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Old May 13, 2005, 08:51 PM
JettPilot's Avatar
Miami
Joined Apr 2005
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Yippee!
Sailplane to 80,000 feet

I have flying Radio control with video for several years now and am turning my video ship into a UAV (Picture Attached). I have also been facinated by the idea of getting an RC airplane to break the altitude record. Once I get the UAV thing working right going to altitude is just a matter of finding the power to get there The biggest problem seems to be the gas engines An electric engine could power an RC plane to an extreme altitude, but the batteries are another big limitation After studying some projects I think that a Solar Powered electric sailplane with NO batteries at all would be the way to go Aside from a radio and link battery, I will just power the motor directly from the solar cells which would make the sialplane very light and there would be no limitation on how long I climb Also there is no wasted energy with trying to charge batteries, just run it full power as long as it will climb Looking at solar cells available now, it would be very easy to put 300 watts worth or more of solar cells on an RC sialplane depending on the size..

You guys in this forum are the sailplane experts and I have some questions as I have very limited experience with sailplanes.. Which large sailplane is not to expensive and would be an efficient slow flyer and be big enough to carry 5 pounds of gear, cells etc ? How many watts would it take to make it climb at a decent rate ? What electric motor would be most efficient ?

Any input you guys can offer would be appreciated !
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Old May 13, 2005, 08:56 PM
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sneu's Avatar
United States, CA, San Diego
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Try looking at what Alan did --you will see that alot went into the plane and ground station. http://www.acpropulsion.com/ACP_PDFs...Solong_UAV.pdf

Steve
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Old May 13, 2005, 09:50 PM
JettPilot's Avatar
Miami
Joined Apr 2005
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What Alan did is just cool beyond words But is is obvously an engineering type and he made it way more complicated than it needs to be for what I am doing... I could fly extremely high with most of the stuff I already have. All I need to do is build a sailplane that will climb well on solar cells alone .
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Old May 13, 2005, 10:53 PM
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United States, CO, Longmont
Joined Jul 2001
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If I'm not mistaken, getting to that altitude is seriously non-trivial due to your stall speed in that thin air approaching the speed of sound. The shrinking margin between the two is called "the throat." Too slow and you stall and break the sound barrier during recovery, too fast and you break it anyway. Result is a busted ariframe unless made for the stresses.

Let's see what some of our resident experts say about this.

Best,
Q
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Old May 13, 2005, 11:46 PM
JettPilot's Avatar
Miami
Joined Apr 2005
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The speed - mach issues apply to heavier aircraft. A RC sailplane will not get anywhere near exceeding mach, even if it is stalled it is not going to go anywhere near supersonic. What you talk about is called the coffin corner, and as an airline pilot I see it (and avoid ) every day , I am very familiar with it, but its just not an issue with the RC sailplane

What I am not familiar with are the electric motors available, how many watts they use, and how big a plane they will power I could also use some good advice on what type of sailplane to use
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Old May 14, 2005, 04:04 AM
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Hong Kong
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Jettpilot,I have seen a very big unmanned glider type plane is powered by motor in the site of astroflight.com site. You may check it out. I think an approipriate solar batt is the most difficult items to get, but maybe it is not the case in nowadays anymore. For the plane, you should have already enough experience to build one based on plane you shown on your pic.. Good luck. David
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Old May 14, 2005, 05:06 AM
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Tuomo's Avatar
Jyvaskyla, Finland
Joined Aug 2003
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This is wild project

Quote:
Originally Posted by JettPilot
What I am not familiar with are the electric motors available, how many watts they use, and how big a plane they will power I could also use some good advice on what type of sailplane to use
You could start from http://www.torcman.de/
Go to "Praxisbeispiele"

Basically any moderl airplane can be electrified. Size and weight are not problems -- if you are prepared to pay for the right equipment.

Your idea of solar power is novel but I do not know have the technical knowledge to predict how it will work in practise. Probably you need a very lightly constructed plane to get reasonably high in reasonable time. 3m/s climb would be good (?) with solar power. With this rate of climb getting to 10km would take about an hour.

Knowing that climb rate gets worse every km you go to a thinner air, I would say it is a days job to get up there (and back).

There are also any other problems to cope with: radio link, temperature, safety, safe decend etc. It is also critical for you to adjust propeller so that its load stays constant regardless of air pressure. If you cannot somehow "increase" propeller size, the power of e-motor will go down very quickly. Perhaps altering propeller ptch is not enough compersate if you want to go real high? Increasing prop pitch is anyway neended because the plane will fly faster in thin air.

Not knowing what the current world record is, I would say even 10km would be a revolutionary achievment.
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Old May 14, 2005, 09:39 AM
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United States, CA, San Diego
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Quote:
Originally Posted by JettPilot
What Alan did is just cool beyond words But is is obvously an engineering type and he made it way more complicated than it needs to be for what I am doing... I could fly extremely high with most of the stuff I already have. All I need to do is build a sailplane that will climb well on solar cells alone .
Alan has been building UAV type "fun" models for many years. It is actually a rather difficult task to make things that will perform well at ranged and alitude and survive the cold. Radios and servos often don't like being cold soaked for hours on end at sub zero temps.

Up-link and data downlink and tracking antenna issues are not easy in their own right.

Building a peak power tracker power controller for solar operation would also take some doing.

The list of electronic items that need to be put into your plane is long and many are not off the shelf.

I wish you luck--but what you want to do is not simple.

