Why two GW's for the RV-9?

While looking at the Van's RV-9 web page (again) I was wondering why there are two different gross weights listed for the RV-9.

Van's Web Site said:

Weights
Empty Weight 1028 - 1075 lbs
Gross Weight 1600 - 1750 lbs

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Could someone explain this to me? Is it based on the empty weight, the engine size, or did they strengthen the airframe after they sold a bunch of kits? If I make mine really light (I've seen one -9 that weighed 998 lbs.) does my GW go down?

Different engines?

I'd guess it has to do with engine size. There is a huge difference between 118HP and 160hp. Normally GW is either based on HP or landing gear strength. If the landing gear is the same, it's gotta be the HP.

9 vs 9A?

osxuser said:

I'd guess it has to do with engine size. There is a huge difference between 118HP and 160hp. Normally GW is either based on HP or landing gear strength. If the landing gear is the same, it's gotta be the HP.

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Don't know but here are the engine weights as I know them: (There might be some variation based on model of each engine.)

O-235 250 lbs
O-290 262 lbs
O-320 278 lbs

The gear legs are the same and the GW's are listed the same for the -9 & -9A.

N941WR said:

While looking at the Van's RV-9 web page (again) I was wondering why there are two different gross weights listed for the RV-9.

Could someone explain this to me? Is it based on the empty weight, the engine size, or did they strengthen the airframe after they sold a bunch of kits? If I make mine really light (I've seen one -9 that weighed 998 lbs.) does my GW go down?

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It's for the small vs large engine setups. The airframes are all the same 9 & 9A, it's just to ensure that you can climb out of your own wake so to speak!

akarmy said:

It's for the small vs large engine setups. The airframes are all the same 9 & 9A, it's just to ensure that you can climb out of your own wake so to speak!

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I'm not sure I buy that Andy. Van's lists the GW climb performance for the small engine RV-9 as 1,000 FPM (The -9A is 950 FPM). Even if you added the 150 lb difference what would your climb rate drop to? 850 & 700 FPM, about the same as a light 172.

Landing gear and HP are secondary factors in determining gross weight. G-loading is the major factor in determining gross weight. That's why aerobatic gross is lower than normal gross. Having said that, HP IS a factor. You want to be sure that your HP is sufficient for the weight. I'm sure this is the reason for the 2 gross weights listed by Van's.
Mel...DAR

N941WR said:

I'm not sure I buy that Andy. Van's lists the GW climb performance for the small engine RV-9 as 1,000 FPM (The -9A is 950 FPM). Even if you added the 150 lb difference what would your climb rate drop to? 850 & 700 FPM, about the same as a light 172.

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I think it's just an attempt by Van to set some guidelines and bounds for expectation of performance on the small engine version. Many overload their RV's above the published GW, so in the small engine case it would get even worse.

What if I...

Mel said:

Landing gear and HP are secondary factors in determining gross weight. G-loading is the major factor in determining gross weight. That's why aerobatic gross is lower than normal gross. Having said that, HP IS a factor. You want to be sure that your HP is sufficient for the weight. I'm sure this is the reason for the 2 gross weights listed by Van's.
Mel...DAR

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Mel,

What if I set my GW at 1750 (or 1850 or 1950) and through the phase 1 GW flights never fly at a GW above 1675 and I never test it at 1750. Can I close out my phase 1 testing or do I need to fly at 1750 to have a paper GW of 1750?

As you may already know, since the RV is an experimental plane, you can set the GW at whatever you, as the builder, determine is correct.
VAN's, as the designer, offers what he believes to be the safe and acceptable GW for each RV type, based on his engineering of the aircraft and the testing they have performed.
In building my RV6, if I remember correctly, he specified a different GW for the TD version versus the Nose Wheel version. In looking at VANs specifications page for the RV6, you will note that he shows 1600 lbs GW for the TD and 1650 lbs GW for the 6-A.
I don't know what the difference in weight for TD versus NW parts is, but I exect that the difference is to provide for more similar usable weights between the two models.
Remember, if you stray too far from the designer's recommendations, you become a real test pilot!

