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Maximum altitude??

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Maximum altitude??

Old 04-05-2012, 08:39 PM
  #101  
jester_s1
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Default RE: Maximum altitude??

On the balloon topic, I didn't mean just using a balloon to get the samples. I meant using a balloon to haul your plan up to altitude then take over powered flight from there. Since the plane wouldn't have to climb under motor power, your electrical system would only need to make enough power to make the plane cruise. That would let you use a much less powerful motor system saving significant weight, or would let you keep the weight the same and have a lot more loiter time up high if that's what you would want. If you don't need any substantial loiter time at altitude, a pure glider could make the flight simplifying the project substantially.
Old 04-05-2012, 11:32 PM
  #102  
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Default RE: Maximum altitude??

Forgot to illustrate BMatthews' advice to use a multi-panel wing with an odd number of panels. The picture shows a 5-panel wing were the center segment is a piece of its own. The biggest bending stress of the whole wing is in the middle of this segment where no wing joiner is. The main spar is C/F reinforced, otherwise the wing is a traditional wood construction. It's a three-piece wing with two joiners quite far outboard which can be simple and lightweight. And the pieces are shorter than the fuselage while two pieces would be longer.

You see the upright V-tail and may imagine that it produces an adverse roll when used as rudder. The inverted V-tail produces proverse roll. The effect is small, though.

Just for the record: Such high-performance electric gliders have usually geared drives for reasons mentioned above. Efficiency of a good gear is about 95% because nearly all friction is rolling friction, like railway wheels on rails have. The bearings are ball or needle bearings and the toothed wheels have involute toothing. That's also why there is nearly no wear. Just an annoying whine due to straight toothing...
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Old 04-06-2012, 06:39 AM
  #103  
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Default RE: Maximum altitude??

ORIGINAL: da Rock

ORIGINAL: j.duncker


ORIGINAL: Von Ohain

IC motors is bad for high altitude because the air is thinner, and the carburettor of model IC motors isn't sophisticated enough to compensate.
So your motor will stop due to thin air even before the model is out of visible range (been there done that).
Notice that full scale planes with piston engines and carburettor has a mixture knob just as easily acessible as the throttle knob.
Pretty sure Maynard Hill cracked the problem on this. I know he set an official altitude record with an IC engine that was around 8k feet and made flights over 10k ft.

Maynard's infernal combustion powered altitude record for a model was something like 26,000 iirc.




ooops.......... post overlap, sorry.
WOW Anybody know what engine setup he used?
Old 04-06-2012, 07:34 AM
  #104  
da Rock
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Default RE: Maximum altitude??


ORIGINAL: j.duncker

ORIGINAL: da Rock

ORIGINAL: j.duncker


ORIGINAL: Von Ohain

IC motors is bad for high altitude because the air is thinner, and the carburettor of model IC motors isn't sophisticated enough to compensate.
So your motor will stop due to thin air even before the model is out of visible range (been there done that).
Notice that full scale planes with piston engines and carburettor has a mixture knob just as easily acessible as the throttle knob.
Pretty sure Maynard Hill cracked the problem on this. I know he set an official altitude record with an IC engine that was around 8k feet and made flights over 10k ft.

Maynard's infernal combustion powered altitude record for a model was something like 26,000 iirc.




ooops.......... post overlap, sorry.
WOW Anybody know what engine setup he used?

Have to look up the magazine article. A number of his different type record attempts required some out of the box solutions. At least one of them used a small percentage of gasoline in the fuel. With any luck the post with the answer will show up in about 10 seconds.
Old 04-06-2012, 07:36 AM
  #105  
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Default RE: Maximum altitude??

If you are hellbent on doing it with piston, you can do it with fuel injection motors (I believe OS had fuel injected competition grade engines for many years now. They are priced as if they were made of gold though). Or as mentioned above, servo operated mixture (and possible automated, if you are into programming microcontrollers).
IDK how Hill did it, but said methods should make it possible. Hill was a skilled chap it seems, so I wouldn't be surprised if he had automated mixture control of some kind.
That would be a minimum requirement in my opinion to have any reliability at altitude with curburettor motors.

