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Thread: Datum Ski Question

  1. #1

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    Datum Ski Question

    For those who run them....

    You're parked outside at -30 for several days and it's time to go. How does the electric actuation work? Sluggish? Stubborn? Has it ever failed to run smoothly? Can the actuators ice up? Get fouled in overflow?

    Thanks.

  2. #2

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    The actuators are quite powerful and will lift the airplane onto the skis while stopped. At -30 ... yes, they will be sluggish when doing that. Puts a lot of stress on the mechanism so I normally only change from wheels to skis and back while in the air. My skis have never failed to work or to run smoothly. I imagine the shaft on the actuator could get iced up easily under certain conditions, but just as easily cleaned off and back in business. In overflow? I don't imagine they'd be worse than any other type of wheel-ski, though I haven't been in that situation .... so far!

  3. #3

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    Can you use 850x6 tires? How's the tail clearance with skis up? The pictures I've received from Datum look like the tails are almost dragging with skis up.

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    Here Click image for larger version. 

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    Stewart,

    Heres a photo of the Rosti ski's. 8.50 tires. The hydraulics will not lift the plane, but as Nunavut pointed out, that's tough on any system. I've had these ski's in nasty overflow, and no problems....landed in overflow and slid up onto a gravel bar to park. Took off into the overflow. Ski's cycled fine airborne. Stuff didn't stick much to the composites. And these things are large and very light.

    MTV
    Last edited by mvivion; 09-28-2016 at 10:30 AM.

  5. #5

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    I know about them and have traded emails with Thomas. This isn't a thread about Rostis or the "best" skis. I have questions about Datums because I want to hear pireps from users. The Datums are $10K+ less expensive than Rostis so I think a conversation is warranted.

    What skis are on your personal plane?

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    mvivion's Avatar
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    Quote Originally Posted by stewartb View Post
    I know about them and have traded emails with Thomas. This isn't a thread about Rostis or the "best" skis. I have questions about Datums because I want to hear pireps from users. The Datums are $10K+ less expensive than Rostis so I think a conversation is warranted.

    What skis are on your personal plane?
    Stewart,

    Sorry for the thread drift, my bad. I don't have skis for my personal plane, which is a 90 hp PA-11. My hangar is a long way over plowed asphalt to anywhere I could operate straight skis, and retractables simply weigh too much for an 11 in my opinion. Not to mention I'm at 4500 msl. with 90 hp available.....

    MTV

  7. #7

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    No doubt the Rosti's are the best, but were way beyond my budget.

    6:00 x 6 tires are the limit with the Datum 2500's.

    I've fiddled with the cables for two years and have finally got the ground clearance I need for our gravel runway, although this puts the skis at a zero angle or maybe down just a bit when flying with the skis up. Not a problem though, and when I select skis down the bungees pull the tips up where they belong. I three-point it when landing on wheels.

    The skis are heavy (but tough) but probably not much (if any) heavier than hydraulic skis since you don't need pumps and hoses. Less stuff and activity in the cockpit with the electrics.

    The only thing I've broken so far (my fault, landing on snowmobile trails) was the fork tip on one of the actuators, and I'm told I have to buy an entire new actuator ($325) because that $2.00 tip can't be replaced!

    Other than that, I'm happy with the skis.
    Last edited by NunavutPA-12; 09-28-2016 at 03:24 PM.

  8. #8

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    I'll send a photo later today so you can see the ground clearance and how mine are rigged.

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    I'm looking at the specs for the 3000s. The tire limits are 22" height and 8" width. I need to find my old 850s and measure the width. Scooter's 800s are under the limits both ways.

    The electric actuators are an interesting idea. Heck, I never thought I'd want electric trim but my new plane has it. I have lots of cordless saws, drills, and nail guns and they make air hoses obsolete for many tasks. DC motors are a lot better than they used to be.

    R-F skis used to be fiberglass and they aren't the most durable things I've seen. The Datums being fiberglass is a bit of a concern. New Rostis are carbon fiber. I know guys who think that's a durability concern as well. Airglas skis are about bullet proof. There's something to be said for that when you hit a drift or frozen snowgo track. There are a handful of ski choices and all have different strengths and weaknesses. I'm just trying to sort them out.

