eric_marsh
Well Known Member
I have been thinking of building a RV-7 but the more I look at the 9 the more attractive it looks. I realize that it is not designed for areobatics but is it suitable for some occasional less intense loops and things?
Van's Air Force
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G loading limits in a 9
- Thread starter eric_marsh
- Start date
G loading in a RV9
Why on earth would you think that it might be ok to perform "loops and things" in a aircraft not stressed for aerobatics if you only did them occasionally? It only takes one time to break them. It's true that done correctly almost any aircraft capable of flying can be looped and rolled but it leaves little margin for error. Are you such a skilled aerobatic pilot that you are incabable of making a mistake? Is anybody?
Do yourself and Van's a favor and either build an 7 or build a 9 and refrain from aerobatics, they are both exceptionaly well designed aircraft.
Chuck Ross
Why on earth would you think that it might be ok to perform "loops and things" in a aircraft not stressed for aerobatics if you only did them occasionally? It only takes one time to break them. It's true that done correctly almost any aircraft capable of flying can be looped and rolled but it leaves little margin for error. Are you such a skilled aerobatic pilot that you are incabable of making a mistake? Is anybody?
Do yourself and Van's a favor and either build an 7 or build a 9 and refrain from aerobatics, they are both exceptionaly well designed aircraft.
Chuck Ross
eric_marsh
Well Known Member
I don't "think" anything. I was unable to find that information on the Van's site so I asked here. After some more digging I did find what I was looking for.
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L.Adamson
Well Known Member
By now (from your second post), It appears that you've seen the the 9 is not rated for any loops or rolls, although I've known it to be rolled a time or two.
But here are a few comparisons between my 6 (not exactly a 7, but close enough) and a 9. I have around 70 9A hours, and fly my 6A along with the 9 on many cross country trips.
The 9 will land slower. About 10 mph slower. Nothing wrong with this, and could be a benefit in a serious situation. It's power off descent speed is also lower. This is all due to it's longer wing and airfoil.
But while the 9 lands slower, it also climbs slower, and is slower on the top end.
Then you find the items that are more the same. There is 1" difference in "wiggle room" height between my 6 and the 7/9's. At 6'1", I just haven't been able to find it or notice. Both the 6 & 9 will fall through the flare to a hard landing with constant speed props if you don't pay attention. The 7 & 9 will also float a long way with fixed pitched props and too high of a landing speed.
Fuel efficiency. My 6A with it's 0360 can do just as well as a 9A with it's 0320, if we both fly at conservative airspeeds. This is kind of a surprise, but is factual, as I've compared with several "well built" 9's. However, as said before, I can still climb and out run the 9, if desired.
So in a nut shell, go with the 7 for any kind of aerobatic thoughts. Both are excellent airplanes.
L.Adamson --- RV6A
eric_marsh
Well Known Member
Thanks for the reply. Sounds like the RV-7 may be my best choice. I was attracted to the idea of greater fuel efficiency but you seem to have more or less negated that.
My gut feeling is that 90% of the time or more the RV-9 would be a fine choice, but if I do want to explore the world of aerobatics somewhere down the road it would eliminate that possibility.
My gut feeling is that 90% of the time or more the RV-9 would be a fine choice, but if I do want to explore the world of aerobatics somewhere down the road it would eliminate that possibility.
RV-9A top end slower?
"...and is slower on the top end".
Is that true at altitude as well? I would have thought the "9A" would allow it cruise faster at altitude than a "6" or "7" due it it's higher aspect ration wing at simliar power setting...is that not true?
Thanks for the education...
Doug Lomheim
90116; electrical / FWF
"...and is slower on the top end".
Is that true at altitude as well? I would have thought the "9A" would allow it cruise faster at altitude than a "6" or "7" due it it's higher aspect ration wing at simliar power setting...is that not true?
Thanks for the education...
Doug Lomheim
90116; electrical / FWF
Keep in mind that it is really no surprise that an RV-6A with an O-360 will out climb and out run an RV-9A with an O-320.
If you compare an exact same engine / prop combination installed on an RV-9A and an RV-7A with the airplanes finished to an equal level of quality and with the same empty weight, The RV-9A will take off and land shorter, will climb initially climb about the same but then do better than the 7 at higher altitudes. At high cruising altitudes (above 8500') the 9 will be as fast or slightly faster (depending on how high you go). The RV-7A will be slightly faster (about 3 MPH) if comparing top speeds at lower altitudes.
