Wing wheel from Craggy Aero

[2G]

I wanted to replace the Cobra wing wheel I had been using because 1) it goes with the ASH26e I have for sale and 2) the tire scrubs the tarmac as I go around turns, putting stress on the wing. I ordered the CA WingWheel from Craggy Aero because the wheel swivels with the direction of travel:
http://www.craggyaero.com/ground_handling.htm
And the length is adjustable which helps greatly for storage. It is also has a spring shock absorber that the Cobra wheel does not have. I tried it out today and towed my ASH31Mi (with the 21M tips) around the Richland, WA airport (KRLD). The wing wheel worked great and put no stress on the wing. The Cobra wing wheel would bend inwards as the tire was dragged sideways in a turn - the CA wing wheel tracked perfectly and was always in a vertical position. The height of wheel was more than adequate to keep the wing tip above obstructions (taxiway markers and signs). This version also has improved straps over the earlier design. Fabrication of all components is excellent - no thin walled aluminum tubing, for example. The tire is not pneumatic, so it can't go flat. It is wide enough so it will not drop into pavement cracks. It is well worth the additional cost over the Cobra wing wheel - I was always holding my breath when I used it.

Tom

[Andrzej Kobus]

The best wheel I have had is the one from MM Fabrication. Very sturdy, well fitting and does not stress ailerons.

[2G]

That wheel does not swivel, so it will suffer from the same scrubbing problem that the Cobra wheel has.

[Andrzej Kobus]

Not true, the other wheels have scrubbing problems because they are flimsy and they fit poorly. I tow on concrete all the time, never have had a problem. I had all kinds of wheels before and they were all terrible, especially on concrete. I had the same concern as you before I bought the MM Fabrication wheel and I asked Mark to modify the wheel to include swivel. He said to try it they way he makes it and it works perfectly. He uses precise wing airfoil to manufacture the wheel, so each wheel fits only one glider type. This is why it sits on the wing perfectly and it does not move at all. I am a very happy customer!

[2G]

While the clamping of the Mark's wing wheel is better than Cobra's, scrubbing is inevitable because of the geometry of towing. I actually tried to buy Mark's wing wheel and even mailed him a check after he complained about others cancelling orders, but he still didn't want to make it. The CA wing wheel works better, is adjustable, has a shock absorber, is well made and is cheaper. And it was in stock.

Tom

[markm...@gmail.com]

Not exactly true. Tom inquired about a wing wheel, wing cuffs and a tow bar. I explained that tow bars were out of stock and wing wheels and wing cuffs are custom fabricated. Because of my involvement in another project, I informed him that delivery times were questionable, if at all possible. I don't recall receiving a check at all.

As far as "scrubbing" being "inevitable," also not true. Over 300 of my wing wheels are out there, and if properly positioned and aligned with the direction of travel, they track well.

But you can't convince Tom, since he is always right.

[doug...@gmail.com]

>
> The best wheel I have had is the one from MM Fabrication. Very sturdy, well fitting and does not stress ailerons.

I second that opinion. The MM Fabrication wing wheel for my Libelle is built like a tank, and fits like a glove. I don't have a scrubbing problem either. My MM wing wheel and tow bar are some of the best money I have spent on gliding equipment.

Doug

[2G]

Come on, Mark. I sent you the check - I've got a copy of it - along with a purchase order, which I also have a copy of. You said you could make more money on another project. I said, "Ok, then shred the check and forget it, no hard feelings."

Scrubbing is what happens when you turn a tire on a radius. I have seen it happen with my Cobra wing wheel. If the wing is long enough and the turning radius tight enough, you get to the limit where the wing wheel is at the exact center of the turn and is being turned around a point. This scrubbing pushes the wing wheel sideways and is very obvious with the Cobra wing wheel. It's not me that's right, it's physics that's right.

Tom

[jpg...@gmail.com]

I am a convert to the swivelling wing wheel - for me the IMI one which is beautifully designed and has a decent sized wheel unlike some others.

