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-   -   Not Just Another 7 vs 9 Thread (https://vansairforce.net/community/showthread.php?t=157062)

tomww 01-22-2018 12:50 AM

Quote:

Originally Posted by N941WR (Post 1233824)
More so when you consider that I wasn't at full throttle on that flight.

So that?s why you were soooooo slow then. :D:D:D:D

N941WR 01-22-2018 06:52 AM

Quote:

Originally Posted by tomww (Post 1233963)
So that?s why you were soooooo slow then. :D:D:D:D

Yep, just cruising at the speed of a herd of turtles!

Seriously, I have a carb and not fuel injection. With the electronic ignition, P-mags in my case, I can run LoP. Down low I can't do it at WOT but at that altitude I could. When I did run it WOT, I couldn't get it to run smoothly. Bringing the throttle back a little bit smoothed it right out. I suspect that the reason was that having the butterfly valve partially closed caused the air to swirl just enough to improve the fuel distribution.

On that flight, I was trying for max duration. So running at the lower fuel burn was a big help. Typically I would have to stop mid way to top off the tanks but because of the tailwinds and high TAS from being that high, I was able to land with a bunch of fuel left. (Shortly after I took that picture, I started downhill for home.)

Here's a link to my write-up of that trip.

Ed_Wischmeyer 01-22-2018 08:59 AM

Surprised that nobody has brought this up yet...

There are several aspects to short landings: steep descent, low speed, and deceleration. The bigger wing of the -9(A) gives you slow speed, the constant speed prop gives you drag (deceleration), on the approach, in the flare, and on rollout.

On takeoff in my -9A, the % power indicator usually indicates in the high 70s. In other words, I'm taking off with maybe a tad less than 130 HP of the 160 HP that the engine is rated for.

And the Sensenich prop has a 2600 RPM redline, so at cruise, I can't go full throttle, not to mention that in west Texas thermals, I'm always fussing with the throttle.

In my book, constant speed prop is the way to go. I wish my -9A had one.

Ed

airguy 01-22-2018 09:19 AM

Quote:

Originally Posted by Ed_Wischmeyer (Post 1234027)
In my book, constant speed prop is the way to go. I wish my -9A had one.

Ed

It is, indeed.

StuBob 01-27-2018 12:12 PM

This thread, combined with further research here, other sites, Van's, etc., brings me to this summary, as relates to the 3000nm AK trip. Assume two airplanes built per Van's recommendations, i.e., 160hp RV9 and 180hp RV7:

1) 100 mi range advantage 7.
2) 100 ft takeoff/landing distance advantage 9.
3) Cruise speed 10+ knots advantage 7.
4) 8 mph stall speed advantage 9.
5) The prices are almost identical, subject to prop choice.

So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?

Because I'm a contrarian, I really want to prefer the 9 taildragger. But this morning's math is providing a hurdle.

Kyle Boatright 01-27-2018 12:31 PM

Quote:

Originally Posted by StuBob (Post 1235310)
This thread, combined with further research here, other sites, Van's, etc., brings me to this summary, as relates to the 3000nm AK trip. Assume two airplanes built per Van's recommendations, i.e., 160hp RV9 and 180hp RV7:

1) 100 mi range advantage 7.
2) 100 ft takeoff/landing distance advantage 9.
3) Cruise speed 10+ knots advantage 7.
4) 8 mph stall speed advantage 9.
5) The prices are almost identical, subject to prop choice.

So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?

Because I'm a contrarian, I really want to prefer the 9 taildragger. But this morning's math is providing a hurdle.

At middle to higher altitudes, cruise speed at the same fuel flow will begin to favor the - 9. IMO, the real differentiatior between the two is whether you'd ever like to do modest aerobatics. If you do, the -7 is your choice.

Mark_H 01-27-2018 01:39 PM

low hours pilot
 
Question: At the altitudes he's going to want to fly over rough country given whatever the rocks reach up to and a likely preference for extra time should it get quiet in the cockpit, how happy is the 7 at 16500?

terrye 01-27-2018 05:12 PM

Not Just Another 7 vs 9 Thread
 
[quote=StuBob;1235310]
So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?[quote]

The 9 gives back efficiency.
Aircraft 7 9
Range 75% 775 710
Range 55% 950 860
Fuel cap USG 42 36
Miles/Gal 75% 18.5 19.7
Miles/Gal 55% 22.6 23.9

I found out long ago you can torture numbers to support one position or another. Try weighting your numbers to give more importance to the performance numbers you value most. Then pick the 9.

