Tuesday, May 30, 2017

Installing a “Bender Baffle” Piggybacked With Regulator Relocation Mod - Part Six

This post will cover the majority of the fabrication of the control hardware that will make the baffle plate assembly inside the air duct move by pulling a knob from inside the cockpit. To adjust the baffle position, a Bowden style cable was chosen. Decided to use an A-740 control cable that has built in friction detents … this is the same control cable that was installed for the parking for the parking brake control.
The A-740 control cable that will be installed in the cockpit to control the “Bender baffle”. The control has a 3" range of motion.

Quite a bit of consideration was given to where the control for the baffle should be located within the cockpit, taking into consideration ease of installation and ease of use. Almost immediately dismissed the idea of mounting the baffle control knob in the center console area along with the other controls because of the way the control cable would need to be run on the forward side of the firewall. Not say’ in it can’t or shouldn’t be done, but it would require multiple bends of the cable and figured it easier if a straighter approach was incorporated.

As previously mentioned, when deciding on a mounting location for the baffle control ease of installation and operation were high on the list but I also desired the control to be out of the way. The location finally decided upon to mount the baffle control knob is to the far left and under the instrument panel base. This location creates a couple of challenges but overall is straight forward. The plan is to tuck the control as far left as practical and still be able to get fingers around the knob but also forward enough so the entire control knob is under the instrument panel when the baffle is fully open (which will be the norm 95% of the time). This will eliminate the possibility of snagging it with a shoe or knee during cockpit ingress and egress. Taking a photo while holding the control in position from outside the cockpit proved very difficult, so I have doctored an older photo and added a red arrow in the photo to show the approximate mounting location for the knob.
The red arrow in this photo points to the general location the control knob for the “Bender baffle” will be located. The plan is to tuck the knob a little forward under the instrument panel so it is completely out of the way when not in use.

The above mounting location presents a couple of small challenges that fellow builders considering this location need to be cognizant of when designing the mounting bracket for the control knob. The first issue is not to drill into the edge of the  flange on the F-1202H-L canopy rib (although if one does decide to do so, it would be OK as long as the hole ends up in the center of the flange … I just opted to avoid it altogether). The second is not to drill into the AV-50000A Control Module. Even with the mentioned concerns, there is still plenty of room to rivet a bracket onto the bottom of the instrument panel base and avoid conflicts with the surrounding items. To avoid the flange of the F-1202H canopy rib, decided to make a mounting bracket with an offset which will allow the control knob to be mounted further to the left yet keeps the rivets used to mount the bracket clear of the flange of the flange on the F-1204H-L canopy rib. Below is a photo of the unfinished bracket that shows the offset which will allow the control knob to be further to the left.
Proof of concept bracket for the “Bender baffle” control cable made from .063" aluminum sheet. The trial fit looks promising although do plan on remove some more material from the bracket to trim it down a little more.

Prior to working on the control arm for the baffle, figured it best to establish hard point stops for the baffle so the overall rotational angles can be determined. This was done by making marks denoting the desired range of motion and using some tracing paper to make a template for cutting a piece of aluminum. Decided to make both stops from one piece of aluminum which complicated the fabrication a little. First an Avery hand seaming tool was used to make a measured bend in a scrap piece of aluminum which I discovered required 3/32" of material to make the bend. Knowing this, I made two marks on the aluminum one where I wanted the stop to be placed and another 3/32" back from the desired line which is where the seeming tool jaws were placed. The fit of the resulting bracket was spot on if I must say so myself …love it when a plan comes together the first try.
The hard stops for the “Bender baffle” are made from one piece of aluminum and meet the baffle plate perfectly square at both ends. Decided to go this route as opposed to making two stops and then needing to drill 4 holes. This bracket uses the rivet holes already drilled in the upper doubler plate. The stop is wider than it needs to be so will likely trim some more material away.
Baffle plate in the full open position on the stop.
Baffle plate in the full closed position on the stop.

Now onto making the baffle assembly swing. For the control arm, decided to use a piece of angle which I drilled a 1/2" hole into so it could be slid over the baffle’s shaft. I did play around with trying to twist a piece aluminum bar stock but think it may have been too thick because I was getting stress marks so decided to scrap that idea. Eventually, two screws will secure the control arm onto the baffle shaft but for the mockup the holes were left undrilled and the control arm material was left longer than necessary.
Drilling the 1/2" hole in angle stock that will become the control arm so it can be slipped over the baffle shaft.

