What's new
Van's Air Force

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

RV-12 Max Gross Weight

L

lawspud

Active Member
A question for you aeronautical engineer types: What determines the maximum gross weight of an airframe?

I understand that Van's has rated the RV-12 airframe and powerplant at 1320# max gross weight, which is (not coincidentally I'm sure) the limit for LSA craft. How arbitrary is this number? For example, if Van designed a plane which met all of the LSA requirements but could support a takeoff weight of 1500#, wouldn't he just arbitrarily limit the max gross weight to 1320# to meet the specs? That might make more sense than de-engineering the craft to reduce its capabilities.

So, if a builder were to go the E-AB certification route, is it possible to have a higher max gross weight for his RV-12? How would that be calculated?
 
lawspud said:
I understand that Van's has rated the RV-12 airframe and powerplant at 1320# max gross weight
Click to expand...

Why bother to over-design? Why not take that 1320 lbs as a starting point and desing everything according to that? Especially when we know that extra weight will hardly ever make it fly better.

So, if a builder were to go the E-AB certification route, is it possible to have a higher max gross weight for his RV-12? How would that be calculated?
Click to expand...
Just make proper simulation model and let it do the calculation or probably easier way for most of us: test it as Van's has done. If they designed it for 1320 lbs and not for 1500 lbs you may notice that your plane won't handle it without permanent changes to construction -- they you got to get new parts and build new.

If you wish to have a bigger MTOW, why not just build an another RV? :confused:
 
It's not so much that I want a larger gross weight. I am more curious as to the actual capabilities of the plane. Is it limited to 1320# because Van designed it around that limit, or because it would no longer be an LSA if it exceeded that limit? I doubt that Van's would ever admit to the latter, even if it were true.
 
Pirkka said:
Why bother to over-design? Why not take that 1320 lbs as a starting point and desing everything according to that? Especially when we know that extra weight will hardly ever make it fly better.
Click to expand...

Actually several other kits are being sold as LSA even though they are also available for higher MTOW (Kitfox and Arion Lightning come to mind - even Rans S19 allegedly was designed for a MTOW of over 1320 lbs but isn't advertised that way). So the question isn't unreasonable.

Pirkka said:
If you wish to have a bigger MTOW, why not just build an another RV? :confused:
Click to expand...

None of the other RV's are allegedly as fast to build as the RV-12. So it has that advantage over other RVs.
 
Structure and Performance

The 1320# is an LSA regulation - so no engineering involved in that decision :eek:
The two basic things that define max weight are structure and performance. The structure has to handle the weight at the load factors desired (aerobatic, normal, utility).
Then you need to meet the stall speed and climb requirements.
Like all designs the end result is a compromise.
When the weight is defined, as it is for LSA's, then the design work is to make the lightest structure to handle the load, and size the wing/tail to get the required performance, typically stall sizes the wing.

So if you decide to certify any E-AB aircraft at a higher gross weight than recommended, those are the primary areas to consider.
 
lawspud said:
A question for you aeronautical engineer types: What determines the maximum gross weight of an airframe?

I understand that Van's has rated the RV-12 airframe and powerplant at 1320# max gross weight, which is (not coincidentally I'm sure) the limit for LSA craft. How arbitrary is this number? For example, if Van designed a plane which met all of the LSA requirements but could support a takeoff weight of 1500#, wouldn't he just arbitrarily limit the max gross weight to 1320# to meet the specs? That might make more sense than de-engineering the craft to reduce its capabilities.

So, if a builder were to go the E-AB certification route, is it possible to have a higher max gross weight for his RV-12? How would that be calculated?
Click to expand...

Jeff,

Your question stimulates a follow up. Why would anyone want to build this slow putz of an airplane and license it as E-AB? Any of Van's other models would make much more sense.

The only reason this machine came into being is LSA. If it is flown at a higher gross weight, it will be a dog of all dogs.
 
David-aviator said:
Why would anyone want to build this slow putz of an airplane and license it as E-AB? Any of Van's other models would make much more sense.
Click to expand...

