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Old Nov 09, 2012, 03:15 PM
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Thanks....almost there!

Quote:
Originally Posted by awmeade View Post
Good progress, I like it
Going to do a fair bit tomorrow.... including the following, in priority order

1. Cut out main gear and move 2 inches forward
2. Make a cut out to give the prop a bit more breathing area, together with tapering the fuselage a bit to allow better airflow to the propeller.
3. Browne paper new tail
4. The two carbon spaís I am currently using to go through the wing are different lengths. 1m and 800mm. I have replaced the 800mm spa with another 1m spa. But the wings donít quite fit all the way on. So make this fit.
5. remove extra long nose section, and possibly strengthen fuselage with the Carbon strip.

On another note, do yo know where I can get hold of a nice large robust nose wheel leg? something similar to the picture perhaps....I'd like to fit an 80mm wheel in it...

Rich
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Old Nov 10, 2012, 02:12 PM
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Hobbyking have a UK warehouse :
http://www.hobbyking.com/hobbyking/s...60mm_12kg.html
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Old Nov 11, 2012, 03:04 PM
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Cardiff, UK
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Almost there...

After doing a fair bit of work over the weekend, relocating gear & fitting the cf tubes in the wings, it's getting there, I have also removed the 100mm nose extension.

The balance point is just under 110mm from LE.which is painstakingly close to 33% MAC.

The weights are now as follows...
Weight without balase & 1 x 5000mah 4s lipo: 4356g
Nose Ballast: 79g - It seems that for every 9-g of weight i add to the nose, the plane balances 10mm forward.
TOTAL - 4435g

I am going to refit wiring, and maiden.next weekend, fingers crossed.
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Old Nov 18, 2012, 10:22 AM
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Maiden flight, a success...kind of!

So the weather was perfect, and thought i'd go to the local field for a maiden flight. I had a couple of issues, one being the slow start on the motor. I thought i'd try a short hop, but the plane just lifted into the air, forcing me to do a slightly laonger flight than planned,

I'm not sure what was wrong, I think there was too much 'up' trim on the elevators, as the CG was at 33%. It was a bit difficult to control, but managed to land it, the landing was a bit heavy. And has highlighted the wek points i nthe rear of the fuselage, it is a clean break, so i will epoxy back together, add a bit more weight in the nose, and try again next weekend.

Overall i'm please with the progress.

Prototype maiden (0 min 45 sec)
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Old Nov 18, 2012, 02:50 PM
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Well done fella - I think you did well to not go straight into a stall there, and actually get a couple of circuits in. CG issues always make for a hairy flight, but at least there were no (major) dramas, and you'll be able to move on with some air time information.
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Old Nov 18, 2012, 04:31 PM
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Quote:
Originally Posted by awmeade View Post
Well done fella - I think you did well to not go straight into a stall there, and actually get a couple of circuits in. CG issues always make for a hairy flight, but at least there were no (major) dramas, and you'll be able to move on with some air time information.
cheers, I was really happy with it even though it did not go strictly to plan, I could probably have powered it up and come round for a second attempt at a more gentle landing, but didn't want to risk flying near other people, so opted for the crash!

After 30 mins of gorilla glueing the plane is almost ready for another flight, with more weight in nose this time!
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Old Nov 20, 2012, 05:35 PM
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A check to make.

Before the next flight, try to check the angle of attck on the main wing and tail.

If the plane is zooming up it may be the difference in angle of attack between the main and tail effectively is giving a constant up elevator. If that is the reason a kludge may be to give the ailerons a bit of reflex to effectively reduce the angle of attack.

To do this, with the ailerons centered and even, turn the adjustable links 4-6 times in the direction required to give both ailerons a slight amount of up. This effectively reduces the angle of attack. It does induce some drag.

Try a short hop. Power up and take off and land immediately after 1 -3 seconds of straight ahead flight. Evaluate what happened. Did you have more elevator control and less pitch up?

