Wheel Alignment

[jiott]

I am just completing a SS7 with the Grove aluminum spring gear. I have seen some good threads on this forum for checking wheel alignment (toe-in, toe-out) but it is a somewhat involved procedure. I am wondering how necessary is this on the Kitfox Grove gear? Is there a reasonable liklihood that the wheels will need some shimming, or is the brand new Grove gear made consistently accurate enough that the alignment procedure is just busywork? I understand the need to do this if you have had an incident where the gear could have been tweaked. What have you guys done?

Jim

[jamesmil]

ours was spot on with no shimming needed.

[HighWing]

Jim,
I had the bungee gear on my first Model IV then switched to the Hammerhead gear rather than the Grove - The two companies were once partners like Avid and Kitfox. The bungee gear was severely toed in as I think they all were, but the aluminum gear was fine. That said, there is a pretty easy way to do a rough check on the alignment. Put a piece of tape on the exact aft - axle height - center of each tire. Make a vertical line with a pen on each and measure the distance between the marks. Also measure the distance between the two gear legs. Roll the airplane forward so the marks are now at axle height on the forward side of the tire. Measure again between marks and measure again between the gear legs. Then compare the differences of the two measurements. Here it may get confusing, but if the measurements are similar, you should be tracking fine. If the marks on the tires are closer together and the gear legs are as well, you likely have some toe in. If both measurements are longer, it would mean that you likely have some toe out. If one measurement is in and the other one is out, forget you read this post as I don't have a clue on that outcome. If both are significantly in our out, you might want to do the follow up hard part. Not being too clear on decades old Trig, I drew the measurements onto a cad program and it gave me the angle of deviation - this of course relative to the axles only with no info as to which axle is bonkers or how it tracks relating to the long axis of the airplane.
Lowell

[Geowitz]

I would imagine it will be pretty close to straight, but really, checking toe in/out can be pretty easy. See my post on the thread below. It takes 2 pins, a level spot, a tape measure, and 3 minutes. Similar to Lowell's thoughts, but practically I take this as the actual measurement. You can figure out the degrees with a little geometry/trig. I have about .8 degrees toe out on each wheel. Ground control seems great.

http://www.teamkitfox.com/Forums/showthread.php?t=2204&highlight=geowitz

* Roll the plane forward for 10 feet or so to settle the gear as it would sit when rolling in an actual taxi/take off. Then measure in the back. Roll forward and measure in the front. If you want to get real technical you can get someone to sit in the plane so you can see what it is at flying weight. Perhaps with tail up in flying position as well as toe in/out will change from 3 point to tail up config.

Just my way of doing things and it seems to be working great.

[jamesmil]

good morning all, i think the imporant thing on this subject is how does the air plane taxi. the only thing we can ajust on the grove gear would be toe in with shims on the spindls as the caster is fixed and the camber is built in to the gear and changes with load on the gear.
that being said the toe is very imporant to how the airplane tracks, when setting up the front end of a race car we had to find the best set up for the driver taking into consideration caster, camber, settings, bump steer, shock travel, ackerman, just to name a small list of things to consider. we would ajust the front end of the car for each track but no mater were we went, short track or super speedway we always made sure the toe was set out. on a short thack we ran 1/8 " toe out. on a super speedway we shot for 1/16" toe out but if the driver complaned about the car wandering down the straight away we would add more toe out. that being said if the airplane tracks good i would leave it alone. if it wants to wander add more toe out after making sure every thing else is right, air pressure, no draging break. ect. my two cents worth. hope this helps.:)

[jrevens]

The camber can be adjusted as well as the toe in with the same type shims. While it may not usually be necessary with the Grove gear, it can be easily done if desired or needed. Most airplanes are all a little different, but I also know that my personal experience with my first homebuilt, a taildragger that I've been flying for over 22 years, is that neutral alignment (or no toe-in or toe-out) is definitely best. The Kitfox lands a lot slower and is definitely more benign, but the Thorp T-18 can be an amazing handful if the alignment isn't correct. Adjust it to neutral and it's a *****cat. Additionally, your tires will last longer.

[jiott]

What I am really trying to determine is how many of you with the Grove gear actually found you needed to shim to get correct toe-in/out?

From the responses so far it seems several of you checked, but nobody (maybe Geowitz) actually did any shimming.

Jim

[Av8r3400]

No shimming for me...

[SkySteve]

Bolt on and fly.

