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Engine / prop selection RV-9A

David Burke said:
How efficient is it to use a throttled back 180Hp instead of a 150/60 which is working at it's optimum throttle setting ? I can see some of the arguements for larger engines - however as Vans designed her to take a maximum of 160HP - why not just go down the RV-7 route instead?
Because of that wing. Much more stable in cruise. There are some differences in the flight characteristics of a 7 and a 9 where the 9 wins out over the 7. The 7 is not just a 9 that can handle more HP (or for those of you who think there is no better plane than the 7; "The 9 is not just a 7 that cannot handle high HP engines"). There are some real performance characteristics between the two that is mostly due to the difference in the wing design.
 
My .02

I have been away from these forums for over 10 days now. I am just getting back to catching up on all the reading. This thread is very much in my mind as I have been dealing with these issues also.

Aussie9A has many of the same thoughts and ideas I have had in the recent past. Lest some out there chastise me for my lack of conformity to the Vans Ideal, I have indeed read everything I can find on the HP ratings of engines for the RV9A. I have even read all the writings by the "great V-man" from the vast NW himself. I do believe that much of his motivation for stating what he does about his airframe kits is predicated by the necessity to "CYA". As others have posted, I don't necessarily blame him for doing so. However, I do feel that the CYA mentality does provide for some challenges for us builders.

I am planning on the ECI IO340 "stroked" engine with the cold air induction fuel injection system for my 9A. I am also planning on the Catto three bladed fixed pitch prop, the James cowl and plenum and an electronic ignition (not sure which brand yet) with one magneto (Yukon, GMCJetPilot and all the others, please note I am very interested in doing my own CYA here. I just want to work with some of the modern technology to improve performance and/or economy while doing it.)

I have talked for two years now with Richard at America's Aircraft Engines. We have discussed the issues with the weight, HP, fuel burn, price and pretty much everything I can think of to go over between the IO-320, IO-340, IO-360. All three engines are close to a wash on price with just a couple of hundred dollars separating any of them. They are within about 15 lbs of each other in weight with the 340 weighing about the same as the 320 and the 360 coming in just a few lbs (less than 10-12) from the other two. The HP is where the three might be different enough with measurements showing that the 340 is outputting more rated HP than the 360 (according to ECI tests).

So when looking at all of these factors I am leaning towards the 340. It is a bit more in price than the other two but it out performs both of the others in rated HP. Its weight is about the same as the 320 so is favored in that category when I compare it to the HP output of the 320. Fuel burn should be reduced when throttling back to 55% to 65%. At that power loading I should be able to maintain a favorable cruise speed while leaning for minimum fuel burn. Another added advantage to running at these lower power settings should be an engine that lasts a very long time. Oh, and one more advantage to running at these power settings should be a decrease in noise and vibrations which is another important factor in the comfort category.

There are some cons to the choice of the IO-340 with cold air induction fuel injection that should not be overlooked. This engine compression is 9:1 so 100LL is the recommended fuel according to ECI. I do not like this limitation and am talking quite a bit with those in the know at ECI about possible fuel options. Another con for choosing this engine in combination with ECI's cold air induction and fuel injection is the fuel return lines and the cowling configurations needed. Both cause some complexity in the installation and construction for these systems. As far as the fuel lines, so far they have not proven too difficult. I am currently constructing the slow build fuel tanks and have the return lines in place. This has not been much of a problem. Yet to be built are the valving mechanisms that could be difficult. However, there are several individuals working on the necessary plumbing for these systems. One of these people is Robbie Attaway at Attaway Air. Robbie has already been very helpful to me. I will be doing much more talking with him in the coming months. He is a great resource for working with these ECI systems.

My plans are to combine this engine with the three bladed Catto Prop. This decision is mainly based upon reports of quieter and smoother operation using this prop from others who have flown with it. I am building a cruising machine for my desires to fly cross country in comfort. This comfort is much more valuable to me than all out speed. Perhaps a two bladed prop would provide a couple of more kts of speed but the smoothness and quietness of a three bladed prop wins out over speed for my needs. One other important factor with the three bladed prop is the ground clearance. My plane will live on a private grass strip. This will mean that at least half of its landings will be done on this grass strip and then taxied to the hangar on grass. With all the concerns of nose overs I want as much ground clearance as I can muster when choosing a prop.

