Building and finishing my 2+2/PA 14

[Marty57]

The test with the caulking adhesive seems to be a success. I am unable to pull the aluminum strips from my test piece. I think I'll use this method to attach the stiffeners. If they happen to come loose over time I can remove and rivet as necessary. I guess this is why it's called experimental.

Marty

 

[CamTom12]

Looks great!

 

[Marty57]

With the doors ready for paint it was on to finishing up the electric trim. I am using parts supplied by Javron. I had mounted the motor bracket before painting the fuselage so finishing entailed mounting the stop switches and temporally wiring everything up to check how it worked. I received a couple brackets from Jay for the stop switches but decided to design my own that would bolt on rather than welding onto the painted fuselage. It took some head scratching but I came up with a set up that works nicely and is easy to remove if servicing any of the parts is necessary. I used the same wiring schematic that Bill used on his Javron Cub (Thanks Bill). It uses a couple of diodes and switches to make everything work. I first tested everything on the kitchen table on a bread board than moved it into the shop and attached to the motor. A little oil on some parts and everything seems to be working nicely. I need to remove and paint the parts I made and re-install and permanently wire everything up. Next will be the trim indicator wire and bungee spring for the elevator before moving on to control cables. Some pictures and a video of the trim parts ......

Marty

 

[fobjob]

I think it would be appropriate to point out that when you fasten down your wires, you make sure that there is a small service loop that prevents any stress to remain on the connector after everything is anchored. No connector lasts long if installed with stress on it.


*I don't like crimp connectors.....

**laying here bored stupid waiting for my new Borg knee to get healed.....

 

[Marty57]

I think it would be appropriate to point out that when you fasten down your wires, you make sure that there is a small service loop that prevents any stress to remain on the connector after everything is anchored. No connector lasts long if installed with stress on it.


*I don't like crimp connectors.....

**laying here bored stupid waiting for my new Borg knee to get healed.....

I agree; I don't like crimp connectors either. I'll solder wires to the motor and use screw terminals on the stop switches with a drop of loctite. The DPDT switch uses crimp fasteners but I may solder those also. I'm not sure what switch I want to use up front yet. I haven't decided if I want simplicity of just one switch on the panel for both right and left seat to access or just one on the pilot stick; not sure yet. Plenty of time to decide that one.

Marty

 

[Gordon Misch]

Crimp vs solder seems to be vigorously debated. In my opinion (worth what you've paid for it), in either case it's important to support the wires so that they aren't stressed at the location of the connection. Electronics International (makers of electronic engine, and other instruments) sez put a small drop of oil on crimp connections to act against corrosion. I used lots of crimp connectors on my rebuild, and so far no issues. I paid a LOT of attention to supporting wires in an effort to eliminate, or at least minimize, fatigue stress at connections.

I think one of the arguments against solder joints is the sudden section change at the joint, begging for fatigue failure at that location. Seems to me that stress relief measures, possibly including shrink tube over the connection would be helpful. Crimp connectors have that built in. Here's a link that might be helpful http://verticalpower.com/_documents/_pdf/connector_service_manual.pdf

 

[Marty57]

I do need to study up on wire support and connectors as I move toward the panel. Any suggestions as to where to get some examples of good wire support? I will be soldering the didoes into the circuit and using heat shrink in those areas but the others ...... time for more learning.
Thanks,
Marty

 

[jimboflying]

What is the purpose of the diodes in your trim control circuit?

 

[Carey Gray]

Good crimp/good connection
Bad solder joint/bad connection
I've been building road striping equipment for years that accumulate more hard hours in a year than most airplanes do in a lifetime, without a solder joint. Whatever you do, if you do it right...

 

[Marty57]

What is the purpose of the diodes in your trim control circuit?

