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Introduction to Landing Gear notes

The main landing gear installation is rather tricky for most builders. There have been several tricks, by builders who have gone on before, that make the process much less challenging. The goal here is to consolidate everyone's tips at a location where we can gain easy access. The tips here are taken from early newsletters, the discussion page, and the library, so there may be some repetition across the site, but this will allow you to see a quick summary. Before starting on the main landing gear, it is advisable that you read everything on this page, the library, and also view all the photos in the photo section of the site. The thumbnails in the text below can be enlarged by clicking, then use your browser back button to return here.

The main landing gear has to be aligned properly to fold up into the wing, and then fold down into a position in proper alignment to hit the runway, at 90 mph, without veering to the side. And, it has to be properly aligned vertically so that it will withstand the landing loads. Alignment is key. As many builders found out early on, there is also a problem with getting the gear attachment points low enough that the upper pivot points don't interfere with the top of the mid deck, and high enough that the lower pivot points don't hit the bottom skin. (Geeez, what a mouthful, you may have to read that sentence a couple of times!)
Get the lower pivot points as low as possible, but be sure to check for adequate clearance for the aft pipe cap that screws on the bushing inside the hull.
Lest I be crucified, let me first say that in my career, I have written dozens of manuals and work instructions, and I know how difficult it is to make them clear. I also know that no matter how good they are, they are subject to interpretation by several people, and we all see things in widely varying and different ways. I think that, for the kit plane industry, the Seawind manuals are pretty typical, and in places, pretty good. Having said all that, the section on the MLG and its associated reinforcements inside the hull are especially dismal and need complete revision.
First, check the revisions in the MLG section. Each page has a different revision. Also, make sure to read the builder letter dated October 21, 1996. I used the dimensions shown on page 4 in the manual (which includes the suggestion from Mike Bowes to lower the gear by inch to better accommodate the upper connection point).
I first located and drilled the hole (about 1/8" lower than the manual and Mike's letter suggest) on the aft face of the gear pocket as shown, then, I varied the position of the hole in the forward face to get the gear leg aligned. As the manual suggests, I started with 1/8" holes, and then if slight repositioning was required, I went up one or two drill sizes and re-drilled the location, and the wooden dowel, to accommodate the new drill size. This all seemed to work pretty well for me.
OK, the next things are the various reinforcements in the hull. First of all, the angle supports shown on page 18 should actually be dry fitted first, not last. They interfere with the MLG aft floor bulkhead shown on page 16. If the manual is followed for their length, they actually extend under the bulkhead two or three inches. After talking with Mike Bowes, I decided to leave them as long as possible because they are tying the hull together across the step. In addition to bonding them as shown in the manual, I also put a lay-up across the flange to the aft bottom, then, I cut the bulkhead to fit over the top of these flanges and lay-ups ensuring a good seal. (see photo below)
Next, the under-floor transverse channel supports shown on page 13 and 15 are not properly described in the manual. In fact, the aft channel support is shown on page 15, but never even mentioned in the text of the manual (let alone installed). Also, the pictures and description are not very clear about the fact the these channels should be trimmed at the floor beam flange, so that they are flush with the top of the floor beams, and fit tightly against the bottom of the aft floor. (Whatever you do, DO NOT cut the flanges on the floor beams. Trim the flanges of the cross members) I also believe that the flanges of the aft channel support face aft, as do the flanges on the adjacent bulkhead sections.
Make sure that the glass cut from templates 5.1 and 5.2 properly fits your hull before cutting up all that 7781.
I did not bond the forward gear enclosure panel in until AFTER the upper retraction arm pivot point was located as seen in the photos below. When bonding in the enclosure panels, align them by setting the exact same dimension between the panels and the wing main spar bulkheads, then clamp a straight edge between the two enclosures, side to side, as shown in the photo below. Then, when bonding in the forward enclosure panels, do the same thing, but in addition, cut an exact 4" block, and clamp between the enclosure panels to establish perfect spacing between the panels as shown in the photos below.
As suggested by Craig Easter and Bob Darrah, a bar (instead of the oleo) is used to set the over-center dimension when locating the upper pivot point. Bob nicely describes this process in the newsletter archive (volume 2, number 2, March 1995) so I didn't repeat it here. I used a wooden bar, cut to the exact dimensions, and trimmed at an angle to set 3/8" over center dimension. Note, the over center dimension is set with the oleo fully compressed length. Then, when the oleo extends, the over center dimension increases from 3/8" to about 3/4." This linkage must remain OVER CENTER throughout it's travel.
As suggested by Mike Bowes, I set the gear legs at about 3 degrees past level when the gear was fully down and the oleo was fully extended. I also checked that with the oleo fully compressed, I had about 1-1/2" clearance between the v-cuff on the keel, and the ground. You don't want to have the belly drag if your oleos lose pressure.
Positioning the "angle support blocks" (I call them pillow blocks) was a real bitch! I used the plate that Mike Bowes suggests below, but after all, when I was trying to get the retract arm to properly engage the notch, I had to shim the aft angle leg toward the inside of the airplane, at the top bolt, with three standard thickness washers. This was necessary on both sides of the hull. These blocks must be positioned during the process of locating the retract arm upper pivot point. I would recommend that you not try to locate them after the arm is installed as suggested by the manual. It is also helpful to have them in place before the forward MLG enclosure panel goes in. This enables you to see them, access, them, etc.

