sbalmos

sbalmos

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So this is a scary thought that I had while driving into work this morning. The fact that I'm holding my -9a tail kit order form in my hands hovering over the office's fax machine doesn't help either. :)

Since the -7 is, essentially, a -9's fuselage with -8s wings, has anyone ever considered or done a conversion of a -9 to a -7 by swapping out the wings? Just from a theoretical design perspective, what else is there to change? Mods to the tail, the fuselage side skins and/or bulkheads where the wings are mounted? etc

I'm picking the -9 almost exclusively because I'm a low-time new PPL, doing the usual local jaunts here and there, and some regional travel. Don't need ultimate speed, aerobatics, etc... for now... The "for now" part is where I started thinking whether this might be a possible conversion a few years or so down the road (assuming I'm not building a -10 by then).

Food for thought?
 
Just order the -7. If you are debating this now you'll never be happy later. The empennage is also different between the 7 & 9. The -7 is a great XC plane and just as easy to fly as the -9 and once flying you'll be surprised how fast your hours build up not to mention the flying hours you'll do while building (I hope). Of course I'm biased having had the -7.
 
Buy the 7....

I learned to fly in my 6,don't worry about the hours. It will all work out.:)
 
Get the -7 and don't paint yourself into a corner. It's no more difficult to fly than the -9. You can't convert them except to throw away the tail and start over.

John Siebold
 
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I like the -9, but I also like the -7. Don't buy a -9 because you're afraid to fly the -7. If you can fly one, you'll be fine in the other.

I like the -9 because it's got a different feel.
 
I had the same difficulty choosing - went with 7A. (It's a great airplane - it can make you think you're better than you are.)

With good transition training I don't think low time would necessarily be an issue.

Dan
 
It sounds like you want a 7 and not a 9. Coming from a 9A flyer, I will tell you if this is what you are thinking about maybe you should just order the 7. There are quite a few other differences between the 7 and 9 besides the wings. And the 9 does NOT have an 8 wing. The wing for a 9 is unique. There are enough differences between the two airplanes that conversion could only happen, if it could at all, early on in the build.

In my opinion, you should not be concerned about flying a 7, even if you are a low time pilot. If you are a conscientious pilot who is always trying to better your skills and are paying attention to what you are doing you will have no problems flying the 7. Of course this holds true for any pilot in any airplane.

There is a statement that has been mentioned many times on this site:
BUILD THE AIRPLANE YOU WANT, NOT WHAT OTHERS SAY YOU SHOULD BUILD!

This is a very true statement. If you feel you may want to do something in the future that you feel the 9 will not allow then you may not want the 9. Don't let anyone, including me, tell you what to do. Trust your own instincts and go with what you feel you want in your airplane.
 
Ya Steve, the same old adage is the best - build what I want, not what others say I want.

Ultimately, during one of my brain breaks at work here this morning (read: waiting for a new software build to finish compiling!), I rethought my mission profile and what I want out of the plane. I'm sticking with the -9a. It'd be cool to do the aerobatics and the sheer speed increase of the -7a. But I don't need it for how I see myself flying. Again, it's nice to have, but probably wasted capability.

Soooo... I just faxed in the order for the -9a tail. N112SB is now officially on its way. As Gene Wilder says in Young Frankenstein... What have I done? My God man, WHAT... HAVE... I... DONE??? :D

Yes, I'll be fine. My wallet won't. Let the mayhem begin.
 
Two of the reasons we choose the 9 vs the 7 were its better glide characteristics and its slower stall speed. We spend a LOT of time in the mountains and along the coast. The 9 gives us more glide distance/time and significantly less impact energy (
4140f53f66a68e92afec2389ba289e25.png
).

Sometimes, cruising from point A to point B I kinda like the idea of having a 200HP 7 ... and then we go to the pump... 10 knots probably isn't worth the 4-6 gal/hr it cost to get it...
 
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sbalmos said:
the sheer speed increase of the -7a.
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Using Van's numbers on 160 HP models at 75% power/8000', the -9 does 189 mph, the -7 192 mph. So unless your pulling a -7 with a 200 HP, there is not much difference, especially since many people are using the 180 HP motor in their -9's.
 
gbrasch said:
Using Van's numbers on 160 HP models at 75% power/8000', the -9 does 189 mph, the -7 192 mph. So unless your pulling a -7 with a 200 HP, there is not much difference, especially since many people are using the 180 HP motor in their -9's.
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Agree with this. The difference in speed is really marginal, at least in the practical sense of things. My 9 has the IO-340 that is rated for 180 HP (same as the 360). Perhaps the 200 HP equipped 7's may outrun me but if I choose to run the throttle wide open and forget about the fuel burn My 9A can run just as fast as any other standard configured 7 out there.

