New die spring landing gear on a Pietenpol, 10 a.m.-4 p.m.
Last week I wrote a report of the weight & balance and performance of Bob Lester’s Pietenpol going from a 65 hp Lycoming to 100 Corvair ponies. Here are some photos of the conversion, and an important improvement Vern and I made in the plane at my hangar. Bob flew the plane over in the morning, we did the work, and he flew it home in the afternoon. In my book, this type of gear is an improvement over bungees. Bob had just replaced his bungees, but had a very hard time getting enough tension on them, so his plane sagged. Bungees have worked on a hundred thousand light aircraft, but here is a look at an alternative system that I have used for many years.
Above, Bob’s aircraft on the ramp in our front yard at 10 am. It is easy to see that the gear is splayed out terribly. The bottom of the fuselage at the front gear attach fitting was only 22″ off the ground. I was motivated to fix this for Bob first because it is dangerous due to poor handling and the potential for a prop strike. Bob isn’t a welder, and I didn’t want him to keep flying it until something happened, The plane did have safety cables under the bungees, but they turned out to be boat cable, something I wouldn’t trust. Beyond all this, aircraft that have the gear like this look as if they are massively overweight. I didn’t want anyone to come to the false conclusion that it was the additional weight of the electric start corvair that was doing this. The only light aircraft that has the gear like this is the ugly “Texas Taildragger” Cessna 150 STC’ed conversions. Besides, gross wheel camber like this reminds me of lowered Honda cars driven by teenagers with their underwear sticking out of their pants, booming rap songs and 4″ diameter mufflers with the exhaust tone of a flatulent elephant sitting in a mud puddle. If you compare this with the photos of the aircraft when it still had the Lycoming, keep in mind that Bob had tried to re-wrap the bungees in between the photos.
Above, on the welding bench in my hangar. The red part is the original bungee strut. Above it is the steel die spring and the tube that houses it. We cut the ends off the red part and grafted them on to the new tubes. The springs are available from A/C spruce for about $100. Their rating is 1200 pounds per inch. They are 1″ ID, 2″ OD, and 6″ long. the spring works in compression. The 2.25″ outer tube is fixed to landing gear frame at the top. The 1″ tube works as a plunger. It passes up the middle of the spring to a washer welded on it above the spring. When the plane lands, this strut elongates by compressing the spring. Many people have seen the reverse of this system with external springs with complex machines slots. I made that style for my Pietenpol in 1997. It required a mill and some precision work. After making it I got a chance to see an aircraft that Bernard Pietenpol himself had built. It used this external tube system. Brilliant, just as you would expect from the patron saint of homebuilding. The tube method has no milling, has no high shear points, is self aligning because the two ends are free to rotate., and had obviously worked for a few decades. But be forwarned, if you choose to put this on your plane, you will still have a handful of people tell you it will never work. (take their photo and name down, send it in and we will all make fun of them together.)
Above, I trim the ends of the main tube square in the lathe before welding. This makes it easy to get a great vee notch for penetration on the end caps. The 1″ bit is sticking into the tube to keep it from going into low earth orbit if it get lose in the chuck. We trim the tube to 6.25″ overall. This length has a great harmonic”ringing” sound if you get the tool shape just so, it gives the feeling of the fillings in your teeth falling out.
Above, a 2,25″ heavy-duty washer gets welded on each end of the main tube. The hole in the middle of it has to be drilled for a slip fit on the 1″ tube. The first weld is done without the spring or 1″ tube in place.
Above shows the 2″ washers welded onto the 1″ tube. The spring has to be inserted before assembly.
Above is a head on view of what Vern and I were working on curing. Bobs plane flies great, but letting this go would not show well and potentially end up putting the word “Corvair” in an accident report some where. I have devoted more than 20 years of my professional life to Corvair powered planes. I am in this for the long run, and letting something like this go, even if it never broke, projects a poor image of the Corvair movement. Besides I have been friends with Bob for 13 years, and I want him to have a sharp-looking, safe plane.
