What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Not Just Another 7 vs 9 Thread

StuBob

Well Known Member
The mission: Fly from the Midwest to Alaska and back in an airplane you built yourself.

The first considerations: What airplane, RV7 vs RV9, nose wheel vs tailwheel, c/s vs fixed, carbureted vs injected? If it weren't for Vlad, everyone would say 7 for fuel capacity, c/s for takeoff performance, injected for LOP, and tailwheel for gravel runways. But Vlad is inspiring!

Assume 180hp RV7 or 160hp RV9, no interest in aerobatics, and no interest in aftermarket fuel mods.
 
If you are not interested in acro, the answer is easy, how with the -9.

Should thee O-360 you will install fail, the lower approach and stall speed could save your life. If you build an A model, then you will be rolling slower when you flip over.
 
Alaska mission

In my opinion, holding true to your mission, the 9/9a is a better cross country flyer. It?s what it was optimized in design to do. At altitude the 0320 combined with a more altitude efficient wing, provides fuel economy without sacrificing to much speed.
170-180 TAS. @ 8.5k. (6.8-7 gph).

Slower landing speed: yes! 1.2 Vso is 58mph.

0320 vs 0360: Do you want more weight on your nose wheel?

Nose wheel vs tail: that one is subjective. They both can land short. Personally I would rather have a tail wheel for an obscure grass strip or off field landing.
 
I'm biased but

I'd go with the 9. That's a long trip, and the 9 was designed to be a cross-country airplane. Its efficiency, especially at altitude, is little short of amazing.

But let's face it, you could go with a -7 (especially with an autopilot) and never once feel like you were missing out. And you could sneak in a loop or two on the way there. :)

It's like choosing between NY strip and filet.

I'm biased against fuel injection due to a history of issues, in other aircraft, with hot starts. I love the c/s prop in my 9 but the performance with a FP is sufficiently awesome that, if I were building, I'd consider putting the $ into avionics instead.

Are you traveling light/solo, such that you could carry extra gas? I know you've ruled out extended range tanks, which certainly aren't a trivial upgrade. But a 9 with extended range tanks would be the hands-down winner, IMHO.
 
Last edited:
Not yet mentioned above, the engine out glide distance differs significantly between the 7 and 9. In mountainous terrain that might factor into your thinking.
 
Last edited:
I'd go with the 9. That's a long trip, and the 9 was designed to be a cross-country airplane. Its efficiency, especially at altitude, is little short of amazing.

Not going to get into the debate, but will point out that the difference between the 7/9 in terms of cruise efficiency is fairly small, and easily overshadowed by other factors such as attention to drag details and even how the aircraft is operated.

Here's a RV-6A that, with its short wing, should be crawling along at Cessna speeds and burning twice the rule needed by a -9A to do it. Instead, it's going faster and burning less fuel than what has been claimed for the 9. I'm aware of RV-8s that will easily best this, and RV-9As that don't come close.

https://m.youtube.com/watch?v=Vt_Xduuc1QU

Either the 7 or 9 will suit the OP's mission just fine in terms of efficiency and speed.
 
9/9A for the reasons mentioned above. Your mission is pretty much what it was designed for. A 7 would certainly do as well, but if you have a choice, why not pick the plane that was designed for what you want to do?

I'd go with field-repairable simplicity:

-Carb, metal fixed pitch prop. Spend that money on autopilot and avionics.
-9 or 9A, whatever you are more comfortable with. Vlad has proven that a properly handled A-model can go just about anywhere the tailwheels can.
-Oxygen setup to really take advantage of that wing up high.
-Dual p-mags will help make up for lost fuel economy from the carb.

If you are really planning on being out in the boonies, maybe a low compression O-340, to take advantage of mogas? Just about the same weight as a 320, and you'd end up about the same HP.

You won't be doing much hot and high flying, so I wouldn't view more HP or a CS prop as being essential. A metal prop will give you enough weight up front to put 100lbs in the baggage area. I would take a constant speed over more horsepower though, if I were going to pick one.

