Why fixed wing is better for mapping than rotary wing

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Until the last few weeks, I had been assuming that we would be looking at using a quadrocopter for this research. I knew this was going to involve a lot more engineering than a balloon or kite, but until looking into it a few weeks ago, I didn’t know how much more.

Essentially, all the parts must be extremely well balanced, and thus tolerances for various parts are very, very low. This drives up manufacturing costs and makes fabricating our own parts with a 3d printer/whatever extremely time consuming and in the end, not really viable. This is compounded by increased software complexity, which I know we are all OK with conceptually, but in practice is not realistic or sustainable. Once we are in Iceland, we don’t want to need to minimize maintenance and not have the most fragile setup possible.

The only benefit of a rotary wing UAV is the ability to generate lift without horizontal thrust, which is not what we require. We are doing one long continuous flight, criss-crossing a terrain. This problem is best suited to fixed-wing UAVs, which are simpler to maintain and fly, can carry greater payloads and are not as sensitive, are much, much more efficient at generating lift, and if we run out of batteries, can glide down to earth. The biggest downside to fixed wing designs is the need for horizontal thrust to generate significant lift, making horizontal takeoff/landing necessary. This is not a problem in Iceland, where we have plenty of space. This is all leading to the final point, which is that this limited lift which can be generated by a rotary wing UAV means a payload would keep our flight times below 20 minutes, making mapping outside of a small radius around us difficult. I think we could easily get up to an hour or more on a fixed wing design with a payload with the same (if not smaller) budget.

So, in summary, even though it’s way less sexy, the fixed wing aircraft is our only real option. My next course of action is contacting old friends who are either hobbyist UAV flyers or in aerospace.

Progress Report: 10/23 – 11/6

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A lot has happened in the last few weeks, so I haven’t really had time to build a kite or really explore that possibility any further. In the mean time, I’ve worked on UAV possibilities we can look into, specifically UAV designs which promote longer flight times. Most of these have been fixed wing designs, which tend to be less of a drain on batteries. One particular inspiration is the Silent Falcon drone, which is designed for LiDAR work, and has 5-12 hour life depending on wing configurations. Building such an aircraft would mean getting carbon fiber moulding equipment in the shop, which I think will be useful no matter what drone we decide to build. Carbon fiber is pretty much the standard for quality UAV solutions, and it will make sense to make as much out of composite materials as we can.


Balloons, hot & cold

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This week, I spoke to a “balloonist” whose hobby of hot air ballooning will hopefully inform us more on the idea of using hot air balloons, and the kinds of things we should be thinking about. Though it’s not the same thing (he balloons at a scale of hundreds of pounds) there’s tons to learn from his informative e-mail. This advice will be critical when we consider the design of our balloon. His email is pasted below.

