Might be considering a 4 over an 8...plus a few other ponderings

So I used to think I really wanted to build an 8, but now..I think I might actually like the 4 a bit better...especially if they might perform better given comparable engines. I also really like the idea that it is more builder intensive, so if something gets dorked up in the hangar, I am more than capable of fixing it. I also really like the way they look, but I also love the 8.

Mission...90% solo vrfr flying..with a passenger on occassion, but I'd definitely want to be able to do mild acro with one, probably a weight limitation dictates this. People also worry about the size..but at 5'10 and 165lbs...I don't forsee a problem.

Concerns...setting up a jig perfectly and ending up with a straight airplane

Landing gear/engine mount combo...this is weird to me..and I understand the 8 might be the only one without this..but I rather like the 8's landing gear in that it seems to be more conventional.(pun?)

Is this even an issue worth wondering about? I mean every other acrobatic RV(to include the first one) uses the combo mount that I am aware of, so it must be ok.

The cost savings of an RV4 vs 8 seem pretty signifigant, almost makes the prop free.

I'm thinking a 180hp Para valve with the BA composite prop on either airplane...day VFR only...with light weight on everything else being ultimate goal...so likely a very simple single screen glass setup with a 496 form factor style garmin.

I don't know if speed is important to you

Just an input from a bystander. The RV-4 looks like a perfect design in an artistic sense, everything belongs where it is and how it is for the whole airplane. To my eye the RV-8 falls short in that sense only in the landing gear but you say you prefer it. Performance in speed - even with the same engine - my competitive experience shows (Dave Anders excepted) the RV-8 is the fastest of the RV designs. If I were to build a tandem seated RV it would be the RV-8 for that reason. Because the design has a larger basic engine capacity and it is exceptionally sleek, the RV-8 automatically puts you at the high end of the RV Blue (360 cu in ) class for SARL (www.sportairrace.org) and AirVenture Cup (www.airventurecup.com) racing. RV-4s are king of the RV Red class (320 cu in) but the Blues are consistently faster than the Reds.

Bob Axsom

Considering -4 over -8

Asking for opinions, I will supply some of mine, and please note they are exactly that, opinions.

If you are a larger pilot, and/or need/want the extra "people space" the 8 wins this one

The cost difference is a little bit of an issue, but if you equip them both the same, the airfame difference ($4,575.00 as of today) is just about the only difference.

Also, as far as jigs go, It is not necessary to have a "perfect' jig, the only requirement is to build it as close as you can, and then use shims or whatever to make your parts measurements line up. There are quite a few RV-4's flying that aren't perfectly straight, I woud guess, so don't get too hung up on that aspect of it.

Another thought, if you really enjoy the building process, the -4 is more of a "builders" airplane, in that there is more work for the builder to do. If your goal is to get in the air as quickly as possible the -8 is probably a better way for you to go.

There was a flight report posted here recently comparing flying an RV-4 to a motorcycle, and I think that is a perfect comparison, with the 8 probably being more of a sports car.

Other than that, it is pretty much your decision, but whichever way you go, the good news is you'll end up with an RV.

I would have assumed the 4 to be faster, interesting. I appreciate the replies, if the 8 is faster given the same engine, then this changes things, I woulda assumed both being 180hp the 4 would be all over the 8.

If you build it plain-vanilla per Vans plans, the -8 will be a tad faster on the same engine/prop. Van's claims 3 MPH faster than the -4. If you build the -4 with speed in mind it will be faster but that applies to the -8 as well.

Build what you want. The difference in airspeed between the 2 "by the plans" aircraft is almost unnoticeable.

I own a -4 and every now and then I wish it were an -8 (big passengers). But then I look at it parked out in the sun, go fly it and then I'm damned glad it's a -4.

wickedsprint said:

I would have assumed the 4 to be faster, interesting. I appreciate the replies, if the 8 is faster given the same engine, then this changes things, I woulda assumed both being 180hp the 4 would be all over the 8.

Click to expand...

Van's performance specs suggest a 180 hp RV-8 has a top speed 1 mph faster than a 180 hp RV-4. The 75% cruise speed of the 180 hp RV-8 is listed as 3 mph faster than the RV-4. But, note that the fine print says the props differ for the two sets of data, so it is hard to be sure how much of this difference is due to the airframe, and how much is due to the prop.

