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

alwaysoutdoor

Active Member
I have a question to other RV-7 builders and what their CG ended up being.

On my project (taildragger) I will be putting on an IO360 M1B and kinda want either the 2 blade or 3 blade catto prop. I will be painting the plane just 1 solid color and only installing the MGL extreme mini EFIS/EM and probably a Nexus tablet for GPS on the instrument panel (I'm keeping it super simple and CHEAP!). Do you think I will have a CG issue once I am finished with everything (being tail heavy)? What would you recommend me changing? Should I put on a metal FP Sensenich instead of the catto? Use catto and add a super heavy crush plate? Would putting the lightweight tailwheel on solve much for the extra $105 (only is 1lb lighter)?

I would like some advice on what I should do so I don't have big problems once I bring out the scales- I see myself wanting to use the baggage compartment on long flights. Thanks for the help

p.s. I already have the finish kit so changing to the 320 mount to get weight forward is not an option.
 
Most likely you will need to add a weighted crush plate for the prop.

I think Catto sells them???

Many have been here before, I made one for Jamie Lee's RV7, and calculated the mass required.

In my opinion a Hartzel C/S is the go, but it is not cheap.
 
There is a W&B thread for 7's here that can provide you with data. The Cato props seem to have a CG an inch further aft. Plotting the data and comparing your weights should help your understanding. Sorry, I don't have access to the plotted data today.
 
Keep building it as light as you can and don't worry. Once you weigh it, you can add ballast, if you need to.

Remember, it is much easier to add weight to a light plane then remove it from a heavy one.
 
Would it be worthwhile to talk to Vans about the 320 mount dimensions?
I understand it moves the engine further forward. It might be a way to KEEP it light rather than adding the weighted crush plate
 
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.
 
I second Stripes comment.

To get mine in a more useful position was going to require way to much dead weight on the nose.
 
I second Stripes comment.

To get mine in a more useful position was going to require way to much dead weight on the nose.

The weight in the front the same if it is a plate or a CS prop. I understand the CS prop gives performance for the weight, but the nose wheel doesn't know that.

I looking at the same issue with my 9A. I have a O-320D2A and will be putting a Catto prop on it because I like how smooth they are. I may have to put a weight in front to get the baggage capacity I want, but Im ok with that. If I ever want to change to a CS prop, it will be an easy change.
 
My RV7/O-360/3 blade Catto weighed in at 1038 with leather/carpet but only a G3X and a handheld. With my typical combined passenger weight of 350 lbs, I was CG limited to about 60 lbs baggage with min fuel. I added the 12ish lb landoll ring to the flywheel and inow I can use the full 100 lbs baggage.
I'm happy with my choice.
 
will you have an issue? maybe but probably not

I was in the same boat as you, a light and simple RV-7 (1050 pounds).

I used a 10 pound crush plate from Sabre. With the 17 pound Catto, it is 30 plus pounds lighter than a CS setup. I also used a light weight tailwheel, which pushed the CG forward 1/4".

Having said all that, there are some situations that I have to avoid. Flying acro with a passenger over 180 lbs is one (not a problem for me) and empty tanks with a passenger and full baggage. I have found that easy to plan around.

You may have to do some soul searching to see if you can live with those limitations. It has been a non issue for me. Good luck.
 
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?
 
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.
 
crush plate and landoll

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.
 
Hartzel

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)?
 
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!
 
Sensenich 42LBS Catto 14LBS

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.
 
7a, Catto3B,9a mount

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

Just my opinion

Scott
 
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.
 
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.
 
Resurrecting this thread, I have a related question that searching hasn't answered. Has anyone here done a build with a CS composite prop? Is that enough weight in the nose to still carry near-full baggage? Or would one need to add more weight to the nose or push the engine forward (likely with a James cowl to fit the IO360 then)?
 
I have an IO360 with Whirlwind 200RV composite prop. Lightweight tailwheel.
EW is 1060lbs empty CG 81.0 - seat upholstery only, no carpet etc.
300lbs combined passenger weight, 10usg fuel and 80lbs baggage puts me right on the rear limit.
To gain full baggage of 100lbs, I would need min fuel of 25usg.

240lb pilot only, 10usg fuel, 100lbs bags, CG is right on the limit.

For me in practise this works out OK Because 80lbs bags is quite generous, and if I ever need to carry extra I can bump up the fuel load.

However, I find my machine fairly sensitive in pitch, probably accentuated by the rear CG.
 
One thing that helps is to make a spot between the pilot and passenger's rudder pedals to securely store heavy stuff like a tool bag, extra qts of oil, etc. I made a box there and mounted my O2 bottle on top of it. Doubles as a glove box for nasal cannulas, pulse ox, etc. When you have lots of baggage, make sure you put as much of the heavy stuff as far forward as you can. I've been known to use an airbed as a booster under my wife's seat. 12 lbs on the cg instead of behind the seat.

Ed Holyoke
 
I have an IO360 with Whirlwind 200RV composite prop. Lightweight tailwheel.
EW is 1060lbs empty CG 81.0 - seat upholstery only, no carpet etc.
300lbs combined passenger weight, 10usg fuel and 80lbs baggage puts me right on the rear limit.
To gain full baggage of 100lbs, I would need min fuel of 25usg.

240lb pilot only, 10usg fuel, 100lbs bags, CG is right on the limit.

For me in practise this works out OK Because 80lbs bags is quite generous, and if I ever need to carry extra I can bump up the fuel load.

