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05-01-2007, 07:23 PM
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Join Date: Mar 2007
Location: Upper ny
Posts: 78
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9 over 7
I have encountered numerous 7 tail builders who had to wake up to the fact that the 9 is a slower quieter plane with a greater choice of true-aircraft engines. I explain that the 6 and 7 are more power intensive. Lots of people are building Vans because they are 1. metal, and 2. kits. The 7's fuel consumption is more of a rude awakening than a 9 and yes, that's important. The most faulty information I find on the subject is that the 7 is a better cross country plane. Cross country wants quietude, less fuel consumption, and lower landing/crashing speed. The final twist is you and your passenger might want the trip to last longer. How many hours a month do you get to spend in the air? Go with the 9.
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05-01-2007, 07:49 PM
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Join Date: Jan 2005
Location: Warner Robins, GA
Posts: 1,187
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This post is totally unrelated. Anyway, I just got in from taking a friend on his first light plane ride in my -9. He spent 12 years as a sheriffs deputy here in GA. He was one of those cops you see on TV dashcam videos who runs towards the shooter and drops the bad guy at point blank range. Seriously, his video runs on court TV sometimes. Really amazing.
Well, we had a great time even if the haze from the Waycross fires killed the visibility.
I really enjoy giving "discovery flights" 
__________________
Bruce Sacks
RV-9 N659DB - Flying since 7/1/06
Hatz CB-1 - Fabric covering with Polyfiber.
Warner Robins, GA
A&P
APRS KJ4EFS
Last edited by bsacks05 : 05-01-2007 at 07:56 PM.
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05-01-2007, 08:14 PM
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Join Date: Mar 2006
Location: Ottawa, ON
Posts: 650
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RV-7A spec w/ Const. Speed. RV-9A spec. w/ Fixed Pitch
Quote:
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Originally Posted by kentb
From Vans website for RV7 160hp and RV9 160hp both at Gross:
RV7 Speed at 75% 8000ft 191 mph RV7 better by 3 mph
RV9 Speed at 75% 8000ft 188 mph
SNIP .
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To add to Kent's comparison post, the performance figures quoted were not comparing apples to apples. Note that Van's performance figures for the RV-9A were demonstrated with a fixed pitch propeller, and the RV-7A was demonstrated with a constant speed propeller.
Performance figures for a constant speed propped RV-9A will certainly beat the presently quoted fixed pitch propped RV-9A specs. (the cruise speed would probably be one spec that would not change much.... but take-off, climb etc would certainly improve)
I believe Vans could have done a better job marketing the RV-9A by providing a more equitable comparison to the other models.
RV-7 Performance
Solo Weight 1400 lbs
Gross Weight 1800 lbs160 hp180 hp200 hp Empty weight and performance measured with Hartzell 2 Blade C/S prop
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RV-9 Performance
Solo Weight 1350 lbs
Gross Weight 1600 - 1750 lbs118 hp135 hp* 160 hp Empty weight and performance measured with fixed pitch propeller
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__________________
Alfio
RV-9A Ottawa, Canada
First flight Dec. 18, 2008
> 1,000 hrs tach.
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05-01-2007, 08:14 PM
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Join Date: Jul 2005
Location: Detroit, MI
Posts: 1,587
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Huh?
Quote:
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Originally Posted by phil9diesel
... The 7's fuel consumption is more of a rude awakening than a 9 and yes, that's important. The most faulty information I find on the subject is that the 7 is a better cross country plane. Cross country wants quietude, less fuel consumption, ...
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Let's assume for the sake of discussion that a Lyc 320 in a 7A is the same as in a 9A. Let's also assume for the heck of it that this same engine runs at the same BSFC at 75%. So, how is the fuel consumption less in the 9? Remember that Van's says the 75% GW cruise with 160 HP is 7A=189, 9A=186.
I'll agree that you can go with lower HP and thus slower and thus better mpg in the 9A. I'll further agree that if you go to 180 hp in the 7A and use it you will burn more fuel per mile. But, I further suggest that if you go the same speed in each even with a bigger engine in the 7A you will burn pretty close to the same fuel per mile.
Is there evidence that I'm wrong?
__________________
H. Evan's RV-7A N17HH 240+ hours
"We can lift ourselves out of ignorance, we can find ourselves as creatures of excellence and intelligence and skill. We can be free! We can learn to fly!" -J.L. Seagull
Paid $25.00 "dues" net of PayPal cost for 2015, 2016, 2017 and 2018 (December).
This airplane is for sale: see website. my website
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05-02-2007, 09:42 AM
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Join Date: May 2005
Location: Canby, Oregon
Posts: 1,786
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Lycosaurus, I hadn't noticed that.
