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04-20-2011, 03:11 PM
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Join Date: Jan 2005
Location: TX32
Posts: 1,891
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Maybe, maybe not...
Lee,
First, RV's are sportsman-level aerobatic airplanes, period. It was designed to yield "total performance" across the board, STOL. exceptional power to weight and excellent cruise speed along with aerobatic capabilities. It is not a Pitts S-2, Extra or Cap-10.
The 0-360 RV4 with C/S prop is less of a CG issue for dual acro unless you have a big, over 200 pounder squeezed in the trunk. The Rocket is better suited for that chore! As mentioned above, the 0-360 C/S birds are a bit heavier so adjust your load accordingly. I normally fly acro with 10-12 gallons on board or less and keep my sorties down to 15 minutes or less. Despite rumors to the contrary, you don't need inverted fuel and oil systems or a flop tube to have fun. All three of my airplanes have used a stock setup with a Carb/injection and an air-oil separator added to catch errant crankcase spillage. The IAC sportsman routine can be flown without inverted systems. To quote Clint: "A man's gotta know his limitations" http://www.youtube.com/watch?v=gXOp37rVr_s
The RV6 is equally adept at aerobatics and easier to instruct out of if you are so inclined. If you fly more solo than dual, buy a 4. If you have a spouse who likes to fly and wants to learn how, go with a six. If you're doing serious acro, buy something else.
My choice would be the lightest weight RV4 or 6 you can find, 0-320 wood or composite prop.
Both are great airplanes.
Have fun!
Smokey
RVX
Competition? http://www.vansairforce.com/communit...p?t-53520.html
I built a lightweight, 0-320 wood prop -4 in the 80's (in a base housing shed!) and enjoyed 1500 wonderful hours, many doing positive G aerobatics. 50 lb tailwheel weight has always been my goal for a nice aerobatic RV. My rule was no more than 100 lbs in the back seat for acro, no more than 200 lbs ever. The RV4 gives you the most absolute bang for your buck in a personal airplane. My HR2 delivered "lots more bang for lots more bucks!" Personally, the lighter weight RV's (like any airplane) just fly better. By definition, they also have a higher useful load.
Last edited by smokyray : 04-20-2011 at 04:19 PM.
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04-20-2011, 04:19 PM
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Join Date: Jan 2007
Location: NC
Posts: 664
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Quote:
Originally Posted by smokyray
The IAC sportsman routine can be flown totally positive G.
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This is true, but you won't score well...if you care about that.  Maintaining positive G, you'll run into problems drawing the inverted 45 lines and rolling during the wedge/cubans...or doing a proper level roll period. But RVs roll fast enough that you could draw a proper negatively-loaded line with minimal time spent flying a glider (if you have a carb) and dumping oil out. There are several zero G up/downlines that can throw oil as well. Unless you use a separator, you might just be spending some time cleaning the belly after a flight.  But even if you're willing to do a wipe down, without a separator, you can lose a significant amount of oil. This is the biggest concern. I heard of one of the TEAM RVers losing 4 qts or so during a flight. Of course this depends on the duration of the flight and number of zero to negative G maneuvers.
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04-20-2011, 06:10 PM
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Join Date: Jan 2005
Location: TX32
Posts: 1,891
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In a flat spin, headed out to sea...
Absolutely Eric, totally agree. Which leads me to my previous link which you so eloquently posted and raises the question: Maybe there should be an RV category similar to the one they use in South Africa. It would stimulate interest from the largest sport flying group in the US, generate some revenue and develop skills many pilots need. It's a win win in my book...but I digress from the original post...
Smokey
http://www.vansairforce.com/communit...p?t-53520.html
Last edited by smokyray : 04-20-2011 at 06:17 PM.
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12-03-2012, 03:33 PM
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Join Date: Jul 2012
Location: FLL
Posts: 120
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I too am looking at an RV4 for 'sport acro'
I did a W&B and found that with me (160) and my wife (120) and 20G fuel (120#) that I am under the Aerobatic limitations. But I did this on someone else's XL sheet and having some exp with W&B I'd really rather do the math myself.
The thing is.... I have found the Aerobatic Aft CG limit listed, but it is listed in % of cord or aft of LE. What is the Aft CG limit in aft of datum?
So, what is the Aft CG limit in inches aft of Datum?
And does my above statement seem true that with me (160) my wife (120) and 120 #s of fuel we would be within Aerobatic CG calcs?
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12-03-2012, 06:13 PM
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Join Date: Jan 2007
Location: Daleville, AL
Posts: 343
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passenger acro
Call me chicken, very old and not bold, but I won?t do aerobatics with a passenger in my RV-4. Now clearing maneuvers without significant changes in altitude and airspeed with low positive Gs are exceptions occasionally. As mentioned many times, when the C.G. goes aft with a passenger, the pitch is very light and super sensitive in a -4. When I had a very temping offer to take two cute young ladies up for a thrill ride (with parachutes), I loaded a tote bag and back pack full of magazines to 110 lbs, and strapped them in the back seat to slowly explore the acro envelope before taking them up. The change from zero and low negative Gs to positive Gs really changed the aircraft pitch angle even when I was expecting it. It scared me, so I didn?t take them up, but then I didn?t get puke on the back of my neck either.
