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

[Raymo]

Originally Posted by longranger

You can also move the CG forward with a prop extension. The ?long? James cowl requires a 2.5 to 4 inch extension, depending on the propeller.

I have a 4" Sabre extension with a 20 lb plate in front of the 7" aluminum crush plate with Catto 3 blade NLE that weighs about 12 lbs. CG is 79.58 and I have no issues loading the plane to max GW with 100 lbs of baggage, though I am usually baggage limited by human and fuel weight.

With just me on board and fuel tanks with 100 lbs of baggage, CG is still well in range no matter the fuel load.

I plan to replace my PC680 with an Earth-X at some point to gain some usable load, which is why I went with the 20 lb plate vs 14.

[scsmith]

Originally Posted by Reaver

Does the 320 mount work with either a 180 or 200hp IO360 and the standard cowl? I?m leaning toward a FP composite prop and a LiFePO4 battery, both of which are great for useful load but not CG. If a 320 engine mount is just a drop-in replacement for the 360 mount that would be excellent!

I'm pretty sure the O-320 mount is a drop-in replacement.
I'm also pretty sure there is enough extra fiberglass on the IO-360 cowl as delivered to reach the extra 2". If it isn't it is very easy to scarf on some more glass.

There was some mention early in the thread that Van's wouldn't sell the O-320 mount with the O-360 cowling. I would love to hear someone report back that they were able to do this.

The principle reason I care (given that I have an RV-8) is that for my composite tapered wings, they shift the wing forward about an inch, which shifts the c.g. range forward about 3/4". This is not a problem for the -8, nor the Rocket-6 that the first wings are going on. But if later we would want to put a set of these on a -7, the O-320 mount for the (i)O-360 would be an obvious solution.

So I would like to hear from anyone that has been able to buy this combination.

[jimgreen]

Originally Posted by Reaver

This is very useful info, thank you! And just to clarify, are you running this as a CS prop with stock Van's engine mount, cowling, and no unusual balast or spacers up front?

And Bicyclops that's also a very useful hint. By chance have you done a write-up of those mods?

Yup, IO360 parallel valve, c/s composite prop. No spacers or ballast, PC680 battery on firewall.

[jimgreen]

Originally Posted by scsmith

I'm pretty sure the O-320 mount is a drop-in replacement.
I'm also pretty sure there is enough extra fiberglass on the IO-360 cowl as delivered to reach the extra 2". If it isn't it is very easy to scarf on some more glass.

There was some mention early in the thread that Van's wouldn't sell the O-320 mount with the O-360 cowling. I would love to hear someone report back that they were able to do this.

The principle reason I care (given that I have an RV-8) is that for my composite tapered wings, they shift the wing forward about an inch, which shifts the c.g. range forward about 3/4". This is not a problem for the -8, nor the Rocket-6 that the first wings are going on. But if later we would want to put a set of these on a -7, the O-320 mount for the (i)O-360 would be an obvious solution.

So I would like to hear from anyone that has been able to buy this combination.

Steve, the 320 mount should fit OK. I'd be interested to know if there is sufficient reserve strength. There is only a slight weight difference (more than offset by a composite prop) and there are some 320s around putting out 180hp.
I can't see a problem, but then I'm not an engineer.

[Jpm757]

IO-360 M1B, standard mount, MT 3 blade CS. With two 200lb. pilots and 6 gals. fuel, I can land with 74 lbs. baggage. So you may not need the heavier Hartzel CS. MT is a little pricier, but includes complete painted & installed spinner assembly. Very smooooth prop, great climb performance.

[Dbro172]

Originally Posted by scsmith

I'm pretty sure the O-320 mount is a drop-in replacement.
I'm also pretty sure there is enough extra fiberglass on the IO-360 cowl as delivered to reach the extra 2". If it isn't it is very easy to scarf on some more glass.

There was some mention early in the thread that Van's wouldn't sell the O-320 mount with the O-360 cowling. I would love to hear someone report back that they were able to do this.

