RV-6 strength Verses RV-7

I am curious about the overall strength of the RV6 verses the 7. I have had several builders tell me the 6 is actually a stronger wing. This seems to go against Vans specs and gross weight for each aircraft as well as VNE. It may be the 7 has a higher weight then the 6 because of the additional wingspan however I understand that the wing attach method is very different between the two aircraft. Any comments or thoughts?

George

Stronger than a Bonanza

I don't know about the 7 but when a friend of mine who is a A&P first saw the main spar on my six he couldn't believe how strong it was designed.
He said something to the effect of "Holy @&%#" that thing is built stronger than a Bonanza's spar.
Gave me a real warm fuzzy feeling about my 6.

Some folks hold this belief due to the difference in the wing attach method. The -6 spars carry all the way through across each other. The -7 spars have short stubs that attach to the center section bulkhead (short, but very stout!). It's understandable why folks intuitively think the newer arrangement is not as strong, or not strong enough, but Van's engineering and test data seems to say otherwise.

This topic has been discussed on the forums before. Use the search function and you should find a wealth of information (or at least a wealth of opinions...).

P.S. VNE is limited by flutter margin, not wing strength.

The lower skin of the aft fuselage on the -7 is also more prone to compressive buckling.

www.vansairforce.com/community/showthread.php?t=36763

Oh boy, here we go...the 6 vs 7 wars...bring it on!

Having built both a 6 and a 7, I suppose I should comment. The 6 wing definitely looks stronger, but that is entirely subjective and anecdotal. It really doesn't make any sense that the 7's wing design should be any less than the 6's. As an engineer, I have to think that the structures calculations have been properly done for both so if they are both designed around the same structural limits (+6, -3 g's), then both should be equal.

The 6 has a carry through spar like the 3 and 4 and is thus perhaps a more conventional Vans design--whereas the 7 uses a cantilever design that is a new look for an RV, but the numbers don't lie--assuming they are correct!

sailvi767 said:

I am curious about the overall strength of the RV6 verses the 7. I have had several builders tell me the 6 is actually a stronger wing. This seems to go against Vans specs and gross weight for each aircraft as well as VNE. It may be the 7 has a higher weight then the 6 because of the additional wingspan however I understand that the wing attach method is very different between the two aircraft. Any comments or thoughts?

Click to expand...

My guess is that the -6 wing is over engineered. I seem to recall some testing of a -6 wing panel that went well past the design limit of +9Gs. While comforting, I'd suggest that means there is a potential weight savings to be had at the expense of reducing the strength to that needed to support 9G.

Along with this, didn't the inflight failure of the -8 wing happen just outboard the fuel tanks? That would seem to suggest the weak point isn't the spar/fuse interface, and I would speculate that the structure here is similar enough to the -6 wing to suggest a similar failure mode.

Of course, your milage may vary - batteries not included - void where prohibited - and all of that. I'm just thinking out loud more than anything.

My guess is that the -6 wing is over engineered. I seem to recall some testing of a -6 wing panel that went well past the design limit of +9Gs.

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I've heard that too. 12 G's or so. But then that's just rumor, as I have no actual facts.

L.Adamson --- RV6A

The RV6 is every bit as good as a RV7. The 7 came along to be able to sell the kit without great increases in the price. Van brought the 6 kit into the 21st centery with the RV7. The six is still the most popular (see the numbers) kit ever offered!!!

The seven allowed more people to assemble a kit aircraft. It was the right move for Van's. But in doing so, the value of the SIX dropped. For no reason.

The SIX is the value leader in the used aircraft market. If you want a great aircraft, find a SIX/SIX-A with good paint and interior and upgrade the panel to your needs. There is nothing that the 7 does that the 6 can't do.................

All said, the 7 has 8 wings.............. and the 8 has broken off the wings. The six has never broken a wing as far as I know........

done.

Not too similar...

