Landing gear Bungee cords

[joea]

Group,

It appears that its time for me to change the landing gear bungees on the Sedan.

I talked with several people at Middletown about this and get various opinons on using the 1280's or 1280HD versions of the bungee's.

Any other suggestions or comments? Any installation tips? Where does everyone get them? Burls, AC Spruce or ?

Mike Hoag told me that he has a tool that helps and after he gets finished with it hope to get a chance to use it.

Thanks,

Joe A

[pmanton]

Is the bungee system similar to thge Piper Pacer setup? I have a Stewart Bungee Buddie at Salome 2AZ1 you're welcome to use.
http://www.flickr.com/photos/massey_aer ... 9469987335

Paul
N1431A
N83803
2AZ1

[joea]

Paul,

Thanks much and let me see if some others have done this job and know which tool it takes. I have never done this so its all going to be new to me.

Thx,

Joe

[deCreeft]

Joe, I just looked in my logbooks and no part numbers entered (gnashes teeth) for bungees...
Sorry!
username and password you provided working fine...
Thanks!

Knowing me I till have the empty wrappers somewhere, will keep my eyes open!

Need to get busy and write ad for " Edo 2000 floats with complete Sedan set-up for sale" but there's a Preview !)
Bill
Alaska

[Matt]

Joe

I purchased the main gear bungees for N1331H directly from the manufacturer, SBC Industries. Their product list does not mention the tailwheel bungee, though, and I can't recall nor find any documents, where I got that one from. But I would guess that SBC makes that type, too. I will ask them and then post the result in this thread: http://www.sbcindustries.com/products.htm

The SBC list obviously differentiates two types of bungees for the main gear legs: 1280 (up to S/N 330) and 1286 (from S/N 330 up).

The Sedan Parts Catalog calls for these types of bungees:
Main gear: 1280
Tail gear: 1286-MT750

Why does this have to be so complicated!?

Here is an interesting article by H.G. Frautschy about bungees in general: http://www.vintageaircraft.org/featured ... 0Cords.pdf

Matt

[joea]

Bill and Matt,

Thanks very much for the info!

Joe A

EDIT, very nice article!

[esandberg]

Hi Joe,

I'll look for pictures and refresh my memory, but it went generally like:

- Remove the seats, carpet and front floors
- Remove the belly pan
- Support the whole nose by hoisting the engine mount (and attached airframe) to lift the wheels off the ground. Don't let the plane rock on the tailwheel and tip over.
- Snip the old bungees
- Remove the safety cable
- Take out the two MLG bolts and remove the whole leg from the airplane
- Inspect the rubber bumper, replace if needed
- Inspect the sintered bronze bushings inside the gear leg hinges, replace if needed
- Inspect the pin-bolts that the leg pivots on
- Now's an ideal time to NDI the gear leg on a workbench somewhere, or at least eyeball all the welds & axle
- Now's an ideal time to perform the service letter that lets you remove the flat bar in the leg and weld in a round (or streamlined) tube for those not-quite-perfect xwind ski landings.
- Put the new cords in position and secure the holder plate to keep them from sliding off
- Slowly lower the nose back down while somebody tries to hold the gear leg close to straight and let the weight of the airplane leverage the hinges against the new cords back into position. The rubber bumper makes a lousy fulcrum, but that's the deal.
- Slide the pins back into their bushings. Don't get wild with a hammer, the sintered bronze is fragile.
- Replace the safety cable
- Repeat for other side

The force of the new cords fights you every step of the way, keeping the legs twisted while you're trying to line up the hinge pins just enough to frustrate the part where you slip the bolts back in. Gravity was the best tool to solve this, eventually they line up if the airplane is straight and the tire is free to slide where it wants to on the floor. It helped me to stick a long screwdriver through the fwd hinge to temporarily hold the thing close to get the aft bolt in, but it's easy to crumble the sintered bronze bushings.

It helped a lot to have

- a couple of big (2 foot square) greased-sandwiched plates to lower the wheel down onto, so the wheel+gear didn't try to shift the whole airplane to the side while gravity+weight aligned the hinges.
- somebody who's confident with an engine hoist, that isn't impatient
- Extra bushings for the MLG hinges, because it's easy to get stupid with a hammer and damage them trying to get the bolts in & out.
- a new MLG hinge bolt a little longer than it's supposed to be, with a rounded bullet tip
- Brass drift pins, to tap the bolts in & out

Check my process with somebody else that's done it before (like Burl). Since my wings were off and the airplane was basically a skeleton, I wasn't worried about weight and hoisting from the engine mount attach points. It could be argued that a finished airplane is too much weight to be hanging off the mount attach points by lifting the engine with a hoist.

