Wing Jacks

[Robert Zambelli]

Sometimes we have to take a break from model aviation in order to accomplish other needs.
I am in the process of rebuilding the landing gear actuators on my Globe Swift and of course it was necessary to jack up the aircraft in order to remove and service the assemblies.
I was not about to spend around one thousand dollars on a pair of jacks that I would be using only once, as I am planning to sell the plane.
The photos show what I designed and built, with a total expenditure of around $100.00 for the pair. Total lift is 8.25 inches and 1,800 pounds per jack.
Suggestions/comments welcome!

Bob Z.

[Steve Helmick]

The jacks look like they'll work fine.

My Dad said he flew a Globe Swift once, not sure why or when. He said "It was the only airplane he ever flew that tookoff at 125, cruised at 125 and landed at 125". What is the stall speed? I hope it's not 125!    Steve

[Dave Hull]

Bob,

A few questions:
1. Do you have fittings for the hardpoints in the wings? Are they compatible with the pads on the jacks? Is it a straight lift, or are things offset? How close to the CG are the lift points? (Worst case scenario is that they slip and you punch a hole in the wing....  A plywood cutout/protector might add emergency protection?)
2. What is the oleo travel on the gear? Is it less than the jack travel? Or, will you have to wrestle the wheels once jacked?
3. Your stand weight rating is based on...? Jack only? Bending loads on the jack at full extension? Bolt tearout at the base of the jack from any eccentric loading? Wheel capacity? Bolted wood joints? Do you have the ability to do a load test?
4. How good are the dolly wheel locks? Are you on smooth concrete? Is it level?
5. What are you doing for the tail jack? Can you strap down the tail to the tail jack and get some sandbags on it? Can you jack the tail simultaneously with the mains to keep things level and (hopefully) avoid any sliding on the contact points?

I have a poster of a Lo Presti modified Swift hanging in the shop. Polished aluminum and yellow & black checkerboard trim. Gorgeous!

[Robert Zambelli]

Thanks for the comments and questions. My Swift is very early, serial number 11.
It has been upgraded (by STC) to control sticks and the engine upgraded from 125 HP to a Continental O-300 with 145 HP.
Empty weight is under 1300 pounds.
Cruises at 140 MPH, Vne is 185 MPH, stall speed 43 MPH with flaps extended.
An absolute BLAST TO FLY!!!

Questions from Dave H:
1. Do you have fittings for the hardpoints in the wings?
Yes

Are they compatible with the pads on the jacks?
Of course! I machined adapters from nodular cast iron, light press fit onto jack pads, secured with three 10-32 UNF stainless steel screws on each jack. The jack point fits into a recess on the top of the adapter.

Is it a straight lift, or are things offset?
Straight – look at the #&$%@*#@ photo.

How close to the CG are the lift points?
6.4 inches aft of CG.

 (Worst case scenario is that they slip and you punch a hole in the wing....  A plywood cutout/protector might add emergency protection?)
CAN’T HAPPEN

2. What is the oleo travel on the gear?
Irrelevant – Swift does not have oleo struts. They are springs/oil.

Is it less than the jack travel?
Of course. Note from the photo that the wheel is off the floor.
Or, will you have to wrestle the wheels once jacked?
N/A

3. Your stand weight rating is based on...? Jack only?
Each jack is rated at 4,000 pounds, each caster at 600 pounds.

Bending loads on the jack at full extension? IMPOSSIBLE

Bolt tearout at the base of the jack from any eccentric loading?
No bolts – each jack secured to top of 4x4 with four #10, 4 inch long wood screws, imbedded in epoxy. Besides, there is NO ECCENTRIC LOADING.

Wheel capacity?  4,000,000.03245 pounds (dumb question deserves a dumb answer)

Bolted wood joints?
Bolted, screwed and glued.
 
Do you have the ability to do a load test?
YES - Already done

4. How good are the dolly wheel locks?
Good is a relative term. Not only good but wonderful.

Are you on smooth concrete? Is it level?
Yes. Beats me.

5. What are you doing for the tail jack?
No tail jack.

Can you strap down the tail to the tail jack and get some sandbags on it?
Tail is weighted down with a sandbag strapped to the fuselage.

Can you jack the tail simultaneously with the mains to keep things level and (hopefully) avoid any sliding on the contact points?
Absolutely not - no need to. IMPOSSIBLE for any sliding

For what it’s worth, I know what I’m doing.

[Dave Hull]

For what it's worth, I thought you had an honest question. Sorry to have intruded. Good luck with your jacks.