Let me see if I can explain how this works. The circuit is below:



The limit switches are normally closed (shown open above) when the motor is rotating. Changing position of the DPDT switch changes the polarity of the motor, reversing the rotation. When the limit switch is engaged, opening the circuit, the motor stops rotation. With the diodes removed, there is no way to re-engage the motor to go the opposite direction. The diode gives a momentary pathway (it's a one-way electrical valve so to speak) for the current to flow when the DPDT switch changes position as the yolk moves off the limit switch. As soon as the yoke is off the limit switch the circuit turns the motor in the other direction. Without the diode, there is no way to move the yoke off the limit switch and the circuit is open with no way to energize the motor and get it turning again. It took me a while to understand it; that's why I first did a test circuit on the bread board. I suppose there is another way to do this with out the diodes but this is pretty simple. This is the circuit that Bill Rusk posted when he set up his trim and it seems to work pretty well with a minimal amount of wiring. I suspect there are other ways of wiring this up but this seems to work well. I hope this explains how it works.

Marty

 

[JeffP]

Let me see if I can explain how this works. The circuit is below:

View attachment 31870

The limit switches are normally closed (shown open above) when the motor is rotating. Changing position of the DPDT switch changes the polarity of the motor, reversing the rotation. When the limit switch is engaged, opening the circuit, the motor stops rotation. With the diodes removed, there is no way to re-engage the motor to go the opposite direction. The diode gives a momentary pathway (it's a one-way electrical valve so to speak) for the current to flow when the DPDT switch changes position as the yolk moves off the limit switch. As soon as the yoke is off the limit switch the circuit turns the motor in the other direction. Without the diode, there is no way to move the yoke off the limit switch and the circuit is open with no way to energize the motor and get it turning again. It took me a while to understand it; that's why I first did a test circuit on the bread board. I suppose there is another way to do this with out the diodes but this is pretty simple. This is the circuit that Bill Rusk posted when he set up his trim and it seems to work pretty well with a minimal amount of wiring. I suspect there are other ways of wiring this up but this seems to work well. I hope this explains how it works.

Marty

This makes sense with a two wire motor, with a three motor wire motor no diodes needed.

 

[fobjob]

The other circuit I sent Bill didn't use diodes, but had about six conductors between the switch and the tail. Bill wisely chose the simpler alternative. I limited myself to a two wire motor because they are far more available than the three wire models....the diodes are very overrated and don't need to dissipate any heat to speak of unless the motor jams at the limit switch*, but it's a good idea to give them a heat sink, anyway.

*make sure that there is rotation room between where the limit switch activates and the end mechanical stop...

 

[skywagon8a]

*make sure that there is rotation room between where the limit switch activates and the end mechanical stop...

So that the motor has room to coast to a stop after the power has been cut off.

 

[Marty57]

I'm not sure if a heat sink would be necessary. The motor shuts off basically instantly when the limit switch comes on, no visible coasting at all . The diode is only allowing power through to open the limit switch. It's pretty simple. Cycling the motor through and no heat or other issues at all. I think it's a pretty simple system. I greased and final assembled everything and it all works very smooth, no binding at all. I just run the over head trim indicator wire and am looking for a light duty spring for up top.

Marty


Marty

 

[skywagon8a]

The motor shuts off basically instantly when the limit switch comes on, no visible coasting at all.

Marty, Unless there is a brake installed all electric motors will "coast" to a stop. If you and I are looking at it and it appears to stop instantly, it is still "coasting". IF the motor came up against a hard stopping point at the same instant at which the power was cut, You would notice an abrupt hard stop.

 

[Marty57]

Marty, Unless there is a brake installed all electric motors will "coast" to a stop. If you and I are looking at it and it appears to stop instantly, it is still "coasting". IF the motor came up against a hard stopping point at the same instant at which the power was cut, You would notice an abrupt hard stop.

I see what you are saying, thanks. The limit switches I have provide a "coast" after the circuit is opened. The yoke can travel a good 1/16" or more before jamming against the switch.

I finished the guides and install of the trim indicator wire across the top of the fuselage. I still need to get a spring for up front and make some sort of guide or pointer; I have a few ideas how that will happen. I made the wire guides I used from HDEP. Very little tension on the wire; I need to find a spring that will stretch about 2-3" and only have a tension of about 1-1/2 lbs.

Marty

 

[skywagon8a]

View attachment 31898

There is a maximum requirement for the change of direction of a cable over a fair-lead of 3 degrees. Above 3 degrees a pulley is suggested. Your trim indicator cable change in direction appears to exceed 3 degrees. I would be concerned that you will develop wear points in the cable at those locations even though you are using a slippery materiel for the fair-lead. One way around this would be to place the cable inside a length of nylon tubing which can just be tied to the steel tubing as needed. Or just keep an eye on it.

 

[Marty57]

There is a maximum requirement for the change of direction of a cable over a fair-lead of 3 degrees. Above 3 degrees a pulley is suggested. Your trim indicator cable change in direction appears to exceed 3 degrees. I would be concerned that you will develop wear points in the cable at those locations even though you are using a slippery materiel for the fair-lead. One way around this would be to place the cable inside a length of nylon tubing which can just be tied to the steel tubing as needed. Or just keep an eye on it.

I'm very familiar about the requirements for change of direction in control cables and fairleads; dealt with that a lot in running all the main cables. The tension on the wire will be less than 2lbs, just enough to take out the slack. The rubber band I have on there is enough pressure to keep the wire where I want it so a spring of equal strength will work fine. The system I used is a copy from a popular Super Cub clone that I spotted at Oshkosh. On that one, the indicator wire runs in this fashion with changes in direction similar to mine but they used fairleads. The HDPE is tougher than and more slippery than nylon so no worries. Thanks for the second set of eyes on this.

Marty

 

[Marty57]

Haven't posted in a while ...... been very busy with Stewart Systems. I did get my web site up to date with the electric trim and everything leading up to it. I'm ready to do the fuselage covering or the fire wall forward next. What's the conciseness? I've seen it done both ways. So, time to vote: Firewall forward and than covering or covering than Fire wall forward? I have the engine, just need an engine mount (PA12 will work). I'm still building in my shop at home; no need for hangar yet. Thoughts and ideas? Thanks

Marty

 

[skywagon8a]

I would prep the firewall forward then remove the engine and mount and cover the fuselage. Just in case something comes up that you need access and there is less likely the possibility of damage to the fabric. This will enable you to rotate the fuselage more easily while covering.

 

[Gordon Misch]

I would prep the firewall forward then remove the engine and mount and cover the fuselage. Just in case something comes up that you need access and there is less likely the possibility of damage to the fabric. This will enable you to rotate the fuselage more easily while covering.

+1 Not all surprises are fun.:smile:

 

[Marty57]

Good advice, thanks. I think I'll order my firewall from the Cub Doctor, get my engine mount figured out (I have one that needs repair) and get my nose bowl ready to mount. In the mean time, I can finish covering the control surfaces and run control cables in the wings. Lots to do! Thanks and I'll keep the posts up as I move forward.
Marty

 

[Marty57]

Well, I've been busy since last post. Between Sebring and Sun N Fun, I covered all my tail feathers and control surfaces. I started in the garage shop but in mid January, even here in California, I needed to turn on some heat. So, I simply moved into the kitchen and did most of the covering on our butcher block table. Yes, my wife was in town and home the entire time I was covering. And yes, we are still married! Currently, all the covered parts are stored in the master bedroom. My wife is beyond amazing ......

Here's a few pictures. I started in the shop, not bad but in the 50's.






I moved into the kitchen after doing a few days work in the shop.





A little more in the shop .....


Than beck to the kitchen to stay.



Time to cover the wood flaps and ailerons.





















Ailerons were next; they require a big table .....




Ailerons were basically a repeat of the flaps but a lot bigger. After working about 100+ hours, everything was done except taping one aileron, time to leave for Sun N fun.



With the second aileron taped and finished, it's time for some yard work before heading up to Alaska next week for the Great Alaska Aviation Gathering. I'll be in the Stewart Systems booth both days, come say hi. Our plans changed for after the show and I'll be by my self for three days in Anchorage. ........ anyone want some hands on Stewart Systems training???? Will work for flying ;-)

 

[Paul Heinrich]

Beautiful woodwork. You must be an artist and carpentry craftsman.

 

[RVBottomly]

Thanks for posting this, Marty. Keeps the inspiration up.

I had forgotten how beautiful those flaps and ailerons are.

