Maximum altitude??
04-01-2012, 07:41 PM
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Maximum altitude??
Hey guys, since I am "new" to this forum, I will first introduce myself. My name is Brandon Landry. I am a Biological Engineering student at LSU and an F3A/pattern competitor. Recently I have been granted by LSU to design/build a UAV for a professional research team, which is headed by an LSU professor. The UAV will have onboard cameras and other various gadgets and gizmos (wont go into detail since its not relative to the aims of this thread) which will hopefully allow myself to easily fly this UAV (at different altitudes) and collect samples of the microbial life that may (or may not) inhabit the earth's atmosphere so that the research team can study/analyze them. As I have already mentioned above, I am pattern pilot and enthusiast. I am not an aerodynamics guro- though I do understand a great deal about basic aerodynamics from my past 8+ years.
Now, here's where the actual thread starts:
Conceptually, I have planned in my head to use a modified glider platform as the basic theme for my UAV design. This glider will be powered by an electric motor, which I have decided to mount the in the rear of the plane so that I can use a pusher propellor system (I have my reasons). The propellor itself will be folding to reduce drag when not "in use". Here's what I'd like to hear opinions about: (These questions may seem vague, in fact I know they are. But, since I am a "newbie" to some of this, Id like to start from gound zero and work my way up and possibly get more specific later on in the thread.)
1. what is a "good rule of thumb" wing area to weight ratio (or just wing loading) for gliders?
2. Which airfoil(s) are best suited for glider-like applications?
3. CG: preferenes for gliders? (i.e. slightly noseheavy/tailheavy)
3. Once I have found the best answers for number 1 and 2, is there any way to use them to determine a maximum alitutude that my design could reasonably be expected to fly at? And yes, I know SEVERAL other factors other than airfoil, wing loading, and CG will influence the answer to number three.
Im willing to listen to any suggestions! Also, I realize there are legal implications with what I am trying to do. Let's not worry about that for now....
Brandon Landry
Now, here's where the actual thread starts:
Conceptually, I have planned in my head to use a modified glider platform as the basic theme for my UAV design. This glider will be powered by an electric motor, which I have decided to mount the in the rear of the plane so that I can use a pusher propellor system (I have my reasons). The propellor itself will be folding to reduce drag when not "in use". Here's what I'd like to hear opinions about: (These questions may seem vague, in fact I know they are. But, since I am a "newbie" to some of this, Id like to start from gound zero and work my way up and possibly get more specific later on in the thread.)
1. what is a "good rule of thumb" wing area to weight ratio (or just wing loading) for gliders?
2. Which airfoil(s) are best suited for glider-like applications?
3. CG: preferenes for gliders? (i.e. slightly noseheavy/tailheavy)
3. Once I have found the best answers for number 1 and 2, is there any way to use them to determine a maximum alitutude that my design could reasonably be expected to fly at? And yes, I know SEVERAL other factors other than airfoil, wing loading, and CG will influence the answer to number three.
Im willing to listen to any suggestions! Also, I realize there are legal implications with what I am trying to do. Let's not worry about that for now....
Brandon Landry
04-01-2012, 08:32 PM
#2
RE: Maximum altitude??
1. It depends.
2. It depends.
3. It depends.
Wing loading depends on the size of model, the expected payload and what the expected power on/off ratio is.
Airfoil depends on expected airspeed, that is, how long you expect to be flying for.
Balance will depend on whether you intend to fly from the ground, or whether you expect the thing to be a bit autonomous.
Altitude will depend on the answers to (1) and (3).
Evan, WB #12.
2. It depends.
3. It depends.
Wing loading depends on the size of model, the expected payload and what the expected power on/off ratio is.
Airfoil depends on expected airspeed, that is, how long you expect to be flying for.
Balance will depend on whether you intend to fly from the ground, or whether you expect the thing to be a bit autonomous.
Altitude will depend on the answers to (1) and (3).
Evan, WB #12.
04-01-2012, 08:41 PM
#3
RE: Maximum altitude??
Hi Brandon!
Judging by the title of your thread, I assume you want to fly as high as possible.
I believe a glider is not the optimal platform for this purpose. No existing model plane, at least to my knowledge, is.
So either you got to compromise, or you have to scratch build something.
A glider fuselage is a good start, because it is designed for very low drag.
Some aspect of a gliders wing geometry (long span, narrow chord) is also good for low drag, so is typical gliders airfoils.
So a glider is a goodish place to start, but I believe it can be done better, if the aim is maximum altitude.
In my opinion you got to scratch build a new wing, starting with choosing an airfoil which gives a high lift coeficcient.
After having choosen a wing profile with a good lift coeficcient, you will have to estimate flying weight of your plane and desired flying altitude (and hence, static pressure at given altitude).
Thats about all you need to calculate your needed wing area.
Chord length will be given by fuselage geometry (wing has to fit when mating with the fuselage), so you will probably end up with a narrow chord, long span wing quite similar looking to a glider, but with a different airfoil.
The best database I know of for airfoil is Dr. Hepperles page http://mh-aerotools.de
He has tons of airfoils to choose from, but he has not sorted them according to lift coeficcient, so you have to go through it manually and find a profile with high lift coeficcient.