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bcmlg13.JPG (15019 bytes)    Good luck, you're gonna need it. BAC SNA Kit# 71

 

Seeing your note on the landing gear positioning stirred memories that I had repressed about my own struggles a few years ago. I ended up making a homemade main landing gear axle out of two 3 in lengths of threaded rods (5/8 in I think). [Others used 1/4" all thread and wooden or nylon bushings with 1/4" id and 5/8" od] These were joined in the middle by a threaded "female" union available from the hardware store. When you turned it with a wrench or pliers, the ends of the axle moved outwards and pressed into the sides of the wheel pocket. At first the ends were ground to somewhat of a point to gain purchase enough in the fiberglass. It had to be stable enough to stay put while working the main gear legs up and down while fitting. Later, I just drilled into the ends of this temporary axle and inserted a short length of 1/4 steel rod. All of the fitting of the gear components was done with these and I had to move the 1/4 hole in the wheel pocket a little on one side or the other to get everything to fit right. It was no problem to finally ream up to the size for the bushing which was the last thing I did. I was so pleased with this invention, that I sent it to another builder. I hope others may find this helpful.

 

Drilling the Main Landing Gear Pockets (this is also in the library)
by Roger Isackson

After reading the instructions for locating and drilling the holes for the bushing installation in the main landing gear pockets, it seemed to be straight forward and logical. However, when I started to actually drill the holes I realized it wasn't quite so simple.

The idea to drill successively larger holes in the pocket and the temporary bushings in the pivot bracket to adjust your hole location to the proper place is sound. But to actually drill the holes in line with each other is a little more difficult! I do not know of an angle drill physically small enough but with a 7/8" capacity which would fit in the pocket. Even then it would be hard to get perfect alignment. I have the quick kit and the 141 & 145.55 bulkheads are installed forward of the pocket so there isn't room to drill from inside the hull from the front. Aft of the pocket the hull curves in and causes interference. With the 141 & 145.55 bulkheads installed one must drill them both to get the shaft in anyway so it seemed logical to purchase some long drills. I located some 20" long drills in McMaster Carr, but the minimum set required by the construction manual ran approximately $160.00. Also, if one reams the holes for alignment a reamer with flutes to reach both sides of the pocket is necessary.

One note about straight chucking reamers or hand reamers is they cut on the nose of the tool. The flutes are only for a place for the chips to go. So to get a perfectly aligned hole either a piloted reamer or an expansion reamer with flutes long enough to reach both sides of the pocket should be used. Another $60.00 to a $100.00.

It was late, I was tired so I called it a night and slept on it. As often happens, when I woke a simple solution popped right into my head! I charged off to the local hardware store and purchased a 1/8" diameter by 12" long drill bit, a 1/4" diameter by 3' long steel rod, and a 7/8" diameter hole saw with a 1/4" diameter pilot hole extending all the way through. 14 Bucks!

