Air Command flight speeds

DennisFetters

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(maybe Dennis can chime in on what type ASI it was) .

The airspeed indicators I used were the same ones on the 503, 532, and even Arrow 120hp engine powered Commanders, of which I never encountered one suffering from hysteresis or backlash.

In the 447 Commander testing when this effect was measured, you didn't see a bounce in airspeed indication, but an increase in airspeed indication as speed increased. There is a definite difference in the speed of the air hitting your face from 60mph going to 70mph. I different wind noise, and seeing the ground rush by faster, or passing someone else flying in a Commander that you just flew by at the air-show after passing over the hump.

It was not an airspeed indicator suffering from hysteresis or backlash. That was not the only indicator of speed, as I just said above. It was an increase in speed, and a sustainable increase of speed.

You all are guessing what the reason is, but I have already told you. It is from flying at a reduced rotor disk angle of attack, where your rotor lift becomes more efficient with less rearward pointing lift-drag. Once you use the extra power of gravity (the JATO bottles if you will) to increase speed over the hump and to over 73mph, then pull back to level off, the pulling back will slightly flare the disk and build a little extra rotor rpm, Then when you push the stick forward, to maintain level flight, the stick will be 1" further forward than what it was at 63mph, and your rotor rpm will also remain a little higher which makes up for the lessoned rotor disk angle of attack.

No, I don't have a 447 Command up my sleeve to run out and video this effect. As I said before, I already know why it happens, and the effect is of no use to me to bother with further. If I wanted to reproduce it on a heavier gyro, I'd just have to install stubby wings, or a partially powered rotor.
 
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gyromike

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You all are guessing what the reason is, but I have already told you. It is from flying at a reduced rotor disk angle of attack, where your rotor lift becomes more efficient with less rearward pointing lift-drag. Once you use the extra power of gravity (the JATO bottles if you will) to increase speed over the hump and to over 73mph, then pull back to level off, the pulling back will slightly flare the disk and build a little extra rotor rpm, Then when you push the stick forward, to maintain level flight, the stick will be 1" further forward than what it was at 63mph, and your rotor rpm will also remain a little higher which makes up for the lessoned rotor disk angle of attack.

Why would this not be repeatable on any gyro?
 

SnoBird

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Great link, thanks for sharing it chuck. I think you may very well be onto something here. I read the guy's calibration verification procedure and although he implies he taps on the ASI indicator during data collection, I'm not sure he does and I'm not sure a few simple taps would be truly representative of the environment an ASI indicator would experience on the nose of an open frame gyro. He also does not mention any concerns about a dynamic signal input. I think he should have introduced a few periodic pressure fluctuations proportional to what would be seen in real flight (and kept the pitot input tube as short as possible).

The environment on the front of an open frame gyro is gusty and constantly vibratory. Ideally he should've put the instrument on a shaker table (with a frequency and amplitude roughly approximating the dominate aircraft cabin freq/amp), or at least placed an electric egg beater next to it, or something (just kidding, sorta). And again he should've periodically slightly perturbed the pressure input (and use a short tube coming off the manometer to reduce damping effects) to simulate the normal pressure perturbations that would occur in real flight (especially for an ASI with a stubby pitot mounted on the nose of an open frame gyro). I'm speculating, but from my experience with other mechanical systems with delicate gears, latches, foliates etc, a good shaking and/or a pulsed signal input will tend to settle the instrument in. I'm not suggesting it will eliminate backlash or hysteresis, but it probably would reduce the error that was observed in the data presented on the eaa link.

Still, this could very well be what's going on the AC 447 - but then, why not on all other gyros as well?
 

DennisFetters

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Why would this not be repeatable on any gyro?

With a gyro of similar weight, same prop and same rotorblades, I'm sure it can be. Problem is, there are few gyros that were as light as the 447 Commander while using the McCutchen rotorblades.
 

DennisFetters

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Dennis,
I might have missed something here.

So you advertised and sold an aircraft as part 103 compliant when you knew it could sustain a higher speed than the part 103 requirements?

An aircraft that doesn't meet ALL of the part 103 requirements is not an ultralight aircraft

Surely the the onus is on you, the manufacturer, not the FAA official to insure that the aircraft is part 103 compliant.

You know bubba, everyone can see what you are playing with here. Again, you pick and choose the words I write and ignore the ones that don't benefit the point you are trying to make, because the facts will confuse your issues.

