about 15 degrees from the
reference line.

And so, yet antother attached drawing...

It still looks a bit extreme to me. And should the CG be forward of
the rotor shaft reference line?

Your thoughts, and other's knowledge, as always will be appreciated.

--del


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