Given that though, the great majority of my flying is cruising LOP with the throttle at 70-75% HP. At this setting I see anywhere from 150-165 MPH and burn around 7.0-7.5 GPH. I really think a 7 comparably configured will not perform a whole lot differently.
 
Since the -7 is, essentially, a -9's fuselage with -8s wings, has anyone ever considered or done a conversion of a -9 to a -7 by swapping out the wings? Just from a theoretical design perspective, what else is there to change? Mods to the tail, the fuselage side skins and/or bulkheads where the wings are mounted? etc

Food for thought?
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Although not impossible, it would be very impracticle to attempt a 'conversion' 9 to 7. There are multiple differences in wing & emp attach points that would amount to 30%(?) of a fuse kit panels that would have to be replaced.
 
Yup. So, ultimately, the airspeed numbers are even closer than I remembered and forgot to check on. In reality, I'm giving up aerobatic abilities by going with the -9a. Big deal. ;) Gross simplification probably, but I'll take the -9a's better glide and slow-speed characteristics over aerobatic abilities.

Thanks again everyone! Now for the long wait until the tail kit arrives at my door.
 
I like the larger tanks on the -7 vs -9. I know you can put extra wing tanks on the -9, but after a stern warning not to do so from a reputable Vans person, I would never do that. If long-range cross country was a major part of my mission, that would be an important factor for me.
 
diamond said:
I like the larger tanks on the -7 vs -9. I know you can put extra wing tanks on the -9, but after a stern warning not to do so from a reputable Vans person, I would never do that. If long-range cross country was a major part of my mission, that would be an important factor for me.
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I agree that it would be nice to have the extra 8 gallons that the 7 tanks provides. If it were up to me I would go for extending the fuel tanks. However, on every trip to date that I have flown with my wife she is not interested in flying for more than 3 hours without landing. At my fuel burn that gives me a 1.5+ hour reserve.
 
sbalmos said:
... and the sheer speed increase of the -7a...
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I guess that one has already been answered.

diamond said:
I like the larger tanks on the -7 vs -9...
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This is not even an issue because they are sized for the IO-360 with 200 HP. Since you are most likely to put in a 160 HP O-320, 36 gallons is more than you will ever need.

It sounds like you have figured out what your mission will be, that's a good thing. The -9 is a great flying plane and doesn't give up much to the -7. Best of luck with your project.
 
N941WR said:
..This is not even an issue because they are sized for the IO-360 with 200 HP. Since you are most likely to put in a 160 HP O-320, 36 gallons is more than you will ever need.
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But that same O-320 on a -7 (or an (I)O-360 at 55%;)) will get you another 45-minutes in the air (6 gallons at 8 gph). Even using 75% of 180hp on both airplanes, it's 30 minutes or more. Yes, if you're limited to 3-hour VFR legs, it won't make much difference, but if your mission is 600nm or more, or IFR, that extra 6 gallons might save you a stop, assuming you have the "personal range" for it. I'm not a big acro guy (yet?), so fuel capacity put me over the edge toward the -7.
 
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longranger said:
But that same O-320 on a -7 (or an (I)O-360 at 55%;)) will get you another 45-minutes in the air (6 gallons at 8 gph). Even using 75% of 180hp on both airplanes, it's 30 minutes or more. Yes, if you're limited to 3-hour VFR legs, it won't make much difference, but if your mission is 600nm or more, or IFR, that extra 6 gallons might save you a stop, assuming you have the "personal range" for it. I'm not a big acro guy (yet?), so fuel capacity put me over the edge toward the -7.
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What numbers are you using?
36 gallons divided by 8 GPH gives you 4.5 hour range. Call it 4 hours with a half hour VFR reserve. If you get that low, you can power back even more and stretch that half an hour even longer.

Using Van's numbers you can pull back to 55% power and still fly at over 140 knots for 730 Nautical miles. That is plenty long enough. If you power up to 75%, then the range is 600 Nautical miles (710 statute miles) until dry tanks.

Truth is, very few people fly their RV?s at 75% power, most throttle back smile at the lower fuel burn.

Either way, everyone will have some reason to justify their choice and they are all valid reasons for the decision maker to drop some major coin on the aircraft of THEIR choice.

If you are still undecided in your 7 vs 9 choice, ask Van?s to hold your order until you can arrange a ride in both. I?m not going to tell you the -9 or the -7 is better because it is all about YOUR mission. They are both fine aircraft.
 