I threaded the long drill into the holes in the pocket facing forward. I had to enlarge the aft hole slightly to do this. Then I "align bored" forward through bulkheads 141 & 145.55 by turning the bit with my fingers. I increased the hole size in the bulkheads to 1/4" then hole sawed them to 1 1/4" (I already had that saw). Then I followed the instructions in the manual. I was able to drill from inside the pockets up to 1/2" with my little angle drill. That was where I was at when I was satisfied with the hole positions.

I made two 1/2"od X 1/4"id bushings out of delrin stock and inserted in each side of the pocket. During a practice cut with the 7/8" hole saw in a piece of scrap I found it to cut oversize, so I chucked it up in a drill press and touched a grinder to the outside of the teeth. In removing just a little of the set, I now had a hole in which the bronze bushing would fit nicely. I ground a flat on the 1/4"rod 6 1/4" from the end for the set screw in the hole saw, and slipped the rod in through the front of the pocket. I locked the hole saw into position and cut the rear hole. Then I made another bushing 7/8"od X !/4"id and pressed it into the hole I had just cut. Now I put the "pilot rod" back into the bushed holes with the cutter facing forward, put my drill in reverse and cut the front hole. No chance of misalignment.

I keep an assorted stock of delrin in the shop and seem to always be finding a use for it. I have the luxury of owning a metal lathe, but accurate bushings can be made with a drill press with a little care. They can be made out of wood too, but the delrin comes accurately sized so it is really handy. Just another way to skin the cat!

Sincerely,

Roger Isackson
Hull # 132

Post #91: This posting comes in response to an email from a troubled builder who is second-guessing himself as he attempts to locate the upper pivot pin bushings for the main gear retract swing-arm. A very, very common issue. I choose to respond here because every one of you will have this problem to some degree. I have rigged ten Seawinds to date, and this is an ongoing problem with all of them. Yes, follow the manual to the best of your ability and when all else has failed resort to Mike's Tactics, as follows. Any of the following tips will help alleviate the problems here. In some cases ALL Of THE FOLLOWING are  required to make this thing work properly!
Understand the basic problem is the lengths of the main oleo plus the swing-arm combine to create an effective total length that threatens to push the aft upper swing-arm bushing right through the mid-deck skin. It follows that anything the builder does to shorten this total length or move the swing-arm inboard (because the skin is rising toward centerline) helps to solve the problem. These tips either shorten the effective total length or move the upper pivot point inboard. You builders are smart. Think about each item and it will be self-evident how it helps you. I really don't need to explain it.
1. Deliberately rig the main gear legs [in the full down and oleo extended position] slightly "bowlegged" like an old cowboy. Not radical...very subtle, about 2 degrees inboard of dead vertical. This is barely noticeable and actually improves ground clearance slightly.
2. Cut excess threads off the main oleo rod ends. Leave only the threads required for a THIN jam-nut. That's all you need. Excess threads hanging out in the breeze are needlessly contributing to overall length.
3. LOWER the gear leg by making and installing a 1/4" spacer plate between the main gear leg and hinge attach plate. You will have to buy longer 3/8" attach bolts, yes, but this moves the whole assembly downward which is exactly what you need. My own airplane has these spacer plates on both sides and, once painted, are barely noticeable. I would have to point them out to you, otherwise they look like they are supposed to be there.
4. Mount a flat spacer plate between the thrust angles and the vertical fiberglass of the mid-deck. Use 1/4" or 3/8" thick stock. Bed the plates into a wet mix of milled 'glass. This serves two purposes, namely a flat, even surface to bolt your thrust angles onto and ALSO moves the upper pivot point inwards, thereby gaining more clearance up above the end of the retract swing-arm. Exactly what you want!

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Some or all of these tips may be required to gain the necessary clearance. You can also remove a little of the inside skin of the mid-deck and the foam at the point of interference on the aft side of the pocket where the stainless pin comes close. " Heal the core" with 2 ply of 7781 bid. Using some or all of these little tricks has solved this problem on every Seawind. Do not modify your swing-arms, as one builder did, with catastrophic results since he employed ordinary mild steel in his revised creations. Believe me, although it may seem like the answer to your woes, modifying the swing-arm is not necessary. JMB N369JB

 

The following is from post 297, from John Ricciotti: I would like to offer to anyone who has not yet rigged the gear the use of some fixtures I have made. 

