ChuckC
Posts: 411
Joined: 1/10/2002
From: Friendswood,
TX, USA
Status: offline
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Here's how I did my speed brakes - keep in mind they're not cleaned up yet, but they work great.
Speed brake installation
Note: This is an optional scale installation step that increases the complexity of the build, but also adds neat realism and will aid in slowing the model some on landing. If you do not wish to add this complexity, you can just sand the parts where they glue together and glue them on. They are not essential for adequate flight characteristics.
Also, attention needs to be paid to the attachment of the off-set hinges to the speed brake and the way the speed brake fits; tack gluing with Cya and test fitting the components is highly recommended. Use just enough glue to barely hold the pieces together so you can break them apart cleanly if you need to. The off set hinges may be anchored either to the fuselage’s fiber glass side in front of the brake (as the author has done) or the fuselage’s former directly in front of the speed brake utilizing a larger set of offset hinges.
Note: When installing the cylinder to operate the speed brake, the cylinder must attach to the rear area of the brake as indicated in the accompanying photos. Attaching the cylinder to the hinges themselves will not produce enough leverage and torque for proper operation in flight. Attaching them to the rear area of the speed brake has the added advantage of holding the doors snugly shut.
Parts Needed:
Speed brakes
Small air cylinders (2 each, not included).
Off set hinges (4 each), not included. The ones shown are used to attach the speed brake via the fuse side. Small off-set hinges, e.g. Airpower, Skymaster or Dreamworks brand are the type used.
Scrap balsa and ply to anchor the cylinder to and to act as spacers.
Self tapping screws, if you wish to anchor the speed brake hinge to the bulkhead instead of the fuselage wall.
2 each, medium or small nylon control horns and self-tapping screws to secure them to the ½ x ¼ spruce/balsa.
Epoxy
Cya
2 each, ¼ inch x ½ inch x 3 ½ inch pieces of balsa or spruce
Masking tape
2-4 each, 2.5 x 6 mm socket head cap screws and matching lock nuts
Drill bit to drill the holes for the 2.5 mm screws
General steps and overall concept behind installation
The following is a real simple installation; you will hinge the speed brake, attach the cylinder to the speed brake, attach wood stick to the cylinder and then glue in place in the closed position.
Steps to Install:
1. Remove the turbine and turbine tail pipe. You need to have good access to the inside of the fuse. It also helps to cut out both speed brake recesses at the same time, allowing access through the holes.
2. Cut out the speed brake recessed area as shown in the pictures. Note to leave as much fiberglass intact as practicable to both act as a lip for the speed brakes to close against and as reinforcement material. The absence of the lip on the forward side of the recess is to permit the hinges to clear. Note that a little extra fiberglass was removed from this area to allow the hinges to clear.
3. Test fit the speed brake to the fuse, ensuring that you have the proper right or left brake- they are not the same. You are now checking the fit and how the off-set hinges will be secured at the hinge line. You may need to sand the edges of the speed brake in some areas to remove flashing.
4. Sand the paint from the speed brake where the hinges attach. See picture
5. Fit the offset hinges (note orientation in pictures-they only work one way) to the speed brake and tack glue near the very edge of the brake at the hinge line. The hinge must be at this location to allow it to deploy properly.
6. Test fit the speed brake to the fuse and notice where it will mount on the inside of the fuse. Mark this location. Also test-operate the speed brake to ensure smooth, accurate operation. Be careful to ensure the hinge pivots line up.
7. Cut an approximately 1 ½ inch by ¾ inch plate (this will vary depending on actual construction dimensions of model) of 1/64 ply out and glue it to this position; the idea is to have a relatively flat mounting plate to which the hinge may attach. The wood should extend from just up against the bulkhead up to just before the speed brake opening where the hinge will mount (see picture).
8. Place a doubled piece of masking tape on the speed brake as shown in the picture – this will set the proper gap between the speed brake ad the fuselage when in operation.
9. Re-test fit speed brake with hinges tack glued and tack glue the hinge down to the wood on the inside. Alternatively, very small self tapping screws may be employed here to facilitate removal of the brakes. See picture.
Fuse side mounted hinge
10. Once the hinge locations on the speed brake are accurately determined, epoxy them into place on the speed brake. You will want to wax or grease up the hinge line to prevent epoxy from getting in or alternatively install the very small self-tapping screws into all of the hinge mounting plates.
Fuse bulkhead mounted hinge
11. If mounting to the fuselage former, make a wood shim out of layers of light ply as shown in the pictures. Once built up, you may need to sand down the spacer to achieve a perfect fit. The appropriate spacing is largely determined by the final position of this former when installed, so spacers will be different.
All installations continue
12. After secured, remove tape from speed brake.
13. Note the approximate position of the cylinder mounted to the speed brake. The position is not super-critical, just that both speed brakes should be mounted in the same location.
14. Mount the cylinder to the speed brake as shown. Note that for Robart cylinders, this means the foot of the cylinder must be against the brake itself. Mount the brake using a single 2.5 x 6 mm cap screw and lock nut as shown. If you wish to, you may use 2 screws on each side, but the installation is secure enough with one.
15. Add a clevis to each cylinder. Use Teflon tape, thread locker or locking screws. Leave enough thread to allow adjustment in and out.
16. Sand a rounded profile to the broad side of the ¼ x ½ x 3 ½ inch sticks that will match the bottom of the fuse curvature from the inside. This gives more gluing area.
17. Trim the two control horns down to leave just the final connection hole.
18. Using self tapping screws, screw the control horns to the middle of the sticks on the flat side of the sticks with the horns facing rear wards. The horns will end up facing towards the inside of the fuse and rearwards. The final position up and down of these horns is determined more by where they are glued to the interior of the fuse later on.
19. Once you have made up the 2 mounting sticks, then test fit the sticks inside the fuse – connect the cylinder. Holding the stick in place with your hand in the fuse, operate the speed brake, noting how the cylinder operates. You want it to open to an approximate 45 degree position – whatever the cylinder allows and will still pull the door completely closed.
20. Take a note of where the stick should mount with the door closed; mark the fuselage here so you can accurately glue the stick in place.
21. Once sure of this location, tack glue in place.
22. Check operation and adjust if needed.
23. Follow up with epoxy and glue the sticks permanently in place.
24. Route air tubing being careful to avoid the area of the turbine pipe. Note that the author secured the tubing to the cylinders, combining them to cross between the hinges. This allows for a subsequent route tight against the fuse.
25. Repeat the above for the other speed brake, being certain they both open the same amount and close smoothly. You do not want the speed brakes to deploy at substantially different angles.
(Pictures next page)
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Chuck Carlisle
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