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Old 15th January 2013, 05:36 PM   #161
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New developments have allowed me to change my HPH design so the two pilots are now under both wing-sets instead of between them. This gives better balance and allows me to choose whatever distance between the wing-sets I want. I'm wondering how much the distance between the wing-sets should be so that the wake from the top set doesn't interfere with the bottom too much. Any suggestions?
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Old 15th January 2013, 06:04 PM   #162
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The lower c.o.g. sounds like a good idea, as per stability.

As per the distance between counter rotating airfoils?
I'd be guessing as much distance as the structure allows.

Yet, the altitude requirement for the prize?

Is this taken from the tallest point of the craft?
Or from the pilots?

That changes everything.
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Old 15th January 2013, 06:25 PM   #163
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Btw, have I mentioned lately that I don't know anything, and I just hang out here like an aging groupie with hairy legs?

Sigh.

It's true.
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Old 15th January 2013, 07:17 PM   #164
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Originally Posted by quarky View Post
The lower c.o.g. sounds like a good idea, as per stability.

As per the distance between counter rotating airfoils?
I'd be guessing as much distance as the structure allows.

Yet, the altitude requirement for the prize?

Is this taken from the tallest point of the craft?
Or from the pilots?

That changes everything.
From the rules . . .

http://www.vtol.org/awards-and-conte...pter/hph-rules
4.4.1 The flight requirements shall consist of hovering for one minute while maintaining flight within a 10-meter square. During this time, the lowest part of the machine shall exceed momentarily 3 meters above the ground.
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Old 15th January 2013, 07:18 PM   #165
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Originally Posted by quarky View Post
Btw, have I mentioned lately that I don't know anything, and I just hang out here like an aging groupie with hairy legs?

Sigh.

It's true.
I used to be a rock drummer. Drummers are people that hang around with musicians.
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Old 15th January 2013, 07:24 PM   #166
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Originally Posted by ynot View Post
I used to be a rock drummer. Drummers are people that hang around with musicians.
Thanks for sparing me the read.

You're still a rock drummer, though.

Some stuff, you just can't dodge.

I've been looking for a drummer, for my new band hpv.
I think it could get off the ground.
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Old 18th January 2013, 11:25 AM   #167
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Could the structural integrity of a thin walled aluminium tube be strengthened by filling it with compressed air?
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Old 18th January 2013, 01:18 PM   #168
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I think you might improve its buckling behavior in compression. I don't see how it could do much for bending or torque loads.
The Gossamer Condor solved this by cutting disks of foam with a sharpened piece of tubing, and pushing them down inside the spar at intervals. Since the disks were cut with the same tubing, they were a pretty snug fit.
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Old 18th January 2013, 01:26 PM   #169
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Originally Posted by TjW View Post
I think you might improve its buckling behavior in compression. I don't see how it could do much for bending or torque loads.
The Gossamer Condor solved this by cutting disks of foam with a sharpened piece of tubing, and pushing them down inside the spar at intervals. Since the disks were cut with the same tubing, they were a pretty snug fit.
Didnít know they did that. Had thought of filling the whole tube with styrene or expanding foam (or bit of both).
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Old 18th January 2013, 03:20 PM   #170
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It seems as though, without the highest tech carbon fiber structures, it's a no-go.

I would love to be wrong.
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Old 18th January 2013, 04:13 PM   #171
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Originally Posted by ynot View Post
Could the structural integrity of a thin walled aluminium tube be strengthened by filling it with compressed air?
Yes. The Atlas rocket has no internal structural members, relying instead on the strength of its' fuel and oxidizer tanks with internal pressure. The skin thickness is about that of a dime. Without pressure the tanks will collapse under their own weight, with pressure the tanks will stand compression loads of over 100,000 lbs.

Whether the increased strength you will gain will justify the additional weight you will have to work out for yourself. I suspect there are more efficient ways to achieve the required strength.
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Old 18th January 2013, 06:23 PM   #172
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Originally Posted by Pope130 View Post
Yes. The Atlas rocket has no internal structural members, relying instead on the strength of its' fuel and oxidizer tanks with internal pressure. The skin thickness is about that of a dime. Without pressure the tanks will collapse under their own weight, with pressure the tanks will stand compression loads of over 100,000 lbs.

