Porterfield Airplane Club

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Question about Headknockers - aileron balance weights

I have a 1940 CP50 that I am restoring from the ground up.  I  built new ailerons and transferred the lead weight from the old aileron to the leading edge spar of the new aileron.  While in Osh Kosh I saw a LP65 with headknockers for balance weights. My CP50 was not equipped with headknockers. I searched for AD's but could not find any for the CP50. Does anyone know if the headknockers was an STC or some other add-on? My ailerons are quite heavy at the trailing edge. I have always been told that ailerons must be balanced to prevent flutter. Comments please?

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Comment by Bill Skinner on March 21, 2018 at 9:26am

I added a Video from 1990 in which W. R. Skinner explains a little bit of background on the aileron balance weights. You have to listen carefully as the audio is not very clear with the background noise ....

Comment by Andy Gelston on February 20, 2018 at 1:15pm

Back in December of 2010, Tom P. was kind enough to post this in the Forum:

Porterfield Airplane Mantenance Manual and CP-50/65 Engine Mount Drawing

Just click on "Forum," above, and go to page 10 of the forums and you should find this.  Hopefully your mechanic will be comfortable with using it.  Always check the old forums and blogs!  They're loaded with all kinds of good info.


Comment by Andy Gelston on February 17, 2018 at 3:22pm

Thank you, Bill!  I'm speculating, but it seems that the CP-50 didn't get the mods for intentional aerobatics because such maneuvers weren't possible with fifty horsepower.  However, when you install an A65 in a CP-50, as has been done with many CP-50's, then it is a good idea to add the noseribs, stouter structures, and aileron balance weights as you would the 55 and 65 series.  I'm curious if there's an STC somewhere for these mods in the CP-50.  Technically, for the CP-50 to meet the specifications of the type certificate, it must have 2-ply tires...good luck finding those!

Comment by Bill Skinner on February 16, 2018 at 10:22pm

attached are some additional details from my fathers files. note that these diagrams are all labeled "preliminary", and apply to Porterfield 55 and 65 series aircraft.




Comment by Bill Skinner on February 16, 2018 at 9:57pm

I was curious, so i began looking through my father's old paperwork and found the following:

Airworthiness Bulletin No. 81-B dated June 20, 1944

Models CP-55, CP-65, CS-65, FP-65, LP-65

Subject: Instructions Covering Changes Necessary to Lift the "Intentional Aerobatics Prohibited" Placard.


(brief summary)

A. Wings.....

(wing modifications...)

B. Ailerons

The Ailerons should be balanced by adding an external balance as shown in Figures 2, 3 and 4. ...

( sub-paragraphs a through e describe the steps to modify the ailerons)

trying to attach the figures below...



Comment by Andy Gelston on February 16, 2018 at 8:02am

You can find the TCDS here:       http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/...

or maybe you can open this attachment: TC690.pdf

The later Collegiates were certificated under CAR 4a (Civil Air Regulations, version 4a), CAR-PART%2004a.PDF and so they continue to be regulated under them, which drives the young punks at the MSDO nuts because all they seem to know about are biz jets, airliners, helicopters and Cirruses.  Seriously, they look at a factory drawing with steel tubing, wood, or fabric covering and they go, "Huh?!"

However, the CP-50's TCDS mentions no CAR, so they may have been certificated under CAR 3. car_part3.pdf

As for aileron and elevator limits: they're not listed in the TCDS's for any of the Collegiates.  I'll have to check the old original rigging instructions for the travel limits, if they exist, and look at my FP-65 to see if there are stops beside the torque tube that the control sticks are attached to.  I don't recall anything out in the wings for stops.  I recall the rudder having fixed stops welded to the tailpost, but I'll have to take a look to verify that.  The elevator stops are the back of the front seat and the front of the rear seat...KISS applied even in the late 30's.

Comment by Victor Briley on February 15, 2018 at 10:09pm

Andy, I just got off the phone with Tim Talen looking for info. on aileron and elevator travel specs and aileron stops. I don't see any aileron stops on the old wings. Is that incorporated into the control stick? Were there ever mechanical limits incorporated in the aileron or wing itself? Tim said the specs should be in the type data certificate sheet which I don't have. Do you have a copy of the type data certificate sheet or can you point me in the direction to find it? He also mentioned something about CAR4A which I had never heard of before. What can you tell me about CAR4A? 

Comment by Bill Skinner on February 10, 2018 at 9:59pm

I vaguely recall my dad saying that someone stupidly exceeded red line in a dive and the ailerons fluttered and ripped off. And as i recall my dad mentioned that the FAA did issue a notice for these... I don't know what the notice was, or if a copy exists in my dad's paperwork. it would take some serious research to find it....

Comment by Andy Gelston on February 3, 2018 at 1:07pm

I don't recall any wash-in/wash-out being  built into the wings, Victor.  They're built flat and then  rigged on the fuselage by screwing in/out the fork on the rear strut.  I have the original rigging procedure that I should scan and post here (unless someone already has and I've forgotten).

The pitot static lines run through the nose ribs, between the root and the Jury strut attach.  You can run 1/4" aluminum, copper, or plastic lines (whatever your IA is comfortable with).  I have no drawing for the pitot static system, so I don't know what material they were originally (41VermonT has 1/4" copper lines, but I doubt they're original).  They have to go ahead of the main spar because the aileron cables run along the aft face it.  In the photo below, you can see the lines behind the ELT.  They're routed down along the outside of the diagonal post, outboard of the aileron pulley bracket, until they pass by the left side of the instrument panel, where they sweep inboard, over to the instruments.

Comment by Victor Briley on January 24, 2018 at 11:03am

Hi Andy,

Yes I did get the drawings. Thank you very much. I just spoke with the A&P/IA that is working with me on building the new wings. He says I need the rigging procedure to build the washout into the wing before I nail the leading edges into place. Do you have that info available for a CP50? Also, where does the pitot/static tube assy go into the left wing. I see that the pitot tube mounts to the left jury strut but I don't have any good pictures, illustrations or another Collegiate to look at for reference. This plane was totally disassembled when I got it so I have nothing to go by. I could sure use some technical data if there is any available. What is available to help guide me through this?

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