Trying to balance the scales...

[Ola]

While putting some meat on the bones of the RV-8 dream, I'm setting up a few different budgets based on various configurations, and I'm hoping the experienced posters can provide some pointers to this:

Between the cheapest (used -320, fixed pitch) and most expensive (new -360, CS, electronic bells and injected whistles) option there is some gray space.

If you had the choice between a used 160hp -320 with a new CS prop and a used 180hp -360 with a new fixed pitch, price being equal for the sake of argument, which way would you go?

The mission profile is the average "total performance" I guess. Economical XC with potential for thrills, some short field but not much and fairly low DA airfields. Norway might be jagged, but it doesn't reach too high or get too hot. Fuel economy is important, but I'm not 100% sure how to balance it against near-overhaul time or the many non-$ factors.

I realize the price scenario might not be perfectly realistic and that there are many factors to consider, I'd just like some opinions to base further research and penny counting on. Thanks!

 

[sf3543]

I can not comment from experience on the RV8, but I can from experience on my RV6. I built an RV6 with a mid time 150 HP O-320 using the Sensenich prop recommended by VAN's. Then, after several years of flying, rebuilt the engine to 160 HP and changed to the constant speed Hartzell, recommended by VAN's. You would not believe the difference in performance! Climb increased significantly and I did gain a few MPH at the top end. Other things I noticed include: Empty weight went up due to heavier prop and addition of governor and controls; however on the RV6 that's good since they tend to be a tad tail heavy with a light prop. Since I did a conversion, there was a bunch of extra work required, like adding the firewall box for the governor, running the prop control and adding the oil line, but on a new build these aren't extras.
If you go with a fixed pitch prop, you will be compromising either climb or cruise performance or both, depending on the prop you choose while a constant speed prop allows more optimim performance at both ends of the spectrum. (But, the cost is about $5000 more.)
If I had it to do over again, I would. As long as the cost is acceptable to you, I think the CS prop is the way to go.
As far as engines go, if you can find a good mid time engine at a good price, I personally don't see a problem with that. But, new is always nice...again it's a cost issue.
I am currently building an RV8 and I opted to go with the Hartzell CS blended airfoil prop behind the IO 360, 180 HP ECI Titan kit engine, which is a clone of the Lycoming 360. Some folks have to have the 200 HP version, but it is heavier and bigger inside the cowling.
Have fun deciding.

 

[Radomir]

it would be very helpful to quantify this compromise, as otherwise it may be mistaken for "poor performance." For example, if 180+FP (set up for high cruise) will yield this compromised climb to be 1000+fpm @gross, it still may be very acceptable, especially if compared to ordinary spam cans (OTOH, if your measure stick is a Rocket.. the discussion takes a whole different path..)

 

[Ola]

If I had it to do over again, I would. As long as the cost is acceptable to you, I think the CS prop is the way to go.

Thanks for posting your experiences.

New engines are always nice and if it turns out I can afford it then I'll go for it, same with more HP, time will tell. But the knots from 170 to 190 are pretty expensive. Another thing I've considered (and mentioned on the forum) is the Deltahawk engine, loads of savings to be had burning Jet A over here. But those savings quite costly at the moment...

By the way, is the Titan kit a self build? Do you attend a session a la Mattituck?

it would be very helpful to quantify this compromise, as otherwise it may be mistaken for "poor performance." For example, if 180+FP (set up for high cruise) will yield this compromised climb to be 1000+fpm @gross, it still may be very acceptable, especially if compared to ordinary spam cans (OTOH, if your measure stick is a Rocket.. the discussion takes a whole different path..)

Exactly. Putting down " additional 700 fpm = $7000" in the Excel sheet makes things a lot clearer. I bet I'd be just thrilled with a 160hp/FP though, since it was MINE! Since the project is a few years away, this makes for fun brain exercise and a foundation for a good decision.

 

[garnt.piper]

Engine - prop choice

Hi, my RV-4 has 180hp and wood FP prop, since first flight have added Ellison TBI and inverted fuel/oil. I TAS 172KTS @36l/hr, and can get to 10kft in about 7-8minutes. CS would be nice, but the extra 50lb would kill any legal load carrying ability with full fuel, and make it more nose heavy. The RV-8 wouldn't be so critical with its greater Gross weight. Another factor with the CS, is the mandated overhaul period. I have just looked at a Laser with a Hoffman CS, it had flown about 300hrs in the last 10 years, but the prop was due OH on calendar time. $7-8k every 10yrs or less must be considered, a FP prop is simple, cheaper, with no ongoing expense.

