B

breister

Well Known Member
After reading another thread about the popularity of the RV6, I am rather puzzled.

If the RV7 is the successor to the 6 (and presumably has improvements), why would anyone choose the 6 over the 7?

P.S. I tried to search for prior threads on this, but wasn't smart enough to figure out which key words might single out such a thread...
 
Opinion, Opinion, Opinion!!!

The RV-6 is a "Classic". Because of some of the early problems with the RV-3, Van over-built the RV-6 and was very conservative with structural limitation. Take a look at how the wings are attached to the -6. Something on the order of over 70 bolts. In my opinion, the -6 is by far the strongest RV ever designed. Shorter wing gives faster roll rate.
Unless you are quite large and/or need longer range, the -7 has few advantages over the -6.
I love my -6 and wouldn't trade even for a -7!
$.02 worth.
 
What Mel said

The -7 is more of an evolution, accomodating CNC machined pieces with a lot less work than the -6 and more than likely, IMO, will have a greater completion rate as a result. There's so little difference in flying characteristics that you would be hard pressed to know which it was if you didn't know beforehand.

The -6 is, as Mel said, a pure joy to fly....the Porsche 911 of the sky.

Regards,
 
That's easy

Everyone knows that the RV-7 is newer, therefore it must be better than the RV-6. Just like Windows Vista was newer than XP, therefore it must have been better. :)

Cheers,
Tracy.
 
thallock said:
Everyone knows that the RV-7 is newer, therefore it must be better than the RV-6. Just like Windows Vista was newer than XP, therefore it must have been better. :)

Cheers,
Tracy.
Click to expand...


Whether it is better is debatable, but it definitely is easier to build, is designed to accommodate a 200 HP engine, has a different spar system, carries more fuel, has more wing area, has slightly better visibility over the nose, carries 40# more baggage and 200# more total weight. I chose it over the 6 because it can be built without wasting time building jugs.

Other than that, they are pretty much the same. :)
 
RVnoob said:
.... thanks for the post.
no wonder a number of "aero" pilots prefer -6 over -7.


along this line of thought... an unfinished -6 tail would worth a lot of money.
Click to expand...


Actually, there are a lot of unfinished -6 kits out there, so they are a dime a dozen (well, not quite). Finding quality workmanship on unfinished kits is harder since the parts aren't match-drilled and require jigging.
 
If you want to start with a new kit, the 6 is no longer available. You can buy buy wings, fuse, etc. because Van's still supports all of those folks still building. If you want to start your build with your own NEW empennage kit straight from Van's, you'll discover it is no longer available. You'll have to by your -6 emp kit from someone else.

Guy
 
David-aviator said:
Whether it is better is debatable, but it definitely is easier to build, is designed to accommodate a 200 HP engine, has a different spar system, carries more fuel, has more wing area, has slightly better visibility over the nose, carries 40# more baggage and 200# more total weight. I chose it over the 6 because it can be built without wasting time building jugs.

Other than that, they are pretty much the same. :)
Click to expand...

But in reality, a lot of 6's are set at gross weights of 1800+, and even up to 2000 lbs. Van's numbers were very conservative when the 6 was designed.

My 6A is set at 1850 gross weight. Mine is not the lightest of the bunch either. Yet, it's much more nimble on the controls than a 9, is much like a 7 feel wise; but I still like that heavy duty spar that was built into the 6!

I wouldn't trade either. I even prefer the shorter "classic" tail.

And BTW--- If that inch of extra of space is really in 7's and 9's, I'll be danged if I can find it! :D

L.Adamson --- RV6A
 
L.Adamson said:
But in reality, a lot of 6's are set at gross weights of 1800+, and even up to 2000 lbs. Van's numbers were very conservative when the 6 was designed.

My 6A is set at 1850 gross weight. Mine is not the lightest of the bunch either. Yet, it's much more nimble on the controls than a 9, is much like a 7 feel wise; but I still like that heavy duty spar that was built into the 6!
Click to expand...

Egads, here we go with this one! :D Conservative of Van's or not, I don't think it's conservative of any builder to raise their gross weight without a LOT of testing. I'm no engineer, but I hope you are (and a wise one, at that) if you're willing to increase the gross weight of your airplane over the designer's limits.
 
lostpilot28 said:
Egads, here we go with this one! :D Conservative of Van's or not, I don't think it's conservative of any builder to raise their gross weight without a LOT of testing. I'm no engineer, but I hope you are (and a wise one, at that) if you're willing to increase the gross weight of your airplane over the designer's limits.
Click to expand...