StuBob 01-29-2018 07:29 AM

Quote:

Originally Posted by terrye (Post 1235363)
I found out long ago you can torture numbers to support one position or another. Try weighting your numbers to give more importance to the performance numbers you value most. Then pick the 9.

That?s how it works, isn?t it? Faced with such a dilemma, someone once told me to flip a coin. ?While the coin is in the air, you?ll wind up hoping for one outcome over another. Take that one, regardless of what the coin does.?

cajunwings 01-29-2018 08:01 AM

7 vs 9
 
Flown them both. Performance overall is pretty much the same when you average out minutes or dollars saved over several hundred hours. Acro of course means the 7. I prefer the way the 6 & 7 respond and handle when flying around for fun, but for long trips or occasional IFR the slightly less sensitive 9 handling is the ticket for me.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

N941WR 01-29-2018 08:59 AM

Quote:

Originally Posted by StuBob (Post 1235310)
...
So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?
...

The -9 is more balanced in its control harmony than the -7.

That is just one reason.

Raymo 01-29-2018 10:02 AM

Quote:

Originally Posted by StuBob (Post 1233611)
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.

Are you planning to build or buy? If buying, I suspect you'll find a -9(A) faster than a -7(A). Either will serve your mission well. The rest is likely nit-picking around the fringes of your mission scope (short field, O2 at high altitudes).

When I was looking for a used kit, everything was on the table but I found a great deal on a -7A first. If I'd found a similar deal on a -9 first, I'd be flying it and be just as happy. I enjoy doing rolls and look forward to loops but that ability was not critical to my decision making.

One advantage not mentioned about an A model is lower insurance cost. The tail-wheel folks (no offense intended) never seem to compare the number of ground loops with the number of nose gears that folded :D

StuBob 01-29-2018 12:07 PM

It?s a motivator to get me stay in the garage.

PerfTech 01-29-2018 03:50 PM

Quote:

Originally Posted by StuBob (Post 1235310)
This thread, combined with further research here, other sites, Van's, etc., brings me to this summary, as relates to the 3000nm AK trip. Assume two airplanes built per Van's recommendations, i.e., 160hp RV9 and 180hp RV7:

1) 100 mi range advantage 7.
2) 100 ft takeoff/landing distance advantage 9.
3) Cruise speed 10+ knots advantage 7.
4) 8 mph stall speed advantage 9.
5) The prices are almost identical, subject to prop choice.

So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?

Because I'm a contrarian, I really want to prefer the 9 taildragger. But this morning's math is providing a hurdle.

... I think there are a few things in this thread that were overlooked and possibly could be misconstrued by some. I see these numbers thrown out from Van's website for comparison purposes, and no one has mentioned (or I missed it) the fact that the RV-7 numbers on Van's site were gathered with a C/S prop, and the RV-9 numbers were with a F/P. This really changes the game as in take off and landing distances for one, as well as climb. I have a C/S on my 9 and believe me that is a real game changer. I routinely fly off a 500 ft. strip with obstacles at gross, and have yet to see that from another model. Also comparing the two aircraft at 8000' where the 7s perform there best isn't exactly apples with apples. My 9-A cruises @ 207 tas. on 7.1 gph. @8000', when up where I usually cruise 14,500 the fuel burn drops to less than 6.5 gph. with no reduction in tas. This reduction also considerably extends the range to five hrs. with reserve, (about 1,000 miles). Another thing I really like with the 9 series is the rock solid feel at higher altitudes. I fly high (16,500) when winds favor it, and the 9 doesn't even begin to drop its tail and mooch around like models designed to fly at lower altitudes. To me, for what I do the 9s are the best I have seen! The 7s in all fairness do have some advantages, as in aero rating, will fit in a smaller hangar, easier to wash, cheaper to paint, and the #7 just sounds lucky...:rolleyes::rolleyes:

StuBob 01-29-2018 04:07 PM

Allan, what engine are you using to get that TAS?