Edit 1: On a side note you should probably also design some aerodynamic washout to the wing, as you will most likely be flying pretty close to stall condition a lot of the time, given your desire to push altitude, and hence pushing the wings maximum lift capacity a lot of the time.
Edit 2: Get inspired by U2, the spyplane. Try to find out what airfoil it has. Similar work has been done before, and you know what they say about standing on the shoulders of giants
What you already know from U2 is that a glider is not a bad place to start. It does also have a narrow chord, long span wing, mated to a traditional, sleek fuselage.
Judging by the title of your thread, I assume you want to fly as high as possible.
I believe a glider is not the optimal platform for this purpose. No existing model plane, at least to my knowledge, is.
So either you got to compromise, or you have to scratch build something.
A glider fuselage is a good start, because it is designed for very low drag.
Some aspect of a gliders wing geometry (long span, narrow chord) is also good for low drag, so is typical gliders airfoils.
So a glider is a goodish place to start, but I believe it can be done better, if the aim is maximum altitude.
In my opinion you got to scratch build a new wing, starting with choosing an airfoil which gives a high lift coeficcient.
After having choosen a wing profile with a good lift coeficcient, you will have to estimate flying weight of your plane and desired flying altitude (and hence, static pressure at given altitude).
Thats about all you need to calculate your needed wing area.
Chord length will be given by fuselage geometry (wing has to fit when mating with the fuselage), so you will probably end up with a narrow chord, long span wing quite similar looking to a glider, but with a different airfoil.
The best database I know of for airfoil is Dr. Hepperles page http://mh-aerotools.de
He has tons of airfoils to choose from, but he has not sorted them according to lift coeficcient, so you have to go through it manually and find a profile with high lift coeficcient.
Edit 1: On a side note you should probably also design some aerodynamic washout to the wing, as you will most likely be flying pretty close to stall condition a lot of the time, given your desire to push altitude, and hence pushing the wings maximum lift capacity a lot of the time.
Edit 2: Get inspired by U2, the spyplane. Try to find out what airfoil it has. Similar work has been done before, and you know what they say about standing on the shoulders of giants
What you already know from U2 is that a glider is not a bad place to start. It does also have a narrow chord, long span wing, mated to a traditional, sleek fuselage.
04-02-2012, 04:13 AM
#4
RE: Maximum altitude??
Basically you need as much lifting surface and as little weight as possible -the rest of it is prety much decoration.
Look at the high altitude loitering craft designed to stay aloft long periods at high altitudes
Look at the high altitude loitering craft designed to stay aloft long periods at high altitudes
04-02-2012, 05:49 AM
#5
RE: Maximum altitude??
Wing geometry matters more than that.
Sure, surface area and wing profile is major determinants for lift, but there is other factors to concider aswell.
Short span, long chord wings for example will have much more induced drag than a long span, short chord wing of the same surface area.
Large sweep angles will produce more stability around pitch axis than plank wings.
Delta wings will be much more tolerable to high alpha flight attitude than plank, tapered or swept wings of the same profile and same wing area.
So there is other parameters to consider.
Without having done any analysis on the subject, my gut feeling tells me that a narrow chord, long span, unswept wing will serve this purpose best.
Sure, surface area and wing profile is major determinants for lift, but there is other factors to concider aswell.
Short span, long chord wings for example will have much more induced drag than a long span, short chord wing of the same surface area.
Large sweep angles will produce more stability around pitch axis than plank wings.
Delta wings will be much more tolerable to high alpha flight attitude than plank, tapered or swept wings of the same profile and same wing area.
So there is other parameters to consider.
Without having done any analysis on the subject, my gut feeling tells me that a narrow chord, long span, unswept wing will serve this purpose best.
04-02-2012, 08:29 AM
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RE: Maximum altitude??
Since it will be a glider like layout but with an electric propulsion system a lot of the "limits" of a glider are not valid for the discussion.
IflyPATTERN, a good starting point is to chart and study the designs of a lot of the bigger compeitition sailplanes out on the market for wing area, weight, the resulting wing loading and the airfoils used.
Note that these designs are set to fly well at a cruise speed of between a speed range of around 15'sh to 30'ish mph. Your use of electric power should be able to extend that sort of speed range to some extent. But I'd suggest that you consider the electric system as more for climbing than for cruising at high speeds unless you find you need it to return to the launch point.
Note that sailplane fliers have learned to work WITH the wind of the day so as to avoid any return issues. The tend to hunt for their thermals by flying upwind and only allow the models to drift downwind while circling in the lift which will allow them the "fuel" (altitude) to speed up and get back to the launch point or carry on back upwind to hunt for another thermal. You'll want to plan on flying your UAV in a similar manner by noting the various wind speeds in each layer you pass through on the way up so you can navigate in a manner to have yourself be "upwind" and glide home instead of being caught "downwind" and have to power back or go hunting for the landing spot. Even a powered sailplane is at the mercy of the winds due to the slower flying speed.
