Increase in Registered Gross Weight?

[BrianDC]

I'm also not going to pass any judgement on the topic but have a more general question about changing the op limits.

To change the op limits (either to increase or decrease) is it as simple as sending a letter to the FSDO to update or change your limits and getting them to agree and re-issue? (Maybe a visit from a DAR to increase vs decrease?)


As mentioned by some they increase their Gross Weight for those one a year trips, not daily flying. Even in the certified world you can get a waiver or even an STC to increase your max gross weight (or as others mentioned the Alaska regs). Any reason why someone couldn't get a waiver if they were going to OSH / etc vs increasing the gross weight, or is the perception that it's easier to get the higher gross weight once vs having to ask for a waiver?

[RV7A Flyer]

Originally Posted by tgmillso

I think you would find that the insurance agent is under no obligation to perform their own structural analysis to verify the acceptability of the increased gross weight prior to accepting your premium payment, just as they don't have to perform a flutter analysis or any other type of analysis. Their position is no different to the representative that "signs off" your aircraft. They have no legal obligation to verify your calculations unless they choose to do so, and chances are, this will only be after there has been an incident.
Tom.

I didn't say they were under of those obligations. I only said that by writing you a policy, they either accepted your Ops Limits weights as being acceptable to insure, or they didn't bother to ask for them and probably wouldn't be able to claim ignorance of them later as an excuse.

[sblack]

Originally Posted by kbalch

This all boils down to rationalizing a gross weight increase (without any supporting engineering data - back-of-envelope pseudo-calculations notwithstanding) for the sole purpose of convenience. The point that doing so, if one can squeak it past the DAR, makes the operation legal is entirely irrelevant.

.

I would not call using well established G limits like Normal and Utility Category, which have been used on 1000s of airplanes over many decades to be "pseudo calculations". If you respect those limits you are reducing the load on the airplane. Simple as that. How many C150s and C172s have used Normal category limits since the 1950s? Or you could be at 1600 lbs and pull 10gs and pull the wings off, but your weight was "legal". It comes down to common sense. I would also argue that using those accepted Normal Category limits IS data with a very solid pedigree. That takes care of the flight loads. If you have a hard landing at those weights you might bend something. And if you have an airplane that is under powered you might not meet the climb gradient requirements. Then there are the CG limits to consider. But the maximum load on the airplane occurs during high G maneuvers and adopting restrictions on maneuvering is a sound method of limiting those loads.

Vne is quoted as IAS for many airplanes because that's what pilots see in the cockpit, but flutter onset is limited by TAS.

I am an Aero Eng with 28 yrs of experience.

[rv7charlie]

Originally Posted by BrianDC

I'm also not going to pass any judgement on the topic but have a more general question about changing the op limits.

To change the op limits (either to increase or decrease) is it as simple as sending a letter to the FSDO to update or change your limits and getting them to agree and re-issue? (Maybe a visit from a DAR to increase vs decrease?)


As mentioned by some they increase their Gross Weight for those one a year trips, not daily flying. Even in the certified world you can get a waiver or even an STC to increase your max gross weight (or as others mentioned the Alaska regs). Any reason why someone couldn't get a waiver if they were going to OSH / etc vs increasing the gross weight, or is the perception that it's easier to get the higher gross weight once vs having to ask for a waiver?

No ideas about waivers, except that it's probably as much trouble to get a waiver as a permanent change to the op limits.

A 'major change' (increasing gross weight would qualify) typically requires a letter/fax to the FSDO defining the change you're making. The FSDO would issue new oplims, with a requirement to fly test time after the mod (typically 5 hrs), and a test area, which you might be able to define if you ask them for a particular area. Before and after you fly the test time, you make log book entries placing the a/c back in Phase 1, and returning it to Phase 2. It would probably help to precede the fax with a phone call, explaining what you're doing. That would likely get you a contact person to deal with, which can help things go smoother.