I thought that the climb numbers looked a little low compared to what I see on my plane. CS will definitely help with climb, takeoff and also landing numbers.
hevansrv7a, I agree that when you use, let's say 120HP (160 at 75%) from a 320 or the same HP from a 360 that the fuel burn will be very close. But we can see from Van's number that the speed between the two planes is on the border of measurement error (I know the 7 is 3 mph faster). IMHO that the longer wing and updated airfoil on the 9 increase comfort and performance for cross country flight. The 7 is the winner if you want to stress your self (aerobatics), but for a more comfortable cross country I think the 9 is the ticket. I think that the 10 would be even better, but is a little pricey.
Kent
__________________
Kent Byerley
RV9A N94KJ - IO320, CS, tipup
AFS 3500, TT AP, FLYING....
Canby, Or
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05-02-2007, 10:19 AM
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Join Date: Jan 2005
Location: Near Scipio, in Southern Indiana
Posts: 1,779
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Apples to apples?
A few mph here, a few fpm there. What's the big deal? I fly a 9A and make no excuses, and the same would be true if I flew a 7 or 7A. If I felt I needed more range, extra fuel tanks are available. So is a CS prop. These are both great airplanes as anyone who has flown them knows.
Personally (and that is a key word here) I like the low sink rate and better (Wow, I I should have said IMHO, please don't flame me) flaps. Next time you have an engine failure as I have had, you will appreciate a few more minutes to set yourself up, and a little lower landing speed. Considerably lower speed percentage wise if you take into account that 20 kt headwind. Kent said it best. You will be about 7.5% happier with one than the other. Maybe 8%. We don't have to justify what we fly. Pick what suits your mission.
Bob Kelly
__________________
Bob Kelly, Scipio, Indiana
Tech Counselor
Founder, Eagle's Nest Projects
President, AviationNation, Inc
RV-9A N908BL, Flying
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05-02-2007, 10:59 AM
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Join Date: Jan 2005
Location: Palm Bay, FL
Posts: 420
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RV-9A flying since June 2005...
It sounds like all the usual facts have been served up in this thread. And of course, the specifics of several builder/pilots flying their RV-9/9A airplanes. Here is my version for N2PZ "Enterprise".
Typical mission to Florida and back for a "day trip" when needed:
Chattanooga to Stuart/West Palm Beach area.
Fuel stop at Alma (KAMG) or Homerville, Georgia (KHOE)
Distance approximately 630 statute miles to Stuart (KSUA)
The stop at Alma or Homerville is based on gas prices and comfort needs. That keeps the flight legs to about two hours each. I have an O-320 with carb, Hartzell C/S prop, and fly at 10,000~12,000 feet for lean burn fuel settings between 5.5 & 6 gallons per hour. The air speed trues out at 160 mph. That's about 25 MPG. Not bad for cruising at 160 MPH. The higher cruising altitudes often can provide better tailwinds going south or east in my part of the country. IF the HEAD winds aloft are more than 10 to 15 MPH, I will get down "low" to avoid them. Low for me is 2500-3500 MSL across Georgia.
When I went to OSH 2002 and sat in all the Van's models, I was interested in comfort, visibility, ease of construction, cross-country flying, and NOT aerobatics. I thought about how many times I fly with someone, and the use of the seat beside me when it is empty.
I did all the math on weight and balance and confirmed that using derated V-speeds, I could load the airplane to 2000 pounds and remain in CG limits. I flew the airplane to OSH 2006 loaded that way. It was like taking off in a 172 at max gross weight, but at cruise, it was business as usual. I have a placard on the panel with two columns of V-speeds. One column for 2000 pounds max gross weight, and one column for Van's recommended gross weight.
You can learn all about these flights and more on my web site at www.n2prise.org, including videos from the 2006 trip in and out of Oshkosh.
I have another Florida "day trip" coming up on May 13th, weather permitting. With lunch at the Florida end, the eight hours of flying in 2-hour increments with the breaks in between is not bad. The autopilot does the work, I just fly the takeoffs, landings, and the radio when needed.
Jerry K. Thorne
East Ridge, TN
RV-9A N2PZ Hobbs = 213.3 hours
Last edited by n2prise : 05-02-2007 at 11:04 AM.
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05-02-2007, 12:44 PM
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Join Date: Jan 2005
Posts: 848
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Lured into this again???
For the life of me I don't know why I'm allowing this to lure me in again. This usually means being flamed by somebody with two clecos holding a brand new tail kit component together who knows everything already. Others on this thread have stated that it is a simple question of whether you will fly acro. On the surface the question is truly this simple. But if you start to peel the layers away kind of like peeling an onion there is much more to the question. As your flying evolves so can your mission. Before going any further here are my qualifications for talking about the nines. They are what they are and I'm making no claims to knowing everything. In fact as my time and flying lessons continue to build my opinions have changed on many things regarding these airplanes. So far I have 452 hours on my plane and just returned from a 5500 mile trip with other RV's. The numbers I'll give are just simply what they are and you can decide for yourself.