As for doing aerobatics in an airplane not designed to aerobatic load limits... I liken it to auto racing and the decision whether to wear a helmet or not. Someone with good racing skills could compete in many races without a helmet and never have an problem (we hear this all the time..."I have done such and such in my RV-9 and have never had a problem").
The helmet is there as a safety net in case something goes wrong. Aerobatic load limits in a way are the same as a helmet. They give you some added safety margin in case something goes wrong. I have never talked to a person that has done much aerobatics in an RV that hasn't eventually had a maneuver go totally bad. They aren't all scary stores, in fact very few are, but they were all in RV's that are approved for aerobatics. Same story's in an RV-9 with its much reduced safety margin and the story's might sound very different.
L.Adamson
Well Known Member
Within the boundaries of 7500 msl to 9500 msl, what I said stands. We are at a 4200' airport altitude to start with. When on cross country flights of three or four aircraft, I have a tendency to head up to 2000' higher (10,500 for instance) , just because I'd rather look at panaramic mountain scenery rather the constant lookout & radio transmissions for nearby aircraft. I don't have good comparison figures for flights that may range from 10,500 - 12,500 for the entire trip.
And FWIW, these comparisons are between airplanes with carbs & ROP, but aggressively leaned for altitude.
L.Adamson -- RV6A
L.Adamson
Well Known Member
And this is why we eagerly await the first flight of Bill R.s (N941WR) RV9 ..... re-born with it's new and much more powerful engine!
I can see that RV smile now!...
L.Adamson
L.Adamson
Well Known Member
But in a way, I've got the best of both worlds. I can out climb and outrun with my extra twenty horses. My plane is even 43 lbs heavier. Yet I can match fuel efficiency if flown conservantly............which I usually prefer not to do.
I would like to see a comparison between mine and an 0360 equipped 9, but we'd both have to have C/S props.
L.Adamson --- RV6A
In my mind, it is not even relevant to say that "my 6A can out run an RV-9A" when comparing performance of the different models, if they do not have the same engine / prop. combination.
That is not much different than saying my 180 HP RV-6A can outrun a 160 HP RV-6A. Something to be expected I think.
Yes and no... If you're comparing full-throttle operation, then yes, the comparison is moot. But if you're comparing fuel flow at equal airspeeds, or have a way to determine that you're both at the same output power when flying side-by-side, then the comparison is totally relevant. If you're flying a 180HP RV-6 throttled back to 150HP, and a 150HP RV-9 wide open, you've got a fair comparison (assuming the same pitch and diameter of prop). The only difference is that the -6 is carrying an extra XX pounds due to the slightly heavier engine.
The air isn't stopping to read "O-320" or "O-360" on the data plate as it rushes past...
which means you also need to fly at the same referred weights which is the Gross Weight of the plane divided by sigma ( the ratio of current air density/standard sea level air density). otherwise you cannot determine which plane is more or less "efficient". Flying a referred weight profile normalizes the effects of both weight and density altitude which are significant.
Defining what you mean by efficiency is a good idea too. I like Knots/GPH at equal W/sigma. If these planes were a little faster we'd have to account for compressibility as well.
Defining what you mean by efficiency is a good idea too. I like Knots/GPH at equal W/sigma. If these planes were a little faster we'd have to account for compressibility as well.
There is the problem... an RV-6A with an O-360 and an RV-9A with an O-320 would never have the same propeller, particularly if they were fixed pitch.
My post wasn't meant to argue whether an O-360 powered RV could operate as efficiently as an O-320 powered one. It was in the context that Larry often posts that his O-360 powered RV-6A can out run an O-320 powered RV-9A...nothing very surprising about that. I say put the exact same engine and prop in both and load them to the same weight and performance differences will swing to the RV-9A's favor.
N941WR
Legacy Member
Eric,
Back to your question. The -7 is an updated -6 and the -9 is an updated -6 with a different wing & HS. Not only is the -9's wing longer and skinnier than the -7, it has a semi-fowler flap. Meaning the flaps move aft as they deploy.
