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Old Mar 04, 2014, 01:15 PM
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My Ambitious, One-tenth Scale, EDF-powered, XB-70A-2, Experimental Bomber Project

Hello, I am contemplating on building an extremely accurate, one-tenth scale version of the XB-70A-2 (specifically the second prototype made by North American Aviation, Air Vehicle No. 2 [SN: 20207], which had five degrees of wing dihedral; it was destroyed during in a crash after a mid-air collision with an F-104 Starfighter). I am planning on spending an exorbitant sum of time and money in order to bring this project to fruition, and I am also very interested in the invaluable learning experience that I will acquire from it.

I'm going to build it out of the exact same metals that were used on the original aircraft, in order to make it as authentic as possible, and it's going to be powered purely by electric motors. The real Valkyrie had a gross takeoff weight of at least 540,000 pounds, and because I'm building this as accurately as possible on a one-tenth scale, we can automatically assume that the gross takeoff weight for the model will be a mere 540 pounds, considering it's made on scale of all the same materials the real aircraft was built out of. It will be roughly 19.5' long (from the very end of the tail to the tip of the titanium pitot), 10.5' wide, and 3' tall.

I am looking only for the absolute best of the best components to fit into this RC aircraft’s airframe from, so I'll just lay out the components I cherry-picked here after scouring the Internet for hours in my research: it will use six ten-bladed (the most blades available for this particular EDF; it also provides the most thrust, as opposed to the five-bladed variant), 147mm Aeronaut TF-8000s, in order to unlock their massive thrust capabilities, six of the most powerful and high-quality ESC offerings by MGM Compro (specifically, the TMM 40063-3 X2-Series Pro), six of the most powerful variant of the Lehner 3080, DC brushless motors, for maximum power, and lastly, but certainly not least, it will use ninety Gens Ace 5S1P (18.5V, 16,000mAh [296Wh]) batteries, to propel this massive beast through the air!

The performance requirements are pretty simple: I'm looking to break a multitude of world records in the all-electric RC aircraft category—one of the main performance records I plan to achieve is at least Mach 0.3 (this would be approximately one-tenth scale speed of the real Valkyrie, which could cruise at velocities in excess of Mach 3) to Mach 0.5 (my preferred goal), at an altitude of at least 30,000ft (I don’t mind pushing it further if enough power is available to ascend), using EDFs. Now, I know what you're thinking: "How in the HELL are you supposed to propel a 540-pound airplane to half the speed of sound at 30,000ft?!" Well, I’ll admit, it sounds complicated, but the main underlying issue to achieve such a level of performance is simply a lack of power: The ESCs I'm using are quite literally the best in the world, and are capable of delivering a continuous power output of 22kW (each one is specified at 15S [55.5V], and is capable of delivering 250A of continuous current!), per ESC, to the Lehner 3080, DC brushless motors (which are more than capable of handling 22kW of continuous power, provided there is sufficient cooling); this means that at full power for ALL SIX motors, I'm delivering 132kW (roughly 177HP) of power to propel the aircraft and its cargo.

The real XB-70A Valkyrie contained 47,708 gallons of JP-6 fuel, with each pound of fuel weighing approximately 6.7264 pounds, which means in total all that fuel weighed approximately 320,903.0912 pounds. On a one-tenth scale, the fuel, or in this case, batteries, I’d be able to use up to roughly 320.9 pounds of them. As for the volume, 47,708 gallons on a one-tenth scale is about 47.71 gallons. Each Gens Ace battery weighs 3.54889 pounds, and all ninety of them would weigh approximately 319.4001 pounds. Each battery takes up 0.186896793 gallons, so all ninety of them would take up about 16.82071137 gallons in space, which is funny because that’s nearly three times less volume than what the fuel would take on the scale, which also means I have more space for more equipment! Now, the entire array of ninety batteries, which altogether contain a total of 450 3.7V, 16Ah, Li-Poly battery cells; each battery contains 296Wh of energy, and in total all ninety batteries contains a staggering 26.64kWh of energy. With this much energy, I could, theoretically, deliver 132kW (177HP) of power across all six engines (22kW, each), for up to twelve minutes.

I’m planning on spending a minimum of $50,000 to build this entire aircraft—with the airframe, cockpit, and landing gear being 100% built from scratch—components and all, over a period of three to five years; so I can expect the first flight to occur between as early as the fourth quarters of 2017 and 2019.
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Old Mar 04, 2014, 01:32 PM
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Si Goodchild's Avatar
Lincolnshire, UK
Joined Oct 2009
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How will you see it at 30,000 ft? And how much power will be left in the batteries after you climb there?

Sorry, but prepare for a torrent of dis-believers!
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Old Mar 04, 2014, 01:37 PM
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I'm planning on using FPV with a decent enough transmitter to see where I'm going with it; I'm not looking to go further than five miles with this thing, at least not on the first flight.

I'm only guessing this, but I "think" it might take me no more than six minutes to achieve that altitude from takeoff. At that point I'd have roughly six minutes of power left in the batteries; and since I'm planning on flying at such a high altitude, the batteries might lose some of their charge, so I'm accounting for a 20% loss, which would mean I'd have shave off about two minutes from the twelve, leaving me with ten minutes. This is assuming I have to deliver the full power capability (132kW [177HP]) to all six engines; I might only need to be at a half or quarter power level to maintain altitude, which means the flight time could theoretically increase by double or quadruple, at best.

