RV-6 strength Verses RV-7

[az_gila]

Thank you...

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

...I found it in section 15 of my older, undated manual under "G-load testing" on page 44.

Hidden in the text is the aerobatic gross weight of 1375 pounds for +/- 6 G.

The same paragraph also stated that the negative G limit is -6, but it was not necessary to flight test to that number....

The section also answered the previous post with this definition...

By, definition, maneuvering speed is the maximum speed at which full and abrupt controls can be applied. It is also the minimum speed at which limit G-load can be produced.

The speed does apply to all control deflections according to this definition.

Again, I do not know the date of this version of the manual (I have several later versions too...)

 

[rvbuilder2002]

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.

It is generally specified by the aircraft manufacturer (in the case of an RV, the designer).

It gets much more complicated for roll because even though the lifting wing is producing more lift, it has an artificially lowered angle of attack because the vector of the relative wind is from slightly above, and the descending wing has an artificially higher angle of attack because the relative wind vector is from slightly below. One of the load conditions done when testing the wings is to simulate this. I believe it is to verify that the Va value for pitch will be a safe value for roll also. Rudder is a whole different issue because it is related to lateral loads on the vertical stab and the tail cone. Once again, I believe that tests are done to verify that the one specified speed value (though requiring adjustment if flying below gross weight) is also applicable to rudder input.
Maybe Kevin or one of the other Aero Engineering guys can clarify, but my understanding is that only one Va speed is ever specified (pilots aren't expected to remember 3 different speed #'s.

A simple definition of Va can be found here

 

[n5lp]

...Rudder is a whole different issue because it is related to lateral loads on the vertical stab and the tail cone. Once again, I believe that tests are done to verify that the one specified speed value (though requiring adjustment if flying below gross weight) is also applicable to rudder input.
Maybe Kevin or one of the other Aero Engineering guys can clarify, but my understanding is that only one Va speed is ever specified (pilots aren't expected to remember 3 different speed #'s.

A simple definition of Va can be found here

The simple definition is the one I think just about all pilots have known and believed. I think it probably is what applies to simple airplanes such as the RV series. However AA587, the Airbus A300 that crashed in New York brought to light that it is not necessarily so. The vertical stabilizer failed on that airplane at a speed less than maneuvering speed because of rudder application. I think that woke a lot of people up and it something to consider that alternate side to side movements of the rudder can build up large loads to the vertical stabilizer.

NTSB report

 

[4kilo]

Va

Larry,

Just for clarification, the traditional limitation still applies to the airbus, and it can pass that. However, the Va definition has never allowed rapid movements from one stop to the other stop. In other words, moving the rudder abruptly from neutral to full deflection will not damage the airplane at or below Va, but moving the rudder from full deflection in one direction rapidly to the other stop may put the aircraft well outside the Va structural envelope. This is what happened with the airbus. The rudder had been deflected one direction and a large sideslip angle established, then the crew deflected the rudder fully in the other direction while the sideslip angle was still on the airframe. The resulting loads caused a failure of the vertical stabilizer.

Pat

 

[Snowflake]

Maybe Kevin or one of the other Aero Engineering guys can clarify, but my understanding is that only one Va speed is ever specified (pilots aren't expected to remember 3 different speed #'s.

A simple definition of Va can be found here

That's a good definition.

My recollection from school is that for light aircraft of conventional configuration (wing in front of tail, engine up front), the elevator is usually the limiting control... ie. Va for aileron deflection only is higher. Someone raised a good point about limit-to-limit control movements... Va definitely assumes straight and level flight and one control deflection to it's stop, not backup and forth repeatedly. I don't recall ever doing a Va calculation for a rudder deflection... I don't remember why.

 

[sailvi767]

Larry,

Just for clarification, the traditional limitation still applies to the airbus, and it can pass that. However, the Va definition has never allowed rapid movements from one stop to the other stop. In other words, moving the rudder abruptly from neutral to full deflection will not damage the airplane at or below Va, but moving the rudder from full deflection in one direction rapidly to the other stop may put the aircraft well outside the Va structural envelope. This is what happened with the airbus. The rudder had been deflected one direction and a large sideslip angle established, then the crew deflected the rudder fully in the other direction while the sideslip angle was still on the airframe. The resulting loads caused a failure of the vertical stabilizer.

Pat

There is still quite a bit of controversy over that accident. There have been several uncommanded rudder movements on that series aircraft. There is also a design error involved. I don't remember the exact numbers but if I recall at the accident airspeed the bus needed only about 30lbs of rudder application through a travel of about 1.5 inches to produce full rudder deflection. Most aircraft in that class take 70 to 100 lbs of rudder effort and about 4 inches of travel for full deflection. Depending on the prior aircraft experience of the pilots easy to see how they could get a lot more rudder then they intended.

George

 

[Rbb469]

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

Huge difference IMO!

 

[moosepileit]

Flown with even skill and similar weights, they are equal. Similar to the S2-A vs. Christen Eagle.

Flown by a "better" pilot in one, either is fine for beating the other- tailchase, judged-aerobatic box, what have you.

In 4 cylinders, weight is the #1 enemy. Both are too slippery to compare to traditional 4 cylinder aerobatic two place mounts, there is not the safety margin and drag for botching and recovering without early and skilled intervention even with a constant-speed prop ripped to idle in fine pitch.

Slippery & Strong= Extras and similar.

Even proven, certified, un-faulted Super Decathalons have shed wings from just parasitic drag overload, not g in botched rolls becoming a high speed, low-g split- S.

Same airfoil and around 2' more span on the 7 from the tip change, same ballpark roll rate, same g onset, if same thrust to weight- same outcome. The 7 may have less absolute margin above its specs due to all the listed reasons for being a later generation. The weight capacity of the 7 adds utility toward passenger weight plus fuel within the aerobatic limits. Higher Va is also a plus, even just 5-10 mph sure comes in handy. 134mph for the 6 and 142 for the 7, right?

So, dual, hands down the 7 specs win. Solo, could easily be a draw, drag races aside.