Grove landing gear

[jtpitkin06]

There have been a few posts about toe-in and toe-out on aircraft without really explaining the geometry of the spring type landing gear design. This does not apply to oleo strut, trailing link or bogie truck type gears.


With no weight on the wheels, a spring type gear has positive camber by design. This means the top of the tire centerline is tilted outward. Negative camber means the top of the tire is tilted inward.

As the aircraft enters a flare the pitch increases. With a pitch increase, the positive camber factors into two components, part positive camber and part toe-in. When the weight of the aircraft settles on the gear, the gear spreads. The spreading changes the positive camber into negative camber. This transition is more pronounced at higher weights. As long as the aircraft attitude is nose up with weight on wheels, the now negative camber factors into two components… part negative camber and part toe-out.

This transition from positive camber to negative camber, and toe-in to toe-out occurs on both conventional gear and tricycle gear.

If the aircraft has conventional gear, and negative camber with weight on main wheels and tailwheel, it will always have toe-out in the three point attitude.

However, if the aircraft is tricycle, the nose lowers after touchdown. This causes the toe-out effect of negative camber to transition back to near neutral toe-in while maintaining negative camber. ( There is a slight decrease in negative camber when some of the weight shifts to the nose gear.)

For tricycle gear aircraft, toe-in is stabilizing. As the aircraft turns, it leans against the outside tire. Because the CG is ahead of the tire the toe-in counteracts the turn much like a vertical stabilizer. Most tricycle gear aircraft are set up with slight toe-in with weight on all three gear.

For conventional gear aircraft, toe-in is unstable. As the aircraft turns it leans against the outside tire which is pointed into the turn. Because the CG is behind the landing gear the aircraft turns sharper and over-steers

Toe-out on a conventional gear is stabilizing. As the aircraft turns it leans against the outside tire which is pointing away from the turn. The tire angle decreases the turning tendency and directional stability is easily maintained by the pilot. . Most conventional gear aircraft are set up with slight negative camber with weight on wheels which results in a small toe-out component.

For an example of conventional gear toe-out stability one can look at aircraft equipped with “crosswind” landing gear. If too much pressure was put on the outside tire, the entire wheel simply casters to an extreme toe-out condition and removes any turning tendency.


If your aircraft is a bit squirrelly on landing, you might check the camber and toe angles with the aircraft loaded to the normal operating weight. If the gear is too stiff or bungees are too tight the gear may not be settling into the preferred negative camber position.


In summary, tricycle gear --- neutral or slight toe-in is best. Convention gear --- neutral to slightly toe-out is best.

I hope this clarifies the differences between conventional and tricycle landing gears and how they react with camber, toe-in and toe-out.

JP

[HighWing]

John has given the perfect explanation, but there is one area that I think needs a little more info.


"If the aircraft has conventional gear, and negative camber with weight on main wheels and tailwheel, it will always have toe-out in the three point attitude."

This is not always true. If the gear is built as engineered, then yes it is true, but the fact that Grove sells shims to adjust wheel alignment and the original Kitfox bungee gear was always a couple of degrees toed in from the factory will indicate that fabrication errors can come into play with the best engineering. Another factor, with the bungee gear, the gear typically rests with the bungees holding the cross arms tight to the fuselage. With this gear, any negative camber will only be in play at the moment of touch down.

My advice still - if the gear seems squirrely, check alignment before tossing the gear or the Kitfox. I have known guys that did the latter.

Lowell

[Monocock]

I had Grove fitted back in December and it has transformed the way my Mk 4 handles on the ground. On the roll out it seems to track far more straight and true and I like the peace of mind of not having to worry about the bungees.

I did find it made the coolant temp a little higher as it blocked the exit air from the radiator slightly but that has now been resolved.

All in all I think it was worth every penny and cannot recommend it highly enough.

My only problem is that I'm still waiting for someone to buy my old gear to make the cost of it less painful!!

[catz631]

Monocock,
EBAY,EBAY,EBAY.... thats the place ! I sold my old gear there

[sdemeyer]

Mark, funny you should mention this. I dropped her in a little hard yesterday and this was the result. I will definitely be looking at a different setup now!

Scott

[Newkid]

One thing that has alsways made our planes squirrelly on the ground is using tires that have a flat profile. They "dart" a lot more, especially on pavement. Normal aircraft tires and balloon type tire make a huge difference. We also never put the cable safety lanyards on the gear. I've seen more airplanes tear up the structure under the seat because of hard landings with those lanyards, but haven't yet seen a bungee truly break and cause damage to the plane. Anyway if you have those flat golf cart type tires they could be causing the squirrellyness.

[Luvn737s]

I used to be active on a Skybolt and related biplane forum and the subject of retrofitting a spring-steel gear like a Grove onto a design that originally used tube/bungee suspension would come up. Some said that the spring-steel gear concentrated the load too much and could lead to fuselage tube cracking. Is the KF design susceptible to this?

[DesertFox4]

There are now probably as many Kitfox on Grove gear as tube steel/bungee gear. Grove is standard now on the Super Sport 7 models so I'd rest easy about the Skybolt like concerns.

[HighWing]

My thought on the Grove gear is pretty much as you state it. Evidence for that is the fact that the newer Kitfoxes have a sheet steel gusset just above the gear attachment points. In the old days there was talk of putting a plywood gusset in that area glued in with structural adhesive. Then there is the fact that Steve mentions about the number of Grove gear installations on all models of Kitfoxes and not much talk of problems in that area.

I do have one area of concern though. The vast majority of Grove gear legs on those flying are made from a different aluminum alloy than they use now. The 7075-T6 that is used in thier current production is tough stuff. In the past there were stories of hard landings bending the gear legs and further reports that Grove would rebend and re-heat treat for their customers of record at no cost - at least to the customer. I don't know for sure what the earlier alloy was, but I know from personal experience, that the 7075-T6 will spring to a point, then if further stressed, something will break. We make tiedown straps for the Rans out of 7075 alloy and it can't be formed at the T6 hardness and the only fuselage component that survived my very hard emergency landing was the 7075-T6 landing gear legs made by the former partner of Grove - Hammerhead, they used 7075-T6 from day one. With the exception of some scratches on the paint, they looked brand new. The fuselage looked like it had been dropped on a brick wall. As a disclaimer, I doubt the fuselage would have survived any landing gear as the conditions then demanded a hard landing. I have no claim to any engineering training except of the seat of the pants variety, but I hope the gear legs on my new Model IV will absorb a bit more of the energy if I'm ever found in a similar situation.

Lowell

[Ironman Al]

Some one mentioned, being able to "tweek" the Grove gear to get adjustment on toe in or out right! Can anyone explain that better, are we talking about a Big cresent wrench here or what? Is there a preferd way?,