Quite a while ago I did the math and figured I would need approximately a 2" control arm attached to the baffle’s pivot shaft to make a 90 degree swing using a 3" pull. However, had to use that data as a reference point because as it turns out, the baffle actually swings a little beyond 90 degrees. So I mocked up a control arm and placed a cotton swab stick at the 2" point from centerline of the baffle shaft and measured how much pull was necessary to go stop to stop. This was done using a piece of waxed cord slipped over the swab stick and using a ruler to measure the pull distance. To do that, the cord was run through the cowl hinge eyelets so the measuring point would not move. The 2" point was close … but finally decided upon using 1 7/8" which seems to nicely move the baffle from stop to stop using slightly under a 3" pull.
The mockup to determine the necessary length for the control arm. Looking closely at the photo, one can see the waxed cord attached to a cotton swab stick (hard to see but it is under the right clamp) placed 2" from center of the baffle shaft. After a little testing, decided to move the stick to the 1 7/8" point which allowed for a full range of baffle motion from stop to stop with a 3" pull on the cord.

At this point, the cowl was placed in position to verify the clearances between the baffle control arm and the Rotax 912’s valve cover, spark plug wire and the three hoses in the vicinity. Looking at the following three photos below one can see the clearances are acceptable … plus the control arm will be shortened a little more because for this trial a fair amount of excess material was left beyond where the hole will be drilled for the control cable attachment point.
Squaring up the baffle control arm and the cotton swab stick for a range of motion test.
Baffle control arm position with the baffle in the fully open position.
Baffle control arm position with the baffle in the fully closed position.

Satisfied the control arm created no interference with nearby objects throughout its full range of motion, the next step was to fabricate a mounting pad that will become the control cable’s mounting point. Once made, the mounting pad was temporarily taped in position to check the overall fit. The “B” nut for the cable end was placed on top of the pad just to verify there were still no clearance issues, even though it is actually higher than what the final position will be when the “B” nut is placed in the mounting hole that will be drilled in the pad.
The mounting pad for the control cable temporarily taped onto the control arm for a test fit. The “B” nut for the end of the control cable was just set on the pad upside down to verify clearances. Later a 3/16" hole will be drilled into the pad at a point 1 7/8" from the center of the baffle shaft so the “B” nut can be inserted into the hole and secured with a cotter pin.

At this point the mounting pad was riveted onto the control arm. Of note: The pad for the “B” nut mounting is still larger than it needs to be. This was done on purpose because the cotter pin or quick release clip used to secure the shaft of the “B” nut will also need to have enough clearance so it does not hit the body of the control arm as it swings through its range of motion.

Return from the future: The mounting pad on the control arm shown below was  miss-drilled  and needed to be remade ... in doing so, the design was changed to a more simplistic version. The new design and reason for the miss-drilled hole are covered in the post  Part 7.
Apologize for the poor lighting it was almost dark when this photo was taken ... would have used the flash, but the camera battery was almost dead. Completed control arm with the mounting pad riveted in place. The mounting pad will be trimmed down more based on the final location of the mounting hole and cotter pin clearances.

The next work session will involve mounting the control knob bracket and securing the Bowden cable.

Thursday, May 25, 2017

Repairman Certificate Granted By FAA

As frequent readers of the DOG Aviation Blog may have noticed, the baffle project has stalled out a bit ... I hit a roadblock while preparing to delve into the wiring. It is not going to derail the instillation but there will be a parts delay. I’ll post more about that in a separate post in the next day or two.

One of the things I had been putting off through the winter months was making a trip to the FAA’s FSDO (Flight Standards District Office) to obtain a repairman certificate. The repairman certificate allows the annual condition inspections required by the FAA to be performed by me. Often times the repairman certificate can be applied for at the time of the airworthiness inspection. However, in my area, the FAA has split the duties between MIDO (Manufacturing Inspection District Office) and FSDO …. where MIDO inspects newly constructed aircraft and issues the airworthiness certificate and the FSDO issues the repairman certificate.