I've been around RV's for over 15 years. A lot of "builder/pilot" testing has gone on, especially with the 6's. You'll seldom find a 6 that uses 1600 or 1650 as it's specified gross weight. When the 6 was designed, Van's wasn't even thinking the heavier constant speed props.

So yes...............I was very willing to expand the gross weight of my 6A. I had a tremendous amount of info to go on. It's called thousands of builders before me. Remember, a 6 has yet to loose it's wing from over-stress.

L.Adamson --- RV6A
 
L.Adamson said:
I've been around RV's for over 15 years. A lot of "builder/pilot" testing has gone on, especially with the 6's. You'll seldom find a 6 that uses 1600 or 1650 as it's specified gross weight. When the 6 was designed, Van's wasn't even thinking the heavier constant speed props.

So yes...............I was very willing to expand the gross weight of my 6A. I had a tremendous amount of info to go on. It's called thousands of builders before me. Remember, a 6 has yet to loose it's wing from over-stress.

L.Adamson --- RV6A
Click to expand...

As long as you're willing to put your life in the hands of the "thousands of builders" who did it before you. I'm not saying that the -6 can't handle being over gross...I'm just saying that I wouldn't necessarily put my trust in anyone else's "experiments" until they're proven. Remember, none of these airplanes are built the same way...even the ones that are built per-plans.

It's only my opinion, but unless YOU performed the over-gross testing at all CG's for YOUR airplane, I think it's a bold move on your part to raise your gross weight and fly it that way. I'm not trying to stir the pot, just trying to make sense of the "everyone else did it, so why can't I" logic. That being said, there may have been a lot of testing and it may be perfectly fine...I just don't know. I think your statement just came across a little cavalier.

I'm not guilt-free of doing such things, either, by the way...I have a Sikaflexed canopy! But, I did a simple bond strength test to see how strong it was and I read of numerous others who tested it, too.

I guess it comes down to the intent of the statement...it almost sounds like some are saying that the gross of the -6 should be 1800 or 1850, without regard to the original design. I think that's a pretty bold thing to do. Just because a data plate is stamped with a higher number, doesn't mean your airplane is going to handle that higher weight the same as an airplane that's designed to do so. The -6 and -7 spars and center sections are quite different. Again, just my opinion, but the -7 center section is far more robust looking than the -6. I'm no engineer, but I would think the design limits are there for a reason.

It would be a great thing to see both designs flipped over on a jig and load-tested to failure! ;)
 
Yeah, that would be interesting to know or an aeronautical engineer could at least do some calculations. I have really been struggling about the -6 vs -7 choice too. Looks like there are some good deals on partial built and completed -6s. Had been planning on a -7 BUT...... Also, I have a completed -7 empennage, is it OK to use with a -6 fuse? It is very tempting to go with a -6 and save a nice chunk of money especially now. Can someone tell me the differences in physical dimensions inside and out?
 
glenn654 said:
Yeah, that would be interesting to know or an aeronautical engineer could at least do some calculations. I have really been struggling about the -6 vs -7 choice too. Looks like there are some good deals on partial built and completed -6s. Had been planning on a -7 BUT...... Also, I have a completed -7 empennage, is it OK to use with a -6 fuse? It is very tempting to go with a -6 and save a nice chunk of money especially now. Can someone tell me the differences in physical dimensions inside and out?
Click to expand...

...they're almost the same inside. I think the -7 seat pan is a bit lower, which gives you an extra inch or so of headroom. Also, I believe the -7 instrument panel is a couple inches further forward than the -6...this gave me the perception of more room.

In regards to the gross-weight discussion, this has been discussed quite a bit before. See this thread for some great information on the subject.
 
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lostpilot28;369839In regards to the gross-weight discussion said:
this thread[/URL] for some great information on the subject.
Click to expand...

And this is a memorable one....... in that thread.



I know we all would like to think that Van's has carefully calculated and tested the engineering load factors on everything from the spar to the glovebox lid, but it's probably a fantasy.

The 1600 pounds that Vans recommended for my 6A didn't leave much room for luggage with two normal-sized people. I had done all the math and it was obvious my airframe was easily capable of well over 2000 lbs gross weight in the air. I figured the 1600 lb limitation must be due to those spindly gear legs.

