P

Pirkka

Well Known Member
Hi,

I've got so good tips from here so far so decided to ask your opinion about the next choice. Money is limited so that's why we need choices.

a) New IO-360 with fixed pitch propeller
b) Rebuilt (I)O-320 with CS propeller

Which one would you pick? Will 320 with CS outperform 360 with FP propeller? How good 360 is with FP for aerobatics?

I've read a lot of discussions between fixed and CS but somehow can't justify the money difference. However if choosing significantly cheaper engine, then that might be possible... If the engine is injected, that would mean likely that it will have inverted oil system as well. I'm currently leaning towards choice A...

Any comments appreciated! But act soon (about to order finishing kit)!
 
Engine Choice

I would recommend the 360 with fixed pitch prop. The cost of coversion from a fixed pitch prop to a CS prop in the future is managable if either you want to make the change of if you sale the airplane and the new buyer wants to change.

To covert a 320 with a CS prop you are really talking about both engine and prop conversion.

In addition, in my experience, a 360 with a fixed pitch prop in cruise will burn less gas than a 320 with a CS prop running the same speed, assuming you don't have the prop pitched as a climb prop.
 
Is weight a factor for you

Weight was a major factor in my choice as I like a plane that has a light feel and am willing to give up a bit of stability to do that.

A 360 is less than 10# heavier than a 320. A FP catto installed is 50# lighter than a metal Harzell. That weight off the nose makes the plane a bit less stable in pitch, but has a much more responsive feel.

IMO the plane will fly nicer aero with the 360 FP if you go with a light prop.

Of course, if you get a composite CS, then you have the best of both worlds, but you are really talking some green.

You will have faster cruise speeds with a 360 and a good FP prop, by at least 10 knots.

I disagree with the above post that states you will get better fuel economy with the 360FP. The 360 burns similar to 320 at the same speed, but the CS will save you a good bit on fuel unless you really pitch the heck out of the FP, but then you suffer in climb.

I considered the same choice and went with a new XPIO360 and Catto prop. The plane is fantastic for acro and cross country. I may not have the same climb rate below 100kts, but above that I get climb performance similar to my friends RV 7 with 200HP and Hartzell CS and I have the same cruise speed. I have a mid range pitch prop (66x74) . All in all, it is a joy yo fly it.

If I ever do go CS, (a possibility for fuel savings in the future), it will need to be a light one. Waiting for one that performs well and does not cost 10 grand.

I would much rather the 360FP, and I've flown a RV-6 with 320 and Hartzell.
 
Actually,

It seems that the CS will help in cruise if you test a number of different rpm levels to find the sweet spot with your airframe/propeller.

You will note very little difference in real world rate of climb, and the CS prop on a 320 will get off the ground sooner than a 360 with a fixed pitch prop.


In top speed however, the FP 360s are fast, infact the FP Sensenich has consistently tested faster in top speed than the CS props. The problem is that we all never fly at top speed.

You will have faster cruise speeds with a 360 and a good FP prop, by at least 10 knots.

The above has not been my understanding at all, there is no dispute that FP are usually a little faster at top speed, but assuming we are talking cruise speed, and at a consistent fuel flow, Every comparison I am aware of and every FP or CS RV I have flown in has better cruise speed at a given fuel flow, than does the fixed pitch. This works especially well for folks that have experimented with different rpm settings as some props are much more efficient at lower/higher rpm than others, and engines can make a similar power level on less fuel when run at lower rpm and oversquare often leading to better BSFC.

I would say that two of the nicest 6's I have flown are 180hp fixed pitch sensenich birds. Simple, good performance, low maintenance.

If you can save money on the 320, I would go that way....again.....but the cost savings was very high in my case, and as a result of career choices, money was low. The cost delta between two brand new engines is small. As for weight, it has been beaten to death, but typical installed weight differences are larger than 10lbs between the two.
 
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Real Savings?

If you are buying new I don't think there is that big a difference between the 320 vs 360, if you stay with parallel valve engine. Price and weight are not that far apart.

Really need to weigh what is most important to you. Airplanes like many other things are a compromise. RV's tend to do more in many areas then most other planes. You need to decide what the important factors are for you. Long distance travel with max cruise speed or economy? Max rate of climb or still excellent climb compared to production aircraft.