FrankH on this forum has a lot of acro experience in his RV-7 with passengers, but he?s had a few unanticipated exciting moments such as an over pitched hammer that got into an inverted spin. Thanks FrankH for writing that one up. The idea of the RV category for IAC events (Smokey) has been tried before, but the RVs just don?t seem to have the interest. For gentleman aerobatics, RVs without inverted systems can participate in the IAC Primary category, which includes a loop, roll, ? Cuban 8, 180 degree turn, and a spin. One of IAC Hall of Famers, Giles Henderson, is flying a Cassutt racer in the primary category, and having just as much fun as the other participant. Eric Sandifer is our best source for acro info, and would be glad to help other RVers join in the IAC fun .
Bill McLean
RV-4 Slider
Alabama
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12-03-2012, 06:14 PM
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Join Date: Nov 2006
Location: Oklahoma
Posts: 672
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Please be careful. It sounds like you are doing the proper research.
Here is one example where over gross and aft c.g. went very bad in an RV 4.
http://www.atsb.gov.au/media/24397/a...701033_001.pdf
Joe
__________________
Joe Schneider
RV-7, IO-360, BA Hartzell, N847CR
Flying since 2008
Last edited by Caveman : 12-03-2012 at 06:17 PM.
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12-03-2012, 07:52 PM
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Join Date: May 2005
Posts: 377
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I hate to bring this up but....
does the weight of the fuel matter? Fuel is pretty much the only thing that you can put in a -4 to move the cg forward and since it is in the wings, it actually reduces the g load on the center spar. The big question is how Vans did the engineering.
__________________
Charlie "T.Bear" Guarino
Springtown, TX
RV-4 Flying again with a fresh overhaul
Exempt but paid
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12-03-2012, 08:14 PM
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Join Date: Apr 2007
Location: Memphis
Posts: 159
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"Inviting the Undertaker"
"Inviting the Undertaker" was an automobile safety cartoon series that ran in the New York Daily News until 1969, penned by one, Clarence D. Bachelor, gaudily depicting driving practices that would ultimately lead to the grave. Had C.D. been alive to this day, no doubt he could draw an interesting cartoon representing the hazards of two up, cavorting in aerobatics in the RV-4.
Barney, in Memphis
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12-03-2012, 10:09 PM
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Join Date: Oct 2009
Location: Victoria, BC, Canada
Posts: 3,932
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Quote:
Originally Posted by cguarino
does the weight of the fuel matter? Fuel is pretty much the only thing that you can put in a -4 to move the cg forward and since it is in the wings, it actually reduces the g load on the center spar. The big question is how Vans did the engineering.
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It has been said anecdotally that Van once said that fuel in the wings does not count towards aerobatic weight. It has never been put in writing by the factory. If nothing else, it flies in the face of common sense... at 1600lb gross, take away the weight of full fuel tanks in the -6, and you're left with the aerobatic gross weight (roughly). So why have separate aerobatic and non-aerobatic gross weights?
While the fuel unloads the bending moment at the wing root, it does not unload the bending moment at the outer tip of the tank. I wouldn't trust it without sound engineering documentation supporting it.
__________________
Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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12-04-2012, 06:36 AM
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Join Date: Jul 2009
Location: Niceville, Florida
Posts: 434
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Light nose = great BFM machine...
A light nose -4 or -6 is a delight to fly (Smokey nailed it)--a classic case of "less is more." Both are limited in the payload they can carry for aerobatics and neither one is an Extra. "Solo only" is about right in most cases. A handling difference between the two is stick force gradient or the number of G's per inch of stick travel. The tandem configuration of the -4 means that a typical example will have a more forward CG/higher stick force than a -6 with a similar load; but again, it's aircraft specific (the scales [if they are properly calibrated] don't lie).
The spin characteristics of the two are different as well. The -6 handles more like a T-37 than the -4. In the -6 (or any of the side-by-side airplanes), just about all of the variable payload is relatively close to the CG and the shape of the fuselage likely contributes to the tendency of the -6 to flatten out a bit more than a -4; so these characteristics make sense.
The other thing about RV's is that once the nose is down, they acellerate fast; so you need to balance G, AOA and nose rate to keep the speed under control (especially if you have a light weight fixed pitch prop). They will easily scoot past redline, and a quick stick snatch above about 135 MPH or so will cause an over-G (I like idle RPM once I'm on my back and starting to pull, and always cross check airspeed before I commit the nose down). With G, the -4 has better buffet cues than it does during a 1 G stall, and if you do pull too hard, the the nose simply stops tracking if you encounter an accellerated stall. The airplane responds immediately to an unload.
Can't really go wrong with either airplane flown within the design limits that has been properly tested to those limits...or you could be like Smokey and splice a -6 with a -4 and get the best of both worlds!
Cheers,
Vac
__________________
Mike Vaccaro
RV-4 2112
Niceville, Florida
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