Productive Flight

[flyguy]

Re: Productive Flight

Anyone know what kind of gizmo they use to sense the change in end play on the crank? Read about that in an article on one of the RV-( )'s that was competing in CAFE. Maybe like a micro switch with a zero adjust screw?

Somewhere on the forum there is a thread about me outdragging my buddy's Thunderbird with my -85. I think I made a guess on the zero-to-sixty time then from the performance. Should be able to do a F=ma from that, right.
Assume 8 seconds, 0 to 60 (88 fps), sounds about right, 1100 lbs. Hank, you're on. Is that a calculus problem? ie ft/sec/sec.


Edit: Well, 88 ft/sec came out to be an easy number to use. That works out to 11 ft/sec/sec for 8 seconds. Convert this whole mess to meters/kilograms and you get (502.8 Kg)X(3.3525 M/sec/sec)=1685.7 kg/m/sec (Newtons), which times 0.22481 equals 378 lbs of force. Is it valid to convert it like that?

Eleven ft/sec/sec is about 1/3 of 1 g (ie 32 ft/sec/sec,) = 0.3 g. That is pretty reasonable too, I think.

Hank, I would say 350 lbs was a pretty good estimate, to put it mildly. I would also say that I am going to get a new piece of rope to replace my worn tail-tie one.

Darryl

[Hank Jarrett]

Re: Productive Flight

CRUD! My idea was to sense the end float of the crank shaft while the engine was running. Anyone know how they did that? I sure haven't worked out he details yet.
Hank

[flyguy]

Re: Productive Flight

I think one could do that with a micro switch.

I was concerned about the micro switch arm catching on irregularities in the prop hub, but realized just now that if you make the actuating arm trailing, it would likely fix that possible problem. Mount the micro switch with an adjustment screw in the mount and adjust it to (open?) contact at midpoint of the crank end-play movement. If it bounces on and off doesn't matter, that is close enough to a zero thrust condition.

You could also do it with a Hall effect device or a magnetic sensing coil I would think. A solenoid coil with it's end close to the hub and an AC signal on it should change characteristics when the hub gets closer. Add a rectifier circuit and a comparator chip driving a LED. That's another pretty simple way.

Still, the micro switch strikes me as being the least complicated.

Darryl

[Larry Lyons]

Re: Productive Flight

Here is a link to the foundation, I looked around a bit but need to do more, so will leave it to some of you smarter folks out there. You need two switchs, one to show "not all the way back and one to show not all the way forward, just floating in between. Or maybe a plunger type that has a mid point with both end points adjustable. I remember they had a rather good explanation of how they acomplished this and it is probably in the Sport Avaition archives some where or on this web site here.

http://cafefoundation.org/v2/main_home.php

[Robert Lees]

Re: Productive Flight

Larry,

The "zero thrust" EAA thing was with a C150 towed aloft with, as you describe, a sensor attached to the crank flange to depict when the tow plane/tow line was producing zero thrust.

The towed C150 had no prop on it.

I recall, because at the time I asked EAA for permission to reproduce their article for our flying club, and I never got a response. I guess it would be about 1994.

Rob

[Dick Smith]

Re: Productive Flight

Here is a link to some basic background: http://home.cogeco.ca/~n17hh/Models/...cleMarch95.pdf

[dmcneil]

Re: Productive Flight

Hey All,

The "Zero Thrust Glide" technique is a really interesting story. The technique and hardware were developed by Jack Norris and Andy Bauer. Jack is a CAFE board member and a longtime Luscombe guy. The technique and hardware were developed using Jack's Luscombe as the test mule.

Here's an article by Jack on the development of the measuring technique. It contains a description of the hardware used (very simple stuff):

http://www.google.com/url?sa=t&source=web&cd=1&ved=0CBYQFjAA&url=https%3A%2F%2Fengineering.purdue.edu%2F~andrisan%2FCourses%2FAAE490A_S2010%2FBuffer%2FAIAA-46372-872.pdf&rct=j&q=zero%20thrust%20glide&ei=KJBeTpbNOIXkiAKp2cWzBQ&usg=AFQjCNHml_gZTBn4reMeKQoP2Pqla7cKVw&cad=rja

(If that ridiculously long link doesn't work just Google "Zero Thrust Glide" and the AIAA article should pop up)

The creation and evolution of the CAFE foundation can be found here:

http://cafefoundation.org/v2/aboutcafe_orderfromchaos.php

That article describes how the towed and propellerless Cessna was used to verify and validate the early zero thrust glide testing.

Jack Norris is a fascinating guy. He has a two volume book that describes flight dynamics and propellers. The Logic of Flight, The Thinking Man's Way to Fly, and; Propellers, The First and Final Explanation.

Well worth the $. If anyone is interested, send Jack a check for $17.50

Jack Norris
11613 Seminole Circle
Northridge, CA 91326

Dan

[flyguy]

Re: Productive Flight

I read the article, most excellent. Question: where is the LOW RESISTANCE electrical path from the crankshaft to the crankcase (ground) when the engine is running, and why doesn't it open by itself when the crank backs off, if, as example, it is through the thrust washer. Does not the thrust washer have a coating of oil on it from the front main?

Does the fact that this circuit works mean that there is intimate metal-to-metal contact somewhere on the rotating crankshaft? With what I know of automotive engines, I would hope not. Gears? Carbon in the oil? Even with the pressurized oil and coated surfaces there is still low Ohms contact?

If it was easy for me to get a good contact point on the rotating crankshaft for a quick check I would do an electrical resistance check myself, but as I don't see any quick and easy method right now, I'm asking, Anyone know where the LOW RESISTANCE path is?

Darryl