Because it frees the builder to do whatever he or she wants (no need to follow the ridiculous E-LSA requirements of building the panel identical to the factory model, etc) and still fly it with a sport pilot ticket, so long as the plane still fits the LSA performance and specification requirements. There's really NO advantage whatsoever in licensing as an E-LSA except for the fact that it can be completed to a larger degree by the factory (no 51% rule). Yeah, it remains to be seen if the -12 kit is E-AB compatible, but I think Van is missing the ball if he doesn't release an E-AB capable kit. After building my airplane, I don't think I would ever enjoy the tedious copycat nature of E-LSA.
 
Dog of all dogs, I don't think so.

David-aviator said:
Jeff,

Your question stimulates a follow up. Why would anyone want to build this slow putz of an airplane and license it as E-AB? Any of Van's other models would make much more sense.

The only reason this machine came into being is LSA. If it is flown at a higher gross weight, it will be a dog of all dogs.
Click to expand...


I totally disagree with the last statement. This plane is a good performer. It is light on the controls and very responsive. It is a delight to fly. I know, because I have flown one. When flying steep turns, the plane was anything but a dog. That made the plane feel like it was twice the normal weight, but it was still very agile to control inputs. I asked Van if the plane was going to be a utility category plane and he said no, so it will be a normal category as far as load factors are concerned. That is no big deal. I learned to fly in an Aeronca 7AC and did all sorts of aerobatics in it. You just have to be very careful not to exceed the load limit or VNE speeed. I had a good instructor who taught me how to do that.

One thing to consider is that if you certify your 12 with a gross weight higher than 1320 pounds, you can never sell the plane as a light sport plane and sport pilots will not be able to fly it legally. That may reduce the resale value.
 
IMHO... Value and Liability...?

Jamie said:
Snip... There's really NO advantage whatsoever in licensing as an E-LSA except for the fact that it can be completed to a larger degree by the factory (no 51% rule).
Click to expand...

I haven't decided which way I will go (E-LSA vs. E-AB)... but am leaning towards E-LSA for several reasons. By building it as an E-LSA... subsequent buyers can obtain a certificate to repair/inspect it. I think that, coupled with a buyer knowing it is built to spec may increase it's value. Another reason is that it is my belief that there may be a bit less liability if you can show that it is built to spec. Those reasons are important, as I am building this as a "first-time" kit that I plan to fly for a few years while I build something more extensive. Then I will sell it to fund the second craft. So resale value and the potential for reducing liability both interest me. The last reason is build time... and completeness of kit and instruction. Just following the instructions and not having to invent/create solutions will speed up the build... especially in the FWF/Panel areas. I hope to have it flying within 18 to 24 months after starting this summer.

As to Gross Weight (which is what the thread was started about)... I don't know the process for a builder to certify it higher. I am sure that Van's could test it and establish a higher gross if they wanted... but with the pretty decent available load now... I doubt they would want to. Issues of degrading the flying speed and responsiveness have been mentioned previous.

Interestingly, Randy at RAN'S did tell me they are planning on providing a higher gross for the S-19 for E-AB builders. However, it is a heavier craft to start with... so it needs it. I am guessing it would probably only minimally exceed the RV-12's available load.

JMHO - DJ
 
David-aviator said:
Jeff,

Your question stimulates a follow up. Why would anyone want to build this slow putz of an airplane and license it as E-AB? Any of Van's other models would make much more sense.

The only reason this machine came into being is LSA. If it is flown at a higher gross weight, it will be a dog of all dogs.
Click to expand...

David,

A fair question. I'm sure that everybody choosing this kit over the other models will have their own reason or reasons. I am a very low time pilot, and the RV-12 (apparent) flight characteristics appeal to me much more than a -7 or -8. The build time and difficulty is significantly lower than a -9, which is a huge advantage to me. With 2 infant children, a commute, and a busy work schedule, the extra ~1000hrs of build time for a -9 simply isn't worth it for me. And, realistically, the -12 fits my needs better than the others. Would I like to get "there" faster? Sure. Would I like more range? Sure. But when I'm likely to spend most of my flight time in daytime VFR within spitting distance of L12, why build anything else? Once I get the RV-12 in the air, if I still feel motivated I will start on a -10. By the time the -10 is done, I'll hopefully be confident and experienced enough to take my whole family around the country without undue concern.

