Tail ski mount

I've had my Datum tail ski mounted up for years, but since I switched over this summer to the T-3 spring, I needed to "engineer" up a new setup.

I bought an additional smaller and wimpier (also lighter and less expensive) Matco tailwheel, the intent being it will stay on the ski, and be just for winter use. One AN-7 bolt and 2 spring rings (just made the term up, but the stainless rings, like on a key chain, that serve as a cotter pin does but are quicker to remove and reusable, common in hang glider and ultralight hardware and very reliable) and the winter wheel is off or on. Not an optimal angle on the marine turnbuckle (had it already in the shop junk drawer, high quality and stainless, plus I had it, this was a project using whatever I had laying around) to the tailwheel bracket, but it should do the job and gives plenty of adjustment range. I think this should work just fine for keep the little ski at a reasonable AOA, I will just need to remember not to do any super high, tail wheel hitting first, type landings while on pavement. When on gravel or mud, the lesser clearance I now have with that smaller tire will just be some extra wear on the ski bottom, no problem as I have a large piece of the type of plastic used on hand, plus I actually taxi little, and lift the tail up often anyway.

I'd be a little concerned with it being unable to flex with changing snow contours.



There is a Burl's ski under this snow. This tail ski has a piston with springs on either side that keeps the ski tip at a positive angle but allows for some movement. As I remember AC43.13 suggests a bungee to the tip to keep it pointed up when unloaded but permits some vertical travel on the snow surface.

Sourcing a Burl's type piston spring may be beyond the capability of my junk drawer, and since my tail is so light (50/60 pounds,) I thought I'd give it a shot as is. There actually is some give, the front attach point of the turnbuckle is an old stainless hang glider tang, and it's hole was 3/8", and the pin is 1/4" so there is some built in slop (at least until I find some bushing material or make another tang) and that translates to a fair bit of movement at the tip. I could of course use a bungee and a limit cable up front, and on the rear, as I do have all I need on hand to do so. But as of now my thinking is the ski attach point bracket can handle the forces involved. Or not....I will keep a close eye on it the first few hours, Having the tip flopped down would not be good, just like the main skis, but I can't see that happening. Worse case would be my brake formed attach bracket gets bent, indicating a redesign is needed, but should be safe enough. One handy feature of that turnbuckle: I'm still on the 29" Airstreaks, and once the skis and the 6:00 hocky pucks are on, it will be a simple matter to re-adjust the AOA of the ski.

I also had to re-do my proven (2 seasons use on my mountain strip, it let's me decide when to start the takeoff, not the downhill grade) tail release gizmo, and it turns out the Matco tailwheel has 2 holes that serve no purpose, (other then lightening I suppose) that worked perfect for the release's attach point, got lucky there. It will now stay permanently attached to the tailwheel, the old design had it pulling off the front spring bolt and it worked fine but was a complicated procedure to take it off and on, the minor cost of the extra tailwheel is paying for itself by really simplifying how it all goes together. I'm losing weight also. The release cable itself is still furled up and zip tied inside the fuselage, it's summertime home.

If I had the time and the video skill, I'd make a video parodying Mike Patey's work, calling it "whatever is in the junk drawer" or something like that, and the catch phrase, instead of Mike's BACK TO WORK, would be TIME FOR A BREAK. I do get a kick out of doing a project with what's on hand, while at the same time have it do the job it was intended for safely and efficiently

The “what’s on hand” tailski ;








Transmitted from my FlightPhone on fingers...

Often don’t need much to stay up.
Here it is riding on top.




And parked next to Glenn running just a wheel..




Transmitted from my FlightPhone on fingers...

Looks like you have a stop, a thru bolt, that comes up against the fork to keep the springs from bringing the tip up too high? Simple enough, now you got me thinking.....the front bungee and limit cable would be easy enough for me to fab up, it was the rear limit cables that stymied me. That I wanted to avoid, your stop does that job but simpler.

My first tail ski mount, that I used for 350 hrs., had a bracket that in effect captured the tailwheel forks, so the ski itself was fixed, with no give up and down. It worked, and I do a lot of steep and uneven terrain. It worked well enough for me to feel the fixed ski concept is , though not optimum, is good enough, and most importantly, safe enough to try again. But now, thanks to your pic, I may have to start over! ha ha....

Farm boy, I like your tail ski. Is that made from black UHMW? How thick? I once made a wooden form to shape a similar ski around but never finished the project. I like your simple approach too.

I run a limit cable and bungee on the ski trip. My ski sits at about a 45* angle when flying. Cable doesn't let ski trip go below horizontal. I use a TW ski when snow gets deeper or a heavy crust. Because I taxi downhill to my hangar a prefer no ski so that I can dig the TW in when needed.

