+++ #1837 From: PFflyerz Subject: [Bearhawk] elevator trim Was working on my elevators today and came across a problem that I will pass along to others so they don't make the same mistake. Bob doesn't specify what size tube to use to make the trim tab hinges, but measuring on the plans I came up with a 1/4 inch OD. X .035 ID will fit a 3/16 inch pin. Jigged and tacked my first hinge, only to discover that it wouldn't pivot. Idiot, I had tacked both sides of each hinge tube. On my second attempt I tacked, then welded it properly. All was well until UPS brought the pins I had ordered. Seems the head of the AN pin is 5/16 dia., so it won't fit between the T5 tubes. A 5/16 OD X .065 ID tube will also fit a 3/6 pin, so I guess I will start from scratch tomorrow. +++ #1838 From: Float-by Shooter Subject: [Bearhawk] Re: elevator trim > tacked, then welded it properly. All was well until UPS brought the > pins I had ordered. Seems the head of the AN pin is 5/16 dia., so it > won't fit between the T5 tubes. A 5/16 OD X .065 ID tube will also fit > a 3/6 pin, so I guess I will start from scratch tomorrow. Is there any reason the head of the pin could not be turned/ground down enough that it would fit, so you won't have to redo your parts? Seems like the head only needs to keep the pin from drifting out, and shouldn't be under a lot of stress. +++ #1839 From: William & Delinda Johnson Subject: [Bearhawk] Re: elevator trim I intend to use a clevis Pin. Page 134 of Wicks. You may still need to grind a slight amount off the head but it is lighter and easier to assemble. See link for picture (cotter pin not installed). http://home.fuse.net/wjohnson/Mvc-737f.jpg +++#1840 From: William & Delinda Johnson Subject: [Bearhawk] Re: elevator trim Pat, I used the 5/16x.065. The .035 is kind of light. I also needed to grind a little off the clevis pin head. Don't feel bad, I also welded both sides on my first attempt! I felt really silly - luckily I only had tacked together the hinge at that point. +++ #2329 From: Russ Erb Subject: Apr 2000 Engr Notice Mike Meador--We need a clarification on this. The engineering notice in the April 2000 Bear-Tracks talks about moving the outboard elevator hinge 4.0 inches outboard. That part is clear. However, cross referencing the drawing with my plans (#164), I notice that on my plans there was a T5 tube running from the outboard elevator hinge directly forward to the leading edge. However, this tube does not exist in the drawing in the newsletter, and no mention is made of its deletion. Mike--would you please confirm that this tube has been deleted? +++ #2350 From: Mike Meador Subject: Re: [Bearhawk] Apr 2000 Engr Notice Yes - That tube has been deleted. The hinge point is close enough now to the end of the stab rib that the tube is not needed. One other question that we got this week was if you could just move the hinge point out and leave the wires where they were. We have seen a few airplanes like this and you can do it if you want - the only problems are now you have two "unsupported" working surfaces and you will have more drag by not incorporating the single nut and bolt to hold the hinge and the flying wires. It might not look good either - Like we said - it is not a mandatory change - build it one way or the other don't try to do both. +++ #6086 From: slester@m... Subject: Welding elevator hinges I'm part of a group building a Christavia Mk1, but joined this egroup because I'd like to build a Bearhawk someday and also because the fuselage construction methods of the two planes are the same (welded 4130) and this group has so many active members. After a couple aborted tries to weld the elevator hinges, here's what worked real well for us last night: We built the structure of the hor. stab. and the elevator before welding the hinges on. That may have made the whole process harder or easier. Maybe next plane I'll do one each way. We laid the stab. and elevator out on a flat worktable with a firebrick under each hinge area and an additional brick to support the leading or trailing (non-hinged) edge of each. We used scraps of sheet, plate, tubing, etc. to position the pieces so as to keep the centers of the different sized spars (1" on stab, 7/8" on elevator) at the same height and the proper spacing apart (we used 5/8" with 3/8" tube hinges). We slid the hinge pieces onto a piece of 1/4" threaded rod -- one piece long enough to go through all of them. Next time it will be long enough to reach past the end of the stab/elevator as well. We supported the threaded rod on a piece of 3/8" tubing to center it on the 1" stab. spar. We used scraps of 1/8" plate to center the 3/8" tube hinge in the 5/8" gap. We started with the single hinge piece on the elevator and welded one to the tube its full length, bridging the gap as we welded. We then verified a small (.020 inch or so) gap between that piece and the ones on either side of it and welded them to the stab spar. We did one side (top or bottom) of all 6 pieces. Oh, yes, I forgot to say that we despaired of ever lining up 3 sets of these things and after verifying that the Cub and Citabria each have only two hinges per surface, chose that for our plane as well. Anyway, after doing one side of all of them, we noticed that the threaded rod had bent at one end due to the one-sided heating, causing one of the end hinge sections to point off at an angle. We heated that weld up again and pried that hinge section into line with a screwdriver. Then we turned the whole thing over and welded the other sides of all 6 hinges. It's pretty free beyond the range of motion of the elevator, and after we file or ream out a little scale and some weld penetration, I expect them to very smooth hinges. Note: it was still pretty tough to get the threaded rod out. Next time, it'll be long enough to put a pair of nuts on the outside end and screw it out rather than having to use vise grips while bending it out of the gap and pounding on the other end :-) Hope this helps someone who hasn't done this part of their project yet! Steven Estergreen +++ #6576 From: "Russ Erb" Date: Mon Jun 18, 2001 7:55 pm Subject: This is a question for Bill Johnson, but should be of interest to many Bearhawkers. Bill installed a universal joint between the trim tab torque tubes on the two stabilizers. I assume that his idea was to allow for slight misalignments between the two tubes. My questions to Bill are: 1. Was this your reason, or was there some other reason? 