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Some questions on performance and ruggedness

Z

ZorgroZ

I'm New Here
(Long-time lurker, first post -- the more I consider the RV3, the more sexy it becomes. So in the end I might just have to get one! :) Hope you don't mind my questions in the meantime.)

I'm trying to get a feeling what cruise performance to expect from an RV3 with different options. For instance, what cruise performance (TAS) are you seeing (or would you expect) for an RV3 at pressure altitude 4000' with a 150 hp O-320 and a fixed-pitch prop (e.g., when dialling in 7 gph)?

Also, do you think an RV3 is suitable for landing on high-density altitude mountain strips? I know it's no SuperCub, but the stall speed seems low enough. However, how about the landing gear? (And is it possible to install larger-size tires for main wheel and tailwheel, and reinforce the landing gear, just in case?)

P.s.: I think it would be useful to collect user-contributed real-world performance data in a database, to be able to analyse, compare, and graph it. This could make modification / upgrade decisions quite objective.
 
RV-3A performance

Good day, I fly a 1998 RV-3A with 641 hrs TT, 15 gal wing tanks, old school wheel pants, 831 lb empty, with an O320-E2A with 8.5-1 Pistons, dual Pmags and a Props Inc fixed pitch 68-70. At 6500 ft at 2500 rpm full rich I true 195 mph, at 2200 I see 140 mph leaned out. Doesn't accelerate on the runway like my 190 hp CS RV-6 did, but once that prop winds up, it scoots along pretty good and climbs very well although I haven't measured ft/min. Hope that helps :)
 
arunnells said:
Good day, I fly a 1998 RV-3A with 641 hrs TT, 15 gal wing tanks, old school wheel pants, 831 lb empty, with an O320-E2A with 8.5-1 Pistons, dual Pmags and a Props Inc fixed pitch 68-70. At 6500 ft at 2500 rpm full rich I true 195 mph, at 2200 I see 140 mph leaned out. Doesn't accelerate on the runway like my 190 hp CS RV-6 did, but once that prop winds up, it scoots along pretty good and climbs very well although I haven't measured ft/min. Hope that helps :)
Click to expand...

Thanks for the data point. That gives me a good impression, although your engine seems more powerful and efficient than the one I'm interested in, due to your 170 hp, 8.5:1 compression, and dual P-mags.

What fuel flows are you seeing at "2500 rpm full rich" and "2200 rpm leaned out" (at 6500')?
 
Performance

You are right on target at 150 mph-4000ft-7gpm. My prop is catto 70x72.
My opinion is bigger tires could be fitted at some cost in drag. I have seen no evidence of frail gear legs. No experience with high altitude landing characteristics.
 
I think if you do a search on RV3 engine mount cracks you will find that it's a pretty common. The attach points cracks are a known problem area on the RV3 and many early RV4's.
Definitely not what I would consider a robust design for rough field landings.
 
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I think I have to agree with Walt on the design of the gear - the gear itself is plenty strong, but the firewall attach points were not made to pound it out on extremely rough strips. The airplane was designed to operate off of grass, sod, etc - farm strips. I'd hesitate to take it into anyplace where I thought I needed bigger tires.

Speedwise, I can't help you with a fixed pitch - with the IO-320 and a constant speed WW-151H, we can easily cruise at 170 knots at 7.2 gph at 8,000'. Normally, I lean it way back and cruise about 165 at 6.5 gph at 10,000'.
 
I flew my rv3 from atlanta, ga to houston, tx last week in 4hrs 40mins at 4500ft. 0-320, 9.1 comp. carbed, electronic ignition on one side and mag on the other, catto 70x77 prop, old style wheel pants. 170mph ias, 179mph tas, 148kts ias, 155kts tas, oat 32degs F, altimeter 30.30, 21.5" map, 2450rpm, 7 gph leaned to 50 ROP.
 
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titanhank said:
I flew my rv3 from atlanta, ga to houston, tx last week in 4hrs 40mins at 4500ft. 0-320, 9.1 comp. carbed, electronic ignition on one side and mag on the other, catto 70x77 prop, old style wheel pants. 170mph ias, 189mph tas, 148kts ias, 164kts tas, oat 32degs F, altimeter 30.30, 21.5" map, 2450rpm, 7 gph leaned to 50 ROP.
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Wow, those are fantastic cruise numbers!

Ok, then let me ask the other way around: I'm aware of an RV3 with O-320 (150 hp, 7:1 compression, Slick mags) and Ed Sterba 68x70" prop with 135 ktas / 155 mph true airspeed at 4000' and 7 gph (with wheelpants).