Van's is known for posting accurate numbers with regard to the performance of their aircraft. Compare the -7 & -9 numbers and you will understand what Scott is saying. Even a 200 HP -7 takes longer to get off the ground than a 160 hp -9. This is the wing at work. ROC is listed as the same for both the 160 hp -7 and 160 hp -9. 75% cruise speed for the -7 is 5 mph fast than the -9, call it a draw in real world flying. (In the big swinging #$#@ contest, the -6A with a CS prop is blazing fast and can out run and climb an SR-71.
)Now that that is settled for the last time, the question is acro or not?
The -9 is much quicker than any factory built plane you may have flown, other than a factory acro bird like a Pitts or some hot rod monoplane acro steed. While the -9 is not as sensitive as the short wing RV's, it still light and responsive enough on the controls to see a Cessna or Piper pilot over control them at first. This makes it fun for yanking and banking, within the G limits of the -9 design.
Your question about the acro capability opens up a can of worms. I know of more than one -9 that has been rolled and at least one that was looped (Not mine BTW). The -9 is stressed for 4.4G's positive, so here is the question. If it takes a 3 to 3.5 G pull to start the loop in that aircraft, it would be very easy to pull more than that if your CG was slightly aft of ideal, not aft of the limit. Then on the down side of the loop you have to pull out, again more G's. These planes are very slippery and it would be easy to let the speed build up on the back side and pull more G's than you should.
Most pilots seem to only think about the wing when talking about G loads. Let us not forget about that little wing in the back is also subject to some good G loads. The long HS on the -9 is strong but it is LONG and thus subject to greater bending moments than the short HS on the -7.
The airplane you are going to spend years and thousands of dollars building will be your plane, build what you want, equip it the way you want, and fly it the way you want.
Good luck with your decision.
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L.Adamson
Well Known Member
That really isn't the point, though. I have the reserve power to outclimb and outrun the 9 with it's 160, yet I can throttle back & still be as stingy on fuel.
We're also carrying near identical loads. That makes my performance overall.........the better.
L.Adamson --- RV6A
It will still be a few months before my new RV-9A with a 260 HP fuel injected Lyc IO-540 is flying, but once it is I am sure I will be able out climb and out run you but I will still be able to throttle back and match your fuel economy; and the extra power will easily offset the extra weight...
Finley Atherton
Well Known Member
I realize that the RV9 was not "designed" for aerobatics however the RV9 and the RV6 both have a max Utility category weight of 1600 lb.(+4.4G/-1.75G), which means they can both take the Utility category G loads at 1600 lb. So why is it OK to have an approved aerobatic weight of 1375 lb for the RV6 but no similar approved aerobatic weight for the RV9. If they can both handle the same G loads at 1600 lb why can't they both handle the same G loads at 1375 lb.
Fin
9A
Fin
9A
N941WR
Legacy Member
Scott,It will still be a few months before my new RV-9A with a 260 HP fuel injected Lyc IO-540 is flying, but once it is I am sure I will be able out climb and out run you but I will still be able to throttle back and match your fuel economy; and the extra power will easily offset the extra weight...
What are you thinking?! For the same price and not much more weight you can have an angle valve 300 HP IO-540.
And don't forget the four bladed constant speed prop.Oh, wait, that was the same argument I made when I elected to replace my O-290-D2 with an O-360.
n5lp
fugio ergo sum
Climb rate and speed are indeed two aspects of performance, but "overall" there are many others.
A big big one is landing speed. Some others are glide ratio, sink rate and high altitude efficiency.
the_other_dougreeves
Well Known Member
At what point is an airframe "designed for aerobatics"? Would you perform aerobatics in an airframe with safe load limits of +5g / -3g? Why or why not?
TODR
TODR
L.Adamson
Well Known Member
It will still be a few months before my new RV-9A with a 260 HP fuel injected Lyc IO-540 is flying, but once it is I am sure I will be able out climb and out run you but I will still be able to throttle back and match your fuel economy; and the extra power will easily offset the extra weight...
Can't wait! By, then my turbine/ four blade powered Rocket should be done! Always wanted a tail wheel!!!