There are 2 factors that can make any fixed wheel twist or rock. Firstly the tight turn or on the spot rotation when if the wheel is not precisely longitudinally aligned it will twist badly. Secondly, if the wheel is not absolutely vertical then there is a castoring effect as you tow straight. This pulls the wheel in or out. On rough ground with unballasted wings it can self-correct with each bounce of the wing and wobble along. When ballasted, especially on smooth grippy hard surfaces, the cuff can't twisted sufficiently to dent the wing skin or damage a control surface - both of which I have had over the years with three different wing dolly designs on three different gliders.

A broad rigid custom fitted cuff masks the underlying concept flaw but a good swivelling wheel eliminates it. The worst designs have heavy legs, a fixed wheels, and a generic cuffs with spongy padding.

[Brett]

But you can't convince Tom, since he is always right.[/i][/color]

Come on, Mark. I sent you the check - I've got a copy of it - along with
a purchase order, which I also have a copy of. You said you could make
more money on another project. I said, "Ok, then shred the check and
forget it, no hard feelings."

Scrubbing is what happens when you turn a tire on a radius. I have seen
it happen with my Cobra wing wheel. If the wing is long enough and the
turning radius tight enough, you get to the limit where the wing wheel
is at the exact center of the turn and is being turned around a point.
This scrubbing pushes the wing wheel sideways and is very obvious with
the Cobra wing wheel. It's not me that's right, it's physics that's
right.

Tom

Go back to school Tom.




--
Brett

[markm...@gmail.com]

> Go back to school Tom.

Brett- Don't bother. Tom installed diodes on his brain. All TX, no RX

[Richard Pfiffner]

On Saturday, May 2, 2020 at 5:54:05 AM UTC-7, markm...@gmail.com wrote:
> > Go back to school Tom.
>
> Brett- Don't bother. Tom installed diodes on his brain. All TX, no RX

I have had one each of MM Fabrication products WingRigger, WingWheel, and TowBar for at least 10 years maybe more. They are great! Thanks Mark.

The only problem I have with the CraggyAero Soaring XX Wingwheel is everytime I set one up for my glider a customer buys it and I have to go back to the old standard MM Wingwheel.

Richard
www.craggyaero.com

[jfitch]

If the wing wheel is biased forward, so that it is inline with the main gear axle, there will be no scrubbing as the geometry is correct for any radius turn. The further behind the main gear the wing wheel is, the larger the problem. My complaint on the Cobra was the wheel was too small for rough ground, so I fitted a much larger one. It seems like the Craggy wheel is much smaller still. Probably works well on pavement.

[Andrzej Kobus]

No offense Tom, but you are coming across as you know best. I have been using his wing wheel for four season on the 31 Mi with excellent results without any "scrubbing" as you put it.

[2G]

Andrzej,

That's because I do my research and I gave my fair evaluation, nothing more. Mark is basically calling me a liar. I could publish the proof that he is blowing smoke, but why bother - he isn't going to change. The scrubbing DOES occur, you are not witnessing it because you may be too far away in your tow vehicle. Anytime you force a tire to go in a different direction to which it is aligned (i.e. a turn) the tire WILL scrub as it realigns to the new direction. just google "tire scrubbing" to learn more than you will ever want to know. There is nothing inherently wrong with Mark's wing wheel. Hell, I tried to buy one buy Mark proved to be more difficult to work with than most.

Tom

[markm...@gmail.com]

OK. Enough is enough. Tom, you ARE a liar. Below is the entire email string between us. You indicated the delivery time was unacceptable for the wing wheel, but you would send a check for the tow bar. I have no record in my bank statements from 2019 that indicate a payment from you, nor is there any evidence that I received one or refunded your money.

What this shows is that you NEVER paid for a wing wheel, and probably not the tow bar either. You are a bombastic, pontificating asshole, an opinion shared by several other pilots who know you and have responded to me privately.

If I ever decide to resume production of wing wheels and tow bars, rest assured that your requests will be denied.

