High Altitude Flying

[N2EC]

Hello,

I wanted input on the safeguards required for high altitude flying and also sharing of experience. The plan is to fly from 10,500 feet and 2,500 to 3,500 feet high (in effect at about 13,500 feet above sea level) with a Zenoah G62 powered airplane with tempereatures in the range of -10 to -20 C. Wing loading of about 45 oz/sq ft. The Zenoah provides plenty of thrust at Sea Level. Takeoff runs are less than 20 meters. Rx and Servos are powered by NiCad Batteries.

I would like inputs on the following:

Battery Operation - Heating necessary before or during flight
Any effect on Tx/Rx Operation and Servo Operation due to the cold weather. Any effect on range of the radio.
Engine - Effect of cold climate and rarified air on power. Prop changes ?
Would composites getting affected due to the cold climate.

Would appreciate your inputs on the subject. Thank You. Attached ia a photo of the airplane.

N2EC

[N2EC]

Javelin X - Photo missed out in the last post.

[dmgoedde]

Hello,

I wanted input on the safeguards required for high altitude flying and also sharing of experience. The plan is to fly from 10,500 feet and 2,500 to 3,500 feet high (in effect at about 13,500 feet above sea level) with a Zenoah G62 powered airplane with tempereatures in the range of -10 to -20 C. Wing loading of about 45 oz/sq ft. The Zenoah provides plenty of thrust at Sea Level. Takeoff runs are less than 20 meters. Rx and Servos are powered by NiCad Batteries.

I would like inputs on the following:

Battery Operation - Heating necessary before or during flight
Any effect on Tx/Rx Operation and Servo Operation due to the cold weather. Any effect on range of the radio.
Engine - Effect of cold climate and rarified air on power. Prop changes ?
Would composites getting affected due to the cold climate.

Would appreciate your inputs on the subject. Thank You. Attached ia a photo of the airplane.

N2EC

I believe Lithium give superior cold performance, however you would need to verify that, plus anyway need a voltage regulator. If you used 2cell LiPo and for voltage control a simple 5V fixed linear regulator, the "waste" heat could be used to keep warm an insulated inner-chamber of the R/C Rx and servos. I don't have any high alt/cold experience yet, but suspect the grease or oil in servos would thicken to the point of impeding servo fucntionality. Maybe there is lease grease that I think between the gears of your garden-variety servo. Another potential concern with the electronics is that the crystal changes frequency spec at temperature extremes. I do think you'd be OK at -20 C though.

Another thing: resist the temptation to use a "hand warmer" as they contain H2O, and as others have discovered the hard way, the moisture evaporates then condenses on cold electronics!!

[ps2727]

You have an interesting project there....
I would think that the engine would need to compensate for altitude by adjusting the mixture...maybe the Walbro carbs do this now, I don't know. Without some method I think the power output would be an issue.

Good luck with your vehicle and please tell me you will be operating in protected airspace!
Paul

[Unterhausen]

the problem with lipos for low power uses is that you probably are not going to be keeping them warm enough to function properly from the current drain. If you were using them to power the prop, that would not be a problem.

[macboffin]

The power will reduce at the rate of 3% per thousand feet Asl. The walbro carbs adjust for ambient pressure, Otherwise the engine would run very rich, BUT power will be down about 30%/35%.Larger diameter and slight pitch increase is helpful.Take off distance will of course be longer, and the "space between stall speed and max speed will become smaller. Nicads or A123s better for cold temps, although best to warm before flight;if you want to get safer, run an exhaust extension adjacent to an airflow over batteries,(but don't cook 'em!) After flight keep equipment warm and dry if possible, to avoid condensation on bits that don't like it!
Been there, done that, aint easy!

[Tra]

I'm curious OM, have you obtained the necessary Air Worthiness Certificate for your vehicle? Without it, US Law forbids any UAV from flying above 500 feet.

I know several high altitude balloonists who have built UAV gliders to return payloads from 100,000 feet, and they are shut down due to current regulations.

Under the law, a remote controlled 'guided' parachute is illegal. A parachute is only legal IF it is totally controlled by the prevailing wind.

Do UAV hobbyists operate anyway, even though it's illegal in the US? I'd be doing UAV's myself if it wasn't for the FAA regulations.