Chris
 
Not going to get into the debate, but will point out that the difference between the 7/9 in terms of cruise efficiency is fairly small, and easily overshadowed by other factors such as attention to drag details and even how the aircraft is operated.

Here's a RV-6A that, with its short wing, should be crawling along at Cessna speeds and burning twice the rule needed by a -9A to do it. Instead, it's going faster and burning less fuel than what has been claimed for the 9. I'm aware of RV-8s that will easily best this, and RV-9As that don't come close.

https://m.youtube.com/watch?v=Vt_Xduuc1QU

Either the 7 or 9 will suit the OP's mission just fine in terms of efficiency and speed.
Let's see a short wing RV do this:


KLVJ+to+SC86.jpg
 
Went to Flagstaff yesterday in my 9A... got to answer the tower's question- 218 mph.
Went to Nome Alaska from Arizona in a Luscombe. No comparison...
Know a guy with a 6 who aileron rolled all the way from Phoenix to Payson. Nutty but fun. To each his own. But you WILL have FUN.
 
Not going to get into the debate, but will point out that the difference between the 7/9 in terms of cruise efficiency is fairly small, and easily overshadowed by other factors such as attention to drag details and even how the aircraft is operated.
Also overshadowed by an extra 6 gallons of fuel.
 
Let's see a short wing RV do this:

The video I posted shows the short wing RV going 5kts faster on 5.8GPH. That's pretty close - and there is no doubt the short wing could slow down while the long wing may or may not be able to speed up. Not sure what your point is, other than going slower burns less fuel. You got me there :rolleyes:

Anyway, my point is that efficiency is the result of many things. The higher aspect ratio wing is certainly more efficient, but it's pretty minor compared to other factors.
 
The video I posted shows the short wing RV going 5kts faster on 5.8GPH. That's pretty close - and there is no doubt the short wing could slow down while the long wing may or may not be able to speed up. Not sure what your point is, other than going slower burns less fuel. You got me there :rolleyes:

Anyway, my point is that efficiency is the result of many things. The higher aspect ratio wing is certainly more efficient, but it's pretty minor compared to other factors.

Ground speed of 162 against 210. Of course wind and everything else matter. At least that is how I read the panel indications. Im still finishing mine up and planning my license check ride cross country in a 172 so these numbers are not even in my range of thought!

Im sure either would be great. I can't wait to find out how much more fun it is flying my 9A than the 172!
 
In addition the rv-9 is in a slight descent. VSI shows -50.

The video I posted shows the short wing RV going 5kts faster on 5.8GPH. That's pretty close - and there is no doubt the short wing could slow down while the long wing may or may not be able to speed up. Not sure what your point is, other than going slower burns less fuel. You got me there :rolleyes:

Anyway, my point is that efficiency is the result of many things. The higher aspect ratio wing is certainly more efficient, but it's pretty minor compared to other factors.
 
Both are similar in cruise, but coming down from altitude in the 7a it is nice to do 190-200 KTAS in calm air and :D
 
A trip to Alaska is but one (albeit a great one) use of an airplane. While the differences are minimal, your decision may be better based on what else you plan to do with the plane.

For me, my decision was for the 7 due to the additional strength of the wing (occasional aerobatics and mountain turbulence), more speed and the landing speed was low enough to not warrant the 9. The issue of slightly less stability of the 7 (slightly more neutrally stable make the 7 more fun like a fighter), can be eliminated with an autopilot. I do not regret my choice of 7 whatsoever, however both are great choices. Kinda like splitting hairs here.

Bevan.
 
The video I posted shows the short wing RV going 5kts faster on 5.8GPH. That's pretty close - and there is no doubt the short wing could slow down while the long wing may or may not be able to speed up. Not sure what your point is, other than going slower burns less fuel. You got me there :rolleyes:

Anyway, my point is that efficiency is the result of many things. The higher aspect ratio wing is certainly more efficient, but it's pretty minor compared to other factors.

I was throttled back for that flight to extend my range.

My point was, the short wing RV's don't perform as well up high as the -9 with that wonder Roncz airfoil does.

The few gallons difference between the two isn't enough to worry about and if you are planning on long range flights, you can always added additional capacity.
 
