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07-31-2008, 06:07 AM
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Join Date: Feb 2006
Location: Europe, Finland (EFTU)
Posts: 542
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Engine selection dilemma
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)!
__________________
Pirkka
- RV-7 -
Tail: Waiting for fiberglass.
Wings: Some priming left, then lot of riveting.
QB Fuse + Finishing kit: in crates.
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07-31-2008, 06:17 AM
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Super Moderator
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Join Date: Jan 2005
Location: Lubbock, Texas
Posts: 645
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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.
__________________
Russ Daves
Lubbock, TX
Proud to be a Veteran
N710RV - RV-10 Sold
N65RV - RV-6A Sold
N686RV - RV-6A Re-Built, Sold
N742PZ - RV-8 Co-Builder Sold
N-867RV -RV-7 Finish Kit
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07-31-2008, 06:50 AM
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Join Date: May 2005
Location: Mandeville, Louisiana
Posts: 179
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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.
__________________
Dale Lambert
RV-6 Flying, XPIO360 Catto 3bld AFS3500EE
'68' C177
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07-31-2008, 06:53 AM
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Join Date: Apr 2005
Location: Twin Cities
Posts: 438
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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.
__________________
John C Conard
J.D.
Citabria 7KCAB (Former)
RV-7 Flying
Last edited by Jconard : 07-31-2008 at 08:28 AM.
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07-31-2008, 10:08 AM
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Join Date: Jul 2005
Posts: 1,346
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Also consider the maintenance/overhaul costs of a CS prop.
__________________
Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS, L3 Lynx NGT-9000
N164WM
N184WM reserved (RV-8)....finishing kit in progress. Titan IOX-370
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07-31-2008, 10:11 AM
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Join Date: May 2007
Location: Northern CA
Posts: 430
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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
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07-31-2008, 10:39 AM
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Join Date: May 2007
Location: Winter Springs, FL
Posts: 249
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Quote:
Originally Posted by Pirkka
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)!
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Just a quick comment. FI does not mean that the engine is likely to have inverted oil. Two different and independent things.
__________________
Jorge Martinez
QB 8A Fuse. Just battled the ^%&@ing gear weldments. Now I can move on.
http://www.rv8alog.com
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08-01-2008, 02:03 AM
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Join Date: Feb 2006
Location: Europe, Finland (EFTU)
Posts: 542
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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.  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.
__________________
Pirkka
- RV-7 -
Tail: Waiting for fiberglass.
Wings: Some priming left, then lot of riveting.
QB Fuse + Finishing kit: in crates.
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08-01-2008, 05:10 AM
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Join Date: Nov 2006
Location: maple grove,mn
Posts: 244
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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.
__________________
Mike Johnson
8A N484M
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08-01-2008, 06:18 AM
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Join Date: Jan 2005
Location: Houston
Posts: 361
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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.
__________________
Jon Baker
RV6A sold, RV4 in-progress
Houston
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