I live in Maine and remember the old battle that raged for years over the governments efforts to use the northern part of the state as a test range for unarmed UAV's (called cruise missiles). Despite their own laws, the people of Maine prevailed against the governments plans to test cruise missiles here, primarily because they did not have an air worthiness certificate for the cruise missiles as they were 'under development' at the time.

Regards,

T

[Unterhausen]

too bad people don't fill out the "location" field of the user profile. Would make a lot of these questions easier. The attached pic doesn't look like it's from the U.S. to me, but it's hard to judge.

[macboffin]

too bad people don't fill out the "location" field of the user profile. Would make a lot of these questions easier. The attached pic doesn't look like it's from the U.S. to me, but it's hard to judge.
Location is possibly Northern India ; and the altitude would be right for surveillance over the Siachen Glacier on the Chines border.Posted a while back about my own experiences around there.

[macboffin]

Noted that some while back N2EC made some posts about sampling volcano smoke plumes, could relate to that.Found a video of a Javelin target, (in grey paint finish) in flight on Youtube which E2EC posted.Goes good, but fast.Don't fancy it at 10k plus feet though.Plus ; volcanic plumes are full of highly abrasive ash particles which kill engines very fast, (Many aircraft brought down because of that) as well as all kinds of electrical activity ; have seen many pictures of lightning crackling around in volcabic plumes. All in all no place for an airplane!
Ok, ok, so I'm a nit picker, but.........

[Tra]

N2EC is in Maryland, at least that's where the FCC thinks he lives. It's public information, although his address doesn't necessarily mean that he is flying in the US.

Any ham radio operators current address can be searched via the many online outlets for such information, I found N2EC's information at www.qrz.com.

Regards,

T

[N2EC]

Thank you all for your responses. The airplane will be flown in military airspace. I am based in India and the picture is from a recent mission in Rajasthan. The airplane is used as a target for aerial gunnery practice and also tows a sleeve behind it.

The video on YouTube is that of ProtoType 1 of Javelin X. I havent been around volcanoes with airplanes though.

Mac- I had experimented with a 22 X 12 on the Zenoah but that resulted in the loss of almost 1,700 RPM. 22 X 10 gives about 6,900. Would it help to stay constant on the diameter and reduce the pitch or do both by trying a 20 X 8 which would result in increased RPM.

On the takeoff I have the option of using a catapult launcher with 1.5 times the pressure that I generally use on MSL. Would this help. Also, another thought was to introduce 15' flaps through flapperons.

Heating Batteries with exhaust seems like an idea. Any pictures or sketches ?

The airplane would be flown as a target/tow airplane at the high altitude. The customer would like to replicate all the tests done on the airplane at MSL only high up. The airplane tows a sleeve with a tow length of 50 meters. I am not too keen on towing the sleeve at that altitude as would not get enough power out of the engine.

"dmgoedde - I don't have any high alt/cold experience yet, but suspect the grease or oil in servos would thicken to the point of impeding servo fucntionality. Maybe there is lease grease that I think between the gears of your garden-variety servo."

Servos - Any special care required. Futaba/Hitech are used.

Thanks again for your quick responses.

[N2EC]

What are your thoughts on adding about 10% nitro to the gas for extra revs.

[macboffin]

What are your thoughts on adding about 10% nitro to the gas for extra revs. That works! Works for glow at altitude also ; ran a O.S.32 on 505 nitro at 10k plus altitude in Kashmir. You have to do your prop tests at altitude, due to "thicker" air your revs will be down anywhere near sea level.Although the air is thinner at altitude, it's colder also, which engines like, colder air being denser than warm ; plus it's dryer.
Was interested to see my guess about locale being India correct!
Towing drogue ? Well, power is down, but drag also less.A case of suck it and see I guess! Take -off with drogue ; flake the drogue down backwards and forwards on itself ; the plane accelerates faster and uses less airstrip that way, as the load comes on gradually. I'd be inclined to test with smaller drogues first, work up to bigger ones.

[Hovertime]

I would check sanyo web site to verify but I think NiCd's are perfectly fine in -20C...
Servos - grease may freeze up, so let it get really cold and then test them carefully.
Some manufacturers can hook you up with servos greased with low special grease for extreme ops, I would email hitec ask for advice regarding that.
Probably use 5 cell pack for RX.

Plastic gets brittle when its cold so probably use some sort of metal geared servos and hardware accordingly.