If I wanted a pure VFR fun plane, I'd have an RV-4. I love the way the RV-4 looks, and the lighter weight would make for a better handling aircraft. But, I plan to do a lot of traveling too, so the extra fuel, rear seat room, and baggage space of the RV-8 swung me in that direction.

I just flew a -4...this morning...

......on a short 74 mile cross-country and saw 207 GS with a 30 knot tailwind, 174 TAS, an 885 mile range on the Dynon and 28.5 MPG fuel economy!!

Yep, hard to beat...on only 160 HP and a cruise Catto two-blade.

I'm impressed and the -4 flies more nimble IMO..I've flown both.

Regards,

Kevin Horton said:

If I wanted a pure VFR fun plane, I'd have an RV-4. I love the way the RV-4 looks, and the lighter weight would make for a better handling aircraft. But, I plan to do a lot of traveling too, so the extra fuel, rear seat room, and baggage space of the RV-8 swung me in that direction.

Click to expand...

I agree with Kevin. One of the first RV's I was lucky enought to fly was a 150 HP wood prop VFR only RV-4. And to this day I consider it the nicest RV to fly. But the RV-8 is considerablly more practical than the -4 and flies almost as nice. Re-sale is another factor to consider. Equip the two the same, and the extra kit cost of the -8 will more than be recovered if you ever want to sell it. Still I know there is a current RV-3 building craze and I dream about another project, for me it would be VFR RV-4 as light as I could build it with 160 hp/CS combo.

Looks like speed and climb numbers Van's gives for the RV-4 are for a FP Wood prop and they quote with a Hartzell C/S prop for the RV-8. That being said, I imagine an RV-4 with 180hp and a C/S prop will probably climb pretty well.

RV-4 better.

If you can fly your mission in a -4 and you like building it is the best choice, probably the best of the RV?s! As for the landing gear/motor mount, it is very durable and ground handling is as good as it gets.

Piling on to original question...

I've had a question in mind similar to Tony's. For now I'm thoroughly enjoying my -6. But from the beginning the plan has been to fly it a few years, then consider either an 8 or 4, just for a variety of experience.
It seems when I read about 4 vs 8 flying qualities, the 4's are usually 320's with a fixed pitch which is probably pretty light and well balanced. The 8's are usually bigger/heavier motors with heavier CS prop, which maybe ends up being a little nose heavy (?). I don't have any first hand knowledge of this, just observation of others descriptions.
So, what I've wondered is if an 8 with, say, an O360, FP composite prop, and battery in back would end up with flying qualities closer to the -4?
The overall utility of the 8 (back seat room, CG range) is certainly very appealing for the Xcntry part of the mission.
Yeah, I know. We should get flying time in both before deciding. But that is easier said than done.

8 is the resale king....

I know you want to build but you will have about the same $$ in a 4 as you will in an 8. The 8 will resale at almost twice that of the four. The 4 is the best value in the RV world right now as many very nice airplanes trade in the $50k or less range. That is a lot of airplane for the money and I would not hesitate to buy a flying 4 if that is what you wanted and start building something else for the fun of it. You will be money ahead if that is any consideration.

Eight isn't enough...

I have been blessed to fly ALL the RV's and can safely share my experiences for what it's worth.
First, it's not all about speed, it's about what you need. If you have 40K to spend, the RV4 is the absolute best bang for your hard earned buck and is by far the most fun to fly. Since you are a private pilot, do you have any tail wheel time? Have you ever flown an RV? I recommend you get both, get a few rides, then make an educated decision. I do RV4 pre-buys for a sideline and look at alot of them, it's a great airplane.
I have about 200 RV8 hours, 1500 in my RV4 and 400 in my Harmon Rocket. Of those 3 the Rocket rules, the RV4 is a very close second and the RV8 is further down the list. Take your time, gather information and if you need any help, email me off line, I'll be glad to help...

Smokey
HR2

PS: The F-16 is my absolute favorite, but is a bit costly to fly every day...

It's about what YOU want!

