Hinge-point Placement (Top, Middle or Bottom) ?

[RichT]

I'm just starting to modify a new wing to add ailerons.

I have flattened out the diahedral (by cutting 3/4 of the way through each side of the middle flat area, flatten and glue to fill the gaps, I'll reinforce with tape and still use wing struts (repositioned) - seemed like less hassle than the trench, CF tube method)

Next step is to cut the ailelons. After reading lots, I will be cutting 2"x 15" or 16", right to the tip.

I know I need to bevel the leading edge of the ailelon to allow it to move. My question is where to place the hinge point ? I've seen examples of all three approches (top middle and bottom).

Middle seems to be the most popular but that seems to me to disrupt airflow at both the top and bottom surfaces of the wing.

Top seems to have the advantage of keeping the airflow over the wing smooth and allowing maximum flex upwards (differential ?).

Bottom allows the airflow under the wing to remain smooth. Does the wing 'sit' on a cushon of air ?

Is one aerodynamically superior to the others ? Any advice, thoughts or recommendations would be great. I leaning to the Top hinge location. Although middle would probably be easier to install.

If I go Top, I'll probably use tape hinges and if Middle, I'll use CA hinges...

Thanks.

I have removed the dihedral using a cut and glue approach

[admiralev]

i went for the middle approach and flat dubro hinges for my ailerons

check these videos for bevelling

www.youtube.com/profile_videos?user=NeCubFlyer

[jmoore atcs]

Blenderm tape across the top works fine. I beveled the bottom of the aileron. On my next aileron mod, I will bevel the wing instead for the clearance. This will allow me to place the control horn in a more proper position.

[admiralev]

i had never thought of bevelling the wing itself...a little backwards but it should work

[retiredbri]

From jmoore atcs:
Blenderm tape across the top works fine. I beveled the bottom of the aileron. On my next aileron mod, I will bevel the wing instead for the clearance. This will allow me to place the control horn in a more proper position.

Can you post a picture of the aileron and Blenderm tape.
I have seen the hinges on Youtube but think the tape could be simpler to use.

Thanks in advance

retiredbri

[ginginho]

Dec 6, 2008 23:40:08 GMT 1 retiredbri said:

Can you post a picture of the aileron and Blenderm tape.
I have seen the hinges on Youtube but think the tape could be simpler to use.

Thanks in advance

retiredbri

I don't have a picture Bri, but found this link in another thread:

www.youtube.com/watch?v=f7HxhJv0KC8

It's not for a SC, but will give you a good idea on how to do it.

I also read somewhere that it's worth placing a thin spacer (1mm) between the top of the wing and the aileron (when fully folded over) when taping across the inside of the two surfaces.

[retiredbri]

Hi all

Sorry to RichT to have hijacked his thread.

To ginginho - I can see now how it works and understand about the gap - this would allow the tape to stick together.
For the Cub, I would mean beveling both the wing and aileron to get the tape to look like the link you gave.
Whereas, link from admiralev and using flat dubro hinges allows just the aileron to be beveled.

How did you do yours?

regards
retiredbri

[ginginho]

Dec 11, 2008 12:11:46 GMT 1 retiredbri said:

Hi all

Sorry to RichT to have hijacked his thread.

To ginginho - I can see now how it works and understand about the gap - this would allow the tape to stick together.
For the Cub, I would mean beveling both the wing and aileron to get the tape to look like the link you gave.
Whereas, link from admiralev and using flat dubro hinges allows just the aileron to be beveled.

How did you do yours?

regards
retiredbri

Haha, you've got me, I've not done it yet! However, I was unable to source any flat dubro hinges (all sold out) so I've ordered the round type. Others have used these and seem to be happy with the results.

When I done, I'll post pictures (will finish the covering after fitting these).

[tlyttle]

Technically, I believe that hinging at the top is the most effective from an aerodynamics view. When the aileron is deflected up, it generates some drag and turbulence on that wing, aiding the turn; meantime the aileron deflected down, presents a somewhat cleaner shape to the air.

I have no scientific proof of this, but it has always worked very well for me.

[retiredbri]

The idea of the hinge at the top would also make a 3M Blenderm hinge along the whole of the aileron work well.
With only one 45 deg bevel on the aileron underside, it will move down with the hinge tape covering the gap to make a smooth airflow. The tape could also be used to cover the bevel to strengthen the hinge and also provide a smooth airflow when the aileron is up.

I have seen the video that used Dubro hinges and they seem to be hard to cut the pockets and to get aligned.

I'm not sure about how difficult it would be to:

From Jmooore: ........On my next aileron mod, I will bevel the wing instead for the clearance.

I haven't thought about:

From Jmooore: ........This will allow me to place the control horn in a more proper position

Why would it make a difference having the wing beveled?

regards
retiredbri

[ginginho]

Just to add another point to this discussion, I read somewhere yesterday (lost the link now, doh!) that taping over any gap between the wing and aileron makes for much smoother operation due to no loss of air through said gap. The article stated it doesn't matter whether it's the top or bottom surface just as long as it seals the joint, stopping air travelling through from one surface to other (i.e top to bottom or vice versa).

On the bevel/control horn quote, could he mean that the aileron wouldn't have a bevel and hence the control horn could be mounted closer to the hinge edge? With the aileron bevelled, a distance (equal to the bevel) from the hinge edge would be lost from the surface that the horn is to be mounted on, so the horn may have to be mounted too far back from the hinge edge than is ideal.
It may not be what he's on about, but I at least hope this makes sense.

[tlyttle]

Ah, now we get into another problem: aileron differential. Moving the horns one way or the other changes the deflection of the ailerons, thereby changing their effectiveness. I have played with this before on sailplanes, and there seems to be no set rule for which way to go, each model seems to react differently. Personally, I would go for larger deflection of the down aileron, thereby increasing the drag on that wing, ie, same reason as for hinging at the top...

