10.1.2 Elevator Trim

This entry is part 10 of 11 in the series 10 - Control Sytem

I don’t mean to go off on a rant here…

One of my jobs when I’m not training (the thing that pays for the airplane) is writing training manuals. So I’m a bit more critical of instructional material than your average person and I’m constantly finding areas of this manual that need improvement.

 After talking with other builders, this seems to apply to a lot of homebuilt aircraft, not just Velocity’s.

On to the task at hand… From the sequenced flow chart, I need to install the “Pitch Trim Actuator”. Up and down movement of the airplane in flight is done with the elevators.  Pull the stick back and the nose goes up. Push the stick forward and the nose goes down. In cruise flight, you don’t want to have to be pushing forward or pulling back just to stay level. So a small electric motor moves a spring to a position that will apply the necessary force so that you don’t have to push or pull the stick to maintain a particular attitude.

This task has to do with mounting this electric motor.

Here’s a page from the manual:

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This is looking from the left side. The canard is on the bottom. The large black object is the actuator. On the left is where it mounts to the canard by means of the “Long Bracket” (Part Number VAB-02). The bracket will be connected to the “Aluminum Hardpoint” which will sit on the “Shim”. Seems pretty straightforward.

Here’s the text:         

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Hmmm. The first sentence is in bold. Must be important, huh? “Located a position for the trim spring that will not interfere with the radios.”?!?!?!

What radios? Installation of the radios is a LONG way away. Heck, I don’t even HAVE the radios. Nor have I even decided what radios or where they’ll be installed. So how do I figure out where to put this thing? I looked at the websites from other builders and looked at their pictures. Hopefully, my location will be fine.

This is the area of the canard where I’ll mount the actuator.

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The piece of blue foam cut and formed to the correct shape is the “shim”.

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A piece of aluminum cut to size on top.

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Everything covered with two layers of BID.

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The actuator.

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The “Long Bracket”.

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Wait a minute… The actuator looks like the picture of the actuator, but the bracket doesn’t look like the bracket. Back to the manual where we see the text “Modify the long bracket (VAB-01) as shown in Figure 10-2 to allow the actuator to move up and down.”

Well this is getting interesting. I’ve got to cut this piece “as shown” in the picture. No dimensions, no template, just make it look like a picture in a Hanna/Barbera cartoon. Okay, that shouldn’t be too difficult, just cut it so the end of the motor will fit.

But wait a minute… In figure 10-2 the “Long Bracket” is part number “VAB-02″ but in the text they say “Modify the long bracket (VAB-01)”!

Now what?

So I reread the entire section repeatedly trying to determine exactly what I’m supposed to be cutting. In the end, I come to the conclusion that the text is wrong and the figure is right.

Long Bracket (VAB-02) after modification.

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Hardpoint drilled, tapped with Long Bracket (VAB-02) and trim actuator mounted.

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If I had to do this task again, I could probably do it in an hour. But with the research on the location, the part number discrepancy and trial and fit for the modification of the bracket, I probably spent the better part of 6 hours on this.

At this rate, I’ll be done in ten years. :-(

10.3.1 – Rigging of the Roll System (Ailerons)

This entry is part 1 of 11 in the series 10 - Control Sytem

Now that the balance of the ailerons has been determined, before the weights are permanently attached, the torque tubes need to be attached. There is a tube embedded in the aileron that extends about 3 inches. This tube needs to be connected to the six foot long aileron torque tube. This is accomplished by joining them using a short steel tube that is inserted into the aileron tube and torque tube. It is then drilled and bolted.

Drilling the hole in the torque tube and joining tube is relatively easy. A centering jig is used with a drill press.

Here’s the torque tube with the joining tube bolted in place.

But the hole in the aileron tube is tough. It’s not long enough to use with the jig. So it has to be done by hand.

We will drill a slightly undersized hole from each side and then redrill with the correct sized bit all the way through. But first the location of the hole is marked.

Marking a spot on exact opposite sides of a tube can be a bit tricky. But as usual, Malcolm’s got a trick. A simple drafting template used for drawing circles.

Then the holes are drilled and bolted together.

10.3.1 Aileron Push-Pull Cables

This entry is part 2 of 11 in the series 10 - Control Sytem

Before we begin with the engine installation, the holes through the firewall for the push-pull cables have to be drilled. The manual says to drill through the firewall from the rear and the gear bulkhead from the front. The challenge is that the two points aren’t on the same elevation. The push-pull cable is angled down.

Malcolm has a really long drill bit that he uses for this.

The location on the firewall is determined and also on the gear bulkhead. Then the hole is drilled through the firewall with a guesstimate of the angle downward. Then after the bit is through the firewall, I guide the bit through the gear bulkhead on the inside. With two people and the right drillbit, it was easy.

10.1.2 Elevator Trim

This entry is part 3 of 11 in the series 10 - Control Sytem

I’ve already created the elevator trim hardpoint and built the bracket. So now it’s time to mount the trim motor. Unfortunately, I miscalculated the bracket so I’ll have to build a new one. But the existing one will work for now.

