Increase in Registered Gross Weight?

[Chris Engler]

Thanks for the thoughts/info. With regards to the FAA/DAR item, it's my understanding that establishing gross weight is the decision of the builder of record (see italicized text below from an EAA article) and gross weight can be established at any number they choose....the FAA/DAR have no jurisdiction on this.

Completely agree on the aft CG issue....my forward most CG will be solo with minimal fuel on board. As the fuel burns or I take a passenger, the CG moves rearward but there's plenty of range in the CG envelope to not realistically approach a rear CG scenario.

From an operational perspective, my concerns would be:

1. Overstressing the airframe

My objective would be a legal take off weight with a passenger and a plenty of baggage (90% of the time I'll be solo so gross weight not a factor). Under the heavy scenario, I'd be back to the factory gross of 1800 in less than an hour as fuel burned.

At the risk of oversimplifying, I'm confident there's less stress on the airplane at 1850 pounds and 3 Gs as compared to 1800 pounds and 6 Gs. I realize the stress loads aren't necessarily linear but I'd have to believe that the 1800 and 6Gs condition is closer to an overstress situation than 1850 at 3. My wife has a rule of no hard G's while she's on board so the flight plan while heavy would be standard takeoff, climb, and cruise....likely nothing close to 3Gs.


It would seem that testing during Phase would include loading to 1850 pounds, flying at 3 Gs, and limiting maximum Gs to 3 when loaded between 1800 and 1850 in the aircraft log


2. Increased stall speed relative to Van's published gross number

Fifty extra pounds would likely increase stall a couple of knots as compared to published gross and would have to be sorted out during Phase I...nothing too complicated here, load the airplane to 1850 pounds, fly, record the data, and document in the aircraft log.

As a point of reference, the gross weights on the Super7s and 8s are running between 2200 and 2300 pounds so adding 50 pounds to gross and limited flight loads while over 1800 would not seem to be an issue.

Anything else I'm missing?




Gross Weight


What determines the gross weight of a homebuilt aircraft?

I'm building a Zenith Zodiac CH601HDS. The specs from the manufacturer state the maximum gross weight of this aircraft as 1200 lb, but I have seen several references from other builders of this model who have stated their gross weight as reset to 1300 lb. Is it as simple as saying "I won't ever go anywhere near 6 G so I can restate the gross to anything I want?


Answer: Your question is a good one, as there is much misinformation floating around regarding gross weight on homebuilts. From a regulatory standpoint, the builder of a homebuilt is in fact the "manufacturer" of that individual aircraft, and is allowed to set the weight limits, including gross weight, anyplace he/she cares to. There is no restriction on what weight a builder lists as the maximum gross weight, regardless of what the aircraft designer or kit manufacturer recommends. This is why you see many homebuilts with gross weights that differ from what the kit manufacturer?s aircraft calls for.

[Chris Engler]

Thanks for the correction Carl....yes, the comparison should be 4.4 Gs at 1800 vs 3 Gs (arbitrarily chosen as a worst case during takeoff/climb/cruise with some unexpected turbulence) at 1850....but I strongly suspect the higher weight/lower G combination would represent less airframe stress.

I'm probably overthinking this but the aircraft ID placard is about to go to the engravers so it's decision time. Just trying to avoid getting dinged on a ramp check for a bit of extra weight on the rare occasion we'll be full of fuel and heavily packed. I suspect most 8s with an angle valve 360 and Hartzell CS prop have less than the otherwise available 125 pounds of baggage when they're full of fuel. I'm sure there would be less issues with the insurance company too if there was a mishap at slightly over 1800 if the registered gross was 1850.

[StressedOut]

Originally Posted by RV8JD

And remember, Vne (Redline) is 230 MPH TAS (not IAS).

You should probably double check this statement. I believe Vne is defined in IAS, not TAS (source).

[tgmillso]

Hi Chris,
If you had a "mishap" I'm sure it wouldn't take much digging by the insurance investigators, given that you list your full name and aircraft N number in your signature, to discover this forum thread:

"Chris Engler, Greene, NY
RV 8 Under Construction (N184CE Reserved), Showplanes Fastback, Superior IO 400; Dual 10.4 HXr
Kitfox 7; Rotax 914, Built and Sold
VAF donation gladly paid through July 2018"

I know insurance brokers frequent this forum and they're probably reading this post right now. They would find that your weight increase engineering was "crowd sourced" and occured after you completed the aircraft without any structural modification. I'm sure they would have a field day with this, especially given that an experienced Van's engineer has publicly warned against such a move. Depending on what the future failure mode was, the insurance investigator would have a grand time arguing that the incident (remember Murphy's Law) was as a result of the increased stall speed and subsequent lengthened landing roll, prop strike from the increased gear loading or fatigue failure from continuously operating at 1850lb or 1875lb (even though you won't be, but that's not going to stop their lawyer from arguing it). Don't get me wrong, I'm all for analysing and applying modifications that improve the safety, maintainability, performance etc. of the aircraft during the build, with solid engineering analysis behind it, as this is the basic theme of the Experimental category. On the other hand, performing pencil whipping exercises after the fact is what makes us the butt of certified industry jokes and gives us all a bad reputation (see link below):
https://www.youtube.com/watch?v=0M4pTuVdq0w
I do appreciate your openness however, and the fact that you obviously take this seriously enough to bring it to the attention of the RV community before you execute your decision.
Regards,
Tom.
RV-7, complete apart from avionics.
Aerospace Engineer.

