helicopter loadings

Let'sgoflying!

Let'sgoflying!

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Dave Taylor
What are examples of 'wing' and power loadings of some typical light helicopters, and how to they compare to our light airplanes?
 
Let'sgoflying! said:
What are examples of 'wing' and power loadings of some typical light helicopters, and how to they compare to our light airplanes?
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This is quoted from the FAA "Rotorcraft Flying Handbook" faa h-8083-21 which is a free download on the FAA website.

Disc loading of a helicopter is the ratio of weight to the
total main rotor disc area, and is determined by divid-ing
the total helicopter weight by the rotor disc area,
which is the area swept by the blades of a rotor. Disc
area can be found by using the span of one rotor blade
as the radius of a circle and then determining the area
the blades encompass during a complete rotation. As
the helicopter is maneuvered, disc loading changes.
The higher the loading, the more power you need to
maintain rotor speed.


To answer your question specifically I don't have any of my POH's for helicopter nearby, but I'll look and get back with you on that.
 
tonycondon said:
that would be a disc loading of 3.62 lbs / square foot. as a reference, my glider flies at a wing loading of 4 lbs / square foot.
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Tony's wing loading is pretty light, but we knew that. I fly my glider between 7 and 9 lbs/sq ft depending of if I am carring water ballest or not.

Brian
 
And for another Datapoint my Ka-6 has a wing loading of 5 lbs/sqf. Modern Racing ships are around 10-12 though.
 
Rotor&Wing said:
This is quoted from the FAA "Rotorcraft Flying Handbook" faa h-8083-21 which is a free download on the FAA website.

"Disc loading of a helicopter is the ratio of weight to the
total main rotor disc area,"
Click to expand...

How do they get away with that??
The blades can't be in more than one place at any one time!
(sounds like cheating to me!)

Honestly. If I pump 700lbs of fuel into an airplane, does that mean the hose is suddenly immovable from the weight? No...it doesn't get the credit of the whole 700lbs! It was only carrying 50lbs of fuel at any one time!

Must be an arbitrary calculation. Unless someone can come up with some convincing evidence.... (I await, with arms crossed, and a defiant visage!)
 
Rotor&Wing said:
From the Swcheizer web site http://www.sacusa.com/products/pdfs/300C_TechData.pdf

For a 300C helicopter the main rotor diameter is 26.83 feet and max weight is 2,050 pounds and is powered with a 190 hp engine.
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From (typed) page 2 if you eyeball that rotor, each blade appears to be about 8" or 2/3' in chord. Length about 12.5' (we lose a little at the hub) Three blades. So the total area that the air is acting upon is approximately:

3 x (.66'x12.5')

= 24.7 sq ft. !!!!

24.7/2050lbs
= pure magic wing loading!!
 
Steve! No change to the avatar yet? :(

Thanks will check it out. 'Oversimplification' may not be enough simplification...for me!
 
Let'sgoflying! said:
How do they get away with that??
The blades can't be in more than one place at any one time!
(sounds like cheating to me!)

Honestly. If I pump 700lbs of fuel into an airplane, does that mean the hose is suddenly immovable from the weight? No...it doesn't get the credit of the whole 700lbs! It was only carrying 50lbs of fuel at any one time!

Must be an arbitrary calculation. Unless someone can come up with some convincing evidence.... (I await, with arms crossed, and a defiant visage!)
Click to expand...

That's why it's called "Disk" loading. It's not directly comparable to wing loading. To begin with the lift generated by the rotor isn't equal across the span (granted it's' not perfectly equal across an airplane's wing either but on the airplane the variation from root to tip is way smaller). In addition, the "airspeed" at the rotor tips is nearly supersonic at something like 500 Kt and it's relatively unaffected by the helicopter's forward speed.

AFaIK it doesn't make any more sense to compare disk loading with wing loading than it does to compare wing loading of an airplane with "thrust loading" of a rocket. Apples and coconuts.
 
Last edited:
A little thread creep, Dave...sorry.

Hope to change it by the end of the week, Lance. Waiting on a new oil cooler and I have to align the new exhaust tail pipes to the lower cowling openings. Once that's done I can button up the engine and hit the start button for the first time since March. Long story...one to go over after its over.