L.Adamson -- RV6A
I realize that the RV9 was not "designed" for aerobatics however the RV9 and the RV6 both have a max Utility category weight of 1600 lb.(+4.4G/-1.75G), which means they can both take the Utility category G loads at 1600 lb. So why is it OK to have an approved aerobatic weight of 1375 lb for the RV6 but no similar approved aerobatic weight for the RV9. If they can both handle the same G loads at 1600 lb why can't they both handle the same G loads at 1375 lb.
Fin
9A
Any thoughts on this question?
n2prise
Well Known Member
MY RV-9A...
What a thread! I seem to remember a post a while back about a guy who tried to spin his RV-9A and got into an inverted flat spin. He recovered, but also learned a lesson about Roncz airfoils like the one on the RV-9/9A.
I did spin recovery training in 1992 as a student pilot in a Cessna 152. I knew I was not designed for aerobatics, so forget about the airplane I finally built.
Even though I live in the east, not near the Rocky Mountains, my long cross-country cruising is all done in the 11,500-13,500 MSL range for the better efficiency of the wing of my RV-9A, and the favorable winds aloft. The last time I flew to Denver was in 2006 and I was lucky that day with only 10 MPH headwinds. The trip home a week later was with 30 MPH tail winds. The leaner mixture settings up there and the smoother ride are what the Roncz airfoil wings are all about.
I have made winter trips to Florida starting from Chattanooga past Atlanta with 50 MPH tailwinds, then 30 MPH down to Jacksonville, FL. After that, the winds in the peninsula of Florida loose any real jet stream advantage, most of the time. My last trip to central Florida November 7, 2009 had 30 MPH winds at pattern altitude coming in from the Atlantic Ocean which was over 50 miles away.
As for the guy with the 260 HP Comanche engine, that one will be a hand full. You will definitely need to have a big battery in the back behind the baggage wall. I saw a super 7 with TWO big Concord batteries back there. That one is shown on my web site about two months before it was completed. Look at this page: http://www.n2prise.org/solberg1.htm
His web site linked from that page is out of service.
What a thread! I seem to remember a post a while back about a guy who tried to spin his RV-9A and got into an inverted flat spin. He recovered, but also learned a lesson about Roncz airfoils like the one on the RV-9/9A.
I did spin recovery training in 1992 as a student pilot in a Cessna 152. I knew I was not designed for aerobatics, so forget about the airplane I finally built.
Even though I live in the east, not near the Rocky Mountains, my long cross-country cruising is all done in the 11,500-13,500 MSL range for the better efficiency of the wing of my RV-9A, and the favorable winds aloft. The last time I flew to Denver was in 2006 and I was lucky that day with only 10 MPH headwinds. The trip home a week later was with 30 MPH tail winds. The leaner mixture settings up there and the smoother ride are what the Roncz airfoil wings are all about.
I have made winter trips to Florida starting from Chattanooga past Atlanta with 50 MPH tailwinds, then 30 MPH down to Jacksonville, FL. After that, the winds in the peninsula of Florida loose any real jet stream advantage, most of the time. My last trip to central Florida November 7, 2009 had 30 MPH winds at pattern altitude coming in from the Atlantic Ocean which was over 50 miles away.
As for the guy with the 260 HP Comanche engine, that one will be a hand full. You will definitely need to have a big battery in the back behind the baggage wall. I saw a super 7 with TWO big Concord batteries back there. That one is shown on my web site about two months before it was completed. Look at this page: http://www.n2prise.org/solberg1.htm
His web site linked from that page is out of service.
pierre smith
Well Known Member
Let's try, Jeff...
In the first place, the longer wings of a -9 have more arm, to more easily bend at the same loading as a -6.
Secondly, I don't know where the 6G requirement to be aerobatic 'certified' originated....but there have been many, many aerobatic performances in standard/utility category aircraft by well-known guys like Bob Hoover in a Shrike Commander and another guy I watched in a Beech-18 at Osh last year.
Boeing 707's have been rolled as have Lears, Citations and my boss in his Cessna 210, plus his Cessna Agwagons and 'Trucks, none of which are built or designed for aerobatics.
The caveat here is that a newbie pilot trying aerobatics in a lower "G" designed airplane, has little margin for errors. Wings have been pulled off airplanes by guys trying to emulate an aerobatic routine by a highly qualified pilot, such as the Bonanza pilot in Georgia who pulled the wings off with four aboard several years ago. He had seen a performance at Sun 'n Fun and just "knew" he could do it too.
