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Catto propeller performance

David-
Not sure if the -7 is the same, but on Dan's calculator full fuel wasn't a problem for aft c.g. on a -9, but low fuel was. Seems like as fuel burns off c.g. moves aft, which is logical. I would think this would be the same for the -7 as well.
 
DanLandry said:
If anyone would like to use my w&b on Dan Checkoway's site, here's the link to my w&b.

Understand this was posted without fairings & wheel pants.


http://www.rvproject.com/wab/wab.jsp?id=163

Dan, are you going to do anything to get more weight up front? From what I've read paint is going to move the weight further back still. I'm building the same configuration as you and if my numbers come out the same I'll be limited to about 70 lbs of bags at 0 gals. Do you know the weight of the prop extension and crush plates you used?

-Rick
 
alpinelakespilot2000 said:
David-
Not sure if the -7 is the same, but on Dan's calculator full fuel wasn't a problem for aft c.g. on a -9, but low fuel was. Seems like as fuel burns off c.g. moves aft, which is logical. I would think this would be the same for the -7 as well.
Absolutely right. That's why I did the calculations for each with full fuel tossed in. I figured if that was still out of the aft CG limit, then empty would be way out. :D
 
rickmellor said:
Dan, are you going to do anything to get more weight up front? From what I've read paint is going to move the weight further back still. I'm building the same configuration as you and if my numbers come out the same I'll be limited to about 70 lbs of bags at 0 gals. Do you know the weight of the prop extension and crush plates you used?

-Rick

Superior will be shipping me a replacement for the ryton sump(next month) which they say is heavier. I'll wait and see how that impacts the cg before I do anything else.
I don't have the weight for the prop extension or crush plate. My 3 blade prop weighed in at 18 lbs.
 
Move the engine mount forward?

I have no experience technical or otherwise in this area so don't beat me up too bad. Could you put appropriate spacers between the engine mount nad firewall to solve this issue? Would not take much distance and you could fix the issue easilly.
 
I think ...

I think you would be better off to focus on building the plane straight and true then adding ballast or shifting weight to get the CG where it should be. CG is a very static thing with empty tanks which is the way I did the weight and balance on my RV-6A. Fuel is a preflight calculation just like everything else loaded in for the flight. The tanks are fairly close to the for/aft CG so it will not cause a gross shift. Anyway, that is pretty easy to deal with but if you get paranoid about this and start changing other areas and mess up the alignment and fit of the engine, alternator pulley, crossover exhaust, baffling, spinner, cowl, airbox, nosegear structure (on "A"s") you can create problems that will be around for a long time.

I have the small pulley on my alternator and I still required a steel striker plate to protect the cowl. I had to cut off sections of the exhaust pipes under cylinders 1 and 2 to get clearance from the cowl (this was caused by a cowl design change by Van's that Vetterman was not able to check for compatibility before incorporation).

Bob Axsom
 
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One update re: lead time on Catto props....

Craig just emailed me back today... while official lead time for 3-bladed props is 6-7 months due to their popularity, the lead time for the 2-blade is only 10-weeks! I know the 3-blade looks really nice and all, but the 2-blade can be had pretty quickly if that matters to anyone.

One thing I still haven't gotten over yet in making my decision is being concerned about prop starting a 3-blade prop. In my flying up here in the colder part of the Northwest, I've had to hand prop all the planes I've rented, as well as the Skylane, at one point or another. (Maybe just because they all had relatively long runs from the battery to the starter?) A lot of places I fly to are small, out of the way airports where there may be no one around if I get stuck with a weak battery or starter. Am I the only one who has to do this occasionally? What do you 3-blade folks do in this instance?

(Just looking for someone to help me make my decision! $1250 and only 10-week lead time--officially, that is--make the 2-blade seem like a fantastic deal though)
 
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Can be done

Hi Steve,
I've propped many a two blade up to and including a 1340 Pratt and Whitney radial :eek:

We have a three-bladed Catto on our 6A which I hand-propped and it's a little dicey because you have a blade near your ear while you're holding the one to prop!! It can be done (and it was) but I'd really rather prop a two-blade.

Another point to remember is that the Catto is very light and when the engine fires, the next blade comes by very quickly......much more so than an aluminum Sensy. I think it's on the dangerous side to hand prop the three-blade IMHO.

Regards,
 
I can only speak for myself, but The only negative issue I've had with my two blade Catto Prop has been damage I got from flying it in the rain before I had Craig install the Rain Guard on the leading edge. The two times I flew it in heavy rain, slowing down wasn't a good option. The propeller seems to run as smoothly as any three blade prop could. My propeller installation has a harmonic balancer.
I've hand propped light weight two blade wood propellers, and that next blade gets around quickly when the engine fires. I'm not sure I'd try it with a three blade prop. 60? closer is quite a bit.
 
Hand propping

Steve,

Not only will the next blade get past (hopefully, anyway) your hand in 40% less time with that third blade, the Catto is a very low inertia prop. It will pick up rpm from the first firing of a cylinder quicker than a metal blade prop. You see that in the quick throttle response. A 320 takes a pretty good pull to hand prop, but I have done it a few times. If I had to hand prop a three blade Catto, I think I would only consider it from behind since your fingers are totally behind the leading edge of the prop. Don't think I would try it, however as I have never hand propped from behind.

Bob Kelly
 
Just wondering, maybe some of the guys that are flying could answer these questions. What are some of the differences in performance between the 3 blade verses the 2 blade Catto prop. Will the plane slow down a little faster having a 3 blade prop? Will 3 blades affect glide in a engine out situation? Will the plane get off the ground faster with 3 blades?