The bracket when the trim actuator connects to the trim spring had to be drilled. Then it is attached to the trim actuator and spring.

Next, the other end of the spring get bolted to the clamp which goes on the elevator torque tube. Malcolm deviates from the factory method in how the spring is attached to the clamp. He likes to stagger the holes. I like his method so that’s what we did.

The question mark looking thing is the elevator trim spring. You can see at the bottom how it’s bolted to the clamp.

We held off on bolting the clamp to the torque tube until we could confirm some measurements. Once the clamp is bolted to the torque tube, it’s too late to turn back.

 

10.3.1 Aileron Cables

This entry is part 4 of 11 in the series 10 - Control Sytem

The holes in the firewall for the aileron cables have already been drilled. So the next step is to route the cables and attach them to the aileron torque tube bellcrank. Mostly, it’s just mounting the cable attach mounts and bolting the rodends to the bellcrank.

Looking down and the bellcrank.

Here you can see the cables as they go outwards and turn towards the back.

From the engine side of the firewall on the co-pilot side

 

10.3.1 Aileron Torque Tubes

This entry is part 5 of 11 in the series 10 - Control Sytem

I want to get as many tasks that require the wings on done before the plane leaves Malcolm’s shop. We can easily get both wings on in his shop. In my shop, it’s a chore just to get one of them on.

Earlier, we attached the (steel) torque tubes to the ailerons. So we’re going to work on the wing root end. First I have to fabricate the brackets that support the torque tube and bellcrank. The factory does this significantly different than Malcolm so my brackets are a LOT different then most others.

Here is the pilot side bracket:

And the co-pilot side:

Then the aileron cable support bracket has to be built. Here is the co-pilot side.

You’ll notice where the cable attaches to the bellcrank that there is a hole in the bellcrank above where the cable is mounted. That hole at the very top was the only hole in the bellcrank. Before we got to this point Malcolm started measuring for this extra hole. I asked him what he was doing and he said “The factory hole is too far out. You can’t get enough motion with that hole so you have to drill another one closer to the torque tube.” This kind of stuff used to make me nervous; Off the cuff mods that aren’t called out in the manual. But I’ve learned to accept it when Malcolm says “do it because otherwise it won’t work.”

After this we drilled the bellcrank and torque tube and bolted everything together. The manual says that we should have 2 1/2″ of aileron travel when the stick is moved from one side to the other. And we got… 2-1/2″. Had we used the factory hole, we would have had significantly less. Then we would have had to pull off the bellcranks and drill the second holes.

10.2.1 Rudder Cable Connections

This entry is part 9 of 11 in the series 10 - Control Sytem

I need to finish the aileron and rudder cable installation.  For this, the wings need to be on. But since my shop is much smaller than Malcolm’s, I can only do one wing at a time. So I repositioned the plane and Steve helped me hang the pilot side wing.

10.3.1 Aileron Control Cable

This entry is part 6 of 11 in the series 10 - Control Sytem

Before the plane came back from South Carolina, we connected the aileron control cables. They worked, but the routing of the cables wasn’t perfect. Malcolm was very happy with the force required but the cable routing just didn’t look right to me.

So the first thing I did was to pull the cable from the firewall and open up the hole a bit. This will allow for a wider radius turn instead of the sharp kink it had. Once I reinstalled the cable, the routing was much better. But now I had a new problem.

Here, you can see with the aileron up, the cable has a noticeable “break” to it at the point where it’s clamped.But the aileron is down, it’s pretty straight. It should be straight at the neutral position with a slight break when full up or down.

I fixed this by rotating the bracket that the cable clamps to. And since I opened up the hole in the firewall, the cable has a nice sweeping radius to it.

10.2.1 – Rudder Cable Installation

This entry is part 7 of 11 in the series 10 - Control Sytem

The rudder cable from the rudder is connected to the cable from the rudder pedals at the wing root. The typical method is to place a pulley where the rudder cable exits the firewall. But where it exits the wing, the cable simply makes a sharp turn towards the front. I don’t know why a pulley isn’t used wing root. Me and Malcolm talked about this and decided to try a pulley on the wing too.

The hardest part was getting the alignment right. To do it I took the cable from the pedals and clamped it (lightly) to the cable from the rudder. Then I placed both pulleys in position and adjusted them until the line of the cable was correct. At that point I marked the position and drilled the mounting holes.

Here is the wingroot with the cables connected.

I haven’t installed the return springs yet. The action of the rudder is very smooth with the two pulleys.

10.2.1 Rudder cable springs

This entry is part 8 of 11 in the series 10 - Control Sytem

There are already springs to pull the rudders from their deployed position. But once the cables from the rudder pedals to the rudders were connected I had to install some intermediate springs.

Now one of the things that I did was to install a second rudder cable pulley on the wing root. This should allow smoother rudder operations. It also makes the return spring installation a tad tricky… but not impossible.

Here’s the pilot-side rudder cable coupler (looking from below and slightly aft) with the return spring mounted.

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And here is a view looking from below and inboard.

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And finally, the co-pilot side.

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