Chuck and Ryan's Build Tips

[ceslaw]

Rotator. When our first cub was built a Bogert Avitaion, Inc., rotator was purchased later in the process. Unfortunately, it was sold once the plane was built. (Who knew a second Carbon Cub would visit our shop?). So, a new one was ordered but this time early in the build. It is so handy to be able to rotate the fuselage. Here are a few tips for fuselage use:

1. The front support was set in the lowest position but the aft was set as high as possible – with the top square pipe inserted only four inches. This accomplishes a couple things. First it places the fuselage in a near level flight position. Second, it keeps the front fire wall surface parallel to the front support to minimize misalignment when rotated.Given its high position a 3/8” hole was drilled through the vertical support and a pin placed for added security and peace of mind.

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2. To secure the front cross piece to the fuselage 3/8 bolts would fit, but 5/16” were used instead. They were NOT tightened snug. When rotated the stand may want to walk slightly, depending upon how high the aft end is elevated, since the front of the fuselage may not be exactly parallel to the Bogert stand. Leaving some slack should prevent any stress being placed on the fuselage when it is rotated. Double nuts were used to lock them in place.

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3. A bit of white lithum was used on the pivoting shaft.

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4. The cross arm that attaches to the fuselage can be installed with the pivot point in either a higher or lower position. The lower position roughly balances the fuselage making it easy to rotate. Indeed, too easy. The top position was preferred so that it will rest normally in an upright position, like the pendulum on that grandfather’s clock that quit working ten years ago. It also permits placing the frame in a level flight position (see paragraph 1). Yet it takes only a little bit to turn it ninety degrees either way and it can then be supported with a stool.

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[PBY Catalina]

To avoid excessive delays and import taxes, I did not buy a Bogert rotator, and I built one from scrap. It cost me about $500 in total.


I took your remarks about the height of the front and the aft supports into account and adjusted them like you said. This has, in fact, significantly improved the ease of movement. Thanks!


To improve the problem you are describing about the stand who want to walk when rotated if the firewall and the rotator plate are not parallel, I have a small knuckle welded on the axis of rotation. It is also a clear improvement.

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But solidarizing the front and aft parts also increases the security and stability of the whole.

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[ceslaw]

Nicely done! Good suggestions.

Chuck

[ceslaw]

Tension relief

Long ago we posted a number of tips for installing the stringers. https://forum.cubcrafters.com/showth...ll=1#post10736 Here are a couple more.

1. The middle stringer on the left side, just below the fuel selector must be pulled up tight to the frame before the fabric spacer is installed and glued in place with methacrylate. It is very stiff and pulling it tight required a lot of force. Indeed, the adjacent steel frame actually bends when it is pulled into place. We did not like that.

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First notches were added, top and bottom, similar to other notches already present in other locations on the stringers. This helped but a lot of tension remained. Next slots were cut, top and bottom to about a half inch from the outside. This really helped. There is still tension, but not so much that it bends the frame.

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Similar notches were cut on the bottom stringer directly below. Obviously, the notch should not be too deep since the integrity of the stringer needs to remain intact. The equivalent stringer on the right side is already positioned well and no flexing will be needed to fit properly with the fabric spacer.A smooth contour on the fabric spacer was the goal. I have no concern about the slots and notch impairing the function of the stringer. It remains incredibly strong.

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2. Before gluing the middle stringer on the left side in place a half circle was sanded out to match the contour of the adjacent frame. It is much easier to add that opening before it is installed than after. Only a bit more sanding was needed for the final fit.

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[aflyer]

This is a great tip because a number of the stringers end up being overly visible after covering. Also, it is clearly wrong to bend the frame for installation.

Thanks Chuck!

John

[ceslaw]

Trim Motor. This proved to be a bit of a challenge. Just bolt it together and test it and you’re done, right? Well, not really.

Indeed, we put it together and tested it and it seemingly worked just fine, but the motor groaned a bit more than seemed appropriate. A bit of investigation was in order.

Two issues were found. First, the hole in the mounting plate that the motor shaft passes through was fractionally misaligned with the jack screw. Because the motor shaft and jack screw are rigidly connected together by a sleeve this created extra resistance. The opening on the mounting plate was carefully sanded on the ‘tight’ side. Essentially the powder coat was removed and a tiny bit more. Not much. (It would have been much easier sanding the excess if the connecting sleeve had been removed).

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Second, the vertical alignment of the motor shaft and jack screw was slightly off. This was corrected by adding thin aluminum shims on the forward side.

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So how do you know when it is aligned? With the motor and connecting sleeve in place, but the lower roll pin NOT in place, one should be able to rotate the jack screw without the motor shaft turning with only slight resistance. By loosening the screws holding the motor in place so it can ‘float’ a bit, the source of resistance can be determined.

Here is a bit of good news. The trim motor is a common item available from multiple sources on the internet, including Amazon, for around $75; probably the least expensive device on the plane. (The addition of the shims required redrilling the hole in the motor shaft for the roll pin, so a replacement motor was needed.)

[aeroaddict]

Great information. You are correct that it is basically an industrial gear driven 12V motor.

My experience (EX-2) was little different but similar. I tested motor after install a cuple of times, everything was good. Then after covering, the motor didn't work! CC's sent me a new motor.

Removing the roll pins after covering was very difficult. Then match drilling the motor shaft to the sleve was another challange. Not much room to work in after covering and the drill angles are impossible.

After I finally got everything lined up and working, I decided to install a shear pin that is cotter pinned as opposed to another roll pin (not sure how I could install a roll pin anyways). I did this in case the motor was to failed again. 200+ hours and no issues or wear on the shear pin.

Just something to consider when installing the trim motor.

[PBY Catalina]

Trim Motor. This proved to be a bit of a challenge. Just bolt it together and test it and you’re done, right? Well, not really.....

I had exactly the same difficulties and I brought more or less the same solutions. I will write a detailed post on this subject.

[aflyer]

When I faced this problem, before covering, I noticed the system binding as it tried to move the trim up and down. I took it apart again, and I noticed there was a large burr on the thread of the worm gear. I chucked the gear in my lathe and took a file to it, removed the burr, and then chamfered the edges of the threads. I also reduced the O.D. of the gear. I may have gotten carried away a little in my zeal (it was still early in the project :-). It seems to work freely now. I haven't yet mounted the horizontal stab, so I am just hoping it all works out, but it may be that reducing the size of the worm gear has introduced enough clearance for the whole scheme to work, in spite of the mis-alignment issues.

John

[Andy]

Three people with similar misalignment problems for the stab drive system. Did anyone tell CubCrafters about this and, if so, what was the answer?