[admiralev]

With only one 45 deg bevel on the aileron underside

you're going to have to bevel both sides of the aileron to get the full range of motion both ways. one bevel wont get the job done. the part of the aileron that will be hinged should almost come to a point due to the bevelling

admiral

[retiredbri]

Hi all - first apologies for this long post.

I've looked into Top Hinges in some detail.

INPUT DATA FROM OTHER SC FLYERS: I've been told that with an aileron hinge along the centre of where the cut is made, the maximum throw up and down would be +- 0.625 in (16mm) that scales to +- 20deg. This is the servo limit.
A low rate on the Spektrum Tx dual rate control gives +- 0.375in (9.5mm) that scales to +- 12deg. This low rate is usually used for flying.

For TOP HINGED Aileron, I made a twice scale drawing of wing section that will use 3M Blenderm tape for the hinge. [For this drawing, I used dimensions given in the Background data section below].



S = Servo, pocketed in wing. This is an HS-55 with the small, thick servo arm (from the supplied accessory pack) with the last hole 0.5in (12.5mm) from the centre.
A, B, C, D are possible positions of the arm at the Servo centre position. This is achieved by moving the arm on the shaft splines.
Rotation of the servo arm is +- 30 deg either side of these servo arm centre positions A, B, C or D shown. Servo Arc shown is 0.5 in (12.5mm) from shaft centre.

H = Top Aileron Hinge (Blenderm tape).
Horn arc is set to be 1 inch (25mm) from the Aileron Hinge. This is the minimum distance that can be achieved with a top hinge and uses the first hole in the 1/2A T style hinge.
(Scaled from Dubro drawing, cat # 107).

The dotted line S to H can be used to determine the servo arm neutral position to get arm, rod and horn close to 90deg but only if the arm and Horn lengths are equal.

A control arm [wire with z bend at servo arm end and clevis at the horn end] transposes servo arm movement to horn movement to result in Aileron deflection. The rod isn't shown but the length would be set so that it achieves a neutral position of the aileron depending which hole (A, B, C or D) in the servo arm is chosen.

Because the last 2.5in (63mm) approx of the aerofoil is flat, I propose to use a square edged piece of wood on the top of the wing to guide the knife blade so as to make a cut perpendicular to the top of the wing [see Note below]. This makes an angle, as shown on the drawing of about 75 deg to the bottom of the wing. I can then cut a bevel into the aileron, so that it is 75deg from the bottom of the aileron. The total gap is therefore 2 lots of 15deg = 30deg. This would allow a maximum downward deflection of 30deg for the aileron.
With the hinge at the top, there is no need for a bevel and in theory, there is no maximum for the upward deflection of the aileron, apart from the practicality of the control rods and horn.

NOTE: This is different to when using hinges along the centre when the cut needs to be made perpendicular to the bottom of the wing.
The ratio of servo arm length to the Horn arm length is 0.5. This means that if the geometry is set to be symmetrical, the deflection would be +- 15 deg (half the servo deflection).
This is not a large as the maximum for the high rate [+- 20deg] but is more than the low rate [+-12deg] quoted in the INPUT DATA for centre hinged ailerons.

I have read that the Ailerons should have differential throws: 20deg up and 10deg down. This small down angle would not really allow for flaperons

By altering the servo arm on the splines (as A, B, C and D), some mechanical differential aileron throw can be achieved.
A = servo arm rearward 8deg. Aileron Up = 14deg, Aileron Down = 14deg, Control Rod = 3.38 in (86mm)
B = servo arm right angles. Aileron Up = 17deg, Aileron Down = 14deg, Control Rod = 3.52in (89.5mm)
C = servo arm forward 15 deg. Aileron Up = 14deg, Aileron Down = 12deg, Control Rod = 3.65in (92.7mm)
D = servo arm forward 30 deg. Aileron Up = 14deg, Aileron Down = 11deg, Control Rod = 3.77in (95.7mm)

I think that the thickness of my pencil is the limiting factor in the values measured. In theory, the best should be 30 deg total whereas B = 31.
The values C and D are lower because the angles of the control rod are too acute.

Where to go from here?

1 Make a scale model with foam from the HZ box and servo/horn/tape hinge to measure real life.
2 Look at getting a longer servo arm so that 20deg up can be achieved.
3 Consider Hinges in the centre - probably not tape hinges!
4 If I want flaps, use the inner 4.9in (125mm) of wing (like Ellis has done)


BACKGROUND DATA
I looked into videos and contacted people before deciding my ailerons would be 12 in (305mm) long, 1.75 in (45mm) wide and finish just before the wing end is rounded.
I measured the wing and have:
Width 7.2in (183mm)
Half span 23.4in (608mm)
Curved end starts 19.29in (490mm) from the centre.
The plastic "elastic band protector" 2.36 in (60mm) from the centre

The thickest part of the wing is 1.22 in (31mm) and is 2.22in (56.5mm) from the leading edge of the wing. .
The wing is 0.67in (17mm) thick at a line 1.75 in (45mm) from the rear edge [where the cut for the aileron would be].
The wing aerofoil curve finishes about 4.7in (120mm) from the wing leading edge. This means that the rear 2.5in (63mm) approx is flat.
The wing back edge is 0.28in (7mm) thick with a 0.12in (3.5mm) radius rear edge

Using the data from others and the wing measurements, the 12 in (305mm) long aileron would have the inside cut for aileron is about 4.9 in (125mm) from the wing plastic protection or 7.28in (185mm) from the wing centre line.

Any glaring errors? or comments? please let me know.

retiredbri AKA must get a life ;D

[ginginho]

Fabulous work Bri, I've PM'ed you with some more info.