2. Would you recommend this to other builders? 3. If so, where did you get the universal joint that you used? Russ Erb +++ #6587 From: "William & Delinda Johnson" Date: Tue Jun 19, 2001 6:53 pm Subject: RE: [Bearhawk] Well, that was my intention. Probably not worth the cost or effort however. My recommendation - just do it as the plans show . . . 023 is still progressing slowly. Summer family events, vacation, etc have slowed me down. I will post some more pictures later. Off to build. Bill, making slow progress, Johnson +++ #6885 Date: Wed, 18 Jul 2001 21:14:54 -0700 From: Russ and Penny Erb erbman@ Subject: Elevator Hinges Been working on welding the elevator hinges. Of course, one of the big problems to deal with is the formation of scale inside the hinge tube. The two tubes would slide over each other easily prior to welding, but after welding it's tough to even get one to slide over the other. In his 4130 videos, Bearhawk enthusiast Kent White talks about the problem. He's discussing hinging rudder pedals, but it's the exact same problem. One of the methods that he suggests to reduce scale formation is to weld it on a mandrel, which basically means put a tube inside it to restrict the access to the air. The problem that arises is getting the part off of the mandrel. Some scale will form and cause a lot of friction. Here's a solution that I stumbled upon that is not mentioned in the video. First (this is important!) let the part completely cool. Otherwise you'll have a quenching problem and end up with a brittle part. This is a good time to go check the Bearhawk e-mail. If I've posted another marathon post, you won't have a problem killing time until the part is cool. Second, shoot between the tubes with some penetrating oil (like WD-40). Wait a few seconds to let it penetrate, and then you should have greatly reduced trouble separating the parts. Third, clean off the penetrating oil. Now you get to spend your time using valve grinding compound and spinning the hinge on a mandrel (another tube) to smooth out the inside and get a low friction fit. This is detailed in the video. Remember, friction in a control system is bad (it's okay, yea needed, in the trim tab system). Strive to eliminate as much friction as you can. It is true that a little bit of friction is useful, but if you try to eliminate all of it, that little bit that is left over will be plenty, because you can't eliminate all of it. Russ "Lappin' them hinges" Erb +++ #6890 Date: Thu, 19 Jul 2001 00:17:38 -0700 From: "Bruce A. Frank" bafrank@ Subject: Re: Elevator Hinges I lucked out at a flymart and found a box of used reams for $10. Just happened to include the sizes I needed for things like the engine mount to the firewall bolt tubes, my flap handle axle and most other places where something had to slide or rotate through. Bruce A. Frank +++ #6891 Date: Thu, 19 Jul 2001 00:21:50 -0800 From: "Float-By Shooter" del@ Subject: Re: Elevator Hinges Has anybody tried polishing out the hinge tube interiors with a small brake cylinder hone in a drill? I used a reamer on the rudder pedal mount tubes I made, and it seemed like it took a lot more force than it should have, even with oil. Del Rawlins-- +++ #6896 Date: Thu, 19 Jul 2001 06:11:25 -0700 From: Budd Davisson buddairbum@ Subject: Re: Elevator Hinges Thoughts on hinges: First, at some point we're changing the hinges for many of the reasons you're all running into buiding them and going to Skybolt type pin hinges. Much cleaner and easier to fabricate. That having been said, we've all built lots of the BH type of hinge because, among other things, that's what's on a Pitts. Several notes about the scale and cleaning them up. First, totally degrease and lightly sand the inside of the tube before welding. That'll prevent most of the scale. For the mandrel use a heavy wall piece of pipe that you can grind some small clearance flats on. That makes it much easier to get out. Then buy a reamer from Viking Machinery in NYC, if they are still in business. I got a bunch of big reamers from them, which at the time cost about $15 a piece. After reaming, lap, as per Russ's method. If you clean it well before welding, you won't have much to clean up after. FYI, nothing, certified Pitts included, uses a Zerk fitting on the hinges. Just an oil hole. Still, I personally hate these kinds of hinges. bd +++ #6899 Date: Thu, 19 Jul 2001 09:33:40 -0400 From: "Sharon Theiss" scat@ Subject: Re: Elevator Hinges Del/Russ I have used an argon purge with great success when TIG welding tubing to eliminate scale formation on the tube i.d. I keep an assortment of small silicone rubber (good to 500 deg. F) "lab" type stoppers, two per size with a small hole in the middle of each one. I tee off the argon line to a small on/off plug valve, then to a Whitey needle valve to adjust flow and attach a small length of Tygon tubing, one end to the needle valve and the other to the stopper. This provides an adjustable throughput argon flow to the interior of the tubing, purging all the air and completely eliminating scale formation. You would have to fab a "Thingy" for both sides of the large, short BH hinges. In the case of small diameter tubing, a small diameter tube can be taped close to the open end to provide flow into the tube. Some cooling occurs but is easily accommodated as the required argon flowrate is very low. If one is concerned about the post weld cooling rate, shut the plug valve. I suppose you could use a foot switch controlled solenoid valve in place of the hand operated on/off valve. The tubing will be deformed after welding, some a little, most a lot, and in the case