ChiefPilot said:

.....
Along with this, didn't the inflight failure of the -8 wing happen just outboard the fuel tanks? That would seem to suggest the weak point isn't the spar/fuse interface, and I would speculate that the structure here is similar enough to the -6 wing to suggest a similar failure mode.
.....

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...since the -6 spar is laminated from strips riveted together and the -8 spar has the same general shape, but is machined from solid. Any tool marks and stresses at the end of each "virtual strip" make them quite different.

The -8 wing underwent a minor redesign after the accident - whilst the original complied with requirements, IIRC the meeting of the spar thinning out, aileron/flap junction, tank/LE skin junction and the failure point might not be ideal, and some of these elements were moved apart (?). This became the -1 wing.

With the -1 wing, the aerobatic weight went from 1550 to 1600lbs. Since the RV-7 is in fact a later design than the 8 (?), and has the 1600lb aerobatic limit, I would suggest it's wing is the equivalent of the RV-8 -1 wing i.e. improved over the RV-8 accident wing design. NB the RV-3B also uses an RV-8 type spar / design.

IMHO the "relative strength" between various RVs might make for an interesting debate, but not worth considering in a purchase decision - we don't have the facts, and even if we did, I doubt they are relevant to actual operation of the aicraft

Andy

Yes, for good reason.

ChiefPilot said:

My guess is that the -6 wing is over engineered. I seem to recall some testing of a -6 wing panel that went well past the design limit of +9Gs. .

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I have been told by very good sources that the factory built wing was tested well beyond the limits. However, 6 wings where not built in the factory. There is a lot of potential for builder variance and error in the 6 wing, especially the spar. That is why the specs where "derated".
The machined spar design of the 7 and 8 removes much of the builder variance.

However, 6 wings where not built in the factory. There is a lot of potential for builder variance and error in the 6 wing, especially the spar. That is why the specs where "derated".

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As you say... the early RV-3 wing problems were laid at a good design, but not tolerant of builder error / ommission / variation.

Andy

This comes up so often...

gasman said:

There is nothing that the 7 does that the 6 can't do.................

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From Van's

6 specs
VNE - 210 mph
Gross - 1600 lb
Baggage - 60 lb
Fuel - 38 gal
Designed for up to 180 hp

7 specs
VNE - 230 mph
Gross - 1800 lb
Baggage - 100 lb
Fuel - 42 gal
Designed for up to 200 hp

hecilopter said:

From Van's

6 specs
VNE - 210 mph
Gross - 1600 lb
Baggage - 60 lb
Fuel - 38 gal
Designed for up to 180 hp

7 specs
VNE - 230 mph
Gross - 1800 lb
Baggage - 100 lb
Fuel - 42 gal
Designed for up to 200 hp

Click to expand...

Hecilopter, you just beat me too it. And furthermore...

6 specs
Vno - 180 mph
Va - 134 mph
Aerobatic gross - 1375 lb

7 specs
Vno - 193 mph
Va - 142 mph
Aerobatic gross - 1600 lb

Is it possible that Vans upped the ranges on the 7 based on the fact that he overbuilt/underestimated the numbers on the 6?? Kinda hard to change the 6s number midstream but as similar as the 7 is, it's still a different design. Also, wouldn't the shorter wing lead to more strength?? Isn't it easier to break a longer board than a shorter board of the same width?

Flybuddy2 said:

Is it possible that Vans upped the ranges on the 7 based on the fact that he overbuilt/underestimated the numbers on the 6??

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It's very possible! Van was very conservative in those old days. In reality, you'll seldom see a "6" that has it's gross weight pegged at 1600 lbs.

L.Adamson ---- RV6A

Early g limits

Seems like I rember the published G-limits in the early days being +6 to -6. Does anyone else remember this or my memory is fading.

N164fj said:

Seems like I rember the published G-limits in the early days being +6 to -6. Does anyone else remember this or my memory is fading.

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That is what it is in my RV-6 manual.

az_gila said:

...since the -6 spar is laminated from strips riveted together and the -8 spar has the same general shape, but is machined from solid. Any tool marks and stresses at the end of each "virtual strip" make them quite different.

