Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

In air RPM

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Old 09-25-2002, 05:44 PM
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PAINLESS
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Default In air RPM

Want to know what your engine RPM is in the air, try one of these. I have and the results where surprising.


http://www.iwc.com/pcrc/dt601.html
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Old 09-26-2002, 12:35 AM
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BruceDana
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Default In air RPM

How about an oscilloscope and a microphone?

The usefulness of an oscilloscope is not limited to the world of electronics. With the proper transducer, an oscilloscope can measure all kinds of phenomena. A microphone is a transducer.

You can measure RPM on the ground by measuring the frequency of the engine firing as the plane passes. At the point of closest approach the dopple shift is zero (which can be discriminated by the scope). Measure the frequency there and you have your RPM.

Now the fun part - you can also measure the velocity of object by measuring the doppler shift.

Check eBay - they sell for little as $20
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Old 09-26-2002, 12:43 AM
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BruceDana
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Default In air RPM

How about an oscilloscope and a microphone?

The usefulness of an oscilloscope is not limited to the world of electronics. With the proper transducer, an oscilloscope can measure all kinds of phenomena. A microphone is a transducer.

You can measure RPM on the ground by measuring the frequency of the engine firing as the plane passes. At the point of closest approach the dopple shift is zero (which can be discriminated by the scope). Measure the frequency there and you have your RPM.

Now the fun part - you can also measure the velocity of object by measuring the doppler shift.

Check eBay - they sell for little as $20
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Old 09-26-2002, 12:46 AM
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ChuckAuger
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Default Well shoot..

I got a mic and oscilloscope, but was just gearing up to crash into a known mass..oh well...
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Old 09-29-2002, 01:48 AM
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Default .

I saw this unit in another post a while back. one guy mentioned a huge unload in the air....
there must be more than one guy out there who has tried this unit..
if the readout unit is inside the plane and you shut off your power switch before reading it, do you loose the reading?
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Old 09-29-2002, 07:38 PM
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Default In air RPM

Yes you lose the reading if you turn off your switch.
It would be easy to mount where it could be seen.
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Old 10-01-2002, 02:08 AM
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Default Surprising - please elaborate

I'm too cheap to spend the $65, but would be interested in your findings. I assume by "surprising" that the rpm achieved in the air was significantly higher than on the ground. On the Diamond Dust we are running a OS .32 that tached at about 16,000 on the ground with tuned pipe. Running a 9x8 prop I think (my buddy has the plane now). It sounds like it unloads a lot in the air.
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Old 10-01-2002, 12:09 PM
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Default In air RPM

When I bought mine about 4 years ago they where $40. I originally bought it to put in a boat to evaluate different props.

I saw 22k and 22.5k on a TT40 pro with a 9x6 prop on a scat cat. I was careful not to put the plane in a dive, just did a few laps. It was turning 16.8k on the ground and the PC/RC tach was within 100 rpm of my hobbico tach. I did have two witnesses.
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