N941WR said:
What numbers are you using?...
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I like to plan on a hour reserve, even VFR. 3.5 hours and bit of headwind and you're down to 600nm range. Yeah, you can power back to increase endurance, but regardless of how you fly it, or wherever you set your reserves, the 42 gallons in a -7 will get you farther than 36 in a -9. That made the difference for me, but I'm sure it wouldn't for everyone.
 
sbalmos said:
Soooo... I just faxed in the order for the -9a tail. N112SB is now officially on its way. As Gene Wilder says in Young Frankenstein... What have I done? My God man, WHAT... HAVE... I... DONE??? :D

Yes, I'll be fine. My wallet won't. Let the mayhem begin.
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WHAT? 2 Sierra Bravo cancel your order IMMEDIATELY! You don't even know what you got yourself into :D 9A is big and slow get the 8 forget the 7.
 
longranger said:
I like to plan on a hour reserve, even VFR. 3.5 hours and bit of headwind and you're down to 600nm range. Yeah, you can power back to increase endurance, but regardless of how you fly it, or wherever you set your reserves, the 42 gallons in a -7 will get you farther than 36 in a -9. That made the difference for me, but I'm sure it wouldn't for everyone.
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It may very well make the difference for me, because one of the cross country trips that I plan on making frequently is 920 statute miles. At 55% power in a -9 with Van's numbers, that doesn't happen without a stop. With a -7, it might work with good conditions. You can argue that it's too long a trip without a break, but I might like to have the option to make it in one hop if ever I want. So for me I weigh the advantages of the -7s longer range with the advantages of the -9s slower stall speed and flight characteristics. I'm not interested in acro, so that doesn't factor in.
 
Let's see a show of hands...how many experienced RV pilots fly there plane 5 hours non-stop and land with legal reserves?

longest time in the seat was 3.5hrs is enough for me, 650miles, still had 11gals on board. I've only flown mine 6.5hrs in one day, OSH-8U8, 975nm with headwinds and one stop. From a safety standpoint, I would think a trip that length would be a major mental & physical drain for most pilots.

I built a 7, but could have easily been happy with a 9. My daughter is starting flight lessons so a 9a would have been perfect. Also, the only time I run 75% or above is racing or testing. other times I'm at 6-7gph puttin' around the valley.
 
diamond said:
It may very well make the difference for me, because one of the cross country trips that I plan on making frequently is 920 statute miles. At 55% power in a -9 with Van's numbers, that doesn't happen without a stop. With a -7, it might work with good conditions. You can argue that it's too long a trip without a break, but I might like to have the option to make it in one hop if ever I want. So for me I weigh the advantages of the -7s longer range with the advantages of the -9s slower stall speed and flight characteristics. I'm not interested in acro, so that doesn't factor in.
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If speed/range is your main factor, and there is no other reason for you to go with the 7 over the 9, just put in extended range tanks. There are some great options that are easy to install that will give you an extra 10 gallons or so total. That doesn't seem like much, but it's an extra 1+ hours of flight, which means another 180 miles or so. Line up a 7 and a 9, and if the 7 has to stop for fuel but the 9 doesn't, all of the sudden the "slow" 9 has a much faster trip speed.
 
skelrad said:
If speed/range is your main factor, and there is no other reason for you to go with the 7 over the 9, just put in extended range tanks. There are some great options that are easy to install that will give you an extra 10 gallons or so total. That doesn't seem like much, but it's an extra 1+ hours of flight, which means another 180 miles or so. Line up a 7 and a 9, and if the 7 has to stop for fuel but the 9 doesn't, all of the sudden the "slow" 9 has a much faster trip speed.
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I considered the extended tank option until I had a discussion about it with Vans personnel at OSH last year. They convinced me that this option carries risks that I'm not willing to take; not the least of which is untested spin characteristics.
 
Choice is yours.

I went through the same decision process 4 years ago. Didnt even have my ppl when for the first year or two of building. The slower land, better glide and arguably better cross country platform sold me. I went 9a, have loved every single hour would not change a thing. I like all rvs, but a side by side is way better with a child or wife in my opinino. A tip up is just awesome for views in flight and you just will be amazed at how easy and fun flying in one is. Build what you want, enjoy the stuffin out of it.

After any rv flight a cessna trip is just painful. :D Enjoy the build.
 
Lightin' The Fuse

Why oh why do some 9 apologists try to make the 7 equal to the 9 IF.... This usually is manifested in speeds. The two airframes are different and Van's design intents are different.

No way does a 9 equal a 7 in top end.

