Announcing the newest version of the Raptor 140! Its main objective is to fly over 120km(75mi) at 115kph(71mph) and send signals (including video!) over 3km(1.9mi). It should be ready to fly early February 2014. Anything you see in my design that I should reconsider?
Estimated Raptor 140c Stats:
Weight: 2100g (4.6lbs)
Max Flight Time: 100min (1hr, 40min)
Max Range: 120km (75mi)
Stall Speed: 35kph (22mph)
Cruise Speed: 115kph (71mph)
Max Speed: 145kph (90mph)
Radio Range: 3.5km (2.2mi)
Energy Carried: 289wh (20,100mAh at 14.4v)
Drive Power: 850w
Meters per Watt/Hour: 450
Features of the 140c (improvements over 140b in parentheses):
Airframe:
-MyGeekShow's Raptor 140: 140cm Wing Span
-CG at 26cm from nose (very, very balanced, almost zero reflex)
-EPP foam construction
-5mil Laminate covering
-Aluminum Motor Mount
-Additional laminate to strengthen leading edge (allow for rougher landings)
-6.4m (21ft) of carbon fiber (had 4.5m) (add additional rigidity)
-5cm x 48.5 elevons for low drag control surfaces
-Laminate elevon hinges (more strength and durability than packing tape)
-14cm winglets for visibility and lift improvement
-Integrated steel launch hook, closer to CG (better bungee launches)
-Parachute ring (allow parachute recover system)
-Velcro battery retainers
-PET plastic battery covers
-Plastic flight controller cover
-Precipitation 100% sealed (can fly in rain)
Flight Systems:
-433mhz EZUHF radio system (500%+ radio range improvement)
-32g servo (additional pull strength and durability)
-1250kv motor, was 1450kv (slower rotation as it is switching to 14.4v from 11.1v)
-24 3.6v Li-Ion 3.3Ah cells in 4S6P, aka 289watt/hours (20.3Ah at 14.4v) Raptor 140B carried 111watt/hours
-10x6 carbon fiber folding prop (140B had a 10x7 due to higher kv motor)
-4.7cm aluminum prop hub
-Wiring lanes in airframe (improved wire management)
-4 Ferrite Filters (cleaner transmissions and reduced interference)
Avionics:
-1080 HD Mobius camera (was 720 808 #16)
-FPV tx 1.3Ghz 400mw
-APM2.6 flight controller
-3DR Current Sensor
-3DR uBlox GPS with compass
-1w 900mhz 900RDF telemetry (had 0.1w telem)
-FAA style lighting (improved visibility)
-3A BEC (provides power to telemetry, camera, etc)
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Learn More:
Raptor Details: http://www.mygeekshow.com/theairplanes/Raptor140.html
USA Trip Details: http://www.mygeekshow.com/usatrip/
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Filmed, Edited, Produced and Published by Trent in Arkansas, USA
Comments
Awesome stuff everyone! Michael said it perfectly: "As with modern passenger jets, their speeds are not based on fuel efficiency, but they certainly work to improve efficiency at the required speeds."
That is exactly it, the first requirement for the USA plane is to cruise at highway speeds, and then second to make it fly at that speed as long as possible (therefore as efficient as possible).
The 140c should be able to cruise at 100kph for about 1.5 hours, or 150km. We'll see of course! Theory and reality are not always the same : )
I'm going to be a pest, sorry!
A little something I composed, yeah, I can always blame Bachus
"Rule of Thumb"
for
My Electric Aircraft
(Or, why I over engineered Talon :-)
And not all my own work, I have to add.
I work on "100 Watts/pound", for sport flying.
Glider type aircraft require less.
Next decision, how fast should that airframe fly ?
Talon, by virtue of it's design, and the load I want to carry,
will definately fall into the "Sport "class.
Talon should fly very well at 70 Km/h, but I might hit a headwind.
So, let us try to design for 100Km/h.