Eric

[Aryana]

Eric's write up is on the money. That's exactly how mine were changed. Had to lift and reposition the gear leg a few times before the bolt holes lined up properly without banging anything with a hammer. Now that I've done them, it's not as bad as I thought. My wings were off the fuselage which if installed would make the whole process a lot more exciting.

[Matt]

Joe

I purchased the main gear bungees for N1331H directly from the manufacturer, SBC Industries. Their product list does not mention the tailwheel bungee, though, and I can't recall nor find any documents, where I got that one from. But I would guess that SBC makes that type, too. I will ask them and then post the result in this thread: http://www.sbcindustries.com/products.htm

The SBC list obviously differentiates two types of bungees for the main gear legs: 1280 (up to S/N 330) and 1286 (from S/N 330 up).

The Sedan Parts Catalog calls for these types of bungees:
Main gear: 1280
Tail gear: 1286-MT750

Why does this have to be so complicated!?

Here is an interesting article by H.G. Frautschy about bungees in general: http://www.vintageaircraft.org/featured ... 0Cords.pdf

Matt

Here is a summary of my yesterday's conversation with SBC Industries, manufacturer of the bungees. Please draw your own conclusions...

Matt:
Dear Ladies and Gentlemen, Do you also manufacture the tailwheel bungee for the Aeronca 15AC Sedan? (The part number listed in the Sedan Parts Catalog is 1286-MT750.) And what is the difference between the bungee types 1280 and 1286, or rather, why do the bungees for S/N 331 and up have to be stronger than those for up to S/N 330?

SBC:
The difference between pn# 1280 and 1286 is the Inside Diameter. The 1286 has a 8.75" ID, 1280 is 8". Loads are the same at like percentages of elongation. We do manufacture pn# 1286. David Valentine, SBC Industries, Inc., 256-259-6609 ph, 256-259-6610 fx.

Matt:
So, can you please confirm: For serial numbers 1 through 330, I would use 4 or 6 of the type 1280 bungee for the main gear (2 or 3 on each gear leg) and 1 of the type 1286 for the tail wheel? For serial number 331 and up I, would use 4 of the type 1286 bungee for the main gear (2 on each gear leg) and 1 of the (same) type 1286 for the tail wheel? And my last question: Do you know, what the "MT750" in the tailwheel's bungee part number (1286-MT750) stands for in the Aeronca 15AC parts catalog? In other words, is your type 1286 identical to the 1286-MT750 listed in the parts catalog?

SBC:
That is what my records show. I don't have any reference for the 'MT' designation. The 750 is a load reference. I have all the Thomas Taylor records which cover decades. The MT is not recorded. The 1286 as we manufacture it is what has been used for this aircraft. The 4-6 units (to be installed) has always been in the documentation for this part on this plane. I'm not sure why it varies (with the aircraft serial number). David Valentine, SBC Industries, Inc., 256-259-6609 ph, 256-259-6610 fx.

[joea]

Eric,

Thanks for the excellent description. Am trying to keep my wings on while doing this.

Aryana,

Good info as well. The comment "would make the whole process a lot more exciting." is something that I am trying to stay away from! Have had enough excitement in my life already!

Matt,

Great to know what they recommend. Evidently the tailwheel system was changed after serial 330 and they re-designed it to work in a different way.

To tell the truth, its going to be 113 in the shade here in Arizona tomorrow, so I am guessing that the airplane will be sitting for another 2 months before I do anything. Just too damm hot out there and even if the gear was working fine I would not be flying until it cools off a bit. At least in late September I need to get some bungees ordered and get ready to do this!

Thanks everyone!

[sedanpilot]

I think I can provide a reason that the bungee part number might have changed, or maybe just confuse things more. If you look at service helps and hints number 50 on Burl's site you can see that at the same serial number that the bungee part number changed, the reinforcement was added to the gear.

It's speculation, but I can think of two reason why the bungee might have changed at the same time.

1) The geometry changed a bit and they therefore needed the extra 3/4 of an inch, doesn't look like it, but maybe there is something I am not seeing.

2) They realized that because the thing was cracking, maybe a little less preload would be wise to make it a softer gear, so made it a little bit longer.

The last time I changed the tail bungee, I used the 1286 since I have an newer serial number and have the gusset and that was what the parts book called for. It was a bit of a grunt to get it preloaded, but not as bad as I was expecting from some of the stories people had told me.


On the main gear, I essentially used the method Eric outlined, but I had a couple of deviations.

