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PA-12 weighing levelling marks

P

Philly5G

Registered User
England
I'm really struggling to find the weighing levelling marks on my 12:

[FONT=&quot]The FAA document for the Piper PA-12, as shown in the LAA Aircraft Data Library, states the levelling means as shown below:[/FONT]
[FONT=&quot]‘Leveling Means - Plumb bob from machine screw at door frame channels near upper rear corner of door to hole in plate near rear seat.’

[/FONT]
Could someone please post a couple of pics of where these marks are and what they and their machine screw and plate look like please!!!! Thanks!!!! ;-)

Philly
 
Also if you have a turn and bank or ball set it to center once you have it in level flight (firewall vertical, level fuselage side to side)


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mike mcs repair said:
Photos in here with a less than virgin fuselage using plumb bob and taking various measurements with a level


https://goo.gl/photos/PuiR5ha2aBDbkUBS8


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Click to expand...

Thanks for the photos Mike! In the pics where the tail is pretty high and looks like it's supoorted by a set of blue ladders, is the fuselage level? I can't see the firewall to judge if it's vertical, but the angle of the fuse looks close to the angle of the fuse in the Piper PA-12 weighing diagram. At that angle in the pics, the root of the wing looks slightly nose down too?

I couldn't find the plumb bob pics though?
 
Last edited:
Level the fuselage first, THEN the instrument. It's just a convenient way of making sure the ball will track accurately.

Web
 
Philly, The issue is sometimes the ball is not properly orientated in the instrument panel when the fuselage is level. Someone may have drilled the mounting screws crooked. You want to use the ball as a level. Is there one built into your electronic AH?
 
I've seen this levelling thing discussed multiple times, here & elsewhere.
The plumb bob method Piper used is great, except the screws hole & prickpunch marks sometimes disappear during a rebuild.
Friend of mine went through this with his Pacer-- firewall plumb, tailpost plumb, MLG axle x" from wing leading edge.....
none of the several methods agreed.
He finally located a factory fuselage drawing, which has a "horizontal reference line" which can be used to level the fuselage for weighing or rigging.
Another friend located one of these for his PA12.
The HRL (originally meant to be used with a water level, but nowadays everyone uses a laser) on the 12
goes from the centerline of the upper engine mount-to-firewall bolt head,
to a point back at the tailpost.
I have a file of these PA12 fuselage prints, I can fwd it if you'd give me your email.
I'll post it here also, but it might not come out clearly.
 
Last edited:
Nope, can't do it-- too large a file to post here.
Maybe I can email it to somebody more computer savvy than me
and they can post it somewhere on the site.
 
hotrod180 said:
I've seen this levelling thing discussed multiple times, here & elsewhere.
The plumb bob method Piper used is great, except the screws hole & prickpunch marks sometimes disappear during a rebuild.
Friend of mine went through this with his Pacer-- firewall plumb, tailpost plumb, MLG x" from wing leading edge.....
none of the several methods agreed.
He finally located a factory fuselage drawing, which has a "horizontal reference line" which can be used to level the fuselage for weighing or rigging.
Another friend located one of these for his PA12.
The HRL (originally meant to be used with a water level, but nowadays everyone uses a laser) on the 12
goes from the centerline of the upper engine mount-to-firewall bolt head,
to a point back at the tailpost.
I have a file of these PA12 fuselage prints, I can fwd it if you'd give me your email.
I'll post it here also, but it might not come out clearly.
Click to expand...

Thanks hotrod180, I've PMed you with my email address, could you please forward me the doc, sounds VERY useful!!

Cheers

P
 
Google FAA AC 43-16 from August 1997. This gives the leveling and rigging for the Pa18, 12, 14. Anyone who works on cubs should have a copy of this.
 
SuperCub MD said:
Google FAA AC 43-16 from August 1997. This gives the leveling and rigging for the Pa18, 12, 14. Anyone who works on cubs should have a copy of this.
Click to expand...

Thanks!!! This is the link to the doc https://www.faa.gov/aircraft/safety/alerts/aviation_maintenance/media/1997/1997_08_Alert.pdf Page 11 applies to levelling and this puts another levelling option into the mix [emoji41]

Interesting that the instructions are to measure the level from the cockpit floor, between the front and rear main undercarriage mounts. I’d say that this floor takes more wear and tear than a lot of areas and i wonder how accurate these angles will therefore be?


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Original service memos.

Web
 

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wireweinie said:
Original service memos.

Web
Click to expand...

Thanks for these Web! The first doc gives a bit more detail on where the top levelling hole should be, I.e. 4 1/2” forward from the rear door frame, but still pretty vague on the bottom plate, other than under the rear seat. I’ll have a look tomorrow and report back [emoji41]


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Philly5G said:
Thanks for these Web! The first doc gives a bit more detail on where the top levelling hole should be, I.e. 4 1/2” forward from the rear door frame, but still pretty vague on the bottom plate, other than under the rear seat. I’ll have a look tomorrow and report back [emoji41]


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Click to expand...

The whole point is the original plumb bob method is useless. It’s assuming a plane that’s never been wrecked/bent. Just use a digital level on firewall and across top of windscreen/floor averaged


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mike mcs repair said:
The whole point is the original plumb bob method is useless. It’s assuming a plane that’s never been wrecked/bent. Just use a digital level on firewall and across top of windscreen/floor averaged


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Click to expand...

Do you mean the floor as in the method in Web’s document and where are the levelling points on the windscreen?


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mike mcs repair said:
The whole point is the original plumb bob method is useless. It’s assuming a plane that’s never been wrecked/bent. Just use a digital level on firewall and across top of windscreen/floor averaged


Sent from my iPhone using SuperCub.Org mobile app
Click to expand...

It's good info to go along with the stuff in the AC-16, called out above. The reading walks you through what was originally intended and then on to techniques that work for 'repaired' aircraft.
I agree with the plumb bob stuff. Not sure I've seen it work on more than one aircraft in the past. I don't really like the fore/aft leveling on the floor (no floor is nice and flat) but sometimes it's all you got.

Web
 
My opinion - keep it simple. Firewall vertical for pitch-axis, and pick something inside for roll-axis leveling. The tube across the bottom of the instrument panel is a good candidate. So is across the wing spar attach bolts. No two reference choices are likely to agree, so pick something and run with it. On the experimental -12 we're building, the cross tube at the forward edge of the rear seat matches the spar attach bolts pretty close, and it's convenient. So that "by definition" is level. Same with my certified -12.
 
Gordon Misch said:
.... No two reference choices are likely to agree, so pick something and run with it.....
Click to expand...

That was my advice to my friend with his Pacer.
He's kinda OCD I guess & was unwilling to accept that, so he kept researching until he found out about the HRL.
I think that method's pretty good because you're not working with something short,
you're working from one end of the airplane to the other.
Kinda like using a 6 foot spirit level as opposed to a 9 inch "whiskey stick".
 
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