About that time, the 7 came out, with its 1800 gross weight.

So I called the factory to see if I could order a pair of those new gear legs for my 6. The response? "They're the same legs". I explained my calculations and how I came to the conclusion that the gear was the limiting factor. He (I think it was Tom) confirmed that, yes, the gear is the limiting factor. "So howcome the 7 can handle 1800 lbs while the 6 is limited to 1600?", I asked.

The answer -- "Because we noticed that so many 6 drivers were using an 1800 lb gross without any problems".

L.Adamson
__________________
 
Back of Fag Packet Calculation for my RV6

Half Span to Fuselage ~60 inch
Load / Wing @ 1600 lb gross 800 lbf
Root BM 24,000 in.lbf
Ult Factor (6g x 1.5) 9 g
Ult Root BM 216,000 in.lbf

Spar Cap Thickness - Root 1.125 inch
Spar Cap Depth 1.5 inch
Spar Total Depth 7.6875 inch

Spar I 32.936 inch^4
y max 3.84375 inch

Max Stress (My/I) 25,208 psi

Ultimate allowable tensile stress for 2024 T4 ~68,000 psi

This is only the main spar and there are some real SWAG assumptions here - not all of the load distribution or geometry is considered - bolt holes for example - but there should still be some reserve margin at 1600 gross.

Having said that I trust Van and set my gross at 1650, the maximum he suggests. There is more than structural integrity involved - stability and control for example.

Jim Sharkey
 
lostpilot28 said:
The -6 and -7 spars and center sections are quite different. Again, just my opinion, but the -7 center section is far more robust looking than the -6. I'm no engineer, but I would think the design limits are there for a reason.
Click to expand...

Just the opposite here. Our six spars go all the way through the center section & meet in the middle. They are not merely bolted to the center section. The six spars are then bolted front and back with four steel plates in addition to those 70 or so bolts that hold them between the bulkhead sections.

L.Adamson
 
glenn654 said:
Yeah, that would be interesting to know or an aeronautical engineer could at least do some calculations. I have really been struggling about the -6 vs -7 choice too. Looks like there are some good deals on partial built and completed -6s. Had been planning on a -7 BUT...... Also, I have a completed -7 empennage, is it OK to use with a -6 fuse? It is very tempting to go with a -6 and save a nice chunk of money especially now. Can someone tell me the differences in physical dimensions inside and out?
Click to expand...

The interior dimensions are the same except the 7 has 1.5" more head room, the bag area is larger, and the rudder pedals can be adjusted 3.5".

The 6 has a 23' span, the 7 has a 25' span.

Specifications are available for each model on Van's web site.
 
L.Adamson said:
And this is a memorable one....... in that thread.



I know we all would like to think that Van's has carefully calculated and tested the engineering load factors on everything from the spar to the glovebox lid, but it's probably a fantasy.

The 1600 pounds that Vans recommended for my 6A didn't leave much room for luggage with two normal-sized people. I had done all the math and it was obvious my airframe was easily capable of well over 2000 lbs gross weight in the air. I figured the 1600 lb limitation must be due to those spindly gear legs.

About that time, the 7 came out, with its 1800 gross weight.

So I called the factory to see if I could order a pair of those new gear legs for my 6. The response? "They're the same legs". I explained my calculations and how I came to the conclusion that the gear was the limiting factor. He (I think it was Tom) confirmed that, yes, the gear is the limiting factor. "So howcome the 7 can handle 1800 lbs while the 6 is limited to 1600?", I asked.

The answer -- "Because we noticed that so many 6 drivers were using an 1800 lb gross without any problems".

L.Adamson
__________________
Click to expand...

Larry, no offense (and I truly am not trying to aggravate you), but I simply can't believe you're arguing this point. Just because "so many 6 drivers were using an 1800 lb. gross" stamped on their data plate doesn't mean you're not asking for problems. Did you read all the other posts in that thread?!? There's some pretty real numbers in there that should be at least a caution for you when operating above the designed gross weight. I'll stop with this: please be careful up there.
 
lostpilot28 said:
The -6 and -7 spars and center sections are quite different. Again, just my opinion, but the -7 center section is far more robust looking than the -6. I'm no engineer, but I would think the design limits are there for a reason.

It would be a great thing to see both designs flipped over on a jig and load-tested to failure! ;)
Click to expand...
You are be kidding, right? The -6 center section is so grossly overbuilt as to be ridiculous. There is no comparison in the "eyeball engineering" department. The -7 and -9 center sections look downright scary by comparison.