Hearing these numbers I was a bit surprised as they're quite a bit lower than what's commonly discussed here, isn't it (and commonly no large discrepancies to Van's book numbers are expected)? So I'm wondering what could be the reason for the discrepancy?

Some things I can think of:
* Engine: 7:1 compression ratio, 150 hp; perhaps worn (doesn't reach rated performance) -- although engine specs same as Van's
* Prop: shape very not efficient, pitch too low (?)
* Fuel: Mogas instead of Avgas (?)
* Aerodynamics: Front CG, not straight, requires trim tab
 
Ironflight said:
I think I have to agree with Walt on the design of the gear - the gear itself is plenty strong, but the firewall attach points were not made to pound it out on extremely rough strips. The airplane was designed to operate off of grass, sod, etc - farm strips. I'd hesitate to take it into anyplace where I thought I needed bigger tires.
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Hi Paul,

Thanks for the insight. Do you think it would be possible to reinforce the engine mounts (on an existing RV) to make it more suitable for rougher strips?

Thanks,

Michael

P.s.: Has anybody ever put skis underneath an RV? :D
 
ZorgroZ said:
Wow, those are fantastic cruise numbers!

Ok, then let me ask the other way around: I'm aware of an RV3 with O-320 (150 hp, 7:1 compression, Slick mags) and Ed Sterba 68x70" prop with 135 ktas / 155 mph true airspeed at 4000' and 7 gph (with wheelpants).

Hearing these numbers I was a bit surprised as they're quite a bit lower than what's commonly discussed here, isn't it (and commonly no large discrepancies to Van's book numbers are expected)? So I'm wondering what could be the reason for the discrepancy?

Some things I can think of:
* Engine: 7:1 compression ratio, 150 hp; perhaps worn (doesn't reach rated performance) -- although engine specs same as Van's
* Prop: shape very not efficient, pitch too low (?)
* Fuel: Mogas instead of Avgas (?)
* Aerodynamics: Front CG, not straight, requires trim tab
Click to expand...

Every airplane is different with build quality, instrument installation, CG, prop selection, etc. my numbers above is 61% power according to the lycoming engine power chart. I think the catto props are the only choice for a FP application, but that is just my opinion. I have since adjust the k factor to make the gph read correctly to 7gph. I also made a fat finger error entering the numbers. It should read 179mph tas and 154kts tas at 7 gph.


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TAS and gear question

My Tas at 7gph is about 160 mph. I always seek Walt and Paul's advice and suggest you take it seriously. That said, there are a few threads declaring the cracking problem was solvedby the six point mount. So, you might consult Russ McCution for additional input.
 
Gear cracks and rough landings

I bought my RV-3 with broken gear. The same cracks that develop in many of the early -3's, mine was first flown in 1984. I had the engine mount replaced with a new 6-point mount from Vans, it was lots of work, but it is more robust and have had no problems with it.
As far as bigger tires, rough strips and such, the biggest factor I have seen is tire pressure as far as stressing the gear. Most people put too much air in the tires and it makes for hard landings. I run tire pressure between 20 and 22 lbs and as long as my technique is good, no problems. If I put more pressure in them, it is less forgiving. The spring gear likes the lower tire pressure, I have the wood stiffeners on my rod gear legs, this cuts the shimmy, but makes the touch down a bit more critical too.....
I usually come down final at 100 mph, pull in the flaps over the numbers and fly it on (wheel landing) at about 80 and roll her out. I find I have a harder time nailing the 3-point landings due to the nose high attitude and she becomes more pitch sensitive with all the flaps in...I really bounced a few early on. I know the RV-3 can fly slow, but the nose is pretty high to fly at lower speeds...I prefer to keep my speed up and grease it in on the mains. I did my transition training in a Pitts, so carrying the speed down final comes easy after that.
Every RV is different, It has taken me a while to figure out the right mojo for mine...but she is a pleasure to fly and very well mannered.
Best of luck
Dave
 
You asked about what one could expect, here are my performance numbers...
http://www.romeolima.com/RV3works/Flying/flying.html#Performance

Obviously they'll be different with different engine/prop combinations, and there are an almost infinite combination of FWF combinations you could install. Paul Dye installed a similar power combo and IIRC his numbers are similar.

One thing I'll comment on, the RV-3 by virtue of it's small size and clean airframe is a very efficient bird. I used to take great joy in getting to altitude, leaning it out, finding a bit of tailwind, and watching my EFIS computer display fuel consumption and MPG numbers that my -8 couldn't possibly match. I love efficiency and this gave me great joy!
 
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