Aluminum gear

[Bob Turner]

On the adapter - I made two out of aluminum - one to fit the jack point (good luck getting a jack that high out in the field) and another using an aluminum block of the correct taper, and steel sides lined with soft leather. Two AN-4 bolts clamp it to the leg without marring the anodyne. Easy if you have a milling machine. I carry them along with a spare inflated tail wheel and some tools. That way I never have flats.

 

[DanO]

Aircraft spruce has the old style adapter that fits on the gear leg. I have one and it works, but is kinda wonky and will gouge up the paint. ACA strongly recommends not using that adapter with aluminum gear, as the angle of the two edges is different. They sell an adapter that fits on the lower strut attach point.

Thanks.

 

[Big Ed]

Anecdotes are not data - I too would like to know how many gear legs have failed by cracking, and not during a ground loop or crash landing. I think one of our participants had one, but there was no discussion of what preceeded the break.

There are at least a dozen collapsed gear on the pre-2008 NTSB database for the 7KCAB alone. However, all but one were ground loops. The 3 Decathlon u bolt failures were just minding their own business and collapsed on normal landing.

The post-2008 NTSB database is awful. Much less functionality. I deal with federal government websites all the time. The escalating incompetence in that area amazes me. We are the world superpower in web-based technology, home of MS, Google, Apple, Amazon, Facebook, Twitter, etc etc etc, and our frigging government can't even do a website refresh without reducing usefulness.

 

[Big Ed]

Here is the factory recommended adapter.

 

[Explorer]

The Scout Legs are more robust than the Citabria Legs, if weight equates to added inherent strength.

I've heard where a gear leg was torn off a Scout with a 31" Bushwheel attached. What let go was the older style U Bolt (perhaps never changed out} and then the inner bolt let go without frame damage. The Leg was not bent. I'm not sure what NDT revealed.

Amazing...

 

[Big Ed]

The Scout Legs are more robust than the Citabria Legs, if weight equates to added inherent strength.

From FB:

 

[Explorer]

"There are at least a dozen collapsed gear on the pre-2008 NTSB database for the 7KCAB alone. However, all but one were ground loops. The 3 Decathlon u bolt failures were just minding their own business and collapsed on normal landing."

Has the NTSB come up with a cause for U Bolt failure? Somewhere it's written that if you are landing frequently on a rough, unprepared surfaces you change out the U Bolts every 500 hrs. I wonder how many follow that advice?

 

[Big Ed]

"There are at least a dozen collapsed gear on the pre-2008 NTSB database for the 7KCAB alone. However, all but one were ground loops. The 3 Decathlon u bolt failures were just minding their own business and collapsed on normal landing."

Has the NTSB come up with a cause for U Bolt failure? Somewhere it's written that if you are landing frequently on a rough, unprepared surfaces you change out the U Bolts every 500 hrs. I wonder how many follow that advice?

Dunno. But failures haven't stopped happening. Here is one from 2017. Aircraft model year is 2004, the year the aluminum gear came out, but nothing in report about gear type. http://www.kathrynsreport.com/2017/12/american-champion-7gcaa-citabria-n519ma.html

 

[Bartman]

I spoke to Dale at the factory today about the aluminum gear legs for the Decathlon

• They're an inch longer than the steel gear
• I think he said you save 14 lbs over the steel gear
• The Grove brakes/wheels/axles are interchangeable with the steel gear, different mounting bolts are needed for the axles because the aluminum gear are thicker
• The extra 50 lbs of useful load increase comes from the extra inch of length (goes back to the drop test and prop strike mentioned earlier in this thread)
• About $7000 for all of the gear parts and about $3000 for the Grove wheels/brakes/axles (I assume this includes the master cylinders, not sure)
• Clear coating the gear is recommended, at a minimum, for corrosion protection

Between the extra 100 lbs of useful load from the wings, the 50 lbs from the aluminum gear upgrade, 14 lbs of empty weight reduction from the aluminum gear swap, about 30 lbs of empty weight reduction related to converting to factory metal spar wings, a few pounds if you leave the carpets out, a few pounds using flat panel avionics instead of all round dials, plus whatever weight savings you can get from a lighter battery, starter, and alternator, it can improve the useful load by almost 200 pounds which is huge.

A friend was telling me when he's in his 1978 180hp Super D, he can bring a 140 lb friend and half fuel which is pretty limiting for non-acro recreational flying. Add almost 200 lbs to the useful load though (via weight savings and increasing max gross to 1950 from 1800) and suddenly you've got a lot more
flexibility in the plane.

More weight can be saved by swapping out your heavy aluminum blade Hartzel prop for a composite prop but that's big big bucks!

 

[Big Ed]

• The Grove brakes/wheels/axles are interchangeable with the steel gear, different mounting bolts are needed for the axles because the aluminum gear are thicker
• About $7000 for all of the gear parts and about $3000 for the Grove wheels/brakes/axles (I assume this includes the master cylinders, not sure)

If I have the old Cleveland wheels, do I have to spring for new Grove wheels?

 

[Bartman]

If I have the old Cleveland wheels, do I have to spring for new Grove wheels?

I don't know Ed, I assume they are not compatible but there is a pretty healthy used market for the Cleveland wheels so you wouldn't have any trouble selling them.

 

[Bob Turner]

Nope. Bolt right on - just need longer bolts.