Its still not worth in in my opinion though, because of price and complication.
If it turns out that electric is not feasible, then go for turboprop.
Turbomachinery is in general a lot more efficient at altitude, and at extreme altitude its also the only thing that will run at all. Because it doesn't have a fixed compression ratio, it will compensate for the thin air by spooling, hence increasing its compression as needed to keep up to rated power.

Heres a price example aswell:

Fuel injected piston:
http://www.jhbol.com/store/index.php...cPath=64_65_70

Turboprop:
http://www.1classifieds.co.uk/-1/pos...ound-1100.html

The price is about the same, dollar for power. The turbo is twice the price, but its twice the power aswell. Plus, it has a lot of features included that the F.I. piston doesn't.

Turbo also has the added benefit of wetstart and integrated starter motor, so IF you shall have a flame-out (motor stops, in jet language) you can just restart it with a push on your radio, IN FLIGHT.
If the piston sucker stops at altitude (which it is a lot more likely to do) you will have to land the plane and restart it manually, on the ground.


That said, I still believe electric is simplest and best, but if it turns out you can't get enough battery into the plane to make electric feasible, then please consider turbo seriously before you go with piston.
Turbo has a lot to show for, for this purpose.
Old 04-06-2012, 07:37 AM
  #106  
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Default RE: Maximum altitude??

Magazine article about the engine used for the trans Atlantic fligth: http://www.progressiveengineer.com/p...aynardHill.htm
Old 04-06-2012, 07:38 AM
  #107  
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Default RE: Maximum altitude??

Here is a conventional airframe balsa and ply with some carbon fiber. Less than 10 lbs. capable of lifting 45 lbs in less than 400 ft. High lift very low speed. 14 ft span 14 inch cord using a Selig 1223 airfoil. Take off roll empty about 4 ft power .65 Flys like a big trainer. This was the maiden flight the landing gives an idea of the slow flight landings.

[youtube]http://www.youtube.com/watch?v=g8xC-pE6RoA[/youtube]

Smaller examples limit 1000 square inches and an OS .61

[youtube]http://www.youtube.com/watch?v=vBgWUceKmR0&feature=relmfu[/youtube]
Old 04-06-2012, 06:01 PM
  #108  
IflyPATTERN
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Default RE: Maximum altitude??

OK guys well...

Im going to stick with electric. Though I do appreciate suggestions for a turboprop or IC engine with a servo to adjust fuel/air mixture, I just think electric is the best option. Its efficient, relatively lightweight compared to the others, reliable, and best for the research application (no exhaust fumes to possibly contaminate data).

Von, thanks for the nice explanation of why a bigger, slower turning prop is more efficient than a smaller, faster turning prop by bringing up Newton's second law and Kinetic Energy formulas. That now makes perfect since to me!

Im looking at some of the RASA propellors. These propellors are very lightweight, folding, and come in a bigger diameter (the biggest I have found is a 21x16 folding prop-link below). Let me know what you guys think about this. Also, I know using a variable pitch prop was suggested; however, this might be making things too complicated again. So, what "ball-park" pitch prop should I go with?? high pitch im assuming?? Keep in mind an overwhelming amount of my testing will be done below 5K feet, and other higher altitude flights will be fewer and farther in between (at least this is my gut feeling at the moment).

http://www.f3aunlimited.com/webstore...products_id=94

Im still working, chipping away (slowly until school gets out) at this project a little at a time. The "gathering information" stage of this process is taking a little more time than I expected, but that is perfectly OK by me. You guys have been a great information bank for this aspect, especially! I want whatever gets implemented into this project to be well thought out and not just "thrown together". This, in my opinion, may save me lots of time down the road and help avoid last-minute retrofitting episodes-as some of you have already wisely pointed out to me.

Brandon
Old 04-06-2012, 11:45 PM
  #109  
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Default RE: Maximum altitude??

Did only a quick check and it showed that the prop pitch could be too big (the Graupner 20x12 would be better) and the NEU drive could be too powerful with a 10s battery (8s would be better). The drive's efficiency would be below 50% but 18k ft could still be made with a 12 Ah battery.

Yet the whole mess has to be re-thought again. (Maybe even less pitch, maybe even bigger prop or, since there is no such prop anyway, BMatthews' idea of a twin.) After all this was only a quick check, not a thorough one.

