[Flyfalcons]

Why beef up what has been working?

 

[N941WR]

Why beef up what has been working?

Exactly. The problem with beefing up one part, you move the stress to another part, that may fail where before, nothing would fail.

Make structural modifications very carefully.

 

[pierre smith]

Yep, the -8 that came apart....

...several years ago, broke about mid-span....it also was determined by metallurgical analysis of the remains that it had been subjected to in excess of 9 G's.

Best,

 

[eric_marsh]

To answer the original question, I would have liked an RV-7 but I am building a 6 because I was able to save so much money on a kit that had never been started on that I can begin building now rather than having to wait until I can afford a 7 from Vans. It will take me longer to build the 6 but I'm OK with trading money for time.

 

[Danny7]

It would be a great thing to see both designs flipped over on a jig and load-tested to failure!

why would they get flipped over? I've seen some load testing done, it was with the flying surfaces upright iirc. i have some video and pictures, i'll dig it out and watch

 

[Kevin Horton]

why would they get flipped over? I've seen some load testing done, it was with the flying surfaces upright iirc. i have some video and pictures, i'll dig it out and watch

If you do the load testing with the wings upright, you need hydraulic rams and a complex arrangement to spread the load, pushing upwards on the lower wing surface. If you flip the wing upside down, you can use the force of gravity pulling on sand bags which are piled on the lower wing surface. This is a much cheaper solution than hydraulic rams, so it is the preferred method for general aviation load testing.

 

[steve91t]

6 or 7. Which one is better?

I hate using the word "better", but I wanted to ask some questions.

Can you use a 200 hp io360 like you can in the 7?
Is the 6 faster than the 7 at the same hp?
Is the slightly smaller size really an issue?

I'm sure flight characteristics are too similar to say which one is preferred.

I know the 7 has the quick build option which means it will probably be built better. Harder to make a mistake.

I just wanted to get some opinions. I've read that some people actually prefer the looks of the 6 over the 7.

Anyway, I really want a rocket someday, but my wife doesn't want to sit in the back. I thought I would look into 6 and 7s a little more. My dad has a beautiful 7 with a 180 hp and 3 blade cs prop. So, I know what the 7 is like, just not sure how different the 6 is.

Thanks,
Steve

 

[ColoCardinal]

6 or 7

Steve,
Here's the link to Van's specs on both planes:

http://www.vansaircraft.com/public/rv-6per.htm

http://www.vansaircraft.com/public/rv-7per.htm

The 7 has a higher VNE, if I recall. that will be the true determining factor as to which is faster. Not enough to really matter. There is truly very little difference between the two once they are built. Slight difference in stall charachteristics, speed, useful load, but they are all very slight.
If I were buyng one, I'd look seriously at a 6 as they are typically a little less $. If building one (I am), I'd get a 7 because the 7 is MUCH easier to build.

 

[twsurveyor]

6 or 7. Which one is better?

Can you use a 200 hp io360 like you can in the 7?
Is the 6 faster than the 7 at the same hp?
Is the slightly smaller size really an issue?

Steve

1) Can you use a 200 hp io360 like you can in the 7?
Yes, although not reccomend by Van's!

2) Is the 6 faster than the 7 at the same hp?
Too close to call!

3) Is the slightly smaller size really an issue?
2' more wing span and 2" more leg room. Other than that, it's the same
airplane!

I, personally, like the 6 wing spar design better than the 7. It just looks stronger although Van will tell you it's not. I like the added utility of the 7 better (a few extra pounds or gross weight and 4 extra gallons of fuel). Given a choice, all being equal, I'd go with the 7. Your fortunate in that you have a choice. When I started building the only choice was a 3, a 4 or a 6!

Long and short of it, you can't go wrong with either airplane!

 

[Flying Scotsman]

It just looks stronger although Van will tell you it's not.

I don't want to sound argumentative, but this is not how engineering works. First, the designers/engineers of the designs will (should) have done both analysis and testing to verify their designs are sufficiently robust. They do not go by what "looks stronger". If the engineers who designed these planes tell me that one design is stronger (and we'd have to be careful to make sure we understand what "stronger" really means) than another, seems to me that one should accept their expertise here. There are many ways to skin a cat, and what looks to a non-expert like a better solution may, in fact, not be.

