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Old Oct 07, 2012, 02:50 PM
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Be sure to post the video
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Old Oct 15, 2012, 04:51 PM
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Build update - 15-10-2012

No video yet... However the surfaces have been hinged, Servos added and wired up. Just need to Add some connectors to the 2 flight batteries. It has turned out a bit on the heavy side..... at 4.2kg AUW with a single 5000mah 4s flight battery...

The Centre of Gravity is causing me problems....pics..
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Old Oct 16, 2012, 06:33 AM
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Shame about the C of G problems. Only suggestion I have (which you probably don't want to hear now you've got this far) is to move the rudder-vator servos into wing, and run snakes / pushrods / closed loop to the surfaces. Might gain you a few centimetres on the CG.

Other than that, looking nice! Have you got the wing loading figures?

Have you used something like this for the CG position calc? http://adamone.rchomepage.com/cg_calc.htm

Cheers,
Andy
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Old Oct 16, 2012, 07:08 AM
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COG results from the Calculator

Quote:
Originally Posted by awmeade View Post
Shame about the C of G problems. Only suggestion I have (which you probably don't want to hear now you've got this far) is to move the rudder-vator servos into wing, and run snakes / pushrods / closed loop to the surfaces. Might gain you a few centimetres on the CG.

Other than that, looking nice! Have you got the wing loading figures?

Have you used something like this for the CG position calc? http://adamone.rchomepage.com/cg_calc.htm

Cheers,
Andy
Hi awmeade,

I did use the Calculator last night, and it said 150mm behind Leading edge, which is great, but the calculator doesn't take into account the Inverted V tail, was unsure what to enter in to the tail info boxes. Image below of the calculation and data input...
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Old Oct 16, 2012, 08:04 AM
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I think in those calculators you have to use the projected area, so not the actual chords x span, but what they would look like from above / below.

20 oz/ sq ft is pretty good, shouldn't need full throttle for cruising I reckon.
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Old Oct 17, 2012, 06:26 PM
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Quote:
Originally Posted by awmeade View Post
I think in those calculators you have to use the projected area, so not the actual chords x span, but what they would look like from above / below.

20 oz/ sq ft is pretty good, shouldn't need full throttle for cruising I reckon.
cheers for the info. My figures are wrong. I went out and bought a digital scales today to weig the plane including 2 x 5000mah flight batteries, the total weight of the plane is now just over 5kg, giving a wing loading of 24.9... Ish

This means that the plane is going to be too heavy to fly and I am unable to get it to balance even with all flight batteries up front.

Therefore I will be starting again from scratch and applying a lot of my lessons learnt to the next airframe. I am not going to bother attempting to fly this one.

anyone else reading this who has helped answer my questions along the way, your input has been very much appreciated and. Has helped me get this far. I will update the thread with progress of airframe number 2. But I expect it will be a while before any decent progress is made.

I have a list of lessons learnt that I will post when finalised...

rich
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Old Oct 18, 2012, 03:36 AM
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We've all been there rich, wether its weight or something crooked or hangar rash... One thing I've learned is the second time usually gets done in half the time. Keep plugging along.

Dennis
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Old Oct 18, 2012, 04:22 AM
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awww Rich, that's not good The wing loading still isn't bad - can you just confirm what power system was in there? If you're over about 70 watts per pound at that sort of loading, all should be fine. But as Dennis said, second one in half the time, and you might be happier with it?

Andy
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Old Oct 18, 2012, 07:41 AM
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This plane will work

Here are some suggestions to make this work and preserve the effort you have made so far.

This list is not in any particular order

1) Move main gear farther forward. The current distance aft of the target CG will make it hard to rotate and climb. Also it will move weight forward. Also if the legs are swept back, it makes more of the weight forward helping the CG issue. The wheel contact point should be slightly aft of the CG ( 1/2 to 3/4 inch ) when in climb angle, say about 7-10 deg of nose up.

2) It looks like the tail booms are Aluminium. If they are, replace them with slightly larger diameter Carbon tubes. Weigh the parts as you choose them.

3) Move the servos out of the tail and mount in the leading edge of the main wing.. Use Sullivan fine wire flexible pushrods, well secured.

4) Recess the motor forward as much as practical within the fuse. This will move weight forward.

5) Taper that ugly square end of the fuse. It should allow smooth airflow to the prop. It will be more important with the motor moved farther forward. You must remove the shading or blocking of the airflow to the prop and to reduce drag. Also cutting this down will remove a large amount of that ply "firewall" which is weight without function.

