I have just finished building a Senior Telemaster (8ft Wingspan).
I want to complete a long range UAV flight.
I am fairly new to the topic of UAVs and was wondering if I should go down the electric route or engine route to achieve the longest flight.
If I went electric - what motor should I consider and how many batteries?
If I went for the engine - what engine is very efficient and what size fuel tank would you recommend?
Thanks
Replies
Steve
Do you knowof anyone who has tried the FlyingFoam Telemaster wings cores?
They have 10" chord 72" wingspan foam cores. I have a 47" Telemaster, and I like the way it flies, so may buy a pair of the 72" foam wing cores to make a custom plane.
Stephen from Tucson
Some thoughts from an RC guy who flies electrics. You can still probably get the max flight time from a nitro engine,and just maxing out the size of the gas tank. I don't like the noise and mess, so I fly electrics.
If you decide to go electric, you will need to get about 80 watts to the prop for every pound of total plane weight
("full up weight") if you want to fly straight up. You need much fewer watts / pound to fly level and climb just a bit.
Say your plane weighs about 9.5 lb empty, and you will have maybe 2lb of extra weight (motor and batteris).
So you will need power to fly about 184 ounces of plane. An aerobatic plane needs about 11.5 x 80watts =
920 watts to the prop. You don't want this much power. You could probably get by with 40 watts/pound, so
you need about 460 watts to the prop. Hobby Lobby says that the Senior Telemaster will fly on a .46 size nitro
motor. So start with the equivalent size of electric. For example, the cheap Hobby Partz Monster Power 46
(cost is about $30.00, with $5.00 shipping).
Go to a website that has a "motor calculator" (such as Diversity Model Aircraft), and load a Power 46 motor, and
start trying out motor/prop/battery combinations. Look at the watts out (watts that actually get to the propeller),
and run time for a standard battery (such as 3S LiPo at 2200mAh). Go for the motor/battery/prop combination
that gets you about 460 watts out, and gives the longest run time.
Ex. a 12 x 10 prop with 4S 2200mAh will give you 457 watts and 106 oz of thrust for 2mins 56 seconds. Figure
that flying at 2/3 throttle will double that time.
Ex. A 6S with 10 x 6 prop will give you 505 watts to the prop with slightly less thrust for 4mins and 14 seconds.
This would be a better choice for endurance.
Now you have to optimize. Putting 2 x 3S in serial is much cheaper, but a little heavier. Buying 6S battery packs
is very expensive, but lighter. The duration that you will get out of your batteries is a ratio = (known run time)/known mAh.176 seconds/2200mAh To fly 10 mins solve for 600secs/?mAh = 7500mAh. The amount of mAh that you carry in the plane is essentially the size of your electric gas tank.
8 x 2200mAh batteries will get you roughly 1408 seconds or 23.46minutes on full power, and perhaps twice that
flight time if you throttle down to at least 2/3 power. Buy a speed controller that will handle maybe 50% more amps than the motor you just tested constantly uses (you don't want it to overheat!).
Warning! You have to find the minimal power that it takes to safely fly your Telemaster, fully loaded. You must
have a motor that can provide this thrust. Then use all the rest of your payload to carry your "gas tank".
A very different approach: Trim your plane for efficient gliding with the motor off. Learn to slope soar it with the
motor off. Learn to catch thermals, like a sailplane, with the motor off. If your Telemaster will thermal, then the
only battery power you need is to run servos, and you can fly for hours on small battery packs.
Tip: more expensive electric motors weigh 2/3 to 1/2 what the cheap motors do, for the same power. For absolute
endurance, the lighter motors are better (but 3 to 4 times more expensive). Tip: don't buy the smallest motor that
will put out your needed power. It may heat up to the degree that your speed controller will shut it down. Tip: put
a separate UBEC in the plane, so that your receiver always has a separate power supply.
And most of all -- have fun!!
Stephen from Tucson
Power?…She-started-life-on-FOX-40-and-struggled-on-take-off
On-second-thought-should-have-installed-flaps
But-went-with-flaperon-instead
Taildragger-for-grass-the-bigger-the-wheels-the-better
Then-old-FOX-60-Eagle-more-than-enough-power-but-sucked-a-lot-of-fuel
Then-OS-60-two-stroke-such-an-over-kill-the-45-would-be-perfert
Then-OS-60-four-stroke-for-max-fuel-efficency
Exhaust-ports-via-high-temp-hose-low-under-right-wing
AP-points-under-left-wing
With-floats-for-water-AND-snow
No-auto-pilot-yet
Only-72MHz-RC-line-of-sight
ArduPilot-on-foam-test-platform-as-we-type
For-long-range-endurance-I-plan-to-use-the-ham-bands.
Two-meter-local-repeaters-for-voice-comms-and-?maybe?-telemerty-plus-sveral-hams-stationed-along-flight-path-with-lawnchairs,72MHz-RC-uplink-and-handheld-2m-XCVRs.
Video-down-via-440MHz-(70cm-ham-band).
Henry,
Not-sure-your-QTH…(home-location)
http://www.arrl.org/
In-the-US-you-only-need-a-no-code-Tech-class-license
John
Pardon-the-dash-myspacebarebitthedust…
We are running an AXi 4130/16 motor, Phoenix 80 speed controller, I can't see the prop label because the spinner is covering it, but it's a 15" prop. If I had to guess at pitch I'd say 7" ???? We are flying with 8000mah 18.5v batteries from truerc.com. We can do roughly 30-35 kt cruise at somewhere between 60-75% throttle and fly about 30 minutes at those speeds.
This is our development/test airframe so we haven't tried to optimize weight or endurance. We are flying with two additional 2000mah NiMH batteries (one for avionics and one for our radio modem.) In addition we have big heavy 6" balloon "tundra" tires from dubros.
Top speed is maybe 42-45 kts in level flight. (Units are in knots because that's what our avionics reports.)
For electrics, the slower you can spin the motor, the longer you can fly.
If you want to fly as long as possible, you'll probably do better with a gas 2-stroke engine. Gas has great energy density than batteries and you burn off weight as you fly. But electric power has many advantages and conveniences for UAV work. Field logistics are usually easier (fueling the aircraft, starting the engine, cleaning up after flying, etc.), you don't have messy exhaust fouling your cameras or sensors, often there is less vibration, generally your aircraft is quieter (although a large portion of the generated noise comes from the spinning prop.) There are still just as many safety issues in terms of working in close proximity to rapidly spinning knives ... and an electric motor could start at any instant and if you stick your hand or arm in the way it won't quit trying to spin the prop, it just keeps cutting and cutting. So be careful and use good safety procedures no matter which power system you use. Always think about where your hands/face/arms are in relationship to the prop ... even when the motor isn't running.
If you want to fly for hours and hours, don't forget to make sure you have enough battery capacity to power your avionics and RC electronics.