They are as follows:

I have made an adjustable 5/8 in. shaft with 1/8 in. pins for setting the main gear pivot points (lower) and also have made a fixture to hold the upper swing arm pivot point in place while checking the fit. The upper fixture also has a 1/4 in. drill guide built in to align the shaft holes on both sides. I am still in the final stages of fitting but they should be available soon.

I would like to add a few observations on helpful items that in hindsight would have made the whole gear fitting process smoother. First, before setting the retract bulkheads, make sure the hull is level fore and aft as well as side to side. In the manual it doesn't point this out very clearly (the fore and aft part) but it will make a big difference in getting the retract bulkheads plumb to the entire gear system. Also note that the upper end of the gear pocket has a slightly different centerline than the bottom where the main gear bushings are set. Getting those centerlines as close as possible from the very beginning of setting the retract enclosure panels will be a big help. It will help to minimize the misalignment problems that Mike Bowes has pointed out in one of the newsletters. To help with that I made a wooden jig to hold the retract panels in place while they were bonded. It was 2 parallel 1x 4 (1x5 cut down) boards set horizontally between the gear pockets with 3 vertical boards connecting the horiz. boards together. Then it was easy to put a level from top to bottom to make sure the whole system was plumb. I am very close to drilling the holes and setting the bushings in place. When I have completed that, the fixtures will become available. I have not drilled a hole yet and hopefully the ones I drill will be the last. I'll follow up with anything more I have learned once the gear is all set up. Any other hints anyone has to offer would be greatly appreciated. Thx, John

A picture of John's fixtures are shown below. Click to enlarge.

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Just one comment on brakes for those of you who might not be familiar with Matco. Every year, George Hepp, owner of Matco Manufacturing has a great display at Oshkosh which shows how to design a more effective brake pedal design.    For those of you not fortunate enough to see his display at Oshkosh, he has reproduced it on the MATCO website, which is www.matcomfg.com     Also you can go directly to the write up on MAXIMIZING THE OUTPUT OF YOU BRAKES by copying this link into your web browser window.

     http://matco.elixirlabs.com/index.php?uid=2192&page=2372

If you have problems copying that link just go to their website and select TECHNICAL SUPPORT then select TROUBLESHOOTING on that page then scroll down until you see the link MAXIMIZING THE OUTPUT OF YOU BRAKES and click on that link.

Below are two pictures from Matco's display at Oshkosh.

 

     

                More effective setup                                                        Less effective setup

 

A recent post from Wally Weller (with some great photos included) details items Wally has learned in trying to design a nose wheel steering system with a linear hydraulic actuator and in correcting poor brake pedal geometry.  Wally bought his non-Quik Kit long before hydraulic nose wheel steering was offered.   His solutions to these problems follow (taken from post 1620):

Graham (Woodd) and I devised a linear actuator steering system with a toggle controlled solenoid blocking valve in an interconnect between the 2 steering pressure lines. CLOSED - hyd. steering for big turns, or hyd. lock for no shimmy. OPEN - free swiveling for towbar handling, or rudder/brake steering straight ahead. A manual nosewheel position indicator eliminates electrics in the saltwater.

(We changed the brake pedal geometry) by redrilling (which) shortened the arm that connects the pedal and brake cylinder clevis increasing the mechanical advantage. We moved both brake cylinders inboard 3/4 inch to clear the rudder pedal stalks and allow full pedal application. While not eliminated, the right pedal "lay down" geometry problem was compensated for by rigging the right pedal about 3/4 inch aft of the left at ZERO rudder position. The pedal stalks are now about the same angle to the deck, the brake cylinders don't hit the deck, and pressure at the wheels has gone from a measured 250psi to 400+ psi. The brakes now hold at 2000+ rpm. Soooo, I now have about 1 and a half inches of "builtin" right rudder travel on T/O with pedals even, (not all bad), and some left pedal forward in cruise. (I actually lessened it with a little padding on the left pedal) I'll take the tradeoff, besides, my Flight Advisor, Ed Kolano, sees it as acceptable.

          

 

Nose Wheel Steering w/linear actuator      Brake Pedal Geometry redesigned

(click to enlarge pictures, browser back button to return to this page)

(Pictures submitted by Wally Weller)