Also setup exponential on the TX for the elevator or reduce the throws by moving out a hole or two at the elevator control horn.. The video seemed to show over control, not so much tail heavy.

J
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Old Nov 21, 2012, 05:06 AM
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Checks before next flight...

Quote:
Originally Posted by small_rcer View Post
Before the next flight, try to check the angle of attck on the main wing and tail.

If the plane is zooming up it may be the difference in angle of attack between the main and tail effectively is giving a constant up elevator. If that is the reason a kludge may be to give the ailerons a bit of reflex to effectively reduce the angle of attack.

To do this, with the ailerons centered and even, turn the adjustable links 4-6 times in the direction required to give both ailerons a slight amount of up. This effectively reduces the angle of attack. It does induce some drag.

Try a short hop. Power up and take off and land immediately after 1 -3 seconds of straight ahead flight. Evaluate what happened. Did you have more elevator control and less pitch up?

Also setup exponential on the TX for the elevator or reduce the throws by moving out a hole or two at the elevator control horn.. The video seemed to show over control, not so much tail heavy.

J
I have made a jig to check the angle of the main wing in relation to the tail. The flat bottom of the Clark-y is exactly parallel with the centreline of the symmetrical profile of the tail. Upon watching the video, and balancing the aircraft before and after the flight. I can confirm that the CG was just behind the 33% mark. I am going to go for 25% for the next flight.

Having already completed one flight, I am confident that moving the CG forward should help a lot, I am basically going to add a second 5000mah 4s battery up front. Based on the performance of the plane. I think it will easily handle the extra weight.

If after doing that, I still experience pitch issues, I will change the angle of the ailerons. But would be hesitant doing something that is going to reduce performance at this stage...

Does that sound about right?
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Old Nov 21, 2012, 04:06 PM
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Clark-Y Angle of Attack

When a Clark-Y airfoil has the base or bottom horizontal, it has a positive angle of attack.

The reason I say this, is because the angle of attack is "usually" measured from the centre of the radius of the leading edge to the center of the trailing edge.

With a Clark-Y having the bottom as a datum, you could have several degrees of angle of attack.

A simple rule is 1/16th of an inch at 4 inches is 1 degree. So if the chord is 12 inches, 3/16ths of an inch is one degree.

What is the height of the centre of the radius of the leading edge, above a straight edge held along the underside of the wing?

See this link for a sample

http://airfoiltools.com/airfoil/deta...foil=clarky-il

The horizontal line is displayed at 0 deg AofA. Note the amount the lower surface extends below the centre line at 0 deg.

Note in the right hand upper plot the angle of attack at 0.0 still shows positive lift, even with Reynolds number of only 50,000. When you plot the Re of 100,000 the Coefficient of Lift Cl is much greater at 0deg AofA

In the bottom right graph you see the impact on drag of an increase in the AofA. It starts to increase dramatically at around 10 degrees and goes up steeply with increasing angle.

Jim H
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Old Nov 21, 2012, 04:21 PM
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O dear!

Quote:
Originally Posted by small_rcer View Post
When a Clark-Y airfoil has the base or bottom horizontal, it has a positive angle of attack.

The reason I say this, is because the angle of attack is "usually" measured from the centre of the radius of the leading edge to the center of the trailing edge.

With a Clark-Y having the bottom as a datum, you could have several degrees of angle of attack.

A simple rule is 1/16th of an inch at 4 inches is 1 degree. So if the chord is 12 inches, 3/16ths of an inch is one degree.

What is the height of the centre of the radius of the leading edge, above a straight edge held along the underside of the wing?

See this link for a sample

http://airfoiltools.com/airfoil/deta...foil=clarky-il

Jim H
O no!

In that case I guess the wing position needs to change. Unsure as to the radius of the centre of the leading edge robably around 5mm Ish.

So does this mean I need to give the elev some down trim to compensate? Or would it be best to give ailerons some trim instead?

