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Old Dec 31, 2004, 07:43 PM
Hot Dawg Glider Pilot
schrederman's Avatar
United States, TX, Weatherford
Joined Nov 2002
7,821 Posts
By the way, all that red is putty. I can't help being a perfectionist... darnit!!

Jack
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Old Dec 31, 2004, 07:53 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
7,821 Posts
I sure wish these web-formatted pictures came in better. I can't do full-size photos any other way.

JW
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Old Dec 31, 2004, 10:32 PM
Registered User
Tennessee
Joined Sep 2003
2,339 Posts
The reversed stab bellcrank looks cool but I have one question. Where is the pivot rod location relative to the stab MAC?. I have used this arrangement for the last 30 years and it helps to reduce the chances of stab flutter IF THE PIVOT IS LOCATED AT OR SLIGHTLY FORWARD OF 25% MAC. That is the reason all my stabs have a slight sweep. The alternative is to move the pivot rod forward relative to the stab but that complicates the drive pin installaton. Your photo looks a lot like my 1974 Tern IV stab. I later added about 10 degrees of stab sweep to simlify construction. The photo also indicates that the bellcrank could be moved forward in the stab.
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Old Dec 31, 2004, 11:00 PM
Hot Dawg Glider Pilot
schrederman's Avatar
United States, TX, Weatherford
Joined Nov 2002
7,821 Posts
Chuck,

The stab axle is just about 50% MAC. It's about 1.5" behind the slot routed for the stab actuator wire. The stab balances on the pivot wire almost perfectly. When the belcrank is added to the mix, the stab is a touch nose heavy. Because of this forward surface cg, it should be just about flutter proof. I stiffened the control up some with an .062 aluminum belcrank that I made, and a better system of anchoring the pushrod.

A friend of mine had an LS-3 sailplane. I hated to see him come looking for assembly help because that ship had full span flaperons. Each was counter-balanced with about 50 pounds of lead to prevent flutter. Assembly was a pure SOB because the wings were SOOOO heavy.

I don't know if you remember my patriotic Legionair from Mid-South a couple of years ago, but it had a lead counter weight on a stick of cf about 1" in fromt of the aerodynamic balance portion of the surface. It works quite well. The rudder was purposely balanced exactly on the hinge.

Thanks for your suggestions to Tommy Lamnek about the stabs. You're stuff got me to think about maybe having a deadband in the stabs of the Hawk. These are NACA 008 and I'll be able to tell if there has been a problem pretty quick.

Your suggestion above sounds like you want the weight of the surface aft of the pivot. Did I not follow that thought correctly? Please explain.

Jack
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Old Dec 31, 2004, 11:28 PM
Registered User
Tennessee
Joined Sep 2003
2,339 Posts
The whole purpose of reversing the bellcrank is to get as much of the heavy structure, bellcrank, and driving rod ahead of the pivot. Reversing the bellcrank with the pivot rod at 25% MAC is usually enough for most models. On my Dragon Lady cross country model, I had to add weight to the stab rood leading edge to balance the stab assembly about the pivot to aleviate a severe stab flutter problem during rotation right after launch. Never did totally eliminage it but it did become managable. The Dragon Lady had a high aspect ration stab which may have contributed to the flutter problem. Don't use high aspect ration stabs any more. Most of my models except for the original 1974 Tern have not needed any lead in the leading edge. I have seen models with the pivot at 50% chord fail due to flutter during rotation right after launch.
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Old Dec 31, 2004, 11:28 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
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I just got a PM asking a question about the 'vented' spoilers. They are mounted on 2 ea. 1/8 size hinge points. The actual hinge line is 3/16" in front of the spoiler blade. This gives just enough room to drill these down without nicking the CF spar cap. There is a block installed under this area of sheet overhang, specifically for each hinge. The hinges are relieved by a slot cut in the top sheet from the spar cap back. They rest entirely below the wing surface. The hinge points go right down the middle of the spoiler cross section. The leading edge of the spoiler has to be chamfered to almost nothing to clear the sheeting in front of it. I'll post more on this when the covering and rigging is done.

JW
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Old Dec 31, 2004, 11:33 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
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Chuck,

On the original Hawk stabs, the pivot is at about 40%. I have heard of only one stab incident but flutter was not the problem. The stabs were strong enough that they bent the 1/8 music wire pivot.

I think as long as the stabs are balanced on the pivot, there shouldn't be a problem. I launch about as hard as anyone so I will be finding out... I hope not the hard way...

Thanks

Jack
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Old Jan 01, 2005, 11:50 PM
Jeff
USA, CA, Redondo Beach
Joined Aug 2003
645 Posts
And so the madness begins... again

Plans cut, parts laid out for matching to the plans...
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Old Jan 02, 2005, 11:47 AM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
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Looks vaguely familiar... wonder why??