There's no reason that a more or less 3 meter glider like craft such as you're looking at will not reach up to around 15K feet. But much more than that and you're going to find that regular props and model designs will begin to suffer more and more as the air thins. But all is hardly lost. Full size sailplanes and certainly UAV's have gone much higher. Even the record for model aircraft altitude is up around 18K feet as I recall. But if you're looking at getting up a lot higher and even touch on the stratosphere then you'll need to go with increasingly bigger and fancier options which stretch the link to the bigger contest sailplane formats.
I think you're still on the right track with a large glider like craft. The long higher aspect wings will give you the sort of efficiency and lift you want for the sort of mission you describe. The real trick will be juggling the drive system and folding prop. As for the prop I'd suggest a way to selectively allow it to lock in the extended position or fold. When folded the craft should make a decently respectable glider. But for descending a large freewheeling prop makes a superb speed limiting dive brake. If you were to set up an option for allow it to lock to stay out you could power up to extend the folded blades, operate the lock then power back off for the braking mode. To go back to folding mode simply power up for a moment to take the pressure off the locking pin and unlock then power off.
Structurally keep in mind that a P-38 style twin boom may provide the ideal place for a large pusher prop but it does give the designer some structural headaches. So often folks want to stick small section carbon tubes or similar on such designs becuase they look sleek and sexy. But the tail booms must be stiff enough to withstand flexing that significantly alters the horizontal tail angle to the wing. Note that I said "stiff" and not "strong". There's a very important difference between the two. In concert with this the wing root areas must also be torsionally stiff enough to properly support the weight and aerodynamic forces generated between the tail booms and fairly heavy fuselage. The nose full of equipment must be heavy enough to counteract the weight of the tail booms and tail surfaces. This tries to torque the wing root area between the booms and center pod. So that area must be torsionally stiff enough to resist much in the way of flexing. In terms of a good solution for the booms I'd suggest that there is nothing at all wrong with carbon tubing. But for each boom do consider the use of TWO tubes separated vertically and joined to form an I beam like structure with a central web of some sort. Something of the sort will provide the sort of vertical stiffness you require while still being quite light and strong.
IflyPATTERN, a good starting point is to chart and study the designs of a lot of the bigger compeitition sailplanes out on the market for wing area, weight, the resulting wing loading and the airfoils used.
Note that these designs are set to fly well at a cruise speed of between a speed range of around 15'sh to 30'ish mph. Your use of electric power should be able to extend that sort of speed range to some extent. But I'd suggest that you consider the electric system as more for climbing than for cruising at high speeds unless you find you need it to return to the launch point.
Note that sailplane fliers have learned to work WITH the wind of the day so as to avoid any return issues. The tend to hunt for their thermals by flying upwind and only allow the models to drift downwind while circling in the lift which will allow them the "fuel" (altitude) to speed up and get back to the launch point or carry on back upwind to hunt for another thermal. You'll want to plan on flying your UAV in a similar manner by noting the various wind speeds in each layer you pass through on the way up so you can navigate in a manner to have yourself be "upwind" and glide home instead of being caught "downwind" and have to power back or go hunting for the landing spot. Even a powered sailplane is at the mercy of the winds due to the slower flying speed.
There's no reason that a more or less 3 meter glider like craft such as you're looking at will not reach up to around 15K feet. But much more than that and you're going to find that regular props and model designs will begin to suffer more and more as the air thins. But all is hardly lost. Full size sailplanes and certainly UAV's have gone much higher. Even the record for model aircraft altitude is up around 18K feet as I recall. But if you're looking at getting up a lot higher and even touch on the stratosphere then you'll need to go with increasingly bigger and fancier options which stretch the link to the bigger contest sailplane formats.
I think you're still on the right track with a large glider like craft. The long higher aspect wings will give you the sort of efficiency and lift you want for the sort of mission you describe. The real trick will be juggling the drive system and folding prop. As for the prop I'd suggest a way to selectively allow it to lock in the extended position or fold. When folded the craft should make a decently respectable glider. But for descending a large freewheeling prop makes a superb speed limiting dive brake. If you were to set up an option for allow it to lock to stay out you could power up to extend the folded blades, operate the lock then power back off for the braking mode. To go back to folding mode simply power up for a moment to take the pressure off the locking pin and unlock then power off.
Structurally keep in mind that a P-38 style twin boom may provide the ideal place for a large pusher prop but it does give the designer some structural headaches. So often folks want to stick small section carbon tubes or similar on such designs becuase they look sleek and sexy. But the tail booms must be stiff enough to withstand flexing that significantly alters the horizontal tail angle to the wing. Note that I said "stiff" and not "strong". There's a very important difference between the two. In concert with this the wing root areas must also be torsionally stiff enough to properly support the weight and aerodynamic forces generated between the tail booms and fairly heavy fuselage. The nose full of equipment must be heavy enough to counteract the weight of the tail booms and tail surfaces. This tries to torque the wing root area between the booms and center pod. So that area must be torsionally stiff enough to resist much in the way of flexing. In terms of a good solution for the booms I'd suggest that there is nothing at all wrong with carbon tubing. But for each boom do consider the use of TWO tubes separated vertically and joined to form an I beam like structure with a central web of some sort. Something of the sort will provide the sort of vertical stiffness you require while still being quite light and strong.