Cheers for the link, it helps a lot.. Even though it's not what I wanted to see!
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Old Nov 21, 2012, 04:34 PM
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Simple method

Put a straight edge vertical against the leading edge. Where it touches the leading edge is very close to the centre of the radius. In reality the centre will be just a bit higher.

You want this straight edge to be perpendicular to a line from the contact point to the centre of the trailing edge. This contact point is the centre of the leading edge.

How high is it above the straight edge along the bottom?

What is the chord?

I will use my calculator to find the AofA

Jim H
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Old Nov 21, 2012, 05:13 PM
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Hi Jim,

Cheers for the instructions, they are very clear and I think I have done the measurements correctly. The distance to Le touch point from a line that goes along base of wing is 15mm. The chord is 315mm...

I won't be able to change angle of attack as wing is glued and secured into fuselage. Will elev trim be good enough, or would ail trim be better.

Guessing mounting the wing properly in the first place would have been good. Does the angle of attack issue create big problems? Not sure if you saw the video of the maiden, but the plane pitched up an awful lot on take off. I could also add extra nose weight to move CG to 25%....?

I'm in the process of designing a. Better fuselage... I'll definitely need to factor this into the new build...
Rich
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Old Nov 21, 2012, 08:50 PM
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Take the Easy Route

Put some weight in the nose.

Move the elevator pushrod out to a farther hole on the control horn, or move the pushrod in closer to the middle on the servo output arm. This will reduce the throw a bit.

Make sure there is no up elevator at the neutral position with the trims in the exact centre. You want to have maximum trim range available.

After a few flights and you get the trims set so the plane behaves similarly from one flight to the next, carefully note the deflection on the control surfaces using card stock templates. Then set the Tx trims on neutral and then adjust the pushrod ends to move the surfaces to match the templates.

Now you will have full trim range available to you with the plane movable surfaces in the correct flying position.
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Old Nov 24, 2012, 10:27 AM
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Going down the easy route!

Quote:
Originally Posted by small_rcer View Post
Put some weight in the nose.

Move the elevator pushrod out to a farther hole on the control horn, or move the pushrod in closer to the middle on the servo output arm. This will reduce the throw a bit.

Make sure there is no up elevator at the neutral position with the trims in the exact centre. You want to have maximum trim range available.

After a few flights and you get the trims set so the plane behaves similarly from one flight to the next, carefully note the deflection on the control surfaces using card stock templates. Then set the Tx trims on neutral and then adjust the pushrod ends to move the surfaces to match the templates.

Now you will have full trim range available to you with the plane movable surfaces in the correct flying position.
Putting some weight has turned into a slightly larger job than i anticipated. Adding the 80g nose weight right at the tip didn't help enough with balance, therefore I have opted to move the nose wheel 90mm further forward, and build a battery box to hold the batteries further forwards. I'm learning a lot for the next build.

During the build i didn't even think about battery position, or the method to secure the batteries in the plane. Hopefully this will do the trick.

My only concern is that if the plane has a hard landing, the box could rip off, and damage both batteries... and at £40 each, i don't particularly want that to happen!

It's been raining all day, so maybe try it out tomorrow...

I've done the trims as well, so fingers crossed she'll lift off in a slightly less aggressive way next time!
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Old Nov 25, 2012, 12:51 PM
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A couple of questions..

What is the best way to hinge control surfaces? I've been using the standard 28mm x 12mm mini nylon pinned hinges, about 3-4 per control surface, but they keep getting ripped out by accident. Therefore I my go back to simple duck tape style hinges. Is there a better way to do this? Taped hinges are quite straight forward if the top edge of the wing and aileron are flush, with each other, but I've cut A v leading edge in the control surfaces for more movement. Again, what's the best way to cut the edges between the wing and hinge.



second question, how do you get a nice shiny coloured finish on fiberglass? I've seen a few different products, not sure which is the best...

1. Mix a coloured pigment into the resin, so you get a coloured finish
2. use gel coat, ths seems quite heavy per m/sq
3. Coat of primer, then spray paint

Any help on the above would be great...

Rich
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