I'm not going to play your morons game any further. I answered you out of courtesy, and you are trying to play with my goodwill towards you while your intent is obvious.

Go backstab somewhere else, and stop playing with what I said.
 

DennisFetters

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Dennis, thanks again for the greatest toy I have ever owned. Had it not been for you, I would probably never have gotten into gyrocopters(the love of my life!)

The 447 Commander...see it , fly it, love it !!!!

That video you made over 20 years ago was all it took to get me started !

Chris and Stan, Thank you.

It was always fun to go to fly-ins all over the world to meet and fly with the hundreds and hundreds of happy Commander owners. I was one of them. The best times of my life flying was in my Commanders, and with you guys.

Thank you for giving me a life that I would trade for no one else's, because you were my customers.
 

C. Beaty

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Snowbird, “step” phenomenon has been claimed for other gyros. A now deceased Sunstate member, EA Van Houten, was well known for claiming he could trim his gyro onto the “step” by diving and returning to level flight and gain a “free” 5-10 knots.

I’ve looked for steps but have never found one.

I expect it mostly depends upon the type of airspeed indicator. After experience with low range airspeed indicators shaking apart and becoming a can of loose brass clockwork gears, I always used propeller driven automotive speedometers that are not subject to the same sort of mechanical problems as aneroid instruments. A turbine driven instrument responds to true airspeed rather than pressure based airspeed, not what’s really needed for flight reference.
 

SnoBird

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The airspeed indicators I used were the same ones on the 503, 532, and even Arrow 120hp engine powered Commanders, of which I never encountered one suffering from hysteresis or backlash.

In the 447 Commander testing when this effect was measured, you didn't see a bounce in airspeed indication, but an increase in airspeed indication as speed increased. There is a definite difference in the speed of the air hitting your face from 60mph going to 70mph. I different wind noise, and seeing the ground rush by faster, or passing someone else flying in a Commander that you just flew by at the air-show after passing over the hump.

It was not an airspeed indicator suffering from hysteresis or backlash. That was not the only indicator of speed, as I just said above. It was an increase in speed, and a sustainable increase of speed.

You all are guessing what the reason is, but I have already told you. It is from flying at a reduced rotor disk angle of attack, where your rotor lift becomes more efficient with less rearward pointing lift-drag. Once you use the extra power of gravity (the JATO bottles if you will) to increase speed over the hump and to over 73mph, then pull back to level off, the pulling back will slightly flare the disk and build a little extra rotor rpm, Then when you push the stick forward, to maintain level flight, the stick will be 1" further forward than what it was at 63mph, and your rotor rpm will also remain a little higher which makes up for the lessoned rotor disk angle of attack.

No, I don't have a 447 Command up my sleeve to run out and video this effect. As I said before, I already know why it happens, and the effect is of no use to me to bother with further. If I wanted to reproduce it on a heavier gyro, I'd just have to install stubby wings, or a partially powered rotor.

Thanks for your comments Dennis, this is really shaping up to be an interesting subject (for me at least). You are being absolutely, 100% non ambiguous in your assertion: there is a step, it is real. You also have a few other people verifying it happened to them too in 447 AC's. And you do have the qualifications, experience and credentials to have observed this thing and not have made a careless mistake in mis-assessing what happened - no question about it. When you say the stick remained an inch more forward, you physically felt the increased airspeed, the rotorspeed picked up, you were outrunning other guys stuck at the slower speed, and you've never seen the ASI behavior in other machines using the exact same ASI...I mean, I'd say that about settles it as much as any man's word can settle something.

As to your explanation that the reason this happened is because the rotor drag is decreased: I agree the net rotor drag coefficient is probably decreased (as exemplified in Chuck's graph he posted earlier), and probably the net drag on the rotor (net drag being the combined induced and parasite drag) is also reduced. But what you're not addressing is the parasite/profile drag of the rest of the airframe. Under normal circumstances this exponentially increases with velocity. And it especially starts taking off around the airspeeds in question (and in fact is the dominant form of drag at these speeds). So the question isn't only a matter of rotor drag, it's a question of airframe/pilot drag too. That's why I mentioned the conjecture about changes in airflow around the bluff body that may have resulted in an unexpected discontinuity in drag behavior (similar to that described in Chuck's graph of the sphere earlier). Also, another equally obviously important factor is available thrust, which again might also be influenced by the nature of the flow around the bluff body. But if I understood you properly, you say the prop you selected for the 447 UL was optimized for lower speed flight (understandably). So it would seem odd for its efficiency to increase at an airspeed that high (meaning that available thrust should drop off). But if the machine really is flying at that sustained speed, the power has to be coming from somewhere. And the parasite drag isn't going to magically disappear either - something must be going on to explain it all, and I'm not sure your assessment of it simply being a reduction in rotor induced drag is all there is to it. Otherwise this behavior should be able to be seen on many other machines. Not trying to quibble with you, I'm just not clear on how you could "intuitively" separate the rotor drag, from the airframe drag, from available thrust and "know" the resultant higher speed was strictly caused by a big reduction in rotor drag alone.