    Thanks for the replies.

  10. #10

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    Well, I'm pretty rough on my Datums, mostly due to my own incompetence, and I haven't yet damaged the skis themselves, just that actuator tip.

    The rear cables have to be tight and at the right angle to pull the back of the skis up for maximum clearance. They have to lead toward the rear so that they come loose as the ski moves back, allowing the bungee to pull the tip up. My front check cables and bungees are attached to the lower engine mount bolt and the rear cable goes to a "Y" connected to the rear landing gear bolt and the float fitting.

    I think you'd bend an axle before you'd break these things!

    Click image for larger version. 

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    Photo taken 30-minutes ago. Yes .....that's snow on the ground!
    Last edited by NunavutPA-12; 09-28-2016 at 02:20 PM.

  11. #11

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    Quote Originally Posted by stewartb View Post
    For those who run them....

    You're parked outside at -30 for several days and it's time to go. How does the electric actuation work? Sluggish? Stubborn? Has it ever failed to run smoothly? Can the actuators ice up? Get fouled in overflow?

    Thanks.
    You're getting good feed back to your questions. I've never looked at a set of Datums, and very few other types either for that matter. However, fixed penetration wheel/skis have served very well in all kinds of situations on our Rans S-7S. (mine are home made, work great and not for sale).
    In March of this year, we tried my brothers new wheels skis from Summit, carbon fibre, plastic bottoms, and those skis also worked Excellant. Judging from the wt., ease of install/uninstall, sturdy build etc., we'd not hesitate for a second to recommend Summit Wheel/skis. Summits also work with 850 tires.
    Just an option to check out.
    Roddy

  12. #12

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    I think the Datums have the best clearance of any wheel ski out there, which is the main reason I bought them as I have "varied" terrain to deal with at my home strip. I have never had any problems with the actuators icing up or anything, though experience has shown it's best to make life as easy for the actuators as possible. As in, don't stuff the front of the ski into a drift and make it pull the plane uphill while pulling the tire onto the ski, or....have big globs of mud on the tires and force the system to deal with that as it retracts.

    Or (I could go on all day) be taxing up the narrow steel ramp from the sloped runway below, that you covered with HDPM sheeting to slick it up, but then the
    big headed pop rivets you used to attach it pulled through the sheeting thanks to the heavy winds, and then you used carriage bolts, and then the sheeting still came loose and you caught a ski wear bar on the bolt head and it brought you to a dead stop and bent the actuator extention tube. Point being, the only issues I've had have been due to gross error on my part. Then again on the other hand, when I had a large drift on slide out (flat light made it unseen) and got launched back up kind of cock eyed and then came crashing back down with zero airspeed pretty much from about 6' and one ski hit first, all was well. The skis are very tough, use the actuators as they are intended and they work fine. Any minor issues are worth it for being able to ski fly while still having the ability to handle grass, gravel, mud, or other rough conditions. Try that with a wheel penetration ski, I wouldn't make it out of the hangar with them, much less to my strip.

  13. #13
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    I just found this old-ish thread. I have a set of 2500 Datums on a 4 place Bearhawk. Our winters have been terrible since installing them, so I have little experience to speak from. ...but so far, they are outstanding!

    Drawbacks:
    - The 2500s max at at 6.00x6 tire as mentioned by NunavutPA-12
    - On the Bearhawk, the calipers don't mount high enough to fit a double caliper with the skis.

    NunavitPA-12's picture shows his calipers mounted at 12 O'clock so they don't hit the skis when in wheel mode.
    --
    Bearhawk, RV-4
    Thanks TopHeavy thanked for this post

  14. #14

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    Quote Originally Posted by kestrel View Post
    .....NunavitPA-12's picture shows his calipers mounted at 12 O'clock so they don't hit the skis when in wheel mode.
    Yeah, I had them in the "standard" nine-o'clock position but the bleeder screw rubbed on the ski. Brakes seem to work fine in the 12-o'clock position though, and I haven't had any problem bleeding them.