And one of the biggest concern is all the electronics cause they seem to be tested at humane operating temperatures for average RC pilot....
Freeze the hell out of it and do lots of ground testing.

[N2EC]

Hovertime, thanks for your inputs. It appears I will have to pre conceive all the things that can go wrong and take precautions in advance as I will not have a chance of testing on an occassion prior to the mission in the required environmental conditions. So take all precautions, necessary or unnecassary and take the leap of faith.

To simulate the cold temperature, would it help to put the rc equipment, batteries etc in a freezer and then test. Can the moisture inside affect the equipment.

Also, to get some results would leaving the equipment in the freezer for say 3 hours and then operating be okay.

[Earl Jr.]

http://members.shaw.ca/sonde/ you might check out this guy's website. He launched a glider from a weather balloon. He didn't mention any problems with the servos at altitude. He actually rigged up a way to keep the batteries warm with excess heat from the other electronics.

[Capt. Crunch]

Most Frost Free Freezers are pretty dry, I'd give it a try.
For most of these tests they 'Cold soak' for 2-3 hours first.
I'd put the batteries, Rx and srervos in, and rig up a load on the servos to quantify the loss of power at low temp.

[N2EC]

http://www.youtube.com/watch?v=nU9J3tmyWNs

[N2EC]

The power will reduce at the rate of 3% per thousand feet Asl. The walbro carbs adjust for ambient pressure, Otherwise the engine would run very rich, BUT power will be down about 30%/35%.Larger diameter and slight pitch increase is helpful.Take off distance will of course be longer, and the "space between stall speed and max speed will become smaller. Nicads or A123s better for cold temps, although best to warm before flight;if you want to get safer, run an exhaust extension adjacent to an airflow over batteries,(but don't cook 'em!) After flight keep equipment warm and dry if possible, to avoid condensation on bits that don't like it!
Been there, done that, aint easy!


Exhaust Manifold Heater Idea from General Aviation Single Engine Airplanes would solve the trick for keeping the batteries heated as suggested by Mac. I am considering a shroud over the exhaust with the air going to the battery compartment.

[dmgoedde]

What are your thoughts on adding about 10% nitro to the gas for extra revs.

Hey - might be esoteric - but what about in-flight adjustable mixture between gas and nitro via some feedback loop?

[Mark Harris]

Exhaust Manifold Heater Idea from General Aviation Single Engine Airplanes would solve the trick for keeping the batteries heated as suggested by Mac. I am considering a shroud over the exhaust with the air going to the battery compartment.

Not sure you'd want to do that on a 2 stroke.. maybe a 4stroke might be OK. By the time you land you'll have your batteries sunk in a bucket of oil...

[N2EC]

Running a 2 Stroke Gasoline on the airplane.

[kd7ost]

Here is my experience with batteries and servos at cold temperatures.

In a HAM radio group we launch small capsules under weather balloons in excess of 100,000 feet MSL. We record temperatures at high altitudes as low as -90 F at times but certainly down to -60 F routinely. (-60C to -50C) We use servos to perform functions at those altitudes as well. Several years ago I dropped a capsule, (cutaway via servo) and allowed it to free fall down to 20,000 feet MSL where another small servo deployed a chute for normal landing. The servos and batteries were not heated but rather were allowed to be open to ambient air and resultant temperatures. Here are a few threads showing the capsule construction as well as the flight day pictures.

http://www.tvnsp.org/modules.php?set_albumName=Aurora&op=modload&name=Gallery&file=index&include=view_album.php&page=1
http://www.tvnsp.org/modules.php?set_albumName=TV04B&op=modload&name=Gallery&file=index&include=view_album.php

Our experience has been as follows as far as your questions.

All batteries begin to lose the ability to put out full rated current as their core temperature drops. The worst in performance are any standard Carbon Zinc and NiCd battery. They pretty well drop to a trickle as they reach the freezing temperature of water. 0C or 32F. Much better in performance are Nickel metal Hydride cells and Lithium Polymer cells. We have never had any shut downs of equipment due to freezing in those chemical technologies.

That having been said there is a power drain to power density performance issue. What I mean by that is that if you are loading cells at the full rated discharge current drain, and you allow the cells to get extremely cold, you will suffer reduced performance. As far as I know this is only an issue in systems like electric power units in extreme cold. If you’re putting a smaller load on batteries that have a fair amount of power delivering capabilities, you will be in good shape. There are two things you can do to maintain optimum servo power performance in cold temperatures.