However, I find my machine fairly sensitive in pitch, probably accentuated by the rear CG.

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?
 
One thing that helps is to make a spot between the pilot and passenger's rudder pedals to securely store heavy stuff like a tool bag, extra qts of oil, etc. I made a box there and mounted my O2 bottle on top of it. Doubles as a glove box for nasal cannulas, pulse ox, etc. When you have lots of baggage, make sure you put as much of the heavy stuff as far forward as you can. I've been known to use an airbed as a booster under my wife's seat. 12 lbs on the cg instead of behind the seat.

Ed Holyoke


Ed,
You wouldn't happen to have any photos of that would you? I'd like to consider something like that for my own build.
 
Define other stations

To maximize the effective distribution of the baggage load for longer trips you can easily define additional load stations on your W&B spreadsheet.

In my case I have defined a station behind the seats and forward of the flap bar, and have divided the main baggage area into a fwd and aft station. You can also put some stuff in bags forward of the spar where they are under your knees and it is easy to mount a strap to keep the bags in place (good place for tiedown/tool bag which can weigh 14 lbs)

If flying solo obviously a lot of baggage can go in the pax seat and as noted above put heavy stuff forward.

So far with good load management and fuel burn planning (to keep the CG in range) the -7 has met all my mission needs including 2 up and stuffed full for a weeks camping at Oshkosh.

Other threads also note that the 320 mount moves the motor 2 inches further forward which would help with lightweight props and the standard cowling blanks have enough extra length to accommodate this. Also battery and starter selection have an impact on the CG.
Figs
 
To maximize the effective distribution of the baggage load for longer trips you can easily define additional load stations on your W&B spreadsheet.

In my case I have defined a station behind the seats and forward of the flap bar, and have divided the main baggage area into a fwd and aft station. You can also put some stuff in bags forward of the spar where they are under your knees and it is easy to mount a strap to keep the bags in place (good place for tiedown/tool bag which can weigh 14 lbs)

If flying solo obviously a lot of baggage can go in the pax seat and as noted above put heavy stuff forward.

So far with good load management and fuel burn planning (to keep the CG in range) the -7 has met all my mission needs including 2 up and stuffed full for a weeks camping at Oshkosh.

Other threads also note that the 320 mount moves the motor 2 inches further forward which would help with lightweight props and the standard cowling blanks have enough extra length to accommodate this. Also battery and starter selection have an impact on the CG.
Figs

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!
 
Oxygen under the panel

Mine is a 6 with a parallel valve IO-360 engine and Whirlwind 74 RV. I put an auxiliary fuel tank behind the passenger seat and couldn't afford the aft weight and space to put the Oxygen back there too. I also have a second battery right behind the firewall which I enclosed in the O2/glove box.

20150307_114623_zpss3x2sgof.jpg


54067513-3602-4031-ac93-890a40b56b2e_zps04pfhelf.jpg


I laid up the carbon fiber sheets under vacuum with hexcell to make it a bit thicker and stronger, then just made the box with hinge material as if it were sheet metal. I glued and riveted. The top will come off by pulling pins so I can get in there to change the battery and service the fuel pump/filter assembly. I push my toolkit all the way forward on top of the battery. I have a tag on it so I can easily pull it back out.

When we want oxygen, it is easy to grab the cannulas, in zip loc bags, out of the glove box, hook it up and get it flowing. The valve is accessible without effort. I like this location much better than behind the seat where I had it temporarily in our 6A. I pull the bottle and clamps to save 12lbs. when I don't expect to need the O2. I do usually pump the aux fuel into a main as soon as I can make room for it, and I have landed with fuel in the aux and a bunch of baggage without the dreaded aft CG sloppy stick issue. Did that once in the 6A and that was the day the tools moved forward. ;-)

Ed Holyoke

The engine mount is stock, no spacers. The Whirlwind is CS. It's lighter than a Hartzell and heavier than FP. I have a PC 680 on the firewall and another right behind the FW. If I change these out for EarthX, I'll have to reweigh, but I think the CG will still work OK. The cowl is modified Van's.

The composite core material I used is: https://store.acpsales.com/products/5635/aero-mat-soric-xf-




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?
 
Last edited:
Resurrecting this thread, I have a related question that searching hasn't answered. Has anyone here done a build with a CS composite prop? Is that enough weight in the nose to still carry near-full baggage? Or would one need to add more weight to the nose or push the engine forward (likely with a James cowl to fit the IO360 then)?

I think the ?long? James cowl is only longer between the front of the engine and spinner opening, to make room for the horizontal induction, and/or room for diffuser ducts between the cooling inlets and the plenum. If you move the engine forward with a longer mount, you?ll have to add length to the aft end of the cowl.

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.
 
To maximize the effective distribution of the baggage load for longer trips you can easily define additional load stations on your W&B spreadsheet.

<snip>

Figs

I have a station right in front of the main spar on my -6. My legs "bridge" over it and I don't even notice items down there. That station is where I generally store my tool bag and tiedowns on trips where CG would otherwise be troublesome.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.)
 
I?ve done it, vans sold it too me.

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.
 
Sorry just reread original post

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?
 
All depends on the mission

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 :D)

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
 
Agree

However knowing what you know now, all things being equal, if you had a choice would you carry the heavy lump of steel?
 
Keep in mind that painting will add weight to the tail! If you decide to paint, keep number of coats to a minimum especially on the bottom surfaces........ One advantage to a heavy prop is the plane cranks and idles better with the inertia of that heavy prop turning.
 
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