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workky

Member
Hey guys, im a lurker, i dont even own an airplane, i suck

I was curious though. What makes a 7 stronger than a 9?

Me and a partner are kicking around the idea of purchasing one or the other, but cant decide which one

I like strong!!!, but really dont plan on doing any aerobatics at this time. I say that lightly. Because i could watch top gun and go out and do some rolls.

But why is the 7 stronger than the 9 or rated higher than the 9 in G's?

Like the corss country of the 9 but like the strength of the 7
 
Different wing designs... One is built for aerobatics, the other cross country performance.

Doesn't make the 9 wing any weaker. It's just rated for normal flight.
 
The -9 has a longer wing and a different (longer) HS.

Unless you are into doing acro, the -9 is plenty strong. If there was an issue with the -9's strength, it would have cropped up by now.
 
"Strong" is not the right way to think about it. Both airplanes are plenty "strong". They do have different "missions" they are optimized for though. Which mission you wish to fly will make a difference in which you choose.
 
Captain_John said:
Don't listen to Bill. He has a 9...

There is nothig that a 9 can do that a 7 can't!

;). CJ
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Except glide substantially farther when your engine fails and land 10 knots slower so that you are more likely to survive the ensuing off field landing! :D:D:D

Seriously, to the OP, this has been hashed out numerous times on this forum. Do an RV-9 vs RV-7 thread search and you'll have plenty of reading.
 
Like others have said here, the wings on the -7 and -9 are not necessarily "stronger" than the other aircraft. The -7 has a wing that is designed to maintain the flow across the top in higher G loading, so it can be flown at higher angles of attack and not loose the "stiction" of the airflow across the top of the wing. BUT... there is some drawbacks to this, like not being as efficient and more "draggy" than other wings. It's a trade-off to get a wing that can fly those higher G numbers.

On the -9 the wing is more of a laminar flow design. Its designed to have a very smooth airflow over the wing, and present a less draggy profile into the wind so its more fuel efficient. Essentially it could fly the same true air speed with less horsepower (and less fuel consumption) as its RV-7 sibling. The larger tail surfaces also combine to give it more positive stability which is highly desired for cross country flying.

They are both fantastic designs, but they are targeted for different missions.

The 7 if you want to go out and do gentlemans acro, as well as a decently capable cross country airplane.

The 9 if you don't really care about acro, but your main mission is a fast, slippery 2 seater for taking on cross countries and being more fuel efficient.

Both wings will give you the same margin of safety if you fly them in their designed envelopes :)
 
CubedRoot said:
The -7 has a wing that is designed to maintain the flow across the top in higher G loading, so it can be flown at higher angles of attack and not loose the "stiction" of the airflow across the top of the wing. BUT... there is some drawbacks to this, like not being as efficient and more "draggy" than other wings. It's a trade-off to get a wing that can fly those higher G numbers.
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I've never really thought along those lines before. "Stiction", eh?

Bottom line is that the -7 airframe is, in fact, stronger. Opinions vary, but numbers don't lie: the -7 is rated to +4.4G at 1800lbs gross weight while the -9 is rated to +3.8G at 1750lbs. Drop it to 1600lbs, at the -7 is rated to +6G while the -9 is rated to 4.4G.

Unless you are doing aerobatics, that should have no practical bearing on your decision though. Both are good airplanes.
 
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CubedRoot said:
...The -7 has a wing that is designed to maintain the flow across the top in higher G loading, so it can be flown at higher angles of attack and not loose the "stiction" of the airflow across the top of the wing.
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I've never seen anything from Vans that supports this claim.
 
Mr Workky,

whats your mission? 7 has more fuel capacity, alittle faster :)eek:) both fly great. I was on the fence about the 7/9 thing for about 2 years, and decided the extra fuel and alittle extra speed was a plus. Just need to finish it!

Tom
 
Captain_John said:
Don't listen to Bill. He has a 9...

There is nothig that a 9 can do that a 7 can't!

;). CJ
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You mean other than cruise at 155 KTAS at 17,500 on 6 gph? Come on out and form up on me, we'll give it a shot... :D

They are both great airplanes, just with slightly different intended missions. The 9 wing is optimized for more efficient cruise at altitude where the 7 was designed with gentlemans aerobatics in mind.
 