[Motorman]

Is that 3/8" plywood? Hope the jacks don't punch through that. Easy enough to double up on it.

Funny jack story: The FBO I was working for started a program where the pilots were going to perform maintenance operations to reduce the work load. There was a Lear 35 up on jacks that needed the oil changed in the main struts. I came back from lunch to people yelling, running everywhere and here comes the fire truck. Pilot used a dolly jack to compress the strut and drain the oil. When the strut bottomed out he kept on jacking it up until the jet came off the wing jack. The dolly jack slid around and came out sideways bringing the wing down on the wing jack and it went right through sticking out the top of the wing. JP-4 gushing everywhere. Next day the pilot maintenance program was ended.

MM

[Robert Zambelli]

Hi, Dave - no intrusion whatsoever.
Your questions were not only interesting but also safety related.
The idea of an airplane falling on my head is most unappealing!
I tried to answer as accurately as possible (except for the sophomoric response about the wheel!).
Needless to say, I was trying to be as thorough as it was a design effort rather than one of engineering.
I did, in fact, make one change to the final design by adding a 2 x 4 to the bottom of the lower platform to increase vertical strength.
Keep up the questions - I find them thoughtful and helping.

Bob Z.

For what it's worth, I thought you had an honest question. Sorry to have intruded. Good luck with your jacks.

[Paul Smith]

The jacks look like they'll work fine.

My Dad said he flew a Globe Swift once, not sure why or when. He said "It was the only airplane he ever flew that tookoff at 125, cruised at 125 and landed at 125". What is the stall speed? I hope it's not 125!    Steve

Somebody I knew bought an Ercoupe and took me for a BRIEF ride.  The same deal, except more like 60-70 MPH.  It barely made a lap around the traffic pattern.  Not to pass judgement on all Ercoupes, but this unit was seriously power limited.

[dave siegler]

Even purpose-built jacks always made me nervous.  There are often accidents.  We put a padded sawhorse under the wing a few times, just in case.  Especially Moneys with wood wings.   
We did a Beech 18 turbine conversion.  it was on the jacks for a few days.    A really heavy beast. we were needing big jacks.

Jacking a Cardinal RG was interesting  The jacks were very long. 

I like that you used bottle jacks,  all the load is in line.  Some DIY solutions use modified floor jacks, which was sketchy for me. 

My only feedback is about the wheels, they narrow the base
And are you worried about the jacks leaking down? 

[Bill Johnson]

And are you worried about the jacks leaking down?

That would be my concern, having experienced a couple of aircraft jack failures over the years. It's why true aircraft hydraulic jacks have a locknut on the ram which should never be more than an inch from the top of the cylinder while jacking.

[Dave Hull]

If you want some insurance against bleed-down on the bottle jacks, consider splitting a piece of steel pipe or tubing lengthwise. Make the length what you anticipate the exposed shaft length of the jack to be  with the plane in the air. Pump the jacks up, then clamp the two pieces of split tube around each jack shaft for a failsafe lock. Some thread-type hose clamps would likely work well.

I had to go out to the airport once to inspect a C-172 that "fell on the ground."  It was at a paint shop where they were chemically stripping it. The slab maingear stress cracked and failed right at the pierce point of the OML. It totalled the airplane. One wing was bent, the stabilizer and elevator were bent, the tailcone was twisted--and just to add insult, the prop was damaged.  Both airplanes and boats laying on the ground are super sad....

[Robert Zambelli]

Hello, All.
Thanks for the questions and helpful hints.
Regarding bleed down, I raised the jacks such that the tires were exactly 3 inches from the floor around two weeks ago.
I just measured the distance and neither jack had crept.
HOWEVER, I still have a means of preventing any creep.
Dave, I used a method similar to your suggestion.  I used two pieces of aluminum angle clamped to the extended portion of the piston, between the base of the pad and the top of the jack.

Motorman: I'm not concerned about the vertical 4x4 pushing through the base (1/2 inch plywood). A 2x4 runs the width of the base directly under the 4x4.
Also, the four gussets will take vertical force and transfer it to the 2x4s along the periphery of the base.
I'd show this in a free-body diagram but I'm too lazy.

Bob Z.

[Motorman]

If you're rebuilding the actuators, is there a way to lock the gear down so you can take the actuators off without jacking?

[Robert Zambelli]

Yes, the gear is temporarily locked down. 
Even though the wheels are three inches off the ground, I want the extra security.
I have already rebuilt the port side actuator and installed it but the linkage and hydraulics are not yet connected.

Bob Z.