As for licensing it as an E-AB, I can think of a couple of reasons some builders might want to follow that course. Perhaps some would want to monkey with the controls or airframe. Maybe an alternative powerplant is used instead of the Rotax. Sure, current rules allow deviation from the S-LSA prototype AFTER receiving E-LSA certification, but what if the rules change?

Or, perhaps more importantly, what if you make a change that results in a faster top speed (or stall speed, or whatever), in excess of the LSA rules. Based on my understanding, once an LSA falls out of compliance, it is no longer an LSA. So if your certification is in E-LSA but your plane is no longer an LSA plane, what happens to your cert?
 
Phyrcooler said:
As to Gross Weight (which is what the thread was started about)... I don't know the process for a builder to certify it higher. I am sure that Van's could test it and establish a higher gross if they wanted... but with the pretty decent available load now... I doubt they would want to. Issues of degrading the flying speed and responsiveness have been mentioned previous.
Click to expand...

For better or worse, E-AB builders can establish the gross weight at pretty much whatever they want (within reason, of course). You simply put your number on the form. :)
 
lawspud said:
David,

A fair question. I'm sure that everybody choosing this kit over the other models will have their own reason or reasons. I am a very low time pilot, and the RV-12 (apparent) flight characteristics appeal to me much more than a -7 or -8. The build time and difficulty is significantly lower than a -9, which is a huge advantage to me. With 2 infant children, a commute, and a busy work schedule, the extra ~1000hrs of build time for a -9 simply isn't worth it for me. And, realistically, the -12 fits my needs better than the others. Would I like to get "there" faster? Sure. Would I like more range? Sure. But when I'm likely to spend most of my flight time in daytime VFR within spitting distance of L12, why build anything else? Once I get the RV-12 in the air, if I still feel motivated I will start on a -10. By the time the -10 is done, I'll hopefully be confident and experienced enough to take my whole family around the country without undue concern.

As for licensing it as an E-AB, I can think of a couple of reasons some builders might want to follow that course. Perhaps some would want to monkey with the controls or airframe. Maybe an alternative powerplant is used instead of the Rotax. Sure, current rules allow deviation from the S-LSA prototype AFTER receiving E-LSA certification, but what if the rules change?

Or, perhaps more importantly, what if you make a change that results in a faster top speed (or stall speed, or whatever), in excess of the LSA rules. Based on my understanding, once an LSA falls out of compliance, it is no longer an LSA. So if your certification is in E-LSA but your plane is no longer an LSA plane, what happens to your cert?
Click to expand...

Well, from your perspective it makes a lot more sense. I have had a ride in the -9 and found it a delight to fly. The quick built version should go together quickly but maybe not as quick as the -12.

I disagree with Jim Cone that it will be OK at the higher gross weight with regard to performance. I would never load that thing up beyond its design weight for any reason. There's nothing more frustrating than having an under powered airplane on a hot summer day.

(At our age, and I know Jim, we came out of the mold about the same time, going the -12 route is a practical thing to consider. I think about it everyday, about as often as doing the -8) :)
 
Jamie said:
For better or worse, E-AB builders can establish the gross weight at pretty much whatever they want (within reason, of course). You simply put your number on the form. :)
Click to expand...

LOL... well, yes... that I knew could be done. ;) What I meant to say is... what legitimate process of design or testing should be done to establish that number. :)

DJ
 
David-aviator said:
The only reason this machine came into being is LSA. If it is flown at a higher gross weight, it will be a dog of all dogs.
Click to expand...
Eh? How do you figure that?