First is to use batteries that supply ample current when cold. This means using NiMHD or LiPo cells. Second is to use servos that will do the job with minimum current drain. In my UAV aircraft I put all the critical flight control surfaces on Futaba, JR or Airtronics servos that are metal geared, dual ball bearing supported, and most importantly, use a coreless motor and a high torque rating in the gear box. High torque in this case means you can perform more work, with less battery power consumed, but at slower speeds. The speeds are a non issue in a UAV flight envelope. The servos shouldn’t be maxing radically full range back and fourth in normal UAV flight. 3D maneuvers yes. UAV flight envelope no.

I have flown my own UAV up to 11,000 feet MSL powered with a Fuji BT32A. The takeoff run was certainly long but once in the air I did not detect any serious performance issues. I could have flown higher if I had the need to do so.

My wing loading is only 37 oz per square foot but as the plane gets bigger in span Reynolds numbers show you can get higher wing loading with increased performance. Depending on your total wing area, you should be OK. The G62 has a lot of muscle.

One more side bar. I talked with Dr Greg Holland of Aerosonde fame a couple years ago when he came to Boise, Id. They are using Futaba servos and LiPo batteries on their aircraft and they fly quite high and have pretty high wing loading numbers. (Engine is different though as they use EFI in a 4S engine and the fuel/air mixture metering changes automatically as the altitude or air density changes.

Dan

[D Hobby F3J WC2]

Hello Kd7ost

My name is David Hobby and I have been on the Aerosonde project for 15 years.

Aerosonde has flown in temps. of -35C in Barrow Alaska

We use JR servos (no modifications) on the flight controls and NiCd batteries (unheated). The servos work fine. The batteries start to loose significant performance below -20C. An onboard generator overcomes this problem.

MiMh cells, we found to be the worst performer in the cold and we have not used LiPo cells.

Cheers

[N2EC]

Hey David,

Thanks for your reply. Your post clears out every doubt in my mind.

Regards

N2EC

[anci3nt]

I'm curious OM, have you obtained the necessary Air Worthiness Certificate for your vehicle? Without it, US Law forbids any UAV from flying above 500 feet.

I know several high altitude balloonists who have built UAV gliders to return payloads from 100,000 feet, and they are shut down due to current regulations.

Under the law, a remote controlled 'guided' parachute is illegal. A parachute is only legal IF it is totally controlled by the prevailing wind.

Do UAV hobbyists operate anyway, even though it's illegal in the US? I'd be doing UAV's myself if it wasn't for the FAA regulations.

I live in Maine and remember the old battle that raged for years over the governments efforts to use the northern part of the state as a test range for unarmed UAV's (called cruise missiles). Despite their own laws, the people of Maine prevailed against the governments plans to test cruise missiles here, primarily because they did not have an air worthiness certificate for the cruise missiles as they were 'under development' at the time.

Regards,

T
Tra, I'm just getting started on a weather balloon project, but some of the initial ideas has gotten me excited about expanding it to a more UAV flavor! I've searched for FAA regulations regarding some of these activities without much luck. Best I could muster was a few mentioned of what 'classified' as a weather ballon. Is that FAA 500' altitude limit state or federal?

Do you have any suggestions on where I might find hobbiest high flyer regulations in general? Any direction would be much appreciated.

- B

[kd7ost]

Hello Kd7ost

My name is David Hobby and I have been on the Aerosonde project for 15 years.

Aerosonde has flown in temps. of -35C in Barrow Alaska

We use JR servos (no modifications) on the flight controls and NiCd batteries (unheated). The servos work fine. The batteries start to loose significant performance below -20C. An onboard generator overcomes this problem.

MiMh cells, we found to be the worst performer in the cold and we have not used LiPo cells.

Cheers

Hi David,

That's some good updated information you provided about Aerosonde. When I mentioned servo's that wasn't a recommendation on my part by any means. I think any quality JR, Futaba, Airtronics etc servo would do the job just fine.

I am surprised you use the Nicds cells for power though just because my own experience with operating batteries in the cold are somewhat different. But thanks for adding info in here. It's great to get information from field users like yourself. That's tangible stuff. And I envy you for getting to work with Aerosonde. Good job.

Is Greg Holland still around?

Dan