Negative G Load Question

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ctmorawetz
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Negative G Load Question

Post by ctmorawetz » Fri May 20, 2016 11:20 am

I'm trying to find a reputable source that explains how aircraft are certified or not certified for negative G loads. The scenario I'm looking at is if you get look at a POH for an aircraft and it shows a Max. G Load of +3.5 but no negative G load limit. Does that mean that aircraft is restricted to manoeuvres between 0 G and +3.5 G or would it mean that no G loading below 1 would be permitted? I'm thinking it would be between 0 and 3.5 but not sure. Thoughts?
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PilotDAR
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Re: Negative G Load Question

Post by PilotDAR » Fri May 20, 2016 11:56 am

A GA aircraft certified as "CAR 3" or "FAR 23" will be certified as follows:
Sec. 23.337

Limit maneuvering load factors.

(a) The positive limit maneuvering load factor n may not be less than--
[(1) 2.1+ for normal and commuter category airplanes, where W = design maximum takeoff weight, except that n need not be more than 3.8;]
(2) 4.4 for utility category airplanes; or
(3) 6.0 for acrobatic category airplanes.
(b) The negative limit maneuvering load factor may not be less than--
(1) 0.4 times the positive load factor for the normal, utility, and commuter categories; or
(2) 0.5 times the positive load factor for the acrobatic category.
(c) Maneuvering load factors lower than those specified in this section may be used if the airplane has design features that make it impossible to exceed these values in flight.
Commonly that works out to +3.8G, -1.5G for a normal category plane. In addition to that is the specified factor of safety, which means that up to 1.5 times those values, the plane will not break, though you might bend something expensive.

Your challenge is measure the G forces! Unless you have a G meter, you're just guessing anything negative.

Bear in mind that though the airframe can take the negative G, the engine oil system and battery won't like it much. You'll also get dirt from the floor up you nose! Avoid fooling around in the plane with negative G, unless you have a G meter, some training for that, and are ready to clean the belly afterward.
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oldtimer
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Re: Negative G Load Question

Post by oldtimer » Fri May 20, 2016 1:20 pm

Is to reduce negative G loading the reason water bombers deploy full flaps duing the dump?
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cgzro
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Re: Negative G Load Question

Post by cgzro » Fri May 20, 2016 1:57 pm

Trust me youll know when you go past -2g :)
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Rockie
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Re: Negative G Load Question

Post by Rockie » Fri May 20, 2016 5:01 pm

cgzro wrote:Trust me youll know when you go past -2g :)
Agreed. Floating in the straps gives most people a head rush and makes them think they're doing something extreme. -2 will scare the bejeezus out of them and all but guarantee they never fly again.
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Re: Negative G Load Question

Post by PilotDAR » Fri May 20, 2016 7:58 pm

Yeah, I had to do flight testing for engine operation to exactly -1G a few times, I don't like that stuff!

An old friend of mine some time ago was telling me about flying jet fighters, and how tight the cockpit was. "What did you do if you dropped your chart?" I asked... He replied "simple, roll upside down, and pick it up off the inside of the canopy!". Better he than I!
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cgzro
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Re: Negative G Load Question

Post by cgzro » Sat May 21, 2016 12:12 am

Negative G beyond -2 is basically painfull but you do get used to it.

Actually the worst is a rapid change from one extreme to the other. Most people never experience this but when a plane is rolled and turned at the same time you go +3/-3 multiple times in a row. Ouch.
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target
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Re: Negative G Load Question

Post by target » Sat May 21, 2016 11:27 am

Can any of the aerobatic guys tell if your allowed to go from either positive to negative or vice versa because of the possible "g LOC"?
I though an airshow official explained that was not allowed. the example was an inverted climb with a pull back onto the showline.
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DSoup
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Re: Negative G Load Question

Post by DSoup » Sat May 21, 2016 11:58 am

target wrote:Can any of the aerobatic guys tell if your allowed to go from either positive to negative or vice versa because of the possible "g LOC"?
I though an airshow official explained that was not allowed. the example was an inverted climb with a pull back onto the showline.
It's called "push pull" effect

And I have no idea if it's allowed, but I would suggest that it's not a great idea to do it. It severely reduces G capacity due to your body compensating for - g and then rapidly switching to + g. Your blood vessels dilate and can't constrict fast enough to give you g tolerance.
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cgzro
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Re: Negative G Load Question

Post by cgzro » Sat May 21, 2016 3:54 pm

Its required in contests above intermediate and allowed in airshows. We call them sleepers.
You need to be in good shape and know your limits and despite popular myth you dont just suddenly pass out, you get a bit or warning and backing off the G instantly will cure it assuming you are not in need if that pos G to avoid the ground. Negative followed by pos to recover close to ground would be something to approach with caution. He who shall not be named's father flew a lovely series of inside outside vertical 8 cominations at Gatineau a few years ago when well north of 70... impressive.
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duCapo
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Re: Negative G Load Question

Post by duCapo » Tue May 24, 2016 9:34 am

He who shall not be named's father flew a lovely series of inside outside vertical 8 cominations at Gatineau a few years ago when well north of 70... impressive.
Who would that be? Beelzebub?
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I_Drive_Planes
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Re: Negative G Load Question

Post by I_Drive_Planes » Tue May 24, 2016 12:56 pm

duCapo wrote:
He who shall not be named's father flew a lovely series of inside outside vertical 8 cominations at Gatineau a few years ago when well north of 70... impressive.
Who would that be? Beelzebub?
Colonel Beelzebub, I'm guessing.
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looproll
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Re: Negative G Load Question

Post by looproll » Thu May 26, 2016 6:48 pm

It's amazing how your G tolerance drops when doing quick transitions from +G to - and back. You certainly build a tolerance with exposure. My first few flights each season are brutal.
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Re: Negative G Load Question

Post by AuxBatOn » Thu May 26, 2016 7:45 pm

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