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Old Nov 22, 2011, 11:43 PM
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How fast was it going ? Define " overspeeding "
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Old Nov 23, 2011, 02:20 AM
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Yes, I am wondering too.
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Old Nov 23, 2011, 02:27 AM
yyz
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Quote:
Originally Posted by DEAN GRADWELL View Post
Day one at Cal Valley I displayed complete lack of airmanship. Overspeeding the glider to destruction.

At the time I just wanted to gather the parts throw them in the box and try to forget about it.

At home I began salvaging components and discovered what actually happened. What happened to my glider is what I believe has destroyed most if not all high altitude blowups.

The left wings servos (flap and aileron) and control horns were ripped free of the wing structure.
Flutter did it and it was the first thing that occured.

After the wing exploded it bent backwards breaking the fuselage in three pieces. The left stab was sheared off the aft fuselage section.
Regards Dean
I highly doubt it was faulty airmanship on your part, Dean. You're a great stick.

Have you given any thought to sacrificing a bit of aerodynamics in favor of longer control arms at both the servo and control surface end? That would give you more leverage and possibly prohibit or delay the flutter.

Kind of stating the obvious but I've pretty much given up on the "hidden" linkages on my planes especially on the ailerons and flaps.

Rick Spicer will likely scoff but I wonder if that airfoil needs some zigzag tape (to trip the airflow) in front of the hinge lines. Easy and wouldn't hurt to try.

That buzzing and sudden breaking up have to be the two worst sounds known to man,

Mike
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Old Nov 23, 2011, 11:35 AM
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United States, CA, Elk Grove
Joined May 2005
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MXC Case

Say Dean, Your plane case is a work of art. I also like your assembly / balance stand. very well thought out and simple.

Do you have any scetches or plans ?
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Old Nov 23, 2011, 03:10 PM
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Mike,
The poor airmanship was in decision making.
Six miles from finish we figured we needed 480 meters to make it home. Was in a nice thermal so decided to tack on a bit of altitude and left at about 680 meters. Left the thermal heading for home and in lift for the next three miles. We were quickly cruising at 60 mph in the Jeep. After three miles of this I decided I needed to go faster. I kept pushing the trim forward as I couldn't detect the glider speeding up, remember I'm pretty high up. Next thing I see the glider is going really fast just before it blew up. GPS datalogger does not show airspeed just GPS speed so I think the highest it recorded was around 70.

The control horns on the broken glider were 30mm in length. The glider with the MKS servos are 20mm in length. This is the shortest I have tried. This measurement is to the top surface of the wing as that is where it is hinged.

You mentioned longer servo arms would be better. I have been doing the opposite with shortest possible servo arms and surface control horns at least twice as long and usually longer. Am I wrong?

Regards Dean
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Old Nov 23, 2011, 03:39 PM
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United States, CA, Diamond Springs
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Quote:
Originally Posted by DEAN GRADWELL View Post
Mike,
The poor airmanship was in decision making.
Six miles from finish we figured we needed 480 meters to make it home. Was in a nice thermal so decided to tack on a bit of altitude and left at about 680 meters. Left the thermal heading for home and in lift for the next three miles. We were quickly cruising at 60 mph in the Jeep. After three miles of this I decided I needed to go faster. I kept pushing the trim forward as I couldn't detect the glider speeding up, remember I'm pretty high up. Next thing I see the glider is going really fast just before it blew up. GPS datalogger does not show airspeed just GPS speed so I think the highest it recorded was around 70.

The control horns on the broken glider were 30mm in length. The glider with the MKS servos are 20mm in length. This is the shortest I have tried. This measurement is to the top surface of the wing as that is where it is hinged.

You mentioned longer servo arms would be better. I have been doing the opposite with shortest possible servo arms and surface control horns at least twice as long and usually longer. Am I wrong?

Regards Dean
Dean,

An MXC can flutter at 70mph????

Steve
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Old Nov 23, 2011, 04:13 PM
Entropy is happening!
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Australia, NSW, Bellingen
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Quote:
Originally Posted by DEAN GRADWELL View Post
....................
You mentioned longer servo arms would be better. I have been doing the opposite with shortest possible servo arms and surface control horns at least twice as long and usually longer. Am I wrong?