6) Use bigger but lighter wheels

7) Find/build a lighter set of landing gear with lightening holes if aluminum.

8) Check the structure in way of the motor and revise to remove material

9) Cut out the centre of that ply bulkhead forward of the batteries and slide the batteries farther forward.

10) Cut out centre areas of aft bulkheads so they are just an outline.

11) Make new tail surfaces that are lighter.

12) If making a new design make span longer, root chord larger, and sweep back leading edge, keeping the trailing edge straight. Done correctly, this will move the center of area aft, making it easier to balance with the same layout and structures. Also the center of lift moves aft as speed increases with a swept leading edge. This means the plane can have a wider speed range without causing the plane to climb as much with increasing speeds.

I would do them in about this order

Cut forward bulkhead, move motor forward, cut down and taper the aft end of the fuse, lighter main gear moved forward. Check balance and continue.

These steps would be a lot less work than starting from scratch. They are all doable without throwing anything away except excess weight and drag.

Let us know how these steps work out.

Jim
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Old Oct 18, 2012, 11:58 AM
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Very nice Jim
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Old Oct 24, 2012, 09:31 AM
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Quote:
Originally Posted by awmeade View Post
awww Rich, that's not good The wing loading still isn't bad - can you just confirm what power system was in there? If you're over about 70 watts per pound at that sort of loading, all should be fine. But as Dennis said, second one in half the time, and you might be happier with it?

Andy
Cheers for the post, I believe it is around 89 Watts per pound, but will now need to go back and double check.

The AUW is 11.18 pounds. And am unsure of the Watts. Think it's around 1000Watts Per Pound. So the above should be okay!
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Old Oct 24, 2012, 09:31 AM
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Thanks for the Help!

Quote:
Originally Posted by small_rcer View Post
Here are some suggestions to make this work and preserve the effort you have made so far.

This list is not in any particular order

1) Move main gear farther forward. The current distance aft of the target CG will make it hard to rotate and climb. Also it will move weight forward. Also if the legs are swept back, it makes more of the weight forward helping the CG issue. The wheel contact point should be slightly aft of the CG ( 1/2 to 3/4 inch ) when in climb angle, say about 7-10 deg of nose up.

2) It looks like the tail booms are Aluminium. If they are, replace them with slightly larger diameter Carbon tubes. Weigh the parts as you choose them.

3) Move the servos out of the tail and mount in the leading edge of the main wing.. Use Sullivan fine wire flexible pushrods, well secured.

4) Recess the motor forward as much as practical within the fuse. This will move weight forward.

5) Taper that ugly square end of the fuse. It should allow smooth airflow to the prop. It will be more important with the motor moved farther forward. You must remove the shading or blocking of the airflow to the prop and to reduce drag. Also cutting this down will remove a large amount of that ply "firewall" which is weight without function.

6) Use bigger but lighter wheels

7) Find/build a lighter set of landing gear with lightening holes if aluminum.

8) Check the structure in way of the motor and revise to remove material

9) Cut out the centre of that ply bulkhead forward of the batteries and slide the batteries farther forward.

10) Cut out centre areas of aft bulkheads so they are just an outline.

11) Make new tail surfaces that are lighter.

12) If making a new design make span longer, root chord larger, and sweep back leading edge, keeping the trailing edge straight. Done correctly, this will move the center of area aft, making it easier to balance with the same layout and structures. Also the center of lift moves aft as speed increases with a swept leading edge. This means the plane can have a wider speed range without causing the plane to climb as much with increasing speeds.

I would do them in about this order

Cut forward bulkhead, move motor forward, cut down and taper the aft end of the fuse, lighter main gear moved forward. Check balance and continue.

These steps would be a lot less work than starting from scratch. They are all doable without throwing anything away except excess weight and drag.

Let us know how these steps work out.

Jim
For some reason i didnt pick up the above... It's most useful, And i am going to follow your advice point for point... Cheers again!

I will post an update shortly..

rich
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Old Oct 24, 2012, 10:57 AM
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glad you are persevering Rich!
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Old Oct 25, 2012, 03:01 PM
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Update...and a few q's

Having had some more time to read through the help from Jim, I have looked at each point and am planning what to do...my comments in italic...