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Excellent point - I had overlooked that since I've seen a -8 spar a few times. I noticed it was the same shape but obviously missed the hugely significant difference you point out.

JonJay said:

.......6 wings where not built in the factory. There is a lot of potential for builder variance and error in the 6 wing, especially the spar......The machined spar design of the 7 and 8 removes much of the builder variance.

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Well said. I might add that back in the day, the builder could enjoy the personal satisfaction of assembling the main spars. There were many small pieces that made up each spar and most were etched with a part number indicating a specific location and orientation on the spar web. At the time, prebuilt anodized spars were an expensive option. By eliminating builder variance, today's simplified kits require much less in the way of tools and skill thus making it possible for Van's to sucessfully target a much wider demographic.

Some of the numbers posted brings up another question. The acrobatic weight on the 6 was posted here at 1375. Vans website does not list a actual number. If 1375 is the acro weight then it means the aircraft essentially can never do acro with 2 people onboard. Is this everyones understanding? Most sixes I have been looking at seem to come in around 1100 to 1140 lbs empty. That leaves a max of 375 for fuel and people if its a light aircraft. Thats not going to work for two people unless they are very very light!! My son and I together weigh 370 lbs. 5 lbs of fuel is not going to last long! Perhaps it will have to be a 7 instead and I had found a really nice 6 I liked.

George

sailvi767 said:

Some of the numbers posted brings up another question. The acrobatic weight on the 6 was posted here at 1375. Vans website does not list a actual number. If 1375 is the acro weight then it means the aircraft essentially can never do acro with 2 people onboard. Is this everyones understanding? Most sixes I have been looking at seem to come in around 1100 to 1140 lbs empty. That leaves a max of 375 for fuel and people if its a light aircraft. Thats not going to work for two people unless they are very very light!! My son and I together weigh 370 lbs. 5 lbs of fuel is not going to last long! Perhaps it will have to be a 7 instead and I had found a really nice 6 I liked.

George

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[ removed potentially incorrect information pending verification ]

Thanks, That makes a lot more sense. Still hard to get two normal people in the aircraft for acro. I also made a 100 lb mistake in my math which makes it even worse. Never do math in public!

George

The aerobatic weight specifically excludes fuel, at least according to my -6A manual.

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I had not yet heard of anybody with a formal source for this... but if you have a definitive Van's Builders Manual quoting that, then that adds something to the "debate".

Whether fuel is included or not, esentially depends on the wing design, and where ultimately it will break under +ve/-ve 'g'. Do bear in mind in the RV-8 accident referred to above, the wings broke outboard of the tanks... so it is fairly clear that for that design, fuel weight would need to be included.

The RV-3 has a possible argument for excluding fuel weight, provided the fuel is in the wings, and the design was based on the fuselage tank.

Andy Hill
RV-8 G-HILZ

ChiefPilot said:

The aerobatic weight specifically excludes fuel, at least according to my -6A manual. If my plane ends up at 1100lbs, for example, I can take 275lbs of people along for acro.

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Whoa! That's not what my -6 manual says, and is contrary to the common understanding in the RV community. Could you provide a page number in the manual for your reference?

Look at it another way- you say I can take 1375 lbs of airplane + people, not including gas, and fly acro. If I add 38 gallons @ 6lbs, I get 1603 lbs as an acceptable aerobatic weight, which is clearly not the case.

Not to jump on you Brad, but this is a dangerous misconception that needs to be addressed, lest other builders get the wrong idea.

sprucemoose said:

Whoa! That's not what my -6 manual says, and is contrary to the common understanding in the RV community. Could you provide a page number in the manual for your reference?

Look at it another way- you say I can take 1375 lbs of airplane + people, not including gas, and fly acro. If I add 38 gallons @ 6lbs, I get 1603 lbs as an acceptable aerobatic weight, which is clearly not the case.

