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Old Nov 07, 2012, 10:46 AM
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Laddie, Wow, twelve motors on a beautiful model! Do you use 12 controllers?

Don, You seem to be at max efficiency on the subject of tandem power and I am loving every word.

Charles
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Old Nov 07, 2012, 07:04 PM
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Quote:
Originally Posted by canard addict View Post
Laddie, Wow, twelve motors on a beautiful model! Do you use 12 controllers?

Don, You seem to be at max efficiency on the subject of tandem power and I am loving every word.

Charles
One 45A controller.
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Old Nov 08, 2012, 08:57 AM
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http://www.rcgroups.com/forums/showthread.php?t=1747810

Don Srull's Do-X, first flown free flight, later converted to radio. Almost too easy a prototype for a real aeromodeller I think the video is of an RC flight - FF models tend to go around in circles the same direction. Inefficient it may be, but it sure flies good.

D
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Old Nov 14, 2012, 04:56 AM
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Hi don

I was reading on your website about adverse pressure gradients causing flow separation. What about high pressure differentials (between windward and leeward surfaces) and flow separation? Is there a relationship?

Also what may be the best LE geometry to maintain flow attachment and gentle trailing edge stall at high alpha? Would a thicker airfoil work better?

Cheers
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Old Nov 15, 2012, 01:48 AM
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Wise words from Don #6482. There's also the human physiological element of when we get tired or fatigued, we are at risk of being lazy or just not as sharp. We can all feel this when we're out with our models for a long session, hot, hungry, thirsty, we need to make a conscious effort to double check our switches etc before switching on, before EVERY flight. The story of the plastic blade going through a guy's heart is frightening.

I fly a Heli sometimes and those things are on a mission to shake themselves apart. I'm pretty pedantic about checking all my parts on a regular basis. I even keep a tech log of the flying time and inspection schedule. I hope I check it over and service it enough! I guess it's never enough...
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Old Nov 15, 2012, 09:12 AM
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Sorry Nick, I overlooked your other question:

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Originally Posted by nickchud View Post
...Any size of a model of the Voyager must be an ambitious project, especially 24'. Was it a success eventually? Getting one to fly at all would be a thrill, but after that I imagine the objective would be to make sure that nothing very exciting happened at all....
Yes, it flew successfully, and was very scale-like. It was flown at a number of airshows and other events, and was reported on in a number of the model magazines.

That said, "scale-like" is not a compliment! It was indeed a serious handful to fly, just like the full-scale Voyager.

The company I worked for back at the time of their round-the-world flight made the props for them, after they suffered a blade failure of their first props. Note, that failure was not the fault of the props, it was because the fiberglass-skinned wooden blades on those were not efficient enough, so they recarved them to thinner airfoils, in an attempt to get better efficiency. Unfortunately that put one of the resonant frequencies in the operating range, and they had a failure between a blade root and the metal fitting that held it to the hub. I talked later with the head and founder of the company that made those props, and he told me that the wood in the blade shank was charred from the frictional heat from the flexing!

In any case, they decided to go with metal props despite the extra weight, and they needed them in two weeks. Two weeks later they picked up the props from us, and the rest is history. The higher efficiency of the thinner blades, plus the greater inertia (which allowed them to run at a lower RPM and higher manifold pressure, improving engine efficiency) resulted in a 17% increase in fuel economy. Given that they landed with only 2% of their fuel remaining, those props obviously made a significant difference (as in not having to land somewhere around Brazil).

After the flight, Dick and Jeana visited our shop and personally shook the hand of every employee, and also gave us their complete lecture and slide show. I remember one side showing them completely surrounded by massive thunderheads, with one little hole in the clouds, through which could be seen an airport. That airport was Entebbe. Uganda was still on very hostile terms with the USA at the time, and no, they did not have permission to be in Ugandan airspace.

The plane itself was also quite hostile. Besides being very marginal in the stability department, dynamic stability in particular, it also had some interesting flutter modes that had to be flown through in various parts of the flight envelope. One in particular occurred just a little above liftoff speed on takeoff. Triggering that would result in the plane going into violent pitch oscillations that could slam the plane back into the ground after only a couple cycles. They had to fly extremely gently through that airspeed band until they were safely above it.

