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My elevators stay at whatever position I leave them. I had an A&P visit me and check out the plane and he was of the opinion that the elevators should drop down due to its weight on the ground. I measured the stick forces and these were between 1.5 - 2 lbs for both the elevators and the ailerons. Since the elevators are balanced I presume they should stay where ever they are left. Comments please?
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This from the assembly manual :
“when the word “balance†is used, that means putting enough lead in the balance area (the part sticking ahead of the hinge line) so that, when the surface has paint and fabric on it, it will balance horizontally (push it down and it comes back up and vice versa). â€
Mine currently stays neutral where I put them, but I’m in the build process with no paint on yet.
I’m still getting some friction through the joystick mounting. If I tighten the bolts (those pesky difficult to access ones) it appears to be slightly deforming the bushing and adding friction.Last edited by Nev; 10-31-2020, 06:01 PM.Nev Bailey
Christchurch, NZ
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They should stay where you put them. Given the substantial friction in hinges and cable pulleys, it would take quite a bit of imbalance for them to do otherwise.Comment
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That is my understanding as well. And a little overbalance is preferred over under balanced, if you have to err. I remember that from many years ago, but I think it was also repeated on this forum.Comment
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Having set the rigging on several Bearhawk’s
I offer the following:
1. An individual elevator supported on the hinge line should go counterbalance down toward earth.
2. An elevator assembled to the horizontal tail, joined together at the control cable attach arms, with the horizontal tail strut and flying wires set to flight tension.
Elevator should drop counterbalance nose toward earth freely. If not something is miss aligned and or binding.
3. The control stick assembly should rotate freely and free fall to the stops when released.
4. After attachment of the elevator control cables and during tensioning, some light friction is expected.
That said I am still able to achieve elevator counterbalance down to the stop with only a slight initial
input from static condition.
Much more friction than that will be difficult for stability to return to pitch airspeed and causes the autopilot and
pitch trim to hunt.
Pilot also smiles better. : )
Kevin D
# 272
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That is a great description, especially the details about have strut, flying wires, and control wires being tensioned, and making sure friction is minimized AFTER all those are accomplished. -
Agreed, good explanation. One other note, on my kit I had to carefully clean out the hinges to achieve the condition described. I little grit or paint over-spray in the hinge is enough to cause objectionable friction. I flushed them out with a syringe and mineral spirits while working them back and forth.
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Mine stay where I put them, unless the wind is blowing
Same with the other Bearhawk / Cessna / etc aircraft with balanced elevators which I have seen.
If they tend to drop down then they are over/under balanced. Bob's design calls for balanced, not "almost balanced". Maybe the person you were talking to didn't clearly communicate what they meant.Last edited by Battson; 11-01-2020, 07:28 PM.Comment
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Thanks for the detailed steps Kevin.
I disconnected the elevator cables from the bell crank and started checking through the list. With everything disconnected my setup passes test 1, but am stuck on step 2.
In step two after attaching the tail strut tightening the flying wires to flight tension, 3/8" movement with 15lbs force, the elevators become stiff and do not drop down easily.
Since there are four places where the horizontal stabilizer is being supported, it is surely an imbalance among these four?
I have a sure way of checking the tension on the top flying wire, but not sure how to make sure the strut and the bottom support corresponding the top flying wire can be accurately tightened.
Wondering if it would make sense to separate the two elevators at the control cable attach arms, get the two elevators properly working independently and then join them at the control cable attach arms? This way I can at least isolate one of the four variables
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You are going down the correct isolation path.
A few pointers.
Any miss alignment that causes a side load on the relationship between any of the hinges will bind.
The elevators should bolt together at the control horn.
if this results in the spacing between the hinges binding on the the sides you will need to place a shim between the two horns or a shim between the horizontal tail and the fuselage when the tail is slid on.
Both the “Spar†tube of the horizontal tail and the elevator need to be straight, in vertical and horizontal.