04-02-2012, 08:52 AM
#7
Senior Member
RE: Maximum altitude??
What's your payload expected to be? That'll drive most of your decisions.
What is their desired altitude? You can reach awesome altitude with a glider platform. Add a motor and you can reach the same but with far better regularity.
It's quite easy to fly large unlimited RC gliders (12' span and more) out of sight vertically. I know they aren't the vehicle you're planning, but I mention that to give you something to think about for your design.
The design problems with electrics revolve around the battery weight needed for the power needed for the flight time needed. If you're going to build something that requires a couple of horsepower to get your job done, you're going to be carrying a fair battery load for average size models.
Electric models can either fly under power the entire flight or do what RC gliders do, which is climb and cruise. If you plan on the latter, you are going to need a glider design unless you're only shooting for lower altitudes. If you plan on higher altitudes and duration over something like a 15 minutes, power all flight long is iffy.
Your plan for the powerplant to be in the tail also muddies the waters on component placement. The dimensions of your collection hardware muddies the waters more.
What is their desired altitude? You can reach awesome altitude with a glider platform. Add a motor and you can reach the same but with far better regularity.
It's quite easy to fly large unlimited RC gliders (12' span and more) out of sight vertically. I know they aren't the vehicle you're planning, but I mention that to give you something to think about for your design.
The design problems with electrics revolve around the battery weight needed for the power needed for the flight time needed. If you're going to build something that requires a couple of horsepower to get your job done, you're going to be carrying a fair battery load for average size models.
Electric models can either fly under power the entire flight or do what RC gliders do, which is climb and cruise. If you plan on the latter, you are going to need a glider design unless you're only shooting for lower altitudes. If you plan on higher altitudes and duration over something like a 15 minutes, power all flight long is iffy.
Your plan for the powerplant to be in the tail also muddies the waters on component placement. The dimensions of your collection hardware muddies the waters more.
04-02-2012, 08:56 AM
#8
Senior Member
RE: Maximum altitude??
ORIGINAL: IflyPATTERN
1. what is a ''good rule of thumb'' wing area to weight ratio (or just wing loading) for gliders?
2. Which airfoil(s) are best suited for glider-like applications?
3. CG: preferenes for gliders? (i.e. slightly noseheavy/tailheavy)
3. Once I have found the best answers for number 1 and 2, is there any way to use them to determine a maximum alitutude that my design could reasonably be expected to fly at? And yes, I know SEVERAL other factors other than airfoil, wing loading, and CG will influence the answer to number three.
Brandon Landry
1. what is a ''good rule of thumb'' wing area to weight ratio (or just wing loading) for gliders?
2. Which airfoil(s) are best suited for glider-like applications?
3. CG: preferenes for gliders? (i.e. slightly noseheavy/tailheavy)
3. Once I have found the best answers for number 1 and 2, is there any way to use them to determine a maximum alitutude that my design could reasonably be expected to fly at? And yes, I know SEVERAL other factors other than airfoil, wing loading, and CG will influence the answer to number three.
Brandon Landry
2. Any glider airfoils presently in use will work. There really aren't any magic airfoils. Almost everything that's been flown in contests in the last 30 years will work for your job.
3. Neither noseheavy nor tailheavy. It's dead simple to balance perfectly and excellent reasons to do so.
4. Gliders soar out of sight every season. How far can we see vertically? I've specked out a 2m and a 14'er. Specking out is when you can only see two dots, a big one that's your wing and a small one. When the small one is no longer visible, it's time to hit the spoilers and get back down to where you can see it. Obviously, the 2m wasn't as high as the 14'er. If your job requires altitude, you need something you can see.
04-02-2012, 11:39 AM
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RE: Maximum altitude??
Hey guys, wow! wasnt expecting this much feedback in such a small time period..
Here's where I stand: The UAV I have conceptually designed will have a 4-5 meter wingspan, 2100-2200 sq in main wing area, and have a aspect ratio in the 13-14 region. Now, the propusion system will be a 10S 25C setup with 10000-12000 mah of capacity. I will also have 2 other, 2s packs which will power my servos, camera equiptment, and microbial capturing device. With this being said, Im expecting a total RTF weight in the 15-20lb area. This should give me a wing loading of about 21 oz/ sq ft @ 20lbs and 15.7 oz/ sq ft @ 15lbs. Is this too much wing loading? Also, after further discussion with my professor, it seems they are most interested in doing initial testing in altitudes below 5k feet. This, in my opinion, should not be difficult to do. However, later testings will push the UAVs limits as far as altitude is concerned. Therefore, reaching high altitudes is still a key constraint that I must design for. How high? well, that what I am trying to find out still! I am hopefull I can at least reach 17-18K feet. The higher I can reach, the better. Feel free to critique my ideas/numbers I have proposed thus far. Afterall, I am still in the brainstorming phase of my work, so you wont be hurting my plans or feelings. Hopefully in the next week or two I can take all of the data I have collected and start building a detailed design on autodesk inventor- which will be presented to LSU for approval.