A huge benefit of building an experimental airplane (special airworthiness certificate) versus purchasing a certificated airplane such as a Piper or Cessna (standard airworthiness certificate) is that the FAA allows the builder of an experimental airplane to perform the mandated annual condition inspections … but ONLY IF the builder applies for the repairman certificate and can prove 51% or more of the work constructing the aircraft was done by the builder. Owners of standard airworthiness certificated aircraft (such as a Piper or Cessna, ect.) are not allowed to perform the FAA mandated annual condition inspection … they MUST use a FAA licensed aircraft inspector to perform the annual condition inspection.

For the benefit of the non-aviation reader viewing the DOG Aviation Blog, here is a quick synopsis of the rules for experimental amateur built aircraft (E-AB). During the certification process, the builder MUST PROVE to the FAA beyond a shadow of a doubt that over 51% of the airplane was built by the builder. The 51% rule applies to all E-AB airplanes … which the FAA allows to be constructed by individuals as a “recreational and educational experience”. The reasoning behind the 51% rule for E-AB aircraft is so aircraft kits can’t be professionally assembled as a cottage industry then sold to the general public and also so individuals can’t pay to have others assemble the aircraft for them. Upon receiving the special airworthiness certificate for an E-AB aircraft, the builder can then apply for a repairman certificate which allows the builder to perform the annual condition inspections required by the FAA … but ONLY on the specific experimental aircraft the builder constructed. Also worthy of noting, at no time can a person other than the original builder of an E-AB aircraft apply for a repairman certificate for that experimental aircraft.

One of the many reasons for establishing the DOG Aviation Blog was to have a method of documenting the building activities so the FAA could look at the Blog and see many hundreds of photos with me in them performing various stages of assembly on the RV-12 accompanied with an in depth write-up of the building process. This proved useful during the certification process and once again last week when I applied for a repairman certificate. So armed with the DOG Aviation Blog, my builder’s log book, a binder with hundreds of photos with me in each photo and the 8610-2 application form for the repairman certificate … a trip was made to the FSDO to yet again prove to the FAA that over 51% of the RV-12’s construction was done by myself.

During the initial phone conversation with the FAA to schedule the interview, we discussed the documentation the inspector expected me to provide. At that time, I mentioned the DOG Aviation Blog and passed along the WEB address of the Blog so the inspector could peruse the Blog prior to my appointment. The day of the appointment I was met by two FAA employees ... while walking into the conference room, I casually asked if they had taken a look at the DOG Aviation Blog and was told “Yes! and there is no question about it, you built the airplane”. So my tip to fellow builders would be: Consider establishing an online Blog or builder log containing plenty of photos showing you performing the various phases of construction and parts fabrication. Of course, it is also in the builder’s best interest to keep a hand written builder log for the inspectors to peruse. My hand written builder log is brief,  just showing the date, which parts were assembled or prepared during each work session and time spent working, whereas, the DOG Aviation Blog contains a very detailed synopsis of each work session.

Since there were no doubts about my qualifying for the repairman certificate under the 51% rule, the interview became more of pleasant meeting to verify that the paperwork was filled out correctly and to discuss the quality of Van’s plans and components. Because the inspectors had taken a good look at the DOG Aviation Blog, not a lot of time was spent looking at the hand written builder log. However, the hundreds of photos I brought were looked at with great interest…   as it turns out, one of the gentleman is giving some serious thought to building a Van’s airplane. So he was very interested in the assembly process/instructions and the various models Van’s manufactures.

An hour later, I left the FSDO with a temporary repairmen certificate in hand. As it turned out the day I visited the FSDO was also my birthday, so receiving the coveted repairmen certificate was one of the best birthday presents ever.
Another monumental day at DOG Aviation and good reason to smile. In my hand is a temporary issuance of the coveted repairman certificate. The repairman certificate will allow me to perform the annual condition inspections on the DOG Aviation RV-12.

