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Bob H

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Jun 9, 2022
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Back in 1977, I worked composites at Douglas Aircraft in Long Beach, CA and McReady's guys working on the Gossamer Condor and Albatross came by and asked if I could shave an ounce of weight off the pedal sprocket by making it from composites. I told them the effort wasn't worth the results but they insisted.They had a standard aluminum bike pedal sprocket so I decided to machine out the hub and retain the toothed ring and make a composite hub and heat shrink the ring onto the hub. No one had ever joined alum to graphite as an interference fit before so we didn't know whether the fit would carry the pedaling torque. I designed the fit to be 1 mil per inch of hub dia interference and at 250F, the parts would expand and slip fit over each other. Seemed good on paper so we went forward and built the parts. My shop techs loved the challenge and we took the new sprocket to a workbench, bolted it down and applied 170 ft-lbs of torque to see if there would be slippage.
Looked great so we sent the sprocket to McReady and it actually saved 2.25 oz over the all-aluminum one. I thought it was trivial but his guys said it was a major weight savings. The sprocket went to England/France and Brian Allen pedaled it across the Channel. The whole vehicle weighed 70 lbs. In all my years building compos2020-12-31 Gossamer Albatross Gear 00001.jpg ite flight structure, this task was the most weight critical.
 

John.Roo

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That makes a lot of sense.

Kenellopoulos pedalled nearly 4 hours using 240 watts.

240 W for 4 hours is great achievement 👍
Unfortunatelly this is far from "standard human" / "standard pilot" performance.

I would love to see solar panels as help, but I am affraid that this technology still needs few improvements...

Take 250-350 W motor for electric bicycle, strip down all you don´t need and you save a bit of weight. 1 kWh of energy = approx 5 kg.
1 kWh of energy in battery will give you 200 W for 4 hours (1x takeoff + I prefer to keep some energy in battery after landing).
I personally prefer to use even more energy (= bigger battery) and do not stress pilot with combination of concentration necessary for airplane control + heavy physical load ;)
 

Sraight'nlevel

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240 W for 4 hours is great achievement 👍
Unfortunatelly this is far from "standard human" / "standard pilot" performance.

I would love to see solar panels as help, but I am affraid that this technology still needs few improvements...

Take 250-350 W motor for electric bicycle, strip down all you don´t need and you save a bit of weight. 1 kWh of energy = approx 5 kg.
1 kWh of energy in battery will give you 200 W for 4 hours (1x takeoff + I prefer to keep some energy in battery after landing).
I personally prefer to use even more energy (= bigger battery) and do not stress pilot with combination of concentration necessary for airplane control + heavy physical load ;)

That is where you need a better design...way better.
 

John.Roo

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That is where you need a better design...way better.
I agree just.... I am not sure what "better" design means 🤔
Longer wings? Higher aspect ratio? Oscilating wings?

In my personal opinion.... I prefer to use actually available materials and technologies. And basic weight saving rule = keep it as simple as possible ;)
 

nerobro

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How did this become about "average human being" No, your general off the street person, even "a good and healthy example" is ever going to have enough power to do this. You need a elite athlete, or at least "exceptional example" to make this work.

This was about winning prizes right?

Your average human absolutely can not do it. Trying to plan for that turns into "add more power somehow" which.. at that point, why not just.. add enough power that you don't need to scrape 50-100-150w from the person on board, and let them burn calories flying the plane. It's silly.
 

henryk

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Last edited:

Sraight'nlevel

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-who can do it in shorter time ???
(You or I ...)


PS=dr Wolf on His hang glider "ZETA77" was perform horisontal fly in
"oscillating " mode...

=I was examinated His "spring"harneese=very low load,circa 0.5 m altitude
of pilot oscillating ,not tired!
Anything that small, if it cannot be made in 18 years, is not viable.

Furtehrmore all pilots hate oscillations.

You see pilot has to stand up...that quadrubles the drag...compared to tight prone positioned cycler.
 

Sraight'nlevel

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How did this become about "average human being" No, your general off the street person, even "a good and healthy example" is ever going to have enough power to do this. You need a elite athlete, or at least "exceptional example" to make this work.

This was about winning prizes right?

Your average human absolutely can not do it. Trying to plan for that turns into "add more power somehow" which.. at that point, why not just.. add enough power that you don't need to scrape 50-100-150w from the person on board, and let them burn calories flying the plane. It's silly.
Yes you need a healthy cyclist who knows how to fly.
 
Last edited:

DennisK

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Back in 1977, I worked composites at Douglas Aircraft in Long Beach, CA and McReady's guys working on the Gossamer Condor and Albatross came by and asked if I could shave an ounce of weight off the pedal sprocket by making it from composites.
View attachment 127236
What sort of fiber orientation did you use on that? Just stacked up sheets of woven fabric with various rotations? Or is there some trick to make sure all fibers in the narrowest points between the holes are oriented radially? It also looks like those skinny spots are not all the same width. Is that just an optical illusion?

Designing round things always gives me a hard time, and I end up going back to metal because so many of the fibers get cut short and don't contribute any useful strength.
 

Sraight'nlevel

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There are two Kremers left. Marathon, 26 miles in under an hour. And sport, 3x500m triangular course, twice in under 7 min total. The really fun bit is the minimum wind speed of 11mph. It also needs to pack in and out of a 26' container.

