I worked on Lockheed Electra fire bombers for a while. They had big square-tipped props, too. This was one of them:There is a limit to how "pointy it can be when subjected to wind speeds of 650mph to 450mph. The "pointy" is less drag but also less strong. The other thing is "pointy" produces little or no thrust, you have to give something to get something and you are going to have to give some drag to get some thrust. Reasonableness.
The DC-6 does 315mph @ cruise @ 25,000ft. How pointy are those propellers? (13ft 6 inches diameter)
The "6" is also very fuel efficient when carrying 15 tons of cargo and is still viable today.
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I've always been extremely skeptical of the IVO props from an aerodynamic standpoint. With standard C/S props, the whole blade twists the same angle as the prop adjusts. With the IVO, the tip twists substantially more than the root, which, unless I'm extremely confused, is the opposite of what you want to happen as the forward velocity changes - the tip is moving a lot faster (rotationally) than the root, so the relative amount of twist that needs to occur to maintain optimum AOA is less than that required at the root.IVO twists a composite blade with an embedded torsion rod and DC motor. Works well, reliable, durable, many thousands in service going back 20 years.
IIRC, he did. But John never did enough testing, with enough rigor, to determine any real performance numbers for his plane, and in the 10 - odd years he flew it, he only put about 125 hours on it. And for reasons beyond my comprehension, he'd take off at about 75% throttle... RIP. Plus, he never put any OTHER prop on it, so as you say, no A to B comparisons.Marc, didn't John Slade eventually use an IVO on his Cozy? I can't recall what his results were.
A comment he made in his blog might give a clue to his reasoning:Thanks for the confirmation that the IVO is not optimal (at least to the extent that a standard C/S prop is optimal) aerodynamically. I agree that that's not the only criteria, and the cost and complexity of standard C/S props is the largest reason that I don't recommend them for canards except in very specific circumstances.
IIRC, he did. But John never did enough testing, with enough rigor, to determine any real performance numbers for his plane, and in the 10 - odd years he flew it, he only put about 125 hours on it. And for reasons beyond my comprehension, he'd take off at about 75% throttle... RIP. Plus, he never put any OTHER prop on it, so as you say, no A to B comparisons.
The last part is what I don't " get'. If the prop is over pitched for takeoff, I would still give 'er all the throttle for takeoff and initial climb. For the next 30 seconds, I don't care about prop efficiency, fuel efficiency, etc. I care about making all the thrust I can during a critical phase of flight. Unless a lower throttle setting and lower rpm somehow gives me more thrust, I'm not gonna do that."Anyway, the more pitch, the harder the prop is to turn, so if you put in too much pitch you wont get enough static RPM to reach the top of you're engine's power curve - thus take off power would be reduced. You also might get some cavitation. Apparantly, one way to get around this is to begin the take off with reduced rpm, then increase throttle as the airspeed increases."
Mr. Slade was never the most logical person, although he was always very calm and civil in discussions. A very nice guy, but difficult to reason with.Unless a lower throttle setting and lower rpm somehow gives me more thrust, I'm not gonna do that.
Your pet peeve too? Sheesh.Oh, and propellers can't cavitate in air, only in a liquid.
The Ivo's twist rod goes out to around 70% of the blade's span, IIRC, and twists that point. So the tip will move about the same amount as the 70% point, and the blade will have less and less change in twist as you move inboard from the 70% point.With the IVOprop, it would seem that to get the optimum pitch at about 75-80% radius (where the chord is typically greatest on most GA props) you'd potentially be overpitching the tip. Given the V² factor in both the drag and lift equations, this could be as/ more problematic than an underpitched root segment. I suppose the answer, which IVO knows, is to shape the blade planform to d
accommodate the blade twist rate, or at least find a good approximation.