Above, the spring is inserted into the tube, the plunger goes through it, and the top cap gets welded on the spring gets a slight compression to prevent it from being noisy. In a ground loop, this system goes metal to metal in compression, just like a bungee system does. The part in the vice grips is the top cap, with the fitting taken from the red strut and blasted clean and pre welded on. If I was building from scratch, I would use a rod end or a fork. (off the topic, but Irwin made vice grips in the USA for decades. Today they are made in China. This disgusts me. CEO’s that make decisions like that should have their citizenship revoked and be sent to China themselves, but then we would have to send the new president of the EAA to Mao Se Tung land also. He was the CEO who sent the Cessna 162 to China. Google his name and the words “60 minutes, CEO, fraudulent engineering degree” for a nice look at his integrity.)http://www.aero-news.net/index.cfm?do=main.textpost&id=d75a19ed-4ce3-4ddf-abc4-7b2da56dc1db
Above, top cap being welded on. You could not gas weld this without hurting the spring inside, but it isn’t an issue for a tig welder.
Above, one side down, one to go. This is a significant drag reduction when you also consider the bungees bags. Heat and some oil are the enemies of the bungees. However, the steel spring would only consider getting baked and a fine mist of oil a form of love and care.
To save people who live for worry, speculation and internet drama the hassle of thinking up their own troubling questions, I provide them the questions pre-made:
Why does that long-haired, opinionated mechanic William Wynne think this system would even work? What makes him think springs are tough enough? Maybe they are no better than bungees. William’s thinking of selling kits to do this, so if he might make 25 cents, and doesn’t that mean we can’t trust him to give us an impartial review? Wouldn’t I be better off taking the advice of a guy on a Matronics list who has never flown nor built one of these? That guy wouldn’t ever write back with an unsubstantiated claim would he?
OK, look above. This is the underside of the hangar gang wagabond. I welded this gear up in 2004. It has flown many hours and landed at over 1600 pounds gross. It works well period. I am not a great pilot, but I was well schooled by two masters. The only time I have in my log book in any tricycle geared aircraft is a single 30 minute flight in a 1963 Cessna 150 in 1999. I went to the airport that day and my old school instructor said “There are some things you should do once in your life, but not speak of….Today you fly the Cessna one filthy.” It was hardly the trip to adult entertainment section of Bogota Colombia I first thought he was hinting at.
Seriously, I have flown a number of classic conventional geared aircraft to know what a well-engineered, well-behaved one feels like. A far better evaluation is that a number of super-skilled pilots flew both my Pietenpol and the Wagabond, and pronounced them to have excellent handling. How tough are the springs? The ones in the Wagabond gear are actually salvaged from my Pietenpol wreck in 2001. They worked for hundreds of hours in the Piet, got smashed into the ground at 15 or 20 G’s, were BBQ’ed by the plane burning to a cinder, laid in a rainy field for 6 months, and then I cleaned them off and saved them for the next project, which turned out to be the Wagabond in 2004. Until they invent the elastic asbestos bungee, you can’t claim a bungee is this tough. (actually someone will, but ignore them.) Bungees are date coded. and they are to be taken out of service every few years. It may creep you out, but steel springs will out live you.
Above, in the fitting process, we held the aircraft up with the hoist and telescoped the original tube bottom into the 1″ tube. We tacked it with a mig welder and rolled it back and forth to have it settle. We checked every thing with levels, and actually cut the tacks on the right side twice. On the third try the plane sat perfectly level. The struts turned out to not be the same exact length because the original builder in the 1970’s didn’t make everything symmetrical. It takes a small error here to make the plane have a wing tip an inch lower on one side. In other planes this could be completely avoided by having adjustable rod ends or forks on the ends. When perfect, we pulled them back out and TIG welded them on the bench with the proper rosette welds. Graces’s Taylorcraft and our 1-26 sit on the front lawn in the background.