In keeping with this thread:

Don't overlook the :smile: in the previous post. :smile:

Let'sgoflying! said:
Steve! No change to the avatar yet? :(

Thanks will check it out. 'Oversimplification' may not be enough simplification...for me!
Click to expand...
 
it doesn't make any more sense to compare disk loading with wing loading than it does to compare wing loading of an airplane with "thrust loading" of a rocket.
Click to expand...

so....there is no way to compare helos to airplanes when it comes to wing loading?
 
Let'sgoflying! said:
so....there is no way to compare helos to airplanes when it comes to wing loading?
Click to expand...

Not that I know of. And in the little rotor wing flying I've done, I can't remember ever being bounced vertically enough to notice (well except for the PIO). One big difference that probably has some effect here is that helicopter rotors don't have enough strength to support the weight of the ship by a long shot. It's the "centrifugal force" (i.e. inertia) of the blades that makes them hold their shape and when the vertical load increases they actually flex into a cone shape.
 
gismo said:
One big difference that probably has some effect here is that helicopter rotors don't have enough strength to support the weight of the ship by a long shot. It's the "centrifugal force" (i.e. inertia) of the blades that makes them hold their shape and when the vertical load increases they actually flex into a cone shape.
Click to expand...

thread creep

3 things I can't wrap my head around.

1. Why don't helos have a "keep body parts below this line" line for ingress/egress with rotors going. Considering all the warnings in today's world, it's sorely missing.

2. Are there helos that address the rotor/boom strike issue by limiting cyclic or something? Seems odd that one can destroy the helo without exceeding g limits.

3. Why are negative g's so bad?
 
Pi1otguy said:
3. Why are negative g's so bad?
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Somebody earlier in the thread mentioned that in turbulence with a positive g-load the blades form a little bit of a cone shape. With negative g-loads they form an inverse cone shape and you could hit the tail or tail boom.
 
Everskyward said:
Somebody earlier in the thread mentioned that in turbulence with a positive g-load the blades form a little bit of a cone shape. With negative g-loads they form an inverse cone shape and you could hit the tail or tail boom.
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Not to mention "unloading" the rotor disc and setting up some really bad juju.:yikes:
 
Pi1otguy said:
2. Are there helos that address the rotor/boom strike issue by limiting cyclic or something? Seems odd that one can destroy the helo without exceeding g limits.
Click to expand...

Look at it this way. The strength of the rotor blade is in centrifugal force. When the rotor is turning within it's prescribed limits centrifugal force will hold the blades in their respective plane. When the cyclic is moved while the rotor is at speed there is no danger of hitting the tailboom. Only when the rotor is slowed down or the aircraft hits hard and the blades flex down will they hit the boom.
 
Pi1otguy said:
thread creep

3 things I can't wrap my head around.

1. Why don't helos have a "keep body parts below this line" line for ingress/egress with rotors going. Considering all the warnings in today's world, it's sorely missing.

2. Are there helos that address the rotor/boom strike issue by limiting cyclic or something? Seems odd that one can destroy the helo without exceeding g limits.

3. Why are negative g's so bad?
Click to expand...


1. On medium category helicopters (think Bell 412 and S76) there are such warnings, especially near the tail on the 412 and the nose of the 76 due to the possibility of blade droop to 4'. I tackled a 6' 300 lb Bubba once who was loping toward my tail rotor on a 412 chasing his ball cap and not looking where he was going. I've also seen the pictures of the few unlucky people who have been cut in half due to a stuck droop stop on the 76. Why there aren't such warnings as in 'don't put your hands over your head' on Schweizers and Robbies? Who knows, but frankly, you are dealing with an aircraft that will carry one to three people besides the pilot. If the pilot cannot properly brief and keep control of 1-3 passengers, well, in all but the rare circumstance of a pax completing disregarding instructions, I'd say the pilot is incompetent. Besides, why would you get in and out of one of those while it's running anyway without an escort to ensure safety?

2. There are control stops in the flight control system that will not allow you to, for example, pull so much aft cyclic under normal conditions that you just chop off the tail boom. Negative G is another story as is low rotor RPM upon ground contact.

3. See definitions of 'bad juju' in above posts.
 
TangoWhiskey said:
It's amazing the blades don't suffer fatigue failure more often, if this video is what it purports to be (blade flex in flight of a helicopter rotor blade):

Click to expand...

Believe it or not, there are rotor blades out there that are considered 'unlimited life' with no time out.
 
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