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  #11  
Old 06-07-2018, 11:31 PM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
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Alan,

Yup!

Cheers,

Vac
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RV-4 2112
Niceville, Florida
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  #12  
Old 06-08-2018, 06:47 AM
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ronschreck ronschreck is offline
 
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Quote:
Originally Posted by luddite42 View Post
It's interesting how complicated the RV community often makes issues that don't otherwise exist in the general flying community. No aerobatic pilot I've ever known, including myself, looks at their airspeed indicator and does a mental calculation of Va based on their flying weight, then using that information to ensure the structural safety of the airframe when pulling. They just know the G limits of the airplane and know what 4G vs. 6G vs. 8G, etc. feels like. They know how to pull the right G for the speed they are flying through feel and experience. Va is meaningless for aerobatic pilots. If slowing down to Va in strong turbulence makes you feel better, by all means. IMO, it just has little significance to actual "maneuvering" unless you are a very mechanical fly by numbers engineer type. But those types don't make for very good aerobatic pilots.

Some of us acro pilots even push nearly as hard as we pull. For airplanes with asymmetric +/- G load ratings, you think anyone thinks about Va when inverted? Ever seen an aerobatic aircraft designer publish a different set of numbers for Va in the negative G realm? Relax, feel, and fly the airplane. And there is no aerobatic maneuver that calls for fully deflecting the elevator anywhere near Va.
If you said this while sitting among a group of experienced aerobatic pilots enjoying a few beers, well you would probably get a few head nods and "that's right on brother" in response. But that's not the case. Many who are reading this thread have never been inverted and had no idea that a snap roll doesn't require full deflection of the elevator and/or rudder. And they have no idea what 4 or 5 Gs FEELS like. I will strongly take issue with your assertion that "Va is meaningless for aerobatic pilots." The finer point of knowing the exact Va for your given weight may be academic but respecting Va is just as important in my book as respecting Vne or maximum G.

One thing we both agree on: your first sentence!
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Ron Schreck
IAC Director and National Judge
RV-8, "Miss Izzy", 2200+ RV Hours
Track Me *** Gold Hill Airpark (NC25)
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"Flying is the art of throwing yourself at the ground and missing."
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  #13  
Old 06-08-2018, 07:46 AM
Southern Pete Southern Pete is offline
 
Join Date: Jul 2015
Location: England
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To me this is all a little back to front. Va is a number generated from formulae specified in the certification standards, FAR23, CS23, etc. During the design stage it is one of the parameters that informs the design team of the loads the aircraft should be designed to withstand. For a certified aircraft (in general) the designer must demonstrate to the certifying authority (eg FAA) the requirements of the certification standard are met. For an experimental most designers use FAR23 to guide their design.

Once in service this is all academic, particularly for an experimental. Va is the speed at which the aircraft should just be able to generate enough lift to reach the max g limit. When the ASI of an RV-7 says 142mph will the wing stall at 6g? Seems unlikely for a whole host of real world factors. Who could predict what the stall load factor would be, might be higher, might be lower.

When flying in severe turbulence should I restrict the speed to Va - seems like a wise move, but what is severe turbulence? How do I tell when I'm about to encounter it?

When flying at above Va should I limit control inputs to less than full deflection available? Who would think full control (particularly pitch or yaw) is a good idea at Va? In a fully aerobatic aircraft perhaps, in an RV probably an unwise choice. When above Va should I avoid a combination of control inputs, yes - again seems like a wise choice. Is Va a magic number? No, of course not.

The real takeaway is perhaps that Va is well below the typical cruising speed of any RV, and so care must be taken with abrupt control inputs.

Pete

Last edited by Southern Pete : 06-08-2018 at 07:48 AM. Reason: typo
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  #14  
Old 06-08-2018, 07:55 AM
luddite42 luddite42 is offline
 
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Quote:
Originally Posted by ronschreck View Post
If you said this while sitting among a group of experienced aerobatic pilots enjoying a few beers, well you would probably get a few head nods and "that's right on brother" in response. But that's not the case. Many who are reading this thread have never been inverted and had no idea that a snap roll doesn't require full deflection of the elevator and/or rudder. And they have no idea what 4 or 5 Gs FEELS like. I will strongly take issue with your assertion that "Va is meaningless for aerobatic pilots." The finer point of knowing the exact Va for your given weight may be academic but respecting Va is just as important in my book as respecting Vne or maximum G.
Maybe I should clarify - I agree all pilots should know and respect Va and not fully deflect anything above that speed. I'm just saying the realities of learning and flying aerobatics leave Va with little practical value. You mention snap rolls. Nearly all aerobatic aircraft have a Va speed that is significantly higher than its recommended max snap speed, including RVs. Nobody should assume Va is OK for doing snaps even if they think snaps are done by fully deflecting the elevator, which they are not. Good instruction and self education takes care of that issue. You can't fix pilots who don't take that approach.