There are several items to consider.  LTA/Balloons w/ABH  or hot air balloons, use a nylon rip-stop fabric that is coated (very lightly) but some are also polyester (still coated).  Rip-stop has, by name, some safety build in and the coating gives it an almost airtight quality.  One of the reasons for using these two materials is the temperature that is needed to deform.  All the hot air balloons have a small tab at the top “tell tale” or “melt link” or “Seriloc”.  These show if the temperature exceeded certain values.  Any temp over 275 def F may have done damage (allowed deformation of the nylon).  Mylar or other thin nylon material may deform at lower temperatures.  The balloons I fly use kevlar support cables that run from the bottom to the top.  They are covered to prevent UV damage.  The envelop, kinda, slides up and down on the support cables.  There are some balloons that use steel cables.
Hot Air Balloon burners are a well engineered device.  The liquid propane comes up to the burner.  The blast value allows the liquid to go into the upper coils.  These coils are in the flame path.  This superheats the propane.  The other end of the coil is in the lower part of the burner and pointed upward to the pilot lights.  Once the propane is superheated and released into the pilot lights – it will explode.  This gives the hot air balloon a very large (8ft long and 8 inch diameter) light blue flame.  This is important as it is not just something burning naturally but boosted to release up to 19 million btu’s.  This energy release can raise the temperature of 7,000 lbs (mass) of air up 100 deg F in just a few minutes.  I worked out all the math & physic’s that a hot air balloon uses to increase the energy and lower the air mass in the envelop to get to a buoyant situation.
I do tether flights for Civil Air Patrol cadets and there are issues with any type of wind when tethering.  The wind, as low as 5 mph, will start to collapse the windward side of the envelope.  This pushes the envelope material over the burner (you see the problem there).  Once the wind gets to 10 mph the risk that the aircraft will break a tether increases.  I use the Cd (coefficient of drag) of 0.3 to 0.35 when calculating the forces when tethered.  Another issue is the wind will push the flame and blow out the pilot lights.
One of the other issues you will need to address it the rate of heat input.  On hot air balloons, the pilot judges the amount of weight, ambient temperature and amount of heat loss.  This allows the pilot to use the blast valve to add heat to maintain level flight.  I can cross a 0.5 mile farm field maintaining a 6 inch height above the soybeans by adding heat at the correct times.  Since temp, humidity, pressure, etc changes daily (hourly) you will need away to adjust the heat input to the envelop.
One of the balloons I fly has a 77,000 cubic foot envelope that supports a maximum lift of 1750 lbs.  All aircraft use  a weight and balance calculation (required by the FAA).  This balloon has a basket weight of 250 lbs and envelope of 200 lbs.  The three ten gallon talks support adding 30 gals or 120 lbs of fuel.   As the fuel burns down the amount of heat needed (lower envelope temperature) requires less fuel to be used.
One of the resources that the US provides is information about weather.  NOAA/Earth System Research Laboratory,, RUC Development Group, provides some valuable information via soundings and model analysis.  We use various model results for the our location.  They provide wind speed, wind direction, temperature, etc from the ground to 45,000 feet.  Today the wind a the ground is 246 degrees at 17kts. and increases to 21kts at 92ft, 31kts at 1407ft, 41kts at 4311ft and 60kts at 10,000ft.  You won’t tether to 10,000 feet but the speed increase from 0 to 500ft can be 10kts more then ground.  That is ok for free flight but very tough for tethered flights.  http://www-frd.fsl.noaa.gov/soundings/java/
Also, when we tether a balloon we use a three point gimbaled harness.  There is a rope from the top to bottom (every 120 degrees around the balloon) and then a second rope that slides/rides the top-bottom rope which will attach to an anchor.  This allows the balloon to remain vertical when a wind hits it.  If you just tie to the top then the bottom would get pushed out from under it and if just tie to the bottom then the top would get pushed over.
It might be better with helium or hydrogen (be careful with hydrogen as it is flammable – remember the Hindenburg Zeppelin disaster).  You might find this interesting http://www.foxcap.org/content/nearspaceballoon
If you have other questions or just want to bounce some ideas, email me.
Mike Gallant”

What I took away from this at first: we need a rigid, lightweight structure to the balloon in order to prevent collapse in windy Iceland. We should really consider using pressurized gas burners, they make a lot of heat and we need a lot of heat. Lastly, we need some seriously heatproof materials, which are also leak-proof. I hope to identify what kinds of materials we will use this week, but it may be more prudent to figure out the design of our balloon first. The design may largely be determined by the following factors: weather (wind speeds at different altitudes, precipitation) and buoyancy needs (weight of balloon, tether, burner, camera/arduino etc).

Progress Report 11/1-7

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This week I stopped working on the alcohol burner (at Charlie’s insistence) and started to look for Sterno. I did not find Sterno at Marsh or Tru Value, so someone else might have to pick that up. Once we have that, I’m hoping to use a lightweight plastic or balsa for a the frame for the envelope, though it remains to be seen if either is can be light and strong enough (I’m counting on balsa) .  Meanwhile I started researching potential DIY kite designs from which we could do our thermal mapping. I like the kite idea because it can be used when the hot air balloon cannot (because it’s too windy) giving us more flexibility over when and where we do our thermal mapping. The designs I’m looking at right now are box kites, due to their relatively simple design, ease of construction, strength and stability in the air. I hope to start building a kite out of dowels and TyVek this week, and if it’s stable, I’ll scale those designs to accommodate the thermal camera.

Progress Report 10/18-24

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During these weeks I explored the possibilities of using hot air balloons. The trick was, how do I generate enough heat to get lift the thermal camera? The answer is, a LOT. We are going to need to not only generate a lot of heat, we are going to need to have a huge envelope which holds this hot air. I’ve built a couple alcohol burners already, which worked OK. Early models exploded from vapour build-up, and later models had too little pressure to stay lit. Calibrating a burner to burn for long enough while still holding together will be quite the trick. In the mean time, I’ve been thinking: hot air balloons usually float on the calmest days. If Skalines is windy, is this the best approach?