The principle reason I care (given that I have an RV-8) is that for my composite tapered wings, they shift the wing forward about an inch, which shifts the c.g. range forward about 3/4". This is not a problem for the -8, nor the Rocket-6 that the first wings are going on. But if later we would want to put a set of these on a -7, the O-320 mount for the (i)O-360 would be an obvious solution.

So I would like to hear from anyone that has been able to buy this combination.

Of course you can by that combination. The spec?d cowl for the IO-320 is the O-360 cowl. The O-360 cowl has a deeper and wider bottom inlet than the O-320 cowl. (And will accept an FI setup on an O-320.)

[Vansrv7arob]

I had to graft about an 1.5 inch to the back edge of the cowl.

320 (2 inches longer) mount with 360 cowl and 360 FWF, the space between the engine and FW is awesome!

A 320 and 360 horizontal induction cowl may be the same, I?m pretty sure the 320 and 360 vertical induction cowls are different.

3 blade mt is going on, it?s ~ similar weight as a fixed pitch metal sensi, which will give you aft cog as well with a standard 360 mount.

If I ever decide I have to have a Hartzel which is quite possible (they are awesome props) at some point in the next 30 years, I?ll chop the cowl and put the correct engine mount for that combination on.

Vans were a bit confused by my request, I spoke to one of the engineers at Vans and suggested that they should offer an uncut cowl option for other builders who knew they only ever wanted a light prop. Engineer didn?t get it. "Who would want that?? I said like everyone that doesn?t fit a hartzel to an rv7, or anyone fitting a solid crank engine, you just don?t give them the option!

The conversation ended something like... ?we haven?t test flown it in that configuration? I said well plenty of people have flown it in the standard config with light props and we know that that doesn?t work great.... what?s the definition of insanity?

Vans should make it a little clearer to builders that they are going to have limited CG issues without bolting on a block o steel and give them an option.

I don?t know how but I hear so many stories from builders just completed weighing and cg calcs surprised they cant carry full luggage.

The RV7 was designed around a Angle valve (the true 200hp IO360) with a hartzel, that combination weighs a ton... anything less than a parallel valve 360 and a hartzel and you loose baggage carrying capacity and or minimum fuel landings. Add a heavy paint job it?s gets worse, It?s that simple.

So it seamed pretty moronic to me to not at least correct some of a known final W&B issue during the build.

Just my 2p.

It of course works but strapping a block of steel behind a Cato is so wrong on a number of different levels for me.

[Vansrv7arob]

Yes you will have a cg issue without bolting on a lump of steel.

Personally if I were you I would look for a cheap second hand metal sensi, they come around pretty often as people upgrade to the Hartzel.

Buy the light weight tail wheel, keep the entire tail light including additions of paint, don?t do anything brainy like stick a transponder or Elt all the way back there.

It will be an awesome 7 just like that.

Is a catto faster than a sensi? Anyway?

[uk_figs]

Catto prop performs better than than the stock sensi metal prop in a number of areas such as take-off and climb performance and the top speed difference is only a few MPH. The Catto also seems to provide a little better cooling with the standard cowl maybe due to to hub design of the blades. I started with the sensi and switched to the Catto partly due to the take-off and climb performance and partly due to the better cooling of the optimized design (and of course the look of the entire aircraft with the 3 blade prop thanks Mel )

When people talk about the CG trade of the Catto versus a constant speed prop the weight is one factor but don't forget that the sensi metal prop and hub weighs 42 lbs versus 14 for the Catto, so by adding heavy crush plates etc what you are getting is a better performing prop for similar weight and CG characteristics versus the sensi FP prop. In my configuration I am not limited in baggage at min fuel but do have to watch gross weight with 2 up and full tanks at take-off.

The other discussion about CS versus FP is not really relevant to this discussion as that is all mission parameters such as cost, complexity, and performance in a couple of areas. In my case the $$$ went into the panel and I wanted to keep the motor/prop combo simple YMMV

[Vansrv7arob]

However knowing what you know now, all things being equal, if you had a choice would you carry the heavy lump of steel?