Other questions:
1.What is a good AoA for the main wing? In pattern, .3-.5 degrees positive seems to be a good ball-park value. But, what is it for a high altitude glider? I plan to keep the stab at zero.
Thanks! I am already starting to get new/better ideas for my design based of what I've already heard.
Brandon
Here's where I stand: The UAV I have conceptually designed will have a 4-5 meter wingspan, 2100-2200 sq in main wing area, and have a aspect ratio in the 13-14 region. Now, the propusion system will be a 10S 25C setup with 10000-12000 mah of capacity. I will also have 2 other, 2s packs which will power my servos, camera equiptment, and microbial capturing device. With this being said, Im expecting a total RTF weight in the 15-20lb area. This should give me a wing loading of about 21 oz/ sq ft @ 20lbs and 15.7 oz/ sq ft @ 15lbs. Is this too much wing loading? Also, after further discussion with my professor, it seems they are most interested in doing initial testing in altitudes below 5k feet. This, in my opinion, should not be difficult to do. However, later testings will push the UAVs limits as far as altitude is concerned. Therefore, reaching high altitudes is still a key constraint that I must design for. How high? well, that what I am trying to find out still! I am hopefull I can at least reach 17-18K feet. The higher I can reach, the better. Feel free to critique my ideas/numbers I have proposed thus far. Afterall, I am still in the brainstorming phase of my work, so you wont be hurting my plans or feelings. Hopefully in the next week or two I can take all of the data I have collected and start building a detailed design on autodesk inventor- which will be presented to LSU for approval.
Other questions:
1.What is a good AoA for the main wing? In pattern, .3-.5 degrees positive seems to be a good ball-park value. But, what is it for a high altitude glider? I plan to keep the stab at zero.
Thanks! I am already starting to get new/better ideas for my design based of what I've already heard.
Brandon
04-02-2012, 12:35 PM
#10
Senior Member
RE: Maximum altitude??
Do check on your legal potential problems if you get in trouble in any way. You will not be covered by AMA even if you are a member as such activities you plan are defiantly not covered by the AMA insurance. Chances of problems (legal troubles) may be slight but they are there. Make sure your sponsor understands this.
04-02-2012, 12:38 PM
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RE: Maximum altitude??
Rodney, please read the end of my first post. My potential sponsors fully understand the legal implications of what im doing. They would be, afterall, a professional research group. They have already done similar projects using balloons. Trust me, nothing illegal will be going on without proper approval. Thanks for your concern.
Brandon
Brandon
04-02-2012, 01:33 PM
#12
RE: Maximum altitude??
Very good thread, you got lucky with this one IflyPATTERN!
Lots of good input, and the "let's do this!" attitude is present, rather than the typical "thats not possible!" attitude so often seen on forums.
Keep up to good work, I'll hope you keep this project on track. Its very interesting
Lots of good input, and the "let's do this!" attitude is present, rather than the typical "thats not possible!" attitude so often seen on forums.
Keep up to good work, I'll hope you keep this project on track. Its very interesting
04-02-2012, 01:41 PM
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RE: Maximum altitude??
Von,
Thanks for the kind words. I find this project to be very interesting myself. It's a double winner for me since I love R/c airplanes and Biology. I look forward to hearing more good info and sharing more with you guys about how things are coming along.
Brandon
Thanks for the kind words. I find this project to be very interesting myself. It's a double winner for me since I love R/c airplanes and Biology. I look forward to hearing more good info and sharing more with you guys about how things are coming along.
Brandon
04-02-2012, 03:06 PM
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RE: Maximum altitude??
Sounds like a fun project, good luck!
I would take a good look at at some U-2 plans, some of what is used there can be a guideline for you I would think where for your plane, as a model, will be pushing similar limits due to air density. Pathfinder and helios also spring to mind as something else to look at as inspiration.
I would take a good look at at some U-2 plans, some of what is used there can be a guideline for you I would think where for your plane, as a model, will be pushing similar limits due to air density. Pathfinder and helios also spring to mind as something else to look at as inspiration.
04-02-2012, 03:36 PM
#15
RE: Maximum altitude??
Well, you can't design in an AOA, that is governed entirely by the speed the model is flying at, the weight it is currently flying at, what it is doing at the time and the pressure altitude at the time. I guess you mean 'do I design in an angular difference between the wing and tailplane?'. This angular difference will set your 'Straight and Level' flight speed, so if you want it to maintain a 'trimmed speed' then a little (2 deg) difference and a slightly forward balance will ensure that you can set a trimmed speed and the model will maintain that speed without further adjustment. If you are flying at the limits of visibility this will ensure that you will not overspeed the model. Those who fly gliders high and above will tell you that it is very difficult to judge the models pitch attitude like that, and speed is governed by this attitude. It is very easy to either stall or overspeed the model like this, and many have met their demise because of this. The wing loadings you quote will result in a model that has to fly pretty fast, it is F3B type loadings, if you want to loiter at altitude then 10 to 15 oz/squ.ft will be much better. Provided you use a low drag foil, and keep the model sleek, then you will have a much greater useable speed range and much more useable power available for the climb, rather than just enough to keep it flying. It's all compromise.
