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  #1  
Old 01-07-2015, 11:54 AM
704CH's Avatar
704CH 704CH is offline
 
Join Date: Apr 2009
Location: Sammamish, WA
Posts: 208
Default Help me understand the advantage of AOA in a 2 seat RV

I understand how AOA works and just don?t understand how great the benefits are for a 2 seat RV. Maybe you guys can help illuminate me. I have AOA in my plane and always use indicated airspeed when landing, when using AOA I might as well be using airspeed since it doesn?t make much of a difference. I know everyone is trying to sell AOA, but I really need help understanding the benefits in an RV. I will say that my AOA does work pretty good as a stall warner, so that is one advantage.

1) AOA makes perfect sense for something like a Pilatus with a large range of landing weights and a higher landing speed. In a big plane, using AOA when landing light vs gross you can really reduce your landing speed. In an RV the weight changes are so minimal they don?t make much difference to me.
2) AOA makes sense for planes with fast landing speeds because due to density altitude and temp changes the variance of AOA due to these factors can greatly help reduce landing speeds.. RV?s don?t have high landing speeds.
3) RVs are bouncy planes and with some thermals on landing your airspeed changes around up to 5 knots anyway with each bounce, so I use airspeed to keep a good safety factor.
4) Maybe RV-10?s have a bit more of a weight change and AOA is more beneficial?

Thanks for any feedback on this topic.
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Sammamish, WA
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  #2  
Old 01-07-2015, 11:57 AM
Mike S's Avatar
Mike S Mike S is offline
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Quote:
Originally Posted by 704CH View Post
I understand how AOA works and just don’t understand how great the benefits are for a 2 seat RV.
I suspect your using the term "2 seat" is exclusive of the RV 4 and 8??
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  #3  
Old 01-07-2015, 12:00 PM
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Infidel Infidel is offline
 
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Scratch that as my opinion has differed.
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  #4  
Old 01-07-2015, 12:09 PM
russcoburn russcoburn is offline
 
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Location: Layton, Utah
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I put one in my RV6 more as a backup instrument for landing speeds if I lost my EFIS or all electrical power by chance. (My airspeed is tied to EFIS in all electric plane). I think it is a better backup instrument than a analog airspeed indicator for that purpose. It's been interesting to adjust and use with stall speeds at different weights. I found my stall speeds varied less than 5-6 mph at min and max weights and full forward and rear CG points so to your point there isn't a lot of variability.
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  #5  
Old 01-07-2015, 12:31 PM
Smilin' Jack Smilin' Jack is offline
 
Join Date: Jan 2011
Location: Cumming, Georgia
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Chad,
You can also use the AOA in case your pitot gets but dont believe that would make a difference in the Skyview system we have. It is handy if you would get distracted while shooting an approach on that GTN you have. It is handy should you get caught in a micro burst. 😃
we use airspeed all the time when flying the problem where AOA has received so much press lately is because of Base to final turns. but the only plane I ever flew which I religiously use an AOA was our 24B learjet. back 30 years ago. In our Challenger 601-3A the AOA is only Valid for full flaps and any other flap setting it is invalid. In our Hawker 800 xp it is handy as it sits infront of your face on the glareshield and works in all flap settings so at night on dark approaches you do not have to be looking down at the instruments you can just pick it up in your field of vision looking out at the runway. So like you state 99 percent of the time it is airspeed.

The problems is with pilots being distracted and when the planes stalls close to the ground there is no margin for recovery.Or stated above on dark night approaches.

Hate to say it but 48 years of doing this for a living the accidents can still pretty much be broken down to how they were in the 60's.

Jack
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  #6  
Old 01-07-2015, 12:40 PM
Sig600 Sig600 is offline
 
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AOA has nothing to do with the size/weight of the airplane. It's the most accurate warning for stall margins, period. On any airplane. Since a wing stalls at the critical angle of attack, even on a two seat RV that means it could be as much as a 20 knot swing, in flight. Your stall speed at the abeam on downwind is going to be lower than it is in a 30 degree bank turn from base to final. You get distracted, lose a gust of wind, inadvertently pull back on the stick a little... You may only change your indicated speed 3-4 knots but you may have increased your stall speed 10 knots. The stall angle of attack however will always remain constant.

That's the simplest example I can give. Plus it's aleady included in most of the pitot/AOA/Efis combos, so it's not like you're going out of your way to install it.

Fly with AOA, and fly the AOA, you'll never need IAS again. If you do any aerobatics you'll really understand AOA and its effects on lift/performance better too.
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  #7  
Old 01-07-2015, 12:41 PM
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rv8guy rv8guy is offline
 
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Try an accelerated stall, and you'll see a big difference from airspeed then.

I'd expect to be more comfortable with low speed close to the stall as well.

Also even a two seater can behave quite differently with one pilot, low fuel vs two passengers at gross wt.
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  #8  
Old 01-07-2015, 12:51 PM
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Bill_H Bill_H is offline
 
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I operate off a 1260 foot grass strip. So every landing is short field. I have a Skyview with AOA. I never like to look down at the screen when landing for either airspeed or AOA indication - and with AOA I don't need to. Because when you get into the yellow range the Skyview starts beeping into the headset. Slow, then faster as you increase AOA. You can get that beeping rate right where you want it, then adjust power/pitch as necessary to keep it there. (I have a dropoff on the approach end and can get some sink there so I'm always ready with the power.)

For conventional landings on a lengthy runway - not really needed. Could save you in that sometimes fatal base-to-final overshoot turn, PARTICULARLY if you have audible output.

I personally think a visual-only AOA indicator is far, far inferior to one with audible output that works as I mention. If you have to be looking down at the AOA you might as well be looking at the airspeed. Yeah, I know you can mount some AOA remote indicators in your field of view but for the reasons mentioned, IMO audible is better.
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  #9  
Old 01-07-2015, 02:37 PM
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akarmy akarmy is offline
 
Join Date: Jan 2005
Location: Auburn, WA
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Quote:
Originally Posted by 704CH View Post
I understand how AOA works and just don?t understand how great the benefits are for a 2 seat RV.
Guess it depends on how you have it setup and if you are using it. For me I've had AOA in both of my 2 seat RV's and use it constantly. I don't fly by IAS anymore during any critical phase of flight.

The key thing is do you need it around our local area when flying at sea level with familiar weights? Not really. But get high and hot while loaded down and it will surprise you how fast you need to be going to keep your margins in place.

I've found that using AOA only for landings makes them very consistent as you always have the same amount of energy at that critical phase so the flare is very similar landing to landing.

I've also really seen the AOA come alive with aerobatics. Top of a loop and as you start to get slow, pull just a touch too much, "angle angle push" lighten up a touch on the elevator and around you go.

For me, it's the best "toy" I added to the build.

The archives are also full of lots of good info on the topic as well.
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  #10  
Old 01-07-2015, 02:49 PM
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Beer30? Beer30? is offline
 
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Location: Longmont, CO
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Default It's all about the stall

Get yourself a copy of Aerodynamix for Naval Aviators, or at least pick one up from the library. To me, it's the definitive text on aerodynamics, which applies if you're flying a Super Cup or the space shuttle.

As others have said, a wing always stalls at the same AOA, but will stall at a different airspeed depending on your gross weight. Also, your airspeed is going to vary with density altitude, the AOA will not. What stall speed are you going to use if you take off from Lincoln NE, and then land in Denver? Do you have an exact number? The AOA will not lie to you, regardless.

Thats it in a nutshell.

David
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