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Ideas on how to build a 12' span model at 1.72 lbs?

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Ideas on how to build a 12' span model at 1.72 lbs?

Old 11-15-2005, 01:17 AM
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VTaerospace
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Default Ideas on how to build a 12' span model at 1.72 lbs?

I'm working an a dynamically scaled model of a Human Powered Aircraft (HPA) that I am doing as a senior design project. To get the proper scaling, I need the plane to have a 12' span and weigh 1.72 pounds. It doesn't have to fly fast so the loads won't be very big... parkflyer speed, about 10 mph.

Looking for ideas on how to build this light at this size. I know its doable; I'm just not quite sure how to go about it.
Old 11-15-2005, 01:34 AM
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Tall Paul
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

1.72 pounds?
How'd you get that number?
A CF rod outline and some CF ribs, Dacron covering, might get the weight that low..
Something like this..
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Old 11-15-2005, 02:13 AM
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

I got the weight via a dynamic scaling analysis from an early 80's NASA technical report.

I'm sure it possible b/c a group of MIT students did a 9' span model at 17 oz in 1979, so I'm sure with modern technology I should be able to do it. I'm just not sure how.

Link to an article on the MIT model: http://www.rcgroups.com/links/index.php?id=3383
Old 11-15-2005, 10:53 AM
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

The thing I noticed right off about the MIT plane was that it was a biplane. Two flying planes allow for cable bracing that eliminates the need for heavy spars. Monoplanes can also be cable braced. Google *Bleriot monoplane*. I also suggest rather heavy crates to transport the thing. Incidents that produce *hangar rash* on a conventional model, could destroy a model built at that weight.
Old 11-15-2005, 12:41 PM
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Tall Paul
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

What does your full-scale look like, if you're attempting to duplicate the look?
That helps in decisions about the structure.
Old 11-15-2005, 01:59 PM
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

I know this got it's start in Aerodynamics so I'll sort of continue it here.

You mentioned there that the aircraft was a 215 lb weight. If this is with the pilot included then your 1.72 lb figure is accurate. If it was for airframe only then you need to factor in the pilot's weight and convert THAT number down to your model. With a 150 lb pilot you're looking at a scale weight of365 x .008 = 2.92 which may just be doable with care and some poetic license in terms of the structure of the model compared to the prototype. Otherwise we are back to the idea that you need radio and motor of some form in that 1.72 lb figure so in reality you're looking at a 1 to 1.2 lb model structure.

I'm going to also reconsider my power option and suggest that with this weight an given that you're looking for at most an uphill glide to replicate the power levels of the actual human powered model you could probably go with something like a Norvel 061 for power or the equivalent electric motor and light Lipo pack.

Also you'll need to design the model structure to suit the size rather than doing a rib for rib and stringer for stringer scale replication.

There's no magic statement or standard set of model design rules that can be given to let someone with no background in superlight model design work suddenly produce such a model. A few years back a fellow named Leon Bennet specialized in very large scale rubber powered models in teh 60 inch span range and found that the structural needs vs weight factors required him to develop a whole new way of designing his models compared to standardly accepted methods. You're in the same boat with this project. Designing a scale model to this sort of weight limit is going to require a total engineering solution to figure out the flight loads and design a minimum weight structure to achieve those goals. It's far removed from just a simple scaling project now.
Old 11-15-2005, 04:46 PM
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

For those wanting to see the start of this topic it appears in the Aerodynamics section under "Anybody know anything about scaling?"

To Tall Paul (what does my plane look like):
There is a slightly out of date Catia model of our design on our website. www.aoe.vt.edu/design/hpa/



BMatthews (To your post in the Aerodynamics section)

Froude number is kind of like Reynolds number in the sense that it is one of those non-dimensional similarity parameters. It is (V^2)/ (L*g). It was originally developed for equating pressure coefficients on ship models and the shape of waves propagating from a ship and its model. Later it was discovered that for a flying aircraft model to have similar inertial and gravitational effects on maneuvering the Froude numbers had to be equal.

And yes weight has to scale by 1/(scale factor)^3. And in case you were wondering speed scales by 1/sqrt(scale factor).

BMatthews (To your post here)
The aircraft weight 215 lbs at takeoff.

Jim Thomerson (To post in aerodynamics section)
There is a VERY large riding arena that was just built here. I'm hoping to be able to fly it in there.
And Just FYI. The the 3.5 to 4 mins that the full scale plane will have to fly a top athelete can produce about 400 to 450 watts.
I'm not going to try to scale the prop. I am just going to try to match the scaled total power output and scaled thrust outputs in certain flight conditions.
Old 11-17-2005, 09:42 PM
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

I would look into cutting the whole thing out of light expanded bead styrofoam, and just leaving the covering or finish off. This might get you in the general area, and it might be worth cutting some foam to experiment and see how much the pieces weigh. That tail boom would probably have to be something like a balsa stick or an arrowshaft type object. A micro radio with micro servos would also help.
Old 11-18-2005, 08:28 AM
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da Rock
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

How?

With air of course. Or I could say, "with nothing", because "nothing" is always lighter than "something."

Kidding?

Nope....

You gotta have covering, right? So wherever you can, double the covering with "tubes" of it. You know how the para-sail chutes work? The air blows up a parachute that's just a bunch of "tubes" of silk, right.

So use some "tubes" wherever you can.

And then think about.... what do you think that parachute would weigh if it was sprayed with CA while inflated? Or sprayed with, say PolyUrethane or something.... sprayed with what? ? ? heck, it's your project, right.... so test some stuff....

Air filled tubes require airflow to work. And that's a limitation for some applications. But if they're "solidified"....

hmmmmmmm good challenge you've got there

let us know what you've worked out
Old 11-18-2005, 08:36 AM
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

hmmm

I wonder if a parasail propeller would be possible. After all, it's going to have to be brought up to speed, so some part of the design could be "blow up"......... You would have to have some stiff members, but seems the bulk of the blades could be blow up.

hmmmmmmmm
Old 11-20-2005, 05:46 PM
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Default RE: Ideas on how to build a 12' span model at 1.72 lbs?

The plane I am currently working on is called THE AIRHOPPER. It is a 1940 vintage. According to the author, it's 96" WS (during that time frame) was a total FREE FLIGHT aircraft and he claimed it to be 15oz, total weight.

I have almost completed my redesigning it, (with a lot of help from the very same people as previous to this post) so that it it flyable with RC. At this point, the overall weight is only 1.5 lbs It still has the servos, ect to be added.

bon chance

marwen

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