Steve
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Old May 14, 2005, 09:54 AM
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Bellevue WA,
Joined Dec 2003
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You may want to think about the legal aspect of what you are attempting. Your AMA insurance will not cover you. If you get into air space that is controled by FAA you may be flying higher than you want.
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Old May 14, 2005, 12:53 PM
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Belfast / Dublin
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you'd probably need some kind of Airtraffic Control clearance for this project - a collision is highly unlikely but possible ...and remember murphy's law!

I don't see solar power giving you a steep climb rate - it will work, but you are looking at a marginally powered vehicle to circle up over a loooong time - use a computer autopilot GPS thingy to zombie it up so you can sleep for the 4 or 5 days that it takes to reach altitude!

this is a nice project. ...If it succeeds, don't be surprised if you get a call from the men in black to either hire you or close you down

just a few thoughts

big bird
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Old May 14, 2005, 12:53 PM
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Palmdale, CA
Joined Oct 2000
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At altitude, the plane's stall speed will be the same (on the airspeed indicator) as it is at sea level.
The true airspeed will be markedly higher though.
The U-2 which stalls around 80 knots is going Mach .6 more or less at its operating altitude, and can't go faster due to flutter considerations, or slower due to stall. Turning at these high altitudes means wiiiiiiiiiiiiiiiiiide turns, as there's no margin for adding "g" in a bank.
It can fly there if there's sufficient power above that needed for straight and level.
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Old May 14, 2005, 02:45 PM
JettPilot's Avatar
Miami
Joined Apr 2005
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I am very familiar with the effects of altitude on an airplane and stall speed etc, as an airline pilot it would be criminal neglegence if i didnt . I would also need and FAA waiver for a certian time and place, but that can be done also with proper applications etc. As far as AMA insurance, I could care less, an electric sialplane over an unpopulated area is just not an issue. I have a far more risk of hurting to someone when driving to the grocery store.

Electronics are easy, I have been a ham operator for many years, and started out as an electrical engineering major before I decided on a career change . I already have the GPS navigation, autopilot, downlink, antennas, etc. etc. that stuff is easy . I could build and fly the sailplane easy enough, that UAV you all see in a picture is designed and scratch built by me. No special electronics would be needed for the motor, just run it full power and see how high it gets, no need for any complicated electronics there. I can get the solar cells easy enough, already know which ones I will use (same ones Alan did) and am calculating power based on those cells. As far as props, If I can get a enough power, I could use a simple fixed prop that is way overpitched on the ground, that way it is optimized when it is at altitude where performance will be diminishing. The basic fixed pitch prop would be lighter, less complicated, and less to go wrong. Most people have the tendency to make things way more complicated than they need to be, and create so many barriers themselves it becomes impossible. There is an engineering term that comes to mind here "KISS" (Keep It Simple, Stuupid) With the stuff that is available, I htink that doing this is just not that hard .

There are a couple things I really need help on though, is what large RC sailplane would be best suited to this, this is critical and you guys know your sailplanes ? I know very little about brushless motors and gearboxes avialable also I what brushless motor would be the most efficient at 200 to 300 watts depending on the size of the plane ?

Thanks
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Old May 14, 2005, 02:48 PM
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Broomfield, CO 80023
Joined Dec 2002
354 Posts
Just a thought, there was a very large multi-engined flying wing (I think) that was done ny somebody like Paul McCready a few years ago that flew by R/C and autopilot to high altitudes, but I don't remember much more than that. Some investigation onto this previous work might be helpful for what you want to do...

JohnC
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Old May 14, 2005, 03:00 PM
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Jyvaskyla, Finland
Joined Aug 2003
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Having spent most of my life in Finland I know something about what freezing temperatures do to RC-gear. Batteries go flat when they freeze and servos start to get slow, loose their centering etc. at around -10-15C. How cold it is up there? -50C in 10 000m, must be even colder if you go higher.

If you want to fly many ours in extreme temperatures, you need special gear.

Quote:
Originally Posted by JettPilot
...As far as props, If I can get a enough power, I could use a simple fixed prop that is way overpitched on the ground, that way it is optimized when it is at altitude where performance will be diminishing. The basic fixed pitch prop would be lighter, less complicated, and less to go wrong....
If you have a large enough propeller for the high altitude, you will burn your motor, ESC etc. Perhaps altering the voltage would be a clever way to get over this problem?

I am not saying it is impossible go to high -- it is just very difficult. I would approach the problem step by step. Even making the thing fly with solar power is a challenge. Making it climb reasonably fast is another one.... When you have a well performing and reliable solar powered plane start to think about how high it it can go. When you get to 5km, you are a famous man in modelling community!
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Old May 14, 2005, 04:24 PM
JettPilot's Avatar
Miami
Joined Apr 2005
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The cold problem is easy to solve, they sell these chemical warmers that last for many hours for like a buck a peice . I just insulate the radio battery and put a chemical warmer in it and im good to go. There must be an RC servo that is tolerant of cold though...... Many servo mechanisims in airliners see temperatures of -60 and work just fine. I wonder what the weak spot in servos is, maybe that would be easy to fix if I knew what it was...

There is a guy that sent his RC plane to 30,000 feet, and its darn cold there, probably almost -40 and he did not report any problems, maybe different kinds of servos are more tolerant of cold...

I would not think a motor would burn up if it wasnt being run to hard, even if it was loaded down by a big prop on climbout. Maybe just a bigger motor would tolerate that just fine... but I dont know that much about the behavior of brushless motors in airplanes, thats why im here .
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