Thursday, May 11, 2017

Installing a “Bender Baffle” Piggybacked With Regulator Relocation Mod - Part Five

Decided to initially drill all the holes in the baffle using a #19 drill bit so  #8 hardware can be used to mount the baffle plate onto the shafts … however, when measuring for the holes, I used minimum edge clearances recommended for #10 holes just in case a switch is made to #10 hardware. As mentioned in the previous post, all the holes in the shafts were drilled to #40 so the baffle could be secured onto the shafts using Clecos …. but that didn’t work out because the Cleco pliers did not have enough clearance to install the Clecos with the baffle in place. Ultimately, a long rivet was used in the first hole drilled to hold the baffle position while a hole in the upper shaft was marked for drilling by hand spinning a drill bit in the hole. After drilling one of the holes in the baffle pate for the upper shaft, the assembly was put together using two rivets to hold positioning so the remaining four holes could be marked using the drill bit.
My fingers are pointing to the two rivets holding the baffle’s position so the remaining holes can be marked for drilling.
As the two rivets were holding the baffle plate’s position the remaining four holes needing drilling were marked by inserting a drill bit into the pre-drilled holes in the shafts and spun by hand. Marking one of the holes in the lower shaft by spinning a drill bit in the hole to make marks on the baffle plate.

Once the remaining holes were marked, the hole locations were center punched and drilled using a tiny drill bit to make a lead hole followed by a #40 drill bit. Next the assembly was secured with Clecos and match drilled on the drill press stepping up to a to a final size of #19 for #8 hardware. If at a later point it is deemed necessary to go with #10 screws, there is still enough material to do so.
The baffle plate secured onto the upper and lower shafts with Clecos ready for match drilling to final size. Note the upper shaft is still quite long, this will be shortened when the exact position for the pivot arm is determined.
Using the drill press to match drill the baffle plate to the shafts with a #30 drill bit … during the next pass went to #19.

After drilling the holes with a #19 drill bit for #8 hardware, the assembly was installed in the air duct for a trial fit using some temporary hardware store #8-32 screws and nuts. All the parts for the baffle fit nicely together and the baffle has a good range of motion.
Test fitting of the baffle assembly in the air duct … baffle in the open position ... looking good.
Baffle closed …. looking good but as one can see, there is very little clearance between the edges of the baffle plate and the fiberglass.

Even when the baffle is in the closed position, there needs to be some airflow … so it is suggested that when the baffle is in the closed position, there should be approximately 1/8" to 1/4" of clearance between the baffle and the air duct. Decided to go with 1/8" because the bushing flange and washer make the gaps at the top and bottom just under 1/4" anyway ... so figure if necessary, it is easier to remove material than put it back on. To mark the 1/8" gap on the baffle plate, a scrap piece of 1/8" aluminum was placed against the fiberglass sides and used to mark the outer edges of the baffle plate for trimming. The baffle plate was then removed and trimmed on the band saw.
Using a scrap piece of 1/8" aluminum to mark the baffle for final trimming to create a 1/8" gap between the fiberglass and the baffle. The red cut line can be seen on both sides of the baffle plate.

Looking closely at the next photo one can see the results of the test fitting after trimming the excess material off the baffle plate. Now when the baffle is in the closed position, there is a 1/8" gap between the fiberglass and baffle plate.
 Now when the baffle is in the closed position, there is a 1/8" gap between the fiberglass air duct sides and baffle plate.

Decided this was a good place to stop for the work session. Next up will be working out the details on installing the regulator onto the baffle plate and working out the details necessary to control the baffle’s movement from inside the cockpit.

Tuesday, May 9, 2017

Installing a “Bender Baffle” Piggybacked With Regulator Relocation Mod - Part Four

This work session began by using the cardboard baffle template to cut a piece of .090" aluminum for the baffle. Because the baffle will have a significant amount of wind pressure applied to it during flight when in the closed position, felt it needed to be of a thicker material even though mounting the voltage regulator onto the baffle will add a significant amount of stiffness. Decided to go with .090" aluminum which is also what Bender used for his original design. The baffle is still slightly larger than necessary, so it will need a little material removed from all the edges after the positioning  is finalized.
A piece of .090" aluminum was marked using the cardboard template then cut to size. A little additional trimming will be required all around once the final positioning for the baffle is established.