Thanks,

Robert Scott
RV 9A Baffels
 
Actually the plane will slow down LESS with the 3-blade because the diameter is smaller. Prop drag is mostly a factor of disk area.
 
rickmellor said:
The rain guard ... is that the tape stuff or does Craig offer something better?
Yes, Craig adds it originally, but he said every few years it should be replaced depending on whether the plane is stored indoors or out. He also said that once it is on you can fly full throttle through rain with no adverse effects. Sounds pretty effective.

Re: the handpropping--I agree that I'm never going to be interested in hand-propping a 3-blader. What I really meant to ask and what I'm most curious about is what do those people who have 3-bladers do when they have a weak battery or starter? Sometimes pulling the cowl and charging or replacing the battery isn't an option in the flying I've done in the past... I assume it must be the same for others, no?
 
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Plug-in

Hi Steve,
We've had to pull the cowl to jump the battery. I'm seriously considering installing a 12 V plug like production airplanes have so we can hook up jumper cables if the battery's flat. Spruce sells the two-pin plug and a flush door that can be mounted on the side of the lower cowl. IMHO, you'd be wise to install one if you're gonna run a three-blade.
Regards,
 
RV-7 with Catto prop, W&B numbers

I just weighed the plane this afternoon so I have some real numbers. So here they are as promised.

Empty weight:1034, Empty CG: 80.01 :D

The particulars are:
RV-7 (no paint, no fairings)
Mattituck TMX O-360 (carb)
Metal plenum
3 bladed Catto prop
Sabre prop spacer with 10lb crush plate
Small rudder.
Day/Night VFR
Everything and I mean everything is mounted as far forward as possible.

With these numbers, I can take my wife and 100lbs of baggage and empty the tanks (down to 5 gal) and still be within CG limits.
 
rscott5559A said:
Just wondering, maybe some of the guys that are flying could answer these questions. What are some of the differences in performance between the 3 blade verses the 2 blade Catto prop. Will the plane get off the ground faster with 3 blades?
Robert Scott
RV 9A

The major advantages to a 3-blade are its smoothness and the added ground clearance in case you screw up. It probably takes off and climbs a bit quicker. My top speed matches Van's top speed spec. But to do that I have to turn 2750 RPM to achieve that speed. The light weight on the front end makes it even easier to hold the nose off until way late into rollout. The main drawback is that removing/installing the lower cowling is more difficult.
Leland
RV9A, 135 hours, finally in for painting
 
I am a little late to this thread because I missed it while we were on our Thanksgiving vacation...

Anyway, I'm in the same boat as Dan Landry right now. With all my fairings and pants now on, I'm only turning about 2650 max at 8000'. This gives me a 197 mph max speed via a three way gps speed run. Verified on several occasions. At 5500' at 75% power I get about a 188 mph cruise. My prop is a 66 x 76.

Craig said I'd expect to see 204 cruise, 215 mph max. So I think I'm overpitched a little as well. Thinking about sending the prop back to him when the aircraft is in paint. Dont know when that will be, though. Craig said he could rework the prop within a week but I'd allow more time based on past experience.
 
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Scott:

Just a point of reference...I sent my 3 blade back to Craig for repitching and got it back in just short of two weeks.

Regards,
 
doing the math

Scott Will said:
...I'm only turning about 2650 max at 8000'. This gives me a 197 mph max speed...
Craig said I'd expect to see 204 cruise, 215 mph max...
Kevin or George, please feel free to correct me...

Scott, let's assume the torque curve is flat between 2650 and 2700. This would mean you are getting 98.15% of what's available (about 135 hp which is 75% of 180 which is what is available at 8000', approx.) or 132.5 hp. You can't gain 7 mph on 2.5 hp without drag reduction. Can you?

To go from 197 to 204 is an increase of 3.55% (1.0355). The cube of this is 1.1104. Thus you would need to go to 2941 rpm for that. Roughly.

Is it just me or should you look elsewhere, too, for the speed? You are getting exactly what Van's said it would do at gross. You have the Van's cowl and pants too, I think. http://www.vansaircraft.com/public/rv-7per.htm

You are the flight engineer and I'm a mere amateur. What am I missing?
 
Howard - first of all thank you for reminding me what Van's numbers are. You're right - I am "right there".

However, I guess I just have the urge to get the numbers that Craig said I'd expect to see. I don't have the invoice right here with me but if I recall he wrote 205/215 mph (cruise/top speed). And I know certain guys are getting that kind of performance... specifically Pierre. I know because I've flown his plane!
 
alpinelakespilot2000 said:
David-
Not sure if the -7 is the same, but on Dan's calculator full fuel wasn't a problem for aft c.g. on a -9, but low fuel was. Seems like as fuel burns off c.g. moves aft, which is logical. I would think this would be the same for the -7 as well.
You had me worried there for a minute or two.

Dan's site only lists W&B for -9A's, no -9's are listed. When I did my estimates (I'm still building but have some numbers from other -9's, not -9A's) and there doesn't seem to be a W&B issue. Unless I have full fuel, a 110 lb pilot, no fuel and nothing in back, and then it is a forward CG that is the issue. I based these number by playing around with my expected EW and CG location. Moving the CG forward and aft 2" from the numbers in the book and adding weight, baggage, fuel, raising and lowering my EW, etc. (Excel is a great tool!)

The A's tend to have more of an aft CG problem than similar planes with conventional gear. Based on the number on Dan's site, the averages are 79.70 for -7's and 80.11 for -7A's. I guess that's what you get for having those big, heavy landing gear behind the CG and as heavy as the nose wheel is, it apparently isn't far enough forward to compensate.

BTW, my two bladed Catto prop is waiting to be hung on the O-290 sitting on the front of my RV-9. I've been paying a lot of attention to W&B and moving everything forward.
 
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