The reason the U bolts fail is because it is a shitty design. An AN bolt has 126,000 psi tensile, an NAS bolt has 186,000, I think, and that U bolt is probably automotive grade. Heat up a round bar, bend it, and thread the ends. Boo!

Replace your U bolts right away. Put an NAS bolt inside, with proper washers, and you won't have to check torque every 50 hours.

Genuine was very good to me - the most expensive bolts were around $125 each from ACA, and Genuine got them for $28 each for me. They have changed management and do not do specials any more. A big loss!

 

[Explorer]

Bob,

"Replace your U bolts right away. Put an NAS bolt inside, with proper washers, and you won't have to check torque every 50 hours."

What is the torque setting? I guess it depends on the aircraft use but if your running on tarmac. When you confirm the torque setting on the Annual Inspection does it require a little touch up, suggesting bolt stretch?

Thx.

 

[Bartman]

If I have the old Cleveland wheels, do I have to spring for new Grove wheels?

I misunderstood your question Ed, I thought you meant if you changed brakes and axles too. Bob is probably right, the Cleveland stuff probably bolts right to the the end of the gear leg making all of your parts compatible but the factory would be the final word on that (I have to say that).

 

[aftCG]

Between the extra 100 lbs of useful load from the wings, the 50 lbs from the aluminum gear upgrade, 14 lbs of empty weight reduction from the aluminum gear swap, about 30 lbs of empty weight reduction related to converting to factory metal spar wings, a few pounds if you leave the carpets out, a few pounds using flat panel avionics instead of all round dials, plus whatever weight savings you can get from a lighter battery, starter, and alternator, it can improve the useful load by almost 200 pounds which is huge.

The 100 lbs is an increase in allowable max gross weight, not useful load. First I've ever seen anyone claim the empty weight goes down with aluminum wings. If it were true a lot more people would be lining up to upgrade. I think you're looking at a 30 lb increase in useful load.

a few pounds if you leave the carpets out, a few pounds using flat panel avionics instead of all round dials, plus whatever weight savings you can get from a lighter battery, starter, and alternator, it can improve the useful load by almost 200 pounds which is huge.

More weight can be saved by swapping out your heavy aluminum blade Hartzel prop for a composite prop but that's big big bucks!

Carbon floor boards are worth a few pounds too. Shame to put carpet on those of course. I've already got lightweight starter and alternator. I can't move my battery because my plane has been converted to O-320. I could install a light battery but it is currently helping balance out my CG.

The panel would gain some for sure. As a bonus I would lose 30-50 lbs because I couldn't afford to eat anymore.

You guys with a constant speed might be able to entertain a composite prop. I inquired with MT about props and they do not have anything for the Citabria. Pretty sure that leaves me with a wood Sensenich option.

 

[Bartman]

The 100 lbs is an increase in allowable max gross weight, not useful load. First I've ever seen anyone claim the empty weight goes down with aluminum wings. If it were true a lot more people would be lining up to upgrade. I think you're looking at a 30 lb increase in useful load.

Carbon floor boards are worth a few pounds too. Shame to put carpet on those of course. I've already got lightweight starter and alternator. I can't move my battery because my plane has been converted to O-320. I could install a light battery but it is currently helping balance out my CG.

The panel would gain some for sure. As a bonus I would lose 30-50 lbs because I couldn't afford to eat anymore.

You guys with a constant speed might be able to entertain a composite prop. I inquired with MT about props and they do not have anything for the Citabria. Pretty sure that leaves me with a wood Sensenich option.

Dale's comment to me was that there is a 30 pound weight savings in converting to the new wings.

if you increase gross weight by 100 pounds you are also increasing useful load by that amount.

 

[Bob Turner]

30 lbs is significant. I have some leftover Cub spars; if I think of it I will get equal lengths of wood spar material and check weights.
So what you are saying is that, everything else held constant, metal spar wings and aluminum gear gets you a 146 lb useful load increase?

 

[Helo pilot]

Important to note to avoid confusion is the fact that late model SDs have two different max gross weights. One is for normal category operations and that is 1950 lbs. The second is for aerobatic ops which is 1800 lbs. Anything to lower empty weight will lower both categories.

 

[aftCG]

Dale's comment to me was that there is a 30 pound weight savings in converting to the new wings.

if you increase gross weight by 100 pounds you are also increasing useful load by that amount.

That's only true if there is no increase in empty weight, and that isn't the case. I've read many different numbers about the increase in empty weight as a result of aluminum wings (as high as 100 lbs), but it sounds like they are acknowledging it is 70 lbs.

30 pounds is awesome, don't get me wrong (for me it would be an hour of flight time with the money handled pulled back). It's an increase in useful load but it is not a "weight savings". My horse math shows that aluminum wings and gear legs get you 30+50=80 lbs useful load. Nothing to sneeze at certainly, and makes the plane more, uh, "useful".

Edit: Oops, my horse forgot the 14 pound (actual) weight savings of the aluminum gear. So 94 lbs.

 

[Bartman]

If the Decathlon wings save thirty pounds, thereby lowering the empty weight by thirty pounds, and they increase max gross by 100 lbs, that's 130 pounds added to the useful load. You're saying they come in heavier, my Milman conversion left me lighter where everyone says they're heavier, so I'm not sure we can resolve this and I've already had to use the word "thereby" so I defer on the matter.