CG of an RV-7

[rjtjrt]

When building an RV7 (not 7A) is it more likely that you will end up with an aircraft with C of G tending forward or aft? I know there are a million variations, but presumably there is a tendency to end up at end of build more one way or the other. I am thinking of whether the tendency would influence if you would want to have a CS prop, whether you may place battery on firewall or further aft. There may be no problem at all. There may be a lot of different solutions.
Unfortunately a search of "C of G RV7 is rejected by search engine.
John

 

[Jim P]

You're right, there are a lot of variations and the engine/ prop combination is a big factor in the equation. I went with an IO-360-M1 (180 HP), with constant speed. Solo, with full tanks, the airplane is a a little nose heavy, but with a passenger, it really feels about right. I found that I can easily go 200 lbs over gross and still be in the CG no problem. I'm sure others will chime in with their experiences but I believe there's good reason why a lot of folks say the 180 HP/ Constant Speed is the best optimization for a -7.

 

[yakdriver]

I also have the IO-360 180hp and Hartzell C/S prop and battery on the firewall. With full fuel I am right on the forward CG and it will also take a lot of weight before it goes aft CG. Seems like the best combo. An angle valve engine gets the Cg too far forward solo and the 160HP fixed pitch you have to watch the aft CG. Don

 

[rgbewley]

CG Issues 7

You might take a look at Marc Ausman of Vertical Power's website on his -7. He has a heavier engine (IO-390), and he probably posted any issues that he had due to weight there.

www.io-390.com

.

 

[Dave Cole]

RV-7 CG tends toward aft

The RV-7 will tend toward the aft CG limit when fully loaded with fuel, passengers, and baggage. If you want to be able to use all of the allowable 100 pound baggage load at max gross, you should do all you can to minimize weight aft of the baggage area (don't mount equipment back there), while adding some useful weight (like a constant speed prop) as far forward as possible. Otherwise, the overall weight should be kept to a minimum.

If you can build an 1,100 pound RV-7, the extra weight of a constant speed prop and a fuel injected engine will help toward keeping CG forward ofthe aft limit with two 175 pound people, 100 pounds of baggage, and minimum fuel. Full fuel (250 lbs) will move the CG forward and put the aircraft at 1800 lbs.

 

[Rockyjs]

Go to Dan C's site. He has a weight and balance section with a lot of RV-7s listed to get an idea.

I have a Superior IO-360 horizontal induction with a WW 200RV constant speed prop. My Empty CG is 79.20" with a weight of 1093 lbs.

I believe most RV-7s are a little on the tail heavy side. When building I was concerned with using the lighter WW prop over the intiially planned Hartzell. In the end things worked out fine.

 

[Mel]

Aft CG limit must be figured with minimum fuel.

If you can build an 1,100 pound RV-7, the extra weight of a constant speed prop and a fuel injected engine will help toward placing the CG at the aft limit with two 175 pound people, 250 pounds of fuel, and 100 pounds of baggage.

Never "push" the aft CG limit with full fuel. You can't always fly with full fuel. As you burn fuel, the CG moves aft. Anytime you want to push the aft CG limit, calculate it with minimum fuel.

 

[Dave Cole]

Misstated point.

You are right, Mel. I misstated my point and have edited it.

 

[tomharney]

mtow rv7

could anyone help me with mtow eg 1800lbs as i am ready to register my 7 and may put tip tanks on at a later date

 

[RudiGreyling]

The RV-7 will tend toward the aft CG limit when fully loaded with fuel, passengers, and baggage. If you want to be able to use all of the allowable 100 pound baggage load at max gross, you should do all you can to minimize weight aft of the baggage area (don't mount equipment back there), while adding some useful weight (like a constant speed prop) as far forward as possible. Otherwise, the overall weight should be kept to a minimum.

If you can build an 1,100 pound RV-7, the extra weight of a constant speed prop and a fuel injected engine will help toward keeping CG forward ofthe aft limit with two 175 pound people, 100 pounds of baggage, and minimum fuel. Full fuel (250 lbs) will move the CG forward and put the aircraft at 1800 lbs.

Ditto on what Dave said...the "reason rumor" why the RV7 tend to be tail heavy is that Vans changed to a bigger vertical and rudder late in the process after spin testing and did not counter it with a design change. The bigger rudder that far back moved the empty CG back.

I have a 'well' equiped FP RV7 and I actively tried to ensure I fit most accesories as far forward as possible. Mine = 1102 pounds and empty CG at 80.7. With 2 x 170 Pilots and I have to limit luggage to 80 lbs to stay withing rear CG minimum fuel.

80 lbs luggage is a lot, just been RV camping this past weekend, and our luggage VOLUME space maxed out out 50lbs.

I am very happy with mine...Good luck,
Rudi

 

[Mel]

Vans changed to a bigger vertical and rudder late in the process after spin testing and did not counter it with a design change. The bigger rudder that far back moved the empty CG back.

The vertical stabilizer did not change, and there is very little difference in the weights of the 2 rudders. Van designed the -7 with a more aft CG is because everyone continues to install bigger and heavier engines and props.
(MY thinking!)

 

[N941WR]

The vertical stabilizer did not change, and there is very little difference in the weights of the 2 rudders. Van designed the -7 with a more aft CG is because everyone continues to install bigger and heavier engines and props.
(MY thinking!)

Mel,

I asked Van if the larger/bigger engines people were installing in the -6 was one of the reasons for some of the changes he made to the -7 and he said yes it was.

The funny thing is how many people are now installing (I)O-540's in -7 and -8's.

I figure if he designed them for the 540 someone would install an IO-720.

 

[Mel]

YEP!

If you offered them IO-720s they would want J-85s.
My O-320 RV-6 has been flying for over 15 years and I still like it. It weighs 1027 lbs.

 

[RudiGreyling]

The vertical stabilizer did not change, and there is very little difference in the weights of the 2 rudders. Van designed the -7 with a more aft CG is because everyone continues to install bigger and heavier engines and props.
(MY thinking!)

Hi Mel, thank you for the correction on the Vertical not changing.
Like it said it is rumor that the bigger rudder was heavier, moving the CG more aft. Wonder how much the rudders differ in weight.

Anycase I think on the RV7 less than 10% of people fit 6 cylinder or 200HP engines so why VAN would 'penalise' the ordinary 90% of us?? or the guys that want to build really really light? does not make sense....Maybe when the design and prototype was done the CG range was close enough that did not warrant design changes to cater for specificaly the people on the lighter side of the spectrum.

Anycase, I am happy! You just have to ensure you KNOW your cg limitations for SURE! And know where to put stuff when you start your build!

Regards,
Rudi