Hi Mark,

I would like to order:

Tow out bar
Pair of wing cuffs
Wing wheel

These are for a ASH31Mi.

Need pricing for the lot plus shipping.

Thanks,

Tom

From: Tom S---
Sent: Tuesday, February 26, 2019 12:29 PM
To: Mark M
Subject: Re: Tow out dolly

Hi Mark,

The delivery is ok for the tow-out bar, but not for the wing wheel. I will send you a check for $275. What is the price for a wing cuff?

Tom

From: Mark M
Sent: Tuesday, February 26, 2019 6:46 AM
To: Tom S---
Subject: Re: Tow out dolly


Tom-


Price on the tow bar is $200. The optional tail lifter is $50. An ASH-31 wing wheel is $700. Shipping on both is $75.


I am out of stock on the tow bars, and wing wheels are each custom fabricated. Delivery is generally 4-6 weeks after receipt of payment, but I am involved in a really big project right now, so my time is limited. It might take a bit longer unless I can squeeze them in.


Best regards,

Mark M


On 2/25/2019 1:06 PM, Tom S--- wrote:
> Hi Mark,
>
> I just called you about a tow-out dolly for an ASH-31Mi. I also need a wing wheel. Please respond with price and delivery costs for both. My address is:
>
> Tom S---
>
> Thanks.

(Email and physical addresses deleted. Last names also deleted, but you can read between the lines.)

Your interpretation of "scrubbing" is based on your experience with the Cobra wing wheel, probably the flimsiest, mass produced, doesn't-fit-anything piece of junk I have seen. It can't be properly aligned with the direction of travel because it doesn't clamp to the wing securely and it flexes so much that the alignment changes when it is in motion. The cheap-ass foam rubber padding slips, dries out and then crumbles into dust.

When I bought my first glider in 2000, I used one a couple of times and immediately started work on a design that evolved into a product that had over 300 buyers, many of them repeat customers. Is it the best? Maybe not, but it evidently satisfied the needs of the customers. I am very glad that you were not one of them.

(And it's not physics, it's simple geometry.)

[2G]

Mark,

OF COURSE you don't have a record in you bank statements, I told you to SHRED the check that I sent you after you told me you had NO IDEA how long delivery would be, if ever. Presumably you did that because the check was never cashed. A week after I told you that you called me back and told you had a break in your schedule and could do the job, but I was DONE with you by that time. Your memory of this is appalling, but mine is perfectly clear - you just don't fantasize sending a $1,200 check to someone. Here is the purchase order I enclosed WITH the check dated 3/6/19:

PURCHASE ORDER

To: MM Fabrication
PO Box 1623
Moriarty, NM 87053
Mark,
Per your previous quotes by email and telecon I am placing an order for the following items:
1 Single-place tow out bar $200
1 ASH31Mi wing wheel $700
2 ASH31Mi wing cuffs $250
1 Shipping $75
Total $1,225
Enclosed is a check for the total amount. Please contact me if the shipping costs exceed $75 and I will pay the difference. I will forward a tracing of the inner panel cross section as soon as available.
The shipping address is:
xxxx
xxxx
xxxx
xxxx
Thanks,
Tom

Scrubbing is a fact of life because of the geometries involved. The forces exerted on the wing wheel are the same, but the Cobra deals with it far worse than your wing wheel.

[krasw]

All wing wheels scuff when glider turns if the wheel axel cannot turn. If the wheel fits wing very well this not a problem and you really notice it only when turning the glider while it's stationary.

Cobra, Schempp and many other older "unisex" wheels don't fit anything. Using them is based on trial and error, you learn to fit it to correct direction and then it sort of works, maybe 60% of the time.

SoarinXX wheel is huge improvement in design. I just wished the would have used real bearing on svivel joint instead of that flimsy plastic bearing. That has to carry wing full of water on uneven ground.