If you plan acro the bigger engine will always offer more performance and constant speeds will give you best climb.

I went for the 360(180 HP) and constant speed and have no regrets. My previous RV was a 6 with an O-320 with a fixed pitch and it performed very well but I always wanted more.

Ted
 
Pirkka said:
If the engine is injected, that would mean likely that it will have inverted oil system as well. I'm currently leaning towards choice A...

Any comments appreciated! But act soon (about to order finishing kit)!
Click to expand...

Just a quick comment. FI does not mean that the engine is likely to have inverted oil. Two different and independent things.
 
Hi all,

thanks for the comments so far. Let me tell a bit more when some questions has raised.

I don't hang around the airfield, I'm always heading somewhere and therefore cruise speed is critical but probably economy as well. The climb performance doesn't sound critical to be at the moment. I'm living at sea level and smallest airfield I can consider nearby is 600 m (~2000 feet). So I don't see any reason to try get to smaller fields. From the previous comments I would read between lines FP wouldn't go far what I'm looking for.

I understand that total performance idea and not looking for competition acrobatics but to have some fun. If paying ~$25 k for new injected engine, why not take inverted oil system as well -- it's not that much more. :p CS propeller is at totally different level... Never have had real negative G's but I didn't have flown RV either when started building so...

Converting IO-360 from FP to CS later. That would mean by selecting hollow crankshaft which may limit operation of propellers (at least Sensenich at certain RPMs). That doesn't sound so good either. Also that CS has later higher maintenancel costs in long run.

Sensenich vs. Catto - that is another debate we don't have to have now. :) But Catto sounded nice option. I want to be able to fly through rain rather than keep avoiding such. Seems that Catto has no problem with that.

This 320 option I've is so that I can get practically free O-320 core so overhauling it would make it suitable and leave some money for CS propeller. CS would mean new crankshaft and injected would mean injection so price would go high with this choice as well.
 
IO-390

does any one have a fp prop on a IO-390? if so wich one? any rpm limits with the hollow crank? I am starting out cheap but would like to upgrade to cs prop later. so i am thinking get the big motor now and cheap prop.
 
The lone voice in the wilderness

My RV6A was an O-320 with a Hartzell. I could outperform any O-360 FP in takeoff distance, landing distance, and climb performance, but the O-360 FP was about 10 MPH faster TAS in cruise at altitude. Frankly, with a 192 MPH cruise speed, I could care less being 10 mph slower, especially since 99% of my flying is hamburger hops, not cross-country dashes.

The combination was really perfect for the RV6. It moved the weight enough forward that there were few scenarios where I could load it out of the CG range. My gross was set to 1950 and I could do it and still be in the CG.

I really wanted a CS prop for the performance and I didn't like the RPM restrictions on an O-360. With the new props there are so many restrictions on the O-360 that it's like having a three speed transmission. Of course, that's better than a one speed transmission, but on my O-320 I could use any combination of RPM and MP I felt like.

A C/S prop is more fuel efficient and generally more fun to fly. You don't have to worry about slowing down 5 miles before you get to the pattern like you do with FP. And climb performance you can feel in the seat of your pants. The only way to tell you've lost 10 mph in cruise is to look at the guage. Yeah, flying in a gaggle, I was usually pulling up the rear behind the O-360's. But I'd always catch the group in the pattern by the time the first guy landed. It's not really much difference. For me it was worth the trade-off.

The downside is the cost and the overhauls. Which is why my RV4 probably won't have one unless I can find a good one used and cheap. Heck, if price was no object, I'd still have my 6. But I'm sure going to miss my Hartzell.
 
As expected, lots of opinions. Here's my 0.5 cent worth. My first "must have item " is the C/S prop. Engine choice would come next. To my way of thinking the C/S prop makes for a more fun, interesting and versatile aircraft. Some things I particularly appreciate about my C/S prop are;
Being able to bring the revs back in cruise for quieter operation and lower fuel flows.
Excellent T/O performance on my short airstrip.
Steep descent on approach if required.
Shorter flare and landing roll.
Pulling the prop back to 75% power and leaving the throttle full in (for better engine cooling) during the climb and then as the climb progresses, pushing the prop in to maintain the 75% power.
Going to coarse pitch with a dead engine to increase the glide.
The C/S prop is more expensive, but it should save you fuel in cruise if you bring the revs back. Yearly maintenance is similar to a F/P with the addition of grease. Don't know the situation in the USA, however in Australia the overhaul requirements for my Hartzell if it was on a certified aircraft are 2000 hrs or 10 years whichever comes first. For me the 10 years will come first so this is a long time period to spread the cost of the overhaul!