As for load testing to failure, what would that prove? Both designs have been tested to ultimate load (150% of the 6G limit) and passed. What useful data is there to be learned beyond 9Gs?

PS- not trying to aggravate you either. My -6 is set at 1650 lbs. However, it has been, ah, flight tested at significantly more than that.
 
It's not a dumb question!

breister said:
After reading another thread about the popularity of the RV6, I am rather puzzled.

If the RV7 is the successor to the 6 (and presumably has improvements), why would anyone choose the 6 over the 7?
Click to expand...

I suspect the other thread is one I started to help me justify starting an RV6. The guys posting were a great help.

So, here we are 2009 and I am, in effect, a new start RV6. Why did I choose the 6 over the 7? Well, actually I chose the 6 over the 7 and the 9. The decision was a rather complex one. PM me if you want the long version, but here is the short version:
1. I didn't want to build a pre-punched kit.
2. The RV6 will cost me many thousands of dollars less to build than an RV7 or 9.
3. I don't want to use an O-360, or constant speed prop, but want to use an O-320 fixed pitch wood prop. I am strongly of the opinion that the 6 suits the 320 and the 7 suits the 360 best. (Larry will shoot me!) :)
4. Like Mel says, I don't NEED the extra things the RV7 has to offer.
5. There were too many little things for me that stacked up against the RV9.
6. I drove a half hour down the motorway here in New Zealand to collect my RV6 tail kit instead of waiting weeks for a 7 or 9 tail kit to be delivered from the other side of the world and dealing with the gallery of crooks with their hands out at the border.
7. I just like "classics"!

I hope that helps!

Cheers,
Andrew.
 
One suggestion

Use a Catto two-blade instead....much higher performane than most wood props. My buddy picked up 6MPH over his Sterba.

Regards,
 
lostpilot28 said:
There's some pretty real numbers in there that should be at least a caution for you when operating above the designed gross weight.
Click to expand...

But the point of the post from that other thread that Larry quoted is: the "factory design" of the -7 gear legs is based on the fact that "so many 6 drivers were using an 1800 lb gross without any problems".

As just one more opinion, whatever GW you put on the data plate of the plane you're building, you better flight test at that GW during phase I. And since you aren't going to flight test to limit or ultimate load, figure what other limitations it may be prudent to apply at that GW, if any (restricted CG, normal vs. utility category ops, reduced Va, etc.). But then go for it if you want.

The builder of our RV-6 did that, at 1800 pounds, and I'm grateful for it. With an O-360 and CS prop, it really improves the versatility of the aircraft.

--Paul
 
I hate to get into this discussion but I saw the term "eyeball engineering" and that bothers me. Just because something looks stronger does not mean that it 'is' stronger. I'll admit that the RV-7 center section 'looks' like it is less robust. It looks that way because there are fewer bolts holding the spar over a smaller length. Just because something has more bolts doesn't make it stronger.

Testing something to 9G's doesn't tell you anything. The only thing that matters is the ultimate load to which it is tested. I doubt that anyone would argue that the center section on a C-17 is carrying a little more load at 1G than our airplanes are at 6G's. I don't know to what load Van's tested either of these spars, but I suspect that since the RV-7 has a higher gross weight it was tested to a higher load. I also don't know if either was tested to failure to determine it's ultimate yeild strength so we may not know which wing is actually stronger.

Recently the Insurance Institute for Highway Safety celebrated their 50th anniversary by crashing a 1959 Bel Air into a 2009 Malibu. Big giant steel gas guzzler vs. little efficient platic car. Intuition might tell you to go with the big steel car, but then you'd be dead.

Now back to the original question. I have an RV-6 tail on my RV-7 because I received my kit 7 days before the RV-7 was announced. I almost kept it an RV-6, mostly because I like to build things and the extra challenge of NOT having the matched hole kit actually appealed to me. After building the tail I decided that I didn't like building jigs and I wanted the extra aerobatic gross weight so I went with the RV-7.
 
Lots of focus here on the wing center section. I'm familiar with the boiler plate design on the RV6 (and 4) CS but the wing will probably fail near mid-span and the rest will hit the ground in one piece.