Whether the increased strength you will gain will justify the additional weight you will have to work out for yourself. I suspect there are more efficient ways to achieve the required strength.
Wouldn’t have thought the compressed air would add too much additional weight but there would also be end caps and a valve. Would be an easy and interesting test to do to see how much strength would be gained and how much weight added.
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Old 18th January 2013, 07:21 PM   #173
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My experience with expanding foam is a little out of date. But the difficulty I had was in getting just the right amount in so that it would just fill when it was expanded. Otherwise, it's denser than its nameplate density. If you consider the weight of 2 lb ft3foam inside, say, a 2.5 inch x .035 aluminum tube, it's a significant fraction of the weight of the tube. For my application, I decided putting that weight into aluminum made more sense.
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Old 18th January 2013, 09:37 PM   #174
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Originally Posted by TjW View Post
My experience with expanding foam is a little out of date. But the difficulty I had was in getting just the right amount in so that it would just fill when it was expanded. Otherwise, it's denser than its nameplate density. If you consider the weight of 2 lb ft3foam inside, say, a 2.5 inch x .035 aluminum tube, it's a significant fraction of the weight of the tube. For my application, I decided putting that weight into aluminum made more sense.
They have some that doesn't expand much after it comes out of the can, advertized as "for windows and doors".
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Old 18th January 2013, 10:40 PM   #175
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Yeah, I've used that for windows and doors. The thing is, that stuff is kind of soft and rubbery. I'd want something that cures rigid to keep a thin wall tube from buckling. There are two-part urethane foams that do that.
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Old 19th January 2013, 12:09 AM   #176
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I've had quite a bit of experience with two part urethane as a friend uses it to manufacture walls for industrial fridges and I often help him. Easy to over-fill the tube and let it expand out holes at either end. Hardest thing would be to get the mix into the centre of the tube to avoid air locks. It's all just random thoughts at this stage anyway. I'm thinking (possibly naively) that I might be able to build wings with no spar by using pre-stressing and cable staying. Don't have anything more substantial than ideas and small scale modelling for this at this stage.
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Old 19th January 2013, 06:57 AM   #177
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I'm a little confused by what you mean by "pre-stressing'. I understand how it's used in concrete construction, but while concrete boats might work, I have some doubts about concrete helicopters.
Do you mean monocoque or semi-monococque, where the loads are all taken by the skin?
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Old 19th January 2013, 12:42 PM   #178
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Originally Posted by TjW View Post
I'm a little confused by what you mean by "pre-stressing'. I understand how it's used in concrete construction, but while concrete boats might work, I have some doubts about concrete helicopters.
Do you mean monocoque or semi-monococque, where the loads are all taken by the skin?
To be more accurate I should be saying post-tensioning or post-compressing rather than pre-stressing but the end effect is the essentially same. If you understand how the principle works for concrete (which I’m sure you do) then apply it to a “beam” (wing) of solid styrene foam.

I would construct the wing from two halves (flat-lengthwise) glued together with lines running down the length between the halves like rebar in concrete. Plates would cover either end of the wing and the lines would be tightened to act as “tendons” and pull the plates together compressing the wing. I can’t see any reason why this shouldn’t work for styrene as well as it does for concrete. Do you see any real or potential flaw?

I'm about to do some smaller scale testing to see if I'm deluded or not.
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Old 19th January 2013, 01:09 PM   #179
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Originally Posted by ynot View Post
To be more accurate I should be saying post-tensioning or post-compressing rather than pre-stressing but the end effect is the essentially same. If you understand how the principle works for concrete (which Iím sure you do) then apply it to a ďbeamĒ (wing) of solid styrene foam.

I would construct the wing from two halves (flat-lengthwise) glued together with lines running down the length between the halves like rebar in concrete. Plates would cover either end of the wing and the lines would be tightened to act as ďtendonsĒ and pull the plates together compressing the wing. I canít see any reason why this shouldnít work for styrene as well as it does for concrete. Do you see any real or potential flaw?

I'm about to do some smaller scale testing to see if I'm deluded or not.
I think solid foam will be heavy at the larger scales required to get a low disc loading. It's the square-cube thing: if you double the linear dimension of your model, it has eight times the volume.

Running a tension member down the middle is not going to be the most effective method of resisting bending moment. You want the tension member to be as far away from the compressive member as possible.
Ideally, the tension member would be on the bottom surface.
Some R/C airplanes are built this way-- hotwire an airfoil, and run a piece of strapping tape along the bottom, relying on the foam's compression strength.