Fact... The three 9A's on the trip used the most fuel at each stop! Again, this is just simply how the numbers came out. There were no 7's on the trip, but there were 6's and 6A's with 0-360's. The best for economy was a six with fuel injection and running LOP. On 3 hour flight legs this ship would use 5 to 6 gallons less fuel than my 0-320/carburated/Hartzell equipped 9A running 50 rich and oversquare to save gas. The carburated 0-360 planes would use similar or less gas than me also. On some fill ups the carburated sixes would come in a gallon or so less than me.
Fact... Down low which I'll call 6500 feet and less the power difference is dramatic. As we got higher though things changed a bit. Don't get me wrong though because the tides never turned enough that the 9A would outrun any of the planes with more displacement. But to run with them low I had to make up either 3 inches in manifold pressure or 300 rpm or some combination of the two. As we got up to the 9500' range I was running similar power settings for the same speed. At 10,500 I could run either 1 inch less or reduced rpm for the cruise speed that we were at. This must be the wing taking over, but the 7 could have less effect from this, I don't know. Never, never, never could I run with or out run the bigger displaced engines if the pilots didn't want me to. This example was running at a more economy based cruise where I had reserve power to add still. If we ran with more power the sixes would leave and check out if they wanted to. This was demonstrated when photos were being taken in flight and there were power reserves to allow the bigger engines to come and go at will to any where in the gaggle.
Fact... I know from flying on other trips with sixes with 0-320's both nose and tail wheel that the nine is faster. Van's claims for the 7's is that they are faster yet, but I don't know this to be true having not flown with one with the smaller engine. Van's numbers are accepted as accurate by everybody and I'm not questioning them.
Fact... The seven carries more fuel meaning more range or reserves.
Fact... The eight is faster than the seven.
Fact... At high density altitude runways my 9A always lifted off first. The sixes with constant speed props would beat me to altitude by about 500'. These numbers are for me only as I don't know the power settings they were holding. I did hear one pilot say he was at 24sq on climbs though. I was all in for throttle and 2500 rpm. With this I could match them enough that they could allow me to fly with them.
Now for my opinions... If I built another nine it would have an 0-360. If I were to actually build again though I'd build a 7A with injection and a constant speed prop. Here's another opinion and advice that was given to me by Ken Scott at the factory when I started. Before taking advice on the net find out if they have finished their plane.
Lastly, I love my airplane. It flys great and does everything that we ask of it. This is no nine bashing, just simply information to help others choose.
Blue Skies,
__________________
Bryan 9A Sold
Beech S35, and daydreams of a Super 8 or a Rocket starting to take over my brain.
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05-03-2007, 08:11 AM
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Join Date: Jan 2005
Location: Palm Bay, FL
Posts: 420
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RV-9/9A likes it up "high"...
Bryan,
You called it right. The RV-9/9A likes to fly above 10,000 MSL. When I flew to LOE5, I was tail-end Charlie to a group of RV's (6, 7, 8) from the DFW area. I ended up climbing higher to take advantage of lower fuel burn, and some wind advantages. When I arrived at the intermediate fuel stop, there were only two of the other planes still in line at the pumps.
At the end of the day, I was no more than 10 minutes behind the other guys, but I flew my RV-9A at normal economy cruise on 6 gallons per hour and 160 MPH TAS. I never was out of radio contact with the others, and that was good since they were out front scouting the weather as we passed El Capitan on the way to El Paso. The weather reports they shared helped me when I got to the mountain.
You can read about that on my web site at this link: http://www.n2prise.org/rv9a174.htm with the story continuing onto the next few pages.
Jerry K. Thorne
East Ridge, TN
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05-06-2007, 04:41 PM
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Join Date: Mar 2007
Location: Upper ny
Posts: 78
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fast Vans faster decision
[quote=hevansrv7a][font=Franklin Gothic Medium]Let's assume for the sake of discussion that a Lyc 320 in a 7A is the same as in a 9A. Let's also assume for the heck of it that this same engine runs at the same BSFC at 75%. So, how is the fuel consumption less in the 9? Remember that Van's says the 75% GW cruise with 160 HP is 7A=189, 9A=186. Is there evidence that I'm wrong?...Add: Wrong as in wrong tree (barked up). The key phrase where you went wrong is "Lets assume for the sake of" . Nothing wrong with the figures. Let's unassume. Unassume that all Vans 2 place go 75 percent/160 ponies in the same cruise mode for the same purpose. Backing down with the 9 is how you save gas and noise, which is a valid role for many owners. My points aren't just that the 9 is different, but that a larger than ever number of kit builders successfully finish or just take on a plane without ever knowing the difference between the 7 and 9 models. In the kit scheme, they start the 7 and find out the 9 would have served them much better. Vans never misrepresented the models. Owners sites leave out the flexibility discussion.
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