I and my family are large (Im 6'5", 250 lb muscular - not a lot to lose). Im curious what a realistic gross weight might be with 200-225HP in a RV-9A; i'm considering a turbocharged wankel engine, so I could actually have a little more power on tap if needed.

Ideally it would be enough for some baggage, full fuel, and ~500 lbs passengers @ 5000 ft base altitude. Im guessing that with the lift of the longer wing and with a little more speed on takeoff, the extra weight wont be a big deal. Anyone know better?

sf3543 said:

In building my RV6, if I remember correctly, he specified a different GW for the TD version versus the Nose Wheel version. In looking at VANs specifications page for the RV6, you will note that he shows 1600 lbs GW for the TD and 1650 lbs GW for the 6-A.
I don't know what the difference in weight for TD versus NW parts is, but I exect that the difference is to provide for more similar usable weights between the two models.

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It was quoted years ago in an article about Alan Tolle's RV-6A..............17 pounds more for the RV-6A versus the RV-6. Take off the tailwheel and its mount, remove one rear bulkhead at the aft fuselage, two maingear mounts and add one nosewheel assembly at the front.

sf3543 said:

... In building my RV6, if I remember correctly, he specified a different GW for the TD version versus the Nose Wheel version. In looking at VANs specifications page for the RV6, you will note that he shows 1600 lbs GW for the TD and 1650 lbs GW for the 6-A.
I don't know what the difference in weight for TD versus NW parts is, but I exect that the difference is to provide for more similar usable weights between the two models.
Remember, if you stray too far from the designer's recommendations, you become a real test pilot!

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Van's web site lists the number I put in the prior post, there is no difference in GW for TW vs. NW, only a difference in empty weight.

cobra said:

curious what a realistic gross weight might be with 200-225HP in a RV-9A; i'm considering a turbocharged wankel engine, so I could actually have a little more power on tap if..

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Cobra,

I'll say it before anyone else does. The RV-9 is designed for a max of 160 hp bla bla bla

Your issue is one of the limits of being a bigger guy. Maybe you sould look at a -7 w/ tip-up (not a -7A), build it light, meaning O-320, day VFR w/o a lot of the instruments, one small radio, no interior, etc. The GW of the -7 is listed at 1800. If you built it light, and it is possible, you would have all the useful load you need. (The reason I recommend the -7 w/ tip-up is that is the lightest combiniation Van's sells.)

Bill,
You are realisticaly supposed to test to gross weight and forward and aft CG limits during Phase I. Does everybody do it? Probably not! If something happened at gross weight and the insurance co. found that the airplane wasn't tested at this limit would they have a reason to not pay off? Probably! Let's not give them ammunition to use against us. BTW, If any of you plan to set gross weight above the designers recommendations, you should talk to your DAR. A small increase is usually OK, but dramatic changes may make certification difficult.
Mel...DAR

Bill,
With an adjustable wastegate controlled turbocharger, it is possible to run the engine without boost and at regular cruise rpm (around 160 HP) without any penalties other than the minor weight for the turbo system. A flip of a switch adds a little boost and allows the engine to operate at a higher, but safe, rpm when more power is needed for takeoff/climb, to get a little better fuel economy when using higher-octane avgas fuel, or to fly with normal power at higher altitude.

The Wankel does not care if you increase rpm or add a little/lot of boost at all, it just burns a little more fuel to achieve the HP iincrease. A turbocharger provides the best characteristics of both a small and large engine, and the Wankel can do it all at approx the same (lighter) weight of a O-320 Lycomming. In fact, the effects of a lighter engine has me a bit concerned regarding cg balance issues with heavier passengers.

I agree with you regarding use of excessive HP if used to achieve higher-than-designed for speeds. My thoughts are that the extra power is a real benefit when it is used temporarily for faster climb or possibly to lift a slightly heavier payload as was suggested earlier.

Van's said:

There are 3 in fact, one for each of the engine types. The smaller engines cannot lift such a large load as the bigger ones, the cg
range is the same for all.

Vans

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So, it does look like it is HP based. I guess if you are ok with 200 fpm climb you could set the GW higher, assuming you test your craft at the higher weight.