But I don't think it will scale up to a lightweight aircraft.
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Old 19th January 2013, 01:28 PM   #180
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I think solid styrene would be lighter than any spar I could use. I've handled large, long pieces of styrene and they are surprisingly light.

This is how I imagine the whole thing with cable-staying.

prestresswing.jpg
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Old 19th January 2013, 01:48 PM   #181
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Originally Posted by TjW View Post
Running a tension member down the middle is not going to be the most effective method of resisting bending moment. You want the tension member to be as far away from the compressive member as possible.
Ideally, the tension member would be on the bottom surface.
Some R/C airplanes are built this way-- hotwire an airfoil, and run a piece of strapping tape along the bottom, relying on the foam's compression strength.
As I understand it strength also comes from the compression. It’s like picking up several books stacked horizontally. To be able to pick them up you have to squeeze the end books hard together otherwise they will all slip apart.

In pre-stressing the tension members don’t take-up the tension, they pre-apply it. The more you stretch or compress something the “stiffer” it becomes. Pre-stressing gains “stiffness” strength from equal and opposite forces of both stretching and compressing (that‘s how I understand it).
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Old 19th January 2013, 03:09 PM   #182
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Originally Posted by ynot View Post
I think solid styrene would be lighter than any spar I could use. I've handled large, long pieces of styrene and they are surprisingly light.

This is how I imagine the whole thing with cable-staying.

Attachment 27483
Using that scheme , you don't really need the line down the middle. The external bracing is taking the tension loads, and the foam would only be in compression.
If the foam can take the bending loads between supports caused by lift, it could work.

You might want to consider the compressive strength of the foam. The extruded wall foam is typically about 25 lbs/ in2. Dow does make some that goes up to 100 psi -- though that's a denser foam.
Also, this spec is at 10% compression-- that would be three feet out of a 30 foot blade.
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Old 19th January 2013, 03:20 PM   #183
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Originally Posted by TjW View Post
Using that scheme , you don't really need the line down the middle. The external bracing is taking the tension loads, and the foam would only be in compression.
If the foam can take the bending loads between supports caused by lift, it could work.

You might want to consider the compressive strength of the foam. The extruded wall foam is typically about 25 lbs/ in2. Dow does make some that goes up to 100 psi -- though that's a denser foam.
Also, this spec is at 10% compression-- that would be three feet out of a 30 foot blade.
To some degree if the cable-staying was under tension (which it would be) it would provide some compression to the foam so as you say “it could work” without internal tension lines. For very little (almost neglishable) extra weight however internal tension lines would provide a lot more stiffness evenly to the whole wing length and provide greater compression. Without internal lines I would be worried about the areas of wing between the spars and the wing ends.

ETA - There would be several lines down the middle (two at least) and they might be angled to the tip to provide triangular strength. The whole wing would probably be angled to the tip anyway.
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Old 19th January 2013, 03:38 PM   #184
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Originally Posted by TjW View Post
Us
You might want to consider the compressive strength of the foam. The extruded wall foam is typically about 25 lbs/ in2. Dow does make some that goes up to 100 psi -- though that's a denser foam.
Also, this spec is at 10% compression-- that would be three feet out of a 30 foot blade.
Am thinking of just using the commonďbig bubbleĒ foam because I think itís the lightest and would do the job.
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Old 19th January 2013, 10:46 PM   #185
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Where's Bucky Fuller when you need him?

Occasionally, it's not even a box one needs to think outside of.

(Dang. I just ended a sentence with a preposition.)

I need to turn it into a proposition.
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Old 20th January 2013, 01:08 PM   #186
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Have been thinking of another possible way of overcoming the heavy spar problem. Use smaller diameter and lighter spar tubes than would normally be possible and give them strength by tying them together with lines like a spider’s web. The spars would have a slight downward angle so that when the wings try to lift them up the lines take the strain. Don’t know how much downward angle would be required and how much it would effect the efficiency of the wings. Hope this quick pic makes it clearer (only drew one wing).

webwing.jpg
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Old 20th January 2013, 03:13 PM   #187
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Here comes a fool rushing in

Give thought to spars with higher stiffness than a tubular cross section bestows. I'm thinking of tubes with, say, twin-ogival or star-shaped cross sections: () or *. Spars like these could be formed by drawing round-cross-section tubes through a series of dies. This would avoid adding weight while (I think) increasing stiffness in at least some directions. I suggest this as a way of reducing reliance on guy-wires, which add drag.

