Working on Chapter 19

updated: 09/05/2022


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Step 6 - Constructing the Landing Brake

This step involves the building of the landing brake in the bottom of the fuselage. I will be using Wayne Lanza's (Composite Design) electric landing brake motor in place of the manual system outlined in the plans.  I started by removing the landing brake flap, prepped back in Chapter 7, from the bottom of the fuselage by cutting along the tape lines with the Fein.  The 5 minute epoxy broke away easily leaving only small holes in the foam, which will be repaired later.

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Making LB-19 & LB-23 from 1/4" Birch Ply was straight forward and these were cut together with the 4 x  5/8" square aluminium slugs.  My LB-18 bellhorns were purchased from CG Products and as they will be placed further apart on LB-19 to accommodate the thicker electric motor drive shaft, I widened LB-19 by 1" (3" width increased to 4") and still placed it on the landing brake flap as per plans, offset from the centre line.  I also noted that the hinge listed and supplied in the Chapt 9 materials list is MS20001-P6, whilst the instructions called for MS20001-P5.  Apparently all the extruded piano hinges MS20001-P6, P5, P4, etc. are all identical, except for the width of the flange and it is easier just to order and stock the P6.  The flange that is fixed to LB-23 will need to be trimmed.  I did this after both LB-19 and LB-23 were setup and glued onto the hinge at 45.  The extra flange width was then trimmed on the band saw. The extra width can be seen in the photo below as the black strip overlapping LB-23.

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I used the plans method for locating the fwd edge of the front seat back and for cutting the slot in the foam using a 1/4" drill bit.  I used a protractor set at 45 to check that I was maintaining the correct angle, whilst cutting the slot.  Just a note of caution at this point, be very careful which end of the hinge you 5-min epoxy LB-19 to, since it is located off centre on the brake flap, that is on the passenger side of the aircraft. The plans show which side it goes on, but there's a lot of interpretation and room for error, since the fuselage is upside down, the landing brake is both upside down and right side up depending on the task, and it's not far off centre. I had to continuously re-check and double check the orientation of the hinge LB-19 & 23, during the setup phase.  I used 3 layers of duct tape behind LB-23 instead of the plans recommended shims and this worked OK when it came time to separate the hinge from LB-23.

With LB-19 and LB-23 loosely fitted in the foam slot, I placed the landing brake flap into position and re-checked the overall alignment to ensure everything lined up OK.  I then used a small amount of 5-min epoxy on the top of LB-19 and glued the landing brake flap into place. After 5 minutes I removed the flap and hinge assembly to the work bench, marked the location of the hinge and LB-19 on the foam, pulled LB-19 free, cut and removed the foam down to the glass, using a craft knife and wood chisel.  16/02/2008 - At this point building was placed on hold whilst we went on a 4 week holiday in New Zealand

27/04/2008 - It has taken me a couple weeks to get back into building again.  The plans call for glassing 2 BID (3 BID locally) in the LB recess area, and then 3 BID on the top of the LB. I decided to glass the 3 BID on the LB first, to ensure that I had removed enough foam and created enough clearance for the LB to fit into the recess.  It would be a lot easier to remove foam than to remove glass. The plans call for removing 1/8" from the Landing Brake recess area, and recommends cutting 1/8" deep grooves and then sanding the rest away.  I used a router set to an appropriate depth, and then easily got a smooth, flat bottom surface with a minimal amount of sanding.  This took me all of 15 minutes.

The fuselage centre line was drawn back onto the bottom of the fuselage, along with the other reference marks specified in the plans for the outside of the seat back brace and the outline for the cut out.  As I'm using the Composite Design electric actuator the cut out will be further away from the side of the brace than the 5/8" specified in the plans and the hole will be smaller (about the size of the LB-18 brackets 1" x 2").

To determine the location and hole size for the cut out, I placed the actuator on the fuselage and using a square to reference the side of the seat back brace, I marked a new centreline for the actuator, this turned out to be 28mm from the side of the seat back brace. From this centre line I then calculated that I would need a cut out approx. 1" wide by 2" long starting 3.5" in from the centre of the hinge pin.  From what I have heard from other builders on Wayne's design is that if you place the LB-18 bellhorns any further away from the hinge centre line (3.5"), you won't be able to get enough deployment and if you place the lb-18's any closer to the hinge line, you could exceed the motor's capacity, when trying to deploy the brake at maximum brake extension airspeed.  Therefore the most the actuator will extend the air brake flap will be about 70 deg and this is inline will what other builders have achieved.

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Using a light I pencilled in the outline for the map pocket supports and proceeded to cut out the 1"x 2" square using the Fein.  The plan from here is to temporary fix the LB-18 brackets to the brake flap and the actuator to the seat back brace and then with a little trial and error determine the best position for the actuator bracket on the seat back brace.  Mounting the actuator took a lot of fiddling and adjusting before I could get it to open more than 60 degrees and still close fully, without the actuator mounting bracket interfering with the map pocket (it didn't help that I was doing this with the fuselage upside down).  

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Once I was happy with the setup I marked the location for the actuator bracket holes and then removed the actuator and Brake flap in preparation for glassing the entire brake depression as per plans.  I also added an extra 3"x 6" 4-ply Bid reinforcement strip over the actuator bracket holes on both sides of the seat back support.  I drilled through the seat back support, installed the compression tubes, bolts and washers as per Wayne's instructions received with the actuator.  The landing brake flap didn't quite sit flush with the surrounding fuselage, I think I was a little too aggressive with sanding the foam down when making the 1/8" recess before glassing. So I decided to sanded everything smooth, remove any high spots and micro the depression level with the landing brake edges. Before plastering on the micro I covered the bottom lip of the landing brake edges with box sealing tape as a release agent. The next day when it was cured I then proceeded to sanded the micro off, down to a nice smooth finish with no gaps between the brake flap and fuselage. I was happy with the end result.  Here is a small video clip showing the operation of the flap.

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The fuselage was then turned over onto it wheels, so that I could finish off the landing gear box, which I hadn't completed back in Step 5.  I managed to get hold of a couple load cells, so out of interest I decided to weigh the fuselage as it stood at the end of Chapter 9 and was surprised to see that the total weight was 71Kg (156.5 lbs).  Not sure if this is good or bad, but all I can stay is that I'm glad to be finally finished with Chapter 9 , a couple weeks short of one year :-(

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Onto Chapter 10