[jpg...@gmail.com]

Look at the IMI swivelling wheel. It is well designed, substantial, suspended, shock absorbed longitudinally, and has a larger wheel than SoaringXX one. Also it uses the same cuff and wheel as their original so I, for example, only had to buy the new arm to upgrade.

The IMI cuff is universal and multi adjustable but its clever trick is the reinforcing contouring of the top sleeve which allows the rear of the top to flex around the top of the wing contour and to grip it. Combined with the new swivelling wheel it is excellent.

I have no connection to IMI but use all their tow out gear, including their rubber block suspension tail dolly. Their own website is not up to date but for you in the USA I see that Wings and Wheels listing is.

[stu8...@gmail.com]

> >
> > Scrubbing is what happens when you turn a tire on a radius.
>

> If the wing wheel is biased forward, so that it is inline with the main gear axle, there will be no scrubbing as the geometry is correct for any radius turn.

Ignoring who said and did what, I just learned a useful geometry lesson.

Assuming 'scrubbing' is when the rubber on a tire rubs instead of rolls over the pavement.

Another symptom is 'hopping' where the wheel tracks wrong and rolls out of position flexing the mount. Eventually, there is enough force from the flex to make the wheel hop back into position. Definitely some 'scrubbing' involved as well. Definitely a worrying situation because the flex is putting weird loads on the flying parts.

If the wing wheel is vertical and in line with the line of travel, why would there be scrubbing when you are going straight?

If in addition, the axle of the wing wheel points to a line directly above the main wheel, why would there be scrubbing when the glider makes a turn?

Maybe in the limit, neither one of these can be aligned perfectly, but if you put the wing wheel in the right place it ought to work pretty good.

That explains why my old wing wheel still hopped on curves even after I adjusted it so it points straight ahead. Also why the new MM one doesn't.

Guess a swivel might be another out of the hole, but not the only way.

[jfitch]

To be correct geometry for a specific radius turn, the wing axle must point towards center of the turn radius. The axle lines of the main and wing wheel intersect at this center. If the main wheel is the center, then the wing axle must point towards it. A swiveling wheel will align itself to this geometry. For a non swiveling wheel to be correct geometry for *any* radius, the axles have to be in line (more specifically their projection to the ground plane has to be on a line), guaranteeing that both axle lines intersect at the circle center regardless of radius. The wing wheel will then not scrub, even if it is the center of the turn. It will turn about its vertical axis, just as the main gear (or indeed the swiveling wheel) must, in other circumstances. That is not "scrubbing" as the term is usually applied.

And now, back to the popcorn....

[jpg...@gmail.com]

That is true assuming that the leg of the dolly is vertical and a non-vertical leg would make a negligible difference on a single tight turn. However with a noticeably non-vertical leg and a fixed wheel (e.g. and in my case, on the dihedraled outer part of a D2C or V3 wing) then on a straight tow, no matter how accurately the cuff is alinged, the wheel will tend to turn itself (like how you lean to turn a bike). It will then either relieve itself by bouncing, or by skidding back to position, or it will twist the dolly until you stop and go and sort it - depending on the surface and the weight on the dolly from ballast.

[jfitch]

For a non horizontal axle, there will be camber thrust from the wheel. There may also be steering force due to trail, steering head angle, and offset causing problems if the attachment to the wing is insufficiently rigid. The polyhedral on the SH gliders creates a lot of ground handling problems, that among them. If you always put the wheel on one wing the angles could be compensated. I'd think the swiveling wheel would work even worse though, as the combination of trail and steering head tilt inward will cause the wheel to steer towards the fuselage constantly. Perhaps you should try a Mecanum or other bi-directional wheel :).

Slightly related, bicycle and motorcycle dynamics (or any two wheeled vehicle) are quite a complex subject and only recently fully described mathematically (in the last ten years or so). The solutions are too complex to solve so numeric methods are used.

[RR]

>Slightly related, bicycle and motorcycle dynamics (or any two wheeled vehicle) are quite a complex subject and only recently fully described mathematically (in the last ten years or so). The solutions are too complex to solve so numeric methods are used.