Old pro's will arguably say about aerobatics in airplanes like -9's and Skyhawks, etc..."If they have wings, they can do aerobatics". True, only if there's a qualified pilot at the controls...remember, wings have been pulled off RV's that were built to +6 /-3...an RV-8 with two aboard comes to mind, as well as Pitt's stressed for even more ultimate G's.
Best,
In the first place, the longer wings of a -9 have more arm, to more easily bend at the same loading as a -6.
Secondly, I don't know where the 6G requirement to be aerobatic 'certified' originated....but there have been many, many aerobatic performances in standard/utility category aircraft by well-known guys like Bob Hoover in a Shrike Commander and another guy I watched in a Beech-18 at Osh last year.
Boeing 707's have been rolled as have Lears, Citations and my boss in his Cessna 210, plus his Cessna Agwagons and 'Trucks, none of which are built or designed for aerobatics.
The caveat here is that a newbie pilot trying aerobatics in a lower "G" designed airplane, has little margin for errors. Wings have been pulled off airplanes by guys trying to emulate an aerobatic routine by a highly qualified pilot, such as the Bonanza pilot in Georgia who pulled the wings off with four aboard several years ago. He had seen a performance at Sun 'n Fun and just "knew" he could do it too.
Old pro's will arguably say about aerobatics in airplanes like -9's and Skyhawks, etc..."If they have wings, they can do aerobatics". True, only if there's a qualified pilot at the controls...remember, wings have been pulled off RV's that were built to +6 /-3...an RV-8 with two aboard comes to mind, as well as Pitt's stressed for even more ultimate G's.
Best,
L.Adamson
Well Known Member
The wing, turbulence & the shakes
A very scientific test...
A friend of mine who owns a 9A, and I (RV6A), have come to an agreement.
If we were blind folded & flying in either smooth or turbulent air, it would be very difficult to determine which airplane we were in, due to flying smooth, or the shakes. We both have time in each others aircraft, as well as just flying on many cross country flights together.
We both have the same seats, have flown at low and high altitudes, and both airplanes have flown through horrible turbulence at the same time. In the end.... his wife get's just as sick of turbulence, as does mine...
L.Adamson --- RV6A
A very scientific test...
A friend of mine who owns a 9A, and I (RV6A), have come to an agreement.
If we were blind folded & flying in either smooth or turbulent air, it would be very difficult to determine which airplane we were in, due to flying smooth, or the shakes. We both have time in each others aircraft, as well as just flying on many cross country flights together.
We both have the same seats, have flown at low and high altitudes, and both airplanes have flown through horrible turbulence at the same time. In the end.... his wife get's just as sick of turbulence, as does mine...
L.Adamson --- RV6A
the original question...
I'd like to explore just a little further, if we could. I understand that the RV-9 was not designed or intended for acro, while the other models (except for the 12 and 10) were. I understand that the wing and tail skins are thinner and that the wings and HS are longer = greater bending moment in G loading. The spar attachments are different than either the -6 or the -7 as well.
But - Like was posted earlier, the -9 and the -6 share similar G limits at "utility weights." Why, then would a -9 not have the same +6 / -3 G limits, if the weight were held down even further, like it is with the aeorbatic weight on the -6?
There may well be a reason. There are smarter airframe design voices here than me. But, in an academic discussion, "don't do acro in a -9, it wasn't designed for it" leaves some questions.
I'd like to explore just a little further, if we could. I understand that the RV-9 was not designed or intended for acro, while the other models (except for the 12 and 10) were. I understand that the wing and tail skins are thinner and that the wings and HS are longer = greater bending moment in G loading. The spar attachments are different than either the -6 or the -7 as well.
But - Like was posted earlier, the -9 and the -6 share similar G limits at "utility weights." Why, then would a -9 not have the same +6 / -3 G limits, if the weight were held down even further, like it is with the aeorbatic weight on the -6?
There may well be a reason. There are smarter airframe design voices here than me. But, in an academic discussion, "don't do acro in a -9, it wasn't designed for it" leaves some questions.
Part of the problem is that it may be harder to hold a -9 to 1375 lbs. That's one FAA-sized occupant and 25 gal of fuel. That puts the CG in the aft 1/3 of it's normal range.
