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Prop dilema

Cmore

Member
Hi Guys,
First time poster so take it easy on me,I'm building a 7a and I have a IO360 A3B6D angle valve engine with the counterweights and I'm in a pickle about what prop to use.
My mission will be cruising/aeros 50/50 and the hartzell is out because of the weight but I'm also thinking the whirlwind 200rv might still be a little bit too heavy with this engine on the nosewheel so I'm thinking about a catto 3 blade.I know it's good to have weight on the front of the 7's for c of g but I don't want it so heavy that I can't take a passenger for aeros,it will be a basic skyview vfr panel with gps,radio and backup asi/alt.
Any of you knowledgeable gentlemen out there have experience with the 7a angle valve 200rv setup and in your opinion would it be too heavy for aeros with passenger?would it be possible to keep this combo around the 1100lbs mark or would I need the catto to stay around that weight.
All opinions welcome as I will be ordering the finish kit soon and have to make up my mind.
Thanks in advance for your replies.
 
If I were in your shoes, I would go for the Hartzell blended airfoil prop and just deal with the W&B issues however I could because the performance of that prop and engine would be worth it.
 
Hi Neal,
I know what you mean and it is a really good combo but it would be a little heavy on the nose for my liking,if it was a taildragger it would be perfect.
 
First question back - why that motor ?

It is heavy, expensive and you really don't get any benefit with the extra horsepower when cruising.

That said, you are looking for a propeller choice.

If you want max performance with minimum weight, I would choose the MT 3 blade prop. I have had 2 now and they are just a great prop. Lightweight, loads of thrust on takeoff, super smooth in the cruise and quiet.

And they look a millions bucks on the ramp :D
 
Hi Mike,
I had every intention of going with the parallel valve IO360 but this engine came along and I got a real good deal on it and although it's not ideal I had to take it.
I hadn't really thought about the MT to be honest,I will do a little research here on it here although I have heard it's quite expensive and has to be sent to Germany for overhaul,is this true?
Thanks for the reply
 
What are you trying to do? Is it a CG issue, or gross weight that you are trying to solve? Have you looked at CG, nose weight and gross weight from collecting the data presented here? I gathered all the 7's and plotted. Then saw the trend and located things accordingly in the fuse.

Battery, ELT, Strobes, lots of things to move around if you want to shift a little.

In the end I will have to weigh it and add lightness (tailwheel etc) if it ends up more tail heavy than I like. But I have a taildragger and lighter parallel valve.

You might just be happy with more baggage capacity!
 
Fair enough reason for getting the motor then !

The MT can be overhauled in the US, There is a service center in Deland Florida. They are very helpful and friendly guys.

Overhaul is 6 years or 2,000 hours - bear in mind, the clock starts after 2 years of storage, so if you go down that route, put off buying it until later in the project.
 
I was looking at a similar option recently and was going to use the 3 blade Catto. You will not need to add a 20 crush plate to bring the CG forward, as I will since that deal fell through and I now have a parallel valve 360.

You should also be fine with a constant speed prop and moving some weight aft, as others have suggested. The concern with a passenger should be a non-issue since you are both sitting very close to the C of G.
 
You say the mission is 50/50, but are you SURE you are going to be doing aerobatics with two people on board that often? It has been my experience that aerobatic "passengers" are pretty rare. Most like it for a roll or two, but after that they are done. That said, it seems like you can do those aerobatic flights with min fuel and no bags and be fine with a typical passenger. I don't want to start yet another CS/fixed debate, but you will be giving up a bunch of cross country utility by going fixed, AND aerobatics are going to require a bunch more throttle manipulation. Neither are show stoppers, but certainly worthy of consideration.
 
BillL
It's a gross weight/nosewheel weight issue,I have looked a lot for other planes with this combination of airframe/engine/prop and I only really found one and he has a very fat although well equipped plane at 1200lbs,I believe it could be done a lot lighter,maybe I'm just looking for reassurance it can be done.

mike
I'm in Australia and I've only ever seen one MT equipped rv here but I'm sure there are more and will look into overhaul shops here.

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

Toolbuilder
When I think about it you're right the majority of my aeros will be solo as I would like to enter the aero competitions but I don't want to give up the option for a passenger either if only for the ability to bring up an instructor to learn new moves,or fix my bad ones.
If I went for the fixed pitch I would have enough room within the w&b and gross weight to add things like the raven half/full inverted systems if I wanted to later.
Cheers guys
 
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
 
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
 
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.
 
RV-7 W&B

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
 
+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).
 
G'day Cmore,
Regarding MT props, there is a prop overhaul shop at Archerfield that assembles and overhauls MT props.
Hope this helps?
Rob.
 
+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.
 
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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?
 
Yeah, I guess I was thinking of lead based primers and forgot about the helium chromate primers.
 
My 7 has the angle valve engine and an MT prop. Empty she is 1090 lbs. CoG is fine she can be loaded up without problem.

I love the climb that I get from her, it's 3000 ft/min solo and light fuel, crushing at 140 Kts I get exactly the same fuel consumption as my friend in his 9a with a 320 engine.

I don't have any carpets and no interior to speak of.

I love her as she is, power, performance and long legs.

But don't get me wrong there is nothing wrong with a 160 or 180 hp and a fp, it's just not my first choice.
 
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