Not to jump on you Brad, but this is a dangerous misconception that needs to be addressed, lest other builders get the wrong idea.

Click to expand...

Fair enough - now I question my memory. I can see the page in my mind but it might not in fact be from the Van's manual and instead an e-mail I received. I will double check.

ChiefPilot said:

Fair enough - now I question my memory. I can see the page in my mind but it might not in fact be from the Van's manual and instead an e-mail I received. I will double check.

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I've also heard that fuel does not need to be included..........so it's not just your memory. But yes............all this needs varification. I've always just figured my 6A is a "one" person aerobatic unit.

L.Adamson --- RV6A

Two person aerobatics in a 6.

My first loop in any airplane was in a 6, the pilot and me. You probably wont get a lot of posters admiting on a public forum that they perform loops and rolls with two people in their 6's all of the time, but they do. I have never heard of an incident or accident related to an over "aerobatic gross" situation. Maybe it has happened.
I am not sure how the aerobatic limit is defined, but it makes sense to me that the limit would tie directly to the maximum G limits rather than just an arbitrary gross wieght number. But the gross wieght number is the only reference.
An aileron roll has no G component, or very little if you count your nose up entry. Why would that be limited by a gross weight number? A loop can be sucessfully executed at 3g's (or less), leaving you a 100% safety margin.
Just curious what the limit really means.

OK, I dusted off my old -6 build manual and re-read section 14 on W&B. It is pretty clear to me from reading that the 1375 aerobatic gross weight includes the weight of fuel. If anyone reads this differently I'd be open to discussion.

Keep in mind that the example aircraft had an empty weight of 965 lbs (which is doable with a light, simple RV-6) which means that you could take two 170 lb people and 12 gallons of gas, go up and do whifferdills for half an hour and land with VFR reserves, all while remaining within the 1375lb weight restriction. So it can be done.

What my old -6 book...

L.Adamson said:

I've also heard that fuel does not need to be included..........so it's not just your memory. But yes............all this needs varification. I've always just figured my 6A is a "one" person aerobatic unit.

L.Adamson --- RV6A

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...gives is another wrinkle in the aerobatic spec.

It says that the aft CG for aerobatics should be at 15.3 aft of the LE, which give an aft CG of 75.3 aft of a 60 inch datum point (there is a typo here also, it appears the datum used to be 50 inches ahead of the LE).

This is in contrast to a 78.6 inch regular max aft CG location.

Section 14-4 of the old typewritten book. This version did not even seem to give a max gross for aerobatics.

Not getting into the aerobatic gross weight discussion, but back to the spar strength:

Everyone has to keep in mind a couple of points:

1) The RV-6 was designed with the spar to be built from plans or a kit. I'm sure Van accounted for quite a bit of "builder error" margin in the design and limits. The RV-7 spar is pre-made and thus under quality control so it can be built with less margin.

2) The RV-6 was a paper design without the use of computer stress modeling, so I'm sure Van also left some room for design error also. How would you like to design an entire aircraft and then figure out you underbuilt the main spar, better safe than sorry.

aerobatic gross weight discussion:

http://www.vansairforce.com/community/showthread.php?t=4595

Jeremy

Thanks Jeremy, but

jjconstant said:

http://www.vansairforce.com/community/showthread.php?t=4595

Jeremy

Click to expand...

This thread just added to the confusion that seems to exist in regard to aerobatic weight. Perhaps we need to start a different thread on the discussion. While it does relate to the original topic it is drifting a bit...

6 vs 7

Hope somebody with more knowledge will step in here and correct this if I'm wrong. I thought the -6 spar is built so that strength is nearly symmetrical (pos and neg) but the -8 has different spar caps so that neg "G" tolerance is less than positive. Thanks to Wendell Voltz I know the -8 flies really well inverted, but if it could really break at 4.5 neg I'd want to know and wouldn't really feel comfortable doing much neg "G" stuff. Would appreciate some good structural info on this! Thanks in advance for any hard info.