  15. #15

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    My Datum experience, in my 5 th. season now: about 30 to 50 hrs a season, depending on the snow (GREAT this year). On my experimental, I am limited to a single brake caliper, while many others that fly the same exp. (without skis) have dual. No big deal, my brakes are fine, I land so slow they are not needed much. On one side, if and when I bleed it, I have to unbolt it, while keeping it plumbed, bleed it while holding it at the correct angle, and then bolt it back down. Another, no big deal, it's not like I need to bleed my brakes often anyway, or ever. The need to use the smaller tires is like everything else associated with ski flying, a compromise and part of the price of admission. I don't like having to move all the snow that drifts in front of my hangar either , and wouldn't if I didn't ski fly, but it's worth it.

    Now here is my latest Datum news, after a 3 hour romp in the Lemhi Range area just yesterday, I stopped on the way home at Mackay for lunch. BTW, the asphalt there for some reason is like a cheese grater, just horribly abrasive, the worst I have ever seen, and I never land it when on the Airstreaks, but use the gravel edge. With all the snow I had to land the tarmac, but of course on the cheap and hard 6:00's I didn't care! I always taxi to the north end as far as possible to park (off the centerline of course) that way it's a 3 minute at most walk to the gas station/cafe "Sammys." They sell ethanol free mogas for the ATV crowd, handy for me too. Anyway, once fed, I took my 16 oz. cup of real hot coffee (they use the machines that brew a cup at a time, and it's as hot as McDonald's used to make their's) in one hand and a 2 gallon jug of mogas in the other (a solid half hour for me, didn't really need it but I was right there so why not), and as I took off a few minutes later, it all went wrong. I was a little distracted by the need to balance the hot coffee in it's to go cup (no thermal cup for me, that'd be cheating, too easy) , but that's something I often do so not that big of deal. But the big distraction was a local LEO of some sort, sheriff deputy I think, that blasted by me, on the parallel to the runway highway, with lights flashing.

    Since we were both going the same direction, I figured I'd keep him in sight and see what the fuss was all about. At one point I almost couldn't keep up, he was doing 100 mph, maybe a bit more. But of course I was going in a straight line so I managed, but at one point I had to fly behind some small hills and lost sight of him. At the same time I saw a large, 50 head or more, herd of elk that were obviously being fed by F&G (I guess) in a field and I circled a bit to check them out. Then I cleared the hills and after a fruitless search I realized that whatever action he was heading towards, was now back behind me, and I lost interest in seeing what it was, going out of my way to gawk at an accident or whatever it was was too creepy, so I just headed for home, about 80 miles away across the high desert.

    Once back in the mountains and over my place, I did what I almost always do, have just a little more fun before putting it away. I have one little knob top just across my property line that I like to spot land on, using the steep side facing my house to slow me down, coming to a full stop at the top, or nearly so, then powering off downhill and using another bump to launch me back up into a max rate of climb high banked turn that turns into a max rate of descent spiral and set up for landing. It's pointless and just a way to celebrate making it home OK again. Plus the next morning, I can look out the kitchen window while drinking coffee and see my tracks, that's priceless.

    By now, most probably know where I'm going with all this.... thanks to the flashing lights on the LEO, and the distraction of "chasing" him, and the damn elk herd, plus the scalding hot coffee, I forgot to "put the skis down," actually they get sucked under the tires by the electric actuators, but you get the idea. I had flown clear across the desert with the extra drag of the high AOA skis hanging down, fat, dumb, and happy, like flying along with one notch of flaps down, not that I've ever done that, or no one else here has, right? That's what checklists are for! So, I arrived on this fairly steep bump with a nice solid set down, with no flying speed left over (as planned) as there is no length for a gentle gliding gradual touchdown. It worked fine, I came to a full stop right on the knob top, rather more abrupt then usual, then right when I advanced the throttle for the downhill takeoff it hit me, and before I thought it through I hit the switches (finally) to "go to skis." To my surprise, they started sliding under the tires as usual, with only further concern being as they did I started sliding downhill even back at idle, but by the time I really had to go to full throttle to avoid a gully the skis were mostly in place and the takeoff was uneventful. 10 seconds later I was landing, a couple minutes later it was back in the hangar, with at least a casual look over showing nothing worse for wear, I'll check everything closer tomorrow but I think I got away with it. I have no idea if others have done this, or I'm the first, but it's good to know that if one is stupid enough to get distracted that you can still land without a major problem. This snow was deep, 3', and all in all this was about a worst case scenario. The one good thing, if I had wrecked it, I could have walked home in a few minutes and looked at it while drinking coffee the next morning. This picture was taken earlier in the day, before I got distracted.
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  16. #16

