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Old Mar 07, 2015, 09:33 AM
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Michael V's Avatar
United States, CA, Torrance
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Originally Posted by leadfeather View Post
I've thought about this a bit. I've wondered about two things:

1) Does airfoil drag play a larger role (in lift/drag) as the Re gets very low?
2) Do the computer models do as good a job in performance predictions as the Re gets very low?
So
In general induced drag (what you called airfoil drag) gets higher and much more preponderant as airspeed reduces. Thus it is not so much a question of Re but of airspeed. Of course lower airspeed means lower Re.
It's not a simple problem, so I'd say at the "scale" (combination airspeed , weight and dimension) we fly induced drag is pretty important.

Computer models in general have more problems with discrete events like flow separation and turbulent behavior (vortices), so I don't think low Re is too much of a problem., even though low Re can create separation issues However again scale plays a role, at the scale we fly let's say for example that skin wrinkles or skin roughness is pretty important in terms of dimensions (0.1mm on a wing thickness of 5mm is a high ratio comparatively speaking) and as far as I know most if not all computer softwares do not factor skin roughness for example. So while the prediction may be good and "accurate", it would take very little in difference to make them "inaccurate' or more precisely not representative.

Not much help I know, maybe someone else has other insights.

AG16 is much better than AG38 in efficiency (L/D in particular max L/D) but from the polars you also see that as Re diminishes, L/D diminishes which is the result of induced drag increasing relatively as speed drops.
Again I understand the question was whether AG16 with slight reflex is better. Difficult to know without plotting (L and D will both change (diminish))
And remember this is all more complex, as D changes for a given plane, then speed changes, thus Re changes, and then L/D changes. There is never one parameter alone. By changing reflex, you're in essence changing airfoil altogether.
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Old Mar 07, 2015, 04:50 PM
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west suburb of cleveland oh
Joined Nov 2004
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leadfether
what is the length of the ultra light fusion fuse. i remember you rebuilding it but i am going blind trying to find that post.
thanks don
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Old Mar 07, 2015, 05:19 PM
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Quote:
Originally Posted by dvk44039 View Post
leadfether
what is the length of the ultra light fusion fuse. i remember you rebuilding it but i am going blind trying to find that post.
thanks don
Don,

I can't find an actual dimension for the ultralight fuse length. I remember it was about 2 inches longer than the original fuse...just to get the glider to balance. All the light weight electronics adds up to very little weight in the nose.

On the electronics, the one thing I would change is to go to a larger servo for the elevator for the ultralight build. I think trying to have enough torque and to get +-90 with a d47 is probably asking too much.

I'll keep hunting for the fuse length.

Dan

ps I got lucky and found the template for the ultralight fuselage. It is 20.5" long minus nose cone.
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Last edited by leadfeather; Mar 07, 2015 at 05:37 PM.
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Old Mar 08, 2015, 11:13 AM
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west suburb of cleveland oh
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thanks dan
got the carbon parts and laminate on order.
don
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Old Mar 10, 2015, 08:27 PM
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push rod test

Today was beautiful ... sunny, warm, light winds; quite a change from full blown winter a week ago.

I've had my Fusion ready for testing the pushrod Mad Stab for some time now. Today was perfect for this test.

The idea is that a push rod is much easier to set up and some people just don''t like pull-pull strings. I wanted to see how well the push rod would work and if it would still allow multi-flips. It worked great! Upright multi-flips were really good as before, control for normal flying is very good; the set up is very easy. The trade-offs are a slight weight penalty and 90 up only... no 90 down. Also the resolution was pretty good. With 100% expo it was quite flyable on high rates.

I was able to get well past 90 up, so I can reduce the servo arm length a little; still get 90 up and improve the resolution further.

I'm gonna keep this Fusion as a motor glider. I need to clean up the front end and add a faring around the motor.

Fusion Push Rod Testing (3 min 27 sec)
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Old Mar 10, 2015, 09:25 PM
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United States, CA, Torrance
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Nice!
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Old Mar 11, 2015, 10:25 AM
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United States, CA, San Jose
Joined Aug 2012
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Just found this thread this morning. Awesome! I have to build one. I was trying to design my own one of these ladder part of last year but was too lazy. Drew plans, but that is as far as I got. LOL
Excited about this plane. It would be perfect for the slope by my house!

Way to go! I love the design.
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