Not only complex but very few people who ride bikes or motorcycles even know how they initiate a turn. Most assume that if you want to turn left, you pull back on the left handlebar, but in fact to turn left (while moving at a reasonable speed) you push on the left handlebar. The dynamics cause the bike to lean left, and the geometry causes the wheel to turn left to compensate. It is one of the reasons it is hard to learn how to ride a bike, the handling changes with speed.

Try it, push lightly with your fingertips, the handlebar will push back after the turn is initiated. Hang glider turning dynamics are related.

Rick

[2G]

All turns, whether on the ground or in the air, have one immutable thing in common: there must be a lateral force to cause an object with momentum in a straight line trajectory to change that trajectory. A wheel can have its axle turned and the tire generates this force by friction with the ground, as occurs while executing a turn in a car. If some other force is applied to the car to turn it, such as a wind gust, the tire will resist this turning force until the applied force exceeds the grip of the tire. The car will then skid. The same thing is going on with a glider's wing wheel as it is being forced to turn around a curve by the towing vehicle. This lateral force will be the same regardless of the design of the wing wheel, it will just be less apparent with some than with others. This force MUST be transmitted to the wing - there is no other place for it to go.

Tom

[markm...@gmail.com]

Tom has sent me a private email accusing me of making a libelous statement against him.

In the interest of keeping the peace, I apologize for any statement I have made.

[stu8...@gmail.com]

I'm bored with cabin fever, so why not talk about how rubber meets...

>
> All turns, whether on the ground or in the air, have one immutable thing in common: there must be a lateral force to cause an object with momentum in a straight line trajectory to change that trajectory...

Here's the logic I'm hearing here.
The glider has momentum which must be countered to make it change direction.
The wing wheel provides this because there is no other place for it to go.

Given that a glider with a castering wing wheel can still turn, perhaps the main wheel can provide most of the turning force?

[Martin Gregorie]

Yes, came here to say that. The two places that carry the main loads
while a glider is being towed are the main wheel and the tow ball.

Side loads when turning or towing cross-wind will be largely carried by
the main wheel while the tow ball adsorbs rotary momentum (of wings and
rear fuselage) at the start and end of a turn or when swivelling the
glider in place.

If the wing wheel is fairly close to the spanwise line through the main
wheel's contact point with the ground and its axle is parallel to the
spanwise line, then there should be little or no side force on the wing
wheel: if your wing wheel cuff can't guarantee that the main and whng
wheel axles are parallel then, or course, all bets are off.

OK, heres an analysis of a light glider (my 201 Libelle). My wing wheel's
axle is roughly under the LE when fitted, so is probably close enough
fore/aft to the main wheel's contact point for scuffing not to be an
issue. The cuff is 280mm (11") wide and a snug fit everywhere including
at LE and TE, so the wing wheel's axle will be fairly accurately parallel
to the main wheel axle. I've never seen any tendency for the wing wheel
to scuff when towing the glider on either grass or hard surfaces.

My wing-wheel assembly weighs 5.4 kg and is on the lighter wing: in still
air with the glider stationary its always the other tip that slowly drops
if I let go of the wing and during airframe weighing the other wing was
around 4kg heavier. Its quite obvious that there's very little load on
the wing wheel when towing because, on our grass airfield, running over a
small clump or a heap of cuttings will make it leave the ground an inch
or two and only briefly.


--
Martin | martin at
Gregorie | gregorie dot org

[jfitch]

Unless you are doing some high speed slalom with your tow bar, the sideways forces on the glider are negligible. This is not what creates the scrubbing and hopping that is being discussed. If you ARE doing high speed slalom with your glider, then the forces contributed by each component depend on the tire traction and slip angles. Since the glider is nearly balanced on the main, it will carry perhaps 95% of the vertical load, the wing wheel carries only slightly more than it's own weight. The main also has a much larger contact patch than the wing wheel, and much stiffer mountings. So it (and the tow bar) would carry nearly all of the lateral force. Which, for normal tow out ops is nearly zero.

