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  #11  
Old 09-20-2017, 08:43 AM
luddite42 luddite42 is offline
 
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Originally Posted by czechsix View Post
I wonder if you'll be happy with how the -14's airfoil works inverted. I recall years ago hearing Van say that one reason he selected the 23000 series NACA section for the 3/4/6/7/8 models is because it works reasonably well inverted. I suspect the -14 airfoil won't do too well inverted since it had very different design goals (originally designed for the -10). Anybody have any data points on how it flies inverted?

The mission of the 14 is more geared toward comfortable XC and oh by the way you can also do loops, rolls, and spins, but if you're wanting to do more serious acro including negative G I'd recommend a 7 or 8.
It may not cruise efficiently under negative G but that doesn't mean the airfoil will not work fine inverted for the brief periods of negative G that RV pilots will ever do. What do you mean by "work well"? I guarantee it will fly inverted just fine. Just takes some forward pressure is all. RV pilots aren't gonna care about how efficiently the RV airfoil pushes around a corner under negative G, since about 0.01% of RV acro pilots have ever even done that anyway. These are not advanced level airplanes. A J-3 Cub also flies OK inverted. The low negative G potential of the RV is more of a limitation than the airfoil.
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  #12  
Old 09-20-2017, 08:51 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by luddite42 View Post
It may not cruise efficiently under negative G but that doesn't mean the airfoil will not work fine inverted for the brief periods of negative G that RV pilots will ever do. What do you mean by "work well"? I guarantee it will fly inverted just fine. Just takes some forward pressure is all. RV pilots aren't gonna care about how efficiently the RV airfoil pushes around a corner under negative G, since about 0.01% of RV acro pilots have ever even done that anyway. These are not advanced level airplanes. A J-3 Cub also flies OK inverted. The low negative G potential of the RV is more of a limitation than the airfoil.
I think Mark's comment is related to the fact that the RV-14 has a different airfoil from the rest of the aerobatic RV's. Until someone tests it (Van's did not) it is an unknown what the inverted flight characteristics will be.
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  #13  
Old 09-20-2017, 09:21 AM
luddite42 luddite42 is offline
 
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I think Mark's comment is related to the fact that the RV-14 has a different airfoil from the rest of the aerobatic RV's. Until someone tests it (Van's did not) it is an unknown what the inverted flight characteristics will be.
Did Vans ever do full testing on the other RV models? Don't recall seeing Van ever publish flight test info on all the inverted spin modes for the 3/4/6/7/8. I know he farmed out regular upright spin testing on the RV-6. Never saw anything in more depth.
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  #14  
Old 09-20-2017, 10:51 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Did Vans ever do full testing on the other RV models? Don't recall seeing Van ever publish flight test info on all the inverted spin modes for the 3/4/6/7/8. I know he farmed out regular upright spin testing on the RV-6. Never saw anything in more depth.
Nope.

The aerobatic RV's have always been advertised as positive G, sport aerobatic airplanes.
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  #15  
Old 09-20-2017, 06:11 PM
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czechsix czechsix is offline
 
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Originally Posted by rvbuilder2002 View Post
I think Mark's comment is related to the fact that the RV-14 has a different airfoil from the rest of the aerobatic RV's. Until someone tests it (Van's did not) it is an unknown what the inverted flight characteristics will be.
Right. I don't know what kind of inverted aerobatic flying the OP has in mind, or what his experience level and expectations are. So I was simply pointing out that the -14 may not be the best platform if he's serious enough about doing sustained negative G flight to bother putting inverted fuel & oil systems in it. I've no doubt it will fly inverted though...
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  #16  
Old 09-20-2017, 08:49 PM
luddite42 luddite42 is offline
 
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Right. I don't know what kind of inverted aerobatic flying the OP has in mind, or what his experience level and expectations are. So I was simply pointing out that the -14 may not be the best platform if he's serious enough about doing sustained negative G flight to bother putting inverted fuel & oil systems in it. I've no doubt it will fly inverted though...
No RV is anywhere close to the "best" aerobatic platform, and I'd definitely be willing to bet that the -14 will serve any RV acro pilot just as well as any of the others. Why speculate that it "may not" be? That's just baseless discouragement.
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  #17  
Old 09-21-2017, 01:51 AM
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czechsix czechsix is offline
 
