Will I have a CG issue? catto prop on a light RV-7

[alwaysoutdoor]

So I have been doing a little more research on this issue and I just found out that reducing 1 pound from the tail is the equivalent of adding 15 pounds to the nose- I think I am still adamant about the catto with crush plate (as light as I can get away with for good baggage capability) and might try to spend most of my effort and some money to lighten the tail as much as I can. I'll probably have to go with the light tailwheel to save a little less than a pound. Has anybody shaved off weight on the rudder counterbalance lead? The plans say nothing about balancing the rudder weight so what have other people done? I would guess that I could place the vertical stabilizer and rudder on the work bench and balance it just like the elevators?

[Kyle Boatright]

Originally Posted by alwaysoutdoor

So I have been doing a little more research on this issue and I just found out that reducing 1 pound from the tail is the equivalent of adding 15 pounds to the nose.

The real ratio is about 2.3:1, which is the ratio of the distance from the CG to the tail vs the distance from the CG to the flywheel (where a Landoll ring would go). I'm assuming a nominal CG of 75".

Doing the math, the distance from the flywheel to the CG is ~65" and the distance from the CG to the tail is 224"-75" = 149".

Comparing the ratios,v149"/65" = 2.29

If you installed the crush plate (instead of the flywheel ring), the ratio would be closer to 2:1 since the crush plate would be farther forward.

[uk_figs]

I have both on my -7, there are a number of threads on this issue in the forums, basic issue is the -7 was designed for the CS or sensenich metal prop (42ILB) so with a light prop like the Catto (14LBS) the CG moves aft and with 2 up and 100 LBS of baggage it will be aft of the aft CG at low fuel levels therefore restricting the baggage weight.

I have a landoll and a sabre crush plate and can carry full baggage down to low fuel levels without problems. There are some other things that can make it more manageable as well, in my case I have a bison bag behind one seat with travel tools and oil, and the tiedowns etc in a case behind the other seat both of which move weight forward of the flap control rod leaving more margin for the baggage area.

In addition I have found that 100 LBS is a LOT of weight and with the baggage compartment stuffed to the top for travel and camping etc it rarely weights more than about 70 LBS and is more about cubic feet than weight. When I pack I also put light gear in the back.

As already mentioned the low fuel at destination can also be managed and so far the configuration has not been an issue for me and I am very happy with the prop and the performance.

Happy to send you my W&B spreadsheet to play around with is you like.

[wirejock]

Originally Posted by tadsargent

The 7 was not designed for a wooden or composite propeller. Your CG will be aft
And the max baggage will be limited. Additionally with 2 average persons aboard you may not be able to land with minimum fuel on board.
My 7a needed more than a 12 pound landoll ring to help the weight. That's why I put on the metal prop which helped. The solution was the Hartzell constant speed propeller.

Stripes
Did the C/S Hartzel fix the landing issue with minimum fuel and full load (pass & baggage)?

[PilotRPI]

How much longer is the O-320 mount than the O-360 mount, and can you put an O-360 on it?

How much does a typical metal FP weigh compared to a catto?

I'm just starting out and would prefer a FP for simplicity sake, as well as cost, but don't want to limit baggage since I want to use the plane to travel.

Thanks!

[uk_figs]

On my -7 i switched the metal sensi for the Catto, weights as in title. The sensi weight included the spacer, the Catto weight was just the prop.

[rhill]

The W&B issue with the Catto is more pronounced with the tail wheel configuration. I have a Catto 3B(it's a work of Art!) with no plans for CS or metal props in the future,for my 0-360,7a and wanted Vans to ship the 2" longer 9a mount.In short,they wouldn't do it,I argued to no avail,I need the 0-360 cowl with it came the 0-360 mount. I'm still in the market for a 9a mount but will make spacers of 1" or more to use on the 0-360 depending on how much extra cowl material I have to work with.In the RV world with weight"Less is More". Chad Jensen built his 7 with Catto 3B and 0-360 using a SJ cowl built for the application 2" longer tail.It improved his CG but didn't cure the problem.It's at times like this I miss the build site formerly known as (Chi.....ay) as he had a great W&B page with everyone's finished weight attached to a spreed sheet you could run different scenarios on.
RHill

[Rhino889]

I love my Catto on the RV8. If I was building a RV7 I would plan for a heavier prop.

Just my opinion

Scott

[bret]

Some one on here, I forget, used a 5/8" spacer for the engine mount. I will be going with the Catto 3B also and may space my engine mount one inch with the SJ cowl. need to do more # crunching.

[tadsargent]

Larry, the C/S prop was the answer. My preference is to not add DEAD weight. Having the correct propeller designed for the airplane has more benefit than than dollars spent. It really opens the envelop for this airplane.