What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Increase in Registered Gross Weight?

Chris Engler

Active Member
Down to the final paperwork on the -8 build and wondering about increasing gross weight to 1850 or even 1875 rather than the Vans number of 1800. The airplane is on the heavier side with the Superior 400, constant speed prop, two 10.4 inch screens, full leather, auto-pilot, fastback conversion, etc. tipping the scales yesterday at 1150. I built with the intent of comfortable fast cross country so consistent with the mission and the higher weight fully anticipated. My question is what weight to register for gross? I could stick with the 1800 and the only time there would be a potential issue is with the wife on board and the airplane full of fuel and packed to the gills with baggage. Together we're 360 pounds and full fuel is 250 so that leaves 40 pounds for baggage....reasonable unless we pack heavy. If I register at 1150 that leaves more room for "legal" baggage and the airplane will be back to 1800 pounds less than an hour into a trip as the fuel burns down. The heavily loaded with 2 on board scenario would likely be less than 10% of the missions so not critical either way but thought I'd reach out for the collective wisdom of the group.

Thanks!
 
Discuss with your DAR or FSDO inspector, they'll be the ones you have to convince.
 
You can play some games with gross weight and probably get away with it, but there are things like the landing gear that you'll need to think about.

However, if you decide to take liberties with aft c.g. limits, you're applying for a Darwin award. Don't do that.

Ed
 
Vans position on this is pretty well established:

https://www.facebook.com/notes/vans...sterpiece-by-dick-vangrunsven/237594966250883

Yes, there is a margin between the design and ultimate strengths. But that margin belongs to the engineer. He owns the margin. It is his insurance against the things he doesn?t know or can?t plan for, and the pilot?s insurance against human error, material variations, and the ravages of time. Wise pilots respect this design safety philosophy and leave this insurance policy in effect by operating strictly within established limits. They don?t try to steal the margin from the designers.
 
I suggest you do weight and balance calculations for all loading scenarios to prove balance limits are not exceeded prior to seeing the DAR. If that is too much/difficult, stay within Van?s weight limits.

Bevan.
 
In my official capacity as an EAA Technical Counselor, I am obligated to advise you to stick with the maximum gross weights specified by the kit manufacturer.

I suggest you deviate from those values only if you can rationally justify an increase with either a comprehensive engineering assessment or practical static test results that show adequate margin throughout the entire primary structure.

Further, I'd be a bit worried that the increased gross weight might possibly increase your legal exposure if you ever sell the airplane. Few if any suits against amateur builders have prevailed in court, but disregard for established limits couldn't possibly help.

--Bob K.
 
Gross weight

Years ago when I would fly in Alaska, there was
A FAR that said it was legal to take off up to 10%
Over gross weight. But only in the state.
So realistically just don?t ?yank and bank?
when your you heavy you should be fine.
So with all the ?experts? out there look up
the FARs and
See if the ?Alaska? exemption is still on the books?
 
Years ago when I would fly in Alaska, there was
A FAR that said it was legal to take off up to 10%
Over gross weight. But only in the state.
So realistically just don?t ?yank and bank?
when your you heavy you should be fine.
So with all the ?experts? out there look up
the FARs and
See if the ?Alaska? exemption is still on the books?

But if it has little to no effect on aircraft performance, it should make us wonder why it isn't allowed in all 50 states?

I bet there is a very good reason.
 
Years ago when I would fly in Alaska, there was A FAR that said it was legal to take off up to 10% Over gross weight....

It's actually 15%, and appears to be still in effect:

Title 14 Chapter I Subchapter F Part 91 Subpart D §91.323

The operative parts of this rule are that it only applies to Part 121, Part 135, or official Alaska State activities--not operations particularly conducive to yanking and banking. It appears to allow the increase so long as the original climb performance is not impeded, and if the airplane will still support a reasonable load factor somewhere around 3.8g.

My guess is that this rule is intended to recognize that Alaska operations generally take place in cold, dry air that is conducive to greater climb rates than prevail in the lower 48 (though conditions on Five-Oh are particularly conducive to good glider climb rates this week).

Edit add: Some interesting discussion here: http://forums.outdoorsdirectory.com...a-gross-weight-increase-quot-are-not-the-same
 
Last edited:
If I register at 1150 that leaves more room for "legal" baggage and the airplane will be back to 1800 pounds less than an hour into a trip as the fuel burns down.

Gross weight on your airworthiness certificate should be 100% based on safety and 0% based on legality when flying.
 
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.
 
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.
 
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.
 
Last edited:
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?
 
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.
 
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. :)
 
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.
 
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.
 
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.
 
Last edited:
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.

How many have you denied because of this?
 
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?

The above is what I did as well but years after the initial airworthiness was issued. For simplicity sake I would suggest you initially certify the aircraft at the recommended 1800 then go back later into phase one and and increase the GW.

Oshkosh is my "heavy" trip and I wanted to keep it "legal" for that once a year excursion where I could exceed the 1800 for a bit.
 
Yep!!! I Agree.

For simplicity sake I would suggest you initially certify the aircraft at the recommended 1800 then go back later into phase one and and increase the GW.

This makes it simpler for everyone.
 
Given how quickly discussions of accidents are shut down, at least partly due to liability concerns, i'm amazed threads about increasing gross weight aren't shut down just as fast. The liability issue has to be just as strong in these.
 
Anybody know of any RV accidents that the probable cause was operating above gross weight?
 
Increased gross in my RV7A

Not advocating one way or the other...
I wrote up my RV7A (2009 inspection year) with a gross weight of 2000 pounds in normal category (knowingly not consistent with Van's specs), 1800 (factory recommended gross weight) for utility category, and 1600 (factory recommended gross weight for aerobatic category). The inspector (a long-time FAA-designated DAR in multiple categories from experimental Amateur Built to Jets) had no issue with that when we specifically discussed it. The airplane was successfully inspected and letter issued that day.
 
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.

It pays to remember (in all sorts of contexts) that having the right/ability to make a choice doesn't render any choice one makes safe, sane, or intellectually defensible. To say nothing of judgement-proof after the fact.

Better by far to stick with the kit manufacturer's numbers. If one really can't fit one's flying requirements within those figures, even if only occasionally, then the airplane in question is simply not right for the mission.
 
One problem with raising the gross weight is that the landing gear may no longer be strong enough. It's based on how much weight is on it, not on whether the plane is being flown at a reduced load factor. And without a series of drop tests, you won't know.

Another is whether the forward and aft CG limits are still realistic. This can only be determined by flight test.

Still another is determining the take off and climb and landing distances and speeds - and lets not forget the other speeds, which are affected by the weight.

Dave
 
I changed my Ops limits to give me 100 more weight for takeoff weight but my landing weight stayed the same. Max weight for GA airplanes is usually predicated upon landing and not takeoff.
 
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?
 
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.
 
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.
 
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.
 
Vne

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
 
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").
 
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%.
 
. . . . . . . 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! ;)
 
Hmm - well then I guess I am in big trouble already when I fly my airplane solo under Vans gross weight! ;)
:D Just an example, to get people to think in greater detail about the practical effect of an increase. Not saying those numbers are exact. :D
 
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
 
Back
Top