How to find the real gross weight a plane can carry?

Talk about airplanes! At last count, there are 39 (and growing) FAA certificated S-LSA (special light sport aircraft). These are factory-built ready to fly airplanes. If you can't afford a factory-built LSA, consider buying an E-LSA kit (experimental LSA - up to 99% complete).

Moderator: drseti

User avatar
Half Fast
Posts: 261
Joined: Fri May 06, 2016 7:27 pm
Location: Central Florida

Re: How to find the real gross weight a plane can carry?

Postby Half Fast » Mon Feb 19, 2018 11:55 am

FastEddieB wrote:I kinda side with Tim here.

If someone told me my Sky Arrow was actually safe up to 1,450 lbs, how would it affect my operations?

It wouldn’t. Not one little bit.

So what difference would it make? And why even waste time on pointless hypotheticals?



Obviously it wouldn't effect your operations.

BUT, if you were plane-less and in the market for an LSA, it might be a consideration in comparing the safety and longevity of one plane over another. It provides a cursory insight into the robustness of the design and construction.

(OTOH - don't know how this works. Your plane is experimental and you can now fly as a PP under Basic Med; could you certify your Arrow to a higher weight and take it out of the LSA category?)
1/2
----------------
I dream of a world where chickens can cross roads without having their motives questioned.

User avatar
FastEddieB
Posts: 2487
Joined: Wed Jan 07, 2009 9:33 pm
Location: Mineral Bluff, GA

Re: How to find the real gross weight a plane can carry?

Postby FastEddieB » Mon Feb 19, 2018 12:01 pm

I think we are all shaped by our life experiences.

I’ve learned to do my best to do things “by the book”. It’s often The Most Conservative Action, so there’s that.

But also, it seems that whenever I’ve tried to get away with something that everyone else is getting away with, I’d get caught and made an example of.

So I envision making the choice to not worry about “a few pounds over” gross weight. And then having some sort of incident, even unrelated to the over gross condition. My luck, an FAA team would be right there with scales, and my four decade run of no violations would be toast.

But I suppose on some academic level it’s comforting to know one’s plane is “overbuilt”, even if it makes no practical difference.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
FastEddieB@mac.com

User avatar
FastEddieB
Posts: 2487
Joined: Wed Jan 07, 2009 9:33 pm
Location: Mineral Bluff, GA

Re: How to find the real gross weight a plane can carry?

Postby FastEddieB » Mon Feb 19, 2018 12:08 pm

Half Fast wrote:

(OTOH - don't know how this works. Your plane is experimental and you can now fly as a PP under Basic Med; could you certify your Arrow to a higher weight and take it out of the LSA category?)


Nope. No modifications allowed that would take it out of Light Sport limitations.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
FastEddieB@mac.com

TimTaylor
Posts: 970
Joined: Tue Feb 21, 2017 7:17 pm

Re: How to find the real gross weight a plane can carry?

Postby TimTaylor » Mon Feb 19, 2018 12:31 pm

3Dreaming wrote:
WDD wrote:So.......

Back to my original question.

How much safety margin is there on LSA planes beyond the 1320 lbs? Do LSA's regularly have performance to spare well above 1320 lbs?

And no this thread isn't on how to overload an LSA beyond 1320 lbs.


You should not look at safety margin in terms of operating beyond 1320, since in fact that is the limit. There are factors that go far beyond the weight an airplane can take off and climb with. You also need to be able to withstand normal flight loads. On a airplane like a LSA an increase of 200 pounds will reduce your safety factor by about 15%. That is certainly something to think about when considering loading beyond the 1320 pound limit.

Who's considering loading beyond the 1320 pound limit? Thanks for making my point. And you have just sent a message that maybe it is OK to consider loading an LSA beyond 1320 pounds. You are setting a bad example especially for your students.
Commercial Pilot Airplane Single & Multiengine Land; Instrument Airplane; Sport Endorsement Airplane Single Engine Sea; Flight Instructor Airplane Single And Multiengine; Ground Instructor Advanced Instrument

User avatar
WDD
Posts: 116
Joined: Sun Dec 10, 2017 2:39 pm
Location: Louisville, KY

Re: How to find the real gross weight a plane can carry?

Postby WDD » Mon Feb 19, 2018 12:38 pm

My thinking is that if a plane is built to safely operate at 1600 pounds, but the only reason it is limited to 1320 is to make it comply with LSA rules, it is going to be more robust and have more reserve performance on tap when one keeps it at the 1320 max. (Sling 2 comes to mind)

On the other hand, if it can only truly handle 1320 pounds or so, its not going to have a lot of reserve performance - if any. You'd probably feel less comfortable taking it to 1320lbs than say the Sling 2.

The Sling 2 thus might be more attractive for that reason.

Not a question of complying with rules or overloading an airplane. A question of which plane might have more reserve performance - and thus be safer and more robust.

