Speed brake actuator

Now that the inside of the speed brake panel was glassed, it was time to trim it, install it and add the electric actuator.

First action was to remove the 2x4 frame that was holding the speed brake panel from warping while the inside layup was glassed. A simple tap with the hammer did the trick...

 I then trimmed the edges to an approximate dimension (fine tune trimming takes place later after the panel is installed so that exact reference lines can be made).

Even though the piano hinge was bonded in place, it still requires bolts. I used the drill press to make pilot holes and then opened them up using a hand drill. I should note that I spent some time making sure the spacing of these holes were correct prior to drilling - making sure the bolt heads were not going to touch with the bolt heads that attach the piano hinge on the fuselage side when the flap is in the closed position.

I used two AN525-10R10 bolts on the inside (that go through LB19) and two AN525-10R8 for the outside bolts (that do not go through LB19). I used four washers AN960-10 and four MS21042-3 nuts.


It was now time to present the speed brake panel onto the fuselage - but first, some reference lines had to be drawn. I placed the longest ruler (carpenters square in this case) on the edges of the recess and traced lines extending past the corners.

I presented the speed brake in place and measured 0.5" towards the outside of the reference lines (the pencil line is the reference line and the red line is what the speed brake will be cut to). This assured I had a nice 0.5" lip all around the recess.

It was now time to drill and tap the threads that will hold the bolts to tighten the piano hinge onto the fuselage. To do this, I needed to know the exact location of where to drill. I only had one shot at this so it had to be perfect. The problem is that to properly align the speed brake, the panel must be closed shut. So how am I supposed to mark the holes on the inside when the panel is shut?!

Simple - I positioned the panel where I wanted it and pressed clay onto the piano hinge.

I then removed the panel (keeping the clay untouched) and removed the pin from the piano hinge. I then used the clay to place the fuselage side of the piano hinge back in the same exact place (since the clay acted like a mold and held the tab in the same position as if the panel was installed).

This allowed me to trace/mark the drill hole locations.

I started out with a small pilot drill and then opened it up to its full diameter. I had to go through the fiberglass, through the LB23 1/4" plywood, and finally through the LB22 2024-T3 puck awaiting anxiously to be tapped.

Here I am tapping away using a 1/4"-28 tap.

Test fitting the AN4-5A (1/4" hex bolt)... perfect match! Then repeated another 3 times....

I was so anxious to see if I had a good fit that I tested it out with only installing two bolts first. And what do you know... perfect fit! I exercised the flap a few times by hand... and moved on to install the remaining two bolts (for a total of four AN4-5A bolts). I should note that I used four AN960-416 washers with these bolts.

Perfect fit all around! Note that the corners were not yet rounded when I took this picture... and I still had Bondo blobs from the 2x4 jig.

So now that I had a happy flap... it was time to install the electric actuator. I purchased one from ServoCity (www.servocity.com). Those guys were great! I placed the order online and it showed up at my door step in less than 3 days. I went with a 115 lb max thrust, 4" stroke (model HDA4-50).  They operate at 12V with less than 700mA.

With a 4" stroke, quick math shows that the bracket to mount the actuator must be placed 4" away from the piano hinge line in order to get the flap to open 60 degrees when fully extended.

To cut the opening for the actuator to go through the fuselage floor, I started out by taping a scrap piece of 'L' angle 4" away from the piano hinge line. I then placed a blob of play on the recess, closed the flap shut and reopened it. The clay showed me exactly where the point was. I then used a small drill to drill a hole through the fiberglass exactly on location.

I then removed the clay from the recess and found the hole (as circled in red below). I then measured a rectangle around it as my starting cut lines. I then kept opening up the hole with a file to allow enough clearance for the actuator to pass through.

Final cut of the through hole.

I then made mounting brackets for the actuator. Pretty fancy. I'll have to alodine them at some point... but for right now, lets continue! I should also note that I will later trim the brackets that mount the actuator to the pilot's seat back (since I had spare 2" 'L' angle) - these are much wider than they need to be - I decided to trim them down to 1.5" wide.

Before going full force and installing the brackets, I wanted to make sure the geometry was correct. So I taped the brackets onto the speed brake panel making sure their center points were located 4" aft of the hinge line.

I then taped the brackets onto the pilot's seat back.... I created a dummy 4"x8" panel using scrap 1/4" plywood, bolted the brackets to the plywood and taped the plywood behind the pilot's seat. I then installed the actuator temporarily and operated the flap. I made sure the flap extended to 60 degrees at max stroke.

After verifying the geometry of the bracket placements, I removed the speed brake and polished it up. I sanded away the Bondo that was left over from the jig...

and rounded the corners for a nice clean finish...