So..., at full power level, I would probably have to spend no more than a minute to takeoff, four minutes to reach altitude, and the remaining five minutes would be used for leeway, so I could at least land safely somewhere.
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Old Mar 04, 2014, 01:48 PM
turbonut's Avatar
upland CA
Joined Dec 2004
7,256 Posts
Well......how about your back round? how is it you think you can do this.....if your in the US its not legal..you will have the feds on your door..new UAV laws restrict how we can fly our models and you are looking way past what we are allowed to fly
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Old Mar 04, 2014, 01:51 PM
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I'd use the FPV hardware to bring me back as well, but does that mean not even an FAA clearance would grant me permission to do this legally? Also, I'm doing this flight 100% manually, none of it's autonomous, just in case you were unaware.
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Last edited by Nuclear Armament; Mar 04, 2014 at 01:56 PM. Reason: Forgot to add some information.
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Old Mar 04, 2014, 01:56 PM
Current project: Electrolyte
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United States, OH, Dayton
Joined Apr 2004
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Love your ambition Gene!
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Old Mar 04, 2014, 02:31 PM
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How much thrust you calculating to be able to squeeze out of the EDFs at 30,000 ft?
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Old Mar 04, 2014, 02:38 PM
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eatond's Avatar
United States, MO, St Charles
Joined Nov 2002
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Hmmm,
I'm thinking you would have much more succeess with this thread if you had waited until 28 days from now. Sometimes, timing is everything.

Dan Eaton
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Old Mar 04, 2014, 03:51 PM
turbonut's Avatar
upland CA
Joined Dec 2004
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Dang nabit did I get Gene ed again...Lol
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Old Mar 04, 2014, 03:57 PM
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Thrust calculations on the ten-bladed, Aeronaut TF-8000 EDF Units

Quote:
Originally Posted by Dirty Dee View Post
How much thrust you calculating to be able to squeeze out of the EDFs at 30,000 ft?
Well, to put it from the perspective from the actual Valkyrie, the thrust was 28,800 pounds per engine at full afterburner, and all six engines produced roughly 180,000 pounds of thrust, to propel a 540,000-pound (270-ton) aircraft up to speeds in excess of Mach 3, at up to 77,350 feet. The thrust-to-weight ratio of this aircraft, when fully-loaded and fully fueled, was about 0.33:1.

At one-tenth scale, I only need to produce twenty-eight pounds per engine, for a total of roughly 180 pounds on all six engines for the weight of the entire aircraft at gross takeoff weight. After researching a little bit on the ten-bladed variant of the Aeronaut TF-8000, I found a test that had gotten 46.7539655 pounds (with an exhaust velocity of 122.62 m/sec, with the efflux being calculated) of thrust, with a power draw of 17.52kW; so that'd be 280.523793 pounds of thrust across all engines, which would make the thrust to weight ratio roughly 0.52:1.

I'm not sure how much thrust would be generated at 30,000 feet, but I could easily get more than fifty pounds of thrust per engine, at max power (22kW), which would mean over 300 pounds of thrust, all in total.
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Old Mar 04, 2014, 03:58 PM
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Quote:
Originally Posted by pdawg View Post
Love your ambition Gene!
Thanks!
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Old Mar 04, 2014, 03:59 PM
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Quote:
Originally Posted by eatond View Post
Hmmm,
I'm thinking you would have much more succeess with this thread if you had waited until 28 days from now. Sometimes, timing is everything.

Dan Eaton
Ha!, that's a good one!
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Old Mar 04, 2014, 04:08 PM
Do it Right, the first time!
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United States, MN, Hermantown
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*******
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Old Mar 04, 2014, 04:25 PM
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Quote:
Originally Posted by CoolerByTheLake View Post
Your comparing thrust from turbines aganist edf's ?

JP-6 fuel- I’d be able to use up to roughly 320.9 pounds

With all your figuring, what's the equivelent in Lipos?
Duration and weight?



Major pipe dream!!
I am only comparing the thrust on a one-tenth scale--which is 1,000 times less when building on that scale as compared to the full scale of the original aircraft--I'm not directly comparing thrust from the actual turbines used on the real aircraft to the EDFs I'm planning on using on mine; and, I already stated the weight of all the Li-Po batteries in my original post: "Each Gens Ace battery weighs 3.54889 pounds, and all ninety of them would weigh approximately 319.4001 pounds," which is pretty close to my target weight, at least on the scale I'm building on.

And, I also already stated that at maximum power level (when it comes to what the ESCs are capable of handling) was 132kW for all six engines, and even at that level of power, it would take just over twelve minutes to drain the entire 26.64kWh battery array that is comprised of ninety Gens Ace 5S1P (18.5V, 16Ah [296Wh]) batteries...

Also, I don't see how it's a "pipe dream," at all!
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Old Mar 04, 2014, 04:45 PM
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Colchester UK
Joined May 2004
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North American XB-70 Valkyrie Jet Power 2009 (2 min 41 sec)


This is the nearest XB 70 to the size of model you were proposing. (Scale 1:13) This model weighs 18 kg , under the weight limit for large models. The one certain thing is that your proposed model would never leave the ground with the weight you suggest. The is not a chance that you could ever make a model from metal especially titanium.

John
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