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No RV is anywhere close to the "best" aerobatic platform, and I'd definitely be willing to bet that the -14 will serve any RV acro pilot just as well as any of the others. Why speculate that it "may not" be? That's just baseless discouragement.
Rick, you'd lose that bet for sure! The -14 most certainly will not serve any RV acro pilot just as well as any of the others. The reason Vans offers so many aircraft models is to cater to the different desires and priorities of the sport pilot community. As already pointed out the -14 design is more geared toward comfortable XC and like all designs there are resulting compromises and trade-offs. It has heavier control forces and is not as agile as the other single and two-seat aerobatic RV models. And yes it has a different airfoil originally designed for a 4-seat, non-aerobatic XC aircraft, so it's not 'baseless discouragement' to question whether it's the best RV to build if inverted flight is an important goal of the OP...it's relevant information that he may not know, and might appreciate learning. If he chooses to proceed with a -14 with inverted systems, great...he'll do so knowing that he may be the first and hopefully he'll give us a PIREP on it when it's flying.
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  #18  
Old 09-21-2017, 07:25 AM
luddite42 luddite42 is offline
 
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Rick, you'd lose that bet for sure! The -14 most certainly will not serve any RV acro pilot just as well as any of the others. The reason Vans offers so many aircraft models is to cater to the different desires and priorities of the sport pilot community. As already pointed out the -14 design is more geared toward comfortable XC and like all designs there are resulting compromises and trade-offs. It has heavier control forces and is not as agile as the other single and two-seat aerobatic RV models. And yes it has a different airfoil originally designed for a 4-seat, non-aerobatic XC aircraft, so it's not 'baseless discouragement' to question whether it's the best RV to build if inverted flight is an important goal of the OP...it's relevant information that he may not know, and might appreciate learning. If he chooses to proceed with a -14 with inverted systems, great...he'll do so knowing that he may be the first and hopefully he'll give us a PIREP on it when it's flying.
Not sure if you have significant experience flying negative G acro in many (or any) aircraft, but if you did, I think you'd realize these potential "inverted flight characteristics" are way overblown in the context of the type of maneuvers RVs are suitable for in the first place. During which phase of what type of maneuver do you think the -14 could possibly be significantly more deficient than the other RVs in? Holding an inverted point on a hesitation roll? Cruising inverted cross country? Inverted turns? Inverted spins? Pushing negative G corners to or from vertical? Outside snap rolls? Not serious about that last one, but I guarantee you a 210HP, 1200 lb, 200 mph low drag airplane will fly inverted just fine for as long as you want (fuel/oil system dependent) for any type of maneuver suitable for any other RV. Worst case, the -14 requires slightly more forward pressure inverted than the others, but so what...you gotta push anyway. And you do have something called trim. Try doing negative G stuff in a Great Lakes. It does it fine, but makes you work harder. I guarantee you the -14 would be a dream compared to that one.

But it's likely the -14 will not appeal as much as the others to those who have specific acro interests, and not because of any inverted flight characteristics. It'll be because it's a heavier, less nimble, slower rolling airplane that just might not be as much fun to toss around even though it's likely just as "RV acro" capable assuming the pilot does their job well.
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  #19  
Old 09-21-2017, 01:18 PM
Bill Dicus Bill Dicus is offline
 
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Default Inverted flight

A British RV-8 owner published results of a very complete spin series in the RVator. The plane exhibited completely normal entry and recovery characteristics for upright and inverted spins when within the specified weight and balance envelope. I have found RV-8 to have excellent inverted flight characteristics. There is a relatively small required change in deck angle when going from upright to inverted. The main limitation for me is the three negative G limit that the RV-8 has. In the heat of the moment and with adrenaline flowing, it would be very easy to exceed this 3G limit.
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