Glenn

If I recall it's 3/8" thick, I have a fairly large heat gun I used for shrink wrapping boats that I tempered it with to bend the edges up.

Yes, there is a simple right angle stop that contacts the fork when the spring tension overrides the snow or air. Now that I think about it, pretty sure I have a boring video of it, on runways but maybe one spot with snow. I'll link it.

I have joined the "the tail ski has to be able to move" crowd. Even though my 360 hrs of fixed tail ski time, all mountain flying with all kinds of weird slopes, shows it's not totally required, I get it now!

Here's the latest: that huge front bungee is a scrap from one of my old front/main bungees, which I replaced last year. The limit cables, 3/32", both sides, are 40 year old hang glider remnants. The grade 5 3/8" x 4.5" bolt dropped in the vert axle of the Matco, will be my "tow hook", when I get cattiwampus taxiing up my approach ramp, or out and about and using the rope comalong, and need the tractor to square things away, I want a dedicated pull point, something easy to rig to. This was another item that had to be relocated/changed with my new T-3 spring. I had to lose the cotter pin that secures the big castle nut, safety wired now, and one side of the bolt ground down to allow it to slide past the wire. Short of pulling straight up, the bolt needs no in place securing, one of those light bulb moments! It will stay in the tool bag normally, along with my front main gear bridle hardware (that pulls off both axles), but when needed can just be dropped into place and used. I've had situations where the plane had to keep running while doing this, making enough thrust to prevent it from sliding down hill (my parking brake goes on the blink every winter) so a tow point quick and simple, and at a location to take some force, can be critical. I also had to drop down my release mechanism, as it's original design failed to take into account the fact the changing position of the tailwheel when in the air and loaded down. It was either move it down or reshape the rudder!


Turns out my brake formed aluminum attach bracket could serve as a stop for the up tilt of the ski while in flight. But, while rummaging around in one my drawers looking for the tail tow ring, I stumbled upon some black bungee ( wait...what's this, oh that's right, I forgot I had this) that I used on my first set of cub like main gear shock struts, before I converted it to Fox air shocks and conventional 1380 HD bungees. In the drawer for 8 years or so, out of the sun point being, seemingly still fresh and springy, I will use it for the rear as I am not willing to tolerate the extra drag of a cocked up at a 45 degree angle tail ski while in the air. Having that huge bungee in front, and the smaller in the rear, should be correct in overcoming the in flight dynamic loads in order to keep the ski at a much more favorable AOA, according to the computer modeling I've done. Or, I'm just using what I have and making it up as I go along....I didn't rediscover the smaller bungee until I had already rigged that bigger stuff, my backup plan is to take off the big stuff, and use a double wrap of the smaller stuff up front, and a single in the rear. Time for a break.

I’d say that’ll give you all the movement you might need. It doesn’t take much but rigid isn’t good IMO.



here’s the form I made about ten years ago. You guys have inspired me to pick up where I left off. The two dowel pins are to keep the UHMW aligned while the edges are formed. The two corresponding holes in the plastic will be cutout when penetration hole for the tail wheel is cut.



This is how I move my tail around and it doubles as a tie down point too. The ring is an eye nut and there is a -7 castellated nut under it. Because an AN7 bolt doesn’t have a long enough thread length for both nuts I used a Grade 5 fine-thread bolt upside down.

This is the T3 spring and in my application it has a little too much positive camber. The tail wheel is difficult to get into the trailing position once it has turned backwards, like when pulling it into the hangar. It is a bit of a fight to get it to trail again pushing it out.

A great flying day forced me to halt the tail ski project for a couple days! It was a quick and easy 2 minute job to take the wintertime small TW, it's tail release mechanism, and ski off, all as a one piece unit, and just as fast to put my summertime TW back on, for some end of the tire season boonie bashing that I didn't want to subject that little ski to. I have a couple small details and I'll post a picture of the finished project, total cost so far has been 5 bucks.

courierguy said:

A great flying day forced me to halt the tail ski project for a couple days! It was a quick and easy 2 minute job to take the wintertime small TW, it's tail release mechanism, and ski off, all as a one piece unit, and just as fast to put my summertime TW back on, for some end of the tire season boonie bashing that I didn't want to subject that little ski to. I have a couple small details and I'll post a picture of the finished project, total cost so far has been 5 bucks.

Click to expand...

I absolutely love the backdrop of that second photo. Thanks for sharing!

motosix said:

I absolutely love the backdrop of that second photo. Thanks for sharing!

Click to expand...