Regards Dean
My understanding is similar to yours Dean. Surely, this provides a "geared" up or increased mechanical advantage of the servo and reduced backlash effect (mostly referred to as "slop").
Any increase in the servo arm length for a fixed or given control surface horn length will decrease these advantages and make the set up more prone to flutter.

Can someone confirm or contradict this reasoning?

And flutter at 70 mph.?? How do the DS gliders regularly fly and many times this speed without flutter?

Jim.
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Old Nov 23, 2011, 05:13 PM
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Of course it won't flutter at 70. I have had this 3 year old plane at 90 -100 several times. Also lost sight dozens of times in 3 years and who knows how fast it could of gone.
As I said this was what the GPS logger recorded as I remember. Heading rapidly downhill there is very little forward progress. Have no idea what actual airspeed was.

Regards Dean
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Old Nov 23, 2011, 05:22 PM
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Quote:
Originally Posted by DEAN GRADWELL View Post
Of course it won't flutter at 70. I have had this 3 year old plane at 90 -100 several times. Also lost sight dozens of times in 3 years and who knows how fast it could of gone.
As I said this was what the GPS logger recorded as I remember. Heading rapidly downhill there is very little forward progress. Have no idea what actual airspeed was.

Regards Dean
Your control surfaces and linkages are always tight on your MXC's so in high speed final dash flight flutter seems unlikely unless something let go in one of the linkages.

My close up look at some of the high altitude MXC wrecks still leads me to suspect the fuse boom ahead of the fin. Even RnR is now beefing them up in that area with some carbon from what I understand. maybe flutter in the empennage?

for servos the hyperions sure look good. can take LifePo voltages too. some people are using UBEC's for voltage regulation but thats just one more point of potential failure in the chain of components

Steve
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Old Nov 23, 2011, 07:29 PM
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Dean

I really like the way you reinforced the control horns. Regardless of whether or not the horns need the reinforcement, I think what you have done will reduce drag.

John
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Old Nov 23, 2011, 08:15 PM
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Steve,
The tail thing is why I'm revisiting this with everyone. I even reinforced with carbon #4, the one I finished Cal Valley with.

While removing the components from the wreck (#4) is when I discovered that the servos and control horns were ripped from the left wing. The left wing came down in two pieces, the right wing stayed attached to the fuselage and maple leafed down.

Flutter is a high speed thing so in my mind it was the first event.

Perhaps the tail flexed causing flex in the fuselage and the glider to tuck resulting in an overspeed, but the glider came apart from flutter. I'm sure of it.

My linkage tightness is probably average not great. I didn't CA pivot points but I do now. After being a licensed aircraft mechanic for almost 50 years dribbling goo on a linkage was something I couldn't come to grips with.

Rich Spicer does the CA trick and Z bends and he goes very fast with his glider with never a blowup.

So anyway my effort is going in the wing linkages and servo mounts.

Regards Dean
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Old Nov 23, 2011, 10:19 PM
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Go have a look in the dynamic soaring threads for servo builds. A great start would be Joe manor D80 or d60 build thread. I always secure to 3 points if I can. Top skin, bottom skin, and spar. Small servo arm & very tall carbon horn ! Don't worry about drag as the cause of flutter is far worse than any minute drag will cause. . . IMHO and would love to come there one day and do some X country with you guys. Very cool
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Old Nov 23, 2011, 11:18 PM
Entropy is happening!
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Australia, NSW, Bellingen
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Top hinged & top driven?

From the picture in post #57, it looks like your control surface is top hinged and top driven. Is this the case Dean?
If so, I assume you must have a reason for this. But that way you need a longer control surface horn for a given drive ratio. With the horn on the opposite side to the hinge, the depth of the LE of the surface is added to the horn length. So it can be shorter for the same mechanical advantage etc.

Forgive me if I am explaining something all too obvious, or if I have mis-interpreted your pics and description.

Jim.

edit: I have just had another look, and it seems that is already top hinged/bottom driven. Please ignore the above and delete if necessary.
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Last edited by Jim.Thompson; Nov 23, 2011 at 11:21 PM. Reason: Additional information.
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Old Nov 24, 2011, 12:57 AM
Nathan Miller
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Peachtree City GA
Joined Apr 2007
137 Posts
On my 100k flight in May I got going downhill Really Fast before I realized, but pulled out with no problems - GPS indicated about 100 mph. I like the carbon reinforcement on the control horns, I'll likely add this to my ship. Thanks for sharing the info, sorry you lost a plane Dean...
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