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Should I be scared -- C172 over Gross



 
 
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  #1  
Old April 17th 08, 10:53 AM posted to rec.aviation.piloting
Tman
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Posts: 68
Default Should I be scared -- C172 over Gross

Flown C172's for quite a while, and never had anybody in the back.
Now I'm planning on quite a trip, with 2 pax and luggage.

When I fill the fuel to the *tabs*, calc everyone's weight honestly and
consider baggage -- I'm 75 lbs over the 2450 gross on departure. Maybe
100 over gross if I assume a "lie about weight" factor or some
inaccuracy with filling the tanks. Now I'm scratching my head about
just how risky this is. I know (others) have pushed over gross in these
planes way more under worse conditions, and have almost always gotten
away with it. I'm inclined to just do it, and be cognizant that it will
perform differently, i.e. don't expect the same picture on climbout that
you would when solo.

Risky? Or just roundoff error on the weight? Here are some other factors:

This is the 160HP C172, standard.
Departure runway is 5000'.
No steep terrain to climb out of.
Plenty of alternates along with the way with 3000 runways.
Not particularly hot, humid, or high. 50 degrees at 1000 MSL for
departure or any point of landing.

I'm figuring I'm 3% over gross, causing most of my V speeds to increase
1.5%, so say -- instead of flying short final at 65 knots, I'd fly at 66
knots... OK wait I can't hold airspeed to +/- 1 knot on most days anyways.

I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. What else should I be
aware of? Am I dangerous?

T
  #2  
Old April 17th 08, 11:32 AM posted to rec.aviation.piloting
Vaughn Simon
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Posts: 735
Default Should I be scared -- C172 over Gross


"tman" inv@lid wrote in message
news
I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. What else should I be aware
of? Am I dangerous?


Like being a little pregnant. Ship the luggage.

Vaughn



  #3  
Old April 17th 08, 12:33 PM posted to rec.aviation.piloting
Mortimer Schnerd, RN[_2_]
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Posts: 597
Default Should I be scared -- C172 over Gross

tman wrote:
Flown C172's for quite a while, and never had anybody in the back.
Now I'm planning on quite a trip, with 2 pax and luggage.

When I fill the fuel to the *tabs*, calc everyone's weight honestly and
consider baggage -- I'm 75 lbs over the 2450 gross on departure. Maybe
100 over gross if I assume a "lie about weight" factor or some
inaccuracy with filling the tanks. Now I'm scratching my head about
just how risky this is. I know (others) have pushed over gross in these
planes way more under worse conditions, and have almost always gotten
away with it. I'm inclined to just do it, and be cognizant that it will
perform differently, i.e. don't expect the same picture on climbout that
you would when solo.

Risky? Or just roundoff error on the weight? Here are some other factors:

This is the 160HP C172, standard.
Departure runway is 5000'.
No steep terrain to climb out of.
Plenty of alternates along with the way with 3000 runways.
Not particularly hot, humid, or high. 50 degrees at 1000 MSL for
departure or any point of landing.



I'd make this flight without hesitation. I would be considerably more reluctant
in the heat of the summer but now?



--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com


  #4  
Old April 17th 08, 02:40 PM posted to rec.aviation.piloting
Jay Somerset
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Posts: 40
Default Should I be scared -- C172 over Gross

I would be much more concerned with the BALANCE part of W&B. Yes, 100
pounds over gross is not wise, at it reduces your safety margin with
turbulence, and landing and takeoff distances.

But you really need to make sure that your CG is not out of the
allowable range -- with rear-seat pax and luggage, it could be pretty
far back. Also, you have specific weight limits in the rear luggage
area -- it's all in the POH.

So, but your heaviest passenger in the front seat, and the lightest
luggage in the rear area, and see where your CG lies.

On Thu, 17 Apr 2008 05:53:07 -0400, tman inv@lid wrote:

Flown C172's for quite a while, and never had anybody in the back.
Now I'm planning on quite a trip, with 2 pax and luggage.

When I fill the fuel to the *tabs*, calc everyone's weight honestly and
consider baggage -- I'm 75 lbs over the 2450 gross on departure. Maybe
100 over gross if I assume a "lie about weight" factor or some
inaccuracy with filling the tanks. Now I'm scratching my head about
just how risky this is. I know (others) have pushed over gross in these
planes way more under worse conditions, and have almost always gotten
away with it. I'm inclined to just do it, and be cognizant that it will
perform differently, i.e. don't expect the same picture on climbout that
you would when solo.

Risky? Or just roundoff error on the weight? Here are some other factors:

This is the 160HP C172, standard.
Departure runway is 5000'.
No steep terrain to climb out of.
Plenty of alternates along with the way with 3000 runways.
Not particularly hot, humid, or high. 50 degrees at 1000 MSL for
departure or any point of landing.

