Model selection and CG

[CDRDATA]

I'm in the process of model decisions. I started with the 7A primarily because there are so many flying. However, I like the idea of a smaller engine as fuel prices continue to climb, which makes the 9A attractive for long-term cost of ownership. Here's the part that makes my question sound fairly stupid: Since I'm fairly rotund and so is my girlfriend, the issue of CG has come up in an effort to find ways to accomodate an FAA non-standard person well above 170 lb PIC and pax. The 7A can handle a larger engine and CS prop which pushes CG forward so we can balance well. The 9A has a smaller engine which pushes CG further aft. Am I missing something? Has anyone run into CG issues related to body mass and the small engine that was resolved by a different model? Of course the easy answer is to lose some weight and I'm working on it, but the practical matter of designing to the good life experienced by those who can afford a personal aircraft instead of the 170 lb FAA standard person seems incongruous. The fact that the fuselage for both models has the same width in the cabin leads me to think the 9A is meant for the same people and CG more sensitive to fat folks. I have not discussed this with Vans yet, was looking for usre experiences. Thanks.

Dennis Snyder, CDR Data

 

[terrykohler]

Weight is the issue more than CG with the 9A

My 9A sports an O320 with FP prop. I have a GW of 1800. With both seats loaded to 425 lbs., I can still put 75 lbs. in the baggage bay and carry 27 gallons of fuel. If I stay within gross, the only way to get out of CG is with one seat occupied with less than 100 pounds.
Terry, CFI
RV-9A N323TP

 

[PerfTech]

Not a Problem!!!!

I'm in the process of model decisions. I started with the 7A primarily because there are so many flying. However, I like the idea of a smaller engine as fuel prices continue to climb, which makes the 9A attractive for long-term cost of ownership. Here's the part that makes my question sound fairly stupid: Since I'm fairly rotund and so is my girlfriend, the issue of CG has come up in an effort to find ways to accomodate an FAA non-standard person well above 170 lb PIC and pax. The 7A can handle a larger engine and CS prop which pushes CG forward so we can balance well. The 9A has a smaller engine which pushes CG further aft. Am I missing something? Has anyone run into CG issues related to body mass and the small engine that was resolved by a different model? Of course the easy answer is to lose some weight and I'm working on it, but the practical matter of designing to the good life experienced by those who can afford a personal aircraft instead of the 170 lb FAA standard person seems incongruous. The fact that the fuselage for both models has the same width in the cabin leads me to think the 9A is meant for the same people and CG more sensitive to fat folks. I have not discussed this with Vans yet, was looking for usre experiences. Thanks.

Dennis Snyder, CDR Data

Not a Problem!!!!!!
We have a 9-A and a food fetish as well. I tip the scales at 285lb & the wife is a tiny 185lb. My plane is virtually impossible to load out of CG with less than 60lb in the baggage area. If you have a 0-320 with a metal prop or C/S prop, it will always be fine and of no concern. I installed a Catto three blade and found that two fat guys, 275lb each and 100lb of baggage with no fuel will put you at the rear envelope. And yes the smaller engine is far more economical and performs in the9-A very well. I cruise at around 10K ft @ 197 mph on 8 gph.Down low @ 4k ft pulled back to 160 mph I only burn 6 gph. Hope this info helps you with tour decision.
Regards, Allan

 

[CDRDATA]

Insightful responses

Thanks for the quick replies. Looks like everyone selected the heavier 320 with no problems. The 9A helps me save in engine cost as well as long-term ownership fuel costs, and this forum helps preserve my interest in Vans. That money can go to nicer seats or whatever. In case you couldn't make it the Vans formation at Oshkosh was very nice and there was at least a football field of RV's of all models.

Best regards,

Dennis

 

[Robert M]

CG limits

Hi Dennis.

Check with the gang in the RV-7/7A forum and see what they say but it seems to me that the RV-7 (not sure about the "A") has had a slight tail heavy problem with most builds, but, again, I'm not sure.

I haven't heard anything about 9/9A CG problems. The only thing I have heard is that the builder should build the 9/9A's as light as possible but I'm sure that holds true for all models.

There's not a lot of difference between the 9 and 7 except that the 7 has some aerobatic ability and goes a little faster because of power plants available. The fuselage is near idetical between the two models.

 

[Camillo]

Actually, I believe that the RV9A with an O-320, a hartzell prop and a 60 amp. has a consistently fore center gravity. At least this is the impression on my RV after 40 hours flying. It is difficult to have the nose up once landed, since it likes to go down quickly and if you keep it up it then goes down hardly starting to "jump".

With Cessnas 172's, 152'2, Socata Tampico, Pinguino F22/C, etc... I can easily play around the center gravity and let the nose wheel go down after landing when I prefer well after the touch down speed. With the RV9A you can keep it up only a couple of seconds and then it goes down.

If I had to build it again, I will install the battery PC-680 behind the baggage compartment. I guess this will not produce any particular problem, since with actual numbers I can place a 45 Kg. stuff in the rear baggage area and stilll be approx. 1/2'' fore of the aft center gravity limit.

So, you can only have a benefit from above average pilot and pax. weight. Of course this will reduce the baggage stuff.

 

[CDRDATA]

Thanks Everyone

Thanks everyone for the continued interest. I checked (and posted to) both the 7 and 9 forums and the results are consistent - well-designed aircraft with plenty of resiliency in CG.

Best Regards,

Dennis Snyder, CDR, USN, Ret.
CDR Data