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-   -   Engine selection dilemma (https://vansairforce.net/community/showthread.php?t=32564)

Finley Atherton 08-01-2008 05:39 PM

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

victor 08-01-2008 06:46 PM

engine choice---
 
Have you considered a rebuilt IO-360 with CS?

Pirkka 08-04-2008 01:26 AM

Quote:

Originally Posted by victor (Post 244309)
Have you considered a rebuilt IO-360 with CS?

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. :(

RAMPEYBOY 08-04-2008 05:42 AM

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

whifof100ll 08-04-2008 09:49 PM

Installed weight
 
Quote:

Originally Posted by Jconard (Post 243934)
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.

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.

jonbakerok 08-05-2008 07:51 AM

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.

Rivethead 08-06-2008 12:52 AM

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.



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

Pirkka 08-06-2008 01:37 AM

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!

L.Adamson 08-06-2008 06:52 AM

Quote:

Originally Posted by Rivethead (Post 245465)
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.

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

whifof100ll 08-06-2008 04:09 PM

Not always is heavy front end a good thing
 
Quote:

Originally Posted by jonbakerok (Post 245227)
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.

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).


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