of hinges I would suggest line reaming (ream the all the hinges at once) to restore the i.d. Lapping or using a brake hone will not necessarily give you a round hole, just a non-cylindrical or a bigger one. The hinge "pin" in this "out of round " i.d. will ride on the high spots in the bore and accelerate the wear in the hinge from lack of proper bearing surface. Perhaps turning a short shank on the appropriate size reamer and welding a long rod with a slip fit hole in the end of it to make a "long shank" reamer might help to maintain a common hole centerline as you ream the hinge "pin" holes. Obviously if the hinge "pins" are not on a common centerline the only way for the control surface to move is to flex the control surface or the part it is hinged to. Talk about generating friction in the hinge! If you are gas welding (as I will be) you are hosed, buy a big bunch of reamers, as scale is not a reamers friend! Or you could save expensive reamers (3/4' dia. chucking reamer from McMaster-Carr = $20.00 - probably cheaper elsewhere) by line drilling the i.d. to within a 64th of the finish diameter to remove the scale and finish ream to size. By the way, I agree with Owen, back off the amperage not the torch at the end of the weld and maintain a short post purge Just a few thoughts Scott Theiss +++ #6909 Date: Thu, 19 Jul 2001 09:34:13 -0800 From: "Float-By Shooter" del@ Subject: Re: Elevator Hinges > FYI, nothing, certified Pitts included, uses a Zerk fitting on > the hinges. Just an oil hole. Still, I personally hate these > kinds of hinges. Budd, will you be doing anything around the hinges to provide a place for fabric to attach, or do you recommend that the builder just leave a hole in the fabric around the hinge as Bob apparently did on his prototypes? I was thinking of forming a piece of thin steel in that area, which would give a place to cement fabric, and also keep whatever lubricant is used on the hinge, out of the control surface interior, where it might discolor the fabric over time. I've thought about a different type of hinge, but this is primary structure which I'm probably better off not messing with. Del Rawlins-- +++ #6913 Date: Thu, 19 Jul 2001 11:20:19 -0700 From: Budd Davisson buddairbum@ Subject: Re: Elevator Hinges You've just touched on one of the many reasons i don't like the hinges. It's impossible to totally seal the elevators from moisture. Even the $185,000 S-2C Pitts has a gap around the hinges. And no, we're not putting a plate there, although we may, since we all think the final fabric fit right there stinks. We're only using these hinges for the first batch of airplanes and will then go to the Skybolt, pin-type of hinge. It puts a slightly bigger gap ahead of the elevator, that you can seal with a little strip of wood before covering and close off the elevator gap. This kind of hinge lets your fabric completely seal the surfaces except for the drain holes. bd +++ #6931 Date: Thu, 19 Jul 2001 21:07:25 -0700 (PDT) From: Jimmy Mathis tallow_98@ Subject: Re: Elevator Hinges Hey Budd: Can you send or tellus where to find a digram of the skybolt pin type hinge? I might want to incorporate this into my bearhawk when I get to this stage. Jimmy 501 +++ #6932 Date: Thu, 19 Jul 2001 21:21:21 -0700 From: Budd Davisson buddairbum@ Subject: Re: Elevator Hinges There are no diagrams at this point, but all they are is rings of .058 one size bigger than the elevator/stab spars with bushing stock welded to them. You make them by welding six inches of bushing stock to six inches of .058, then you cut them into sections, two 5/8" pieces on the stab and a 7/8 piece on the elevator and run a pin through them. Super easy, strong, easy to cover. At this point Bob hasn' made the drawings for us and won't for some time. Chances are it won't change for the plans-built birds. Just the kits. 'Cause we're lazy. bd +++ #6937 Date: Thu, 19 Jul 2001 21:57:29 -0800 From: "Float-By Shooter" del@ Subject: Re: Elevator Hinges > There are no diagrams at this point... I'm sold. The only possible drawback I can think of, is the effect of age. My brother's Citabria has pin type hinges for the tailfeathers, and when we first picked it up and transported it home (as a wreck, to be rebuilt), some of those pins were a real bugger to get out. Although come to think of it, I bet the bolts holding the bearhawk/pitts type hinges to the stabilizers could get well and truly siezed up in their hole given the same amount of time. Are there any other drawbacks to the pin type hinge? Del Rawlins-- +++ #6945 Date: Fri, 20 Jul 2001 06:22:18 -0700 From: Budd Davisson buddairbum@ Subject: Re: Elevator Hinges > Are there any other drawbacks to the pin type hinge? It depends on good weld penetration, although my calculations show that a half inch of this type of hinge can hold 2600 pounds even if it's only welded on one side of the bushing. bd +++ #7152 Date: Sun, 12 Aug 2001 13:36:54 -0700 From: Russ and Penny Erb erbman@ Subject: Trim tab pushrod A question to the likes of Bill Johnson and Pat Fagan: On the plans, the external pushrod to the trim tab is T1 tubing (1/4x.035), which has too small an ID to accept a 10-32 rod end. The plans imply a larger diameter tube welded on the end right before the nut, but do not specify. Bill's pictures look like he has a larger tube at one end with a rod end bearing and a tube welded on the other end in a tee instead of the rod end bearing. Those of you who have made this part, would you please comment on how you did it? Bill, why the tee instead of the rod end bearing? Russ Erb +++ #7156 Date: Sun, 12 Aug 2001 19:37:16 -0400 From: "William & Delinda Johnson" wjohnson@ Subject: RE: Trim tab pushrod See below for the pictures Russ refers to . . . http://home.fuse.net/wjohnson/Mvc-845f.jpg http://home.fuse.net/wjohnson/Mvc-844f.jpg http://home.fuse.net/wjohnson/Mvc-848f.jpg Yes, I welded a tube on the end with enough wall thickness to thread (I don't remember the exact size) and used jam nut. Actually, I turned the larger end tube on the lathe so it would slide over the smaller tube slightly as well. On the elevator (front) end, I changed the design. I did not see any reason for rod ends on both ends. Additional weight and the linkage would tend to move side to side in the breeze around the rod end bearings. So, I made as shown (with bushing so the bolt can be tight). Bill, real close to assembling my wings, busy working on a Culver, looking for Ranger engine parts, needing a Waco SRE engine mount, flying a Meyers, Johnson opps, I forgot. Question for Russ, Pat or anyone who has an opinion! Did you put the rib strength angles on the 'outside' or non-flanged side of the .032 ribs? I am in the process of doing so for the following reasons: 1. I won't have any rib strength angles in the gap between the fuselage and wing to scrape my hands on. Easier to rivet nut plates for fairing. 