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Not Just Another 7 vs 9 Thread

So...are you 6 and 7 guys saying the 9 wing is NOT more efficient up high?

….The 9 is far more efficient everywhere! Go on Flight Aware, search
N-91AN, Look at my flights in track logs. It is vary rare to see speeds
less than 200mph once in level cruise at any altitude. Up high is a bit
better with far less fuel consumption. Thanls, Allan
 
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I'm not asking what the 9 guys are saying. I'm asking what the 6 and 7 guys are saying. Are they calling BS on Vans 9 assertions?
 
I'm not asking what the 9 guys are saying. I'm asking what the 6 and 7 guys are saying. Are they calling BS on Vans 9 assertions?

In the first place, if they are flying a 6/7 and not a 9 then they really don't have any basis to do so.

In the second place, who cares? Build and fly what you want - those other people don't pay your bills and you don't have to care what they think.
 
I'm in the market for a side by side so yeah I have a personal interest. I'd really like to know what the true performance comparisons look like. On here, to listen to the 6/7 guys there is zero or negative advantage to 9 efficiency. So...are they really pedaling that or is it just my toy is the best thing ever bs?
 
I'm in the market for a side by side so yeah I have a personal interest. I'd really like to know what the true performance comparisons look like. On here, to listen to the 6/7 guys there is zero or negative advantage to 9 efficiency. So...are they really pedaling that or is it just my toy is the best thing ever bs?

I'll tell you that I flight plan for 155 KTAS on 6.5-6.8 gph in the mid-teens running WOTLOP, and routinely see 22-24 nm/gal efficiency. That's my personal experience, some others see better and some worse. Most people don't like to cruise as high as I do so they don't get the full benefit of the wing on the 9. My cruise efficiency testing, and it's been pretty extensive with my plans for a RTW trip, show my best efficiency between 14,000 and 17,000. How does that compare to a 6 or a 7? Dunno and don't care - I didn't build one of those.

Down low and don't care about the fuel flow, sure it'll go 170 knots - but there's precious little of that type of flying in my typical missions. I'll boom up above 10,000' just to go 50 miles in the cool smooth air up there, because it's so easy to get there.
 
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My cruise efficiency testing, and it's been pretty extensive with my plans for a RTW trip, show my best efficiency between 14,000 and 17,000. .
Having gotten that impression is why I'm thinking 9. Arguments from 6/7 crowd?
 
Having gotten that impression is why I'm thinking 9. Arguments from 6/7 crowd?

Same altitude is good for the short wing RVs. The aspect ratio / spanwise loading is only one factor in overall efficiency that can be reduced or even overcome by other factors. Carbed vs. FI, electronic vs. traditional ignition, fixed pitch vs. constant speed and so on all factor in. Attention to detail also plays a part - did the builder need to install louvers or other changes to increase mass cooling flow? If so, then you have more cooling drag vs. a tight baffle setup.

As posted much earlier in the thread, this is video from my RV-6A doing what others claimed a short wing RV couldn't do. 164 KTAS on 5.8GPH at 15,500MSL / 16880 density altitude.

https://m.youtube.com/watch?v=Vt_Xduuc1QU
 
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For my point of view. In practice I fly my 7 with a friend in his 9. The difference in our real world is not that great.

My take.

If you want to turn it upside down it?s a 7 you need. If you don?t then a 9 is probably best.

Obviously it has to be a vp taildragger with a tip up. Cos everyone KNOWS that?s the best combo. 😊😊😊.

Seriously, build what you want. If you build it light without loads of aerial and keep it clean and straight well maintained then you will love it.
 
Mark,

THIS POST quoting figures from Vans for the 14, 9 and 7 may be useful. (Note that apparently experience has shown better figures for the 14).

I built the 9 rather than the 7 for the better short field performance needed on my somewhat marginal airstrip.

Fin
9A
 
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Obviously it has to be a vp taildragger with a tip up. Cos everyone KNOWS that?s the best combo. 😊😊😊.

.

Pilot wife says the little wheel has to be in front. :(

Maybe that will be her plane to visit the kids 1274nm away and I'll buy a 3 for myself. :)
 
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