Author Topic: SR-71  (Read 463 times)

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Offline Cut4fun .

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Re: SR-71
« Reply #10 on: October 16, 2015, 10:01:26 pm »
How many of you think you could fly and land this incredible micro aircraft without crashing?

I know I easily could   ;D




What did you do put words into my quote. I dont remember asking that. LOL
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Offline 660magnum

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Re: SR-71
« Reply #11 on: October 16, 2015, 10:57:55 pm »
I've been at the flying field with one of those flying. You can see a lot better perspective being there but that thing is still moving on. With all my years experience flying them, I wouldn't attempt one of these.
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Offline Moparmyway

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Re: SR-71
« Reply #12 on: October 17, 2015, 04:58:33 am »
I've been at the flying field with one of those flying. You can see a lot better perspective being there but that thing is still moving on. With all my years experience flying them, I wouldn't attempt one of these.
I got used to 175-185 mph pretty quickly and have buddied on a turbine


What did you do put words into my quote. I dont remember asking that. LOL
Its that memory thing again ? :-[
First post, last line ...............  :)

Offline Cut4fun .

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Re: SR-71
« Reply #13 on: October 17, 2015, 08:09:36 am »



What did you do put words into my quote. I dont remember asking that. LOL
Its that memory thing again ? :-[
First post, last line ...............  :)

Thanks

LOL I know why now. That was copied pasted  article.  Read it but forgot about that part.


What is that whine sound of the motors in your video. Electric of some kind able to go that fast?
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Offline 660magnum

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Re: SR-71
« Reply #14 on: October 17, 2015, 08:48:19 am »
They are a brushless DC motor. There is a driver or electronic module that conditions the DC voltage to have alternating pulses to run the motor. The module's output frequency for the motor is regulated by the radio control system.

You are hearing a combination of the electric pulses and the pulses of the motor as it runs. Also the propeller blades make a noise as the tips approach or exceed the speed of sound.

Makes it sound like a little two stroke nitro engine running 25,000 rpm?
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Offline Moparmyway

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Re: SR-71
« Reply #15 on: October 17, 2015, 09:28:20 am »

What is that whine sound of the motors in your video. Electric of some kind able to go that fast?

Electric, yes .......... and that is one of my slow ones

660 Magnum is mostly correct, except that the motor really makes no noise at all. It is basically a modified 3 phase motor run by a VFD

The noise is the propeller crossing the the airframe, actually grabbing no air when it is in line with the airframe, then grabbing air as it crosses the airframe and hits air again. it is in a pusher config, meaning the prop is at the rear of the airframe.

IIRC, that setup was spinning at 33,500 rpms ............ or Mach .78 at the tips, which is less than 80% the speed of sound. Once the tip actually get above 95%, they make a churning sound and start to fray. Also the props start to become inefficient at about 95% the speed of sound

Offline Moparmyway

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Re: SR-71
« Reply #16 on: October 17, 2015, 09:44:56 am »
Here is one with the prop tips just exceeding the speed of sound.
At launch (16-17 second mark, clean by the 18 second mark) high pitched resonating whine, you can hear it up close
In the air, you can hear it at the 42-44 second mark, sounds like its churning, then its clean at 45 seconds

https://www.youtube.com/watch?v=VfUORpkTcCY

Offline 660magnum

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Re: SR-71
« Reply #17 on: October 17, 2015, 11:41:03 am »
An electric motor on the front of a plane makes noise too especially at full speed.

But pusher props make a lot of noise as described above.

At work we had a lot of server motors to drive machinery at regulated speeds. We had a new big furnace conveyor stop. But you could hear and feel the motor running but the output shaft was not turning. The problem, to make it short, was that there was extra friction in the conveyor system and indeed it was stalled - motor and all. But the electrical pulses were still going to the motor and making a noise and vibration as if the electric motor was running.  We had to install a more powerful motor and driver system on the machine.
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Offline Cut4fun .

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Re: SR-71
« Reply #18 on: October 17, 2015, 11:41:14 am »
Holy Chit great info and way over my pea brain.

I will watch video later as just set down to warm back up with some coffee. Been putting coils on sons car and other stuff before heading back to college tomorrow.
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Offline ch74

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Re: SR-71
« Reply #19 on: October 17, 2015, 11:01:45 pm »
SR-71 my fav, airplane. That lil micro craft is bada@@. Wish i could afford more then one hobby, other then chainsaws and climbing.
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