Not just the wing

Bill Dicus said:

Hope somebody with more knowledge will step in here and correct this if I'm wrong. I thought the -6 spar is built so that strength is nearly symmetrical (pos and neg) but the -8 has different spar caps so that neg "G" tolerance is less than positive. Thanks to Wendell Voltz I know the -8 flies really well inverted, but if it could really break at 4.5 neg I'd want to know and wouldn't really feel comfortable doing much neg "G" stuff. Would appreciate some good structural info on this! Thanks in advance for any hard info.

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The +/- G ratings don't just apply to the wings, it's the whole airframe. The wing spar may well be +/- 6Gs but if something else important breaks, it's not much consolation Many aerobatic planes are rated at +6-3Gs.
Using the term 'comfortable' and 'neg G' in the same sentence is an oxymoron

DGlaeser said:

The +/- G ratings don't just apply to the wings, it's the whole airframe. The wing spar may well be +/- 6Gs but if something else important breaks, it's not much consolation Many aerobatic planes are rated at +6-3Gs.
Using the term 'comfortable' and 'neg G' in the same sentence is an oxymoron

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Depends on who the user of the terms is, I guess.

I wouldn't use the two terms in the same breath, but Bill, being the studly Pitts pilot he is, can get away with it!

Its a good question though, and as a Super Six owner, I'm interested in the strength issues discussed herein. I'm into gentleman's acro, versus the gnarly stuff Bill does in his Pitts, but I have a heavy 6, and he has an 8, so the concerns are similar...how to stay away from the margins!!

Good discussion of g ratings applying to more than just the wings...concur...there's that whole tail thing too, right!

Cheers,
Bob

A few facts as I know them...
All RV models up through the 6 had wing spars that were symmetrical top to bottom (same spar cap structure top and bottom) which should in theory make the wing capable of the same load factor + and -, but my understanding has always been that the 3, 4, and 6 were promoted as being good for +6/-3. I don't remember ever seeing anything published +6/-6 (though I may have forgotten).

All models after the 6 were designed with asymmetrical spar structure. In a positive G load condition the top spar caps are loaded in compression and the bottom in tension. A tension loaded member can take more load before failure than an equally sized member in compression. Making the bottom smaller provides weight reduction but reduces the allowable neg. load factor (who wants to push -6 g's anyway).

"I have been told by very good sources that the factory built wing was tested well beyond the limits."

Totally true. Because "limit" load is 6 G's (the load at which no damage or deformation occurs). This is the maximum intentional flight limit.
The Ultimate load is the load which the wing must be capable of holding one time for 3 seconds without a catastrophic failure. It is 150% of limit load so in the context of designing for aerobatics the wing must be tested to 9 G's.

The RV-6 wing did go beyond 9 G's with no failure. I do not feel that the amount it went beyond is important for this reason. The precision level of the testing on all wings tested after the RV-6 was improved. If you look at photo's in old RVator news letters you will see huge piles of 75 lb bags of sand on the wings. These bags are big. It is difficult to get a load distribution with a high level of precision. All wings from the RV-8 on, have been tested with lead shot bags loaded on cell stations that are only about 6" X 12". This allows for a very accurate load profile for any given test. There is an RV-7 test wing on display in the hangar at Van's. It also was tested to 9 G's without failure. Some of the skins are cut away to allow inspection of the interior for any evidence of damage. If I remember correctly, there isn't any.

So is the RV-6 wing stronger than the RV-7? I don't think anyone can really say that.

Does fuel need to be factored in when calculating gross weight for aerobatics? Ken Krueger, Vans head of engineering has told me it does.
Van has apparently in the past said that it didn't need to be for the RV-3. I think that is related to its wings originally being designed for the use of a fuselage fuel tank. I think a miscommunication happened somewhere, and a statement Van made may have been taken out of context. I don't believe Van ever meant to say you didn't need to consider fuel in aerobatic gross weight for all models. But I can't speak for him.