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    Quote Originally Posted by courierguy View Post
    My Datum experience, in my 5 th. season now: about 30 to 50 hrs a season, depending on the snow (GREAT this year). On my experimental, I am limited to a single brake caliper, while many others that fly the same exp. (without skis) have dual. No big deal, my brakes are fine, I land so slow they are not needed much. On one side, if and when I bleed it, I have to unbolt it, while keeping it plumbed, bleed it while holding it at the correct angle, and then bolt it back down. Another, no big deal, it's not like I need to bleed my brakes often anyway, or ever. The need to use the smaller tires is like everything else associated with ski flying, a compromise and part of the price of admission. I don't like having to move all the snow that drifts in front of my hangar either , and wouldn't if I didn't ski fly, but it's worth it.

    Now here is my latest Datum news, after a 3 hour romp in the Lemhi Range area just yesterday, I stopped on the way home at Mackay for lunch. BTW, the asphalt there for some reason is like a cheese grater, just horribly abrasive, the worst I have ever seen, and I never land it when on the Airstreaks, but use the gravel edge. With all the snow I had to land the tarmac, but of course on the cheap and hard 6:00's I didn't care! I always taxi to the north end as far as possible to park (off the centerline of course) that way it's a 3 minute at most walk to the gas station/cafe "Sammys." They sell ethanol free mogas for the ATV crowd, handy for me too. Anyway, once fed, I took my 16 oz. cup of real hot coffee (they use the machines that brew a cup at a time, and it's as hot as McDonald's used to make their's) in one hand and a 2 gallon jug of mogas in the other (a solid half hour for me, didn't really need it but I was right there so why not), and as I took off a few minutes later, it all went wrong. I was a little distracted by the need to balance the hot coffee in it's to go cup (no thermal cup for me, that'd be cheating, too easy) , but that's something I often do so not that big of deal. But the big distraction was a local LEO of some sort, sheriff deputy I think, that blasted by me, on the parallel to the runway highway, with lights flashing.

    Since we were both going the same direction, I figured I'd keep him in sight and see what the fuss was all about. At one point I almost couldn't keep up, he was doing 100 mph, maybe a bit more. But of course I was going in a straight line so I managed, but at one point I had to fly behind some small hills and lost sight of him. At the same time I saw a large, 50 head or more, herd of elk that were obviously being fed by F&G (I guess) in a field and I circled a bit to check them out. Then I cleared the hills and after a fruitless search I realized that whatever action he was heading towards, was now back behind me, and I lost interest in seeing what it was, going out of my way to gawk at an accident or whatever it was was too creepy, so I just headed for home, about 80 miles away across the high desert.

    Once back in the mountains and over my place, I did what I almost always do, have just a little more fun before putting it away. I have one little knob top just across my property line that I like to spot land on, using the steep side facing my house to slow me down, coming to a full stop at the top, or nearly so, then powering off downhill and using another bump to launch me back up into a max rate of climb high banked turn that turns into a max rate of descent spiral and set up for landing. It's pointless and just a way to celebrate making it home OK again. Plus the next morning, I can look out the kitchen window while drinking coffee and see my tracks, that's priceless.

