VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 01-20-2018, 07:28 AM
StuBob StuBob is offline
 
Join Date: Oct 2015
Location: Indianapolis, IN
Posts: 254
Default Not Just Another 7 vs 9 Thread

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.
__________________
Stu F.
RV8
Reply With Quote
  #2  
Old 01-20-2018, 07:41 AM
N941WR's Avatar
N941WR N941WR is offline
 
Join Date: Jan 2005
Location: SC
Posts: 12,887
Default

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.
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
Reply With Quote
  #3  
Old 01-20-2018, 08:09 AM
agirard7a's Avatar
agirard7a agirard7a is offline
 
Join Date: Aug 2009
Location: Newport, RI
Posts: 705
Default 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.
__________________
Al Girard, Newport, RI
N339AG
RV-9
Reply With Quote
  #4  
Old 01-20-2018, 08:45 AM
Dugaru's Avatar
Dugaru Dugaru is offline
 
Join Date: Jan 2016
Location: Richmond VA, USA
Posts: 456
Default 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.
__________________
N929JA, 2007 RV-9A
Based W96: New Kent International Aerodrome
(near Richmond, VA USA)
2020 Dues Paid

Last edited by Dugaru : 01-20-2018 at 08:47 AM. Reason: forgot about fuel injection and prop questions
Reply With Quote
  #5  
Old 01-20-2018, 10:05 AM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
Join Date: Jan 2005
Posts: 3,646
Default

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.
__________________
Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto

Donation reminder: Jan. 2021

Last edited by alpinelakespilot2000 : 01-20-2018 at 10:10 AM.
Reply With Quote
  #6  
Old 01-20-2018, 11:24 AM
ChiefPilot's Avatar
ChiefPilot ChiefPilot is offline
 
Join Date: Jan 2005
Location: Twin Cities, MN
Posts: 1,565
Default

Quote:
Originally Posted by Dugaru View Post
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.
__________________
Brad Benson, Maplewood MN.
RV-6A N164BL, Flying since Nov 2012!
If you're not making mistakes, you're probably not making anything
Reply With Quote
  #7  
Old 01-20-2018, 11:33 AM
YellowJacket RV9 YellowJacket RV9 is offline
 
Join Date: Oct 2012
Location: Clearwater, FL KCLW
Posts: 1,281
Default

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
__________________
Chris Johnson
RV-9A - Done(ish) 4/5/16! Flying 4/7/16
Reply With Quote
  #8  
Old 01-20-2018, 11:34 AM
N941WR's Avatar
N941WR N941WR is offline
 
Join Date: Jan 2005
Location: SC
Posts: 12,887
Default

Quote:
Originally Posted by ChiefPilot View Post
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:


__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
Reply With Quote
  #9  
Old 01-20-2018, 11:47 AM
flightlogic's Avatar
flightlogic flightlogic is offline
 
Join Date: Nov 2013
Location: Prescott, AZ
Posts: 1,614
Default

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.
__________________
"Kindness is never a bad plan."

exemption option waived. Donation appropriate.
Reply With Quote
  #10  
Old 01-20-2018, 11:52 AM
StuBob StuBob is offline
 
Join Date: Oct 2015
Location: Indianapolis, IN
Posts: 254
Default

Quote:
Originally Posted by YellowJacket RV9 View Post
I'd go with field-repairable simplicity:...
Excellent line of thinking!
__________________
Stu F.
RV8
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 12:56 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.