From gut feel and experience, I go for a 6" pitch prop.
If you do the math, this prop @ 10000 rpm will give you about 91.5 Km/h.
That was the easy part.
Talon with electronics and a thumbsuck motor weighs 1 Kg, 2.2 pounds.
Right, I need at least 200W.
But Talon can safely carry another 1 Kg, so we now sit at 4.4 pounds.
So I need 440 Watts, for Sport flying, remember !
All I have in the junk box is a 3548 900Kv motor.
Google tells me this motor can do 570 W, and 8910 rpm on a 3S (depleted) pack.
And that gives me 81.5 Km/h...., Still kind off in the ballpark.........
But now, you need to peruse the manufacturers specification, on what length prop the motor can turn.
To remain in the power band.
I'm flying a 12X6 APC electric.(Gut feel now tells me a 12X7 will be more efficient)...
And since we have been very conservative with our aircraft, add another 500 grams for a camera !
Still means you can have 1 Kg of battery, nice!
Just so happens, 3S 12000mA/h weighs 1Kg....
And that gives you a total of........ roughly 144 Watts, to fly with.
Just so happens, my Talon only draws 220W, at full throttle, on the ground.
Yet, flight tests shows me, at 3/4 throttle, it runs at +- 70 Km/h, and should stay in the air for 45 minutes.
I'm going to digress...
Max LD.......
Most sailplane pilots will be very familiar with this term, hang glider pilots even more so!
Every single winged flying thing has an optimum flying speed, where you cover the most distance, for the least energy expended.
Fly to fast, you fall short, fly too slow, you fall short. As simple as that.
Google "MaccReady Ring", and "en.wikipedia.org/wiki/Speed_to_fly"
That is a factor I rarely see addressed on RC forums.
Happy flying!
You can manually change speed during an Auo mission through MP under the Actions tab on the Flight Data screen, or insert predetermined Do_Change_Speed commands between waypoints on the Flight Plan screen.
Trent will probably run in the same practical problem I am trying to work out for my own project.
To maintain LoS on motorway/freeway is easy if you fly alongside at 60mph. That's not the problem. The problem occurs when you have to switch to a winding backroute for one part of the route. For example, my route has a narrow section with 8 switchback in it - the plane will be running at the same speed as before, and very quickly will be way out of LoS ahead of the car.
So I have to slow down the UAV over specific waypoint sections, without altering the route onroute. But isn't WP_SPEED fixed for the entire route?
Trent said:
"My main concern is that 170kph of "travel speed" with a 14in column of air is TOTALLY different than a 170kph of "travel speed" with a 10in column of air..."
Is there a difference between these two flying modes, although both are going at the same speed?
Since your cruise speed is determined by speedlimits on the highway, you measure how much throttle you need in the air and measure the grams of thrust on the ground with this amount of throtle (removes many of the theoretic assumptions and formulas). Then you can compare motors/props and pick the one that has the most grams/watt for that amount of thrust. A picture always illustrates things best, why you can get 50% improvements when hitting a sweetspot in terms of efficiency:
Ok... it only took two pages, but I'm glad we all can finally agree to agree. ;)
@Trent, sorry to go back to a question I already asked in regards to your cruise speed. Can you give more detail in your answer? Do you mean your selected cruise speed (115 kph)is the min point of your Power/Velocity curve, or is it selected based on a target current draw?
Ah, I missed the post by Gary M,
Exactly what I was trying to point out, a big prop turning slowly is way more efficient than a small prop screaming like a banshee.....
So, can we agree, for a given task, you require X Kg, or "Watts" of battery?
Granted, at higher voltage, that can be done at a lower current, but my gut feel is that any efficiency you win electrically, you lose in the smaller prop.
I'm gonna pour another glass of wine...........................
Thanks Michael for your great post and for pointing out my somewhat blinkered way of looking at things.
Also thanks to Gustave for doing actual testing.
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