1) Move main gear farther forward. The current distance aft of the target CG will make it hard to rotate and climb. Also it will move weight forward. Also if the legs are swept back, it makes more of the weight forward helping the CG issue. The wheel contact point should be slightly aft of the CG ( 1/2 to 3/4 inch ) when in climb angle, say about 7-10 deg of nose up.
Main gear has been glued in pretty well, so am going to rip this out and see how much weight i can save. The GRP reinforced main gear is quite heavy at 200g, excl wheels and axles. So may look at trying to lighten it somehow. It looks like it would take a good knowck though and bounce back to shape. Alloy gear tends to bend quite a lot, having said that, I am seeking alloy gear weighing less than 100g for the frame.

2) It looks like the tail booms are Aluminium. If they are, replace them with slightly larger diameter Carbon tubes. Weigh the parts as you choose them.
The current weight of each boom is 133g. 1000m long, 16mm diameter. I identified the same boom made form Carbon fiber here - I phoned the company up and they say a meter weighs 122g. So a weight saving of 11g per boom, 22g in total

3) Move the servos out of the tail and mount in the leading edge of the main wing.. Use Sullivan fine wire flexible pushrods, well secured.
This will save around 38g at the tail, as each servo weighs 19g. Ideally i need to be able to break the aircraft down for transport. I wil almost certainly look at the practicalities o this, but will be later on in the list.

4) Recess the motor forward as much as practical within the fuse. This will move weight forward.
I am going to taper the back part of the fuse, and move the motor forward, so the distance between trailing edge of wing and prop is around 1 inch. is that too close?

5) Taper that ugly square end of the fuse. It should allow smooth airflow to the prop. It will be more important with the motor moved farther forward. You must remove the shading or blocking of the airflow to the prop and to reduce drag. Also cutting this down will remove a large amount of that ply "firewall" which is weight without function.
agrees, I will do this as part of the above point 4

6) Use bigger but lighter wheels.
I have just weighed and measured the wheels - they are 70mm diameter and weigh 20g Each, I am finding it difficult to source wheels of equivalent size at a lighter weight.

7) Find/build a lighter set of landing gear with lightening holes if aluminum.
I have weighed my landing gear prior to installing on the aircraft, it weighs 200g excl wheels and axles. It was the lightest i could find at the time for a 4.5kg Aircraft. I have looked around and found a set on hobbyking which are 84g for a pair of alloy legs, but they dont look strong enough for the plane. I have also found a carbon fiber set designed for 28cc planes (unsure of weight of an average 28cc plane) here. at 107g, they look like a contender, unsure of strength though

8) Check the structure in way of the motor and revise to remove material
I will chop out a large section of aft fuse to remove weight

9) Cut out the centre of that ply bulkhead forward of the batteries and slide the batteries farther forward.
Already complete, I have also extended fuse by 70mm ish, i did this prior to reading your post, and will probably undo the change if the other points enable me to balance the plane with a single lipo. Ideally i'd like to maiden as light as possible with a single 5000mah 4s lipo

10) Cut out centre areas of aft bulkheads so they are just an outline.
There are only 2 bulkheads on plane, one at front, and one at back where motor is stuck onto

11) Make new tail surfaces that are lighter.
Right, this is an interesting one. Original balsa rib construction was too fragile, and broek all the time when i so much as touched it. Mark 2 was made from EPS foam, reinforced with 135 g/sq/mt glass all over, but came out at 450g, 500g with servos. I have since remade a mk3 tail, only used thick glass on join, and to line the circles where it slides onto booms, total weight with servos is no 357g. some more guidance on this point would be great if possible..

12) If making a new design make span longer, root chord larger, and sweep back leading edge, keeping the trailing edge straight. Done correctly, this will move the center of area aft, making it easier to balance with the same layout and structures. Also the center of lift moves aft as speed increases with a swept leading edge. This means the plane can have a wider speed range without causing the plane to climb as much with increasing speeds.
I will certainly increase span for next one, to 2.4metres, and possibly keep chord the same, climbing at different speeds is not so much of an issue as the autopilot takes care of that, would you recommend using a clark Y again? I have been recommended kfm airfoils, unsure as to there performance, or how much more difficult they are to cut. I would like to do swept leading edge, but dont think i could cut those..

I'll begin working on this over the weekend, and see how much weight i can lose...

Currently she weights 5093g with 2 5000mah lipos and 1000mah lipo for rx!!

this is going to be a challenge!

Thanks again
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Old Oct 25, 2012, 03:53 PM
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Current weights - in pictures on scales

Quite surprised at wings.. outer wingpanels weight over 1kg - i'm sure this could be made lighter.

This does include servos at 40g each. Which could be reduced to 20g servos
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Last edited by richie967; Oct 25, 2012 at 04:22 PM.
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