    By now, most probably know where I'm going with all this.... thanks to the flashing lights on the LEO, and the distraction of "chasing" him, and the damn elk herd, plus the scalding hot coffee, I forgot to "put the skis down," actually they get sucked under the tires by the electric actuators, but you get the idea. I had flown clear across the desert with the extra drag of the high AOA skis hanging down, fat, dumb, and happy, like flying along with one notch of flaps down, not that I've ever done that, or no one else here has, right? That's what checklists are for! So, I arrived on this fairly steep bump with a nice solid set down, with no flying speed left over (as planned) as there is no length for a gentle gliding gradual touchdown. It worked fine, I came to a full stop right on the knob top, rather more abrupt then usual, then right when I advanced the throttle for the downhill takeoff it hit me, and before I thought it through I hit the switches (finally) to "go to skis." To my surprise, they started sliding under the tires as usual, with only further concern being as they did I started sliding downhill even back at idle, but by the time I really had to go to full throttle to avoid a gully the skis were mostly in place and the takeoff was uneventful. 10 seconds later I was landing, a couple minutes later it was back in the hangar, with at least a casual look over showing nothing worse for wear, I'll check everything closer tomorrow but I think I got away with it. I have no idea if others have done this, or I'm the first, but it's good to know that if one is stupid enough to get distracted that you can still land without a major problem. This snow was deep, 3', and all in all this was about a worst case scenario. The one good thing, if I had wrecked it, I could have walked home in a few minutes and looked at it while drinking coffee the next morning. This picture was taken earlier in the day, before I got distracted.
    Courierguy, you are one heck of a discriptive writer! You are in "print" like Swingle was in video-always interesting. Keep up the posts!
    Roddy

  17. #17
    kestrel's Avatar
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    Quote Originally Posted by courierguy View Post
    I have no idea if others have done this, or I'm the first, but it's good to know that if one is stupid enough to get distracted that you can still land without a major problem. This snow was deep, 3', and all in all this was about a worst case scenario.
    Dang! I had wondered if they would work as "penetration skis"! It may depend on the installation details of where/how the weight is carried on the ski when in wheel mode. I think mine would work. It could also depend on the details of the spring/bunch tension, cable geometry, etc...

    I have found that I can not "lower" the skis to ski mode when there is weight on the skis. I once tried raising one ski to help with a turn. When the turn was complete, lowering the ski resulted in the motor stalling and the circuit breaker popping. ...I was probably at 2,100 lbs or so. I was able to reset the breaker, get out, flip the switch and then lift on a wing strut before the breaker popped again to get back into ski mode for take-off.

    The one good thing, if I had wrecked it, I could have walked home in a few minutes and looked at it while drinking coffee the next morning. This picture was taken earlier in the day, before I got distracted.
    That would have been a sad sight while sipping morning coffee!
    --
    Bearhawk, RV-4

  18. #18
    C-FIJK's Avatar
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    What hold the ski on the axel , just that stub in the axel ?




    Quote Originally Posted by NunavutPA-12 View Post
    Well, I'm pretty rough on my Datums, mostly due to my own incompetence, and I haven't yet damaged the skis themselves, just that actuator tip.

    The rear cables have to be tight and at the right angle to pull the back of the skis up for maximum clearance. They have to lead toward the rear so that they come loose as the ski moves back, allowing the bungee to pull the tip up. My front check cables and bungees are attached to the lower engine mount bolt and the rear cable goes to a "Y" connected to the rear landing gear bolt and the float fitting.

    I think you'd bend an axle before you'd break these things!

    Click image for larger version. 

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    Photo taken 30-minutes ago. Yes .....that's snow on the ground!
    Gerry Marcil

    Every day spent flying is a great day !

  19. #19

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    Yes. Solid steel stub inserts into axle, held with a cotter pin. Stub is fixed, ski pivots around the stub. Ski is held to stub by a big nyloc nut.

  20. #20

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    I have a solid machined insert that is inside my hollow 1 1/2' axles. It is what extends out past the wheel and engages the Datum bracket, it's held in place with a 1" nylock nut. With the skis in their normal position, the landing loads are transmitted through the tires and gear in the usual fashion. So you get a little cush from the tires, the tires are also somewhat faired by the skis. Yes, that is all that holds the ski to the plane, that and I guess the pressure of the tire on top the ski. It seems to be enough, I've landed a lot of brushy and wind drifted, compacted snow, some of it side sloped, and they seem to hang in there just fine.

    What I did, near as I can tell, was put ALL the landing forces on that machined solid insert, and if it held up without damage I'll be impressed, as that sure as hell is not the way it was designed to be used. I emailed the Datum guy in Quebec, fessing up to what I did, a few hours ago to get his take, but I'm pretty sure I know what to look for. I got the heat on now in the hangar and will be giving everything down there all the close up look see today.
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  21. #21

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    It's all good, nothing tweaked, all checked out. I'd be flying now but the fog has moved in. I really had wanted to eyeball the tracks I left when landing with the wheels downs, but I'm not going to snowshoe up there.

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