I also do like the flying qualities of the 6. A little more of a sinker than the 8 because of its shorter wings. And by the way, I think the ailerons on the 6 are shorter, so the roll rate isn't any better than the 7/8. It does feel lighter in roll, maybe due to lighter rolling inertia. BUT - my personal favorite is still a well balanced 4 with lots of giddy-up.
 
You don't need to be an engineer for those calculations

glenn654 said:
Yeah, that would be interesting to know or an aeronautical engineer could at least do some calculations. I have really been struggling about the -6 vs -7 choice too. Looks like there are some good deals on partial built and completed -6s. Had been planning on a -7 BUT...... Also, I have a completed -7 empennage, is it OK to use with a -6 fuse? It is very tempting to go with a -6 and save a nice chunk of money especially now. Can someone tell me the differences in physical dimensions inside and out?
Click to expand...

It doesn't take an engineer to figure that one out:

The Vans published, AEROBATIC gross weight for the RV6 is 1350 pounds with a published, allowable G continuous loading of 6G's.

Therefore, the wing is capable of supporting a sustained load of 8100 pounds:
1350 x 6 = 8100 pounds

The legal minimum G-rating required for any aircraft certified in the NORMAL category is 3.8 G's.

Therefore, the airframe of any aircraft rated for 6G's at aerobatic gross is capable of safely flying in the NORMAL category at 2,131 lbs., so long as 3.8 G's is not exceeded.
8100 / 3.8 = 2,131 lbs.

HOWEVER, that does not mean that the landing gear is capable of tolerating that much weight. It doesn't take a very hard landing to put 2G's on a G meter.

So the question comes down to how much weight can the gear support. The fact is, the 6 has exactly the same gear legs as the 7, except that they're a couple of inches shorter (and actually a little bit stronger) than the 7. Since the 7 has an approved 1800 pound gross, you can be sure that the 6 gear legs can handle at least that much.

I solved the problem by declaring in my POH a normal category gross weight of 1950 pounds for take off and 1800 pounds for landing.
 
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jonbakerok said:
I solved the problem by declaring in my POH a normal category gross weight of 1950 pounds for take off and 1800 pounds for landing.
Click to expand...

Hehe - that sounds just about the weight of one mother-in-law...

Thanks everyone for your responses, did not intend to stir a hornets nest. In all it sounds like most folks think the -6 performs a tad better and the -7 is a bit easier to build, but not everyone agrees with even this...

:D
 
Don't Forget Stability and Control!

While I agree completely with the above calculations for pure load, please don't forget that Gross Weight is not simply defined by structural capability! Stability and Control also factor in, as does performance (although performance is unlikely to be limiting in a typical RV). The CG envelope is not always linear, and how the airplane handles can be affected by weight.

I am not arguing that there isn't wiggle room in the factory numbers - I am simply making sure that folks look very cautiously at ALL factors that can determine gross weight, or be affected by aircraft weight, before arbitrarily upping the number....

Paul
 
Two more points...

The roll rate of the 6 is quicker than the 7 and 8 if that matters to anyone. (it was incorrectly noted in an earlier post). I have flown all three, and flown a few 8 drivers in my 6, and it always surprises them.

A "very good source" told me that builder variance was taken into consideration when setting aerobatic and gross limits on the 6. They are a very strong design. However, there are many areas of the build that can vary from one to the next. Fabrication, finishing, and riveting the bar stock is just one. I spent hours sanding, buffing, and filing the bars to take every nic and mil mark away. Not all builders did that, nor am I sure it is necessary, but that is just one variable in the construction of the 6 spar. I believe Van's took this into consideration and "under" grossed the spec. (I was told the factory built wing stood up to considerably more....., but I wont say who told me ;)
The newer spar designs in the 7/8/9 take those variables away from the builder. It is easier to build the wing with fewer builder variables.
 
Ironflight said:
While I agree completely with the above calculations for pure load, please don't forget that Gross Weight is not simply defined by structural capability! Stability and Control also factor in, as does performance (although performance is unlikely to be limiting in a typical RV). The CG envelope is not always linear, and how the airplane handles can be affected by weight.
Click to expand...

I can say that without doubt, in the normal category & CG limits, that an 1850 lb. gross weight RV6A ( at gross weight) is very stable, very controllable, very nimble, and very fun to fly. It also takesoff & climbs fast with a C/S prop. It just has a real good feel to it. Don't expect it to float like a Cessna 172 on landing.........though.. :eek:

L.Adamson --- RV6A
 
JonJay said:
I believe Van's took this into consideration and "under" grossed the spec. (I was told the factory built wing stood up to considerably more....., but I wont say who told me ;)
Click to expand...