It's Idaho's highest peak FWIW. And, where I watched the recent full eclipse a few years ago. The normally empty adjacent area was full of other watchers (down lower though) and even 3 days later local traffic was heavier then usual. It was quite the event, best of all was being able to overfly all the traffic when it was over!

After we got just enough snow to make me install the Datum skis on the main gear, I could wrap up the tail ski mod. The AOA difference between the 29" and 6" tires made me wait.

I used a electrical split bolt I had on hand as the main keeper for the doubled up bungee, and also a couple hog rings I also had on hand for some gabion work I was doing earlier this year. Pull tests in my vice showed the bungee would probably break before the split bolt would let things slide, the hog rings are the suspenders, the bolt, the belt. Setting the bungee tension was of course done in the three point position, and I liked the adjustability the split bolt gave me. I initially thought to put a bungee on the tail ski rearend, and did so, at a tension that I thought would overcome/ignore the inflight forces on the ski wanting to make it tip up. This inflight attached pic, besides making me nearly lose my phone, shows the aero forces took precedence, tipping the ski up to it's hard stop. Rather then getting into a bungee war, playing with rear and front bungee adjustments to see if the I could find a balance that kept the tip up for landing, while also not letting it ride up in flight, I decided to take a tip from Farmboy and just not worry about it, problem solved!

So, the first ski landing of this season, on a sloped hillside, I come in slow and nose high, and tail first. Not uncommon, I have real good elevator authority in the Rans S-7S and VG's....but right at touchdown I felt a bump that got my attention. After completing the landing I got squared away and took off again immediately, and remembered that unlike the tire season, I now had the ability to eyeball my tracks, and did so. Sure enough, the tail hit first, my theory on the bump I felt was that with the ski cocked up while in flight, and then making a high AOA landing/really dragging it in, the tail ski hit first before it had a chance to swivel down. So I landed again, this time making a more normal/not so high AOA landing, and it felt good, no bump. Once shut down I inspected everything, thinking that maybe my tow release was trashed and maybe my rudder, and found all was fine. So, I have to decide if it's worth messing with, bungees front and rear, each at different tensions, or just let the ski sort it all out as nothing got hurt, and maybe dial back the high AOA touchdowns a bit.

Is the tow release the red contraption and is it always attached even during flight?

That tow mechanism attached to the tailwheel and attached to a T3 looks pretty marginal to me. In my experience and feedback the T3 is a pretty stout unit but it does not tolerate much in the way of side loading and with that lever arm sticking out the back there I would imagine that pulling laterally on it is exerting a pretty stiff side load.

Could be fine too. The newer T3's are very beefed up on the attach points but man, I wouldn't want to push my luck there. What are you towing with a Courier anyway?

The release is meant just to be strong enough to let me, while parked at the top of my ski ramp, to transition to the skis, and then start the engine and do a mild run up, all while not yet going anywhere. Once it's released the slope means I'm launching, whether I've changed my mind or not.

Or are you talking about the bolt dropping into the top of the tail wheel, THAT is my tow point, I guess I should have responded to that first. Any tail spring setup I have had hasn't been much for side loads, and I agree this T-3 is probably the same. Hard to design something that has a 2 or 3 " wide base, where it mounts to the tail cone, to stand up to a lot of side torque. IF I need to tow there, I'll make sure its straight in line with the fuselage, hopefully! I have not needed to tow the last couple years, I've gotten used to using the right amount of speed/power to make it up the ramp without continuing through the (closed) hangar door. This varies with snow conditions of course, keeping things interesting. Stalling out half way up the ramp is not good, full power won't climb it from a dead stop, throttling back and shutting down and I start sliding backwards, hopefully eventually getting a bit cockeyed to the slope so I can shut down, if not I have to set the throttle to hold the plane on the slope, and then climb out and manually get it cockeyed enough to shut it down. This all makes summer flying seem pretty simple.

Well I was just generally referring to the tow bar being attached to the tailwheel head which is on the end of the T3 swingarm. Get too enthusiastic about pulling laterally on that tow bar and it'll damage the cross bolts and bushings in a hurry. As long as you're not pulling sideways on that towing mech then it should be all fine.

Got ya, should be fine, it will only be used after I push the plane straight out the hangar far enough to close the Hydroswing door. Then I close the door and rig to it's bottom truss as a tie down, everything all in column. That release is the least of my worries regarding mountain ski flying! Got my first injury of the season on my second landing of the season, making my turnaround on a side slope, greatly extending my turning radius, I got a bad charley horse in my calf muscle from tensing up on the rudder pedal so much. Not the first time either, sure is fun though.