User avatar
Half Fast
Posts: 261
Joined: Fri May 06, 2016 7:27 pm
Location: Central Florida

Re: How to find the real gross weight a plane can carry?

Postby Half Fast » Mon Feb 19, 2018 12:56 pm

FastEddieB wrote:I’ve learned to do my best to do things “by the book”. It’s often The Most Conservative Action, so there’s that.




Wouldn't "most conservative action" mean to purchase a plane that is structurally sound for a weight greater than that for which it is certified?
1/2
----------------
I dream of a world where chickens can cross roads without having their motives questioned.

3Dreaming
Posts: 2388
Joined: Sun Jan 10, 2010 6:13 pm
Location: noble, IL USA

Re: How to find the real gross weight a plane can carry?

Postby 3Dreaming » Mon Feb 19, 2018 12:57 pm

TimTaylor wrote:
3Dreaming wrote:
WDD wrote:So.......

Back to my original question.

How much safety margin is there on LSA planes beyond the 1320 lbs? Do LSA's regularly have performance to spare well above 1320 lbs?

And no this thread isn't on how to overload an LSA beyond 1320 lbs.


You should not look at safety margin in terms of operating beyond 1320, since in fact that is the limit. There are factors that go far beyond the weight an airplane can take off and climb with. You also need to be able to withstand normal flight loads. On a airplane like a LSA an increase of 200 pounds will reduce your safety factor by about 15%. That is certainly something to think about when considering loading beyond the 1320 pound limit.

Who's considering loading beyond the 1320 pound limit? Thanks for making my point. And you have just sent a message that maybe it is OK to consider loading an LSA beyond 1320 pounds. You are setting a bad example especially for your students.


From the statement above no one is considering loading beyond the 1320 pound limit. It in no way makes your point. At most he is asking the wrong question to get the answer he is looking for. Asking about increased safety margins does not indicate intent to overload the airplane.

Now I would like you to explain how my saying loading an airplane beyond the limits reduces the safety margin is an indication that I am advocating that it is OK to exceed the gross weight limit. Considering the reduced safety margin if you are thinking about overloading the airplane should be seen as a deterrent, and not as a factor in thinking that it might be OK to overload.

TimTaylor
Posts: 970
Joined: Tue Feb 21, 2017 7:17 pm

Re: How to find the real gross weight a plane can carry?

Postby TimTaylor » Mon Feb 19, 2018 1:04 pm

I believe our response should be, "never consider loading your LSA beyond the certified weight of 1320 pounds."
Commercial Pilot Airplane Single & Multiengine Land; Instrument Airplane; Sport Endorsement Airplane Single Engine Sea; Flight Instructor Airplane Single And Multiengine; Ground Instructor Advanced Instrument

chicagorandy
Posts: 122
Joined: Fri Sep 08, 2017 2:39 pm

Re: How to find the real gross weight a plane can carry?

Postby chicagorandy » Mon Feb 19, 2018 1:10 pm

I'm a total rookie with exactly one flight in an Evektor under my belt, and 1 Xmas present of a 172 one hour flight experience yet to cash in when the weather is nicer.

That said, knowing that my current cruiser motorcycle is able to hit near 100 on a super slab IS comforting when I'm going the speed limit of 65-70 and want to pass a truck. Much less when I had the Ural and the rig was pegged at about 55-60mph on the slabs with no ponies left in the stable.

I would suspect that flying at 1300lbs gross weight in an airframe 'designed and capable' at 1800lbs gross is more 'comforting' than flying that same gross in an airframe 'designed and capable' at only that 1300lbs max weight? I acknowledge that flying an 1800# rated plane at 1800# again removes that 'comfort zone'.

As someone with a body frame build for traction, not for speed - lol - I would have no problem with LSA's being rated for 1500#, in fact it might mean I could fly with full fuel?

TimTaylor
Posts: 970
Joined: Tue Feb 21, 2017 7:17 pm

Re: How to find the real gross weight a plane can carry?

Postby TimTaylor » Mon Feb 19, 2018 1:13 pm

I don't know anyone who wouldn't like to see the definition of LSA be changed from 1320 pounds to 1500 or 1600 pounds. However, it is 1320 pounds and that is the limit, period.
Commercial Pilot Airplane Single & Multiengine Land; Instrument Airplane; Sport Endorsement Airplane Single Engine Sea; Flight Instructor Airplane Single And Multiengine; Ground Instructor Advanced Instrument

3Dreaming
Posts: 2388
Joined: Sun Jan 10, 2010 6:13 pm
Location: noble, IL USA

Re: How to find the real gross weight a plane can carry?

Postby 3Dreaming » Mon Feb 19, 2018 1:19 pm

TimTaylor wrote:I believe our response should be, "never consider loading your LSA beyond the certified weight of 1320 pounds."


The reality is people do consider it. My point was if you are considering it, the reduced safety factor should disuade you. It is one risk factor that is easily mitigated.

User avatar
WDD
Posts: 116
Joined: Sun Dec 10, 2017 2:39 pm
Location: Louisville, KY

Re: How to find the real gross weight a plane can carry?