Is the allowable CG range altered for a -6 when operating at aerobatic weight? I.E. is the range narrower?
Is the allowable CG range altered for a -6 when operating at aerobatic weight? I.E. is the range narrower?
Andy Hill
Well Known Member
Well, apart from the other issues, some simple maths would show:
RV-6 cleared to +6g at 1375lbs (Aerobatic Category) - what equivalent at 1600lb? Answer +5.16g. So your:
the answer is they cannot handle the same at 1600lbs, the RV-6 can handle more. Just there is not a "category" for +5.16g. so it is downgraded to the Utility limits...
Just a guess as to part of the answer
Andy
Mel is exactly right. It is much more than simple load limits. Manuevring stability is a great example, which is Stick force / g-load. Airfoil, CG, elevator control power, mechanical gear ratio from stick to elevator, etc.. all affect Manuevering stability. Many airplanes with fairly high load limits have nearly neutral manuevering stability when flown at certain CG/DA configurations. You might not want to find out at the back half of a loop that your airplanes stick force drops really low as the g-load increases. Why? because stick force provides the cueing that tells you to ease off the stick. If it goes light or even negative (which it can) even an experienced pilot can then overstress the plane.
Some on this thread will argue that its been done 10000000's of times and therefore its ok. I have a couple of words for that approach but don't want to get booted off...unless the plane (YOUR plane) has been designed and TRULY tested you will never know where the handling qualities cliffs are. Leaving it to the randomness of all your buddes flight hours is very risky as it doesn't ensure the condtions for the day you decide to "try it" have been verified as safe. C'mon, think about it, we are building wings and control surfaces in our garages and not in a jig or controlled environment. Every little twist, every little angular difference creates an opportunity for disimilariaty in results between airplanes and flight conditions. Please do not let someone EVER convince you that because they do it, or their buddies buddy does it, that it will work for you in your very unique plane.
If you approach flying YOUR plane aerobatically (not acrobatically, which is what circus clowns do) in a well thought out, systematic approach and limit to low g manuevers after a thorough test program, I tend to agree that any plane can fly aerobatically within the limits of its pilots training, flight and handling qualities envelopes.
Some on this thread will argue that its been done 10000000's of times and therefore its ok. I have a couple of words for that approach but don't want to get booted off...unless the plane (YOUR plane) has been designed and TRULY tested you will never know where the handling qualities cliffs are. Leaving it to the randomness of all your buddes flight hours is very risky as it doesn't ensure the condtions for the day you decide to "try it" have been verified as safe. C'mon, think about it, we are building wings and control surfaces in our garages and not in a jig or controlled environment. Every little twist, every little angular difference creates an opportunity for disimilariaty in results between airplanes and flight conditions. Please do not let someone EVER convince you that because they do it, or their buddies buddy does it, that it will work for you in your very unique plane.
If you approach flying YOUR plane aerobatically (not acrobatically, which is what circus clowns do) in a well thought out, systematic approach and limit to low g manuevers after a thorough test program, I tend to agree that any plane can fly aerobatically within the limits of its pilots training, flight and handling qualities envelopes.
Robert M
Well Known Member
I had the same feelings when I went for the Van's curtisey flight. I went up in the -7 because I was convinced that was what I wanted. That changed when I sat down and gave it real serious thought. "What kind of flying do I do and will I do?" The choice was clear, I'm an RV-9 style of pilot. It has been said by many others on this Forum, build the plane that best suits your style of flying. I'm building a -9. When it comes time for me to want to do loops and rolls (you mentioned 10% of the time), I'll ask a friend to take me up in his/her -7 and play.
I'm not real versed on the in's and out's of the performance of the -7's vs the -9's vs the 6's or 8's., so when I was reading some of the earlier posts, it kinda sounded like some of the comparisons were more like apples to oranges or maybe even grapefruits to bananas rather than apples to apples.
Again, Bill R. said it and I'm saying it - it's YOUR plane, build the one that best suits YOUR style of flying. If you want more speed and some aerobatics, build the -7/A with a 200 hp engine and throttle back for a more efficient cruise.
my opinions only.
eric_marsh
Well Known Member
Well, I just bought a -6 kit. It's close enough to a -7 and I paid $.50 on the dollar. Guess I've got something to do in my spare time for the next year or two.