PerfTech 01-29-2018 04:22 PM

Quote:

Originally Posted by StuBob (Post 1235814)
Allan, what engine are you using to get that TAS?

....160 HP 320. I do run my rpm up higher, as my prop is modified to work better at the higher rpm. This will allow the engine to make a few more horses. I have also paid a lot of attention to eliminating as much aero drag as possible, as well as some rigging changes etc. Thanks, Allan..:D

tomww 01-29-2018 05:01 PM

Quote:

Originally Posted by PerfTech (Post 1235811)
... I think there are a few things in this thread that were overlooked and consequently misrepresented. I see these numbers thrown out from Van's website for comparison purposes, and no one has mentioned (or I missed it) the fact that the RV-7 numbers on Van's site were gathered with a C/S prop, and the RV-9 numbers were with a F/P. This really changes the game as in take off and landing distances for one, as well as climb. I have a C/S on my 9 and believe me that is a real game changer. I routinely fly off a 500 ft. strip with obstacles at gross, and have yet to see that from another model. Also comparing the two aircraft at 8000' where the 7s perform there best isn't exactly apples with apples. Me 9-A cruises @ 207 tas. on 7.1 gph. @8000', when up where I usually cruise 14,500 the fuel burn drops to less than 6.5 gph. with no reduction in tas. This reduction also considerably extends the range. Another thing I really like with the 9 series is the rock solid feel at higher altitudes. I fly high (16,500) when winds favor it, and the 9 doesn't even begin to drop its tail and mooch around like models designed to fly at lower altitudes. To me, for what I do the 9s are the best I have seen! The 7s in all fairness do have some advantages, as in aero rating, will fit in a smaller hangar, easier to wash, cheaper to paint, and the #7 just sounds lucky...:rolleyes::rolleyes:

Interesting idea that something can be overlooked and thus misrepresented.

One of the strengths of the 9, IMHO, is the lower stall speed and all that implies.

But you won?t find me ignoring the advice from Vans is it? A A pilot of an RV- 9A who is exceeding structural cruise speed, no matter how carefully and skillfully he flies, is not in control of the critical factors and is putting himself and his passengers at risk.

Have a look at the advice on engine size before pushing the limits. If you are going into that territory you might be much safer in the 7 due to its extra strength. If you choose to fly close to VNE I hope your guardian angle or whoever looks after you is looking out for you.

N941WR 01-29-2018 06:32 PM

Quote:

Originally Posted by tomww (Post 1235821)
...
But you won?t find me ignoring the advice from Vans is it? A A pilot of an RV- 9A who is exceeding structural cruise speed, no matter how carefully and skillfully he flies, is not in control of the critical factors and is putting himself and his passengers at risk.
...

207 mph TAS is not beyond the Vne of 210 mph TAS. It is close, very very close.

Allan must have some tricks up his sleeve because my O-360 powered -9 tail dragger will hit the wall right at 200 MPH / 175 knots, which is just fine by me.

His comments about flying high are right on the mark. Even at 17.5 the -9 is still flying nose down. Whereas the short wing RV's are flying nose up at those altitudes.

ChiefPilot 01-29-2018 08:29 PM

Quote:

Originally Posted by N941WR (Post 1235840)
207 mph TAS is not beyond the Vne of 210 mph TAS. It is close, very very close.

Tom wasn't referencing Vne. Max structural cruise speed, Vno, is something different.

ChiefPilot 01-29-2018 08:34 PM

Quote:

Originally Posted by N941WR (Post 1235840)
Even at 17.5 the -9 is still flying nose down.

The picture you posted earlier in this thread, in post #8, shows this to be false.

tomww 01-29-2018 10:55 PM

Quote:

Originally Posted by N941WR (Post 1235840)
207 mph TAS is not beyond the Vne of 210 mph TAS. It is close, very very close.

Allan must have some tricks up his sleeve because my O-360 powered -9 tail dragger will hit the wall right at 200 MPH / 175 knots, which is just fine by me.

His comments about flying high are right on the mark. Even at 17.5 the -9 is still flying nose down. Whereas the short wing RV's are flying nose up at those altitudes.

The point is that those speeds are getting near the edge for the RV9. Read the warning on the Vans web page link. That is dangerous territory for the 9. Good luck if you go there deliberately.