I've changed oplims on homebuilts several times over the years, and it's always gone smoothly for me, but a lot of this stuff is very FSDO-dependent. Your experience might be different.

[skylor]

Originally Posted by sblack

Vne is quoted as IAS for many airplanes because that's what pilots see in the cockpit, but flutter onset is limited by TAS.

I am an Aero Eng with 28 yrs of experience.

And Vne is even quoted as IAS in older Van's Builder's Manual such as the one for my RV-8.

I suspect that the real reason Van's changed from IAS to TAS is because they saw a trend of higher-power and forced induction engines going into their kits and became concerned that high-altitude flutter margins were being reduced or exceeded on these aircraft, thus they changed to TAS.

Skylor

[RV7A Flyer]

The poll (in the other thread I started) is currently showing a 60/40 split viz-a-viz no change/increase amongst those who responded, so upping the max GW seems to be a pretty common thing that builders are doing (granted the small sample size, self-selection, etc., of the "poll").

[Snowflake]

Originally Posted by sblack

I would not call using well established G limits like Normal and Utility Category, which have been used on 1000s of airplanes over many decades to be "pseudo calculations". If you respect those limits you are reducing the load on the airplane. Simple as that. How many C150s and C172s have used Normal category limits since the 1950s? Or you could be at 1600 lbs and pull 10gs and pull the wings off, but your weight was "legal". It comes down to common sense. I would also argue that using those accepted Normal Category limits IS data with a very solid pedigree. That takes care of the flight loads. If you have a hard landing at those weights you might bend something. And if you have an airplane that is under powered you might not meet the climb gradient requirements. Then there are the CG limits to consider. But the maximum load on the airplane occurs during high G maneuvers and adopting restrictions on maneuvering is a sound method of limiting those loads.

This rationalization is unfortunately flawed in that it assumes a few things that are not necessarily true. First off, it assumes the load on the wing is the only consideration you have at high G-loading (it's not). Second, it assumes the increase in weight is uniformly applied throughout the airplane, like a thick paint.

That extra 100lb that you're adding may look like only ~5% of the gross, but think about where will it go on the airframe. Think about how much more weight will be there, than was designed to be there. For example: If you want to plan for the extra weight to go in the passenger seats, and if those seats are designed for approximately 200lb people, then an additional 50lb per seat is a 25% load increase, concentrated just on that one part of the structure... A much more significant change than just pushing the limit by 5%.

[Dan Langhout]

Originally Posted by Snowflake

. . . . . . . For example: If you want to plan for the extra weight to go in the passenger seats, and if those seats are designed for approximately 200lb people, then an additional 50lb per seat is a 25% load increase, concentrated just on that one part of the structure... A much more significant change than just pushing the limit by 5%.

Hmm - well then I guess I am in big trouble already when I fly my airplane solo under Vans gross weight!

[Snowflake]

Originally Posted by Dan Langhout

Hmm - well then I guess I am in big trouble already when I fly my airplane solo under Vans gross weight!

Just an example, to get people to think in greater detail about the practical effect of an increase. Not saying those numbers are exact.

[spatsch]

I think what people frequently overlook in those matters is the fact that they might eventually sell the airplane.

Now you could argue that you can increase your max cross to 2000lb as you really only do it to not violate FARs and you fully understand that you have to be very careful when you are over 1800lb as you effectively are a test pilot now. However, the buyer after you or the buyer after that reads the weight and balance sheet and says great I have a 2000lb max cross airplane and as I am in Alaska I add another 300lb. So now that guy is flying the airplane you build at 2300lb assuming still normal G limits and a landing gear that can sustain the occasional rough landing without any shred of evidence that it actually could.

Is that really safe? For you it probably is but is it safe for the buyer?

I find it similarly inconsiderate to subsequent owners to claim a VNE without testing it in phase 1 or claiming that a list of acrobatic maneuvers are allowed and were tested in phase 1 (by log book entry) when they were not. All things I have come across in the past.

Oliver