The 7 carries more fuel, has greater range - which can often be useful for tankering for price/availability. Cheek/bladder endurance are not the only metric.

The 7 airframe is stronger. Aerobatic abilities aside, Van's limits 9 baggage to 75 pounds, 100 in the 7. That's a very useful difference.

The 9 can fly slower than the 7. It's an efficient climber with a tad higher spec'd service ceiling (take a deeper breath before crossing 14,500). The handling is more docile.

They are different. A lot of the number differences are not great percentage-wise, but they exist.

You pays your money and takes your choice. Yet they're both delightful in their own way.

John Siebold
 
RV7ator said:
Van's limits 9 baggage to 75 pounds, 100 in the 7. That's a very useful difference.
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Not correct. The build manual confirms 100# for the -9. (See p. 14-2 "Maximum Baggage Weight") The structure is built for up to 100#. What you placard it at is dependent on weight and balance numbers. I used some weight on the crush plate to be able to use the full 100#. According to Bruce Reynolds, the 75# Van's originally had advertised was due to the low weight of the very smallest engine.
 
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Of course I am not trying to stir the pot but going on the best figures I can find it appears that a 9A may cruise slightly faster than a similarly equipped 7A.

Vans figures compare the 7A with a Hartzell C/S prop and the 9A with a FP prop.

CAFE figures for the 160 hp factory 9A with a MT C/S prop show about 192 mph TAS at 8,500 ft DA with the engine at 2,605 rpm and 23.7".

Vans gives 189/190 mph TAS for a 160 hp 7A at 8,000 ft and 75%. So maybe the 9A is faster at 75%??? Also factor in that the MT is considered slower than the Hartzell so the 9A with a Hartzell may be even faster again. This is borne out by my 9A with a Hartzell which does 194 mph TAS at 8,500 DA WOT and 2,700 rpm (4 leg GPS spread sheet method).

Much is made of the fact that the 7A with 180 hp can cruise faster than a 9A with 160 hp.
Using the CAFE figures above for the 160 hp 9A and Vans figures for the 180 hp 7A at 75% the difference is about 5 or 6 mph (or about 3 or 4 mph using my figures). So lets be generous and say maybe 5 mph faster for almost an extra gal/hr. :eek:

Fin
9A
 
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Capflyer said:
Just order the -7. If you are debating this now you'll never be happy later.
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Exactly. I had the same concerns when I was deciding what to build. Flying a 7A is not hard. I never thought I would find acro as fun as I now do.
 
Finley Atherton said:
Of course I am not trying to stir the pot but going on the best figures I can find it appears that a 9A may cruise slightly faster than a similarly equipped 7A.

Vans figures compare the 7A with a Hartzell C/S prop and the 9A with a FP prop.

CAFE figures for the 160 hp factory 9A with a MT C/S prop show about 192 mph TAS at 8,500 ft DA with the engine at 2,605 rpm and 23.7".

Vans gives 189/190 mph TAS for a 160 hp 7A at 8,000 ft and 75%. So maybe the 9A is faster at 75%??? Also factor in that the MT is considered slower than the Hartzell so the 9A with a Hartzell may be even faster again. This is borne out by my 9A with a Hartzell which does 194 mph TAS at 8,500 DA WOT and 2,700 rpm (4 leg GPS spread sheet method).

Much is made of the fact that the 7A with 180 hp can cruise faster than a 9A with 160 hp.
Using the CAFE figures above for the 160 hp 9A and Vans figures for the 180 hp 7A at 75% the difference is about 5 or 6 mph (or about 3 or 4 mph using my figures). So lets be generous and say maybe 5 mph faster for almost an extra gal/hr. :eek:
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My 6A with 180HP/Hartzell CS could outclimb and outrun 9As with 160HP & Hartzells. Therefor, a 7 would have to be a slug compared to the 6, if slower than a 9. At the same time, I could power back to get the lower fuel consumption of a 9, while flying at the same speed. I don't know about fuel economy of 200HP powered 7's.....to make any comment.
 
L.Adamson said:
My 6A with 180HP/Hartzell CS could outclimb and outrun 9As with 160HP & Hartzells. Therefor, a 7 would have to be a slug compared to the 6, if slower than a 9. At the same time, I could power back to get the lower fuel consumption of a 9, while flying at the same speed. I don't know about fuel economy of 200HP powered 7's.....to make any comment.
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Hi Larry,

Thought I would get a bite.:)

I never said a 180 hp 7 (or a 6 ) would not out-climb or out-run a 160 hp 9.
I was comparing a 7A and a 9A both with 160 hp using the best figures I could find. I would be interested to see any documented figures you have.

