• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Bottom bungee spring

F

Fortysix12

Registered User
RanchAero Grand Vista, Brooksville
It is common to remove or omit when building the bottom elevator bungee spring. It seems that I have heard from both builders and certified owners that certain aircraft run out of forward trim. The question is for those airplanes experiencing lack of forward trim-would it not be a good idea to install the bottom bungee to assist with the problem ? I think I know why Piper had trim bungees on both upper and lower points of the elevator but what ya'all think?
 
I hear ya, but I have an airplane that runs out of nose down pitch, wouldn't the lower spring attatched correct this? Ya roll the nose over and the top becomes relaxed the bottom assist with the elevator.
 
I think that if Piper certified the plane with the lower bungee spring, then there was a reason for it and to remove it would require an approved major alteration. Field approval, STC or a service bulletin from Piper. The real question is, why does the plane now run out of nose down trim? Under what condition? It sounds as though it is being flown outside of the aft CG limit. That is what needs to be corrected. OR Maybe the airplane was rebuilt at some point in time and the stabilizer angles are out of limits.

A friend of mine was getting a STC on his Cub and it would not pass a certain test. The FAA engineer told him to take 1/2" out of both lower longerons under the tail to change the stabilizer angle. I did the welding and 337 for a repair and the next day the Cub passed the test. The was done in Anchorage.
 
Lower bungee cable P/N 40123-92 and -88 used on PA-18, 105 HP, Serial Number 18-1 to 18-548.
 
skywagon8a said:
...The real question is, why does the plane now run out of nose down trim? Under what condition? It sounds as though it is being flown outside of the aft CG limit. That is what needs to be corrected. OR Maybe the airplane was rebuilt at some point in time and the stabilizer angles are out of limits.
.... The FAA engineer told him to take 1/2" out of both lower longerons under the tail to change the stabilizer angle. ...
Click to expand...


that would be my guess, stretched lower longerons.....
but don't over do it... shortening them...
 
They were only there for the military contract. Piper has a SB to remove them from those aircraft.
 
PA-18 dual elevator bungees

We did the standard tear down to frame and build back up, getting close to being completed. I can't figure out where to connect the lower elevator bungee, none of the pictures I find are clear enough, anyone have some advise on how it is connected?


Sent from my iPhone using SuperCub.Org mobile app
 
elevator bungee

20170413_182442.jpg

Is this what you are looking for? Piper service letter #150. Applies to PA18 105s, but I believe they are the same attachments. Advises you can remove them. Never seen one on any 18. Jon
 

Attachments

  • 20170413_182442.jpg
    20170413_182442.jpg
    1.8 MB · Views: 1,039
I'd like to put the spring back on, the picture I took when disassembled has the standard bracket still attached to the lower cable with the cotter keyed bolt. I don't see anything in the pic to attach the spring to like in the drawing that was posted. I tried to attach a pic but the app keeps closing.


Sent from my iPad using SuperCub.Org
 
4b6f9a75e614a710aa961365b77ba7be.jpg
h

Here is a pic of a bracket I found but the holes do not line up, the black bracket. The grey bracket is what was attached to the cable


Sent from my iPad using SuperCub.Org mobile app
 
In the picture that Steve posted there appears to be two brackets, (one for the elevator cable and one for the bungee spring attachment).
 
There are two attach brackets... The heavy one that is your lower control cable attach bracket that also acts as the stop... And a lighter one that is jogged over to attach to the same lower elevator bolt...

The lower spring is removed on most Cubs and the upper left in place... I have a couple attach straps laying around...

Brian
 
This is strictly my OPINION, but if the bottom spring makes any detectable improvement in the flying quality, there is something wrong with the plane. I think it's original purpose was to make the plane pass a specific pitch upset/oscillation recovery test. With the spring in place, you'll have a heavier aft stick when banking and flaring. I'd leave it out.
 
The later model fuselages didnt even have the pulley brackets welded into the fuselage. I would throw those parts away and follow the drawings, service memo and IPC.
 
You must log in or register to reply here.

Similar threads

F
Lower Elevator bungee spring.
Replies
4
Views
2K
Fortysix12
F
E
Bungee Spring question
Replies
2
Views
1K
willyb
W
Steve Pierce
Elevator Bungee Cable
Replies
2
Views
2K
Steve Pierce
Steve Pierce
Binty
Definitive Elevator / Stab ajustment
Replies
7
Views
3K
Glidertow
G
E
Elevator Bungee Cable and Spring loose
Replies
3
Views
2K
Steve Pierce
Steve Pierce
Back
Top