I'm assuming the 7 is similar in landing performance to the 8? If so, you may not want to discount it's short field performance. My Dad's 8 with a constant speed prop can land freakishly short. The prop allows me control the speed bang on and set up a fairly steep descent profile. And the Hershey bar wing does not float, so it's pretty easy to hit your spot. I used to have a Piper PA-12 (think Super Cub without flaps) and on a good day the 8 would turn off sooner. Getting out isn't a problem, but ours has an IO390 so it shouldn't be.

Have not flown a 9 so can't compare.

DEM
 
I'm assuming the 7 is similar in landing performance to the 8? If so, you may not want to discount it's short field performance. My Dad's 8 with a constant speed prop can land freakishly short. The prop allows me control the speed bang on and set up a fairly steep descent profile. And the Hershey bar wing does not float, so it's pretty easy to hit your spot. I used to have a Piper PA-12 (think Super Cub without flaps) and on a good day the 8 would turn off sooner. Getting out isn't a problem, but ours has an IO390 so it shouldn't be.

Have not flown a 9 so can't compare.

DEM
It is the same but will get off quicker than an -8, when equipped with the same engine and prop combination.

All distances are from Van's site and are for the 160 HP tail draggers versions at GW:

RV-7
Take off: 650'
Landing: 500'
ROC: 1,400 FPM
Ceiling: 18,500'
75% Cruise: 191
Stall: 58 mph
Range: 835 SM

RV-8
Take off: 650'
Landing: 500'
ROC: 1,400 FPM
Ceiling: 18,500'
75% Cruise: 195 mph
Stall: 58 mph
Range: 855 SM

RV-9
Take off: 475'
Landing: 450'
ROC: 1,400 FPM
Ceiling: 19,000'
75% Cruise: 188 mph
Stall: 50 mph
Range: 710 SM

Out of curiosity, I looked up a 260 HP Maule M7.
(http://www.pilotfriend.com/aircraft performance/Maule/24.htm)
Take off: 600'
Landing: 500'
ROC: 1,650 FPM (Well below GW.)
Ceiling: 20,000'
75% Cruise: 164 mph
Stall: 40 mph (Well below GW.)
Range: ? (But this thing hauls a bunch of fuel!)
 
Yep, I am carbureted and to have the engine run smoothly at LOP settings, I and to pull back a little bit. I don't recall the ROP settings, so I can't give you any kind of numbers for that.

And yet there is that pesky video that seems to suggest otherwise.
Yep, that pesky video showed you were running 28.3 NMPG and I was running 30.6 NMPG

The -9 wins again. :rolleyes:
 
Tailwheel

Regardless of the model or the performance numbers.

Ditch the pole vault nosewheel design and be a real man.

Put the little wheel in the back;)...I changed my mind on my build to tailwheel. Hope I like it.

Uh oh....now I did it.
 
Let me see now.....RV7 owners are suggesting the OP build an RV7, and RV9 owners are suggesting the OP build an RV9....and there are builders who haven't even flown yet who are extolling the flight virtues of their aircraft.

Some things just never change on VansAirforce. :rolleyes:
 
Yep, I am carbureted and to have the engine run smoothly at LOP settings, I and to pull back a little bit. I don't recall the ROP settings, so I can't give you any kind of numbers for that.


Yep, that pesky video showed you were running 28.3 NMPG and I was running 30.6 NMPG

The -9 wins again. :rolleyes:

Do you really not realise your ground speed and MPG are due to a stonking great tail wind?

I flew for 3 Long flights with my friend in his nose dragger 9. When we added up the fuel used I had use 1L more in my 7. Don’t choose you airframe for fuel speed etc there is not enough to make a difference.



For the OP. If you are not interested in Aeros then a 9 is the way to go. The lower landing speed is the advantage of the 9.

Me. I’ll stick to my 7 with 200hp and the ability to turn it upside down thanks.
 
Last edited:
Regardless of the model or the performance numbers.

Ditch the pole vault nosewheel design and be a real man.