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airguy said:
You mean other than cruise at 155 KTAS at 17,500 on 6 gph? Come on out and form up on me, we'll give it a shot... :D

They are both great airplanes, just with slightly different intended missions. The 9 wing is optimized for more efficient cruise at altitude where the 7 was designed with gentlemans aerobatics in mind.
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ChiefPilot said:
Many RVs can do that - it's not that difficult. Most that can probably don't even need to go that high.
Here's an RV-6A doing it at 11k (12.5k DA) on 180hp: https://www.youtube.com/watch?v=dSDvj4cvP8A
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Better get the popcorn! I see where this threads headed! :D
 
airguy said:
You mean other than cruise at 155 KTAS at 17,500 on 6 gph? Come on out and form up on me, we'll give it a shot... :D

They are both great airplanes, just with slightly different intended missions. The 9 wing is optimized for more efficient cruise at altitude where the 7 was designed with gentlemans aerobatics in mind.
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Greg, honestly I've never tried to go that slow in cruise configuration.

I will give it a try on my way to the airshow and let you know how I make out. Are you going to be at the beer thing on Sunday? We can talk there.

:) CJ
 
alpinelakespilot2000 said:
Except glide substantially farther when your engine fails and land 10 knots slower so that you are more likely to survive the ensuing off field landing! :D:D:D

Seriously, to the OP, this has been hashed out numerous times on this forum. Do an RV-9 vs RV-7 thread search and you'll have plenty of reading.
Click to expand...

....Don't forget speed, 9 is faster, more economical, takes off shorter, lands shorter, climbs faster, and allows you to say,"Mine is bigger than yours". :D:D
 
ChiefPilot said:
I've never really thought along those lines before. "Stiction", eh?

Bottom line is that the -7 airframe is, in fact, stronger. Opinions vary, but numbers don't lie: the -7 is rated to +4.4G at 1800lbs gross weight while the -9 is rated to +3.8G at 1750lbs. Drop it to 1600lbs, at the -7 is rated to +6G while the -9 is rated to 4.4G.

Unless you are doing aerobatics, that should have no practical bearing on your decision though. Both are good airplanes.
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Most likely it's related to bending moment at the wing root. The longer wings on the -9 will generate more bending moment for a given amount of lift than on a -7. The design trades g loading for cruising efficiency and somewhat lower stall speeds. And while the lower aspect ratio and different airfoil on the -7 may well be capable of a bit more AOA before stalling (I don't know), that's not a primary driver in the design, nor is it related to g capability.

I've kicked around the idea of making my wingtips quick-swappable and building a pair of raked "cruise" tips for my -7. I could swap them out for longer trips and realize some small efficiency gains, at the cost of giving up some g capability while they're installed. But I'd have to do the engineering on that to make sure I wouldn't be increasing the bending loads outside the original design envelope. I do know it's been done before on a -6.
 
Captain_John said:
Greg, honestly I've never tried to go that slow in cruise configuration.

I will give it a try on my way to the airshow and let you know how I make out. Are you going to be at the beer thing on Sunday? We can talk there.

:) CJ
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Unfortunately no - my airplane is (finally!!) in the paint shop right now and won't be out in time for Oshkosh, and I am completely buried at the office right now (good thing, not complaining) so I'm out for Oshkosh.

As for the performance - I know my 9A is superior to all other aircraft, because it's mine! :D

How's that logic fer ya?
 
airguy said:
Unfortunately no - my airplane is (finally!!) in the paint shop right now and won't be out in time for Oshkosh, and I am completely buried at the office right now (good thing, not complaining) so I'm out for Oshkosh.

As for the performance - I know my 9A is superior to all other aircraft, because it's mine! :D

How's that logic fer ya?
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Lol, I love it!

I always say that there are two kinds of planes out there... RV's and everything else. I suppose we could all say that there are two kinds of RV's also... Mine and everyone else's!

Hahaha

I did a little math. If you take your 155 knots at say... 7 gph (I am not bringing oxygen to Oshkosh, so 7 gpg at 12,500 will have to do), it comes back at a little over 22nmpg. Lets say I plan 160 knots at 8 gph, it comes back at exactly 20 nmpg.

I wonder what happens if I bring the black knob out a little bit farther and dial in your aforementioned 155 knots?

I will let you know what I discover!

:D CJ
 
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You guys with your fully built RV's, bragging about which one is faster and/or more efficient...

And here I am, poking around in my 47 year old Cessna wishing my RV was done. HAH!
 
Captain_John said:
Lol, I love it!

I always say that there are two kinds of planes out there... RV's and everything else. I suppose we could all say that there are two kinds of RV's also... Mine and everyone else's!

Hahaha

I did a little math. If you take your 155 knots at say... 7 gph (I am not bringing oxygen to Oshkosh, so 7 gpg at 12,500 will have to do), it comes back at a little over 22nmpg. Lets say I plan 160 knots at 8 gph, it comes back at exactly 20 nmpg.

I wonder what happens if I bring the black knob out a little bit farther and dial in your aforementioned 155 knots?

I will let you know what I discover!