By the way, if you define two different mission profiles it could well be that for the 18k ft mission, which is determined by climb, a low-pitch prop is best and for the 5k ft mission, if it's determined by cruise, a high-pitch prop.
Old 04-07-2012, 12:18 AM
  #110  
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Default RE: Maximum altitude??

Another idea for the pot.

I understand that, on the Continent, some of the free-flight bods use underslung engines. These are mounted such that they fall away from the models after the fuel is exhausted ... recovery by parachute.


Alternatively, piggy-back to altitude, a la Shorts Mayo composite aircraft.







I'm definitely not recommending these ideas, btw. My own preference is for KISS ... off-the-shelf components and a tolerance for imperfect design. First thing I'd do is determine the effect operating altitude of a conventional engine; by experiment, if necessary. A rule-of-thumb is that there will be a 7% loss of power for each thousand feet of altitude gained.




Also, any thoughts on how the Walbro carb would function at altitude? Would it automatically maintain the appropriate fuel/air ratio? It does, in essence, function exactly as a diver's demand valve.
Old 04-07-2012, 01:14 AM
  #111  
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Default RE: Maximum altitude??

I think you guys might have overlooked something in propeller selection.
Air is rapidly getting a lot thinner, and the correct propeller at sea level (where we modellers practically operate, and where we select propellers).
The correct prop at sea level will be way too small at high altitude.
So this setup should be heavily overproped by our conventional standards, to be operating well at altitude.
I think a big diameter, fine pitch propeller is best for this project.
Just look at any plane whos flying slowly and carving for efficiency and pulling power. (slow flyers, 3d planes, helicopter rotors..)
They are all big diameter, fine pitch.
The big diameter steep pitch stuff is for speed planes, and is typically used on hotliners.

Walbro carbs does not automatically adjust for altitude.
If you used a chainsaw in the mountains, don't forget your mixture adjustment screw, because if it ran well at home, it won't up in the high mountains.
Old 04-07-2012, 04:10 AM
  #112  
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Default RE: Maximum altitude??

That's all accounted for. There are just no big enough folding props. And I think fine-pitch is a makeshift if your drive is actually turning too fast. At least the prop can be big enough for good efficiency, but instead of gearing the drive rpm down the prop pitch is reduced. Peak efficiency is generally achieved at advance ratio of about 1, however well the prop is designed and made. I don't know any 3D model, heli or even parkflyer that has an efficient prop. Would be just too big and slow. Even full-size props on smaller airplanes are not efficient because they would be too big, low-rpm engines would be too heavy, and a gear would be too delicate and expensive.

By the way, I have a restraint writing your RCU name because this name does mean something to me. Are you the inventor of the jet engine or is it your real name?
Old 04-07-2012, 04:52 AM
  #113  
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Default RE: Maximum altitude??

Aha, good job then I overlooked that you had taken thinner air into account.
Well thought =)

No, my real name isn't Von Ohain.
I choose the name because at the time I registered here, I had an interest of scratch building gas turbines.
and i picked the name in honor of the gas turbines inventor.
I believe Whittle is given too much credit, and Von Ohain is given far too little credit for inventing a much more sophisticated gas turbine, independently at the same time.
Old 04-07-2012, 02:04 PM
  #114  
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Default RE: Maximum altitude??

Thanks, now it's clear.

Just to show what "quick check" means a few diagrams. I know it's not really an explanation, at least for non-engineers, but anyway (because it's fun for me).

The NEU-F3A-1 (1300 kv, 6.7:1 gear) was assumed with the data published on the website. Impedance of ESC, battery (8s 12 Ah LiPo), and so on is only estimated. The data for the Graupner CFK 20x12 prop are calculated with Martin Hepperle's program and quite reliable, except near static. A rather simple airframe was assumed with 20 lbs weight, 2200 sqin wing area and 5m (197") span, giving 17.6 aspect ratio. (Quite ambitious, and seems no case for a composite construction, at least for wing and tail.) Horizontal stab is 20% of wing area and vertical stab 10%. Tail moment arm 51". Airfoil is Anderson SPICA flat bottom (sorry BMatthews) because it's quite cambered (4.62%) and I have data.

