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Old Mar 16, 2014, 12:15 AM
Gary
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USA, CT, Sandy Hook
Joined Dec 2009
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Sommer Monoplane 11 inch span

Newest project is a repeat of a model that I built in college. At that time it was a rubber powered Sommer Monoplane. I cannot remember where I got the plans, but it had about a twenty inch span – long gone to that model plane place in the sky. This time I am going much smaller with an 11 inch span and of course r/c. Since I tend to build a little heavy we will see if I get it off the ground.

I started from a Bill Hannon plan and scaled it to a 11 inch span. This equals the span of my Sperry Messenger but that had two, squared tipped, wings of course so the wing area was substantially greater. The Sommer will have a wing area of approx. 26 sq. inches. I will be attempting actuators for this one which will be a first for me. Not decided yet on a power plant but am leaning towards a brushed motor and prop from the Blade Nano QX (if the plane is not too heavy). Perhaps after I see how heavy I end up on the airframe.

The wing became a real mixed media project. The very skinny curved ribs I felt would be too fragile to cut as the balsa grain would “run out” of the rib shape. So I took the rib cross section, replicated it for sufficient quantity, took a sheet of 1mm depron – laminated tissue to the foam, and ran it right through the ink jet. Then I simply cut the ribs out with a scissors. I did not bother to remove the tissue. 1/64” ply was used for the root ribs and where the outer flying wires will be anchored. The leading and trailing edges were made of bamboo. This goes with my general style of “if it isn't heavy enough – add more!” The tips were interesting. After some thought and examination of the plan I thought that I could print a rib that was stretched to be the tip outline. Some estimation resulted in splitting the rib into two sections and applying varying amounts of stretch. The advantage was that the tip followed the curvature of the wing precisely. The tip “ribs” were then cut out of 1/64th, dropped in boiling water and wrapped around a quick balsa form. After installation the dremel sanding drum was used to thin the rib. Sounds like a lot of steps but actually worked well and was quick – not including the overnight on the form. Carbon rod was used for the top spar. I am going from memory here but I think I used .020” or .025”. The bottom spar was made from balsa (about time!).
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Old Mar 16, 2014, 11:06 PM
Gary
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USA, CT, Sandy Hook
Joined Dec 2009
795 Posts
Framing came up to 4 grams but the covering will add that much again I'll bet.
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Old Mar 17, 2014, 07:56 AM
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Centreville,VA,USA
Joined Apr 2001
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Looks cool and looks like a lot of work...Keep it going!

Pete
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Old Mar 30, 2014, 10:14 PM
Gary
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USA, CT, Sandy Hook
Joined Dec 2009
795 Posts
Still moving forward. Working on the radio installation. This is my first time working with actuators and I am definitely struggling. I am using thread for a pull/pull configuration and have redone it several times. I keep seeming to get the tension too tight and the actuator will not provide enough oomph. Used figure 8 thread hinges - getting close.
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Old Mar 31, 2014, 10:04 AM
I love my ID.
Fairfax VA
Joined Aug 2004
649 Posts
I feel your pain. Won't micro vapor brick fit in that fuselage?
I am avoiding actuators at all cost. With micro vapor bricks and lighter modules, I don't see any point of using actuators unless the wingspan is around 8 inch or less or target weight is less than 10 gram. Even if you make the rigging work, maintaining the tension before every flight will be a major pain.
How much is the weight saving with actuators versus using Micro vapor brick?
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Old Mar 31, 2014, 10:18 AM
I love my ID.
Fairfax VA
Joined Aug 2004
649 Posts
following is the link to my Mrs. Lil

http://www.rcgroups.com/forums/showthread.php?t=1184647

I sort of used pull pull system. I removed centering magnet from the actuator and installed centering magnet on the control surface.
When actuator moves to one direction one of the string is not in tension. This was the only way to make the control reliable i could think of.
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Old Mar 31, 2014, 07:32 PM
Gary
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USA, CT, Sandy Hook
Joined Dec 2009
795 Posts
Jing you are right. This plane at 11 inch is simply too big for the actuators that I am using. I finally got the rudder somewhat o.k. and started on the elevator only to see that the actuator is not strong enough to keep the elevator centered. It falls under it's own weight. I am done - ripping them out and switching to servos. I can't fit any brick in the fuselage - even my supermicro gear, so I will keep the DT receiver and go with discrete linears.
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Old Mar 31, 2014, 08:26 PM
I love my ID.
Fairfax VA
Joined Aug 2004
649 Posts
I bet you will find the best way as you did on past projects. What actuator did you use? For that elevator I would have used mini (not micro!) from plantraco with pushrod system if the linear servos were not available.
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Old Apr 01, 2014, 09:05 AM
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I can't fit any brick in the fuselage - even my supermicro gear, so I will keep the DT receiver and go with discrete linears.
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Old Apr 01, 2014, 09:22 AM
Gary
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USA, CT, Sandy Hook
Joined Dec 2009
795 Posts
Quote:
Originally Posted by jingjingjing View Post
I bet you will find the best way as you did on past projects. What actuator did you use? For that elevator I would have used mini (not micro!) from plantraco with pushrod system if the linear servos were not available.
You are probably right. I used the micro on both surfaces. But I don't understand the mini actuator. Once you are over one gram you might as well use a linear as you mentioned.
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Old Apr 07, 2014, 01:54 PM
Gary
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USA, CT, Sandy Hook
Joined Dec 2009
795 Posts
Having abandoned the actuators I wanted to try learning from Shagrug and applying his lightening techniques to some linear servos. I am not as successful as he was but managed to bring down the weight from an initial 1.3 grams to 0.8 grams. A link to his thread on this topic is:

http://www.rcgroups.com/forums/showt...897330&page=25

I highly recommend reading the thread - some great work there. My electronics will now total slightly under two grams. Not quite as good as the actuators (where I would have had to move to heavier ones anyway) but damn close.

I really enjoyed modding the servos and found it to not be very hard at all - just need a little patience. (Admittedly my weak point!)
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Old May 04, 2014, 06:00 AM
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Sweden
Joined Oct 2002
821 Posts
And... (looking good) Hows it coming along???
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