Drawing aluminum tubes through a series of forming dies? Why, any garage inventor can do it! Shouldn't increase costs more than 200% or 300%! You're welcome. I'm glad to help.
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Old 20th January 2013, 03:32 PM   #188
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Originally Posted by sackett View Post
Give thought to spars with higher stiffness than a tubular cross section bestows. I'm thinking of tubes with, say, twin-ogival or star-shaped cross sections: () or *. Spars like these could be formed by drawing round-cross-section tubes through a series of dies. This would avoid adding weight while (I think) increasing stiffness in at least some directions. I suggest this as a way of reducing reliance on guy-wires, which add drag.

Drawing aluminum tubes through a series of forming dies? Why, any garage inventor can do it! Shouldn't increase costs more than 200% or 300%! You're welcome. I'm glad to help.
You make it all sound so easy. The guy-wires of the web-wing design I just posted would pretty much be inline with the direction of rotation so wouldn't add much drag at all. They would also weigh less than one shoe of one pilot. If needed to be to fly my pilots would be barefoot and almost naked.

Thinks . . . two naked female pilots . . . Ynot increases sponsorship fee . . .
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Old 20th January 2013, 03:37 PM   #189
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Originally Posted by ynot View Post
You make it all sound so easy. The guy-wires of the web-wing design I just posted would virtually be inline with the direction of rotation so wouldn't add much drag at all. They would also weigh less than one shoe of one pilot. If needed to fly my pilots would be barefoot and almost naked.

Thinks . . . two naked female pilots . . . Ynot increases sponsorship fee . . .
Yeah, but wouldn't they need to be bald?
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Old 20th January 2013, 03:38 PM   #190
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Originally Posted by quarky View Post
Yeah, but wouldn't they need to be bald?
A couple of Brazilian waxes wouldn't cost much
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Old 21st January 2013, 07:28 AM   #191
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Originally Posted by ynot View Post
Have been thinking of another possible way of overcoming the heavy spar problem. Use smaller diameter and lighter spar tubes than would normally be possible and give them strength by tying them together with lines like a spiderís web. The spars would have a slight downward angle so that when the wings try to lift them up the lines take the strain. Donít know how much downward angle would be required and how much it would effect the efficiency of the wings. Hope this quick pic makes it clearer (only drew one wing).

Attachment 27486
I'm not sure I understand. If you transfer load from one spar to the other, you haven't made the spar stronger, you've just redistributed the load.

Transferring bending load with tension members at small angles puts a large compressive force on the compression member, and requires a lot of tension in the tension member.
I'm sure you're familiar with the old chestnut of someone trying to pull an engine by suspending it from an overhead cable. If the cable has only a little sag, it's easy to break it, because the angles at the end are very shallow. If it sags a lot, it can work, because the angles at the ends are steeper.

The length of the lower structure on the Gossamer aircraft was sized so that the wire bracing wouldn't collapse the spar in compression. Shorter would have been better aerodynamically, longer was better structurally.
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Old 21st January 2013, 03:02 PM   #192
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Originally Posted by TjW View Post
I'm not sure I understand. If you transfer load from one spar to the other, you haven't made the spar stronger, you've just redistributed the load.
Yes thatís more what I meant to say. Sorry I worded it so poorly. The ďspiderĒ lines spread the load sideways and in a complete circle. The load isnít just transferred from one spar to another itís also transferred to the opposite side of every spar so every spar experiences equal and opposite sideways pulls in opposing directions. The spar gets compressed along it's length.
Originally Posted by TjW View Post
Transferring bending load with tension members at small angles puts a large compressive force on the compression member, and requires a lot of tension in the tension member.
Thatís why this method would require many circles of ďspiderĒ lines so that the forces are spread evenly at intervals along the length of each spar. Length-wise cable staying (as explained earlier) might have to be used as well. Essentially this method creates an inverted cone shape which is quite a robust structure.
Originally Posted by TjW View Post
I'm sure you're familiar with the old chestnut of someone trying to pull an engine by suspending it from an overhead cable. If the cable has only a little sag, it's easy to break it, because the angles at the end are very shallow. If it sags a lot, it can work, because the angles at the ends are steeper.
The length of the lower structure on the Gossamer aircraft was sized so that the wire bracing wouldn't collapse the spar in compression. Shorter would have been better aerodynamically, longer was better structurally.
Are you thinking that the angle required would have a too negative effect on the efficiency of the wings? If so then the wings may be able to be designed so they donít exactly follow the angle of the spars.