:D CJ
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....I cruise and plan cross country at 175 knots on 7.3 gph! Not to bad?:D:D
 
PerfTech said:
....I cruise and plan cross country at 175 knots on 7.3 gph! Not to bad?:D:D
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Is that TAS, IAS, CIAS, GS? What altitude? Van's numbers for the 9A (9 is 1-2 MPH different): at 8K DA: Vne = 209 MPH, Top Speed = 195 MPH, 75% Cruise = 187 MPH.

Your 175 knots is right at 201 MPH. That is very close to Vne. There is no way my 9A can cruise at that TAS number. And I have even put more engine in my plane than Van's engineers recommend (Why can't I use a larger engine?, page 4). I have done many GPS speed tests with my 9A at 8K DA. I am pretty much hitting Van's numbers every time I do the tests. If you truly are cruising at that speed I am all ears hoping to hear your secrets. Secrets on how to achieve that cruise speed and secrets on how to protect the airframe structure while traveling in that speed regimen.
 
CubedRoot said:
You guys with your fully built RV's, bragging about which one is faster and/or more efficient...

And here I am, poking around in my 47 year old Cessna wishing my RV was done. HAH!
Click to expand...

We do these things.... because we can! :D
Keep pounding those rivets!
 
RVbySDI said:
Is that TAS, IAS, CIAS, GS? What altitude? Van's numbers for the 9A (9 is 1-2 MPH different): at 8K DA: Vne = 209 MPH, Top Speed = 195 MPH, 75% Cruise = 187 MPH.

Your 175 knots is right at 201 MPH. That is very close to Vne. There is no way my 9A can cruise at that TAS number. And I have even put more engine in my plane than Van's engineers recommend (Why can't I use a larger engine?, page 4). I have done many GPS speed tests with my 9A at 8K DA. I am pretty much hitting Van's numbers every time I do the tests. If you truly are cruising at that speed I am all ears hoping to hear your secrets. Secrets on how to achieve that cruise speed and secrets on how to protect the airframe structure while traveling in that speed regimen.
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....Mine originally performed as yours, right on Van's numbers as well. I have made many subtle changes, and a few not so subtle ones over the years. these changes in drag, along with engine peak performance and many many hours of propeller work culminated in the performance numbers I now achieve. The quoted performance is true airspeed, and I do fly as high as possible when going any real distances. Also I will add this, I do slow down if I begin to feel any turbulence at all. I worry sometimes at these speeds about there being a big, unexpected bump or wind shear that could damage the plane as it is almost at VNE. Thanks, Allan.. :D:D
 
As you can see, both are GREAT airplanes and everyone loves the plane they built. Even thought the -9 is a better airplane, a -7 is still a really good choice. :p
 
PerfTech said:
....Mine originally performed as yours, right on Van's numbers as well. I have made many subtle changes, and a few not so subtle ones over the years. these changes in drag, along with engine peak performance and many many hours of propeller work culminated in the performance numbers I now achieve. The quoted performance is true airspeed, and I do fly as high as possible when going any real distances. Also I will add this, I do slow down if I begin to feel any turbulence at all. I worry sometimes at these speeds about there being a big, unexpected bump or wind shear that could damage the plane as it is almost at VNE. Thanks, Allan.. :D:D
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Sooooo......are you injecting NOS or what? please share, we are all family here right? :rolleyes:
 
RVbySDI said:
If you truly are cruising at that speed I am all ears hoping to hear your secrets. Secrets on how to achieve that cruise speed and secrets on how to protect the airframe structure while traveling in that speed regimen.
Click to expand...

PerfTech said:
....Mine originally performed as yours, right on Van's numbers as well. I have made many subtle changes, and a few not so subtle ones over the years. these changes in drag, along with engine peak performance and many many hours of propeller work culminated in the performance numbers I now achieve. The quoted performance is true airspeed, and I do fly as high as possible when going any real distances. Also I will add this, I do slow down if I begin to feel any turbulence at all. I worry sometimes at these speeds about there being a big, unexpected bump or wind shear that could damage the plane as it is almost at VNE. Thanks, Allan.. :D:D
Click to expand...

bret said:
Sooooo......are you injecting NOS or what? please share, we are all family here right? :rolleyes:
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As I said, "I am all ears"! Speaking from experience with increasing HP on my 9, I don't think increasing HP will get you there. Allen, I would love to know some details on what you modified to reduce drag. I have my ideas although I have yet to implement any of them yet.
 
Allan I've heard you say this before. I still don't believe it. I think you need to check your pitot static system.

:) CJ
 
I apologize for kicking off a firestorm here. I was just curious what made it stronger.

I so appreciate all the responses though, very good info.
I'm not sure what my mission is ' and I think that is my main issue.