[2G]

On Sunday, May 3, 2020 at 9:02:02 PM UTC-7, markm...@gmail.com wrote:
> Tom has sent me a private email accusing me of making a libelous statement against him.
>
> In the interest of keeping the peace, I apologize for any statement I have made.

Thank you.

[2G]

I load the wing wheel with a gallon of water to prevent gusts from dropping the opposite wing. I think it is near impossible to get perfect alignment of the axle of the wing wheel with the axle of the main, but this is negligible. The other issue is the wing dihedral tilting the wing wheel off of vertical. I have observed the Cobra wheel tilting badly in a turn. If there were no lateral forces on the wheel it would maintain its vertical position regardless of poor the clamping was to the wing. Perhaps once the wing wheel starts to tilt the forces on the wheel increase, aggravating the situation. But scrubbing is taking place, which I showed by taking the wing wheel to the limit where it is at the center of the turn. At this position the wheel isn't rotating at all, but is being scrubbed as it is rotated. This is reduced, but not eliminated, as the wheel is moved away from the center of rotation.

Tom

[Brett]

But scrubbing is taking place, which I showed by taking the wing wheel
to the limit where it is at the center of the turn. At this position the
wheel isn't rotating at all, but is being scrubbed as it is rotated.
This is reduced, but not eliminated, as the wheel is moved away from the
center of rotation.

Tom

Sooo much talk about scrubbing. Who really cares? Who has ever had a wing
wheel tyre (tire to you guys) wear out? Sooo many people offended by you
Tom.
It's actually International Hand Scrubbing Day today. It might be more
constructive to discuss that in the context of todays issues.




--
Brett

[markm...@gmail.com]

I've worn out two or three tyres (sic). But I have to tow a kilometer each way on asphalt. (and the tire just shows wear down the middle. Motorcycle racers call that sort of wear "the chicken strip.")

[markm...@gmail.com]

> Sooo much talk about scrubbing. Who really cares?

It's not the tire wear we care about. It's the nasty torque load imparted to the wing trailing edge and control surface that occurs when the wing wheel skips from side to side if it is not aligned correctly with the direction of travel.

[MNLou]

I just replaced a wing wheel tire on Saturday. When I went to pump up the tire I noticed exactly what Mark said - a "chicken strip" of wear with some wear down to the cords.

Imagine my surprise when I realized the wheel bearings were very"crunchy". (I never noticed any resistance while in use.)

After some TLC, she is now spinning like a top.

It might be worth giving your wheel a spin and listening.

Lou

[jfitch]

There may be lateral forces on the wing wheel, they not due to centripetal forces in a slow speed turn. It is due to misalignment of the wing wheel axle with the instantaneous direction of travel. All you need to do is draw the axle extensions of all the wheels involved on a piece of paper - main gear, wing wheel, tow vehicle wheels. If these do not meet at a single point, there is scrubbing on the axle that doesn't (traveling in a straight line, that single point is at infinity). It is geometrically impossible to achieve this for any turn radius (less than infinite) unless: the wing wheel axle is allowed to caster, or the wing wheel axle lies on the same line as the main gear. On some gliders the latter is difficult as the main gear is well ahead of the wing and a castering wheel is your only option. On most though, all that is necessary it to tilt the wheel fork forward a bit to get the wheel approximately under the leading edge which is typically the location of the main gear. The further aft of the main it is, the greater the problem. If you cannot keep the axle pointed in the direction you want, then bets are off. The Cobra wheel is not the best in this aspect.

This isn't really rocket science - vehicle builders have been doing this for millennia - it is true for oxcarts as well as race cars. Ackermann described it in the early 1800's for horse drawn carriages, and he stole it from others.

