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HelicopterMain Discussion › Best heli related question asked..
01-24-2007 06:07 PM  10 years agoPost 1
frankg11

rrVeteran

Bellevue, WA

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Looking as some of the tag lines, and field related question receintly, I recalled a great question asked of me while flying.

"How fast to those blades go?"

The kid was very interested and about 13 or 14. I asked him if he knew algebra and what the formula for a circle was..

He looked a me kinda wierd and his dad say, you can do this problem. The kid firgured it out and said, "WOW thats fast"

I just though it was neat that the kid's dad made him use math and I didn't just want to give up the answer.

Kid took a few steps back when I started the heli after that <LOL>

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01-24-2007 06:13 PM  10 years agoPost 2
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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I like that. Kid's got a head start w/a dad like that.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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01-24-2007 07:01 PM  10 years agoPost 3
helicrack

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Indiana

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I was never worth a damn at math so I give up. How Fast?

".........said the joker to the thief"

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01-24-2007 07:04 PM  10 years agoPost 4
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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I give up. How Fast?
The tips of a Rap50 (53" diameter) turn a circle that's 166" around (π x 53).

At 2000 rpms the tips are traveling 332,000 inches per minute (166 x 2000).

That's 5.24 miles per minute. (332,000" ÷ 12" per foot ÷ 5280' per mile).

That's 315 mph at the tip (5.24 x 60 minutes).

The tip speed of a T-Rex at 3000 rpm is about 250 mph.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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01-24-2007 07:11 PM  10 years agoPost 5
AirWolfRC

rrProfessor

42½ N, 83½ W

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Average between 300 and 350 mph at the tip.

Full size is between 450 to 500mph at the tip.

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01-24-2007 07:12 PM  10 years agoPost 6
heligoole

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yorkshire,uk

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glad i read this thread,i never knew how fast,never thought about it really.Good post.

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01-24-2007 07:13 PM  10 years agoPost 7
Yug

rrMaster

UK. Herts

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Now do the maths on the centrifugal forces and you'll figure out why it's dangerous to hover at head height or below

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01-24-2007 07:15 PM  10 years agoPost 8
helicrack

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Indiana

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HOLY CRAP that's fast! Knew it was fast but not that fast! Faster than most general avation aircraft.....

".........said the joker to the thief"

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01-24-2007 07:17 PM  10 years agoPost 9
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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You'll find that blade tip speeds on all sized aircraft produce optimum lift (or thrust) when they're near a certain percentage of the speed of sound. The tip speeds we see are similar no matter how large or small the bird.

Faster -- greater drag makes them less efficient.

Slower -- too high an angle of attack is required to do the work (less efficient).

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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01-24-2007 07:22 PM  10 years agoPost 10
sharam

rrElite Veteran

Northern California - Fly at Morgan Hill Field

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I usually tell people about "half the speed of sound." Now they have a double dilemma if they don't know the speed of sound!!

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01-25-2007 12:34 AM  10 years agoPost 11
frankg11

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Bellevue, WA

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so what is the best questions you all have been asked?

Ones that don't count:

How high does it go.
How far away.
etc.

Come on you have to have some good ones.

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01-25-2007 12:51 AM  10 years agoPost 12
Big Chris

rrNovice

Bournemouth UK

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Can I have a go?

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01-25-2007 02:59 AM  10 years agoPost 13
NitroPolymer

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Southeast Florida

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Faster -- greater drag makes them less efficient.

Slower -- too high an angle of attack is required to do the work (less efficient).
At slow speeds the total drag is composed primarily of induced drag as a result of the high angle of attack, and at high blade speeds most of the drag is parasite drag. THe most efficient speed (LD MAX) is where the parsite drag curve and induced drag curve meet at their lowest points. Although this speed could be converted into a mach number, the relationship of this speed to the speed of sound is not what makes it the most effecient, as there is most likely not transonic flow over the blades. The speed of sound through air is a function of air temperature, and therefore the local mach number of the blade would vary depending on where it was flown. (i.e. the blade mach number would be higher in northern canada in winter than it would be in south florida during the summer).

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01-25-2007 03:51 AM  10 years agoPost 14
marc8090

rrElite Veteran

Long Island, N.Y.

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It costs how much? As they're in disbelief.

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01-25-2007 04:39 AM  10 years agoPost 15
3Dx

rrElite Veteran

Monterrey NL

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Now do the maths on the centrifugal forces
This is a very interested question!!!!
I am sure the answer will be IMPRECIVE NOMBERS!!

Come on GimbalFan hive us a hand whit this....

Team JR/Spektrum, Team Vibe, Team CYE, Team Next D/Rave, Team Outrange Batteries, Team RedFox Fuel

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01-25-2007 02:36 PM  10 years agoPost 16
AirWolfRC

rrProfessor

42½ N, 83½ W

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Here's some help for the math,
http://runryder.com/helicopter/p2243030/

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01-25-2007 06:07 PM  10 years agoPost 17
arceye

rrVeteran

UK

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I usually tell people about "half the speed of sound." Now they have a double dilemma if they don't know the speed of sound!!
A triple dilemma as the speed of sound is not fixed , All I ever tell people is "flippin Fast" or "about 300mph"

Andy


Kasama Head :(
The Blingiest DOWNGRADE a Raptor can have

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