It was now time to bolt the brackets in place... I had the lines drawn prior to test fitting them with tape.

I drilled out the holes and torqued everything up. For these brackets, I used four AN525-10R14 screws, four AN960-10 washers and four MS21042-3 nuts.

With the brackets of the actuator on the speed brake panel installed, it was time to focus on mounting the brackets onto the backside of the pilot's seat. I started out by making a 4"x4" puck out of 1/4" plywood. I rounded the edges/corners (to allow for a smooth transition after it gets glassed) and installed four stainless steel T-nuts. Here is the front side...

Here is the backside. I wanted to recess them by grooving out a notch with my router... but the T-nuts were 1/4" high. If I applied a recess, it would have caused the tip to stick up beyond the 1/4" plywood. Knowing that the flox would add some space between the plywood and the back of the pilot's seat, I didn't worry about it and kept them as shown below.

I then bolted the brackets onto the plywood puck. Ignore the over-sized aluminum tabs - they will be trimmed later on (notice how they stick out past the plywood edges). Also, ignore the GRADE 0 Home Depot bolt going through the bracket - this is just temporary hardware until I get everything aligned during installation.

I then reinstalled the speed brake flap onto the fuselage, mounted the actuator (to the speed brake panel side), closed the speed brake flap shut and fully retracted the actuator - I now had the exact position of where the plywood puck needed to be mounted (I should note that I have a total of 5 push-rod turns on the thread to adjust the final position of the flap) - I started out with 2 just in case I needed to adjust it in the opposite direction).

The less riskier method of installing this puck would have been to flox it with the actuator mounted - but that would have required me to wait a whole day for it to dry before glassing the puck over with BID.

So I opted to take a riskier approach by marking the outline of where the puck needed to go. This allowed me to remove the brackets from the puck, flox it in place according to the outline drawn, and proceed to glassing it the very same day. This method is riskier since there is a higher chance of the puck not aligning with the marks made.

Before floxing it in place, I pre-cut 5 plies of BID at 45 degree. Also, because I had originally only applied a single layer of BID as the backside of the pilot's seat, I was now left with the daunting task of having to apply an additional layer for reinforcement - so I cut that as well.

I flipped the fuselage upside down on sawhorses and placed a shop stool just forward of the passenger seat back. This created a relatively painless work area. So I got to work by sanding the backside of the pilot's seat dull, taped the cloth from sliding out of place... and glassed it. Here is a picture of it just before pouring resin over it...

With the pilot's seat back ready for the plywood puck, I forced cling-wrap into the T-nuts to prevent resin creeping inside during glassing.

I used an exacto knife to trim off the excess cling-wrap.

I then applied flox to the backside of the puck...

And installed it exactly where I had drawn the outline (never mind the pencil mark outline - that was used to position the temporary puck when testing the geometry).

Now that the puck was in place, it was time to glass 5 plies of BID over it. Here I am prepregging...

I added a bead of wet flox all around the puck and painted the surface with plain epoxy to assure no air bubbles and a good bond.

I then placed the 5 layers of BID over the puck and peel plied the edges.

The next day, I carefully drilled out the fiberglass where the threads were using a very small drill bit. I then used an exacto knife to remove the cling-wrap inside the threads. They did a good job at keeping resin out.

I then reinstalled the actuator onto the flap...

Closed the flap shut and fully retracted the actuator. My gamble worked! The actuator mounts landed right on top of the threads! I then bolted them on using four AN3-4A bolts and four AN960-10L washers.

With everything bolted down, it was now time to activate the actuator and see the speed brake flap move! This part was exciting! The first moving part on the airplane! I actuated the flap open and close until my girlfriend told me to please stop and come inside for dinner... see the video here - speed brake video.

A perfect fit!

::UPDATE::

So I finally got around to purchasing the proper hardware that connects the actuator to the brackets.

The bolt is an AN3-17 --> the actual bolt that goes through the brackets and through the actuator rod. Notice how I got the drilled type so I could install a pin and prevent the nut from coming off.

The bolt goes through a standoff - McMaster Carr P/N 91125A220; 18-8 stainless steel female threaded round standoff 1/4" OD, 1" length, 10-32. McMaster did not have the 0.190" inner diameter I needed so I opened the ID by drilling through it (removing the inner thread).

Over the standoff goes a sleeve bearing - this allows the bolt to act like a hinge pin - reducing wear and tear. McMaster Carr P/N 2868T44; SAE 863 Bronze Sleeve Bearing, for 1/4" Shaft Diameter, 5/16" OD, 3/4" Length.

AN310-3 castle nut holds everything together. I also used a few washers to center everything.

In case you missed it, here is the link to the video:
Speed brake video.