I'm figuring I'm 3% over gross, causing most of my V speeds to increase
1.5%, so say -- instead of flying short final at 65 knots, I'd fly at 66
knots... OK wait I can't hold airspeed to +/- 1 knot on most days anyways.

I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. What else should I be
aware of? Am I dangerous?

T

--
Jay (remove dashes for legal email address)
  #5  
Old April 17th 08, 02:55 PM posted to rec.aviation.piloting
WingFlaps
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Posts: 621
Default Should I be scared -- C172 over Gross

On Apr 17, 9:53*pm, tman inv@lid wrote:
Flown C172's for quite a while, and never had anybody in the back.
Now I'm planning on quite a trip, with 2 pax and luggage.

When I fill the fuel to the *tabs*, calc everyone's weight honestly and
consider baggage -- I'm 75 lbs over the 2450 gross on departure. *Maybe
100 over gross if I assume a "lie about weight" factor or some
inaccuracy with filling the tanks. *Now I'm scratching my head about
just how risky this is. *I know (others) have pushed over gross in these
planes way more under worse conditions, and have almost always gotten
away with it. *I'm inclined to just do it, and be cognizant that it will
perform differently, i.e. don't expect the same picture on climbout that
you would when solo.

Risky? *Or just roundoff error on the weight? *Here are some other factors:

This is the 160HP C172, standard.
Departure runway is 5000'.
No steep terrain to climb out of.
Plenty of alternates along with the way with 3000 runways.
Not particularly hot, humid, or high. *50 degrees at 1000 MSL for
departure or any point of landing.

I'm figuring I'm 3% over gross, causing most of my V speeds to increase
1.5%, so say -- instead of flying short final at 65 knots, I'd fly at 66
knots... OK wait I can't hold airspeed to +/- 1 knot on most days anyways.

I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. *What else should I be
aware of? *Am I dangerous?


Not really. The slight excess is fuel which will be burnt off. before
landing time. Remember the structure is stressed to much higher G
than 1.015 and if you just slapped a bigger engine in the MTOW would
be increased to as much as 2500. What is dangerous is the position of
the COG and the reduced climb. Make sure you do a weight and COG calc.
for the trip. I can tell you that you should probably expect a more
tail heavy feel than you are used to which will promote a tendency to
rotate too early. Just raise your Vx by 5k and she'll be fine. Your
climb will be reduced to (say) about 400 fpm at 2000' (if I remember
correctly). Don't crash it or you will be in real trouble :-0

Cheers

  #6  
Old April 17th 08, 04:21 PM posted to rec.aviation.piloting
Michael[_1_]
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Posts: 185
Default Should I be scared -- C172 over Gross

On Apr 17, 5:53*am, tman inv@lid wrote:
I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. *What else should I be
aware of?


Many things. That's inherently the problem with operating outside the
certified limits. The certification limits provide you with certain
protections. By operating outside those limits, you give up some
protection. What do you give up? Well, that depends on what set the
limit.

Now there are two basic ways to approach this. First, you can
approach it the engineer way. That's how (modern) test pilots
approach this sort of problem. They operate outside the defined
limits all the time (it's in the job description) and most of them are
trained engineers anyway. They figure out what they are doing, what
they can expect out of the operation, decide whether the risk is
acceptable, plan for it, and fly the plan.

So how do you do this?

Start with the basics. What is the maximum available gross weight for
that make and model? Are there STC's that increase it? What sort of
gross weight limits are handed out on ferry permits?

Consider the effect on cg. The cg envelope generally narrows with
increasing weight.

Consider performance - what will climb be like? Cruise? How about go-
around with flaps? Perhaps you need to limit flaps on landing (in
case they don't retract)?

What about the g-loading? Normal category is 3.8, now you may have
less (or not - is that what limits gross weight on that plane?) - how
much turbulence can you expect?

Don't forget that for older planes, the W&B is mostly a work of
fiction anyway. The only real W&B is the kind you do with scales.
Most of them are done by subtracting the weight of equipment removed
(generally overestimated, because the cabling for avionics is mostly
left in) and adding weight installed (often underestimating because
fabbed cables and such are not included) and ignoring the
(significant) accumulation of dirt and grease.

Ultimately, what you are doing is substituting your judgment for
regulation. This has a lot in common with deciding that while the
speed limit is 55 here, in your judgment 60 is safe enough, even with
passengers in the car. If that's not something you would do, you
probably should not do this either.

Or there's another way. Hey, people do this all the time, seems to
work out OK, why not give it a shot? That's a lot how test pilots
used to operate way back when. A lot of them died that way, too.

*Am I dangerous?


Of course you're dangerous. You're considering transporting your
passengers by light airplane rather than a car. That's demonstrably
more dangerous. The question is whether the risk is reasonable for
you and them.