Put the little wheel in the back;)...I changed my mind on my build to tailwheel. Hope I like it.

Uh oh....now I did it.
I'm not worried about the third wheel reflecting my manhood; I fly floats!

I am concerned about chuck holes in the runway, though. On the one hand, a nosewheel makes it easier to see and avoid them. On the other, if I don't see one and roll into it, I'd rather tear off the tailwheel than pogo over the nose.

My original choice for this project was a Carbon Cub. Then I realized I'd be spending a lot of money to go awfully slow.
 
Regardless of the model or the performance numbers.

Ditch the pole vault nosewheel design and be a real man.

Put the little wheel in the back;)...I changed my mind on my build to tailwheel. Hope I like it.

Uh oh....now I did it.

Well I have built and flown both, I do think the tail wheel may be a little cooler looking but I will always fly the nose dragger going forward. The pole vault issue is pilot error but it is true the nose gear is not a big heavy Cessna design.

Both the 7Aand 9A are great, if you want a more dousal landing airplane with no aero buy the 9A, but IMO the more rounded airplane is the 7A. The rest of the comparable differences are so small there not worth discussing. As for the short wing 6, some are way off on this one. The 6A is a very good performer, I have flown on cross country trips with several. The numbers are very close and the 6 or 6A is the best RV value of all, but if you buy one get the O360.
 
Last edited:
Do you really not realise your ground speed and MPG are due to a stonking great tail wind?[/url]

Do you realize those MPG numbers were calculated using TAS, not GS?

If I had used GS, the -9 is over 40 MPG and the -6, with a slight tailwind is at 28.1 MPG.

One other thing I noticef, the -9 is flying at 17.6 DA and the -6 is at 16.6 DA.

Impressive numbers for both aircraft. (Even though the -9 is the better aircraft for high altitude cruising.)
 
Last edited:
Do you realize those MPG numbers were calculated using TAS, not GS?

If I had used GS, the -9 is over 40 MPG and the -6, with a slight tailwind is at 28.1 MPG.

Wrong. The EMS-D10 in the -6 computes MPG via groundspeed; it has no access to TAS data.
 
Last edited:
Regardless of the model or the performance numbers.

Ditch the pole vault nosewheel design and be a real man.

Put the little wheel in the back;)...I changed my mind on my build to tailwheel. Hope I like it.

Uh oh....now I did it.

Do you have great BIG oversized tires on your truck also to compensate for.....:rolleyes:
 
Stu,

See if you can arrange back-to-back rides in both, if you can find one of each with the same engine - prop combination.

That is the only way you can make an honest assessment of what is best for you.
 
You guys are great

Well I knew I was headed to forbidden territory with the the tailwheel comment. Serves me right.

But....mission accomplished. I managed to get Captain Avgas to chime in. Nowadays, That's a rare feat.

The reality is that either model is sufficient. I personally prefer a 45 stall speed for various reasons.

I actually drive a piece of junk rusted out Toyota Tacoma that I have to keep the drivers side window cracked open so I can open it up from the inside because both door handles are broken....but that little engine keeps on purring. Not even sure if I could put bigger tires on.
 
Last edited:
I must admit though....I'm puzzled. In your signature, you have an 8 in progress, but you are are asking about a 7 or 9? Are changing?

I think a carbon cub would be fantastic....until you have to travel a long distance..so I hear you on that one.

Do a search on here for videos of a gentleman from Seattle who recently flew his red and white 7 to Alaska. One of the best videos I've seen to date.
 
Hindsight, wish I would have gone with a -9 Tailwheel. How about a -9 with a YIO-360-M1B with Smooth bottom cowl, maybe some big tires up front and a baby bushwheel in the back, that would be cool.
 
I must admit though....I'm puzzled. In your signature, you have an 8 in progress, but you are are asking about a 7 or 9? Are changing?

I think a carbon cub would be fantastic....until you have to travel a long distance..so I hear you on that one.

Do a search on here for videos of a gentleman from Seattle who recently flew his red and white 7 to Alaska. One of the best videos I've seen to date.

Long story.
 