Second, *both* designs may be "strong enough" to meet the requirements. Part of engineering is to design and build things which meet a set of requirements, in efficient, elegant ways. There's no need to build them "stronger" if a given design is "strong enough". E.g., if design X meets a +9g ultimate load design requirement, there's zero point in designing and building it to meet a +10, or +12 or +20 or +100g limit, even if one *could* do such a thing.

Unless and until you have both the engineering analysis and the test data in hand, it's all basically guesswork and reverse engineering. Reverse engineering is fine, IF you're an expert.

Anyway, hope that didn't come across as too pedantic or argumentative...

Steve

 

[Jerry Cochran]

QB vs. SB

I know the 7 has the quick build option which means it will probably be built better. Harder to make a mistake.

I would not assume that at all. I'd prefer a meticulous builder over a factory overseas anytime. Mine was a QB and was certainly not mistake free by any stretch. Just one for instance were the mismatched firewall/engine mount holes.

 

[Snowflake]

I don't want to sound argumentative, but this is not how engineering works. First, the designers/engineers of the designs will (should) have done both analysis and testing to verify their designs are sufficiently robust. They do not go by what "looks stronger". If the engineers who designed these planes tell me that one design is stronger (and we'd have to be careful to make sure we understand what "stronger" really means) than another, seems to me that one should accept their expertise here. There are many ways to skin a cat, and what looks to a non-expert like a better solution may, in fact, not be.

There's a lot of info on the strength of the RV-6 wing if you do a search here for "increasing gross weight" and things like that. There's been a lot of discussion, and a lot of armchair reverse-engineering by experts and yokels alike.

There's also been anecdotal reports of even Van himself saying that the -6 wing was over-designed. Looking at the carry-through structure and the number of bolts, vs. how it was done on the -7, I would tend to agree although I haven't done the calculations to find out. There are reports that Van used to give letters upon request authorizing increases in gross weight on the RV-6 to 1800lb, same as the -7. This would suggest that at some point Vans realized that yes, it was overdesigned and could be just as strong as the -7.

But at this point, there is no good business reason for Van to continue authorizing an increase (if one was ever authorized... Nobody has been able to produce a copy of one such letter, despite repeated requests here and elsewhere). To do so would cut into sales of the -7. It would also encourage a lot of -6 owners to start flying with an extra 200lb on board, without a lot of thought as to how it would be distributed... Nobody wants that liability risk, so now when people ask, the answer is that the gross weight is what it is. If you want more, build a -7.

The reality is that a -6 is a great airplane. If you're not a heavy person, and your partner isn't either, the two of you will have a blast in it. We've had full camping gear (less cooking equipment) for two people and we easily flew between the CG limits, at both ends of the fuel budget. A -7 would let us carry more, but we don't really need to.

 

[L.Adamson]

It would also encourage a lot of -6 owners to start flying with an extra 200lb on board, without a lot of thought as to how it would be distributed...

In reality, there are a lot of 6s that have been carrying that extra 200 lbs. At least for 17 years that I know of. Of course we do figure in the proper W&B..........which amounts to no problem at all. Gross weights ranging from 1750 - 1850 lbs. are common. I've seen as high as 2000.

L.Adamson --- RV6A

 

[Flybuddy2]

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,

not sure why you are so against those who accept higher gross weight because of hundreds of others who have tested it in use with no problems vs accepting a canopy with less actual use because "numerous others tested it".
The initial 6 tests at factory were done at 1600 because of Vans strong feeling toward minimalistic light weight aircraft short field performance, not because caalculations said that was the limit. If a higher weight were used it would have showed longer take off runs and slower speeds. Vans admitted to the higher gross being ok when the RV7 numbers were set. The 6 & 7 are very similar with the main diff being a longer wing and weaker spar on the 7 . G stress further out on the arm and less integrity are not conducive toward supporting more weight under load but that is exactly what was done (on paper) with the 7.