2. No rib strength angles in the fuel bay area - easier to rivet nut plates for bottom panel. More room as well. Off to build, back in the lurking mode - Bill +++ #7157 Date: Sun, 12 Aug 2001 16:59:37 -0700 From: Russ and Penny Erb erbman@ Subject: RE: Trim tab pushrod > opps, I forgot. Question for Russ, Pat or anyone who has an > opinion! Did you put the rib strength angles on the 'outside' > or non-flanged side of the .032 ribs? I am in the process of > doing so for the following reasons: I put the angles on pointing the same direction as the flanges. I don't see any difference if you put them on the other side as long as they don't interfere with anything. Thanx for the answer. Russ Erb +++ #7161 Date: Sun, 12 Aug 2001 23:50:53 EDT From: pfflyerz@ Subject: Re: Trim tab pushrod > The plans imply a larger diameter tube welded on the end right > before the nut, but do not specify. I don't know what you see on the plans that shows a larger diameter tube. It looked to me like Bob just welded a nut to the ends of the tube, which is what I did. Pat Fagan #232 +++ #7162 Date: Mon, 13 Aug 2001 00:03:18 EDT From: pfflyerz@ Subject: Re: Trim tab pushrod > Did you put the rib strength angles on the 'outside' or > non-flanged side of the .032 ribs? I am in the process of > doing so for the following reasons: >> I guess I split the difference. I put the angles on the flange side in the fuel bay and on the opposite side at the wing root. I didn't give it much thought at the time, other than I felt it made the wing root look cleaner. I can't imagine how you manage to make any progress splitting the time between so many projects. Here's to ya. Pat Fagan #232 +++ #7260 Date: Sun, 19 Aug 2001 08:33:09 -0700 From: Russ and Penny Erb erbman@ Subject: More Useful Info From Erbman You may want to file this one away for future reference. Per my calculations, the fabric weight and cg for the elevator is 14.1 ounces at 8.1 inches aft of the centerline of the hinge. To balance my elevator, I used a 1 lb weight hung at 7.1 inches aft of the hinge centerline to represent the fabric. Russ Erb >>> 2mar02 #7686-9153 +++ #8396 From: Russ and Penny Erb Subject: Elevator installation Been working on the tail section of #164, and just finished tacking the horn on the elevators. Thanx to Bill Johnson for suggesting that the elevator horns be tacked in place against the up stop with the elevator deflected 30 degrees. This worked out very well, as in my case the horns were not exactly perpendicular to the surface of the elevator (though they are close). The down stop will be installed as required to get the right travel. I fabricated the two elevator horns together and bolted them together. They were tacked into place in this fashion to ensure the bolt holes lined up. Prior to this, I spent several hours getting the elevator axes to line up very, very closely. What a pain! This was driven because I know too much--at the USAF Test Pilot School, we teach in the flying qualities phase about the evils of friction in a control system. A very small amount of friction is useful, but you'll have plenty if you do everything reasonable that you can do to eliminate friction. The end result is that my elevators have an acceptably low amount of friction when joined together (they flop back and forth) and I haven't even greased the hinges yet! How did I get there? After mounting the horizontal tails and installing the elevators, I took a lot of time moving them back and forth, trying to figure out why they weren't lined up. I slowly eliminated the problems. The left spar was still straight, but the right spar appeared to be about .035 (a tubing thickness) out of line. I put the elevator in a vise, stuck a thick tube in the end, heated the offending area and gave it a gentle tug. That straightened in out in that direction. Then I found it out of line about the same amount at 90 degrees to the first direction. Same thing again, and the right spar was straight also. So everything was lined up now, right? Of course not! Else I wouldn't have asked... More study showed the problem to be one of the hinges out of alignment. Not only was it too far forward (again, about .035), but it was also slightly rotated around the rear spar of the horizontal stabilizer. What to do? First I attacked the rotation. This was done by sanding down one of the support legs (the V between the tubes) down with a belt sander. Of course, this removed too much metal. Pull out the torch and welding rod and build the leg back up. Then, using a file, I carefully filed until the hinge would rest in the proper position with the elevator spars aligned. Now the other leg of the V was too short, so I built it up with the torch and rod, then filed it back down. Now the holes in the strap of the elevator had to be moved. Using the torch, I made the hole in the upper strap larger and oblong so that it would not interfere with the drill. On the lower strap, I welded the hold closed. Put the elevator back in place, and line up the elevator spars with a close fitting tube over both of them. Clamp the hinge in place, and drill through the oversized top hole and tube on the horizontal stabilizer to make the new hole in the bottom strap. Pull