The whole point in flying for me is to get somewhere fast, and I have a legitimate business reason for flying an airplane in the SE. By fast, anything faster than sitting in Atlanta traffic.

I really like the fact the 7 is faster and appears to have more useful load, but it might be twitchy on the stick, which I guess is something you get use to.

All though aerobatics are not very appealing to me right now, one day with the proper training it might be fun to roll, and loop. And I could see that happening
 
ok i'll bite

The -9 don't seem to loose their tails at the same rate the -7 do. As a matter of fact, I don't think the -9 has lost it tail yet.

just sayin...... :)
 
workky said:
I apologize for kicking off a firestorm here. I was just curious what made it stronger.
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There is that statement from you again. That is what is "kicking off a firestorm"! To say that the 7 is "stronger" is just not the appropriate way to think about the two planes.

workky said:
I really like the fact the 7 is faster and appears to have more useful load, but it might be twitchy on the stick, which I guess is something you get use to.
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The useful load of the 9 is not necessarily different from the 7. I carry just as much in my 9 as does a 7. There are other weight considerations in addition to useful load to consider also. The CG can potentially be different for the two airplanes. A 7 (or a 9) can end up with CG issues that can affect the useful load of the plane.

As for speed, well, I would expect a 7 with constant speed will out climb my 9 with fixed pitch but as far as standard cruise speed, I fly just as fast in cruise as my 7 buddies and burn less fuel doing it.

workky said:
All though aerobatics are not very appealing to me right now, one day with the proper training it might be fun to roll, and loop. And I could see that happening
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If that is what your mission is then that should drive your decision and that decision would take you to the 7. I think you will be very happy with whatever you choose.
 
Equal

Well most 7s have an 360 and CS in the nose and most 9s a 320.

In my opinion, the longer wings make for slower landing speds and more fuel efficient high altitude cruising. Inwould expect the 7 to be faster down low, higher climb rate and acro.

Pick what you want accordingly.
 
As I already stated earlier, I fly with several buddies that have RV7's. Several with constant speeds and IO-360 setups. One with O-360 and fixed pitch Catto. Climb equally with the fixed pitched 7, although he sometimes has cooling issues where I don't. No question the constant speed guys out climb me. However, when we level out in cruise we will all see similar cruise speeds. When doing same speeds I will end up burning less fuel. They can go faster than I if they increase power and burn more fuel, but then so can I. If we get above 10.5 or especially 12.5 I think I can begin to outpace their speed also. However that has never been put to the test. Truth is the 7 does have a higher top speed than a 9 but not sure how that top speed fairs up high compared to a 9.

Flying back from OSH yesterday with 7 buddy with IO-360 constant speed prop we were side by side for 3 hours. The first half of our flight to our fuel stop at 6500, the rest of the way at 8500 before landing for fuel. Identical speeds the entire way. I burned 21 gallons, he burned 25 gallons.

P.S. Just in case readers have not noted my 9A configuration. I have an IO-340 with Catto fixed pitch 3-blade (68 X 74) prop. Slick mag on left, Lightspeed Plasma II on right; forward facing cold air induction; Vetterman 4 straight pipes.
 
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RVbySDI said:
Flying back from OSH yesterday with 7 buddy with IO-360 constant speed prop we were side by side for 3 hours. The first half of our flight to our fuel stop at 6500, the rest of the way at 8500 before landing for fuel. Identical speeds the entire way. I burned 21 gallons, he burned 25 gallons.[/I]
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Not quite Steve. Remember I didn't fill to the top at Oshkosh due to trying to keep fuel from venting overboard in the heat, but I did at K81. There is no doubt I used more fuel but it wasn't that dramatic. In years past it was more in line with a few tenths per fuel stop. There is no way I burned 4 gallons more in a 3 hour flight. I'd be surprised if it was a gallon.
 
Ok. I stand corrected on yesterday's flight. However in past flights, not necessarily with you, the differences have been more than a few tenths of a gallon. The point I have wanted to get across on this thread is that if someone is looking to build a 9 they can build it to the point where they can fly cross country with 7's and not be left behind in the dust. I still think the fuel burn for the 9 is less than the 7 given comperable flight parameters, however slight they may be. I wish I had a constant speed. Then we could do closer comparisons.

All in all, everyone ends up building what they think works best for them. I don't think anyone looking for cross country flying is going to go wrong with either plane.
 
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RVbySDI said:
There is that statement from you again. That is what is "kicking off a firestorm"! To say that the 7 is "stronger" is just not the appropriate way to think about the two planes.
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Even if it's correct? Structurally, it is definitely stronger. The gross weight and G loading limits show that to be true.
 
Could sell you a lead weight.

Structurally, it would be stronger... But, you probably wouldn't be able to fly it very well. :p
 
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