Let's say you increased the MGTW from 1,320 to 1,420 lb to give you 100 lb more payload. Power loading goes from 13.2 lb/hr to 14.2. This is in the same league as the O-235 powered RV-9 (15), DA40 (14.7), IO-240 powered DA20 and 180Hp 172 (14.2). None of these are speed demons, but I wouldn't call them dogs either.

TODR
 
Structural integrity

Surely Vans has designed the RV-12 down to a structure that will withstand just 4G (6G absolute) at 1320 pounds. That's how the useful load is good. It's not aerobatic, so he has not overdesigned the airframe. So if you artificially specify a higher gross weight you are reducing the G tolerance of the airframe. Not for me thanks, if I have to fly in the mountains.

Cheers...Keith
 
Is it possible that Lawspud is the question to see if it is safe to fly the -12 at a higher GW than the LSA limit.

I suspect a few of the new KitFoxes will be flown above 1320# limit set by the FAA.

Here is a question regarding the 1320# GW limit on LSA's, why that number? Was the FAA trying to match a type of aircraft allowed in other countries?

(I still don't see why Cessnas and many other two seat aircraft are excluded by this regulation.)
 
N941WR said:
...Here is a question regarding the 1320# GW limit on LSA's, why that number? Was the FAA trying to match a type of aircraft allowed in other countries?...
Click to expand...
I don't know the answer to the question but we do like round numbers and this is one (600 kilograms).
 
What are you thinking?

Guys, guys, guys.......

Have you seen the VANS releases on how they tested the RV-12 airframe? It was done in a thoroughly professional manner within the current regulations which means that with a high degree of confidence, it will withstand foreseeable conditions and use without falling apart.

Going above that weight has nothing to do with performance - it is about SAFETY. The structural integrity of the aircraft cannot be guaranteed above that weight. OK, go ahead and convince yourself that you will only ever fly in smooth air, never use more than 60 deg of bank, never get caught in a downdraft, or turbulence or have to avoid a late-spotted aircraft .........

The US experimental category allows the builder to declare the aircraft at whatever weight he desires. Fine, provided you justify that with appropriate analysis and testing. VANS do this and give you a weight. Why does everybody then want to arbitrarily increase that weight on the basis that "it'll be OK"?

What are you thinking?....... :confused:
 
paul330 said:
Guys, guys, guys.......

Have you seen the VANS releases on how they tested the RV-12 airframe? It was done in a thoroughly professional manner within the current regulations which means that with a high degree of confidence, it will withstand foreseeable conditions and use without falling apart.

Going above that weight has nothing to do with performance - it is about SAFETY. The structural integrity of the aircraft cannot be guaranteed above that weight. OK, go ahead and convince yourself that you will only ever fly in smooth air, never use more than 60 deg of bank, never get caught in a downdraft, or turbulence or have to avoid a late-spotted aircraft .........

The US experimental category allows the builder to declare the aircraft at whatever weight he desires. Fine, provided you justify that with appropriate analysis and testing. VANS do this and give you a weight. Why does everybody then want to arbitrarily increase that weight on the basis that "it'll be OK"?

What are you thinking?....... :confused:
Click to expand...

Easy there. Since the only example of this craft is currently under the control of Van's, I think it is safe to assume that no-one has done any un-approved loading of an RV-12 yet. It is an honest and, I think, legitimate question.

Since Van designed this plane to meet the LSA specs, it may actually be true that it was engineered around the 1320# max gross limit. But, if it wasn't, Van's may never be forthcoming about its true capability because they can't afford to lose S-LSA certification on this project. At least, not until the 51% checklist is clarified.

Really, can you blame me (or others) for expressing curiosity? Personally, if I wasn't curious about the plane, what it can do, how it works, and why it works, I'd go out and buy a plane. Instead, I'm educating myself and building. Just because E-LSA is the safest route to go, meaning that mine will likely be a carbon copy of the prototype, doesn't mean I'm done asking questions.
 
lawspud said:
Since Van designed this plane to meet the LSA specs, it may actually be true that it was engineered around the 1320# max gross limit. But, if it wasn't, Van's may never be forthcoming about its true capability because they can't afford to lose S-LSA certification on this project.
Click to expand...