elevator off, weld the hole in the top strap closed. Put back in position, align the elevator spars, get the hinge in the right place, then drill up from the bottom to make the hole in the top strap. Like I said, I'm quite happy with the end result, but sometimes getting everything lined up is a pain. Some day I'll get to mount the wings...oh, boy... One important point I'd like most of you to take from this--welded structures (and in a similar fashion composites) have a interesting characteristic--if you drill a hole in the wrong place or make the wrong cut or otherwise screw up a part, many times you can replace the metal with the torch and rod and have another go at it. I had one part I drilled the hole three times to get it right. Aluminum structures don't lend themselves to that kind of reversibility very well. Enough for now--it's past my bedtime... Russ Erb >>> 4sep02 #9154-11297 +++ #9667 From: "t18cox" Subject: Re: More ribs from Africa > Secondly any advise on bending the T3 and T13 material on the > elevator, each time I bend it it kinks on the curve. The bending tool Bob shows in an early news letter works very well. Another thing is to bend around a 10 or 12" v belt pulley. With either tool the key is to make multiple passes bending a little each time until the proper bend is achieved. >>> 20may03 #11298-18250 +++ #11388 From: "Bruce A. Frank" Subject: Piper Question Email this weekend sure is slow. Not even getting any spam. On the jack screw adjustment on Piper high wing aircraft, particularly the PA-22 TriPacer/Colt, the yoke has two cables attached. These appear to route rearward through a couple of pulleys, one above and one below the hinge line of the elevators. Each of the cable ends are attached via a coil spring to the control arms on the elevator. The action appears ( I say "appears" because these parts were not attached when I obtained the fuselage) to be that as the leading edge of the horizontal stabilizer is trimmed towards the top of the fuselage (the airplane's nose down attitude) the elevator is biased slightly downward. And similarly for the nose up trim position. What are the purpose of these cables? Would there be any noticeable change in control feel or handling of the aircraft if these cables and springs were left out? +++ #11389 From: Drew Schumann Subject: Re: Piper Question Anyone with experience, chime in, but we have a Tri-Pacer in the shop and I believe, from reading the rigging instructions in the Operating manual, that these are tensioners, designed to maintain constant tension due to unequal expansion/contraction of fuse/cables. In theory, if you left them off, the controls would be stiff as the OAT went up and loose as it went down, as cables are relatively non-expansive, compared to tube fuselages. I'm really going out on a limb, here, as my "experience" is totally classroom/lab in this subject. Anyone else care to comment? Drew +++ #11390 From: "handainc" Subject: Re: Piper Question The Tri-Pacer, from what I am told, has an aileron, rudder interconnect system to aid in co-ordination of flight controls. Earlier Tri-pacers and the Pacer did not have the interconnect system and fly beautifully. I have about 500 hours in an early (1950) Piper Pacer, and love the responsiveness of the airplane. It is really easy to coordinate the flight controls. I also have a Tri-pacer fuselage that I will be rebuilding into a custom Pa22-20 taildragger, and I will install the control cables according to the rigging data for the Pacer. You can order the aircraft manual from Univair or other sources, and if you are going to be working on the plane, I highly recommend buying the parts and service manual. Also the Univair catalog is worth it's weight in gold just in finding the proper parts numbers. Hope this helps. M. Haught +++ #11391 From: "Bruce A. Frank" Subject: Re: Piper Question I have the manual and this isn't covered. I am aware of the interconnect between aileron and rudder, but this is a Colt fuselage with no interconnect. Both the Colt and TriPacer have this trim connection I questioned. Bruce A. Frank +++ #11843 From: pfflyerz@c... Subject: control surface balance There was quite a discussion a while back about how to balance the control surfaces with various estimated weights and techniques bandied about. Now that my surfaces are have finish paint I rechecked them for balance. I used Erbman's estimate for elevator weight and came up 8 oz. light in each elevator. I was able to solve that problem easy enough by drilling through the T25 channel, at the elevator tip and pouring a lead shot/resin mixture into the elevator tube. I next checked the ailerons and found I was 2.5 lbs light in each of them. Although I didn't pour my aileron balance tube with molten lead, I think I came pretty close to filling it up by pouring a lead plug on one end, filling with lead shot, then pouring another plug on the other end. All that primer and nice shiny paint must really add up if Bob was able to balance his with just that central tube. I can add 2.5 lbs by almost filling two more tubes and placing them in the remaining leading edges. I cut a hole in the fabric to allow me to slide the tube in, but I will have to drill out the rivets holding the skin to the ribs as they are preventing me from inserting the tube. Just a heads up for those of you that haven't gotten to that point yet. Pat Fagan #232 Pearblossom, CA +++ #13293 From: "Dan Shilling" Subject: Elevator Rudder Hinges In the second sentence of the "Building the Rudder & Elevator Hinges" section on the Erbman CD, it says "(If you are interested in a simpler design, contact AviPro.)" I am interested. Budd...?? Also, I seem to have a slight twist in one of the ailerons I just finished. One corner is raised about 1/4" off the table. Anybody have any suggestions before I lean real hard on it. Dan Shilling +++ #13299 From: Budd Davisson Subject: Re: Elevator Rudder Hinges > In the second sentence of the "Building the Rudder & Elevator > Hinges" section on the Erbman CD, it says "(If you are interested