Snowbird, “step” phenomenon has been claimed for other gyros. A now deceased Sunstate member, EA Van Houten, was well known for claiming he could trim his gyro onto the “step” by diving and returning to level flight and gain a “free” 5-10 knots.

I’ve looked for steps but have never found one.

I expect it mostly depends upon the type of airspeed indicator. After experience with low range airspeed indicators shaking apart and becoming a can of loose brass clockwork gears, I always used propeller driven automotive speedometers that are not subject to the same sort of mechanical problems as aneroid instruments. A turbine driven instrument responds to true airspeed rather than pressure based airspeed, not what’s really needed for flight reference.

Thanks again for the valuable input Chuck. I sense that you don't believe in the "step speeds." I know you're super knowledgeable, super smart and probably have more experimental experience in homebuilt rotorcraft than any living person (that I'm aware of anyway). What do you think about Dennis' statement about the stick being farther forward and the higher rotorspeed and outrunning other dudes flying at the lower speed etc etc? I believe what he says, and I think he has the knowledge and experience to not be fooled by measurement error. I'm not trying to instigate a flame war, it's just for the life of me we seem to have a clash o' the titans here, both with compelling information and experiences that seem to counter one another. I'm really curious to know what might actually be going on, we may have discovered an interesting anomaly pertaining to at least one particular aircraft...or??? :noidea:
 

SnoBird

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Dennis, oh there is one other thing. Is there a significant attitude change in airframe pitch during the transition to the higher speed? Reason I ask is because if the thrustline was more aligned with the flight path at the higher speed, that also would contribute to increased net propulsive efficiency, which might also play some role (albeit small) in why the higher speed could be sustained.
 

SideKick

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This has been very interesting to me since I have Stan Fosters old AC447. I can't try out this theory since I weigh 200lbs and can't get close to 63mph. Some one said that Chris Burgess was around 160. I live about 3 hours from Mr. Burgess and would be glad to let him try it on mine if he chose to.
 

DennisFetters

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But if I understood you properly, you say the prop you selected for the 447 UL was optimized for lower speed flight (understandably). So it would seem odd for its efficiency to increase at an airspeed that high (meaning that available thrust should drop off).

I never said the propeller efficacy increased, nor did I experience that. I only experienced a reduction in rotor-disk drag. When you decrease the angle of attack to the rotor-disk, you not only lower the reverse lift from the disk being angled back (I believe for the 447 Commander that was around 70 pounds of rearward lift), but you also decrease the frontal area of the rotor-disk that is creating drag.

Why? In forward flight, the drag of the rotor blade area plus the approximate 9 degree aft offset of the Rotor Thrust Vector cause a considerable and variable resistance through the air. Take for instance, a standard 23 foot diameter by 8 inch cord set of rotorblades flying through the air with 3 degrees of coning and at 9 degrees angle of attack, in forward flight presents 360 square inches, or 2.5 square feet, of frontal area of resistance to the air stream. I'm not going to take the time to calculate what the frontal area would be by reducing the angle of rotor-disk attack from 9 degrees to 8, but to give you an idea, by reducing the rotors angle of attack to zero, or level, this will instantaneously reduce the rotor systems frontal area down to 64 square inches, or 0.444 square feet! That is over a 80% reduction in drag of the rotor system.

So what I am saying, is with this change of lift vector position and reduced frontal area of the rotor-disk, there is enough reduced drag for the propeller to sustain a forward flight 10mph faster after you pushed over the hump.

Dennis, oh there is one other thing. Is there a significant attitude change in airframe pitch during the transition to the higher speed? Reason I ask is because if the thrustline was more aligned with the flight path at the higher speed, that also would contribute to increased net propulsive efficiency, which might also play some role (albeit small) in why the higher speed could be sustained.

