![]() |
Converting a -9(a) to -7(a)?
So this is a scary thought that I had while driving into work this morning. The fact that I'm holding my -9a tail kit order form in my hands hovering over the office's fax machine doesn't help either. :)
Since the -7 is, essentially, a -9's fuselage with -8s wings, has anyone ever considered or done a conversion of a -9 to a -7 by swapping out the wings? Just from a theoretical design perspective, what else is there to change? Mods to the tail, the fuselage side skins and/or bulkheads where the wings are mounted? etc I'm picking the -9 almost exclusively because I'm a low-time new PPL, doing the usual local jaunts here and there, and some regional travel. Don't need ultimate speed, aerobatics, etc... for now... The "for now" part is where I started thinking whether this might be a possible conversion a few years or so down the road (assuming I'm not building a -10 by then). Food for thought? |
Just order the -7. If you are debating this now you'll never be happy later. The empennage is also different between the 7 & 9. The -7 is a great XC plane and just as easy to fly as the -9 and once flying you'll be surprised how fast your hours build up not to mention the flying hours you'll do while building (I hope). Of course I'm biased having had the -7.
|
Buy the 7....
I learned to fly in my 6,don't worry about the hours. It will all work out.:)
|
Get the -7 and don't paint yourself into a corner. It's no more difficult to fly than the -9. You can't convert them except to throw away the tail and start over.
John Siebold |
I like the -9, but I also like the -7. Don't buy a -9 because you're afraid to fly the -7. If you can fly one, you'll be fine in the other.
I like the -9 because it's got a different feel. |
I had the same difficulty choosing - went with 7A. (It's a great airplane - it can make you think you're better than you are.)
With good transition training I don't think low time would necessarily be an issue. Dan |
It sounds like you want a 7 and not a 9. Coming from a 9A flyer, I will tell you if this is what you are thinking about maybe you should just order the 7. There are quite a few other differences between the 7 and 9 besides the wings. And the 9 does NOT have an 8 wing. The wing for a 9 is unique. There are enough differences between the two airplanes that conversion could only happen, if it could at all, early on in the build.
In my opinion, you should not be concerned about flying a 7, even if you are a low time pilot. If you are a conscientious pilot who is always trying to better your skills and are paying attention to what you are doing you will have no problems flying the 7. Of course this holds true for any pilot in any airplane. There is a statement that has been mentioned many times on this site: BUILD THE AIRPLANE YOU WANT, NOT WHAT OTHERS SAY YOU SHOULD BUILD! This is a very true statement. If you feel you may want to do something in the future that you feel the 9 will not allow then you may not want the 9. Don't let anyone, including me, tell you what to do. Trust your own instincts and go with what you feel you want in your airplane. |
Ya Steve, the same old adage is the best - build what I want, not what others say I want.
Ultimately, during one of my brain breaks at work here this morning (read: waiting for a new software build to finish compiling!), I rethought my mission profile and what I want out of the plane. I'm sticking with the -9a. It'd be cool to do the aerobatics and the sheer speed increase of the -7a. But I don't need it for how I see myself flying. Again, it's nice to have, but probably wasted capability. Soooo... I just faxed in the order for the -9a tail. N112SB is now officially on its way. As Gene Wilder says in Young Frankenstein... What have I done? My God man, WHAT... HAVE... I... DONE??? :D Yes, I'll be fine. My wallet won't. Let the mayhem begin. |
Two of the reasons we choose the 9 vs the 7 were its better glide characteristics and its slower stall speed. We spend a LOT of time in the mountains and along the coast. The 9 gives us more glide distance/time and significantly less impact energy (
).Sometimes, cruising from point A to point B I kinda like the idea of having a 200HP 7 ... and then we go to the pump... 10 knots probably isn't worth the 4-6 gal/hr it cost to get it... |
But what would Frau Blucher want you to build?....neiiiiiiiiiighhhhhhhh!!!!!
|
Quote:
|
Quote:
Given that though, the great majority of my flying is cruising LOP with the throttle at 70-75% HP. At this setting I see anywhere from 150-165 MPH and burn around 7.0-7.5 GPH. I really think a 7 comparably configured will not perform a whole lot differently. |
Quote:
|
Yup. So, ultimately, the airspeed numbers are even closer than I remembered and forgot to check on. In reality, I'm giving up aerobatic abilities by going with the -9a. Big deal. ;) Gross simplification probably, but I'll take the -9a's better glide and slow-speed characteristics over aerobatic abilities.
Thanks again everyone! Now for the long wait until the tail kit arrives at my door. |
I like the larger tanks on the -7 vs -9. I know you can put extra wing tanks on the -9, but after a stern warning not to do so from a reputable Vans person, I would never do that. If long-range cross country was a major part of my mission, that would be an important factor for me.