in > a simpler design, contact AviPro.)" I am interested. Budd...?? It's a Bob Approved change we haven't instigated yet. We'll let you know when we dod. +++ #14281 From: "Mark Goldberg" Subject: Re: flap return springs The flap springs got delivered to me Friday afternoon. I'll get you a set this week. Yes, there are two trim tabs that need to be cut loose. They were built this way so the trailing edges would line up nice. When you assemble the horizontal stabs, and the two tubes that connect in the middle that actuate the trim tabs - you will see how they work. The cables stay in the middle of the fuselage (almost the middle). The cables are connected to the bell cranks on the ends of the previously mentioned tubes. These bellcranks are bolted together. We will send you the two push rods for the trim tabs. If you look at your plans and still have trouble figuring out how it goes together, let me know and I will shoot a digital picture of mine and email it to you. Mark +++ #15181 From: "conohawk" Subject: Trim tab deflection angle Two questions for the folks who have constructed the trim tab system: 1. How many degrees max deflection are produced? 2. And how many degrees deflection would be needed during actual flight, say during the climb-out? I'm working through calculations for the deflection number; but, hope to get some real-world data. Thank you, Mark Conover +++ #15213 From: Del Rawlins Subject: Re: Trim Tabs >> A friend and I were working on the elevators this weekend and he >> asked the question, "Why are there two trim tabs instead of just >> one?" Anyone know? > Bob has been asked this before and it's because he (as do most > engineers) like loads to be symmetric. I had assumed that there were two, so that in the event of an autopilot installation, one would be for the mechanical pilot and the other would be for the biological one. Then again, since an autopilot involves electricity, I should have known better. -- Del Rawlins +++ #15219 From: Russ and Penny Erb Subject: RE: Trim tab deflection angle Mark--I asked a similar question in December 2001. Here is the answer that Mike Meador gave me, courtesy of the Bearhawk CD: "I gave the question to Bob and he said that Max 5 degrees up or down is all that we have ever used in both aircraft. The swing of the trim wheel is about 2.5 - 3" for 5 degrees. The total swing available is 10 degrees up and down at the flap and that is 180 degree turn at the wheel - you could get more with a longer chain on the sprocket of the style that we use. Bob said to tell you that the trim tabs are very powerful and he would not add more travel to the trim than 10 degrees. I hope this helps - If I didn't answer the right question let me know. Later - Mike " Russ Erb +++ #15348 From: Pat Fagan Subject: Re: Trim tab deflection angle Your question had already been answered by others by the time I waded this deep into the messages, but maybe I can provide some more insight. The trim tabs are indeed very powerful and don't require much deflection. I measured the throw of the small arm protruding below the stab. on Proto 2 and found it only moved about 2 inches. I duplicated that movement on #232. That gives the trim tab about 1 thickness of movement above and below center, which seems to be plenty. Pat Fagan +++ #15372 From: "Mark Conover" Subject: Re: Trim tab deflection angle Thanks for the good data. I noticed yesterday that the single trim tab on a Cessna 182 deflects downward about 15 degrees. Upward about 20 degrees. To my eye, the ratio of elevator area to trim tab area on the Cessna is smaller than that of the Bearhawk. And of course the dual tabs on the Bearhawk double the tab force. No wonder you flying B'hawkers are having to be gentle with your trim inputs. I have a MAC servo laying about that I intend to connect to the trim horn that is attached to the torque tube inside the tail. Mark Conover +++ #15412 From: Del Rawlins Subject: Re: Re: Trim tab deflection angle >>> Wouldn't the bird be more efficient if you could find the cause for >>> the out of trim condition? >> What out of trim condition? > The condition requiring one to push, pull, or bend trim tabs to fly > straight and level. What airplane *is* perfectly trimmed for pitch at every airspeed within the normal operating range? That's why we have an adjustable elevator trim in the first place. The issue at hand, is that the elevator trim in the Bearhawk is a bit overpowered, and very sensitive to adjustments. I'm really interested to see how Russ' worm drive trim wheel works out once he starts making test flights. On the other hand, I have a friend who managed to make a safe landing in his Citabria (which also has a powerful trim system) when the stick got jammed forward, using the trim alone. So it's a matter of finding the right balance between power and sensitivity. +++ #15459 From: Del Rawlins Subject: control surface hinges I will shortly begin compiling a list of materials to order for my tailfeathers, and want to do something for the hinges other than what the plans show, primarily for aesthetic reasons. Last time we discussed this issue, Budd described the Skybolt type hinges that he was eventually planning to incorporate into the kit production. I was wondering what sort of progress has been made on that front, since it seems like you are now starting to make design improvements (like the new strut link fitting). Would you be able to make any recommendation as to tubing size and length, and hinge pin size? I've also thought that using stainless steel pins with oilite bushings might be a good idea and reduce maintenance, although I am concerned that being softer, stainless steel would wear faster and might not be strong enough. -- Del Rawlins +++ #15535 From: Del Rawlins Subject: tail hinges, again Hey Bruce, what do the elevator and rudder hinges look like on your Piper project? Are they the typical arrangement with 3 aligned tubes with a hinge pin? If so I'd be interested in knowing what the tubing and pin sizes are, and whether or not the tubes are bushed