Now all is put together in spreadsheets. I made these 10 years ago and unfortunately didn't automate them so far because I dislike Excel programming. So they are virtually useable only for me. I will share them anyway if requested.

First a comparison of drive rpm and efficiencies at ground level (standard atmosphere), full power and cruise power. Yellow is rpm, dark blue motor-gear efficiency, medium blue prop efficiency, light blue total drive efficiency, that is the power effective on the airplane. All dependent on airspeed. The airplane's minimum power demand is at 12 m/s (27 mph) airspeed.

At full power the drive's maximum efficiency would be at 23 m/s (52 mph) so in this case the prop's pitch is too big. Second diagram the same except at partial power (0.465 of full power). That's just enough to cruise at 12 m/s which is not the absolute minimum speed/power but still gives a small amount of speed stability. Now the drive's maximum efficieny is at 10 m/s (22 mph) so the prop's pitch is a bit too small. That's what I meant in my previous post, but it's merely a "theoretical" comparison. What really matters you'll see now.

Yellow is drag of the airframe, pink is drive thrust at full power, blue at cruise power. It's not easy to imagine at which speed the height will be maximized. Next diagram: yellow is airframe power consumption, pink is power delivered to the airframe at full power, dark blue at cruise power setting. Light blue is difference between full drive power and airframe power demand. This difference is climb power. Dotted pink is reachable altitude/height with maximum 6700 m (22k ft) at 16 m/s (36 mph). Climb rate is 5.6 m/s (1100 ft/min). Of course that's ground air density.

But next two diagrams show the case of about half ground density, that is 18k ft. Because the air is thinner the airplane flies faster (airspeed 17.5 m/s, 39 mph) for maximum reachable height. This reachable height is slightly reduced (6300 m, 20.6k ft) because the power delivered is lesser and a bigger part of it is needed to overcome drag. Here you see that the airframe's aerodynamic quality is still of minor importance (maybe except aspect ratio). But cruise flight requires a higher power setting (0.605). Climb rate is 3.1 m/s (610 ft/min). So even though some parameters change with altitude and climb rate gets lower and lower, target altitude could be reached with even a bit charge in the battery for some loitering and landing approach.

There are no reserves which means the accuracy (not to mention correctness) of this calculation would be crucial. So no responsibility is taken for the correctness of this information.

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Old 04-08-2012, 03:08 AM
  #115  
Von Ohain
 
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Default RE: Maximum altitude??

Very good job!
You deserve credits for that.
Also nice to make graphs of it in excel.
If i were to do it, I would just stick up the calculations in plaintext.
Making graphs makes it a lot more readable, especially for those not so into mathematics.
Old 04-08-2012, 03:43 AM
  #116  
UStik
 
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Default RE: Maximum altitude??

Thanks! As to mathematics - count me in! I can't imagine these things in abstract form (equations) and need something visual. That's exactly why I made these spreadsheets. And once I had them I found them very enlightening.

The 18k ft case has been adjusted (Reynolds number, airfoil coefficients) and isn't quite as "quick" as before. Looks even better now, but still more drive efficiency is needed, that is less power per prop disk area. The airframe's power demand is a given so more prop disk area is needed.

Since I don't know of any bigger folding props I'd try the twin solution with the same prop and two smaller geared outrunner motors. Could be a true twin boom configuration with the inverted V-Tail split into halves (paddles). The two booms could be located quite far outboard for more aileron effect and a better mass distribution (wing bending load would be much smaller). The booms could be just tacked to the wing's flat bottom.
Old 04-08-2012, 07:25 AM
  #117  
Propworn
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Default RE: Maximum altitude??