Having owned both an -8 and four -4s, there is no doubt that an -8 is:
1)Faster on the same engine prop combination than a -4 with same combo
2)While the -4 'looks 'faster' the -8 is aerodynamically cleaner. Believe it or not, the cowl cheeks on the -4, while very WWII fighter like, like WWII fighters, they did not really understand aerodynamic principles yet either and when Vans got CDCAM, it made designing airplanes easier and more efficient. The -8 is a computer designed airplane.
3)The -8 is MUCH easier to build. Match holes ROCK!
4)Not much difference in building cost but the -8 sells MUCH better and easier. Not as small a niche market.
5)The -8 is much more easily weight and balanced with the two luggage compartments. My wife got the back, I got the front.
6) The -8 allows just about anyone to sit in the back...comfortably. My wife liked the -8 better than the -4s.
7) The -8, even for the same cost to build, sells for almost twice as much.
8) The -8 can be built with a nose gear and that save $$$ on insurance, landing ease etc
9)The -8 can be flown from the back much easier than the -4, especially in the pattern.

So why am I building a -4 again???

I like the way they fly better. I like the way they acro better. I like the way the roll axis is on my nose and not on my chest, makes me feel more 'in tune' with the acro. I like the way there has never been an inflight failure of the very stout wing....ever! I like the way it fits me like a glove. At 6'1" and 200 pounds, I fit perfect and usually am solo for my fun rides so...perfect! I like the way the RV-4 taildragger is a non-event...the easiest tailwheel plane out there! Lastly, I just like the way they look. I asked Mr Van himself at OSHKOSH three years ago when he came over to look at my father in laws -8 Showplanes Fastback which model he liked the best. He said the -3 will always be his hands down favorite. But very close behind was the -4. I'd say he should know better than most!

As everyone has said, it is a matter of choice. But if you choose an RV-4, that choice needs to be built on knowing YOU want it because well, it's hard to justify it from an aerodynamic/$$$$ sense....just in your gut I guess.

P.S. My wife likes flying in our -6 best!

Tailwinds!

Smokey, I have one lesson in a Citabria, I enjoyed it a lot...but am otherwise a training wheel pilot.

Having learned to fly in Wyoming, I already knew a little what the rudder was for since we get plenty of opportunity for crosswinds I'm gonna get my endorsement when I return from this deployment. I was pretty proud of myself for 3 pointing the Citabria first go with simply the instructor talking me through it. Was a nice day though.

Jet, Thanks for pointing out the benefits of the 8, I also have to echo WyoDave's question about a lighter 8..wondering if an 8 can be made to fly closer to a 4..but with the benefits of easier building and cleaner aerodynamics.

smokyray said:

PS: The F-16 is my absolute favorite, but is a bit costly to fly every day...

Click to expand...

Always been a fav plane of mine too, although never had the opportunity to fly one

Too bad you don't still fly them, wonder how my ZX-10R would fare against one in a 1/4 mile drag race. I think up to 150 it'd be close, but after that I'd be smelling JP8.

4 / 8

I own a RV4 and a RV8. I like the 4 over the 8 in flying qualities, landing qualities, and its easier to move around the hanger. The RV4 is my choice for fun flights, local flights, and run errand flights. Local lunch flights too.

When I go Aircraft Camping or on vacation we fly the RV8. More baggage capacity. Both are fine airplanes. You cant go wrong with either one.

You can’t really make a -8 fly like a -4 because regardless of weight and balance your seating position is high (your face is well above the roll access), your feet are close together and the cockpit is bigger, it will never feel the same.

A light CS prop like an MT or WW RV-200 or WW 151 will fit you RV-4 and still keep it very light & fun.

Also if you build your seat cushions right you can run the gas out with no trouble.

Bob Axsom said:

RV-4s are king of the RV Red class (320 cu in) but the Blues are consistently faster than the Reds.

Bob Axsom

Click to expand...

...IMO the best engine for the -4 is the 160hp Lyc. If we compare a ratio of mph:cubic inches, the Blues lose.

At the Taylor air race this year there were three RV-8s, and two more RV Blues. The fastest of them (fuel injected, tricked out, and VERY nice) ran the 125NM course averaging 231.64 mph. The equivalent speed with an IO-320 would be 205.9 mph. My speed in my carbureted RV-4 was 204.86 mph.