Now I happen to know (having faced almost this situation and done the
above analysis) that the margins are acceptable for me - and were
acceptable even when I had something like 100 hours. But who the hell
am I? Maybe I have graduate degrees in engineering, an ATP, and an
A&P - not to mention several kinds of CFI. Then again, maybe I'm just
a guy who plays flight sim a lot. Only the people who have met me and
flown with me know for sure.

If you're going to operate outside the rules, you really should know
what safety margins, if any, you are giving up - and that means doing
your own analysis.

Michael
  #7  
Old April 17th 08, 04:27 PM posted to rec.aviation.piloting
Robert M. Gary
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Posts: 2,767
Default Should I be scared -- C172 over Gross

On Apr 17, 2:53*am, tman inv@lid wrote:
Flown C172's for quite a while, and never had anybody in the back.
Now I'm planning on quite a trip, with 2 pax and luggage.


The biggest problem with flying a little overgross is the same problem
with flying at high density altitude. The plane will perform different
and a pilot who isn't expecting this can run into serious problems.
The site picture over the nose will look a bit different. This is why
I always teach my students to climb out on airspeed. I know some CFIs
focus on the site pitch picture but that only works with consistant
weight, altitude, etc.
Many pilots have bitten the big one because they keep pulling the nose
up when climbing out of mountain airports until they stall it. They
keep trying to achieve the site picture their CFI taught them down in
the valley.

-robert, CFII

  #8  
Old April 17th 08, 04:27 PM posted to rec.aviation.piloting
Dudley Henriques[_2_]
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Posts: 2,546
Default Should I be scared -- C172 over Gross

tman wrote:
Flown C172's for quite a while, and never had anybody in the back.
Now I'm planning on quite a trip, with 2 pax and luggage.

When I fill the fuel to the *tabs*, calc everyone's weight honestly and
consider baggage -- I'm 75 lbs over the 2450 gross on departure. Maybe
100 over gross if I assume a "lie about weight" factor or some
inaccuracy with filling the tanks. Now I'm scratching my head about
just how risky this is. I know (others) have pushed over gross in these
planes way more under worse conditions, and have almost always gotten
away with it. I'm inclined to just do it, and be cognizant that it will
perform differently, i.e. don't expect the same picture on climbout that
you would when solo.

Risky? Or just roundoff error on the weight? Here are some other factors:

This is the 160HP C172, standard.
Departure runway is 5000'.
No steep terrain to climb out of.
Plenty of alternates along with the way with 3000 runways.
Not particularly hot, humid, or high. 50 degrees at 1000 MSL for
departure or any point of landing.

I'm figuring I'm 3% over gross, causing most of my V speeds to increase
1.5%, so say -- instead of flying short final at 65 knots, I'd fly at 66
knots... OK wait I can't hold airspeed to +/- 1 knot on most days anyways.

I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. What else should I be
aware of? Am I dangerous?

T


I never advise a pilot to load any airplane over gross.
I will tell you that the big killer in these situations is the cg
location, especially the aft cg.
Tell you what; instead of my "advising you" on what to do specifically
with this flight, let me suggest to you that you run a weight and
balance for this aircraft at full tanks, THEN run the same pax and
baggage loading figuring 1/4 tanks, just to see what this does to the cg.


--
Dudley Henriques
  #9  
Old April 17th 08, 05:12 PM posted to rec.aviation.piloting
gliderguynj
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Posts: 34
Default Should I be scared -- C172 over Gross

On Apr 17, 5:53*am, tman inv@lid wrote:
I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. *What else should I be
aware of? *Am I dangerous?
T


There's safe, and there's legal. If you take passengers up over gross
as PIC....you've busted a rule or two. If you've posted about it here
and still do it.....

Why not take a few gallons of gas out of the equation and stop for a
refuel a bit sooner?

Doug

  #10  
Old April 17th 08, 05:32 PM posted to rec.aviation.piloting
B A R R Y[_2_]
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Posts: 782
Default Should I be scared -- C172 over Gross

gliderguynj wrote:
On Apr 17, 5:53 am, tman inv@lid wrote:
I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. What else should I be
aware of? Am I dangerous?
T


There's safe, and there's legal. If you take passengers up over gross
as PIC....you've busted a rule or two. If you've posted about it here
and still do it.....



Then there's ethical...

Should you announce to the pax that the airplane is being operated
outside of the manufacturer's limits, with possible consequences explained?

I see one side of the coin where all pax are licensed pilots, the PIC
shows the W&B info to all involved, and all involved make individual
decisions to get in, or not, based on full awareness of possible
outcomes. Still not legal, but...

The other side is allowing unsuspecting and unknowing people, who
believe the PIC is fully trustworthy, to board a known out of limits
airplane.

No way, no how, am I ever going put one foot on the slippery slope of
the second case.
 




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