Israel has had this one for a while looks pretty conventional without the monster props and gear boxes that are being discussed. 16000 ft plus. Easily hand launched. Looks to use a standard Graupner Cam Prop
http://www.israeli-weapons.com/weapo...k/Skylark.html

Fine tuning your prop with 3.5 and 5 degree twisted yoke spinner.

http://www.hyperflight.co.uk/product...ead-this-first

The Tigershark UAV twin boom pusher UAV

FAA would have to authorize high-altitude test flights
By GCN Staff
Jul 13, 2011
Oklahoma officials and business leaders business are looking to make the state a center of activity for unmanned aerial vehicles.
They want to designate a strip of airspace between Fort Sill and the Clinton-Sherman Airport as a test zone for UAVs in which commercial developers could routinely fly UAVs at high altitudes, reports Steve Metzer at the Lawton Constitution.
The agreement in the making would build on efforts begun in 2006 when the Oklahoma State University Multispectral Laboratory (UML) worked with the Defense Department to locate a UAV-dedicated airport at Lawton-Fort Sill where the lab has an existing agreement with the Army to fly UAVs over part of Fort Sill up to an altitude of 40,000 feet — something not allowed in civil airspace.
A request has been sent to the Federal Aviation Administration for a certificate of authorization allowing flights of a UAV called a TigerShark in and out of the Clinton-Sherman Airport and, if that’s granted, a second certificate would be applied for to allow flights of TigerSharks between Clinton-Sherman and Lawton-Fort Sill, Stephen McKeever, the state’s secretary of science and technology and also the executive director of the UML, told the Lawton Constitution.

From this site http://www.pathfindersystems.com/techpub/haleuav.htm

A Practical Design of High Propulsive Efficiency
Old 04-08-2012, 07:49 AM
  #118  
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Default RE: Maximum altitude??

It's not a Graupner prop, it's one of the aeronaut CAMcarbon linked to above (I think they are better, design by Rudolf Freudenthaler). The Skylark UAV is smaller and seems faster than what is discussed here, of course that prop fits. Hand launch is as well possible with a 16.4 ft span, 20 lbs weight UAV, but I'd prefer a bungee launch because it's safer / more predictable.
Old 04-08-2012, 09:11 AM
  #119  
Propworn
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Default RE: Maximum altitude??

ORIGINAL: UStik

It's not a Graupner prop, it's one of the aeronaut CAMcarbon linked to above (I think they are better, design by Rudolf Freudenthaler). The Skylark UAV is smaller and seems faster than what is discussed here, of course that prop fits. Hand launch is as well possible with a 16.4 ft span, 20 lbs weight UAV, but I'd prefer a bungee launch because it's safer / more predictable.

After enlarging the photo I can see you are correct. The link simply shows that a smaller airframe of basic plan form can achieve what you are after as far as altitude. Your idea of a larger plan form should also work as in the second link.

From your posts two different prop/motor combinations would be ideal. Would it be possible to use the Tigershark type of plan form with both a tractor and pusher engine. The pusher could be propped for lower altitudes and the tractor could be propped for high altitudes both with folding props. Engines could be individually selected or even run in combination. Boom diameter could be increased in diameter to contain the entire payload you need plus easy retracts. You could even make the low altitude engine fuel burning to get to altitude and save the batteries for high altitude work.

If in fact you would consider the twin boom as in your previous posts you could outfit both electric motors with the high altitude props and still use an internal combustion engine as a pusher to get the airframe to altitude before engaging the electrics.

I find what you are doing interesting however if I have nothing of value to contribute to the topic please pm me and I will stop.

Dennis
Old 04-08-2012, 09:45 AM
  #120  
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Default RE: Maximum altitude??

Please don't stop, your posts are inspiring! It's good to have other ideas to compare. Two different propellers are a great idea. I just tried to keep it simple and use only commercially available components. You had the idea how that could be done with a twin configuration, but - without really thinking about it - wouldn't that require two full-blown motors making for some weight? And wouldn't one motor/prop suffice because the mission / drive selection is dominated by climb?

I just checked the twin with two AXI 2860/12, AXI PG4/33 4:1 gear, the Graupner 20x12 prop, and a 5s 12 Ah LiPo battery for each motor (effectively 5s2p). That is more battery than before (8s1p 12 Ah) and more weight. Now the drive's peak efficiency is at 12 m/s airspeed as is the airframe's lowest power demand. But the drive efficiency is 10% lower, prop efficiency is the same, so there's virtually no benefit. A bit more maximum height comes from the bit more battery. Climb rate is really low. It's no practical solution.

Seems it's better to use the single-drive variant (push or pull doesn't matter), put a bit more battery in it (15 Ah instead of 12 Ah), and - above all - make the airplane faster by using a less cambered airfoil. The aspect ratio could be reduced.
Old 04-09-2012, 12:45 AM
  #121  
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Default RE: Maximum altitude??