The issue is that fuel in the tanks does reduce the bending moment on the wing, but as Kevin pointed out it only effects the portion of the wing where the fuel is. In an RV, the portion of the wing outboard the tank would be loaded higher than intended. If the wings were originally test to 9 G's using the aerobatic gross weight value, then the wing is only proven to that load value. If you fly at a weight higher than that, but with all of the extra weight in the cabin area, it is true that you have downward fuel load (induced by G's) counteracting the upward bending moment of the wings. It is possible that it would make the bending moment at the root end of the wing no higher than it would have been at a lower weight. The problem is that the portion of the wing without fuel actually does have a higher bending moment on it; beyond what was tested.

Regardless of what you have heard, or where you have heard it... my opinion is that you are reducing your safety margin if you do aerobatics at higher than the published gross weight Period

How are aerobatic gross weights determined?

Vary good points from Scott via Ken.
Keeping in context, the 7 has a higher aerobatic weight than a 6 so some argue the 7 must be stronger.
How is it determined? As mentioned, a roll is an aerobatic manuever, but you dont need to pull any g's to do one. What are the limits that aerobatic gross imply?
I guess I can ask KK next time I see him for the full blown description but it would be nice for all that do aerobatics in our 6's that frequent here to know. What are we dealing with?

rvbuilder2002 said:

...my understanding has always been that the 3, 4, and 6 were promoted as being good for +6/-3. I don't remember ever seeing anything published +6/-6 (though I may have forgotten)...

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To check my memory I looked again at my RV-6 builder's manual (1997 ish) again this morning. It does indeed refer to +6/-6 and also lists the baggage weight capacity as 100 pounds versus the 60 pounds listed on the Van's site today. I would be happy to take photos if anyone would like. There seem to have been changes over time, not in the airplane, but in the specs.

Mine too

n5lp said:

To check my memory I looked again at my RV-6 builder's manual (1997 ish) again this morning. It does indeed refer to +6/-6 and also lists the baggage weight capacity as 100 pounds versus the 60 pounds listed on the Van's site today. I would be happy to take photos if anyone would like. There seem to have been changes over time, not in the airplane, but in the specs.

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It also states that the airframe is stressed for aerobatics up to a gross weight of 1375lbs. per the manual... "This means that is has a design strength of 6 positive and 6 negative G's (plus a 50% safety factor) at up to this weight." It goes on to state that the RV6 is effectively a single place aerobatic machine.
I would suggest that it is a single place aerobatic machine for many manuevers, but low G manuevers, like aileron rolls or conservative loops, could be done safely beyond the 1375 weight limit. However, as Scott mentions, it was never tested, or documented beyond 1375lbs. It also goes on to say that the RV is a pilot limited airplane. I believe they where very conservative in their testing to cover for the wide variance in pilot skill and training.
Someone loan their 6 to Van's for some desctructive testing and let's see how she really does....ha!

n5lp said:

To check my memory I looked again at my RV-6 builder's manual (1997 ish) again this morning. It does indeed refer to +6/-6 and also lists the baggage weight capacity as 100 pounds versus the 60 pounds listed on the Van's site today. I would be happy to take photos if anyone would like. There seem to have been changes over time, not in the airplane, but in the specs.

Click to expand...

Like I posted previously, I was going from memory. The 6 & 4 maybe have always been +6, -6. I do know that the 7 and teh 8 are +6, -3.
(I sure hope the 4 and 6 pilots don't do -6 G's with a standard harness.)

JonJay said:

Vary good points from Scott via Ken.
Keeping in context, the 7 has a higher aerobatic weight than a 6 so some argue the 7 must be stronger.
How is it determined? As mentioned, a roll is an aerobatic manuever, but you dont need to pull any g's to do one. What are the limits that aerobatic gross imply?
I guess I can ask KK next time I see him for the full blown description but it would be nice for all that do aerobatics in our 6's that frequent here to know. What are we dealing with?

Click to expand...