The second fastest RV-8 flew the course in 217.46 mph. The equivalent on 320 ci would be 193.3 mph. 11+mph slower than RV Red.

The point might be to focus on the best engine/airframe combo. (After all, we want the plane to be balanced.) Assuming the RV-8 uses the Lycoming 360 and the RV-4 uses the Lycoming 320... displacement for displacement the -4 may beat the -8 in the speed category too.

Flying qualities are a topic that's quite different than efficiency or speed. Just search previous threads and you'll get a feel for how sweet the -4 flies.

You guys are making a heck of a case for the 4...

Tony, I am 5'9" and 160lbs and space is not a problem in a -4. This is mine. You need to plan a few cubby holes to keep things in though

Its a joy to fly. My reasons are here.

Your interests sound like mine, mainly local/solo with a few long trips/two up. We are just planning our first trip outside the country, UK/F/G/NL. We will be inside gross.

I spend most of my time at 2050rpm and 22.5" so the last mph is clearly not important to me. She covers the ground pretty well like that. O-320/2 blade MT. Keep it light by spending less.

Have fun whatever you decide!

Steve, funny you linked that, I spent the better part of the last hour reading about your build, love the paintjob and panel too. I have been having similar thoughts about a single efis and round transponder/radios as well. I'm probably going to skip the autopilot though, have not 100% decided yet. The 4 is more and more sounding like my cup of tea, either with a 320 or a 360 and some form of a composite CS prop, be it either the BA composite or the WW200.

Tony, glad you liked the read!

If you do go the -4 route can I suggest you stick with an O-320. I really struggle to see what the advantage of a 360 would be, unless 8mph on the top speed is SO important and you need to exceed red line on the level!

I can climb at over 2200fpm solo and half fuel, though never do in reality.

The 320 I believe is the 'balanced' engine for the aeroplane and as Van designed it. The engine is lighter, the prop is lighter, the fuel lasts longer and my pocket is heavier.

My thoughts on the AP are these. Part of the delight of the -4 is in role, it is close to neutrally stable, and its very light in pitch. If I have to do some serious map reading etc., for a pilot of my (in)ability it is quite useful to have a second pair of hands to keep it going as I want, and to me that is what it is. Also, for very long straight lines. Holding the stick for 300 miles without a turn....I would rather eat a sandwich.

Dittos to what Steve said:

Although I stuck 360 cubes into my RV4, I must agree with the sentiment about keeping the plane balanced. Nose heavy 4's can become a bit sled-like, and the control balance of a well built 4 is one of the pure joys about the airplane.

And for those of you who haven't done so, take a look at Steve's website. He has a stunning 4, and a great site to go with it.

opinion

Tony,
I'm 5'10" and weigh in at about 220. (wifes a good cook, I'm lazy) Anyway, I fit in the 4 just fine. LOVE the way it flys, and I have flown all but the three and the 10.
I bought it flying, so I could play with it while I decide what to build. So far, my one hour in a rocket has screwed me up the most... ;-) Everything gets compared to that now...
That said, I LOVE my four. Does everything well. (can't vouch for straight and level however, I haven't tried it yet...) <BG>
Dennis

Similar Capabilities for 40K Less

Think of the 4 as the 8's smaller brother that the market under appreciates to the tune of about forty thousand dollars...

Hans

Steve Sampson said:

Tony, glad you liked the read!

If you do go the -4 route can I suggest you stick with an O-320. I really struggle to see what the advantage of a 360 would be, unless 8mph on the top speed is SO important and you need to exceed red line on the level!

I can climb at over 2200fpm solo and half fuel, though never do in reality.

The 320 I believe is the 'balanced' engine for the aeroplane and as Van designed it. The engine is lighter, the prop is lighter, the fuel lasts longer and my pocket is heavier.

My thoughts on the AP are these. Part of the delight of the -4 is in role, it is close to neutrally stable, and its very light in pitch. If I have to do some serious map reading etc., for a pilot of my (in)ability it is quite useful to have a second pair of hands to keep it going as I want, and to me that is what it is. Also, for very long straight lines. Holding the stick for 300 miles without a turn....I would rather eat a sandwich.