I noticed no significant attitude change....... except that I was a little happier going faster....:flame:
 

DennisFetters

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This has been very interesting to me since I have Stan Fosters old AC447. I can't try out this theory since I weigh 200lbs and can't get close to 63mph. Some one said that Chris Burgess was around 160. I live about 3 hours from Mr. Burgess and would be glad to let him try it on mine if he chose to.

I was 200lbs when I was doing it.
 

raton

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Yes, it is a shame that this person is now the last and main offenders of disrupting these threads of interesting topics, and he is still around. The last of the Mohican's. Here he sounds so remorseful of his evil ways, and then turns around and sends me a private message stating the exact opposite. No, I won't post someones private message, no matter who or what its about without their permission. But this forum has sure been a lot better since the mediators has been cleaning up the place by getting rid of trouble makers, just like this guy. I'll be glad when we can see his posts no more too, someday sooner than later, I hope.

It would be nice to have uninterrupted conversations here.

An apology is widely acknowledged to be an effective means of resolving conflict and apology is tied to forgiveness,in the best case, when an offending party offers an apology, the offended party offers forgiveness. But the risk is that if the prompt is too harsh, directive, insistent, or clumsy, it could generate resistance rather than reflection, that is, the offender finds it hypocritical to hold on to the idea that the other’s misdeed makes him a “bad dog” but to attribute his own past misdeeds to difficult circumstances. Hypocrisy (sometimes called “dissonance”). is an uncomfortable feeling…..wow..!

raton
 

C. Beaty

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Rotor drag, rpm, angle of attack, etc is progressive and repeatable without switchbacks or hysteresis. It makes no difference whether a final airspeed is approached from above or below.

Rotor rpm increases with airspeed because the stalled region of the retreating side of the disc spreads outward, reducing the blade area that is still flying. The rpm must increase to make up for the reduction of effective blade area.

That also increases profile drag; that due to dragging the rotor airfoils through the air. Power consumption increases as the cube power of rotor rpm; increase the rotor rpm by 10% and the power consumed increases by 33%.

Induced drag, that portion of rotor drag chargeable to producing lift decreases with airspeed at the rate of 1/airspeed squared.

At 70 mph, rotor drag is much less than airframe drag; 47 lb. for the rotor and 120 lb. for the airframe from the chart in my post #56. This chart was calculated for 23 ft. DW rotors on an open frame gyro of 500 lb. AUW.

If there is a switchback or hump in gyro performance, it can only be due to some pecularity of airflow around the fuselage and into the propeller; attached vs. separated flow.
 

Tex~N~Oz

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If there is a switchback or hump in gyro performance, it can only be due to some pecularity of airflow around the fuselage and into the propeller; attached vs. separated flow.

I know I was grasping for straws but I envisioned some sort of leveraged fulcrum that changed the dynamics of the machine as a whole.
This is kind of like proving how a UFO levitates.. First we should find a UFO and see that it does...
 

C. Beaty

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NACA and their successor, NASA have been running rotors in wind tunnels since the 1930s without a single finding of rotor switchback or hump.

The phenomenon of flow reattachment to smooth spheres is well known and well reported. With smooth surfaces, the boundary layer is always laminar at low Reynolds numbers but laminar boundary layers aren’t very sticky whereas turbulent boundary layers are. The reason golf balls are dimpled.

With a smooth sphere, the boundary layer abruptly transitions from laminar to turbulent at a Reynolds number of just under 400,000 and the airflow, at least in part, reattaches, leaving a smaller wake and reducing pressure drag. More than makes up for the increase of skin friction drag.
 

SnoBird

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I never said the propeller efficacy increased, nor did I experience that. I only experienced a reduction in rotor-disk drag. When you decrease the angle of attack to the rotor-disk, you not only lower the reverse lift from the disk being angled back (I believe for the 447 Commander that was around 70 pounds of rearward lift), but you also decrease the frontal area of the rotor-disk that is creating drag.