Evan, WB #12.
Evan, WB #12.
04-02-2012, 04:03 PM
#16
Senior Member
RE: Maximum altitude??
Looking at your power system suggests you've worked out some details.
18K hmmmmmmmmm
Have you roughed out what kind of climb those 'batteries' can provide? Pulling 15-20 pounds aloft requires power. Flying it to altitude requires time.
18K hmmmmmmmmm
Have you roughed out what kind of climb those 'batteries' can provide? Pulling 15-20 pounds aloft requires power. Flying it to altitude requires time.
04-02-2012, 04:57 PM
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RE: Maximum altitude??
Da Rock,
I said I was hopeful I could reach 18K. I am also hopeful of other things that may or may not be realistic
. Hopefully you can tell me a more realistic altitude based off the details I have provided. After all, I wouldnt start a thread asking a question I already know the answer too!! 
[8D]
Brandon
I said I was hopeful I could reach 18K. I am also hopeful of other things that may or may not be realistic
. Hopefully you can tell me a more realistic altitude based off the details I have provided. After all, I wouldnt start a thread asking a question I already know the answer too!! [8D]Brandon
04-02-2012, 05:06 PM
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RE: Maximum altitude??
pimmnz,
Thanks for your info. Judging the orientation of my UAV will be no problem since I will have an on-board camera system shooting live video footage back down the ground zero (an FPV system). Also, I am more interested in finding out the optimal AoA for altitude based performance- not speed. I'm not sure if there is a difference, but I do understand that decreasing the AoA and keeping the CG constant will result in less lift and potentially more flying speed. I just would like to know what kind of AoA soaring/gliding competitiors are using on their airplanes to get me in the ball-park
Brandon
Thanks for your info. Judging the orientation of my UAV will be no problem since I will have an on-board camera system shooting live video footage back down the ground zero (an FPV system). Also, I am more interested in finding out the optimal AoA for altitude based performance- not speed. I'm not sure if there is a difference, but I do understand that decreasing the AoA and keeping the CG constant will result in less lift and potentially more flying speed. I just would like to know what kind of AoA soaring/gliding competitiors are using on their airplanes to get me in the ball-park
Brandon
04-02-2012, 05:22 PM
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RE: Maximum altitude??
Brandon,
Some "back of the envelope" calculations...
Let's say you end up with a gross weight of 20 lb., a wing area of 2,200 sq in., and an Aspect Ratio of 13. Unless you do something really strange with the planform (or twist), I would expect your lift distribution to be pretty close to elliptical (especially with an aspect ratio of 13). For an elliptical lift distribution, the lift coefficient is approximately: CL = 2 * pi * Aspect_Ratio * AoA / (Aspect_Ratio + 2).
For your configuration, I would expect your CL to be about 0.09 per degree.
AoA at seal level would be roughly: AoA = 4,100 / TAS^2 (where AoA is in degrees, and TAS is in knots)
So, for example, if your speed at sea level was 25 kt, your level-flight AoA would be about 6.5 degrees. At 35 kt, your AoA would be 3.3 degrees.
I would recommend a wing incidence that puts the fusealge "into the wind" at your cruise airspeed (i.e. about 3 degrees if you plan to cruise at 35 knots).
If your cruise L/D ends up being about 25:1 (achievable with some care), your drag would be just under a pound. The power required for level flight would be about P = 1.8 * TAS (where P is in Watts, and TAS is in knots). At 35 kt, your power consumption would be about 65 Watts. For a 10S setup, this would mean a current of 1.75 Amps. With a battery capacity of 12,000 mah (and 100% motor and propulsive efficiency) this would give a cruise endurance of 6.8 hours.
For a 10S setup, the battery charge used during a 100% efficient climb (without drag) would be: Ch = 0.204 * Alt (where Ch is in mah, and Alt is in feet). For a climb to 15,000 ft, this would equate to a charge of 3,062 mah. If you were to assume a more realistic net efficiency (prop and motor) of 65% and try to account for the aerodynamic drag during the climb, I think the climb energy would be more like: Ch = 0.37 * Alt (again Ch in mah, and Alt in feet). So a climb to 15,000 ft would probably consume more like 5,500 mah.
Putting everything together:
Endurance = (12,000 - 0.37*Alt)/2,700
As an example a mission at 15,000 ft would have an endurance of about 2.4 hours. This assumes you're willing to use all of the battery capacity and you don't need any power for descent or landing.
I would definitely check my math. Hope this is useful.
Some "back of the envelope" calculations...
Let's say you end up with a gross weight of 20 lb., a wing area of 2,200 sq in., and an Aspect Ratio of 13. Unless you do something really strange with the planform (or twist), I would expect your lift distribution to be pretty close to elliptical (especially with an aspect ratio of 13). For an elliptical lift distribution, the lift coefficient is approximately: CL = 2 * pi * Aspect_Ratio * AoA / (Aspect_Ratio + 2).
For your configuration, I would expect your CL to be about 0.09 per degree.