inside. The Bearhawk rudder/elevator hinges are one of the few aspects of the design that I don't care for, so I am exploring other options. -- Del Rawlins +++ #15543 From: charles.k.scott@d... Subject: Rudder hinges > Hey Bruce, what do the elevator and rudder hinges look like on your > Piper project? You might be interested to know how the Christavia is set up as the fuselage is similar to the Bearhawk. The plans call for three bushings of unequal size for each hinge. The two outer bushings are about 3/4" while the inner one is about 1". The bushing stock is the size that uses a 1/4" pin, or a bolt on which you have rounded down the hex head so that it fits. The bushing stock is typically .065" wall thickness and you simply ask for the stock that can then be reamed to 1/4". Available from Wicks or Aircraft Spruce or probably any aircraft supply vendor. lining these up and welding them so that everything stays in line takes a LOT of care and ingenuity. I had to weld mine twice as the first time things managed to shift enough so that even I rejected it. Then there's the difficulty in reaming them (I used a foot long drill). This goes double for the elevator hinges and the tubes that form the elevator and horizontal stabilizer spars as the tubing wall thickness isn't as thick as the rudder post. But there is another way... One of the wanderers in the Christavia group came across an old Fairchild that was in the process of being recovered and rebuilt. He focused on the elevator hinges and discovered something that might be of relevance to the group. Instead of welding the bushings to the spars, this airplane had bushings welded to straps that were then clamped to the spars, and then riveted to the spars to lock them in place using two pull rivets. This is the way it worked out for me when I fabricated the hinges for my Christavia recently: I cut up a bunch of .050" stock to use for the hinge straps and filed the edges smooth. I had two different widths, 3/4" and 1". I cut up the bushing stock using a tubing cutter to get square ends. Then I pre-bent the straps so that they fit around the spars (1" .049" tubing) and bent up the ends so that I could drill a 3/16" hole through them and use a small AN-3 bolt to pinch them tight. I made up a set of three, two 3/4" and one 1" in the middle and slid them on a spare 1" tube I used as a mockup. I lined them up and pinched them tight with bolts. Then I turned the tube over so that the pinched ends were on the bottom and lined up the bushings on top of the straps. This took a little thinking. In order to get them lined up, I used a VERY long phillips screwdriver that happened to be just the right diameter to fit inside the bushings without reaming them. I slid the bushings on them and then decided I needed more help. I fit spare bushings on either side of the three what I was trying to align and spaced them away from the tube using scraps of .050" stock to match the straps so that everything was at the same distance from the tube. So on either side of the bushings I was going to weld in place, I had alignment bushings that were in turn spaced out from the tube the same amount as the straps that were under the hinge bushings. All was held in alignment by my two foot long phillips. Now, I clamped the two end bushings using stainless hose clamps that I dug out of my whatnot drawer. I spent another half an hour making sure all was properly adjusted, spaced apart and in alignment, then welded the bushings to the straps on both sides. When everything cooled, I bent up three more straps to fit over the bushings and welded them to the straps that circled the tube. You have to be careful here and not weld them too far around the tube straps or you will not be able to open the straps up to fit them around the actual spar. The cover straps lock everything in place so that there is no possibility of that bushing going anywhere or shifting. They also serve as spacers to keep the pin in proper alignment and not being bent in the middle by the pressures of the opposing forces when all is clamped in place. Finally, I now removed the phillips screwdriver and reamed the set of now welded bushings in place. I fabricated four sets of hinges, and after cleaning them up, pried them open and snapped them in place around the horizontal stabilizer and elevator spars. The beauty of this method is that the pin literally causes the hinges to find the proper alignment. You just force the pin in and then spend some time getting the two spars level with each other, then pinch the straps tight with a bolt in each clamp. The elevator operated effortlessly, with no binding, first time on both sides! Now granted, these straps were a pain to fabricate, and took a long time to finish and install, and I'm not done yet of course, I still have to blast the parts and prime and paint them. And I still have that last step of drilling and pulling the rivets once all is in final alignment, but I thought it would be interesting for builders to hear that there is an alternative to the weld the bushing to the spar method. I still have the Jpeg and drawing that Dave from the Christavia group sent me, is anyone is interested. Please send me an e-mail asking for the pictures and I'll enclose them and send them to you. In addition, this method was successfully used by the Fairchild all these years, and the same hinges were now being re-installed on the airplane as it goes back together for more service. Also, I held this setup in front of our local EAA technical counselor who visited the project last weekend and asked for his opinion and he thought they would work fine. Corky Scott +++ #15621 From: Bearhawk Subject: New file uploaded to Bearhawk This email message is a notification to let you know that a file has been uploaded to the Files area of the Bearhawk group. File : /Bearhawk Rudder Hinges.zip Uploaded by : cvuxton Description : Description and pictures of Corky's Rudder Hinges You can access this file at the URL http://groups.yahoo.com/group/Bearhawk/files/Bearhawk%20Rudder%20Hinges.zip Regards, cvuxton +++ #15639 From: Budd Davisson Subject: Re: Pin hinges There's an easier, more fool proof way of making pin hinges and is the way most people do it. Get about a foot of 1 x .058. That size will slide over the elevator/stab spars with practically no slop. Weld a foot long piece of bushing stock with an I.D. the size of the pin you want, e.g. 7/16 x . 