It?s not chance that link is only on the 9 page. The dangers are there for any aircraft but it?s a tighter corner for the 9.

As for how Alan gets that extra 7mph. Well I?ve seen all sorts of things claimed on the internet, I certainly don?t believe it all. Let?s hope however it?s done that he has covered the dangers inherent in that speed in the 9.

PerfTech 01-30-2018 06:35 AM

Quote:

Originally Posted by ChiefPilot (Post 1235868)
Tom wasn't referencing Vne. Max structural cruise speed, Vno, is something different.

....Only cruise in smooth air at the quoted speeds, and have
performed many mods to add some extra strength in critical
areas. We may offer some more of these mods on our website
in the future. We see lots of interest in these, but are still in
the testing stage at present. Thanks, Allan:D

N941WR 01-30-2018 09:07 AM

Quote:

Originally Posted by ChiefPilot (Post 1235869)
The picture you posted earlier in this thread, in post #8, shows this to be false.

Looks pretty level to me. Besides, the -9 seems to fly more nose down than the short wing RV's. At that altitude, it is still nose down, just not as much as at 8,500'

N941WR 01-30-2018 09:13 AM

Quote:

Originally Posted by ChiefPilot (Post 1235868)
Tom wasn't referencing Vne. Max structural cruise speed, Vno, is something different.

Good point but is Vno TAS or IAS?

N941WR 01-30-2018 09:18 AM

[quote=tomww;1235892]The point is that those speeds are getting near the edge for the RV9. ... [/url]

Yep, they are close but not over.

It is up to the pilot to manage the speed. Even an O-235 powered -9(A) can hit those numbers going downhill.

grubbat 01-30-2018 09:18 AM

AIRSPeed
 
Vno is indicated and Vne is true. Interesting huh?

Somewhere north of 8500ft, Indicated becomes secondary to True AIRSPeed.

ChiefPilot 01-30-2018 09:43 AM

Quote:

Originally Posted by N941WR (Post 1235950)
Looks pretty level to me. Besides, the -9 seems to fly more nose down than the short wing RV's. At that altitude, it is still nose down, just not as much as at 8,500'

The PFD does not show any kind of "nose down" indication. And, "Looks pretty level to me" would seem to contradict "it is still nose down".

N941WR 01-30-2018 10:34 AM

Quote:

Originally Posted by ChiefPilot (Post 1235969)
The PFD does not show any kind of "nose down" indication. And, "Looks pretty level to me" would seem to contradict "it is still nose down".

That might be because "level flight" is nose down and the EFIS is so calibrated.

rvbuilder2002 01-30-2018 10:58 AM

Regarding smooth air......
 
The two worst turbulence events I have had in my flying career (both while flying RV's at high speed cruise and bad enough to cause major head impact on the canopy even with very tight belts) were surely encounters with wake turbulence, since the air had been glassy smooth for the previous 1/2 hr and it was for the half hour after the event.

N941WR 01-30-2018 11:42 AM

Quote:

Originally Posted by rvbuilder2002 (Post 1235991)
The two worst turbulence events I have had in my flying career (both while flying RV's at high speed cruise and bad enough to cause major head impact on the canopy even with very tight belts) were surely encounters with wake turbulence, since the air had been glassy smooth for the previous 1/2 hr and it was for the half hour after the event.

Ditto for me. Even bruised my shins from hitting the bottom of the panel.

Raymo 01-30-2018 11:50 AM

Quote:

Originally Posted by N941WR (Post 1235988)
That might be because "level flight" is nose down and the EFIS is so calibrated.

Likely true with some AHRS but the Dynon AD-AHRS must be mounted within 1 degree of all three aircraft axes. (Page 5-9 of the install manual).

PerfTech 01-30-2018 12:46 PM

Quote:

Originally Posted by rvbuilder2002 (Post 1235991)
The two worst turbulence events I have had in my flying career (both while flying RV's at high speed cruise and bad enough to cause major head impact on the canopy even with very tight belts) were surely encounters with wake turbulence, since the air had been glassy smooth for the previous 1/2 hr and it was for the half hour after the event.