It works well at model size but that doesnít mean it would work as well at full size.
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Old 21st January 2013, 07:51 PM   #193
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Just about anything can be made to fly at small scale. I've recently been playing with making hand launch gliders out ouf energy drink cans.
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Old 21st January 2013, 08:20 PM   #194
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Originally Posted by TjW View Post
Just about anything can be made to fly at small scale. I've recently been playing with making hand launch gliders out ouf energy drink cans.
We used to gather dead butterflies and bring them up an observation tower, and release them. If they died with the wings out fairly straight, these dead butterflies would glide down, taking many minutes on a 150' tower, and looking exactly like live ones on the way.
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Old 21st January 2013, 09:23 PM   #195
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Originally Posted by TjW View Post
Just about anything can be made to fly at small scale. I've recently been playing with making hand launch gliders out ouf energy drink cans.
By "works well" I didn't mean I made a flying model. I was testing structural integrity at different angles and found quite a shallow angle could be used. Too little angle however and it turns inside out like an umbrella in a strong wind. To have a chance of working HPH designs need to be engineered at the knife-edge of structural failure.
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Old 21st January 2013, 09:59 PM   #196
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Originally Posted by ynot View Post
By "works well" I didn't mean I made a flying model. I was testing structural integrity at different angles and found quite a shallow angle could be used. Too little angle however and it turns inside out like an umbrella in a strong wind. To have a chance of working HPH designs need to be engineered at the knife-edge of structural failure.
.
Seems right.
Pity is, we can't tell where that edge is, exactly, without wrecking lots of stuff.

Computers can go a long way. Maybe all the way?
Not sure. Always seems like you discover a flaw in the process; human error, even.

I like the spider-web better than the pre-stressed foam filled blade concept.
Pre-stressed concrete beams need some verticle depth, to be very effective.
Much like a rafter. In a flatter configuration, you'd get little added strength.

Cool thing is, the tension lines can be so small these days.
I suspect their drag compensates for the equivalent gravity drag of beefier wings.

Where's Dan?

His approach was different, though, I suspect, it too would be dependent on the strongest, lightest possible structure.

Gamera is freaking huge, and weighs less than 100 pounds.
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Old 22nd January 2013, 01:04 AM   #197
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The spider lines would also run through the wings and help to keep them in position and attack angle. Not sure I'm right but I think rotating wings might work even better with a slight downward angle to their tip to compensate for air being centrifugally thrown out from them. Think spider-web is my favorite design at this stage but there are a few options in the bag and there will no doubt be more before I get to the stage of building and testing actual wings. At present I'm building a full size working test-rig for the transmission system.
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Old 23rd January 2013, 12:28 AM   #198
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The Atlas team are going to have a shot at the prize in few days. . . .

"On January 25th we will be making an attempt at a Sikorsky Prize flight! We feel that with many of the improvements to-date and the few incremental steps remaining we will be ready to make prize-flight attempts in the early afternoon. All are welcome to come watch the dayís testing, from 9am-5pm at the Ontario Soccer Centre in Vaughan."

http://www.aerovelo.com/2013/01/21/j...-january-25th/
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Old 25th January 2013, 12:06 PM   #199
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I’m following the Atlas teams attempt at winning the Sikorsky Prize on Twitter - @AeroVelo

So far it seems they have had a - “Successful flight with canards“.

In a second flight had - “Another successful flight, rotors are looking balanced, just over a meter off the ground”.

At present the - “Team is taking a quick pizza break thanks to the AHS“.

Good luck to them.

ETA - Team Gamera are also following the attempt - "Don't let your pilots eat too much! Good luck today!"
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Old 25th January 2013, 03:12 PM   #200
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Latest Team Atlas Tweet - “Testing summary: Flight 7: Todd has an excellent 30 second flight, slowly bringing it up to 5'. Rotors and balanced and not close to lines”.

Unless they have a lot in reserve they’re only half way there height and time wise. And they’re the “easiest” halves.

Oh dear it seems gravity is winning - “Flight 8: Todd does a higher power start aiming for 2m. Rotors quickly go out of balance and flight is blown down“.

ETA - It’s all over and the prize has yet to be won - “Flight 9: Not safe to go for an AHS Sikorsky prize attempt. One last flight to play with controls. Strange results, need to do more thinking”.
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