It was to avoid that flutter mode that caused them to drag the wingtips on the takeoff for the round-the-world flight. The plane had a tendency to leap into the air at liftoff, which is precisely the wrong thing to do if they wanted to avoid exciting that flutter mode. To prevent that, they let some air out of the nosewheel oleo strut to lower it, so that the plane would tend to stay on the ground until they (VERY GENTLY) deliberately flew it off with up elevator. In addition, the fuel tanks in the canard and the noses of the booms were full, causing the canard to bend downwards. The effect was to add washout to the outer panels, to the point that they had a negative angle of attack at the tips. As they gained airspeed on takeoff, this caused the wing tips to "fly" down onto the ground, dragging them and grinding off the winglets (which were only there to give them a higher place for the fuel tank vents, so the fuel would not dribble out of them when the wing drooped on the ground under the weight of all that fuel).

Dick Rutan could not see the tips from the cockpit during takeoff, and was busy concentrating on the liftoff and avoiding flutter. They used 14,200 feet of a 15,000 foot runway to get safely in the air. Yes, they could have burned off a bunch of fuel, landed, then repaired the tips and tried again, but that would mean having to go through another takeoff again! They elected to continue the flight despite the damaged tips.

One of the first things they did after landing was to cut the tail booms off just behind the wing. This shortened the length enough that the plane could be fit sideways onto a flatbed trailer, but more importantly it made the airplane unairworthy, so no one could pressure Dick Rutan into ever having to fly it again. He said "Anyone who wants to try, go ahead, the keys are in it."

Glenn's model was not quite as bad, not too much trouble with flutter, but the control response was very weak and the inertia very high, in yaw and roll in particular. The pilot had to be thinking WAY ahead of the plane, anticipating any control inputs way in advance. Power was adequate (once the prop pitches were sorted out, so that both motors were doing their fair share of the work), but just barely. He was in pretty much white-knuckle mode whenever the plane was in motion. However, it sure did look spectacular in flight!
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Old Nov 15, 2012, 02:00 PM
What could possibly go wrong?
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The incredible skill and bravery of these guys - unjustified optimism too.

When Bleriot crossed the channel, I believe that was the first time the engine he used had ever kept running for long enough to get there. When Amundsen and Ellsworth failed to reach the N Pole in 1925, they took 3 weeks building a runway on the pack ice to get airborn again. How many more incredible stories are there?

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Old Nov 15, 2012, 02:12 PM
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If I recall, Bleriot's flight was also the LAST time anyone got that engine to run that long!
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Old Nov 19, 2012, 09:04 AM
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Would love to try an 8% to 10% version on a flying wing. She has her reflex up front!

http://airfoiltools.com/images/airfoil/s823-nr_l.png

http://airfoiltools.com/airfoil/details?airfoil=s823-nr
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Old Nov 19, 2012, 09:35 AM
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Thanks Guys and especially Don for the interesting discussion. It is Fall and the yard work here and at my Daughter's house has kept me busy in between flying sessions. I am excited about the new design and will show my progress. With the new slim nose as compared to the Twin, it seems that the main wing's vertical fins can be reduced in size or even eliminated. At our flying field there are lots of Grayson's Super sonic V2 motors on flying wings and foam jets. The APC 6-4E props are selling so fast that I have not been able to buy one. The little motors at 19k rpm are rather pleasant to hear compared to what I expected.Today, I will start on fuselage first since it is different from anything yet and will have to be sturdy in the middle. I hope that all are well and are enjoying the hobby.

Charles
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Old Nov 19, 2012, 09:52 AM
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Originally Posted by captarmour View Post
Would love to try an 8% to 10% version on a flying wing. She has her reflex up front!

http://airfoiltools.com/images/airfoil/s823-nr_l.png

http://airfoiltools.com/airfoil/details?airfoil=s823-nr
Looks pretty awful to me.

Performance at low Re's is all over the map. Cm is low, but only because the airfoil is just randomly churning air. At higher Re's, the Cm is fairly high (as could be expected from all that aft loading), and that "reflex at the front" is actually making it worse.

Not clear what they were trying to accomplish with this section.
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Old Nov 19, 2012, 04:47 PM
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here is a link

http://wind.nrel.gov/designcodes/pap...or%20HAWTs.pdf
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Old Nov 19, 2012, 04:58 PM
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this modified 0012 (0012H) also used for HAWTs, seems to outperform the 0012

http://airfoiltools.com/airfoil/deta...l=naca0012h-sa

http://airfoiltools.com/airfoil/deta...rfoil=n0012-il
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Old Nov 21, 2012, 02:23 PM
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Duck Single Fuselage

Made a bit of progress on strange construction which is more fun.

Charles
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Old Nov 21, 2012, 07:12 PM
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http://www.av8rdan.com/2007/12/magic...-few-days.html

Just had to share this guys, Really nice!
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