Forums: Skydiving: General Skydiving Discussions: Re: [DuckDodger] Collapses and Turbulence: Article: Edit Log

BrianSGermain  (D 11154)

Feb 1, 2006, 6:21 AM

Views: 13819
Re: [DuckDodger] Collapses and Turbulence: Article

In reply to:
Great thread. There is a lot to learn here.

I see you mention manuevering speed and this got me thinking about a question I have had for years. I was a pilot long before a skydiver, maybe something to do with going to Rhinebeck Aerodrome back in '75. That was cool.

Anyway, manuevering speed increases as you increase weight/loading, which to me seems absolutely backwards on the surface. I thought that maybe this had something to do with inertia, that generally, increasing weight made the aircraft more stable, or less likely to move to a critical angle of attack and overstress the wing.

On the other hand increasing weight, should actually increase loading on the wing, so not wanting to stress my little mind, like we seemed to be doing with the wing, I left it there.

A few years later, a good friend of mine said the reason manuevering speed increased was totally dependent on the testing of aircraft. In respect to my friend, I didn't tell him this sounded like crock to me. Then I thought about our dear Gov and thought, maybe so.

Doesn't seem to be much parachute application, other than the thought about inertia, like a more heavily loaded boat crushing through heavier seas. The parachute translates weight to the lines so that sort of makes sense to me, but it might just be acid flashbacks. What do you think?

Although there clearly are some discrepencies in government testing standards, weight tends to decrease maneuvering speed because, as you said, inertia plays into the equation. Yes, the larger the mass, the less it wants to change direction. However, the larger the mass, the more force will be exerted on the vehicle itself when it is changed in flight path.

The magnitude of positive and negative "g's" that an airplane can handle without risk of structural failure is, in essence proportional to the mass of the vehicle as a whole. You would think that a larger airplane would be able to handle more loading on the wings, and you would be correct. Nevertheless, the percentage of the overall mass is what is in question here, and this figure decreases with the mass of the vehicle.

Size does matter. Small parachutes, for instance, experience less damage from opening than large ones. This is due in part to the fact that there is a larger amount of volume in the wing, and the increased amount of air moving in at opening time exerts a greater amount of force on the fabric. Further, the increased surface area collects more energy in the decelleration from terminal velocity, so the stresses on the fabric are greater. Yes, the force is distributed over a larger area, but the force localized on any given part of the fabric are still greater. So big parachutes tend to blow up with a much greater frequency. That is why tandems are so heavily reinforced.

Likewise, forces do not scale in a linear fashion when it comes to the ability to handle weight on the airframe. Big things just don't like to change direction. They are slow to alter their path, but they also resist the change with great lethargy. Like a fat person trying to get off the couch, it requires a great amount of effort, and they are more likely to break a hip in trying to do so.

Does that work for you?

(This post was edited by BrianSGermain on Feb 1, 2006, 6:28 AM)

Edit Log:
Post edited by BrianSGermain () on Feb 1, 2006, 6:26 AM
Post edited by BrianSGermain () on Feb 1, 2006, 6:28 AM

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