[RV7A Flyer]

Originally Posted by Chris Engler

Thanks for the correction Carl....yes, the comparison should be 4.4 Gs at 1800 vs 3 Gs (arbitrarily chosen as a worst case during takeoff/climb/cruise with some unexpected turbulence) at 1850....but I strongly suspect the higher weight/lower G combination would represent less airframe stress.

I'm probably overthinking this but the aircraft ID placard is about to go to the engravers so it's decision time. Just trying to avoid getting dinged on a ramp check for a bit of extra weight on the rare occasion we'll be full of fuel and heavily packed. I suspect most 8s with an angle valve 360 and Hartzell CS prop have less than the otherwise available 125 pounds of baggage when they're full of fuel. I'm sure there would be less issues with the insurance company too if there was a mishap at slightly over 1800 if the registered gross was 1850.

First, just make it Normal Category above 1800 and below your chosen max gross...that's -1.5 to +3.8. Utility between 1600 and 1800, Aerobatic below that. Simple.

Second...what's the ID placard got to do with it? You only need 3 things on that...Builder, Serial Number and Model. Anything else is not required, so why put it on there?

[RV7A Flyer]

Originally Posted by tgmillso

If you had a "mishap" I'm sure it wouldn't take much digging by the insurance investigators, given that you list your full name and aircraft N number in your signature, to discover this forum thread:

"Chris Engler, Greene, NY
RV 8 Under Construction (N184CE Reserved), Showplanes Fastback, Superior IO 400; Dual 10.4 HXr
Kitfox 7; Rotax 914, Built and Sold

I know insurance brokers frequent this forum and they're probably reading this post right now. They would find that your weight increase engineering was "crowd sourced" and occured after you completed the aircraft without any structural modification, as you state your are about to get your data plate etched. I'm sure they would have a field day with this, especially given that an experienced Van's engineer has publicly warned against such a move. Depending on what the future failure mode was, the insurance investigator would have a grand time arguing that the incident (remember Murphy's Law) was as a result of the increased stall speed and subsequent lengthened landing roll, prop strike from the increased gear loading or fatigue failure from continuously operating at 1850lb or 1875lb (even though you won't be, but that's not going to stop their lawyer from arguing it). Don't get me wrong, I'm all for analysing and applying modifications that improve the safety, maintainability, performance etc. of the aircraft during the build, with solid engineering analysis behind it, as this is the basic theme of the Experimental category. On the other hand, performing pencil whipping exercises after the fact is what makes us the butt of certified industry jokes and gives us all a bad reputation (see link below):
https://www.youtube.com/watch?v=0M4pTuVdq0w
I do appreciate your openness however, and the fact that you obviously take this seriously enough to bring it to the attention of the RV community before you execute your decision.
Regards,
Tom.
RV-7, complete apart from avionics.
Aerospace Engineer.

I'll bet a decent lawyer could argue that by writing the policy, they accepted the values that are listed on the Ops Limits, whether they ever asked for a copy or not (and if they didn't, the negligence would be on their side for not doing so in the first place). This *is* "experimental" aviation, after all.

And if they were provided with a copy of the Ops Limits, then I'd say they're on the hook for it.

[RV7A Flyer]

Originally Posted by StressedOut

You should probably double check this statement. I believe Vne is defined in IAS, not TAS (source).

Nope. The original statement is correct...Vne is TAS, and many EFISes will now display redline as a function of TAS (computed using altitude, temp, etc.).

It's shown as a red line on an old-fashioned ASI because that's all they could do, what with no way to calculate TAS for you, and IIRC, manufacturers set Vne as a function of Vd at a low enough value to avoid flutter. Something like that.

[tgmillso]

Originally Posted by RV7A Flyer

I'll bet a decent lawyer could argue that by writing the policy, they accepted the values that are listed on the Ops Limits, whether they ever asked for a copy or not (and if they didn't, the negligence would be on their side for not doing so in the first place). This *is* "experimental" aviation, after all.

And if they were provided with a copy of the Ops Limits, then I'd say they're on the hook for it.

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.

[SuperCubDriver]

I incresed the max weight of my RV-7 to 1854 lbs and will do so on my -8. However with the increased weight the airplanes are in normal category with a max g-load of 3.8. These limitations went into the AFM so my planes are "certified" in all three categories - aerobatic, utility and normal.

I had the same idea - higher legal useful load for the occasional trip with pax, full fuel and baggage. After one hour flight I?m back in the utility envelope.

[Mel]

Originally Posted by Chris Engler

Thanks for the thoughts/info. With regards to the FAA/DAR item, it's my understanding that establishing gross weight is the decision of the builder of record (see italicized text below from an EAA article) and gross weight can be established at any number they choose....the FAA/DAR have no jurisdiction on this.

The FAA/DAR can deny airworthiness certificate for any reason they consider unsafe. If you have increased the gross weight from that established by the designer, the inspector may require engineering data to justify the weight increase.