Progress Report 10/4-10

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During this week, I actually got to use the thermal camera! It’s super cool to just look at the thermal output from things I would never have imagined was detectable. This includes tracking footprints from the thermal signature left by our feet, the heat given off by the switch panels in CST, tracking living things such as squirrels and people, and trying to identify factors that effect the thermal signature of humans. Thick clothing seems to obfuscate heat, making other places seem to give off more heat. For example when my friend was without a coat, their face registered as 87 degrees F (on the surface) and torso around 82 F, whereas with a coat, torso was practically indistinguishable from ambient temperature (Ok maybe +10, but my point being that coats reduced heat output. I forgot to record this data precisely.), and their head warmed up to 92 +-2 degrees Fahrenheit. I’m still unclear on which birds exactly we will study, and will probably leave that decision to the ecologists in Iceland and perhaps Erin (if she has a preference). Once we know that, it might be possible to more accurately model the birds with maybe a local animal with similar insulative properties and heat output, but that remains to be seen…


In the mean time, I’ve tried to track squirrels with only a thermal camera and my success was very limited. The first problem was that it is hard to find a fixed focus at which the squirrel appears sharp. This might be fixed with the balloon-tether idea which would yield a fixed height from the ground and thus static focal range. However most pressing was the battery life on the camera. I had trouble getting 5 minutes out of the device. If this is standard, we might need to design a new battery, and if it’s a result of slow degradation of the battery, maybe we should purchase a new one. Next week I’ll be sure to post pics of us looking for small animals and how well that works!

Progress Report 9/27-10/3

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Apparently Erin and Charlie are talking to the Maintenance Dept. here at Earlham College about using their thermal camera. This would be an ideal solution, because it removes a huge amount of reinventing of the wheel. It would possibly take decades to get to the level of refinement found in a real thermal camera. In the mean time, I’m mostly waiting on info from the ecologists in Iceland who will tell us which birds we can actually study in Skalines. Until we have an idea of what birds to study, I’m not sure what kind of progress I can really make.

Progress Report 9/20-26

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In this week I explored more options for thermal imaging. None of these seemed particularly promising, many of these are either expensive, inaccurate, slow, or the range is limited. So far the thermal sensor options seem to be a “pick any two” of the following options: range, accuracy, cost. Unfortunately, because picking up the thermal signature of a small animal at a sizeable range requires a significant amount of all three, there’s either going to need to be a massive engineering breakthrough on my part, or a massive budget. The same problems persist for other parts of the camera, for example, the optics. Focusing long wave IR requires exotic materials which cost an enormous amount of money to procure individually or manufacture.


My conclusion is that thermal imaging is a field with an extremely high barrier to entry. I doubt that I have the skills or expertise to surmount the difficulties I’ve touched on, and I hope that another solution will present itself.

Preliminary research

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I was kindly reminded today by Tara to post some of my research so far.

My plan so far, to use a non-contact thermometer to better identify nesting sites, has been primarily based on a paper summarizing the use of thermal cameras to identify nesting sites. Using a Thermographic Imager to Find Nests of Grassland Birds by Edward W. Galligan, George S. Bakken and Steven L. Lima appeared in Wildlife Society Bulletin in Fall, 2003.

This paper, in summary, finds that thermal cameras cannot discern nests from any considerable distance, and found that they were useful in tandem with rope-dragging as a way of confirming nesting sites after potential nests had been previously identified. This is useful for my approach in Iceland, where years of rope-dragging will hopefully mean potential sites have been identified can we can then focus on that data rather than mapping massive swaths of terrain with painstaking detail. My primary ambition is to improve on the technique described in the paper by causing reducing nest disturbances caused by rope dragging.




Testing Sensor Possibilities

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Beginning this week, I plan to first test the sensitivity and capabilities of a non-contact thermometer. If this is successful, I will start looking for a potential thermopile to use in an array in order to detect heat more quickly. This array will probably covering a 360 degrees view, though much of the configuration depends on the results of our testing with the non-contact thermometer and studies into cost and effectiveness.

Possible variables include:
At what range are these thermometers accurate and fast? Should we be scanning for heat from a UAV or the ground? If we decide to scan from the air (UAV), should we use a quadrocopter or build a RC plane? What angle should we be scanning at? Should there be redundancy or overlap in the thermopiles? Should the sensor array be moving? How fast could it be scanning?

There are many other considerations, but I hope that my testing this week will reveal answers to some of my questions. Hopefully by the end of this week I will have a general idea of how the sensor array will be designed.

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