Wasn't it something like 11G's worth, before permanent deformation? :D

L.Adamson --- RV6A
 
Back to one of my questions which was never addressed...can a -7 empennage be used on a -6? I already have one and would be nice to be able to use it if I went w/ a -6 instead.

Also thanks for all the good info.

Glenn Wilkinson
 
jonbakerok said:
It doesn't take an engineer to figure that one out:

The Vans published, AEROBATIC gross weight for the RV6 is 1350 pounds with a published, allowable G continuous loading of 6G's.

Therefore, the wing is capable of supporting a sustained load of 8100 pounds:
1350 x 6 = 8100 pounds

The legal minimum G-rating required for any aircraft certified in the NORMAL category is 3.8 G's.

Therefore, the airframe of any aircraft rated for 6G's at aerobatic gross is capable of safely flying in the NORMAL category at 2,131 lbs., so long as 3.8 G's is not exceeded.
8100 / 3.8 = 2,131 lbs.
Click to expand...

These numbers would be pretty good if the additional weight was distributed evenly across the entire wing span. But it isn't, it is concentrated in the fuse so the bending forces at the wing/fuse junction increase disproportionately. The numbers above are most likely stating a margin larger than reality.
 
Yes

glenn654 said:
Back to one of my questions which was never addressed...can a -7 empennage be used on a -6? I already have one and would be nice to be able to use it if I went w/ a -6 instead.

Also thanks for all the good info.

Glenn Wilkinson
Click to expand...

The original RV7 had an RV8 empenage with balanced rudder which was also used on the last of the RV6s. This was soon replaced on the RV7 with a version that used the RV9 rudder. I can't see a reason why they aren't all interchangeable.

I love my RV6 but can't see any reason why anyone wouldn't want to build an RV7. From my experience on the 6 the 7 has to be quicker and cheaper to build in the long run. Jigging, measuring, marking and drilling is educational and satisfying in its own way but oh so time consuming. Add in more head room in the 7, factory blessed higher gross, more fuel capacity, roomier behind the panel gap for easier wiring, better resale prices, etc, etc. It's a no brainer.

Now buying a decent completed RV6 is a whole other question :D

Jim Sharkey
RV6 - Phase 1
 
glenn654 said:
Back to one of my questions which was never addressed...can a -7 empennage be used on a -6? I already have one and would be nice to be able to use it if I went w/ a -6 instead.

Also thanks for all the good info.

Glenn Wilkinson
Click to expand...

There's a pic I posted a 3 days ago showing my RV6 with the large RV7 tail on it in the thread titled "7a Tailkit to 6a ??" HERE where this exact subject was discussed....it comes up once or twice a year!

Cheers,
Stein
 
Bottom line is.....

If you like the -6, find a tail kit and build a -6. You won't be disappointed!

If you like the -7, build a -7. You won't be disappointed!

In other words, build the airplane YOU want, not the one that others want you to build!

Wait a minute; Haven't I heard that somewhere before?
 
let me read the hidden lines...

you've got a 7 tail at a bargain,

you found some 6 wing/fuse kits at even greater bargain...

mmm... let me see if i can...
 
My 6A at 1950 lbs

Ironflight said:
While I agree completely with the above calculations for pure load, please don't forget that Gross Weight is not simply defined by structural capability! Stability and Control also factor in, as does performance (although performance is unlikely to be limiting in a typical RV). The CG envelope is not always linear, and how the airplane handles can be affected by weight.

I am not arguing that there isn't wiggle room in the factory numbers - I am simply making sure that folks look very cautiously at ALL factors that can determine gross weight, or be affected by aircraft weight, before arbitrarily upping the number....

Paul
Click to expand...

You're right of course, Paul, but I found that a 6A with a Hartzell didn't suffer much as far as control and stability from the extra weight. The Hartzell moves the CG forward enough that I found I could load it to 1950 without exceeding the aft CG limit. In fact, that's why I chose that number -- with two 200 pounders in the seats and 70 pounds of luggage in the back, it was exactly on the aft limit. I also found it was still easily controllable at that weight. But anybody who's flown an RV at the aft limit can tell you that keeping it on altitude was a chore. Other than that, it didn't suffer much. Sea level climb out was still in excess of 1000 fpm. The stall was more radical when it broke, but the difference in stall speed was hardly enough to notice -- maybe 2-3 MPH. Cruise speed was for all practical purposes the same.