So that?s why you were soooooo slow then. :D:D:D:D
Yep, just cruising at the speed of a herd of turtles!

Seriously, I have a carb and not fuel injection. With the electronic ignition, P-mags in my case, I can run LoP. Down low I can't do it at WOT but at that altitude I could. When I did run it WOT, I couldn't get it to run smoothly. Bringing the throttle back a little bit smoothed it right out. I suspect that the reason was that having the butterfly valve partially closed caused the air to swirl just enough to improve the fuel distribution.

On that flight, I was trying for max duration. So running at the lower fuel burn was a big help. Typically I would have to stop mid way to top off the tanks but because of the tailwinds and high TAS from being that high, I was able to land with a bunch of fuel left. (Shortly after I took that picture, I started downhill for home.)

Here's a link to my write-up of that trip.
 
Surprised that nobody has brought this up yet...

There are several aspects to short landings: steep descent, low speed, and deceleration. The bigger wing of the -9(A) gives you slow speed, the constant speed prop gives you drag (deceleration), on the approach, in the flare, and on rollout.

On takeoff in my -9A, the % power indicator usually indicates in the high 70s. In other words, I'm taking off with maybe a tad less than 130 HP of the 160 HP that the engine is rated for.

And the Sensenich prop has a 2600 RPM redline, so at cruise, I can't go full throttle, not to mention that in west Texas thermals, I'm always fussing with the throttle.

In my book, constant speed prop is the way to go. I wish my -9A had one.

Ed
 
This thread, combined with further research here, other sites, Van's, etc., brings me to this summary, as relates to the 3000nm AK trip. Assume two airplanes built per Van's recommendations, i.e., 160hp RV9 and 180hp RV7:

1) 100 mi range advantage 7.
2) 100 ft takeoff/landing distance advantage 9.
3) Cruise speed 10+ knots advantage 7.
4) 8 mph stall speed advantage 9.
5) The prices are almost identical, subject to prop choice.

So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?

Because I'm a contrarian, I really want to prefer the 9 taildragger. But this morning's math is providing a hurdle.
 
This thread, combined with further research here, other sites, Van's, etc., brings me to this summary, as relates to the 3000nm AK trip. Assume two airplanes built per Van's recommendations, i.e., 160hp RV9 and 180hp RV7:

1) 100 mi range advantage 7.
2) 100 ft takeoff/landing distance advantage 9.
3) Cruise speed 10+ knots advantage 7.
4) 8 mph stall speed advantage 9.
5) The prices are almost identical, subject to prop choice.

So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?

Because I'm a contrarian, I really want to prefer the 9 taildragger. But this morning's math is providing a hurdle.

At middle to higher altitudes, cruise speed at the same fuel flow will begin to favor the - 9. IMO, the real differentiatior between the two is whether you'd ever like to do modest aerobatics. If you do, the -7 is your choice.
 
low hours pilot

Question: At the altitudes he's going to want to fly over rough country given whatever the rocks reach up to and a likely preference for extra time should it get quiet in the cockpit, how happy is the 7 at 16500?
 
So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?
The 9 gives back efficiency.
Aircraft 7 9
Range 75% 775 710
Range 55% 950 860
Fuel cap USG 42 36
Miles/Gal 75% 18.5 19.7
Miles/Gal 55% 22.6 23.9

I found out long ago you can torture numbers to support one position or another. Try weighting your numbers to give more importance to the performance numbers you value most. Then pick the 9.
 
I found out long ago you can torture numbers to support one position or another. Try weighting your numbers to give more importance to the performance numbers you value most. Then pick the 9.
That?s how it works, isn?t it? Faced with such a dilemma, someone once told me to flip a coin. ?While the coin is in the air, you?ll wind up hoping for one outcome over another. Take that one, regardless of what the coin does.?
 
7 vs 9

Flown them both. Performance overall is pretty much the same when you average out minutes or dollars saved over several hundred hours. Acro of course means the 7. I prefer the way the 6 & 7 respond and handle when flying around for fun, but for long trips or occasional IFR the slightly less sensitive 9 handling is the ticket for me.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
Back
Top