....Actually now that you said this, it reminded me of one we experienced in one of our RV-9As, going through the Banning pass in So Cal. It was violent enough to break the canopy, and the back of it lifted up, loosing our headsets and some baggage out the opening. My G-Meter was pegged at +6 & -4.2 and must say this was the hardest hit I have ever had. When my head hit the top it almost knocked me out, causing me to loose control and 3,500 ft of altitude prior to regaining control. This took the fun out of flying for a time but the plane survived it remarkably well. A testament to how good these little planes are. ...:eek:

tomww 01-30-2018 03:07 PM

Quote:

Originally Posted by grubbat (Post 1236022)
...... then I woke up. 😁

In reality, ive never hit clear-air non-forecasted severe turbulence before but it?s one thing that does keep me up at night. Those are the times you are glad you are operating with lots of margins. By the way, the -9 is better. 😂

The 9 may be better at some things. The amount of margin is not one of them. Not this post, but some of the posts in this thread seem to ignore reality and are trying to operate very near the edge.


Hope the man who over stressed his 9 to 6G had it checked by a competent engineer.

PerfTech 01-30-2018 04:36 PM

Quote:

Originally Posted by tomww (Post 1236037)
The 9 may be better at some things. The amount of margin is not one of them. Not this post, but some of the posts in this thread seem to ignore reality and are trying to operate very near the edge.


Hope the man who over stressed his 9 to 6G had it checked by a competent engineer.


...Yes!
That would be me. Thanks, Allan..:rolleyes:

170 driver 01-31-2018 06:28 AM

The RV9 may not be the fastest model but I did outrun a M20C Mooney with 180 hp retractable gear and a cs prop with my fixed gear 150 hp and a fp prop, one person in each plane.

N941WR 01-31-2018 06:42 AM

Quote:

Originally Posted by Raymo (Post 1236005)
Likely true with some AHRS but the Dynon AD-AHRS must be mounted within 1 degree of all three aircraft axes. (Page 5-9 of the install manual).

And then you can adjust it. Same as a steam gauge.

Raymo 01-31-2018 07:40 AM

Quote:

Originally Posted by N941WR (Post 1236167)
And then you can adjust it. Same as a steam gauge.

If, by "adjust it", you mean modifying the AD-AHRS mount, that would be true. There is no adjustment otherwise. Why someone would want or need to adjust this in an EFIS is the question in my mind.

bret 01-31-2018 07:50 AM

Question for those that hit the canopy, do you have a 4 or 5 point harness, and how close were you to the canopy, almost 14 mod?

PerfTech 01-31-2018 09:39 AM

Quote:

Originally Posted by bret (Post 1236179)
Question for those that hit the canopy, do you have a 4 or 5 point harness, and how close were you to the canopy, almost 14 mod?

....When we had our experience, we only had four points, I ordered five points the very next day! I now absolutely refuse to let anyone in my airplane unfasten their belts, in flight in my RV after this incident. Had one or both of us not been fastened in, we no doubt would have been ejected for sure. The seat mod does provide about three more inches of head room, but in the case of violent turbulence, I really don't believe it would make much difference. The reason is, the attach points for the shoulder harnesses and seat belts, are really designed for a crash or forward impact, and not to help hold you down. Its not improper design, but more a case of the using the strongest points for attachment available. There is a way to remedy this, and if there is an adequate amount of interest from others, we can create a kit that will address, and eliminate the issue. If this is of interest to you, please send send a PM so we know and can look at it more. Thanks, Allan..:D

N941WR 01-31-2018 09:47 AM

Quote:

Originally Posted by Raymo (Post 1236177)
If, by "adjust it", you mean modifying the AD-AHRS mount, that would be true. There is no adjustment otherwise. Why someone would want or need to adjust this in an EFIS is the question in my mind.

It helps if you read the manual:

Quote:

Originally Posted by Dynon SkyView Manual
How to Enter the In Flight Setup Menu
When airspeed is greater than zero or groundspeed is greater than 15 knots, simultaneously pressing and holding buttons 7 and 8 when on the Main Menu will open the In Flight Setup Menu. This menu gives users access to SkyView system tools which may be useful during flight such as the Flight Angle Pitch Adjust Page and the Angle of Attack Calibration Wizard.
You may also access the Setup Menu from the In Flight Setup Menu by using the ENTER FULL SCREEN SETUP MENU? option.



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