Weight is another important determiner for choosing the Catto prop. I am not willing to add weight, complexity and costs (this is important too considering I am looking at $2K compared to $7K-$12K) in order to have a constant speed prop. As everyone flying the RV's has attested these planes do not fly like spam cans. Therefore, the three bladed cruise prop I intend to put on this plane should be very adept at providing enough climb for my needs while giving me very adequate cruise speeds. All this while shaving off somewhere around 30 lbs from that of a constant speed prop installation.

I had mentioned above that comfort was more valuable to me than speed but that is not to say that I do not value speed. Because of this I believe the James Cowl and Plenum is the way to go on the cowling of this engine. Perhaps it may give more speed, perhaps not. Perhaps it will be an easier install than Van's cowl, maybe not. Whatever it turns out to be I am convinced that I will give them a go.

One last thing that I have plans for that is very much in the experimental realm of our endeavors. I have never been a fan of the loud roaring open header sound of a throbbing internal combustion engine. So with that in mind I also intend to work on a muffler installation as proposed by Tony Bengalis. If successfully installed this muffler should contribute a great deal to silencing the sound and vibrations of my airplane. I have a great respect for Tony Bengalis and have no reason to believe anything contrary to what he has written about and experienced. It shall yet to be seen whether this swiss muffler system will be as beneficial as I hope, but if so, not only will it provide for a more comfortable cross country airplane but it should also be less of an annoyance to those around the airport as I take off or land.

Well, sorry for such a long post but I wanted to share my thoughts as I have wrestled with the idea of what engine to place in my airplane for the past two years or so. I am sure there are many other ideas that I have not mentioned here that have had an influence on my decision or may have an influence on you as you decide. I am sure many others will be more than willing to hit upon any or all of them. I hope my .02 has been beneficial as others wrestle with these decisions.

As always,
Live Long and Prosper!
 
Mel said:
It has nothing to do with RVs. I have quite a few friends who fly RVs IFR. Anyone who gets an instrument rating is much better off for it. I fly strictly VFR. I have looked into getting the rating but could never justify the time or expense for the type flying that I do.
Absolutely nothing against fly RVs IFR.
Now, do I think that the RV is a GOOD instrument platform? Not particularly. Being aerobatic, the RV is not inherently stable. For IFR, if your aircraft is not inherently stable, you do NEED an autopilot.
Just my opinion.
Kudos to Mel for sharing his personal choices / limitations and the reasons why.

As for RVs and IFR, wouldn't the -9 be a decent IFR platform, certainly better than the -4/6/7/8? I would still want an autopilot and would design the panel with the AP in mind. IFR is actually one of the reasons I would build a -9, the others being lower landing speed and better stall behavior. Yes, I know, the -9 is slower and not (officially) aerobatic.

TODR
 
Aussie 9A said:
USCANAM said:
Interesting topic, and a subject that has been number one in my mind ever since I purchased my engine/prop combo for the 9A which I hope to fly by the end of the year.

Very interesting. are you using f/p or c/s MT prop? Also carb or F/I? Do you have an opinion on FADEC?
Sorry about not including that.. We have vertical Fuel injection, and a constant speed 3 blade MT prop with the MT gov.
As for FADEC, I think pilots like to twiddle. Mooney tried it many years ago with the Porche engine. Never was popular.
Regards
Jack
 
TODR,

The roll rate on the 9 is significantly slower than the 7 and 8 which makes it somewhat more stable. The 7 and 8 roll rate is one of the reasons these machines are such excellent aerobatic/sport aircraft. I was not interested in aerobatics but wanted an efficient cross country flyer so I selected the 9. I might mention that the Ronz airfoil on the 9 really loves flying in the 9-14k ft range which adds to its cross country viability. Additionally, I would recommend any serious cross country machine have an ap--I have the TruTrak Pictorial Pilot and Altrak---on long cross country flights it does most of the flying!!