That may be true. In which case, they will then declare the max recommended weight for experimental. However, all their literature suggests they started with the 1320lb limit and designed around it. In any case, I guarantee people will then take it above THAT weight. It's done on all VANS types - I read about it all the time and it horrifies me since I strongly suspect most people don't do any more structural testing. They simply assume that the 1.5x safety margins will keep them safe. Well, those margins are built in to take into account building errors, deterioration with age, pilot mis-handling and other unforeseen circumstances.

I don't want to preach here but if someone was to trim margins on reserve fuel or weather limits, everyone would be shouting "SAFETY" - but arbitrarily increasing max weights seems to be accepted.
 
Quote
Sure, current rules allow deviation from the S-LSA prototype AFTER receiving E-LSA certification, but what if the rules change?

I would like to know where this is stated in the regulations. I have read the regulations and I don't find it. After a change, does the aircraft become an E-AB or would it still be an E-LSA? It was my understanding that any deviations from the kit prototype required written approval from the manufacturer. Am I missing something here?
DeltaHotel
S/N 027
Waiting for wing kit.
 
DeltaHotel said:
Quote
Sure, current rules allow deviation from the S-LSA prototype AFTER receiving E-LSA certification, but what if the rules change?

I would like to know where this is stated in the regulations. I have read the regulations and I don't find it. After a change, does the aircraft become an E-AB or would it still be an E-LSA? It was my understanding that any deviations from the kit prototype required written approval from the manufacturer. Am I missing something here?
DeltaHotel
S/N 027
Waiting for wing kit.
Click to expand...

I can't cite you to the regs. I can only point you to this thread, in which our resident DAR made the statement. Mel seems to be extremely knowledgeable about such things, but I would certainly verify this for myself before I did anything to my E-LSA plane.
 
DeltaHotel said:
Quote
Sure, current rules allow deviation from the S-LSA prototype AFTER receiving E-LSA certification, but what if the rules change?

I would like to know where this is stated in the regulations. I have read the regulations and I don't find it. After a change, does the aircraft become an E-AB or would it still be an E-LSA? It was my understanding that any deviations from the kit prototype required written approval from the manufacturer. Am I missing something here?
DeltaHotel
S/N 027
Waiting for wing kit.
Click to expand...

Mel can chime in here, but I believe that the caveat here is that any change CANNOT make the plane perform outside of LSA parameters. Once lost, LSA status is gone for good (and your plane is a really nice hangar queen). Any change to an ELSA that is made to the plane with regard to the standard equipment lists must be approved by the manufacturer (Van's) in order to retain compliance.

Mel, did I miss anything?

Anthony
 
Newbie_Doo said:
Mel can chime in here, but I believe that the caveat here is that any change CANNOT make the plane perform outside of LSA parameters. Once lost, LSA status is gone for good (and your plane is a really nice hangar queen). Any change to an ELSA that is made to the plane with regard to the standard equipment lists must be approved by the manufacturer (Van's) in order to retain compliance.

Mel, did I miss anything?

Anthony
Click to expand...
Anthony is correct. The actual rule that allows change after certification to an E-LSA can be found in 8130.2F. I can't quote the paragraph right now. I just discussed this with the guys at Ok. City a week or so ago because a guy wants to build a Texas Sport as E-LSA and the kit manufacturer only offers it as amateur-built. I'll have to look it up again.
 
lawspud said:
So, if a builder were to go the E-AB certification route, is it possible to have a higher max gross weight for his RV-12? How would that be calculated?
Click to expand...

I think the accepted algorithm is to start at #1320, do the +4/-2G maneuvers, add 20lbs, repeat. Radio the final weight to the ground crew when the airframe fails so they can post the number up.:)

sorry, it's a legit question, but I couldn't resist...
 
You must log in or register to reply here.
Back
Top