Above, the finished product at 4pm. Ugly and dangerous duckling transformed in 6 hours, including a lunch siesta. The new ride height is 26.5 inches under the fuse at the front fitting. While it looks tall, scratch built gear on a piet can be much taller. Look at Photos of my blue Piet and you will see that the gear was 30″ under the fuselage. This extra angle of attack available in the three-point attitude allows the plane to land far slower, and stop shorter. It also looks a lot better. If anyone says “but you will not be able to see over the nose.” suggest that they go ask the guy they paid for a conventional gear check out for a refund. Ask an old school instructor if looking over the nose in the flare is a “technique,” and he will probably slug you like Buzz Aldrin decking a conspiracy nut job.( http://www.youtube.com/watch?v=tRBesDx1WQc )
Very important to handling, when the plane is empty and at rest, the tops of the tires should be slightly further apart than the bottoms. Only when the plane is actually taxing at full gross weight should the tires come close to vertical. When the plane lands, the gear, if it is steel leaf, steel coil, bungee or Aluminum, has spring rate, but no damping itself. All the damping comes from the action of scrubbing the tires from the orignal camber, through vertical and then a little bit further. This is a very powerful damping force, especially on pavement. If the tires start out as vertical, the system forfeits much of the available damping, and starts heading back to the original incorrect camber. I know arcane details like this because I spent 5.5 years of my life at Embry Riddle. (If I had only known that I could one day be president of the EAA with a fake engineering diploma for credentials, imagine how much time and money I could have saved.)
Above, Bob with his re-done aircraft. This is a radically different aircraft than it was a few months ago. It when from barely having a positive rate of climb with two people on a hot day to being able to climb 800 feet per minute at the same load and conditions. It now has safe and smart-looking gear that works correctly. The plane is 25 mph faster now on the top end. For reference, Bob is 5’7″ or so.
Above Grace, Chris Welsh, Terry and Vern stand at the edge of our lawn and the runway. They are watching Bobs test taxi and flight on the new gear. The plane looked so much better than it had a few hours before, I was filled with a sense of pride in the skills, understanding, tools and capability I had painstakingly worked for over the last two and a half decades.
If you have never met me, but read this and think that I am charmed with myself, you got it all wrong. I know countless humans who are better people than I. They are kinder, smarter, and harder working. I can’t sing nor dance, I learn slowly, and I can’t stand to hear my recorded voice nor see my image on film. If I was once handsome, all trace of it is gone along with my uncorrected eyesight. I can be a conversational bore, and I deeply wish I had given my parents more moments to be proud of me. At 50 I look back on my life with a very critical eye and stand on the far side of a very wide gulf from the heroes of my youth. Even our dog, impeccably honest and loyal as canines are, Loves Grace and only tolerates me.
Honest evaluation leads to harsh thoughts like this. I spend a lot of time alone and have long bouts of insomnia, which can lead to thinking about things excessively. But the secret I would like to share with anyone who at times feels the same way, is that I have a sanctuary where I am insulated from much of my self-criticism, and a have a front, where at 50, I am much better on than I thought possible in my youth. When I am building things with my hands in my shop, I rarely feel poor. Although I now need glasses to do any close work, and my hands have lost a lot of dexterity, I am a far better craftsman than I ever was in my youth. I am not a great craftsman, but over a very long time I have worked to develop these elements in my life, and I compete with no one except who I was last year. While all else fades, these things flourish. It is a gift I am most thankful for.
I was aware of this in my youth, but it did not come into focus until 1999, the worst year of my life. (getting burned was 2001, but it was a picnic compared to ’99.) Feeling dangerously low, I sought the council of a guy I knew. He had come back from such a year. He is an artist, working as an incredibly detailed wood carver. He tells me to forget everyone and everything else, go back to your tools and work with your hands. Give up your apartment, but never your hangar. Explore all the things you can’t forget, have stolen, give away or loose. At the moment, I was having a hard time picturing another week, and I asked him how long it took him. The thought with great care a slowly said “two, no really three..” I was jolted and blurted out “Three months?” he looked me in the eye and said “No. Years. It’s probably your only way out.” It turned out to be a painfully accurate prediction.
In the years since I have read letters or posts from many people in a tough spot, who have sold their project or tools. I often think their ship is sinking and they have just traded their life jacket for five more minutes on the deck. I have also met a number of successful builders who have said that when everything else in there lives was broken, they had a place of refuge in work and creation. Of the thousands of people I have met in aviation, these people are truely brothers, for we share the same salvation.