JonJay said:

It also states that the airframe is stressed for aerobatics up to a gross weight of 1375lbs. per the manual... "This means that is has a design strength of 6 positive and 6 negative G's (plus a 50% safety factor) at up to this weight." It goes on to state that the RV6 is effectively a single place aerobatic machine.
I would suggest that it is a single place aerobatic machine for many manuevers, but low G manuevers, like aileron rolls or conservative loops, could be done safely beyond the 1375 weight limit. However, as Scott mentions, it was never tested, or documented beyond 1375lbs. It also goes on to say that the RV is a pilot limited airplane. I believe they where very conservative in their testing to cover for the wide variance in pilot skill and training.
Someone loan their 6 to Van's for some desctructive testing and let's see how she really does....ha!

Click to expand...

It is very common for people to say rolls are ok because they induce very little G load. Maybe, but mistakes get made doing aerobatics all the time. Just ask someone that does it a lot.
One botched roll can quickly turn in to a manuver that induces a G load that the pilot never intended on that particular flight. Like I said before...it is all about safety margin. I prefer to keep my margin as large as practical.

Side note...G load isn't the only limiting factor for aerobatic flight. Something that is often over looked is that manuvering speed limitations apply to all flight controls at all times (not just elevator). Be carefull with how much aileron and rudder you are using at high speed doing aerobatics.

DGlaeser said:

The +/- G ratings don't just apply to the wings, it's the whole airframe. The wing spar may well be +/- 6Gs but if something else important breaks, it's not much consolation Many aerobatic planes are rated at +6-3Gs.
Using the term 'comfortable' and 'neg G' in the same sentence is an oxymoron

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Point about other parts of airframe being limiting is absolute correct! Tail (as mentioned) and motor mounts spring to mind. When people get involved in acro and the adrenalin ramps up you might not feel the g's as you usually do. The Pitts is rated for +6 and -3 g's to qualify for the Acrobatic category. At contests it's not rare to see g meter tell-tales at +8 and -5 g's after a competition flight . The Pitts fortunately seems to survive this treatment. If the true negative limit for the -8 is -3 g's then the wing could break or be severely damaged with a moment's carelessness or over-enthusiasm. It doesn't take much force on the -8 stick to generate in excess of that -3 g's with the c.g. somewhat aft (that is, two folks up). That's the basis of my comfort comment. This has been an interesting discussion about the -6 and manual changes - thanks to all who participated. I too think fuel should always be included in the flying weight for acro unless there is very hard evidence to the contrary.
An aeronautical engineer who took me is his RV-4 extrapolated tolerable g loads for different weights and flew accordingly. He was very happy flying to 4 g limits 200 pounds or so over design acro weight. His plane is still flying after many years..... Funny that neg "g" is not really comfortable but is a little addicting, at least to some folks! YMMV!

Bill Dicus said:

An aeronautical engineer who took me is his RV-4 extrapolated tolerable g loads for different weights and flew accordingly. He was very happy flying to 4 g limits 200 pounds or so over design acro weight. His plane is still flying after many years..... Funny that neg "g" is not really comfortable but is a little addicting, at least to some folks! YMMV!

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The most fun I have had flying inverted was in a Grob aerobatic glider... You could stay upside-down as long as you like, there's no engine to worry about. And once you get comfortable upside down, it's really not that hard. What is hard, is inverted formation... Your ailerons are reversed!

I see the comments about extrapolating the tolerable G-loads. The catch in the case of the RV-6 is, you can't extrapolate in any mathematically-justifiable manner. 1375lb at 6G = 8250lb. 1600lb at 4.4G = 7040lb. Which limit is correct? Extrapolating from the Aerobatic gross, coming back to 4.4G means you can carry 1875lb. Extrapolating from the Utility gross, doing 6G aerobatics means you have to be down to 1173lb.

It might be a good place here to ask yet again if anyone has a copy of the letter Vans used to issue to people who asked for approval to increase their gross weight. The existence of such a letter has been mentioned many times, but as yet nobody has been able to produce one.

