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  #41  
Old 10-08-2010, 03:24 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by n5lp View Post
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.
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.)


Quote:
Originally Posted by JonJay View Post
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?
Quote:
Originally Posted by JonJay View Post
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!
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.
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RV-6A (aka "Junkyard Special ")
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  #42  
Old 10-08-2010, 03:50 PM
Bill Dicus Bill Dicus is offline
 
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Originally Posted by DGlaeser View Post
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
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!
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  #43  
Old 10-08-2010, 04:15 PM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by Bill Dicus View Post
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!
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.
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  #44  
Old 10-08-2010, 04:22 PM
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rvmills rvmills is offline
 
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Quote:
Originally Posted by Bill Dicus View Post
I too think fuel should always be included in the flying weight for acro unless there is very hard evidence to the contrary.
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).

Quote:
Originally Posted by Bill Dicus View Post
Funny that neg "g" is not really comfortable but is a little addicting, at least to some folks! YMMV!
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
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Bob Mills
RV-6 "Rocket Six" N49VM
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  #45  
Old 10-09-2010, 09:34 AM
Bill Dicus Bill Dicus is offline
 
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Default G's

Bob: Pls see PM.
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  #46  
Old 10-09-2010, 10:20 AM
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az_gila az_gila is offline
 
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Question Which section...

Quote:
Originally Posted by JonJay View Post
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.
....!
...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...
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  #47  
Old 10-09-2010, 06:35 PM
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rvmills rvmills is offline
 
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Quote:
Originally Posted by Bill Dicus View Post
Bob: Pls see PM.
Bill, no new PMs recvd, and looks like your inbox is full (u popular guy!)

Cheers,
Bob
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President/Sport 47/49, Sport Class Air Racing
President, Formation Flying Inc (FFI)
Flight Lead, Lightning Formation Airshows
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  #48  
Old 10-10-2010, 02:50 AM
Bob_pipedream Bob_pipedream is offline
 
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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...
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  #49  
Old 10-10-2010, 07:15 AM
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Alan Carroll Alan Carroll is offline
 
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Default maneuvering speed

Quote:
Originally Posted by rvbuilder2002 View Post
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.
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.
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  #50  
Old 10-10-2010, 09:04 AM
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Default Final Inspetion and Flight Test, Section 15

Quote:
Originally Posted by az_gila View Post
...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...
My manual is dated on the bottom of each page as follows.
6515.DOC 5/22/97, page 15-17
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