Overview of Chapter 16 - control system

This is a very fun and exciting chapter! After years of building and working with fiberglass, I finally get to dive into the mechanical world and get to play with metal parts. Also, seeing my creation come to life as the control surfaces hinge and move is exhilarating!

In this chapter, we build and install the main control assembly. This is made from various metal torque tubes and pushrods that run along the starboard (right side) of the fuselage. They connect the pilot and passenger control sticks, a forward pushrod to control the elevator, and an aft bellcrank at the firewall that connects with the aileron pushrods.

Here is a schematic of the pitch and roll control system:

Although the details of the aileron control system is outlined in Chapter 19 in the plans, I decided to post everything that is "controls" under this section of the blog.

In most chapter overviews, I like to discuss modifications, CP's and/or other deviations from the original plans. There are four items I would like to note in this chapter:

1. Bearings:
The original control system was designed to rotate on phenolic plates (CS108, CS117,CS150). Past Long-EZ builders claim that over time, the steel tubes wears the phenolic and develops a slop. To solve this problem, I'll be replacing these phenolic plates with actual bearings. More details on that on future posts.

Plans version using phenolic:

I'll be using something more like this:

2. Replacing aluminum for steel aft of the firewall
CP #49, LPC #131 has us replace all aluminum pieces aft of the firewall with steel. This change is to assure that in the event of an engine fire, the steel components would retain strength longer than aluminum parts, and thereby maintain roll control for a safe emergency landing.

Since steel is about 2.5 times heavier than aluminum, CP#50 under 'builder hints' recommends to substitute 0.5" OD .035 wall aluminum pushrods aft of the firewall with 0.5" OD .028 wall 4130N steel tubing to save on weight. HOWEVER, changing the wall thickness of the tubes would complicate things since this would require different size threaded inserts for the rod ends (since changing the wall thickness changes the inside diameter of the tube).

At first, Ken Brock Mfg (where Long-EZ builders used to get the rod end inserts from) was supplying these modified threaded inserts (known as CS-50) to fit .028 wall tubing. In order to keep the number of insert types down, CP#79 pretty much says to disregard the wall thickness change and to keep the .035 wall thickness for steel tubing. Yes, this results in adding more weight, but this way you only need two types of inserts rather than three.

Case and point: 0.5" OD .035 wall aluminum tubing aft of the firewall gets replaced with 0.5" OD .035 wall 4130N steel tubing. Their corresponding rod end aluminum threaded inserts will also be replaced with steel inserts. I will also make sure all aluminum brackets aft of the firewall are replaced with stainless steel brackets.

Oh, and don't forget about the rivets used to attach the inserts onto the rod ends. The plans originally say to use AN470AD-4-10 rivets. Since these are aluminum, CP#50 says we should use Cherry #CCP-42 rivets since they are made of stainless (aft of the firewall).

3. Heim joints and inserts:
If you study Chapter 16 in the plans, you'll notice that the majority of heim rod ends are HM-3, except for the elevator pushrod. Those call for HM-4.

HM-3 heim joints are rod ends that have an eye-hole diameter for AN3 hardware with AN3 thread (10-32). Following the designation, HM-4 heim joints have an eye-hole diameter for AN4 hardware with AN4 thread (1/4-28). Simple, right?

This is why the plans calls for 10 CS1 inserts (aluminum inserts with 10-32 thread) and 2 CS1A inserts (aluminum inserts with 1/4-28 thread). However, somewhere along the line, all HM-3 heim rodends were changed to XM-3 rod ends. XM-3 are a hybrid of HM-3 and HM-4 in that they still have an eye-hole for AN3 bolts, but have AN4 thread at the base. This allows us to use the same CS1A inserts for ALL rod ends. (XM-3 rod ends on Aircraft Spruce is part number: 04-03527)

BUT WAIT! What about the previous note about changing all aluminum parts to steel aft of the firewall?! Ok, so we have to change ALL inserts aft of the firewall to steel (CS50 inserts). 

Case and point: I will need 4 CS1A aluminum inserts (2 for the elevator pushrod that go on CS102 and CS136, and 2 for the CS110 pushrod that connects the pilot control stick to the passenger control stick). I will then need 8 CS50 inserts, that go on all pushrods aft of the firewall (since those have to be steel). CS1 inserts are no longer used since we did away with HM-3 heim rod ends.

4. Elevator pushrod connection:
The last obvious deviation from the original plans I will note is how the elevator pushrod gets attached to the elevator bellhorn. Recall from Chapter 11 (the elevators), I used the Cozy Girls elevator torque tube offsets. This mod ends up having a single elevator bellhorn next to the right inside fuselage wall, and a single elevator bellhorn close to the left inside fuselage wall. This means that the way the elevator pushrod gets connected to the bellhorn (page 16-6 view B-B) is no longer valid. Details on how I attach the elevator pushrod with my elevator bellhorn will be shown in posts to follow.

No comments: