Parachute installation

[Luked 71]

Not to be argumentative, but a lightly loaded plane will experience less stress on the airframe in the same turbulent conditions as a more heavily loaded plane. It's counter intuitive because a heavily loaded plane rides more smoothly in turbulence.

 

I guess I'm not very good at explaining the concept, so I looked up a reference to a good explanation. Take a look at this page:

 

http://www.mountainflying.com/pages/mountain-flying/turb_va.html

 

Here is a quote from the section that talks about this:

 

 

MISCONCEPTION

 

Pilots notice that a heavily loaded airplane rides smoother in turbulent air. They perceive this as an indication that the airplane should be loaded to its maximum whenever turbulence is expected. This is a bad assumption.

 

Consider an airplane that has a maximum allowable gross weight of 3,000 pounds. If it encounters a +30 fps gust that results in an additional 2-g load factor, the airplane experiences a total of 3 Gs load factor. Multiply the 3-g load factor by 3,000 pounds and the wings are supporting 9,000 pounds.

 

Assume the airplane is loaded to 1,500 pounds and that it is subjected to the same gust. With half the inertia, the gust acceleration is doubled, causing the airplane to experience a 5-g load factor (4-g force plus 1-g level flight). Multiply 1,500 pounds by 5 gs and the wings are supporting 7,500 pounds.

 

The lightly loaded airplane is subjected to 1,500 pounds less load when encountering the same gust. Even though the heavy airplane realizes less load factor, it incurs more strain. The pilot recognizes load factor; the airplane recognizes load.

 

Last time we discussed this, I think I got overruled, so I'll put on the flame suit now 

[EDMO 1078]

Luke,

I know that you have some engineering education, and probably the one who wrote that does too.

However, I have read some "experts" writings that contradict the above. I don't claim to know much about the physics involved, so I cant present a valid disagreement with either.

What I can say, is that lighter GW planes cannot safely fly in the same winds and turbulence as the heavier GW aircraft - Just ask any Ultralight pilot who is staying in the hanger while I take off in a Cessna 150 in 40 knot winds to look for horses driven off by a forest fire where turbulence is wicked - So that tells me what I am more comfortable flying in any weather.

But, most everyone knows, that even the strongest plane may not survive in a thunderstorm turbulence.

Now, go back to the original posts: "There have been no recorded in-flight wing failures of an Avid or Kitfox plane."

(as validation for not wanting a BRS in mine).

EdMO

Edited 29 Aug 2015 by Ed In Missouri

[1avidflyer 1983]

Here is a article that asks the question: Why does maneuvering speed increase with weight. Is he correct? You be the judge... Jim Chuk

http://www.aviationchatter.com/2012/05/why-does-maneuvering-speed-increase-with-weight/

another one http://www.lapeeraviation.com/maneuvering-speed/

[akflyer 1427]

The ultralight flys at 25 MPH and would not be able to get out of the hangar without lifting off and then damn near flying backwards.  The 150 is not yet flying at 40 MPH therefore he can do an extremely sporty taxi and take off if he is lucky enough to get out to the runway without flipping the plane over.  I've been in my Avid loaded up in turbulence that rolled me better than 90° and winds that turned a 1.2 hour trip into a 4 hour trip.  No the soon to be Ex was not a happy pregnant wife that flight but we survived

 

[Luked 71]

Ed, you are correct. About larger aircraft with higher wing loadings being able to handle more turbulence than smaller lighter aircraft. What I was talking about would be where you compare two identical aircraft with the same structure, but one is loaded heavier than the other one.

 

Jim, you bring up a good point about maneuvering speed. Maneuvering speed increases as wing loading increases because maneuvering speed is calculated based on stall speed, and stall speed also increases with wing loading. The reason Maneuvering speed is based on stall speed is the stall acts kind of like a pressure relief valve for the structure. When the wing stalls, load decreases dramatically avoiding damage.

 

I hadn't considered that fact. I was only considering the basic physics described in the quote I included above. So, I think I may have been correct for certain situations where damage may occur directly from the motion caused by the turbulence. I think you guys were more correct in how turbulence usually causes damage the the airframe (sudden increase in angle of attach that overstresses things). This is one case where stalling is actually a good thing for the structure at least. I guess you learn something every day 

[EDMO 1078]

Luke,

I have been learning for the past 60+ years, both from my experience and others - I am still learning!

BTW: I celebrated my 49th birthday for the 25th time this year!

Most of my early experience was in commercial training many years ago. The first job offer I got was Co-pilot on call for a late-night HOT run from St. Louis to Detroit to pick up and return a load of heavy car parts for a plant here, with maybe thunderstorms on the route. I very quickly made up my mind that I would fly when I WANTED to fly, and NOT when TOLD to fly, and settled into a Toolmaker job for the next 40 years.

These kind of conversations are really good.

Thanks to all,

EdMo

Edited 29 Aug 2015 by Ed In Missouri

[Altifly 1]

on MKIV , thanks to Derek from BRS US