Fin
9A. 0-320, Hartzell C/S
 
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victor said:
Have you considered a rebuilt IO-360 with CS?
Click to expand...

Yes of course, but at currently I don't see any 360 cores around here (been looking them for ~2 years now), at least for the price which I would get 320 core, which would be practically free. So with the core offers so far and rebuilding the engine I would end up to the new price of experimental 360 engine but with some old parts... I.e. I can get all new with same price. :(
 
I say, if money is an issue, go with the CS prop, and 320. The largest benefit to increased HP is in climb. You should be able to get close to same climb performance with 320 and CS versus 360 and FP. Then you get the added benefit of fuel savings in cruise with CS prop. Plus, with the CS prop you can really whoa her down in the pattern..
Like you, I have noticed a big difference in core value of the 360 versus the 320. Like others mentioned, if you go new, then there's no real difference between parallel valve 360 and 320 engines...but that defeats your purpose.
Again, I say, save the money, and get a 320 core, and rebuild. Beware, the machine shop will always find something needs attention, and there are lots of parts in aircraft engines that are replaced as a matter of "better safe than sorry" as opposed to auto engines where you may reuse some component. Be prepared for some expenses if you choose to rebuild. Good luck!
Boyce
 
Installed weight

Jconard said:
Actually,

You will have faster cruise speeds with a 360 and a good FP prop, by at least 10 knots.

The above has not been my understanding at all, there is no dispute that FP are usually a little faster at top speed, but assuming we are talking cruise speed, and at a consistent fuel flow, Every comparison I am aware of and every FP or CS RV I have flown in has better cruise speed at a given fuel flow, than does the fixed pitch.

I would say that two of the nicest 6's I have flown are 180hp fixed pitch sensenich birds. Simple, good performance, low maintenance.

If you can save money on the 320, I would go that way....again.....but the cost savings was very high in my case, and as a result of career choices, money was low. The cost delta between two brand new engines is small. As for weight, it has been beaten to death, but typical installed weight differences are larger than 10lbs between the two.
Click to expand...

On the cruise speed, the point I was making is that a 360FP will cruise faster than a 320CS because it has 20 extra horsepower. No argument with you on the benifits of fuel flow with CS, but that holds true for either 360 or 320.

On the installed weights, comparing built aircraft weight is not a good comparison, as the data is skewed by non engine related choices. Many 360's have CS props and many 320's have FP props. Look at the raw specification data from the powerplant manufacturers. Use the clone makers, as they offer the same induction systems on 320 and 360. There is about 7# difference in a completed parallel valve engine with carb or fuel injection on either the 320 or 360. Fuel system, cowl, induction and all other choices required to support either engine weigh the same. The installed weight is indeed less than 10# given all other choices are the same. Lots of folks I've spoken with have the perception that a 320 equipped plane is much lighter than a 360. It might be true, but it is has little to do with the engine choice.

If the final thought is cost, there is also more to the story as well. If the core is really that cheap, will it be a good deal to overhaul. What kind of shape are the crank and cases in? How much life do you expect to get out of the core vs. how much will you fly. Either will fly great in the end, but the service life may be very different.
 
Engine weight comparisons

The decision he's trying to make is O-360 FP vs. O-320 CS.

Yes, it's true that the weight of an 360 vs a 320 is about the same. That's exactly why recommended the O-320 with the CS prop -- because the O-320 with a C/S prop will weigh MORE then the O-360 with a fixed prop. That's a good thing. It moves the CG forward, which makes for a more useful airplane.
 
I 'm building what I originally thought was an odd ball turns out to be more common than I thought. My RV7-A will have an I0-360 fixed pitch on it. Considering the price break and less maintenance I don't care if someone can beat me off the ground or land a little shorter. I'll fly my plane not the prop.

enfr.jpg


Just like a proud parent I gotta show my engine off.
 