Regarding not knowing what 4 or 5G feels like, this is all part of the learning process. But aerobatic instructors do not teach as if, "OK now we are below Va and can try a maneuver". Not much can be accomplished at Va with two up in most aerobatic trainers. You quickly learn what G feels like and how hard to pull. G meters certainly help with this. If someone wants to get a feel for a new airplane by first starting below Va before pulling, then I can't fault anyone for that. It's just not the way aerobatics is generally taught, and you learn so quickly in one flight how to handle the controls properly, that's it's not really an issue. And anyone with even the most rudimentary level of aerobatic experience has no real reason to reference Va for maneuvering, since as I mentioned before, there is no maneuver that calls for anywhere near full elevator deflection near Va. Snaps are the closest thing and I've already mentioned that snap speed and Va don't correlate.

Just trying to ensure the RV crowd doesn't overcomplicate the acro flying...I mean they are already busy looking at their AOA every time they pull.

Last edited by luddite42 : 06-08-2018 at 11:51 AM.
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  #15  
Old 06-10-2018, 08:09 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
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Default Variable Limitations

Hi Luddite!

Since we’ve still got folks losing control of airplanes and removing structural parts due to handling error, I think there may be some benefit in discussing these topics and glad Carl brought it up. For folks so inclined, learning to fly aerobatics is the single best way to explore the flight envelope; so it sounds like other than semantics, we’re in violent agreement

Every fighter pilot I know, including myself, knows what their speed is before applying G, and makes a mental calculation of how much G to apply after the lift vector is either set for a straight pull, or what my G limit is if I’m rolling and applying G. I even know where my speed is relative to corner velocity (a much more practical application of Va). Van is adamant about “smooth application of G” as am I, I just quantify it by onset rate. All that may sound complicated at first blush, but as you wisely state, after you develop a feel for it; it becomes second nature. It’s actually just a different way to think about handling than you might be used to, and might help one or two folks conceptulize the concepts. Physics is physics and I’ll always defer to the right answer or a better way to describe things!

RV’s are different from other many civilian types insofar as G limits, Vne and Va actually vary. In many cases, these variations can be designed out of an airplane (or operational restrictions can be placed on it); but since our community likes speed, our airplanes have a wide speed band, low drag, are each a bit different, and don’t come with a detailed flight manual, it’s incumbent upon the pilot to know what the limits are when “pulling on the pole” whether those limits are structural or aerodynamic.

Because I’m not the best pilot I know, it helps me to keep the airspeed indicator and G meter in my cross check and AOA cues help me precisely nail L/Dmax and on speed. I’m confident there are folks that can precisely manage Ps with just their finely calibrated elbow and butt, and I hope after some more practice, I might be one of ‘em.

Sincerely,

Vac

PS: I’d be happy to discuss over a beer how snap maneuvering correlates structurally with asymmetric maneuvering speed. I’ll be up at OSH and happy to buy!
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Last edited by Vac : 06-10-2018 at 07:41 PM.
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  #16  
Old 06-11-2018, 12:07 PM
luddite42 luddite42 is offline
 
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Any discussion is good of course, but I think this talk of mental calculations, corner velocity, L/D max, etc. overcomplicates and muddies the waters on how pilots are supposed to use Va in a practical sense when it comes to actual maneuvering. I'm still unable to glean concise and clear advice from this thread unless (consistent with my simple mindedness) the only useful application of Va during aerobatic maneuvering is to recognize that yes you are in fact either above Va and can possibly bend/break something if you have zero feel for what you're doing and pull like a gorilla...or no you are in fact at or below Va and will not pull the wings off if you handle the controls like you have zero feel and no clue what you're doing.

Again, I just don't know any aerobatic pilots who have ever even considered Va while doing acro. It's all about G load and feeling for what G load is most efficient for what we're after, but airframe protection related to the very specific Va number doesn't enter the equation. We simply don't exceed the G load limits regardless of airspeed. Maybe fighter pilots are different. Regarding LD max, this is not necessarily always the goal, depending on what you're trying to accomplish in your aerobatic maneuvering. But again, I'm not connecting this separate topic to Va. If you are letting a newbie or some kid yank your airplane around, it might be wise to limit your speed to Va in case they handle the controls like they're playing a video game, despite your best efforts at briefing them.

Regarding max recommended snap speeds, I've never thought about that in the context of asymmetric G/load and maneuvering speed. Never seen any analysis on it either. Interesting question. Snaps put high loads on the tail and longerons even if min. G is used to initiate a snap. "Rolling G" is easier to visualize and analyze in terms of G load plus aileron use, but snap dynamics are different, since they are not aileron driven and snaps very quickly break and unload. Aerobatic aircraft suitable for snapping typically list a recommended max snap speed and pilots should respect that regardless of what the higher Va (asymmetric or otherwise) number is.

Last edited by luddite42 : 06-11-2018 at 12:24 PM.
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