|
Quote:
|
Quote:
Quote:
It sounds like you have figured out what your mission will be, that's a good thing. The -9 is a great flying plane and doesn't give up much to the -7. Best of luck with your project. |
Quote:
|
Quote:
|
Quote:
36 gallons divided by 8 GPH gives you 4.5 hour range. Call it 4 hours with a half hour VFR reserve. If you get that low, you can power back even more and stretch that half an hour even longer. Using Van's numbers you can pull back to 55% power and still fly at over 140 knots for 730 Nautical miles. That is plenty long enough. If you power up to 75%, then the range is 600 Nautical miles (710 statute miles) until dry tanks. Truth is, very few people fly their RV?s at 75% power, most throttle back smile at the lower fuel burn. Either way, everyone will have some reason to justify their choice and they are all valid reasons for the decision maker to drop some major coin on the aircraft of THEIR choice. If you are still undecided in your 7 vs 9 choice, ask Van?s to hold your order until you can arrange a ride in both. I?m not going to tell you the -9 or the -7 is better because it is all about YOUR mission. They are both fine aircraft. |
Quote:
|
Quote:
WHAT? 2 Sierra Bravo cancel your order IMMEDIATELY! You don't even know what you got yourself into :D 9A is big and slow get the 8 forget the 7. |
Quote:
|
Let's see a show of hands...how many experienced RV pilots fly there plane 5 hours non-stop and land with legal reserves?
longest time in the seat was 3.5hrs is enough for me, 650miles, still had 11gals on board. I've only flown mine 6.5hrs in one day, OSH-8U8, 975nm with headwinds and one stop. From a safety standpoint, I would think a trip that length would be a major mental & physical drain for most pilots. I built a 7, but could have easily been happy with a 9. My daughter is starting flight lessons so a 9a would have been perfect. Also, the only time I run 75% or above is racing or testing. other times I'm at 6-7gph puttin' around the valley. |
Quote:
|
Quote:
|
Choice is yours.
I went through the same decision process 4 years ago. Didnt even have my ppl when for the first year or two of building. The slower land, better glide and arguably better cross country platform sold me. I went 9a, have loved every single hour would not change a thing. I like all rvs, but a side by side is way better with a child or wife in my opinino. A tip up is just awesome for views in flight and you just will be amazed at how easy and fun flying in one is. Build what you want, enjoy the stuffin out of it.
After any rv flight a cessna trip is just painful. :D Enjoy the build. |
Lightin' The Fuse
Why oh why do some 9 apologists try to make the 7 equal to the 9 IF.... This usually is manifested in speeds. The two airframes are different and Van's design intents are different.
No way does a 9 equal a 7 in top end. The 7 carries more fuel, has greater range - which can often be useful for tankering for price/availability. Cheek/bladder endurance are not the only metric. The 7 airframe is stronger. Aerobatic abilities aside, Van's limits 9 baggage to 75 pounds, 100 in the 7. That's a very useful difference. The 9 can fly slower than the 7. It's an efficient climber with a tad higher spec'd service ceiling (take a deeper breath before crossing 14,500). The handling is more docile. They are different. A lot of the number differences are not great percentage-wise, but they exist. You pays your money and takes your choice. Yet they're both delightful in their own way. John Siebold |
Quote:
|
Of course I am not trying to stir the pot but going on the best figures I can find it appears that a 9A may cruise slightly faster than a similarly equipped 7A.
Vans figures compare the 7A with a Hartzell C/S prop and the 9A with a FP prop. CAFE figures for the 160 hp factory 9A with a MT C/S prop show about 192 mph TAS at 8,500 ft DA with the engine at 2,605 rpm and 23.7". Vans gives 189/190 mph TAS for a 160 hp 7A at 8,000 ft and 75%. So maybe the 9A is faster at 75%??? Also factor in that the MT is considered slower than the Hartzell so the 9A with a Hartzell may be even faster again. This is borne out by my 9A with a Hartzell which does 194 mph TAS at 8,500 DA WOT and 2,700 rpm (4 leg GPS spread sheet method). Much is made of the fact that the 7A with 180 hp can cruise faster than a 9A with 160 hp. Using the CAFE figures above for the 160 hp 9A and Vans figures for the 180 hp 7A at 75% the difference is about 5 or 6 mph (or about 3 or 4 mph using my figures). So lets be generous and say maybe 5 mph faster for almost an extra gal/hr. :eek: Fin 9A |
Quote:
|
Quote:
|
Quote:
Thought I would get a bite.:) I never said a 180 hp 7 (or a 6 ) would not out-climb or out-run a 160 hp 9. I was comparing a 7A and a 9A both with 160 hp using the best figures I could find. I would be interested to see any documented figures you have. Fin 9A |
Quote:
P.S. --- I see that you have a C/S. Good man, and smart too!!! :) |
Quote:
To clarify the points I was making. I am questioning the common beliefs that: 1. The 7A cruises faster than the 9A for the same HP. 2. A 7A with 180 hp at 75% cruises a lot faster than a 9A with 160 hp at 75%. Fin 9A |
Quote:
So, I would say there isn't a dimes worth of difference between any of them given the same power. ( I know Bob, but 180 isnt 160 ) :p Now if you want more speed, you need a 8. That really IS faster. :D:D And I should know! |
Of course the best reason to build a 9 is because it's the better looking airplane. With it's long slender wing and reflex airfoil, it makes a 7 look like a cherokee!
-Andy |
I went back back and forth deciding between the two, i finally settled for an 9A , like all problems, make it simple and you will find it easier to decide.
|
Very difficult
Quote:
That is major surgery! There are probably going to be differences in the rear spar center section. While not impossible, it sure would not be practical. You would need to speak to one of Vans engineers to find out what other differences exist. Best to figure out what you really want, before you order. Charlie |
Quote:
|
| All times are GMT -6. The time now is 11:58 PM. |