AoA at seal level would be roughly: AoA = 4,100 / TAS^2 (where AoA is in degrees, and TAS is in knots)
So, for example, if your speed at sea level was 25 kt, your level-flight AoA would be about 6.5 degrees. At 35 kt, your AoA would be 3.3 degrees.
I would recommend a wing incidence that puts the fusealge "into the wind" at your cruise airspeed (i.e. about 3 degrees if you plan to cruise at 35 knots).
If your cruise L/D ends up being about 25:1 (achievable with some care), your drag would be just under a pound. The power required for level flight would be about P = 1.8 * TAS (where P is in Watts, and TAS is in knots). At 35 kt, your power consumption would be about 65 Watts. For a 10S setup, this would mean a current of 1.75 Amps. With a battery capacity of 12,000 mah (and 100% motor and propulsive efficiency) this would give a cruise endurance of 6.8 hours.
For a 10S setup, the battery charge used during a 100% efficient climb (without drag) would be: Ch = 0.204 * Alt (where Ch is in mah, and Alt is in feet). For a climb to 15,000 ft, this would equate to a charge of 3,062 mah. If you were to assume a more realistic net efficiency (prop and motor) of 65% and try to account for the aerodynamic drag during the climb, I think the climb energy would be more like: Ch = 0.37 * Alt (again Ch in mah, and Alt in feet). So a climb to 15,000 ft would probably consume more like 5,500 mah.
Putting everything together:
Endurance = (12,000 - 0.37*Alt)/2,700
As an example a mission at 15,000 ft would have an endurance of about 2.4 hours. This assumes you're willing to use all of the battery capacity and you don't need any power for descent or landing.
I would definitely check my math. Hope this is useful.
04-02-2012, 05:32 PM
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RE: Maximum altitude??
Shoe, thanks for your calculations! This is exactly the kind of info I am looking for. I have also contemplated using solar cells to prolong flight times. What do you think about this idea? It seems like a logical application of the technology since light intensity would increase with altitude, but there would of course be a wight penalty.... thoughts?? http://www.outsidesupply.com/72-volt...lar-panel.aspx
Brandon
Brandon
04-02-2012, 05:53 PM
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RE: Maximum altitude??
Ifly,
If you can incorporate solar in to the mix that's great, keep in mind that you would probably have to add more wing area. At 100 ma per panel you would probably need around 55 panels to equal your motor draw at the 10S voltage. So with just the cells alone your adding 11 oz of weight to the airframe, add the associated wires and control circuitry for charging your batteries, and I would figure a more realistic estimate would be about 2 lbs...
I have to agree with what Evan said about what you want for wing loading, I would be even more conservative and want to try to get it well under 10oz per square foot.
One other note of caution when figuring out you battery size needed because of the drop in temperature at altitude your batteries are not going to be able to supply their rated level of output so it is something else you should take a good look at.
I like the solar option it would make sense for what you are doing...
While you in the deign stage try to address all of the possible issues now, it a lot easier than retrofitting to solve a problem.
Edit to add:
I just did a bit of quick math as far as the soar cells...
For your 10 cell operating voltage your going to need between 4 and six cells in series (depending on their actual voltage output) to equal your 10S voltage.
Now for charging they are saying to limit your current to 10% of your battery capacity. so if your using a 4000Mah battery for example you will need 4 of your series panels(4-6 in series) in parallel to achieve even that charge capacity. At that point your talking anywhere between 16 to 24 panels at the rated 0.2 oz each your talking about 1/4 lb for the solar cells alone (then add about 1.5 lbs for control circuitry and wiring). Realistically your talking anywhere between 1.5 to 2 lbs for the solar option.
If you can incorporate solar in to the mix that's great, keep in mind that you would probably have to add more wing area. At 100 ma per panel you would probably need around 55 panels to equal your motor draw at the 10S voltage. So with just the cells alone your adding 11 oz of weight to the airframe, add the associated wires and control circuitry for charging your batteries, and I would figure a more realistic estimate would be about 2 lbs...
I have to agree with what Evan said about what you want for wing loading, I would be even more conservative and want to try to get it well under 10oz per square foot.
One other note of caution when figuring out you battery size needed because of the drop in temperature at altitude your batteries are not going to be able to supply their rated level of output so it is something else you should take a good look at.
I like the solar option it would make sense for what you are doing...
While you in the deign stage try to address all of the possible issues now, it a lot easier than retrofitting to solve a problem.
Edit to add:
I just did a bit of quick math as far as the soar cells...
For your 10 cell operating voltage your going to need between 4 and six cells in series (depending on their actual voltage output) to equal your 10S voltage.
Now for charging they are saying to limit your current to 10% of your battery capacity. so if your using a 4000Mah battery for example you will need 4 of your series panels(4-6 in series) in parallel to achieve even that charge capacity. At that point your talking anywhere between 16 to 24 panels at the rated 0.2 oz each your talking about 1/4 lb for the solar cells alone (then add about 1.5 lbs for control circuitry and wiring). Realistically your talking anywhere between 1.5 to 2 lbs for the solar option.
04-02-2012, 06:31 PM
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RE: Maximum altitude??