Now that the bushings are bonded in place and the baffle plate cut, moved on to making the two shafts that will slide into the bushings and secure the baffle. Felt it best to create a flat spot on each shaft for mounting the baffle … so decided on making a 3" long flat spot. This was accomplished by removing enough material to make a flat area for the aluminum baffle plate to mate onto. I think 3” is enough surface area for three holes and also keeps the holes within minimum hole edge distances (two times the hole size measured to the center of the hole based on #10 hardware). Now is the time it would be nice to have a milling machine … I see a lot of sanding/filing/measuring/repeat in my future.

The process for making the shafts began by using the band saw to remove a 3" thin strip of metal from the aluminum rod to create the beginnings of a flat spot. Next a belt sander was turned upside down and clamped onto the workbench and used to smooth down the flat spot enough to remove the scores left from the band saw. This was somewhat dangerous and NOT a method I would recommend …. but you work with the tools you have. I would caution about trying to use the belt sander to get to the final size ...  it is very easy to begin rounding the edges, so I just used it to get the beginnings of a smooth 3" long flat. To get to the finished size, required A LOT of hand filing and sanding with a sanding block until the final thickness of 13/32" was achieved … so basically 3/32" was removed from the rod. Oh, also used flat back riveting plate with sticky sandpaper on it to get the flat spot as close to perfect as possible. Seemingly, removing 3/32" leaves enough of a flat spot for good support for the baffle plate, yet leaves the shaft thick enough to support the three mounting holes that will need to be drilled.
Using the belt sander to begin smoothing the roughness left from the band saw.
After a little hand filing and use of a sanding block and a flat back riveting plate covered with sandpaper, a uniform final thickness of 13/23" was achieved.
The finished flat spot ready for drilling the mounting holes. As one can see, the shaft thickness at the flat spot measures 13/23". One down, one to go.

After completing the 3" flat spots on both shafts, the three mounting holes for each shaft were marked and drilled to #40. The actual final assembly will begin with establishing the correct positioning of the baffle while in the closed position and drilling one of the mounting holes in the baffle. Because brass washers will be used between the bushings and baffle, a little excess material will need to be removed from both ends of the baffle to establish the correct spacing.
A brass washer with a 1/2" hole in it will be used between the baffle and the bushings.

The goal was to first establish the fit of the bottom shaft first … then strive for a snug fit to the upper bushing with a minimum amount of up and down play by trimming the upper edge of the baffle to achieve a non-binding fit to the upper washer/bushing that just has a very small amount of vertical movement. This is the reason why the cardboard baffle template was left a little long … it insures the capability of being able to make a snug fit. Prior to cutting the lower shaft to length, some measurements were made based on 3" for the flat spot, 3/32" for the brass washer, 1/2" bearing depth plus 1/8" + excess at the bottom of the bearing … so the lower bushing shaft was cut to a length of 3 24/32".
Completed lower bushing shaft with #40 holes drilled … The #40 holes will be enlarged later to accommodate the mounting hardware either #10 or #8 ... haven’t decided just yet.

My game plan did not work quite as envisioned: My initial thought behind only drilling the holes to #40 at first was … mark the first hole to be drilled into the baffle by inserting a #40 drill bit into one of the holes in the lower shaft then spin the drill bit by hand to leave a mark on the baffle so a #40 hole can be drilled in the baffle. Once the first hole is drilled, the plan was to secure the baffle onto the shaft using a stubby #40 Cleco to hold positioning so the remaining holes in both the upper and lower shafts could be marked, then drilled in the baffle. The roadblock I discovered was due to the shape (angle and length) of the handles on the Cleco pliers …. the handles on the Cleco pliers hit the side of the cowling long before allowing even a stubby Cleco to be inserted into the hole in the baffle. Ultimately, a long #40 rivet was used to hold the alignment of the baffle on the lower shaft.
Baffle plate in place with the upper hole on the lower shaft drilled into the baffle. Looking good so far it is starting to come together and look like a baffle assembly. Due to the clearance issues mentioned above, used a long #40 rivet at the location my finger is point towards as a pin to hold positioning so the remaining holes can be marked ... it can be seen if one looks closely at the photo.

Before drilling the holes for the upper shaft, the top edge of the baffle will require a little more trimming to accommodate the brass washer.  This seemed like a good place to quit for the evening.