Vic

 

[tempdoug]

those clamping sawhorses are the handiest thing. very nice work.

 

[Gordon Misch]

Well Marty, I sure hate to see that beautiful woodwork covered up. Couldn't you have used a clear cover material? Haha. Stay with it, sir!

 

[Marty57]

Gordon,
I did feel a bit of a twinge as I covered all the wood. Only consolation is there are no rivet heads or screws sticking up on flaps or ailerons after covering the wood. The wood wings are next to cover; that will be a lot harder to have disappear. Oh well .....
Marty

 

[Marty57]

I guess I strayed my posts over to another 2+2 build post, time to get things back on track here. Some good progress to show on my 2+2.

After a lot of frustration with a stock engine mount not fitting my fuselage, I made a couple attempts at making my own mount; big mistake. With the dimensions off a bit on my mounting lugs and the angles of the bushings off a bit, a mount needed to be fabricated to my fuselage. I built one mount using O/A but was not satisfied with the heat distortion. Needing to Tig weld a mount, it was time to learn to Tig weld. After a bit of frustration, I got ok on bench work with Tig but was still having difficulty on thin tubes away from the bench. Needing to move forward, I took the advice of Gordon Misch and contacted Steve at Super-12 Aircraft.

Steve came up with suggestions and I built a very solid oak frame that properly bolted to my fuselage.



From that frame, I build another oak frame that now matched my fuselage and sent both frames up to Steve.



Steve used the wood frames to build, in very short order, a stock length and design PA12 engine mount that matched the irregularities of my fuselage. I received mount today and it fit as designed.

Over the past couple of weeks, while waiting on the engine mount, I got started on the firewall forward sheetmetal. Like many things on the 2+2, there are some subtle differences between the 2+2 and the PA12/14, the firewall being one of them. Since I built all the gingerbread channel work up front to match the 2+2 firewall drawing, I couldn't use a stock 12 or 14 firewall so everything needed to be fabricated.

I bought some stainless steel and cut a firewall.







Next, using the shrinker and stretcher, I fabricated the flange for the firewall.









I'll be building a three piece boot cowl with the cooling tunnel at the bottom, so I'll be using nut plates for disassembly. Some of the nut plates at the bottom tunnel area needed to be installed as the flanges were made, the remainder will be installed as I get the patterns made for the boot cowl.

Today, it all came together and I have a firewall and engine mount hanging on my fuselage.



Boot cowl patterns are next. Scratch building is not for the faint of heart!

Marty57

 

[Marty57]

I have the boot cowl patterns finished up in cardboard; not to difficult to figure out. Spacing for the nut plates need to be located before I can trim the side of the boot cowl patterns. Next will be the aft patterns where they form up the lower corner of the windshield area corner.

I decided to pull out the windshield and get a look at how it will fit up on the boot cowl before i fit the next patterns.



I am working on figuring out the windshield mounting before I make more patterns. I'm assuming that the windshield fits in the flange above at the top of the fuselage, and behind the side trims at the front door posts. What's the best tool for trimming the windshield safely; i can see I have a fair amount to remove.



Do I need any screws in either of these locations? It seems that a seal of some type here would be just fine. There will be an inner and outer trim piece at the lower corner of the windshield just aft of the boot cowl patterns that could easily have screws through the windshield into nut plates.

The trim pieces will be fitted to the bootcowl; sandwiching the windshield between the front and rear trim piece as on the Super Cub. Once the front trim on the boot cowl is screwed in place with the windshield, that will hold it in place . I haven't found any of the trim pieces specifically for the PA12 or 14 yet, most seem to be for the '18 or J3. Any clues on who makes them for the 12 or 14? If I go with pre-made pieces i know I will need to shrink and stretch to fit but maybe easier than starting from scratch? I don't have a bead roller so it might be easier to modify what i can find on the market. I'm just in the thinking stages of this but there doesn't seem to be a need for too many screws in the windshield with this set up? Time will tell as I get the boot cowl built in aluminum and tackle the trim rings that attach to the boot cowl.

Next step will be to finish up the patterns and than get some aluminum .
Marty


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