For these reasons, I can honestly say that the only time I allow myself to feel anything most people would call pride, is when I exercise my skill knowledge to make something good. Much of the time, this is far better in the company of Grace or friends like Vern. It’s not real often that I indulge myself for an hour and give in to being pleased with something. Maybe two or three times a year. Watching Bob’s plane fly away with the gear fixed was one of these moments. There was stuff to do, but instead we sat around outside and enjoyed the evening. -ww.
6 Replies to “New die spring landing gear on a Pietenpol, 10 a.m.-4 p.m.”
William, I’ve met you at Brodhead (I’ve been going since 1999) and have talked with you several times. I fly Ken Perkins Piet N34KP when he brings it up. I’ve been an aircraft mechanic (light and heavy) since 1975. Right off the top of my head I can’t think of any light airplane I’ve worked on with conventional gear that DOESN’T have an outward cant to the top of the tires when they are light. The Cessna singles (172,182 etc.) have it in the main gear also, when light. It’s essential to the damping of the landing loads. Scrubbing the gear as you said. Don’t let them get you down.
ps. I read your article about the “C” spars used in a Piet. Yes, it worries me too.
I have skimmed through this article before, but only just now read to the end. The last few paragraphs are most poignant and self identifiable. Thank you.
Gary, I had also read the article some time ago and had decided to go the route of the coil springs as my bungees were sagging and there was no way of knowing how old they were. As I remember the cost of new bungees were not a lot different than the springs which were a permanent fix. I used the same springs that WW recommends. I however, used the external spring method. Two reasons, first I have a GN-1 and it is heavy as most GN-1’s are and I thought the external springs with smaller tubing would be a tad lighter overall. (probably not a deal breaker, however) The main reason was that I like to do my own work and I only have a gas welder. Welding near the spring with gas (as WW indicated) would damage the spring from excessive heat. I found the design I used on line at a Piper forum and it was for a replacement for a Cub. I modified the design slightly and only needed to cut 1 set of slots for each strut rather than 2 sets shown in the design. I used fork ends from some old wing struts I had so my gear is adjustable. I also can take it apart should I ever need to do repair work. As it sits now I have 28″ clear at the front gear leg attach point and about 7/8″ threaded adjustment to shorten each strut. The adjustment is at the top end of the strut and I will need to drill a small hole at the bottom of each strut to let out any moisture that may get inside the tubing through the open slot. I am very satisfied with the results but It seemed like a major undertaking. I thought about it for many months. The hardest part was figuring out how to support the fuselage at the proper height in my shop. I had the engine in place so it was quite heavy. That actually turned into a slight disaster when I had the fuselage engine and all do a snap roll to the floor while I was removing an original gear strut. Luckily I was unhurt except for my pride and in a couple of weeks I had repaired all the damage, I had become a smarter builder and was a bit more methodical as I proceeded. I am not sure I will gain any more speed as the GN-1 has a lot of exposed structure hanging down for the gear attachment on the belly but I won’t loose any either.
Jon Coxwell, firstname.lastname@example.org
I am currently building an Easy Eagle 1 designed by Ron Grosso. The original built by him had a Cub style gear although any pictures available do not expressly show the total design of the gear. When the plans etc. were picked up by Great Plains Aircraft, the design changed to a one piece aluminum gear which in my opinion is out of character with the biplane design and maybe a tad heavy. In my search for a reasonably easy to build Cub style gear I came across this article. Thank God for Google. The spring from Aircraft Spruce and the original Pietenpol is more to my liking and in line with my idea of design. My gross weight will be approximately 750 pounds and this spring would be over kill as I’m sure the Pietenpol with the Corvair engine, fuel and pilot could handle the spring rate as built in this article.
For anyone having any advice for me in this regard as to shortening this spring or finding another appropriate one for my application. Please drop me a note at email@example.com.
How much preload on the springs?
I can imagine anything from none to 100% static empty weight just barley getting off metal to metal…