Hi all,

decision has been made (ordered the finishing kit) and thanks for you comments -- they really guided the decision. As said, the take off distance and such are not that important for me so I rather save some bucks (at least for the beginning) and go for FP propeller. Only thing I could say I miss would be the slowing down in final, but you can't get all. As said Rivethead as well I rather save some bucks and have less maintenance -- both will allow to fly more. :)

What comes to the fuel economy, does CS propeller really pay off here? If savings will overcome when initial price and overhaul price difference between FP and CS is considered for CS, wouldn't everyone get it?

So the plan is now to get IO-360 (horizontal induction) with FP propeller in some day. But before that day comes, there is a lot to do with the plane!
 
Rivethead said:
My RV7-A will have an I0-360 fixed pitch on it. Considering the price break and less maintenance I don't care if someone can beat me off the ground or land a little shorter. I'll fly my plane not the prop.
Click to expand...

Sounds "catchy"; but the prop is certainly part of the plane. Living at a high altitude airport, where the format of the prop makes quite a difference in getting off the ground, I didn't even consider a fixed pitch prop. Other things would go, well before the C/S would.

L.Adamson --- RV6A/0360/Hartzell CS
 
Not always is heavy front end a good thing

jonbakerok said:
The decision he's trying to make is O-360 FP vs. O-320 CS.

Yes, it's true that the weight of an 360 vs a 320 is about the same. That's exactly why recommended the O-320 with the CS prop -- because the O-320 with a C/S prop will weigh MORE then the O-360 with a fixed prop. That's a good thing. It moves the CG forward, which makes for a more useful airplane.
Click to expand...

If you plan it right during the build, you don't need to load the front of an RV-6 down with weight to make it usable. I planned the build to keep the tail light and weight forward in my plane. I am at the aft CG with 3 gal fuel, 340# for pilot and passenger, and 80# in the baggage bay. I test flew it this way during phase 1 with no problem (using weights). I had neutral dynamic stability at this W&B. I also do not plan to need 340# and 80# bags, and my personal limits are to have 8 gal in the tanks min, so it is all the utility I need.

For me, acro is important, and I would rather have the extra margin. My wife and I can take off with 15 gallons and we are within the acro limits. Not possible if I would have hung a metal prop on the front! Also not possible with a bigger wife! IMO the airplane is more usable if it is kept light. Depends on your mission I guess.

I also think the plane handles better light. Glide is only better if you have oil pressure to move the pitch to fine. I've heard reports of guys getting good glide by pulling the blue knob back, but I have test flown an RV-7 with an angle valve IO360 and Hartz, and pulled the black and blue knobs all the way back. It went down like a rock. It decended much faster than my RV-6 with the red knob pulled back (yup, I did that).
 
Pirkka said:
What comes to the fuel economy, does CS propeller really pay off here? If savings will overcome when initial price and overhaul price difference between FP and CS is considered for CS, wouldn't everyone get it?
Click to expand...

I don't think anyone actually said that the fuel savings would overcome the extra cost of a C/S prop, although with fuel prices rising, who knows?
I think there would be too many variables to give accurate figures for any fuel savings. However here are some figures from the Lycoming 0-320 Operators manual that might help.
Engine IO-320 B & D series, mixture "Best Economy", producing 65% power at each of the following RPMs:
2000 rpm, 7.1 g/h
2200 rpm, 7.4 g/h
2400 rpm, 7.6 g/h
2600 rpm, 7.8 g/h
2700 rpm, 8 g/h
The figures are taken off a small scale graph so there could be a 0.1 inaccuracy.
I cruise at around 2,250 rpm & 61% power with my Hartzell. We work in litres in Australia and I suspect the C/S prop may be good for at least 1 ltr p/h (possibly more?) at cruise over a F/P prop. With fuel at around $2 AUD ltr this would be a fuel saving of at least $2,000 per 1000 hrs on current fuel prices.
This is all very speculative as I have no experience with a typical F/P prop in an RV and therefore do not know the RPMs and FF that would be needed to match my TAS. No doubt there will be others with a different point of view!

Fin
9A
 
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