Fin
9A
 
Finley Atherton said:
Hi Larry,

Thought I would get a bite.:)

I never said a 180 hp 7 (or a 6 ) would not out-climb or out-run a 160 hp 9.
I was comparing a 7A and a 9A both with 160 hp using the best figures I could find. I would be interested to see any documented figures you have.
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No documents. We just have a lot of RVs around here for comparison sake.:) I just don't see a point in a 160HP RV7, when the larger engine can be throttled back, for the same fuel savings.

P.S. --- I see that you have a C/S. Good man, and smart too!!! :)
 
L.Adamson said:
No documents. We just have a lot of RVs around here for comparison sake.:) I just don't see a point in a 160HP RV7, when the larger engine can be throttled back, for the same fuel savings.

P.S. --- I see that you have a C/S. Good man, and smart too!!! :)
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Fully agree. Can't see why anyone would put a 160 hp in a 7 all other things being equal (and I love my Hartzell).

To clarify the points I was making. I am questioning the common beliefs that:

1. The 7A cruises faster than the 9A for the same HP.

2. A 7A with 180 hp at 75% cruises a lot faster than a 9A with 160 hp at 75%.

Fin
9A
 
Finley Atherton said:
Fully agree. Can't see why anyone would put a 160 hp in a 7 all other things being equal (and I love my Hartzell).

To clarify the points I was making. I am questioning the common beliefs that:

1. The 7A cruises faster than the 9A for the same HP.

2. A 7A with 180 hp at 75% cruises a lot faster than a 9A with 160 hp at 75%.

Fin
9A
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I've spent a few hours chasing 6's and 7's with my 9. In my experience the 6 and 7 are effectively equivalent. I have spent a fair amount of time on the wing of a 6 with the same 160 hp and Hartzell that I run in the 9. The airplanes are identical in speed, MP, and rpm.

So, I would say there isn't a dimes worth of difference between any of them given the same power. ( I know Bob, but 180 isnt 160 ) :p

Now if you want more speed, you need a 8. That really IS faster. :D:D

And I should know!
 
Of course the best reason to build a 9 is because it's the better looking airplane. With it's long slender wing and reflex airfoil, it makes a 7 look like a cherokee!

-Andy
 
I went back back and forth deciding between the two, i finally settled for an 9A , like all problems, make it simple and you will find it easier to decide.
 
Very difficult

sbalmos said:
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Since the -7 is, essentially, a -9's fuselage with -8s wings, has anyone ever considered or done a conversion of a -9 to a -7 [or 9A to a 7A] by swapping out the wings? Just from a theoretical design perspective, what else is there to change? Mods to the tail, the fuselage side skins and/or bulkheads where the wings are mounted? etc
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The "for now" part is where I started thinking whether this might be a possible conversion a few years or so down the road (assuming I'm not building a -10 by then).

Food for thought?
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First, let me state that I have never attempted to do the conversion you propose. Maybe I don't get it. Four pages of replies and I only see Ralph's has any info regarding the questions above about ease or difficulty in converting a 9 to a 7. [I've just skimmed the replies, so I apologize if I missed another reply of a technical nature] Since the 9 wings are thinner [lower main spar] and of less cord [shorter fore to aft] not only would the attach points for the wings differ, but you would have to tear out the ENTIRE main spar center section from the fuselage, to convert a 9 to a 7 [or a 9A to a 7A]
That is major surgery! There are probably going to be differences in the rear spar center section. While not impossible, it sure would not be practical. You would need to speak to one of Vans engineers to find out what other differences exist. Best to figure out what you really want, before you order.
Charlie
 
chaskuss said:
First, let me state that I have never attempted to do the conversion you propose. Maybe I don't get it. Four pages of replies and I only see Ralph's has any info regarding the questions above about ease or difficulty in converting a 9 to a 7. [I've just skimmed the replies, so I apologize if I missed another reply of a technical nature] Since the 9 wings are thinner [lower main spar] and of less cord [shorter fore to aft] not only would the attach points for the wings differ, but you would have to tear out the ENTIRE main spar center section from the fuselage, to convert a 9 to a 7 [or a 9A to a 7A]
That is major surgery! There are probably going to be differences in the rear spar center section. While not impossible, it sure would not be practical. You would need to speak to one of Vans engineers to find out what other differences exist. Best to figure out what you really want, before you order.
Charlie
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I think the drag spar attachment point is in a different location, so that would have to be moved, which would change the fuselage floor. And the flap mechanism has to move. Then the steps are in the wrong place. Also the tail attachments may not quite fit. Yuck.
 
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