JW
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Old Jan 02, 2005, 11:51 AM
Think Thermals!!!!
SoCalGliderFlyr's Avatar
Costa Mesa, California
Joined Mar 2004
2,964 Posts
It's amazing how much modeling we can get done when work doesn't get in the way.
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Old Jan 02, 2005, 11:54 AM
Hot Dawg Glider Pilot
schrederman's Avatar
United States, TX, Weatherford
Joined Nov 2002
7,821 Posts
Just a note about the new rudder... It's scrap because it's crap... Unfortunately, I covered it last night and the trailing edge wouldn't hold up to Monokote. I'll be building 2 new original rudders today to get these 2 Hawks on schedule. The first should fly next weekend... maybe!

Jack
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Old Jan 02, 2005, 11:55 AM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
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As Mainerd G. Krebs, one of my heros, would say... WORK!!!!

JW
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Old Jan 02, 2005, 01:18 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
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Well, in true Mainerd form, instead of scrapping the rudder, I replaced the trailing edge. I will cover it again and see if this result is better. I think my lightening holes did me in on the first trailing edge.

JW
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Old Jan 02, 2005, 01:52 PM
Jeff
USA, CA, Redondo Beach
Joined Aug 2003
645 Posts
Ramblings

Quote:
Originally Posted by SoCalGliderFlyr
It's amazing how much modeling we can get done when work doesn't get in the way.
Ain't it the truth! and

I flew yesterday in the Postal Woodie contest. SoCal you'da been proud. Yeah the air was fallin' up, but I speck'd out the 2m Gnome several times. Anyway that is why I only got the plans cut a bit and labeled/numbered the ribs. While some ribs have the same Id there are differing thickness'. As Ray Hayes would say, read the plans! The plans are your friend! The plans show the order of the ribs thick and thin. So I got that done and started tapering the ply box sides (FWB and RWB). Then mama said it was time to pay attention to her. Also I emailed Don about get a couple of bellcranks (one for a spare or another ship or hawk). I have two whole pieces of 1/2 x 1/8 spruce. Zero margin for error. Thats all Superior Balsa had. They ain't what they used to be. Mr B says he might have some at his shop nearby. Gotta call him and head over there. And no 1/16 x 1/4 spruce so I am hoping Jack will send me his snail mail address so I can get the plans for the new stab with a carbon rod spar and forego this spruce. Good thing I went to Superior and got the Mirage spruce a year ago when they had some. I am going to give the Heat-Tac .007 carbon ribbon a shot on the wing's trailing edge. Don't have the plans in front of me... but from some pictures there is no cap strips on the ribs. Jack would they help? Hmmm prolly not... since the rib profile does not account for the extra thickness of caps. More pain than gain I suspect.

What was the purpose of the spuce on the trailing edge? To allow for a sharp sanded TE or for strength? I think I can accomplish both with the carbon ribbon and medium CA.


OK gotta run... Today I am going notebook shopping since mine went the way of the doe doe bird when I lost my job. I am computerless, an intolerable situation. And my wife wants her computer back! That does not mean we'll buy... but we'll look. Also have to get a spyware blocker for this beast as I am tired of doing it manually.

With some luck I'll get the spars boxed and wrapped. I warn all of you, I build at a glacial pace. (And I'd like to work on a GWS Formosa as well - you know, while the epoxy sets etc... ) But unless disaster strikes, a Hawk will fly in the L. A. region at some point.

Best wishes,
Jeff
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Old Jan 02, 2005, 11:51 PM
Hot Dawg Glider Pilot
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United States, TX, Weatherford
Joined Nov 2002
7,821 Posts
Jeff, you're right, no cap strips. This wing derives it's torsional strength from 2" spacing and a deep D-box. The 1/16 X 1/4 spruce is for sharpening and strength. You can use balsa as I did bit the .007 stuff will be a bit thick. If there's time, I'd order the .2 oz. carbon mat and gut it in 1" strips, adding it to the bottom is enough to stiffen the t.e. so it can be sanded sharp. The W1 ribs come in several flavors. The W1-R is the root rib area where there's sheeting top and bottom. There are 1/16 ribs there. and the actual root rib is 1/8. All the rest of the ribs except the poly joint ribs are 3/32. The poly joint ribs are 1/8. For that joint there will be a W-1 for the inboard and a W-2 to begin the outboard. Remember to taper the main panel shear webs very slightly to match the airfoil. They will not be quite as tall at the aft edge, allowing the spar cap to be flush with the back of the spar slot in the ribs. NO VOIDS- ABSOLUTELY - between the spar caps and the shear webs.

By the way, if you decide to order 1/2" joiner from HiLaunch.com, you'll need to sand a relief in the middle of the plywood root shear webs to clear the 17/32 tubing required to accept this larger joiner... highly recommended...

Jack
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