Bill Dicus said:

I too think fuel should always be included in the flying weight for acro unless there is very hard evidence to the contrary.

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I agree with you Bill, and Scott made some very good points to that effect. I've never seen any discussion of zero fuel weight limits, but I understand the rationale behind postulating that fuel in the tanks opposes the bending moment of the wings. However, without a clear statement that g limits depend on zero fuel weight only, and total gross weight is not a factor, I'm of the mindset to stick with gross weight, and count the fuel in my calcs.

I also understand the concept of limiting g to lower limits at weights above max aerobatic weight, but I feel that's a slippery slope...as you mentioned, just a little adrenalin, and a little airspeed, combined can result in a pretty high g load...whether you wanted it or not. I had a few maintenance master chiefs want to skin me (or my buds) when we brought back an over-g'd airplane. I never felt it...but my RIOs did (grunting, "I-think-that's-a-little-too-much-g!")

I dunno, like the Vne discussions...we may not know the exact ultimate limit, but we have conservative limits that we can live long and prosper by! And that's whether its a 6 or 7 (or 8) (Not meant to sound preachy...just IMHO).

Bill Dicus said:

Funny that neg "g" is not really comfortable but is a little addicting, at least to some folks! YMMV!

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Is that why the whites of your eyes are a little red Bill! Thanks for taking mercy on Matty and I on our Pitts rides!

Shouldn't you be building on your 8?

Cheers,
Bob

G's

Bob: Pls see PM.

Which section...

JonJay said:

It also states that the airframe is stressed for aerobatics up to a gross weight of 1375lbs. per the manual... "This means that is has a design strength of 6 positive and 6 negative G's (plus a 50% safety factor) at up to this weight." It goes on to state that the RV6 is effectively a single place aerobatic machine.
....!

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...is that in?

I couldn't find it in the W&B section (14) of my early manual....

And "Aerobatic Gross Weight" isn't even in the definition of terms at the intro. to that section.

It's a pity Van never versioned or dated the earlier manuals...

Bill Dicus said:

Bob: Pls see PM.

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Bill, no new PMs recvd, and looks like your inbox is full (u popular guy!)

Cheers,
Bob

You know I love these RVs, even though I am yet to get the full grin due to various small issues and an absence of time...

However, it really strikes me that it is time for Vans to update via a two page addendum, all the specs for the older models and list them conclusively on the website. Probably including the manuals too...

Reason is that these build books and specs have gone all over the world to people who may not have English as their first language and there are many older RV kits still in build or on their 5th owner without yet flying (I have two that were both started in 96 and 97). Drawings have been changed and typos made - it would be good for someone at Vans to just spend 5-10 hours producing a 2-10 page definitive document with a vans stamp of approval - Hopefully also uprating the max load by 50 - 100lbs...

This would not devalue the RV7 kit, but actually make all the RV6 owners feel more loved and supported! Especially after wondering through the haze of incorrectly sized armrests, F608 bulkheads and canopy frames that just do not want to fit...

maneuvering speed

rvbuilder2002 said:

Side note...G load isn't the only limiting factor for aerobatic flight. Something that is often over looked is that manuvering speed limitations apply to all flight controls at all times (not just elevator). Be carefull with how much aileron and rudder you are using at high speed doing aerobatics.

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Scott,

This is an interesting point, which raises a question - is there any way to know the actual maneuvering speed that applies to abrupt aileron and rudder deflection? For elevator deflection it is directly related to stall speed (which is easy to measure), but I've never heard how to calculate Va for other controls.

Final Inspetion and Flight Test, Section 15

az_gila said:

...is that in?

I couldn't find it in the W&B section (14) of my early manual....

And "Aerobatic Gross Weight" isn't even in the definition of terms at the intro. to that section.

It's a pity Van never versioned or dated the earlier manuals...

Click to expand...

My manual is dated on the bottom of each page as follows.
6515.DOC 5/22/97, page 15-17