I understand you didn't claim the prop efficiency increased, I was just discussing possible factors (other than induced rotor drag) that might help to explain the higher speed you describe. But when you say you didn't experience increased prop efficiency, how can you tell what's happening with prop efficiency by simply sitting on the gyro and flying it? That's my point, you've definitively identified a reduction in induced rotor drag as the one and only factor that allowed you to achieve the higher speed (and no one's doubting that the rotor induced drag is lower at the higher speed). You point to external observables like stick position, rotor angle and increased rotor rpm to "prove" your case. But without a bunch of sophisticated test instrumentation, how can you discern the effects of the other pertinent physical factors in play that are not observable? (but are definitely in play) How can you "know" what prop thrust and airframe drag are from your vantage point as a pilot? My point of course is that you cannot know what those other forces are, and furthermore there are several fundamental aerodynamic facts (as previously discussed) that contradict this being possible strictly as a result of a reduction in induced rotor drag at 73mph vs 63mph. The profile/parasite drag of the airframe, pilot and rotor are dominant at the airspeeds in question. And normally they all should be going up exponentially when transitioning from 63 mph to 73mph - unless some unexpected, "counterintuitive" discontinuity is occurring that serves to diminish them at the higher speed.

Respectfully, that's why I don't understand your definitive declaration that the higher airspeed was exclusively and only caused by a reduction in rotor induced drag.
 

AIRCTOM

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Dennis, thank you for answering my original question. I am sorry the discussion had become such a fiasco. Perhaps I will stick to e-mailing you off the Rotary wing forum to eliminate all the harassment to which you have been subjected.
It was a relatively simple question and of all the 447 Air Command EXPERTS on the forum, you are the only one who has answered.
How could others have flown the 447 for all these years and never determined a "best rate of climb speed" for themselves ?
Instead of gaining information from the others, the thread turned into a mud slinging contest. I am new to the Forum, but I am disappointed in the results.
 

Doug Riley

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The rotor is not likely the source of the reported "double hump." It's more probably attributable to the quirks of 2-stroke engines and unsophisticated props.

The original stock 447 Commander came with a 4-blade Ultra-Prop. This prop has/had some oddities, possibly traceable to ancestry as a windmill for boat generators (I'm speculating about its origins; it sure looks like one).

One oddity is that the blades are untwisted. This means that the blade roots operate at a lower angle of attack than the tips. As airspeed rises, the roots will generate first zero, then negative, thrust.

Another oddity is that this prop's blades' leading edges are knife-sharp. This will cause fluky, early stalls -- and un-stalls, as airspeed picks up.

Then there's the peaky 2-stroke engine. As we all know, these engines perk up dramatically as they "come onto the pipe" in the early-mid 5000's of RPM.

You can imagine the Ultra-Prop coming into its own above a certain airspeed, as the (relatively over-pitched) tips finally un-stall and start pushing. At the same time, you can picture the puny 447 being unable to get up to that airspeed because it's a bit overloaded at 60 mph and hasn't yet come onto the pipe.

I didn't fly my 447 with the Ultra-prop. Mine had a high-pitched wood prop installed when I bought it (used). It was a total pig at 45-50; it would cruise at 5300 RPM, but could barely climb at all. It took off over 70, though. Unfortunately, the gyro was so pitch-unstable above 70 that it was unpleasant to fly at those speeds. I only did it when necessary to keep up with buddy Bill Raub, who always flew fast. His 447 Commander had the stock Ultra-Prop. Maybe he had to dive to get up to those speeds, but he never said so. He certainly could do 80 or better, or so my Hall wind meter claimed as I paced him.
 

DennisFetters

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Dennis, thank you for answering my original question. I am sorry the discussion had become such a fiasco. Perhaps I will stick to e-mailing you off the Rotary wing forum to eliminate all the harassment to which you have been subjected.
It was a relatively simple question and of all the 447 Air Command EXPERTS on the forum, you are the only one who has answered.
How could others have flown the 447 for all these years and never determined a "best rate of climb speed" for themselves ?
Instead of gaining information from the others, the thread turned into a mud slinging contest. I am new to the Forum, but I am disappointed in the results.

Tom, you are very welcome.

Don't worry about the lowlifes here that make things personal, at the cost of everyone wanting to read and participate on these discussions. The mediators are doing a very good job at weeding out the trouble makers now. I certainly don't mind people questioning what I say, or even debating that I'm wrong, or even proving me wrong. Believe me, I've been wrong many times, but I've been right many more times than being wrong, so although I do keep an open mind to anything, I also rely on my hands on experiences. It's when people get belligerent and insulting that gets my gander up, but these types are dying off, getting weeded out or overcoming their previous misconception's, as I said.

I believe it is better to keep your questions within the public forum, so that others can share their experience and everyone learns. I'll handle the bigmouths when they rear their ugly heads.
 
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