With
P = thrust power in watts
m = mass in kg
g = metric gravity
L/D = lift to drag ratio
V = speed in m/s (1 m/s = 2.3 mph)

V = (P * L/D) / (mg)

the internet tells me that top athletes can manage 400W for an hour. 100kg may be total weight. We need a pretty good L/D for any kind of speed.
That means a lot of span. McCready pointed out that at low speeds, the drag from wires etc isn't great and allows more span in the very limited weight budget.
Here is a notion that the second is muscle powered plane that can be flown in normal weather conditions.

 

Jay Kempf

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Tough corner of the performance envelope basically the opposite corner to the altitude Mach stall cruise corner.

Drag and weight are king. Drag is the tougher part. For all of aviation light weight meant low drag: flying wires, fabric non laminar skins, etc... Then new materials like carbon fiber came in and we have been learning to optimize using them for decades now. The only way to reduce drag is to reduce intersection drag, fair everything, and try for any laminar flow you can. At low Re tripping laminar flow is troublesome but you can get away with a bunch of compromises like trip strips. So it seems to me that you have to look at projects like eta and Diana. VERY high AR and cantilevered flexible wings that are optimize for torsion. Helios is sorta in the correct direction but much higher AR without the solar weight fraction. The wings would have to have wheels so they could start moving without dragging on the ground. Very flexible structures are tricky to design and build and can then have huge bands of destructive harmonics to work around so very fragile.

Somewhere in that direction would/could get a longer endurance or close to continuous or slightly climbing flight on current best human output. Tough problem.

That oscillating platform has nowhere near enough wing area or AR. It also has way too much drag and would have to be towed to starting position. There is no way to make a stiff enough wing big enough and cantilevered to go in that direction. Air is 830 times less dense than water approximately. The oscillating thing works well in water with hydrofoils.

Much easier problem to solve with solar and electric and no pink squishy propulsion.
 

henryk

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Somewhere in that direction would/could get a longer endurance or close to continuous or slightly climbing flight on current best human output. Tough problem.

=Vladimir Toporov was able to slightly climbing flight on His GIORDANO 2
4-wings,legs powered ornithopter !

(main problem was controlability in active/passive phases !)

 

Sraight'nlevel

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Nov 4, 2021
Messages
366
Tough corner of the performance envelope basically the opposite corner to the altitude Mach stall cruise corner.

Drag and weight are king. Drag is the tougher part. For all of aviation light weight meant low drag: flying wires, fabric non laminar skins, etc... Then new materials like carbon fiber came in and we have been learning to optimize using them for decades now. The only way to reduce drag is to reduce intersection drag, fair everything, and try for any laminar flow you can. At low Re tripping laminar flow is troublesome but you can get away with a bunch of compromises like trip strips. So it seems to me that you have to look at projects like eta and Diana. VERY high AR and cantilevered flexible wings that are optimize for torsion. Helios is sorta in the correct direction but much higher AR without the solar weight fraction. The wings would have to have wheels so they could start moving without dragging on the ground. Very flexible structures are tricky to design and build and can then have huge bands of destructive harmonics to work around so very fragile.

Somewhere in that direction would/could get a longer endurance or close to continuous or slightly climbing flight on current best human output. Tough problem.

That oscillating platform has nowhere near enough wing area or AR. It also has way too much drag and would have to be towed to starting position. There is no way to make a stiff enough wing big enough and cantilevered to go in that direction. Air is 830 times less dense than water approximately. The oscillating thing works well in water with hydrofoils.

Much easier problem to solve with solar and electric and no pink squishy propulsion.
Yes it is the opposite corner.....but like JohnRoo said..light weight and low sink rate.

With drag you have to check out the lift...if you are creating clever lift...the plane can be lighter ( like thicker foils etc).
 

Bob H

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Joined
Jun 9, 2022
Messages
11
What sort of fiber orientation did you use on that? Just stacked up sheets of woven fabric with various rotations? Or is there some trick to make sure all fibers in the narrowest points between the holes are oriented radially? It also looks like those skinny spots are not all the same width. Is that just an optical illusion?

Designing round things always gives me a hard time, and I end up going back to metal because so many of the fibers get cut short and don't contribute any useful strength.
I made a stackup of 8HS woven graphite/carbon with 0/90 and +-45 orientation. I forgot the final thickness , around 1/4". It's called psudo-isotropic which means mechanical properties are fairly equal in all directions. Didn't make any attempt to optimize design. Just made a flat panel and cutout the hub. Then put a bunch of lightening holes in it. Some were off track, leaving slightly varying widths between holes.
I was doing this as a G-Job back then. The surprising result was that the hoop pressure to provide a stress of roughly 1/3 of yield in the toothed alum ring was sufficient to withstand the high test torque applied. And one of the possibilities with the concept was that you could make a series of rings with different tooth ratios and change them by heating parts in home oven at 250F. Aircraft companies had great shop capabilities then and could build anything.
 

henryk

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Messages
7,311
Location
krakow,poland
Could ground effect be the solution...it is still flying isn't it ?

-in youth we was flying on selfbuild hang gliders=very long distances upon allmost flat surface...(thanks ground effect).

-when flying in athermic air we was "pumping" (weavy fly)=much longer distance iff compare with passive fly !

PS=polish sculptor Jan Wnek from Odporuszow on His "LOTA" wing was made
0.5-4 km trips (1866-69) from 40 m high tower !!!
 
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