stunthanger.com
Building Tips and technical articles. => Building techniques => Topic started by: Trostle on January 09, 2021, 12:43:25 AM
-
Here is another approach to tweaking flaps. Two-part horn held together with a # 6 bolt. Small access hole on the side of the fuselage aligns with the bolt. Works a lot better than trying to bend (twist) the horn wire.
Keith
-
That of course does the job, Keith. And when made well, is pretty reliable. But my question is how easy it is to make really small trim changes? Do you use some angle measuring tool to verify the changes?
Oh, and Happy New Year!
Lauri
-
Another system I tried and failed to improve upon.
-
The horn in the photo looks like the one designed and built by Bob McDonald. I used one of his horns with great success on the 2016 Snoopy airplane (PA 40, 585 sq.in., 50 oz.).
Mine has a #6 bolt.
Making small changes to level the wings was doable, but painstaking and iterative. It requires two people and a depth micrometer on the flap to make the adjustment. Then of course a test flight. Once the wings are leveled, they tend to stay that way.
The horn has proven to be reliable and I am using an identical unit on the new airplane in construction now.
The Paul Walker system has the advantage of precise and repeatable adjustments. This is preferred for the situation where one arrive at a contest, say the World Champs, and you have extremely limited opportunity and time to get the wings level should that be necessary.
-
That of course does the job, Keith. And when made well, is pretty reliable. But my question is how easy it is to make really small trim changes? Do you use some angle measuring tool to verify the changes?
Oh, and Happy New Year!
Lauri
Dennis - and Happy New Year to you too. It is always good to hear from you.
You have a good question regarding how to accurately make adjustments with the horn that I have pictured. (It is the horn like Bob McDonald makes discussed by Jim Hoffman above.)
Hopefully, the picture below shows the flap gusset between the flap and the fuselage. When the bolt is loosened, one flap can be clamped to the gusset. The other flap can be moved in very small increments. I feel that I can make accurate adjustments with the movable flap trailing edge in probably 1/4 mm increments or less in the desired direction. It solved a slight outboard wing high problem in level upright flight in two flights when I started flying the Martin Baker last Fall. The total adjustment was less than 1/32" at the trailing edge of a flap. A lot nicer way to "tweak" the flaps rather than twisting the horn which has proved disastrous for me on several occasions with solid, one piece horns.
I think what you and Howard are discussing is a very elegant method to enable flap tweaking. So is the Paul Walker system, but I wonder if the Walker approach allows too much flex from right to left flap under different loads. Yes, it is better than just using split or separate horns, but still allows flex in the system from one flap to the other. Any unnecessary flex between the flaps is not good.
Keith
-
Because the adjustable flap horn,
which side should be adjustable and wich one is fixed,
inside wing-outside wing?
Dietmar
-
Because the adjustable flap horn,
which side should be adjustable and wich one is fixed,
inside wing-outside wing?
Dietmar
The horn pictured at the top of this thread and with the access hole to the adjuster bolt on the left side of the fuselage, the pushrod from the bellcrank is directly connected to the right flap. This means that the adjustment is made on the left (inside) flap when the adjustment bolt is loosened. Yes, this means that the the trim changes between the flaps and elevators. This is minuscule since the flap adjustment at the trailing edge of the flap will probably be 1/32" or less. If there is a need to adjust elevator/flap trim by adjusting the flap/elevator pushrod length, that is where it is worthwhile to be able to change that elevator/flap trim which should be a feature built into the airplane whether it has any kind of flap adjuster or not.
If this horn is turned around and the the access is to the adjuster bolt is on the right side of the airplane, then the left flap is the one directly connected to the bellcrank and the right flap becomes "adjustable".
Keith
-
The horn pictured at the top of this thread and with the access hole to the adjuster bolt on the left side of the fuselage, the pushrod from the bellcrank is directly connected to the right flap. This means that the adjustment is made on the left (inside) flap when the adjustment bolt is loosened. Yes, this means that the the trim changes between the flaps and elevators. This is minuscule since the flap adjustment at the trailing edge of the flap will probably be 1/32" or less. If there is a need to adjust elevator/flap trim by adjusting the flap/elevator pushrod length, that is where it is worthwhile to be able to change that elevator/flap trim which should be a feature built into the airplane whether it has any kind of flap adjuster or not.
If this horn is turned around and the the access is to the adjuster bolt is on the right side of the airplane, then the left flap is the one directly connected to the bellcrank and the right flap becomes "adjustable".
Keith
I am making one for the logarithmic horn right now. I am adding your idea. I think your post answers the question "how much adjustability do you need". I will have about 1/8" both directions. If I need more than that then I have other problems. I have used 1/16" steel for the horn and I plan to tap 4-40 threads into the horn and use a hex head with a lock washer. Will that be sufficient to keep it from slipping. I will have an access hatch and I routinely check bolts on everything after about 10 flights. My biggest concern is slippage.
Ken
-
I am making one for the logarithmic horn right now. I am adding your idea. I think your post answers the question "how much adjustability do you need". I will have about 1/8" both directions. If I need more than that then I have other problems. I have used 1/16" steel for the horn and I plan to tap 4-40 threads into the horn and use a hex head with a lock washer. Will that be sufficient to keep it from slipping. I will have an access hatch and I routinely check bolts on everything after about 10 flights. My biggest concern is slippage.
Ken
Hi Ken,
I agree with your statement that if you need more "adjustaibility" than the +/- 1/8" you plan, then you have other serious problems, like maybe start over with a new wing.
I only have experience with the Bob McDonald horn that has been pictured. I am certain that Bob has used this idea on his airplanes. I would be a bit concerned with only a 4-40 bolt threaded into the 1/16" steel horn. The horn in the picture uses a 6-32 bolt with a nut brazed onto the horn. I would think that this lessens considerably the thread stripping with only a 4-40 bolt tapped in the 1/16" horn as well reducing the chance of the bolt becoming loose. If that happens in flight, I can only imagine the disastrous results.
Keith
-
Hi Ken,
I agree with your statement that if you need more "adjustaibility" than the +/- 1/8" you plan, then you have other serious problems, like maybe start over with a new wing.
I only have experience with the Bob McDonald horn that has been pictured. I am certain that Bob has used this idea on his airplanes. I would be a bit concerned with only a 4-40 bolt threaded into the 1/16" steel horn. The horn in the picture uses a 6-32 bolt with a nut brazed onto the horn. I would think that this lessens considerably the thread stripping with only a 4-40 bolt tapped in the 1/16" horn as well reducing the chance of the bolt becoming loose. If that happens in flight, I can only imagine the disastrous results.
Keith
I will swap it out for a 6-32. Haven't drilled the hole yet. I was planning to braze a nut to the other side as well. With the outboard having the bolt it should not cause a disaster if the bolt slips. Worst case a little flutter and some outboard roll. I have learned the hard way to "assume the level flight position" if something feels funny with the controls.
Ken