RR Rated M For Mature
HOME   rrTV-PHOTO   GALLERIES   MY GALLERY   HELP-FAQ
myHOME PM pmRR MEMBERS 441 ONLINE 77 EVENTS SEARCH REGISTER  START HERE
 
1 page2226 viewsPOST REPLY
CarbonXtreme . Midland Helicopters . HeliProz

.
.
Safety - RC Helis are not toys > Wow! Someone check my math...
 
 
canardman
Senior Heliman
Location: Waco, TX

My Posts This: Topic  Forum		I was doing some figuring this morning, and was kind of shocked at this. I have some #'s that I came up with. If you have a rotor speed of 2000 rpm. A 50 size heli has a disc dia. of 53" (53 * pi ) = (13.866 ft*2000 rpm)= (27,732 fpm/60)= 462.2 fps.
A .38 special travels at 600 fps. So, the tip of a 50 size heli is traveling only about 150fps slower than a bullet. Now if my math is wrong, someone please correct me. It is early in the morning, and I may be way off.

Enrolled full time A&P school... No time for flying :-(
12-17-2005 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   HOMEPAGE   GALLERY
 
 
Rotor Trash
Senior Heliman
Location: Higginsville, MO

My Posts This: Topic  Forum		Hi Canard, I did some checking and a .38 depending on which bullet is used travels at about 1200 fps.

Hope that helps.

Brent

VP Mid-Missouri Modelers: http://webpages.charter.net/mmmodelers/

Load'r High and Let'r Fly !!!
12-17-2005 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   HOMEPAGE   GALLERY
 
 
canardman
Senior Heliman
Location: Waco, TX

My Posts This: Topic  Forum		I got my info here..

Bullet speed

Enrolled full time A&P school... No time for flying :-(
12-17-2005 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   HOMEPAGE   GALLERY
 
 
Rotor Trash
Senior Heliman
Location: Higginsville, MO

My Posts This: Topic  Forum		LOL I got mine here http://www.reliancearmor.com/misc i...istic Chart.pdf

Load'r High and Let'r Fly !!!
12-17-2005 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   HOMEPAGE   GALLERY
 
 
vavavoom
Veteran
Location: London, England

My Posts This: Topic  Forum		Id have to agree that your figure for the speed of a 38 bullet is too low. A 9mm (9mmx19 96 grain) travels at around 1100 fps.
Still......... I wouldnt fancy getting hit by either!!!

## Inteligence is knowing a tomato is a fruit...Common sense is not putting it in a fruit salad
12-17-2005 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE  
 
 
Rockohaulic
Elite Veteran
Location: Valencia, CA, USA, 3rd Rock from the Sun

My Posts This: Topic  Forum		Depending on conditions, temp, altitude, etc, the speed of sound is around 1100 fps, which is 750 mph.

Some bullets are subsonic, around 900 to 1000 fps, and some are supersonic (like a .357 Mag or any rifle bullet). The muzzle velocity of a .357 is around 1400 fps.

I did the calculation for my nitro helicopter, and at hovering headspeed, the blade tips are doing 270 mph or 396 fps.

270 is far short of supersonic, but I don't want to be hit by that much mass at that speed!!

Rockohaulic
01-06-2006 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   GALLERY
 
 
Yug
rrMaster
Location: UK. Herts

My Posts This: Topic  Forum		Thats about right, somewhere between 200 to 300mph. Now for the scary bit, the centrifugal force..........
I did some calculations on the centrifugal force on blades.........

F=m*v*v/r where v = (rpm/60) * 2 * pi * r
F is in newtons where 1N=0.225 Lb

So if we take say a 30 size carbon blade weighing 0.12Kg, where its CG from root + root to shaft distance is 0.36m
and the head speed is say 1850rpm

Then v = 70m/s

subs this into F = mvv/r = 1621 newtons = 364 Lb

1 pound = 0.0714285714 stone

Therefore force on each blade = 26 stone
The 2 blades is therefore applying a force of 52 stone on the feathering spindle !

The forces will actually be less than this due to being displaced by the tangential vector, but you get the general idea.

You can work out the force on the tail hub. thats pretty alarming too.

This gives you an idea as to why helis are bloody dangerous.
Just imagine how these numbers bump up on a 90 running 710s !!!!!!!
It's a staggering 716Lb or 50 stone per blade ie double a 30 size.
You can work out the stored energy if you like. KE=1/2*m*v^2 if memory serves correct.

All that force on a poxy little M4 spindle bolt. I wonder why none of the figures are printed on the boxes ? This is one good reason why hovering should be with skids at eye level so that if a blade flys off, it will go over your head (& hit somebody in the pits). I am allways most nervous at take off; even more so than doing piro loops.

BTW, sorry about the use of 'stone', I'm just old fashioned. I could easily judge how many stone somebody weighed, but haven't a clue what it would be in pounds or Kg
01-07-2006 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   GALLERY
 
 
webbhost
Key Veteran
Location: england - Leicester

My Posts This: Topic  Forum		1 stone = 6.35026 kg, so

Kg of force on the blade spindle = 52 * 6.35026, making a staggering 330 kilograms

A 90 size heli:

100 * 6.35026 = 635.026 kilo's of force

Thats some cool info guy martin

meh
02-19-2006 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   HOMEPAGE   GALLERY
 
 
oldboldpilot
Key Veteran
Location: Southern California

My Posts This: Topic  Forum		Fortunately the pair of 26 stone / 1630 Newton / 367 lb centripetal forces the blade grips have to provide is balanced..stresses are very manageable.

But you can see why it doesn't take much imbalance to raise hell

Helis are Man's Defiance of the Laws of Nature - OCHC
02-23-2006 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   GALLERY
 
 
Yug
rrMaster
Location: UK. Herts

My Posts This: Topic  Forum		Yes but all that force on a poxy little screw head

Be afraid, be very very afraid.

Buy 2 helis, get a foo shield free
02-23-2006 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE   GALLERY
 
 
gipper6
Senior Heliman
Location: Mckinney, Texas

My Posts This: Topic  Forum		Terminal velocity is only 125 mph. A bullet is much faster. Both are lethal. The rotar blades are somewhere in between. Also lethal. I can't do math, but I agree, I don't want to be anywhere near those things.

The best way to make a small fortune in RC Helis is to start out with a large one. Debt from above!
03-03-2006 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE  
 
 
foo
Veteran
Location: Richfield, Minnesota

My Posts This: Topic  Forum		Get a foo shield. Helicopters ARE dangerous...

Raptor 30 v2 / OS .32 / JR 8103 / GY-401+9253 | Raptor 50 V2 / OS .50 Hyper
03-28-2006 Over year old.
PROFILE   PM   EMAIL   POSTS   BUDDY   IGNORE  
 
 
1 page2226 viewsPOST REPLY
Ron’s HeliProz South . MTA Hobbies . Model Rectifier Corp

.
.
Safety - RC Helis are not toys > Wow! Someone check my math...
 Print TOPIC Advertisers 

Subscribe to This Topic

Tuesday, March 16 - 11:32 am - Copyright © 2000 - 2010 runryder.com | email | link to rr | START HERE | NF