I'll admit it didn't feel like a typical RV at that weight. But by the time I'd flown off enough fuel to get it down to 1800 pounds, it was a normal RV again. Certainly not aerobatic, but at 1800 lbs it was a Ferrari again.

Sam Buchanan said:
These numbers would be pretty good if the additional weight was distributed evenly across the entire wing span. But it isn't, it is concentrated in the fuse so the bending forces at the wing/fuse junction increase disproportionately. The numbers above are most likely stating a margin larger than reality
Click to expand...

Sam, I understand what you're saying. 6G at 1350 lbs has a somewhat lower percentage of the 8100 pounds located at the center of the wing than 2131 pounds at 3.8 G's. So I guess we're back to eyeball engineering, since figuring that one out is beyond my meager math skills. Personally, I eyeballed all those bolts and doublers in the center section and knocked off 181 pounds just for good measure.
 
Catto prop

Pierre,
For info what's the pitch/diameter on the catto prop you say suits an 0320 RV6? And is that 150 or 160hp, or some other number!
Thanks,
Craig
 
Buying an RV-6 vs an RV-7

Most of the answers of this thread refer either to the Gross Weight issue or the differences when building one of the two planes.

But can anyone give a list of advantages or disadvantages of either plane when shopping for one already flying? Thanks in advance.
 
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Easy: Cost. 7's are anywhere from 40% to 100% more expensive to buy than 6's once completed. That alone is a huge incentive to stick with a 6 if you're in the used market. I've flown both, and i'd be hard pressed to convincingly argue that one "flies better" than the other. About the only difference was that the 7 was faster, because it had 180HP, and the 6 was slower, because it had 160HP. But we're only talking a few mph here. Both were a delight to fly.

Another factor... If you ever need to remove the wings, that'll be a lot easier on a 7 than on a 6.
 
Biggest bang for the buck...

....definitely goes to the -6. In this economy, you can't go wrong with a -6 or -6A. Many airplanes out there priced below their parts cost. Besides, if you didn't know whether you're flying a -6 or -7, you'd be hard pressed to tell from the cockpit.

The best,
 
Reading the gross weight discussions and the firm stance by some to stick with Manufacturer recommendation reminded me of an old Mooney's VNE. When Mooney engineers were queried as to why the older C models had such a low VNE as opposed to the newer ones (given that they use the same exact wing, spar and vast majority of fuselage). The explanation went that they initially tested it to only 188 mph because it was quicker, cheaper, easier and didn't fly that fast anyway. As they tested further on newer models with more HP varieties both VNE and yellow arc went up dramatically. Remember, this was certified stuff.
We're all aware of Vans preferences for light, simple, lower HP airplanes. The gross weight setting simply reflects this, it was never a definitive, heavily tested number.
 
Flybuddy2 said:
We're all aware of Vans preferences for light, simple, lower HP airplanes. The gross weight setting simply reflects this, it was never a definitive, heavily tested number.
Click to expand...

And that's exactly it. And those of us who have been around these planes long enough.............know it!

L.Adamson --- RV6A with "classic tail" & wings built like a tank..
 
TThurston said:
I know very little myself, but I just read this article, and wonder if it applies at all to this issue of gross weight:

http://www.vansairforce.net/safety/2nd_98.pdf
Click to expand...

It's all relative. I've seen a Cub & Stearman do a mighty quick 180 degree reversal from downwind to final............ that would probably put any RV into the ground quickly. All depends on weights and wing loading, but not so much on structure in this case.

Of course, right off the bat, you'll find that a RV6 does not land like a Cessna 172, especially a 6 with a C/S prop. I don't even think that my 6A knows what ground effect supposably is... :)

It's either flare at the exact right time with power off, or keep a bit of power in. It doesn't float at all. There is just no big Cessna wing overhead, and a C/S prop that wants to decelerate quickly.

L.Adamson --- RV6A
 
I agree with Bill Wightman (post 25) that a wing failure will probably happen midspan 'tween the aileron and flap. So what can be done to "beef up" this apparent weak spot?
Perhaps one piece lower wing skins(.040) , add one or two more ribs?
Couldn't add enough weight to be of any consequence.

Opinions Please.

Glenn Wilkinson
 
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