Iron eagle,
I dont think I would want to replace the electrical draw of the 10s setup, but if the solar cells could replenish say, 10-15% of the draw- I think it could be beneficial. With that number in mind, it might be possible to make the upward ascent in "stages"- stopping at various altitudes and gliding for a couple minutes to allow my 10S setup to recharge. Using 5-6 solar cells would only weigh about 36 grams, and the distance between the solar cells and battery packs minimized to reduce wiring weight. As far as reducing the wing loaading... Im really not willing to make my wingspan any greater than 14ft... plus anymore wingspan I add to the wings will require more and more reinforcement to an already likely weak structural area. I do think the wing loading will be adequate. The fuselage itself will have body lines and a nice planform which will generate SOME lift...
Brandon
I dont think I would want to replace the electrical draw of the 10s setup, but if the solar cells could replenish say, 10-15% of the draw- I think it could be beneficial. With that number in mind, it might be possible to make the upward ascent in "stages"- stopping at various altitudes and gliding for a couple minutes to allow my 10S setup to recharge. Using 5-6 solar cells would only weigh about 36 grams, and the distance between the solar cells and battery packs minimized to reduce wiring weight. As far as reducing the wing loaading... Im really not willing to make my wingspan any greater than 14ft... plus anymore wingspan I add to the wings will require more and more reinforcement to an already likely weak structural area. I do think the wing loading will be adequate. The fuselage itself will have body lines and a nice planform which will generate SOME lift...
Brandon
04-02-2012, 06:48 PM
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RE: Maximum altitude??
These cell only produce 7.2-10 volts at 100 ma (the actual output voltage is something you'll have to test each panel for) and keep in mind with photovoltaic cells their actual rating is dependent upon the angle of the cell to the light, as well as their operating temperature.
Having run a cal lab for Crystalonics where we did both environmental and stress testing for semiconductors for military and space applications I can tell you there are a lot of factors you'll have to take a good look at with this type of project. It's a good thing that your not looking at powering exclusively by solar but keep in mind even charging is going to be an issue your dealing with mah not instant output...
Still all in all an interesting project good luck with it!
corrected some of the math added to earlier post:
I just did a bit of quick math as far as these solar cells...
For your 10 cell operating voltage your going to need between 4 and six cells in series (depending on their actual voltage output) to equal your 10S voltage.
Now for charging they are saying to limit your current to 10% of your battery capacity. so if your using a 4000Mah battery for example you will need 4 of your series panels(4-6 in series) in parallel to achieve even that charge capacity. At that point your talking anywhere between 16 to 24 panels at the rated 0.2 oz each your talking about 1/4 lb for the solar cells alone (then add about 1.5 lbs for control circuitry and wiring). Realistically your talking anywhere between 2 lbs for the solar option.
Having run a cal lab for Crystalonics where we did both environmental and stress testing for semiconductors for military and space applications I can tell you there are a lot of factors you'll have to take a good look at with this type of project. It's a good thing that your not looking at powering exclusively by solar but keep in mind even charging is going to be an issue your dealing with mah not instant output...
Still all in all an interesting project good luck with it!
corrected some of the math added to earlier post:
I just did a bit of quick math as far as these solar cells...
For your 10 cell operating voltage your going to need between 4 and six cells in series (depending on their actual voltage output) to equal your 10S voltage.
Now for charging they are saying to limit your current to 10% of your battery capacity. so if your using a 4000Mah battery for example you will need 4 of your series panels(4-6 in series) in parallel to achieve even that charge capacity. At that point your talking anywhere between 16 to 24 panels at the rated 0.2 oz each your talking about 1/4 lb for the solar cells alone (then add about 1.5 lbs for control circuitry and wiring). Realistically your talking anywhere between 2 lbs for the solar option.
04-02-2012, 07:02 PM
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RE: Maximum altitude??
Iron Eagle,
Well now I dont whats worse- the weight penatly of adding 160 solar cells or billfold weight loss of spending almost 5K on the solar cells haha Thanks for your tabulations. I still may opt to have a few solar cells. I believe they could have some benefit... even if it is miniscule.
Well now I dont whats worse- the weight penatly of adding 160 solar cells or billfold weight loss of spending almost 5K on the solar cells
haha Thanks for your tabulations. I still may opt to have a few solar cells. I believe they could have some benefit... even if it is miniscule.
04-02-2012, 07:06 PM
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RE: Maximum altitude??
Brandon, to fly optimum AOA (L/D) then you fly AIRSPEEDS. If you have any telemetry at all then AIRSPEED must be the first. There will be two SPEEDS you will want to fly at, the first is 'Best L/D' or 'greatest distance from a height', this will be equal to the models lowest drag per pound of lift. Then there will be 'Best c/l' or the most lift per mph your model will do. This SPEED is somewhere not much above stalling, and will give you the best 'duration from height'. Climb at best L/D, or travel from point to point at best L/D, and loiter, or climb in lift, at best c/l. Airspeed = AOA in these cases, and as indicated airspeed is not height affected, it works at all altitudes. Using a calculated model speed that is independant of altitude, GPS or similar, will have to be altitude compensated. Talk to a full size glider pilot, and you will find that they too fly airspeeds.
Evan, WB #12.
Evan, WB #12.