Sorry, made a mistake. I was so fixated on getting the max. drive efficiency at the airframe's best climb speed that I overlooked that the motors were underloaded. One cell more (6s1p 12 Ah for each motor) brings them into their range of best efficiency. Overall drive efficiency is now 50%, initial climb rate is 3.9 m/s (760 ft/min) at 12 m/s (27 mph) airspeed, and maximum height is 9800 m (32k ft) at 13.5 m/s (30 mph) airspeed. Two 6s1p 10 Ah batteries would still give 8100 m (26.5k ft) maximum height and two 6s1p 8 Ah would give 6500 m (21.3k ft).

Sounds fine especially regarding the structural benefits of having the heavy drives outboard on the wings. Counter-rotating props would be fine as well but I think there are no left-turning props. Could check now the same airframe with a bit higher-kv motors and/or a different airframe with faster (less cambered) airfoil and less aspect ratio. Would give small differences, though. What would be really needed is different prop pitch. The props linked to in post #113 look interesting and the aeronaut props as well but I have no data about them.
Old 04-09-2012, 03:41 AM
  #122  
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Default RE: Maximum altitude??

I guess I would differentiate the equations to find bestpoints to aim for, rather than feed them into excel for graphs. But now that I see the graphs side by I think your way is better.
Its easier to not get confused with the graphs side by side, rather than pages with equations.

Most importantly, and what would been achieved either way, is that you have demonstrated mathematically is that electric propulsion is realistic for this project, and since OP preferred electric propulsion, I would assume the matter of propulsion is settled.
I do not quite understand your airfoil selection (flat bottom), but you made it work theoretically so why not.
Old 04-09-2012, 05:45 AM
  #123  
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Default RE: Maximum altitude??

Well, that flat-bottom airfoil is just what I had readily available because I calculated my Telemaster. With some amount of work I replaced it by SD7037 what gave an airframe better suited to the task. Actually I think the OP really needs an airplane with something like a RG15 airfoil and a F3A drive as he already considered. It would not resemble a F3J machine but rather a F3C or even F5B one, but the drive would have the efficiency assumed for this project. It was just not what I had at hand data-wise.

I do have data for another F3A drive (AXI) which show that those 20x13 F3A props are really optimized. The Graupner CFK 20x12 is just not suited to such an application. Notice efficiencies well over 60%. The UAV would just climb with more than 20 m/s airspeed and more than 10 m/s climb rate, but why not with a RG15? The airframe could have less span and aspect ratio but should be a composite build for rigidity and accurate shape.
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Old 04-15-2014, 06:32 PM
  #124  
IflyPATTERN
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Old 04-15-2014, 06:54 PM
  #125  
IflyPATTERN
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After two years since the last post to this thread, I've finally made full circle on this project. The pictures above shows an x-8 that once was a foam FPV kit that has been modified heavily in order to be able to serve as a platform for my senior design project on bioprecipitation. In addition, I've teamed up with other professors at my college to use this UAS for land erosion studies and general agricultural remote sensing.

As for constructing the airplane, all surfaces were fiber glassed with .6oz cloth. The vertical fins on top were added to aid in yaw stability. Lower rails were added for attachment points for gear. Both rails have two servo hook-up channels for auxillary purposes. Leading and trailing edges are laminated with carbon tissue to minimize wing flex at the tips and to increase overall durability. E-flite 60-120 retracts were installed. The center portion is a 2 axis camera gimble. The front nose rails were added for a crash landing bumper. The list of modifications goes on...

Thanks for all the previous interest/comments. You guys aided in motivating me to fulfill this project. The first flight is just around the corner, which will be a normal R/c piloted flight. Subsequent flights will be guided via GPS and on-board microprocessor. Only take off and landing will be flown by traditional R/c methods.

With respect to the original thread's purpose, 3x5000mah 5S packs are going to power a 2Kw motor. Hopefully this can carry us far and high enough to do all that is needed. I believe max prop clearance is 16 inches.

Brandon Landry

Last edited by IflyPATTERN; 04-15-2014 at 06:55 PM. Reason: typo

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