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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. |
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. |
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.
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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 |
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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. |
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