090 for 1/4 pins, the full length of the 1" piece. It works best with TIG, but gas works fine. Now chop it into pieces. Each hinge will be two pieces 3/4" long (outside pieces) with a 1- 1 1/4 long piece in between on the other surface. You slide the pieces down over your stab/elevator spars before putting anything else on them. Then you build the surface with the hinges still loose. When the surfaces are finished, you line the surfaces up, put pins in your hinges and weld the hinges in place. Simple as slipping on a squashed gopher. bd +++ #15655 From: charles.k.scott@d... Subject: Re: Pin hinges > Get about a foot of 1 x .058. That size will slide over the > elevator/stab spars with practically no slop. That's actually pretty much what the Fairchild straps for the elevator hinges were, except that you get to put them on after the horizontal stabilizer and elevators are fully made because they are clamped on, then riveted. Corky Scott +++ #15658 From: Budd Davisson Subject: Re: Re: Pin hinges > Budd, do you think it would be worthwhile to install bronze bushings > in the hinges? Yes and no on the bronze bushings. It'll eliminate the wear and friction but I don't think either is a factor worth being concerned about. The biggest problem with bushings is that they require such a large diameter piece of tubing to hold them that it pushes the elevator that much further away from the stabilizer. As it is, you need to glue a spacer, something like a dowel, to the back side of the stabilizer spar to fill the space between the surfaces. bd +++ #15659 From: lisankejm@g... Subject: RE: Re: Pin hinges I was looking at my Avipro built fuselage and tailfeathers (thanks Budd) and following the hinge pin discussion. I think that if a small spacer or flat piece was mounted in the surface next to the hinge loop, it would give the fabric something to attach to, and would negate the effect of the fabric curling up in that area. Then the hinges could be built per the plans and still have a nice finished look. Joe Lisanke +++ #15677 From: Russ and Penny Erb Subject: RE: Re: Pin hinges budd--for those of us building the hinges per plan, would you recommend adding a dowel or some other spacer under the fabric to (mostly) fill the gap between the fixed and moveable surfaces of the tail? Russ Erb +++ #15681 From: Budd Davisson Subject: Re: Re: Pin hinges It can't hurt and it's easy to do. The gap isn't very big, but it's bound to hurt the efficiency of the surface. bd +++ #15683 From: Del Rawlins Subject: Re: Re: Pin hinges >>Yes and no on the bronze bushings. Should I bother with oil holes or just pull the pins and re-grease at annual each year? > As it is, you need to glue a spacer, something like a dowel, to the > back side of the stabilizer spar to fill the space between the > surfaces. That makes sense, cause the extra gap is about the only downside I can see to this method. Of course, enough room on one side of each hinge will have to be left to allow for inserting and removing the pins. Oh well. -- Del Rawlins +++ #15696 From: Pat Fagan Subject: Re: Re: Pin hinges > It can't hurt and it's easy to do. The gap isn't very big, but it's > bound to hurt the efficiency of the surface. I noticed on the Maule demonstrator at OSH that the elevator/stab has a piece of clear plastic bridging the gap between the two surfaces, attached to the top of the stab and passing into the gap and attached to the bottom of the elevator. Don't know what the material is or where to get it, but looked like a simple solution as a gap seal. Pat Fagan #232 +++ #15701 From: "Bruce A. Frank" Subject: Re: Re: Pin hinges There are tape like gap seal kits used in the gap between the horizontal stab and the elevator; sometimes also between the aileron and wing. You see them on aerobatic and STOL converted aircraft. At my old airport a high quality urethane packing tape was commonly used on experimental aircraft. Was replaced as needed, about once a year on hangared aircraft. Bruce A. Frank +++ #15705 From: "Shannon Spurgeon" Subject: Re: Re: Pin hinges I kind of figured that Black Baron fabricote would do the job nicely on the B/H +++ #15719 From: Budd Davisson Subject: Re: Re: Pin hinges There are pros and cons to the grease holes. I don't see them in the pin hinges I see being used. I think that's what WD-40 is for. bd +++ #15720 From: Budd Davisson Subject: Re: Re: Pin hinges We gap seal control surfaces on akro airplanes as a matter of course. For certified Pitts there is an STC'd rubber extrusion that has around concavity on each side and is trapped in place by the surfaces. The effect is most noticeable at high alpha operations and during flair. As Bruce mentions, the quick fix is two piece of packing tape, over lapping in the middle of the gap, sticky side to sticky side. A more permanent system is to snake a piece of fabric painted the same cover as the surfaces and polytacked in place. bd +++ #15722 From: "Mark Conover" Subject: Re: Pin hinges We can take a lot of comfort in the long history of the simple technology that exists for this type of aircraft. I snapped off a lot of digital photos of a friend's PA-12 yesterday. He is about to recover it. Here's a so-so image of its elevator hinge pin (with a temporary AN bolt partially inserted). http://www.conotech.com/public/av/supercub/photos/DCP02870.JPG I'll organize these photos when I find the time. Feel free to browse the directory: http://www.conotech.com/public/av/supercub/photos/ BTW, for a good shot of the fuel lines, take a look at: http://www.conotech.com/public/av/supercub/photos/DCP02891.JPG Mark Conover, #502 +++ $Id: 2.2.4-Tail-Elevator,v 1.8 2003/05/22 03:18:07 bentonh Exp $