Prop dilema

[Raymo]

Originally Posted by Cmore

Raymo
What made you go for the angle valve initially, was it just because like me you got a good deal on it?

Correct. Had a line on a deal but someone else got the cash before I did.

[jay bell]

You could substitute the Earth-X EX680 for the standard PC680 which would reduce weight and improve CG without relocating the battery and increasing the weight of wire.

Based on your reasons for buying the angle valve engine, I assume you are trying to keep a low budget, which the Catto will do better than a CS prop.

I would encourage you to keep the plane and nose light to improve flying quality. My Catto/parallel valve/nose dragger combination weighs 1093 with paint and interior, and tends toward tail heavy. I love the way it flys light acro and handles soft field. I can fast taxi with nose in the air. Today I was able to raise the nose immediately upon starting the roll on a snowy grass strip. On the other hand, I reach the factory aft CG limit at 400 lb of passenger weight, 100 lb baggage, and 15 gallons of gas, which means handling is touchy after a long cross country.

I sometimes consider replacing my Catto with one of the three props mentioned in the thread, so I won't try to suggest you don't "need" the enhanced performance the CS prop can deliver.

Best of luck whichever you decide. It will still fly nicer than most other planes!
Jay

[Cmore]

Hi Jay,
Using the Earth-X battery is something I have looked into and would use it if going with the whirlwind for sure.I definitely am on a budget but the catto with the hardware,nickel leading edge and spinner comes in about $4000 cheaper than the 200rv as I already have a governor.Although its a significant amount of cash it wouldn't be a deal breaker in the grand scheme of things but I can understand what you mean about keeping the nose light,its one of my priorities even though I've started at a disadvantage with the heavy engine.
I see you have the IO375 so presume its the 195hp version,if so what dia/pitch are you running,did you need the heavy crush plate and what numbers are you getting with it.
Cheers

[R. Daniels]

Having built a number of '7A's including one with an angle valve engine here's what I would do. Sell the engine and get a parallel valve engine. The '7A I built ended up needing a 14 pound block of lead in the tail to make the forward CG issue tolerable. I could have moved the battery aft but I was working with a customer and didn't want to go that route. It's still a nose heavy airplane.
By far the best flying RV'S have lighter engines.
I'm sure some would disagree but we all know that lighter is better. So far in my 20 years of building, servicing and flying many RV'S of all sorts, I've yet to see any real speed advantage with using a larger, heavier engine "higher horsepower" You can gain more speed by doing aerodynamic modifications.

[Bob Redman]

G'day Cmore,

I have an RV-7, IO-360 M1B, 180hp & Hartzell BA. Basic weight 1085lb (492kg). Empty CofG is 78.24" aft of datum (limits: 78.7 to 86.62, and aft limit 84.5" aft of datum for the 1600b max aero limit).

With 2 x 190lb people I would need to be below 85 litres (22.44 USG) fuel remaining to be below 1600b gross. At minimum fuel (32 litres - 8.5 USG) the CofG would be 83.12".

I hope this helps your choice. My phone number is in the SAAA magazine if you would like to discuss your decision.

Regards

[rzbill]

+1 for Mr. Daniels comments.

From my experience with my own build and reading this site for ten years, -7A's with a Hartzell tend towards being nose heavy and -7's with a fixed prop tend tail heavy. There are exceptions as always. Mine fits the nose heavy 7A tendency (Impossible to go out rear of CG if 100 lb baggage limit followed).

If you continue with the angle valve, mount everything you can think of in the rear fuselage so you minimize putting lead in the tail. And remember, its not just the CG, there is also a nose wheel weight limit (375 lbs memory says) that will be at its worst at the end of a solo XC. (solo and low on gas).

[chopperchops]

G'day Cmore,
Regarding MT props, there is a prop overhaul shop at Archerfield that assembles and overhauls MT props.
Hope this helps?
Rob.

[Walt]

Originally Posted by rzbill

+1 for Mr. Daniels comments.

And remember, its not just the CG, there is also a nose wheel weight limit (375 lbs memory says) that will be at its worst at the end of a solo XC. (solo and low on gas).

Just to clarify, fuel moves the CG forward so worst case for the nose wheel is light solo pilot with full fuel and no baggage.

[Cmore]

Hi Guys,
Thanks for the very informed advice and help from everyone, its much appreciated and its really helped me to make up my mind to go with the catto,probably a 68x76 cruise prop.
The main reason is to keep the nose light as possible but also as we know the 7's like a bit of weight up front so as I was researching I noticed a lot of the parallel valve guys had to bolt 20lb sabre spacer behind the catto for w&b reasons,my logic is that according to vans (this is from memory so correct me if I'm wrong) the A16B angle valve which is very similar to my engine is around 26lbs heavier than than the M1B parallel valve engine which should leave me around the sweet spot as far as w&b/nose wheel weight is concerned.
This would mean instead of having 20lbs dead weight bolted on the nose I would have 26lbs usefull weight in the form of 20 extra horsepower,does this make sense to anyone else?

[aerhed]

"as we know the 7's like a bit of weight up front "

That's from too much primer in the tail.