With everything as straight as possible. Secure the outer hinges first, look and see if the holes on the inboard strap hinges are in line and will accept a bolt.
if parts are not aligned there will be binding.
repeat by bolting in the inboard and checking the outboard alignment and friction.
You may find that the strap hinge holes need a bit of love to align. I had one scratch built plane, nicely done, that required doubler washer welded to strap and re drilled, hole location was out 3/16 of an inch.........
Hope this helps sort out the process.
Kevin D
# 272
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Great description On how to get smooth elevator action Kevin!
Like Battson, I followed the plans and weighted the elevators so they stay where put. A bump gets them moving and they coast for second then stop. Mine might be a smidge under-balanced, I can’t remember for sure, but I wanted keep the tail as light as possible for CG reasons. With that long of an arm ounces matter.
I use grease in my hinge points. I currently just use a disposable chainsaw nose sprocket grease gun. I’ve thought about getting a refillable grease gun and using the same grease I use on my boat trailer wheels bearings but so far I haven’t seen a need.
What is the reasoning for overbalancing the elevator?Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.Comment
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I added small grease fittings to my hinges as any grit will cause binding. I emphasis the comments about alignment. I built a long straightedge today makes sure the elevators are in a perfect line with tail wires brought up to tension. There is not much margin for error in the tail alignment otherwise the elevator will bind.Last edited by spinningwrench; 11-03-2020, 07:56 PM.Comment
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There are some great threads in the archives. Sometimes they are in threads titled something different. Jared does rename or move stuff occasionally. I think this one might be a good one to make easier to search for.Comment
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Since this thread has been used to discuss excessive elevator friction...i hope someone has run into this problem and solved it.
I'm in the final assembly stage of the build, and was unahppy with the amount of stick force required to actuate the elevator. With the flying wires and control cables torqued to spec, I'm seeing 4-5 lbs force at the stick to actuate.
I think ive isolated the problem to the elevator hinges. If I simply loosen the nuts on the 4 elevator hinge bolts, stick force drops down to 1-2 lbs (stick assembly and pulleys are smooth as butter). If I keep those nuts tight and change anything else, there's still 5 lbs required on the stick. The hinges are super smooth when removed from the stabilizer.
The only issue I can fathom that would be exasperated by tightening the hinge bolts is that one or more are very slightly misaligned in the roll axis. This could be addresses by slightly widening the bottom hinge hole, but I wanted to solicit input from the forum before doing anything rash. Thoughts?
We are aiming at an FAA inspection and first flight in April.
-Nic
4-place #1217Comment
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Nic,
Just to elaborate a bit on my previous posts and Johnathan's comments.
It is critical that the fixed horizontal stabilizer be square and straight on the aft main spar tube.
The rear spar tube must be free from dihedral and anahedral as well as forward and aft sweep.
Loosen all the nuts on the 4 strap hinge locations.
Loosen the lower flying wires and adjust the upper wires until the fixed horizontal stabilizer is level and true by adjusting the Upper Streamlined wires.
Slacken the elevator cables.
Then raise and lower the elevator by hand, looking for any indication that the fixed horizontal stabilizer is warping or pumping up and down as the elevator is moved stop to stop.
Look carefully at the strap hinges individually, top and bottom for any rocking / sliding / translating motion. This should lead you to the point that is out of alignment.
As Johnathan noted it may be necessary to place a thin shim or washer between the horizontal tail and the faying surface of the strap hinge. Might be on the top or bottom of the horizontal tail.
On occasion I have had to slightly elongate a strap holes, fore and aft in an oval fashion on one hinge point to eliminate bind. You will know which one, which direction when removing the bolt and seeing that the binding is gone and how far the offset is from the bushing hole in the fixed horizontal stabilizer.
Not uncommon for me to spend a day sneaking up on this............
I find that STP is a great lubricant for the strap hinges and stick bushings. Stays put and has good capillary action to migrate all around the part.
Kevin D.
#272
KCHD
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