1) I used a wing jack on one wing instead of the engine mount and did the gear one at a time. That way it was supported on three points far apart and fairly stable. If you are outside and the wind come up during this project, it could get interesting.

2) I didn't have a grease plate, so I used a floor jack on wheels under the axle and a custom cut block of wood to protect the axle. It's easy to screw it up and mess up the axle if you aren't careful.

3) On tools, I used extra drifts and bullets to line up the bushings instead of screw drivers, easier on the bushings. As Eric implied, lining up the bolt holes is tricky. I made my own bullets by taking the old pivot bolts and grinding off the head into a dome/cone shape so it would help line up the holes. I lined up the holes with two drifts (Tapered punches) first, then pushed the drifts out with the bullets and pushed the bullets out with the new bolts. (Sounds complicated, but it helped line things up with the bungees under preload) Grease the bullets and the bolts so you don't scar the ID of the bushings any more than necessary. A bright flashlight helps to tell when the holes are lined up. The bullets make sure you don't drag the holes with the threads of the bolt.

If you are going to put on ski tabs, this is a good time to install them. I tried to do it at first without removing the fairings on the floor that cover the bungees inside the cabin. Didn't work, but I did not remove the floor boards completely, only the metal fairings. I know one person that found a broken rudder centering spring when he changed the bungees.

[joea]

An update on my end.

The summer weather has broken and its finally under 100 most every day here in the desert.

Getting ready to put the bungees on the Sedan in another week or so when work slows down a bit.

Thanks for the info everyone!

[joea]

A question for you old timers who have done this before.

I was trying to use a tool that one of our members made to be able to change bungees without taking the landing gear loose. So far am not having much luck with it.

Am to the point of giving up and loosening the main gear (one at a time) and doing this the "old fashioned" way.

My question is, when doing this are you guys able to get this done without loosening the brake line? Have been looking and its the only thing that I can see that would prevent me from totally removing the landing gear on either side. Would really rather not remove this if at all possible as I am alone and bleeding the brakes once done is not going to happen.

Suggestions? Recommendations?

Thx,

Joe

[GeraldCox]

Joe,
The shock cords (1280CW) were replaced on 15AC-264 a few weeks ago at Northwoods Aviation in Cadillac. Used the chain fall winch that they use for float planes to lift the airplane with wings on, front floorboards removed. The previous post by E Sandberg is a very good guide and it took two experienced guys with occasional help from a third to get the job safely done.

The brake lines need to be disconnected to remove the gear. I also had to replace the bumpers (main landing gear stops part #1-3669) as they were deteriorating and did not hold up to the 'pivot stress' of re-installing the gear.

My Sedan only had one safety cable on each side as shown in the service manual gear diagram. However, the parts list calls for two on each side. Burl advised that one cable will not keep the wing from striking the ground if the cords break. Two cables will (snare arrangement #7-821-11)), and it was a good time to correct that also.

Burl has new bumpers and a safety cable (4) kit if you need them. I hope it goes well.

[Matt]

Hi Joe

It can be done without removing the gear legs and disconnecting the brake lines. Whether this procedure is easier, though, I don't know. It is what we did, during the restoration of N1331H. The pictures might help to explain what I mean, but I wish I had more to show you the interior details.

1. Remove the bottom gear leg fairings.
2. Remove the top engine cowl section.
3. Suspend the plane at the engine hoist point just slightly in order to take the load off the tires and to permit the gear legs to swing inward against their stops.
4. Using a span set, pull the gear legs together from axle to axle and/or use 2 span sets inside the belly to pull the horizontal gear leg tubes up to the fuselage. For this you will most certainly have to remove the floor boards.)
5. Cut a piece of wood at the correct length and position it between the wheels.
6. Use two small blocks of wood to prevent the large piece from dropping/shifting.
7. Position one "end" of a bungee over the rear Shock Ring Retainer (looks like part 7-818-30 on page 59/60 of the parts catalog, but is not removable).
8. Pull the other "end" of the bungee over the fuselage cross tube and pull down, using one or, for safety reasons two, span sets which are attached around the large piece of wood that you positioned between the wheels.
9. Slide the front "end" of the bungee over the respective tube (Sounds easy, but....).
10. Repeat steps 7 through 9 for each bungee ring, install the safety cables and front Shock Ring Retainers (part 7-818-30) again.









And here are links to old photos of 15AC-429 having its bungees replaced in the UK.
Again, without removing the gear legs!
http://n1331h.com/sedan_gallery/15ac-42 ... ious-photo
http://n1331h.com/sedan_gallery/15ac-42 ... ious-photo
http://n1331h.com/sedan_gallery/15ac-42 ... ious-photo

Good luck!

Matt