[Geowitz]

Yeah, I shimmed because I had 1 degree of toe in.

In case anyone was wondering my reason... There are different schools of thought, but I erred towards the toe out camp. The thought being, in a developing ground loop situation where weight is transferring to the wheel to the outside of the direction of the swerve, a wheel at toe in will exacerbate the ground loop because it is getting more traction to steer more into the swerve. In the same situation of weight transfer and increasing traction toe out would help to fight the ground loop.

However, the grove flexes quite a bit and having the wheels straight will actually give you a little toe out under forward stress.

[jtpitkin06]

Jim,

Back in September you asked for specific degrees. I can’t tell you what will work best for your airplane as only by doing several taxi test will you find the best. However, we can use information from certified airplanes as to what works for them.

Cessna’s Service letter SLN 46 concerning wheel alignment for the 120, 140, 170, 180, 190, 195 tail draggers recommends a range of 1/16 inch toe in to 1/8 inch toe out. On a 6 inch wheel 1 degree is 1/10 inch. The reason you can have 1/16 inch static tow in on a tail dragger is the drag on the wheels when in motion will force them to tow out. Within that range I have a personal preference for tow out on tail draggers. As I stated back in September, tow out improves tail dragger stability.

http://www.teamkitfox.com/Forums/showpost.php?p=25923&postcount=7

Start with 1/2 degree tow out and see how it tracks in taxi. If the aircraft wanders, try a little more tow. If you have tire scuffing but it tracks OK then back off the tow a bit. This is assuming you have correctly set the tail wheel.

Far more critical than tow in or tow out on a taildragger is the tailwheel plane of rotation. (The vertical swivel axis) If it is not correct you will have horrible handling, excessive shimmy, or even an uncontrollable airplane. The tailwheel swivel must be vertical or tilted slightly forward. This ensures the tailwheel will naturally seek a position in trail with weight on the wheels.

If the tailwheel swivel is tilted aft the aircraft tail must be raised to allow the wheel to center and it is inherently unstable. As the pilot tries to steer the airplane the tailwheel will flop back and forth over center or even lock to one side.

There are frequent posts on this forum by owners installing big balloon tires. Doing so raises the front of the airplane and changes the tailwheel plane of rotation. If you change tire sizes at some point in the future, it is imperative that you reset the tail wheel plane of rotation.

Hope this helps,

John Pitkin
Greenville, TX

[HighWing]

Far more critical than tow in or tow out on a taildragger is the tailwheel plane of rotation...

Good info, but a couple of things I might disagree with based on my personal experience.

Early Kitfoxes were notoriously unstable on the ground. Factory recommendations and fleet experience focused on wheel alignment, regardless of tailwheel geometry. Whenever tailwheel geometry came into the discussion it was always regarding wheel shimmy. I personally dealt with both - about 200 hours with the original bungee gear and the rest with a Grove analogue. In my experiece, a degree or so toe out will help greatly in landing stability.

A tailwheel tilted slightly forward will introduce a shimmy tendency. Tilted too far aft will indeed result in the tail being raised when taxiing straight ahead, but I never found it to be an issue except possibly when doing tight turns during slow taxi and when hand moving the airplane with the side handle - and neither were sufficient to motivate me to make adjustments. I have had the tilt to the point that if sitting straight and the tail is nudged a bit it would slip to the side, but just like John mentioned with very slight toe in, dynamic forces when near flying speeds tend to move things where they should go. Then keep in mind that when landing in three point, conventional wisdom is to keep the stick full back during taxi which will essentially add a downward force to the tail which will collapse the spring a bit moving the pivot forward. For those with shimmy problems, the quick fix was to move the stick forward to reduce tailspring flex - uprighting the pivot. For me, I would rather have stability at the point of first touch, than stability when slow taxiing or moving the airplane into or out of the hangar.
Lowell

[Av8r3400]

I'd like to add a little more to this discussion. Toe in/out is always a matter of debate and discussion, so here we go again...

What I want to bring up is the idea that these toe adjustments of the gear helps with taxiing. These planes should only taxi to 10 or at the absolute maximum 15 mph. Anything more than that and you are entering into the transition to flying phase of operations. (Also the reason why "Highspeed Taxiing" is a serious game of Russian Roulette) At the slow speed of taxiing, toe adjustment is almost irrelevant.