Cheers,

db
 
Kind of an old thread

Just curious. I see a lot comparing O-320 to O-360. I wonder about taking an O-320 to 180-200hp for more hp and have more hp with less wt. And I would suppose less torque because of the shorter stroke.? Any thoughts?
 
Just curious. I see a lot comparing O-320 to O-360. I wonder about taking an O-320 to 180-200hp for more hp and have more hp with less wt. And I would suppose less torque because of the shorter stroke.? Any thoughts?

TANSTAAFL. The only way you're going to do that is with high compression, shortening the life of the engine.

Torque, by definition, cannot be lower. It must be higher. Horsepower is torque*rpm/5252. If you are keeping the rpm constant (2700 redline), but you want more horsepower, you MUST increase the torque - no other way to get there. To get a high enough torque with the shorter throw, your cylinder pressures have to go up quite a bit, raising the load on the piston, wrist pin, connecting rod, crank, and main bearings.
 
TANSTAAFL. The only way you're going to do that is with high compression, shortening the life of the engine.

Torque, by definition, cannot be lower. It must be higher. Horsepower is torque*rpm/5252. If you are keeping the rpm constant (2700 redline), but you want more horsepower, you MUST increase the torque - no other way to get there. To get a high enough torque with the shorter throw, your cylinder pressures have to go up quite a bit, raising the load on the piston, wrist pin, connecting rod, crank, and main bearings.

Increasing the stroke just increases displacement. Engine power is directly related to how much fuel/air gets pulled in (i.e. displacement times VE) as well as how much it is compressed. Therefore three ways to increase power with a fixed cyl bore. Increase stroke or increase VE (including going over 100 via forced induction) or increase CR. First two will introduce more fuel/air into the chamber and therefore increase torque. Performance shops that re-work chambers and valves get their increases by upping VE.

When you increase stroke with the same bore, you also increase cylinder pressure, as you have introduced more fuel/air mix acting on the same area of piston top. Wear is related to the force on the piston top near TDC and when bore is held constant anything that does this increases that pressure and therefore increases wear.

Larry
 
New Gear WB

I am curious if anyone flying with the new A gear knows if the weight and balance is better?

Also, there is a lot of discussion about the WB in the 7A forum and how people are adding heavy crush plates when using a lightweight prop. But how does the RV9A fair with a light weight prop?
 
My 9A w/ new nose gear

I have a newly flying 9A with new nose gear, IO-360 thunderbolt, 2 blade ground adjustable composite Sensenich, full IFR Garmin Panel, EarthX battery. The light prop did move CG back. Mine weighed 1130 (a little hefty) in spite of prop and EarthX with CG at 79.12". So at least in my configuration the new nose gear didn't cause any problems with forward CG.
 
Thanks

I have a newly flying 9A with new nose gear, IO-360 thunderbolt, 2 blade ground adjustable composite Sensenich, full IFR Garmin Panel, EarthX battery. The light prop did move CG back. Mine weighed 1130 (a little hefty) in spite of prop and EarthX with CG at 79.12". So at least in my configuration the new nose gear didn't cause any problems with forward CG.

Thank you for the data.
 
I am curious if anyone flying with the new A gear knows if the weight and balance is better?

Also, there is a lot of discussion about the WB in the 7A forum and how people are adding heavy crush plates when using a lightweight prop. But how does the RV9A fair with a light weight prop?

I have a Catto 3-blade prop. It weighs 12 lbs. prop extension 7 lbs. my CG is right in the center of the Vans published range for the 9A.
 
I'm rebuilding a RV9A that was originally equipped with a conical O320 / extended engine mount / Sensenich aluminum prop. Owners felt it was a bit aft CG with this combination.
In it's reincarnated form, I will have the new style engine mount & nose gear leg (so not extended) / now Dynafocal O320 / Hartzell C/S prop with 7666 blades. So I think the CG should move forward a bit, all should be good!
 
Great

I have a Catto 3-blade prop. It weighs 12 lbs. prop extension 7 lbs. my CG is right in the center of the Vans published range for the 9A.

Great to hear, because this is closest yet to my setup. I was worried I would need a heavy crush plate, but good to know your configuration is in the middle range.

I will have the wings on in a month, so should know then.....
 
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