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Building Tips and technical articles. => Building techniques => Topic started by: Brian Courtice on February 18, 2022, 10:12:14 PM
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The photos in the build instructions show the wire pre-bent. My wire is straight, no bend.
I'm afraid to bend it myself, because I know that the bend has to be at the correct distance from the bellcrank (that you can't even see) to prevent an off center bellcrank and differential flap travel.
I'm almost tempted to open a temporary hole in the wing sheeting so I can see the connection at the bellcrank, and to have access if I get the bend wrong and end up having to make a new pushrod.
Any tips on how best to proceed?
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The photos in the build instructions show the wire pre-bent. My wire is straight, no bend.
I'm afraid to bend it myself, because I know that the bend has to be at the correct distance from the bellcrank (that you can't even see) to prevent an off center bellcrank and differential flap travel.
I'm almost tempted to open a temporary hole in the wing sheeting so I can see the connection at the bellcrank, and to have access if I get the bend wrong and end up having to make a new pushrod.
Any tips on how best to proceed?
I used a 4-40 to wire adapter silver soldered to the push rod and a ball joint threaded onto the adapter at the flap horn. this allows you to trim the wire to perfect length when pre-fitting the adaptor to get perfect neutral with proper throw; then silver solder the adaptor on and make final neutral or trim adjustments as needed. I then used a 90 degree wire with keeper at the flap horn to arrow shaft with threaded rod and ball joint at elevator horn end. Gives you reliability and adjustability of throw and neutral at both surfaces.
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A bit late now, but if you make sure the leadouts are the same length when installing the bellcrank, you can then put it at neutral after the wing is closed up by lining the ends up.
In your case, you could put the bellcrank at mid travel, by alternately pulling one leadout fully out, find the mid travel position.
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Thanks guys.
I can see enough of the bellcrank through the pushrod slot to get it pretty close to straight I think.
I definitely prefer an adjustable flap linkage so I can trim the bellcrank, and so not have to bend a pushrod perfectly. Soldering on a 4-40 ball linkage is my preference.
The instructions want you to use two adjacent holes in the horn, which makes it hard to get two linkages hooked up next to each other without them interfering with each other.
It looks like a 4-40 ball link for the flaps and a z-bend for the elevator will just barely give enough range of rotation.
Skipping a hole on the horn would make for lots of room and more linkage options, but moving the elevator pushrod down a hole on the horn is going to increase the elevator travel in relation to the flap travel. I don't think I want to mess with the flap/elevator ratio.
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That is why they have several holes on the horn. You can space the ball links or clevis at the flap horn and make the the adjustment at the elevator end. I have even put the ball links on opposite sides of the flap horn using a longer bolt. D>K
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That is why they have several holes on the horn. You can space the ball links or clevis at the flap horn and make the the adjustment at the elevator end. I have even put the ball links on opposite sides of the flap horn using a longer bolt. D>K
Thanks for the reply.
My concern was that stacking two linkages on one hole, or leaving an empty hole between the flap and elevator linkage would change the ratio of movement between them.
Anyway, I think I have a workable arrangement figured out.
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This oughta work.
I soldered on a 4-40 ball link. I even managed to get the length correct.
Looking into the pushrod exit hole I can see one arm of the bellcrank and it looks to be perfectly straight.
A z-bend wire clears the ball link spacer enough to allow full bellcrank rotation.
I plan to fabricate a carbon pushrod with probably another ball link at the elevator horn.
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I built same ARF and posted pictures here last September.
One important thing should be done: secure the belcrank mount with some extra glue and sticks. And when wing is in place in the fuselage drill holes trough the fuselage bottom, trough the wing sheeting into the belcrank bottom plywood mounting plate. Glue the bamboo stick trough the hole, but not to far past the plate, so belcrank will be free. If proper pull test is applied to the unmodified belcrank mount it will break loose. Not enough glue in the AFF at the factory.
Correct way of making control- is to use an offset flap horn. In this way the linkage to the elevator will not interfere with the flap.
I used 3/32 music wire for joining the flaps and same 3/32 wire to join the elevator half’s. The kit joining U shaped wire is too weak. I think it’s 2 mm in diameter, I trow it away.
I used all components from the kit. Marked the place and bent the flap wire, marked and bent the flap to elevator push rod wire. No adjustments. Elevator pushrod wire was bent to clear the flap. Model was built in four days, flew fine.
Jerry
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I did replace both joiner wires with 3/32 music wire.
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I bent mine to align w/ the flap horn. Was not difficult and does not take much offset. Bent and aligned before I cut to neutral length for the solder clevis.
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Any tips on how best to proceed?
Curious how it worked out.
Ken
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My bent/aligned pushrod arrangement seems fine in the air, but I am still learning the model.
The bigger problem I have is that I used the kit provided (ARF) flap/elevator joiner wires which are not very stiff, and the model has a lot of differential flex in the adjacent control surfaces. I consider myself still a rookie builder and did not know any better at the time. Should have used heavier music wire. I pretty much fly sport and basic stunt so for me not really an issue. The model still flies reasonably well. I really don't want to cut into the model now and use stronger joiner wires. But any serious flyer should not use the kit provided joiner wires.
I just chalk it up to experience and will factor this issue into a future model.
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My bent/aligned pushrod arrangement seems fine in the air, but I am still learning the model.
The bigger problem I have is that I used the kit provided (ARF) flap/elevator joiner wires which are not very stiff, and the model has a lot of differential flex in the adjacent control surfaces. I consider myself still a rookie builder and did not know any better at the time. Should have used heavier music wire. I pretty much fly sport and basic stunt so for me not really an issue. The model still flies reasonably well. I really don't want to cut into the model now and use stronger joiner wires. But any serious flyer should not use the kit provided joiner wires.
I just chalk it up to experience and will factor this issue into a future model.
You are going to have to accept my apology for not pointing that out initially. It is one of my "pet peeves" and I chose to skip it. My bad. I do not use any flap mounted horns and never anything but 1/8". Normally I have to give the lecture on differential flap resistance but you have figured that out by yourself. There have been some build threads that had the horn on the outside. That is a disaster waiting to happen. On the inside you have a roll problem, but it is in the right direction. Unless you plan on entering the plane in Advanced or above PA, don't worry about it and just have fun. You know what to do next time.
Ken
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You are going to have to accept my apology for not pointing that out initially. It is one of my "pet peeves" and I chose to skip it. My bad. I do not use any flap mounted horns and never anything but 1/8". Normally I have to give the lecture on differential flap resistance, but you have figured that out by yourself. There have been some build threads that had the horn on the outside. That is a disaster waiting to happen. On the inside you have a roll problem, but it is in the right direction. Unless you plan on entering the plane in Advanced or above PA, don't worry about it and just have fun. You know what to do next time.
Ken
No worries Ken. It is just real-world lessons-learned for me. No plans to compete, just have fun building and flying. But this type of experience will only make my future models fly better. The Brodak P40 ARF does still fly pretty well for me at my flying level.
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An adjustable, threaded end added to either the elevator or flap push rod would allow adjustment needed to get both surfaces in sync.