 

[Snowflake]

In reality, there are a lot of 6s that have been carrying that extra 200 lbs. At least for 17 years that I know of. Of course we do figure in the proper W&B..........which amounts to no problem at all. Gross weights ranging from 1750 - 1850 lbs. are common. I've seen as high as 2000.

And none of them have any engineering data to show that it's safe... They're just taking it on faith that if the last guy who did it is still alive, it might be okay.

 

[L.Adamson]

And none of them have any engineering data to show that it's safe... They're just taking it on faith that if the last guy who did it is still alive, it might be okay.

If that's what you would like to believe.........

Go back & read up on the issue for 15 years or so.

L.Adamson --- RV6A

 

[woodmanrog]

I have owned and flown 3 RV6 models. A 6 with 150HP and a Catto prop, a 6A w/160 HP and a Catto prop and our new baby a 6A with 180HP and a Sensinich metal FP prop. I have flown 7's, 9's and a 10. Here is my simple opinion. Being "full figured", 220lbs, and having flown with at least 1800 lbs gross on all of my planes, I can only say that they all fly great. I still prefer the Catto prop over the metal one as it is lighter and tends not to windmill when the power is shut down thereby making landings a little more predictable. Quoting a friend of mine," the only time my plane acted like a real airplane was when I was loaded at over 1800lbs and took off at 6000 ft density altitude." I am always more concerned with proper CG loading than actual amount of weight. (Of course this means within reasonable limits) Higher weights just mean that I will have a takoff roll almost as long as a Cessna 172. That being said I do prefer 180HP for getup and go. I still can't justify a CS prop. After all that, just get one and go. You won't be sorry with any RV of choice.

 

[L.Adamson]

I have owned and flown 3 RV6 models. A 6 with 150HP and a Catto prop, a 6A w/160 HP and a Catto prop and our new baby a 6A with 180HP and a Sensinich metal FP prop. I have flown 7's, 9's and a 10. Here is my simple opinion. Being "full figured", 220lbs, and having flown with at least 1800 lbs gross on all of my planes, I can only say that they all fly great. I still prefer the Catto prop over the metal one as it is lighter and tends not to windmill when the power is shut down thereby making landings a little more predictable. Quoting a friend of mine," the only time my plane acted like a real airplane was when I was loaded at over 1800lbs and took off at 6000 ft density altitude." I am always more concerned with proper CG loading than actual amount of weight. (Of course this means within reasonable limits) Higher weights just mean that I will have a takoff roll almost as long as a Cessna 172. That being said I do prefer 180HP for getup and go. I still can't justify a CS prop. After all that, just get one and go. You won't be sorry with any RV of choice.

I've been told............that at sea-level altitudes, the difference between CS & FP is less noticeable. I personally wouldn't know.

At my airport altitude of 4607', it's easy to get 6000' density altitudes. And with my CS prop & around 1800 lbs gross, the difference between my aircraft & a Cessna 172 on the takeoff is dramatic. The CS prop also allows landings to be precision. That's one of it's main advantages over FP, as it's so easy to manage the airspeed.

L.Adamson --- RV6A, 180 HP, Hartzell CS

 

[twsurveyor]

"Reverse Engineering"

In reality, there are a lot of 6s that have been carrying that extra 200 lbs. At least for 17 years that I know of. Of course we do figure in the proper W&B..........which amounts to no problem at all. Gross weights ranging from 1750 - 1850 lbs. are common. I've seen as high as 2000.

L.Adamson --- RV6A

I am so glad that we've finally had this "reverse engineering" thing explained to us! but,.............. I still think the 6 spar LOOKS stronger!

BTW, I saw a 6A at OSH, a couple of years ago, that had a GW of 2,150 lbs on the data plate!

 

[Snowflake]

If that's what you would like to believe.........
Go back & read up on the issue for 15 years or so.

Well, I admit that i've only been following the issue for 12 years. So I may be a little out of touch... In all that time, I have not seen one complete analysis of an RV-6 loaded above 1600/1650lb. Lots of people assuming that 6G at 1600 equals 5.somethingG at 1800, because the math works out, but that's not the only consideration.