If you haven't started the project, you have time to think on these things. I found building a 'plane a bit like my house, buy the time you get near finished, patience and money are always limited and you just want it done, now. Keep it simple, keep it light, get it flying, make provision for CS as you go along, if things get tight near the end, go FP and retrofit CS later if still desire it.

Overall, enjoy.

VH-PIO
Australi

 

[Ola]

Keep it simple, keep it light, get it flying, make provision for CS as you go along, if things get tight near the end, go FP and retrofit CS later if still desire it.

Good advice, thanks. Less $ up front without limiting later options. I might get to experience "Wow!" upgrade that sf3543 mentioned. the How does one go about? Do you buy a CS engine, then "plug the holes" so to speak?

 

[sf3543]

The Titan kit is a Lycoming clone. You can purchase the kit and build it your self or purchase it already assembled. I chose to build it myself and save a couple of thousand dollars. Per ECI, you build using the Lycoming manuals and parts are interchangable.
If you purchase an engine to start out with a fixed pitch with plans to change to a CS prop later on, you must make sure the engine is capable. There are several things to look for: The accessory case must have a pad for the governor to mount on. Usually, there is a blank cover over this pad if a FP prop is used. There needs to be an oil line access plug on the front crank case. The crank shaft has to be a hollow crank to allow oil to the prop. If a FP prop is used, there is a plug installed in the crank to keep the oil in the engine. When it gets converted, the plug is removed and a different plug gets installed further aft on the crank which keeps the oil headed to the prop rather than back to the interior of the engine. All this assumes an engine with a rear drive for the governor. Some engines mount the governor on the front of the crank case near the air inlet of the cowl.
When adding the governor, you will need the drive spacer and gear, the oil line to the front of the crank case and of course the control cable.
This is pretty high level but I think it covers the main parts.
On an existing engine, the best time to do this would be at OH. That would facilitate inserting the proper crank plugs and making sure the correct front bearings are installed so that the oil from the governor can get to the prop. I'm sure all of this could be done without cracking the case, but just more difficult.
Oh, you'll also need a new spinner since the FP spinners will not fit on the CS prop. Also, make sure the bolts on the crank flange are correct for the prop. I had to change mine out, but it was not difficult. If it's during the OH, the crank shop can do all of these things for you.

 

[osxuser]

Personally I'd rather have an injected 320 with a CS prop. Look for a nice used Twin Commanche engine or like.

 

[Kevin Horton]

It all depends on your priorities ...

If you are interested in T/O and climb performance, go with the O-320 and the C/S prop. The O-330/FP won't spin up to full rpm at low airspeed, so it's perf will be lower (but still very acceptable).

If you are interested in cruise speed, go with the O-360/FP. The extra 12% power will get you about 4% more speed.

If you are interested in low noise during cruise, go with the O-320/CS - you can pull the prop control back, leave the throttle wide open, and still get decent speed at a lower rpm. If you try low rpm cruise with a FP prop you end up at low manifold pressure, low power, and very low speed.

Personally, I would go with the O-320/CS.

 

[Mel]

A word of caution on the "Twin Commanche engine"; That particular engine uses a type II dynofocal mount. It differs from the type I in the angle of the isolation mounts. You will need to order this particular mount from Van.
Mel...DAR

 

[f1rocket]

My RV-6 had a O-320 and FP Sensinich prop. My friend's RV-6 had a O-360 and CS Hartzell prop. Do you need the extra performance because of where you're located? (e.g. mountains, high altitude, etc) My friend could definitely out climb me and slow down faster because of the CS prop. I could cruise nearly as fast as him and the installation was much simplier.

Pick your poison. Much of it depends on what you can afford. There's no substitute for HP.

 

[Ola]

Do you need the extra performance because of where you're located?

Definately not. If I don't change locations the next decade, it would operated from a 10K feet runway at 170 ft MSL. There are some nice fields around the country (Norway) which sort under "short&high&obstacles" but nothing that doesn't scare the 172s away.

Comfortable, swift (relative term), economical cruise is perhaps my top pri's.

Much of it depends on what you can afford.

Exactly, hence my budgets. At some point in the project my wallet would make the decision for me and having as much info as possible on options can only help. The replies so far have been excellent for putting thought to the numbers, thanks all!