Postby WDD » Mon Feb 19, 2018 1:26 pm

ChicagoRandy - Exactly! I ride a fz1, a liter bike. It can drag your knee and go over 100 in a heart beat. I ride it by my rules - like an grandmother. My choice - don’t drag knees, stick to speed linits / traffic flow. “Preflight” the bike before each ride, always wear all gear, etc

Yet I know if something unexpected happens I can scoot out of problem. I have a lot of traction on reserve.

And I know that my bike will last forever, vs if I was flogging a ninja 300.

User avatar
drseti
Posts: 5853
Joined: Sat Nov 28, 2009 6:42 pm
Location: Lock Haven PA
Contact:

Re: How to find the real gross weight a plane can carry?

Postby drseti » Mon Feb 19, 2018 4:28 pm

3Dreaming wrote: On a airplane like a LSA an increase of 200 pounds will reduce your safety factor by about 15%.


Actually (and you know this, Tom; this response is for the benefit of others), that's only part of the story. Yes, a 15% increase in weight will reduce safety factor, but by far more than 15%. Here's why:

What leads to fatalities in aircraft accidents is the kinetic energy which must be dissipated while decelerating. Some of that energy (we can debate the percentage, but clearly some of it) gets absorbed by the occupants, leading to traumatic
injury. And KE = 1/2 m v^2.

So, increasing m by 15% starts by increasing energy 15%. That's Strike One. (Stick around; the other strikes are related to velocity).

What velocity do planes crash at? In LSAs, most accidents occur during takeoff and landing, so they occur at or near stall speed. This is one of the reasons for the safety-motivated 45 kt LSA stall speed limit. And stall speed varies with load factor, which in turn is a function of mass. So, when weight went up 15%, stall speed also went up 15%, compounding the Kinetic Energy problem. That's Strike Two.

But wait, there's more. KE = 1/2 m v squared. So Strike Three happens because that 15% safety degradation happening from the v factor occurs twice.

The total increase in KE becomes (1.15)x (1.15) x (1.15) = 1.52. That's a 52% total increase in KE, resulting in a 52% decrease in the margin of safety for occupants in a takeoff or landing LSA accident.

Think about that when someone tells you the LSA rules are arbitrary.

Corollary: all else being equal, a plane flown 15% below it's safe design weight will thus have a 52% greater safety margin in a takeoff or landing accident.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

RTK
Posts: 94
Joined: Sat Mar 14, 2015 10:43 pm

Re: How to find the real gross weight a plane can carry?

Postby RTK » Mon Feb 19, 2018 4:54 pm

To the OP, I think you can call Vans and ask what weight they tested the spar to, or even the structure. While that does not answer your question of how much an aircraft can fly over FAA mandated max gross weight for an LSA, it should help provide some confidence that the design may have been tested to sufficiently robust strength.

We have all heard of people flying LSA over gross. I don’t condone it, and I’m sure this happens by accident frequently (guestimated weight of passenger or baggage), but in my opinion, you suddenly become a test pilot above 1,320 pounds.

In my aircraft and my weight, I have to be cautious not to exceed gross weight if carrying a passenger. But I’d rather err on the side of caution and remain under 1,320 than risk even a little above. I have a family and I do all that I can to help assure that I can come home to them after each flight.

I too ride (rode?) a motorcycle. I had a liter bike as well - Ducati ST3 that I sold and went small thinking that it would be “safer.” I currently have a 250cc Adventure Bike that is for sale. Why? Smaller doesn’t change safety in any way, and I deluded myself into thinking that it might. (And hence why my bike is for sale). Flying a LSA offers better safety margins, but the inherent dangers remain the same. As stated above, I would do all that I could to remain complaint with the 1,320 rule to stack the odds in favor of a safe return.

User avatar
FastEddieB
Posts: 2487
Joined: Wed Jan 07, 2009 9:33 pm
Location: Mineral Bluff, GA

Re: How to find the real gross weight a plane can carry?

Postby FastEddieB » Mon Feb 19, 2018 5:28 pm

WDD wrote:On the other hand, if it can only truly handle 1320 pounds or so, its not going to have a lot of reserve performance - if any.


You and most others here probably are aware of this, but the word "performance" here can be misleading.

I've heard time and time again that a plane limited to 3,200 lbs, let's say, has "performed" just fine up to 3,500 lbs, with excellent rate of climb even at the higher weight. I honestly think that many think that engine output and rate of climb are what establish maximum weight. It may be a factor, but weight limits are more often the result of loads on the structure at higher weights, regardless of horsepower reserves. I guess "performance" can include the ability of the structure to handle loads, but again, I don't think thats the way its normally used.
Last edited by FastEddieB on Mon Feb 19, 2018 6:15 pm, edited 1 time in total.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
FastEddieB@mac.com


Return to “Light Sport Aircraft”

Who is online

Users browsing this forum: No registered users and 3 guests