On takeoff, acceleration is so brisk that by the time speed instability issues arise, you will be flying away from the runway.

Where it becomes critically important is at the moment of touchdown and the following rollout. I tend to agree with Geowitz's above statement of zero to slight toe out (on a tail dragger) and his reasoning. A tri-gear IMO should have zero to slight toe in.

Toe out is inherently unstable. In most cases it exaggerates turning tendencies - this is why road racing cars use zero to toe out more than in, like your street car would. Taildragger airplanes are that famous exception to the rule.

[jrevens]

A tailwheel tilted slightly forward will introduce a shimmy tendency....
Lowell

I agree with Lowell 100%. It is my experience, having flown many different types of taildraggers, that the swivel axis should definitely not be angled forward. This is counter-intuitive to many people, but is a fact. I believe that the best is a perfectly vertical axis with the airplane loaded to max weight, with the corresponding spring deflection. This will necessitate it being angled back when lightly loaded or empty. I learned this the hard way with tailwheel shimmy so bad that it caused damage.

[jiott]

You guys convinced me I should check wheel alignment on my new SS7 with the Grove gear (taildragger). I did that today and found that the right side was perfect at neutral toe-in/out. The left side was also nearly perfectly neutral within 1/16" (on a 16" tire). This is with the airplane leveled in a flight attitude. This is as close to perfect as I can reliably measure so I am going to leave it as-is.

I am not surprised at the accuracy of the Grove gear. After all, the gear legs axel mounting pads are machined as are the axels themselves. It would be pretty sloppy manufacturing if they were not dead on. On welded gear, like the Kitfox bush gear, I can see much more chance for alignment error.

Oh well, my mind can rest easy now even though I think that it was kind of a waste of time to check brand new Grove gear. The process was educational as I studied up on recommended alignment for taildraggers. You all were also very helpful.

Jim

[Straightandtrue]

Hi Guys

Must say John is very accurate for without weight there will be a positive camber and with weight a negative camber, therefore because you mostly fly with weight it is always better to adjust a total toe of 2mm toe in depending on the true camber of wheels on a full load. That way you will get the most out of a set of tyres and increase your landing life.

also to watch out for is one side must not have a positive camber where the other side have a negative camber (very important) because it will make your aircraft known as (CRAB) and will decrease your handling.

Front wheel and known as steering it came to my attention that allot of aircraft's have a high negative castor witch is also bad. if you look at a shopping trolley to make it easy. with the high negative castor when you push it fast the two front wheels shake from side to side and the same with big aircraft's when empty load or half load sometimes it feels shaky when landing.

i have been studying and doing research on my own for a few years now to do and increase not just Tyre life of aircraft's but also the handling and controlling of aircraft's to make it better and more stable on taking of and landing. but as I read over the internet there is allot of people with this problem but no one to give a change to help them increase it.

i am originaly from South Africa and currently in New Zealand and have 14 years of commercial vehicle wheel alignment and axle straightening experience and are still looking to get in the market to help airlines/aircraft's to achieve the best out of there suspensions.

have a good one guys:)

[inzersv]

Ok, I have been reading all these posts for wheel alignment on the Grove Gear, but I don't see any numbers. I thought that Paul Lederbrand at S&R told me the SS should be slightly toed in. If so, to what degree? The Grove Gear website has shims in 1/4 degree, 1/2 degree & 3/4 degree increments. Neutral to slightly toed in seems appropriate, but what is slightly? Thanks for all your input. Also, today I was discussing this issue with a couple of airport bums and they said that I should use grease plates to make my measurements. Any thoughts on that idea?

[jiott]

I think grease plates are good for ultimate accuracy, but I dare say very few of us used them. Just jockey the plane around before you take measurements to relieve any locked-in deflections on the landing gear. I doubt very much that grease plates would help toe in/out measurements on the Grove gear; camber yes maybe.

INMHO "slightly" would be 1/4 degree or less.

I case you haven't seen it somewhere in the wheel alignment threads, I like and used John McBean's suggested method for measuring toe in/out, using a 4' straight edge (level) bolted at its center to the flat surface on the tip end of the axle. This machined surface and therefore the straight edge is now accurately parallel to the wheel plane of rotation. Then you can measure from the fore and aft tip ends of the straight edge in to the aircraft centerline chalked on the floor. This 4' spread gives you 0.20" difference to equal 1/4 degree (tan 0.25 degree x 48" = 0.20").