[Andy Blackburn]

On Tuesday, May 5, 2020 at 6:31:53 AM UTC-7, markm...@gmail.com wrote:
> > Sooo much talk about scrubbing. Who really cares?
>
> It's not the tire wear we care about. It's the nasty torque load imparted to the wing trailing edge and control surface that occurs when the wing wheel skips from side to side if it is not aligned correctly with the direction of travel.

I think alignment parallel to the main wheel (and path of travel) is the key thing. I've run through the geometry and I don't think turning generates appreciable (or any) lateral loads on the wheel at the tip if it is aligned properly when you put it on. Certainly it will travel a shorter distance on the inside of a turn and longer distance on the outside of the turn, but that just means it'll spin on its axel a bit less or more (it's why cars need a differential). It's free to do this. Try drawing two concentric arcs and a radius through both to represent the angular offset in a turn. Both arcs are perpendicular to the radius. Sure, if the tip wheel is mounted so it trails the wingtip by many feet (imagine tens of feet and the main wheel going in a circle so small that the glider is essentially pivoting on the center of the main wheel and you get the picture - the tip wheel would look like an additional tail boom and would scrub), but that's not the situation we are talking about here. Towing your glider with your car generates pretty gentle turns and all tip wheels I know of don't mount very far off the perpendicular line from the main wheel. All the scrubbing I've seen is due to wheel misalignment when you put it on.

That's not to say a castering tip wheel isn't useful. It is. It allows the user to be more casual in aligning the wheel when mounting it. I have a Cobra wheel and the fancier IMI wheel. I like the design of the IMI wheel a bit better - but it is also a more expensive design.

Andy Blackburn
9B

[2G]

Obviously not you. What do you tow on, grass? I have worn out two tires in a few years. Sorry if you're offended - suggest you stop reading this thread as a remedy. Who wudda thought that wing wheels would be so controversial? Welcome to RAS.

Tom

[Duster]

A few years back, someone showed me his unique design for a w/w. He mounted a basket-ball sized, round utility ball (with a bladder) that freely rotated against an upside-down "cup" which housed a dozen or so ping-pong ball sized "bearings". The ball allowed easy movement in any direction. (Picture one of those roller-type deodorant applicators in motion). He made a brake for it from a metal band that was actuated by a thumbscrew. Clever

[jfitch]

Andy, not sure what you drew and this antiquated site will not allow pictures. If the wing wheel is behind the main gear, the arcs they are trying to describe are not concentric. The worst case is a turn towards the wing wheel. Let us suppose an 18m glider turning a 40' radius (center of turn is about 10' beyond the tip). Further assume the main is at the leading edge, and the wing wheel 1' aft of that, centered under the wing, and 25' out from the main. The wing wheel will be 3.8 deg off of the correct Ackermann geometry, and that is a significant difference: in just 10 deg of turning it will try to move 8" towards the fuselage, or experience 8" of sideways scrubbing. You would never mount your wing wheel 3 deg off, this is easily seen by eye. Turning away from the wing wheel things are not so bad, less than a degree misalignment.

This is also easy to observe: if the wing wheel is mounted accurately and securely, it will still scrub noticeably in turns, if aft of the main gear axle line. Even spinning the glider stationary on its main gear will cause scrubbing with these assumptions: the wing wheel is over 2 degrees off of the correct angle and each 10 degrees of turn will require 6" of scrubbing.

The only solutions are: 1) live with it, 2) move the wheel in line with the main, or 3) caster the wing wheel. Most opt for 1 as it is typically a manageable problem. But 2 is pretty easy to do, or at least get closer to, if your wing wheel is adjustable. Moving the axle just 6" forward in the example reduces the scrubbing by 50%. C is also a solution, but requires a more complex, heavy, and costly wheel.

[2G]

I went with 3 and it was cheaper and easier than 1 or 2.

I have long noted that when towing trailers the trailer tires track inside of the vehicle tire tracks. I have explained this to my wife, but last year she made a turn in a parking lot that caused the glider trailer tire to bounce over a curb that the towing vehicle easily made it around. This blew the tire. Needless to say, I wasn't happy.

