Slotted flaps, am I on the right track?

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Jonny o

Active Member
Joined
Oct 31, 2015
Messages
31
Location
Fairbanks, AK USA
Attached are pictures of the hinges I have built. They are basically Bearhawk style wing side (spherical bearings go in the holes) and RV-10 flap side. I rounded the front of the flap itself as you mentioned. So you wouldn't be concerned about the torsional loads on the rear spar from the bellcrank itself. (Which I will have to double the arm length on the flap side while keeping 4 inches on the cable side) I like the idea of simplicity. I feel that I could probably set the hinges to transfer the loads across the hinges as they will only be 1/2 inch between them.

Man, you are flat going for it ! Awesome.

If you could get your hands on some scrap spar pieces, I think it would be worth your while to mock things up. I buy wrecked wings for parts and keep the straight part of the spars. I like to build a mock up and leave it hanging on the wall for a few days, so I can pick apart the faults of my new design.

A slight critique on your welding procedure. Start welding on the end of the V with the gap. Build up some weld on each side of the gap until it almost touches. Each buildup should be allowed to cool to room temp. Tack both ends of the V and let that cool to room temp. Weld from large gap side; letting it cool in several stages. It will warp a lot less.

Doubling the length of the flap side of the bellcrank is going to double the force on the flap handle. Are you doubling the length to get more flap travel ?

Again, AWESOME !

Jonny
 

Jonny o

Active Member
Joined
Oct 31, 2015
Messages
31
Location
Fairbanks, AK USA
You need a P ...place.

At what point does the high speed flow from a propeller start to increase in size?

The high speed flow from the propeller starts to increase DIAMETER as soon as the aircraft starts to move forward.

5/8 diameter at zero
3/4 diameter at 30
7/8 diameter at cruise

If you dive the airplane and go faster than the air coming off the back of the prop the prop wash diameter will be larger than the diameter of the prop. This is because the prop, even though it is at cruise power is acting like an obstruction and the air is having to go around it as if it where a CIRCLE of plywood.

Jonny
 

Pilot-34

Well-Known Member
Joined
Apr 7, 2020
Messages
813
I ment where does the flow from a propeller begin to increase in diameter? Standing or moving.
At some distance from the prop it Has to quit getting smaller and start getting bigger.
 

flyingforx

Active Member
Joined
Nov 7, 2020
Messages
33
I am doubling the length of the bellcrank to get 50 degrees of travel on the flap while not allowing overcentering of the arm on the flap side. Since the hinge is now 2.5 inches lower, my thoughts are that the mechanical advantage is more on the distance between the hinge point and pushrod on the actual flap. As a result it will take more throw on the bellcrank now to get 10 degrees of flap than it did before. I don't know how much longer I can add to the cable side without rib/false spar interference with the smaller space behind the rear spar.
 

Jonny o

Active Member
Joined
Oct 31, 2015
Messages
31
Location
Fairbanks, AK USA
I am doubling the length of the bellcrank to get 50 degrees of travel on the flap while not allowing overcentering of the arm on the flap side. Since the hinge is now 2.5 inches lower, my thoughts are that the mechanical advantage is more on the distance between the hinge point and pushrod on the actual flap. As a result it will take more throw on the bellcrank now to get 10 degrees of flap than it did before. I don't know how much longer I can add to the cable side without rib/false spar interference with the smaller space behind the rear spar.

Flyingforx,

Yes, moving the attach point of the pushrod down, closer to the hinge point, will definitely add to the amount of pull it takes on the flap handle. Another option might be looking to see if you have room for a longer flap handle or could add more travel. More travel of the flap handle can equal less load or more movement of the flap.

When I build or change a system I make a quick mock up to check loads and distances by just pounding nails or screws into a thick sheet of plywood. It makes it easy to measure how much distance you are getting with each change. I attach a cheap fish scale to the flap handle ( which is just a piece of 2 x 2 ) so I can measure how much force it takes to lift a 20 pound plate. Right now, I have an entire flap system mocked up on my garage wall. When I walk by I give it a pull and think about it for 15 seconds.

Be careful about getting within 25 degrees of overcenter. Things get sloppy over time and you don't it to snap past or loose effectiveness.

Is your flap handle down low or overhead ?

Jonny
 

flyingforx

Active Member
Joined
Nov 7, 2020
Messages
33
The mock up idea sounds good, might have to try it. My bellcrank is going to resemble Backcountry supercubs in shape. I thought about shortening the flaps, but I'm pretty sure I'll just use four hangars and two bellcranks for ease of mind. Just built my aileron bellcranks yesterday and will hopefully be working on the flaps today. I kept the flap handle where it was since it is a Pacer, which I feel is a practical location, just more pulleys. You have me thinking about adding bearings to them now. Maybe after the project is flying...
 

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Jonny o

Active Member
Joined
Oct 31, 2015
Messages
31
Location
Fairbanks, AK USA
Looks great.

I make my bellcrank mockups out of plywood. They are square shaped, so I can put pivot point holes in wildly different positions to see how different positions work.

Jonny
 

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flyingforx

Active Member
Joined
Nov 7, 2020
Messages
33
Nice, yep. I used flap 2h to shape mine and the location they recommended at 50 degrees. The TOWS strangely resembles the naca report posted at the beginning of this forum. My bellcrank mockups were sticks of wood so I could have them in place and make sure they fit in the TE box, I'm too far in to go back now!
 

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