Now that you've gone this far... I've seen a video of your down and up the ramp before and it looks like the next step is, (getting ahead of me here?) release with power on in a kind of delayed cat shot. Then upon returning use your tailhook to stop you on the apron in front of the door. From what I've seen on this thread, the engineering talent is here.
Boldly go.

Gravity is my cat shot, no real need for a full power tail hook release! Same with landing. That "just enough power but not too much" to make it up the ramp is the tricky part, but so far my hangar door remains unscathed. Also, the bottom of the earth ramp has a fairly abrupt transition to the main runway angle, and I like to refrain from hogging the throttle until I'm past it.

Very good. Here's to light airplanes, plenty of power and 2020 behind us! Enjoy the snow gentlemen.

My T3 API home made wheel ski







Glenn

Yeah that'll work! I bought my tail ski when I bought my Datum skis, what was another few $$ was the thinking, I didn't even consider making one. I didn't know anything, NOTHING, about ski flying, so decided to just suck it up and pay.

Mine does allows 360 degree movement of the tailwheel and attached ski, that was really needed for the way I get mine back in the hangar, making that happen complicated things, but after messing with it long enough the solution turned out to be simple after all.

Cruising along yesterday from a 3 hr. flight to the Grand Tetons and back, with lots of screwing around on the way back, I started to become obsessed with the idea that my tilted up tail ski, while in flight, was causing unacceptable drag. Don't ask for any numbers, just a gut feeling, it started to remind me of when I first installed cub style gear on my S-7S, unfaired and uncovered. The original spring rod gear gear legs (like a VANS) were nicely faired and quite low drag. I flew with the new gear for 15 hours before it gradually sunk in that the slight performance loss was persistent and real, before committing to covering and fairing it, with very good results. It wasn't a huge difference, and the additional drag was minor enough to at first write off to "bad air", having a big payload/full fuel, etc. The same may be happening with my new tail ski mount. If I wanted to really prove it, I could take it off the plane and stick it out the car's window while doing 80 mph, and check the drag on my arm while playing with it's AOA, but that sounds like a good way to dislocate a shoulder or get road rash on the ski after it got ripped out of my hand so I'll pass on that.

It could be all in my head, if so, all the more reason to take steps to eliminate the issue! So, this morning I rigged an aft bungee, with enough tension on it to lower (and hopefully keep it lowered) the AOA of the ski. This picture is at a flying attitude (putting a hard point in my hangar ceiling for a rope hoist to lift the tail to whatever attitude I want is a handy feature). But....once I lowered the tail, the ski appears to be at too small of an AOA, where before the bottom surface was parallel to the ground/snow, now is tilted up a bit. But my thinking is I do a heck of a lot more flying then I do taxiing, and the upturned ski tip should still tend to float the ski rather then let it dig in. If on gravel I get a little light contact on the plastic bottom, screw it, if and when it wears down enough to matter I have a 4x8 sheet of the stuff. Flight testing will commence as soon as this fog I'm in right now lifts.

That entire tailwheel you have should be a pretty big drag issue. You might want to start with simple stuff like not flying with the toe bar attached. The ski angle will effect drag so I think you are on the right track. DENNY

The reason for the tow bar being there is the reason I can't take it off. It holds me in place once the skis are down, the engine is fired up, and I'm perched right on the edge of my ramp, down to the sloped terrain that comprises my runway. All of it too steep to just sit there, engine on or off, once on the skis. I forgot to mention I was comparing the apparent drag of my new tail ski setup, to the one I had the previous 9 seasons, complete with the same tail hook release. That one had a fixed mount with no give or flex, and one good thing about it was it kept the ski AOA inflight down. What I want to achieve is as neutral as possible AOA, but while still having the flex of a pivoting ski. The only real disadvantage of my old setup was the original mount bracket got tweaked over time, no doubt by it's inability to pivot. Rather then redesign the fixed mount, I went this direction. Until I see if this works like I hope, my next direction may be to go back to a fixed mount, but with a better/strong fixed attach bracket.

I should also mention, any extra expense is not an issue. As long as the costs don't rise over the 5 bucks or so out of pocket this has cost me so far (2 new quick links from Ace Hardware), all else was on hand all ready.

I also just noticed, in my picture in post #6 of this thread, taken a few years earlier, that's the same LZ in post #13, been landing it for a while I guess. My reason for going to Driggs ID yesterday was to see somebody I've known off and on for years, and when I asked him for a lat/long of his property so I could possibly land there, he said "it's the same place you landed that first time, but there's too many houses there now." He claimed it was 20-25 years ago, but after digging out my old log books I saw it was 38 years ago, that made me feel better in forgetting all about.