This same geometry affects towing of gliders, but we don't notice it as much because we have big ramps. This paper puts theory to this principal:
https://epa.oszk.hu/02400/02461/00023/pdf/EPA02461_acta_polytechnica_hungarica_2010_02_025-037.pdf
Well, if the trailer pulling angle is different than the towing vehicle turning angle, the center of rotation of the trailer has to be different than that of the vehicle. This must result in scrubbing of the trailer tires and, by extension, the wing wheel. The experiment in this paper shows a substantial difference between the turning angle and the trailer towing angle (4°, fig. 10) that is constant once the turn is established.

[da...@sculptressfashions.com]

If anyone upgrades to a swiveling wing wheel, I'm in the market for your old one. Please send me a message if you have something that will work with my Pik-20E.

[jfitch]

Glider trailer tires will not scrub in a normal turn of any radius. If you draw a line through the axles of the trailer and vehicle wheels, they will intersect at a point - the center of the turning circle. The radii of each of the 6 wheels will be distinctly different, but the center of turn the same and no scrubbing. This will not be true of a two axle glider trailer, those axles are parallel and lines drawn through them cannot intersect, hence they will scrub. The scrubbing is why a dual axle trailer is difficult to turn. Similarly a fixed wing wheel that is not in line with the main gear will scrub, for the same reason. Get it in line with the main and it will not.

I was able to alter my Cobra wheel to get it nearly in line for about $20.

[krasw]

Yes in theory non-scrubbing wing wheel is possible, like the existence of black matter.

[jfitch]

On Friday, May 15, 2020 at 12:22:35 AM UTC-7, krasw wrote:
> Yes in theory non-scrubbing wing wheel is possible, like the existence of black matter.

More like a black swan. I've got one if you want to see it.

[2G]

Yes they will - I saw it happen EVERY time I towed out my glider for many years using a Cobra wing wheel.

[Daryl Kabatoff]

On Sunday, May 3, 2020 at 10:02:02 PM UTC-6, markm...@gmail.com wrote:
> Tom has sent me a private email accusing me of making a libelous statement against him.
>
> In the interest of keeping the peace, I apologize for any statement I have made.

No, it is true, Tom is indeed a liar as you stated earlier. Today he posted crap here and attributed it to my name. See Exodus 20:16, Thou shall not bear false witness against thy neighbor. In posting his crap, Tom violated God's Ninth Commandment. Likely he turns trees into decorated idols, and by doing so violates God's First Three Commandments as well. People have no fear of God, they turn trees into decorated idols and then import members of alternative fertility cults. They defend turning trees into decorated idols by mocking those who question the practice, others brutalize the messengers. Tom managed to not just mock me, but did so by violating God's 9th Commandment.

[John Foster]

Daryl, you have some serious issues. Every time you post your crap, I report it as "hateful". Unless you want to participate in soaring discussions, GO AWAY!

[2G]

Oh, fuck off, Daryl. It's called satire and as a public figure you should EXPECT IT! I will continue posting it EACH TIME you post your shit. Furthermore, you have a VERY bad rep - here's a sampling:
https://waxy.org/2002/05/dar_kabatoffs_i/
https://alt.flame.psychiatry.narkive.com/6RWZzNx9/daryl-s-kabatoff-at-it-again-was-barrie-glen-macgregor-october
https://www.math-forums.com/threads/daryl-brings-shame-to-the-kabatoff-name.1168/

[Charlie M. (UH & 002 owner/pilot)]

Stop feeding trolls.....it feeds their ego.....see my just posted thought in a similar thread....wish to see some US tax dollars at work....

[2G]

On Friday, June 12, 2020 at 12:19:35 PM UTC-7, Charlie M. (UH & 002 owner/pilot) wrote:
> Stop feeding trolls.....it feeds their ego.....see my just posted thought in a similar thread....wish to see some US tax dollars at work....

The dolt keeps on posting regardless - I am just jerking his chain (and WILL continue to do so). Don't read it if you don't like it.

Tom