Click to expand...

Does 10lbs really make that much of an impact? ( I think a 320 vs a 360 is like 10lbs) I think I like the idea of the WW200RV for the prop, or the 151..and the goal is to keep it light. The 320 is a bit cheaper too, and I suspect vibrates less as well.

I am building a -4. The other alternative for me was the -7. I am still some years from flying it, so I havent purchased an engine yet. I was planning on installing an IO 320, but the increase in cost and weight of the 360 are negligible. The IO 360 will at the same cruising speed use less fuel (alternatively it will cruise faster at the same fuel flow, or faster still at more fuel flow )

The TMX IO320: 277 lbs, 160 HP
The TMX IO360: 284 lbs, 180 HP

So this is 12,5 % more power at the cost of 7 lbs or 2.5 % increase in engine weight. Something to consider.

Regarding speed, I know for a fact (through laborous experience ) that if you build the Horizontal tail strictly according to the plans and manual, you will en up with a twisted tail. This will cost you some knots (2-5??) in trim drag or higher fuel consumption.

I don't know. The -7 is easier to build, much more practical and with higher resale value (the same goes for the -8). Still I chose the -4, and would do it again.

wickedsprint said:

Does 10lbs really make that much of an impact? ( I think a 320 vs a 360 is like 10lbs) I think I like the idea of the WW200RV for the prop, or the 151..and the goal is to keep it light. The 320 is a bit cheaper too, and I suspect vibrates less as well.

Click to expand...

Tony, I am not sure if the question was rhetorical or not, so I had better answer. 10 lbs is 10lbs, but its more a frame of mind. Van had an idea when he designed the aircraft, why walk over it. If you make the 360 decision you will make a number of other equipt decisions, and end up 25lbs heavier.

I hesitate to repeat what I said before, but....

If you go for the bigger engine my thougts are these;
1. The prop will weigh a little more.
2. You will have to order the bigger lower cowl, which to my eye, doesnt look so pretty, (and presumably weighs a couple of ounces more). It must give the aircraft a slightly larger frontal area also, so is less efficient.
3. It will reduce your pax and fuel by a few pounds, which you might regret. The -4 gross is quite low.
4. As I write I see Svingen's post. The problem with running bigger engines at lower power - to my mind - is that they need to be worked hard, hence glider tugs run to TBO: full power only operation. I doubt that most 320 powered -4 get enough thrashing. Mine doesnt. Running too cool is a problem I have been working on.
5. Your point about vibration is probably true though not something I had thought about. The 320/MT/P-mags is very smooth.
6. For me, heavy is not an option because of my runway length. Recent light tailwinds have been quite character building!

Personally I can see no use for the power, but every lbs shaved off is a big help to why a -4 is such a delight to handle. (I feel really bad about the weight of the two TT servos in the AP!)

If its not fast enough I would suggest you build a Harmon Rocket. Thats a -4 designed with (I think) an O-540 in mind. Again, its a plane that is in 'balance'.

Just my thoughts, no intention to offend the 360 or 540 powered -4 drivers!

PS There is a -4 in the UK which has so many toys, paint and bondo, on board that its empty weight is close to my solo weight. The owner can never know what a joy to fly a -4 can be. The owner is quite large so for aeros to stay legal I think he has to leave the fuel out. But I bet it can exceed redline on the flat! Is that good?

Perhaps my engineering background gives me an over developed sense of 'balance'.

SvingenB said:

The IO 360 will at the same cruising speed use less fuel (alternatively it will cruise faster at the same fuel flow, or faster still at more fuel flow )

Click to expand...

How do you work out that the 360 will use less fuel then? On that logic a 540 would be better still!

Perhaps equal, surely?

Steve Sampson said:

How do you work out that the 360 will use less fuel then? On that logic a 540 would be better still!

Perhaps equal, surely?

Click to expand...

That is what I have heard based on experience by others (one -4 with 360 and CS prop and one or two with 320). I don't know why exactly, but the 360 is a 320 with larger stroke more or less. This enables it for the same HP to turn a larger prop at lower RPM and this is more efficient than turning a smaller prop at higher RPM. Maybe this has something to do with it?

I'm with Steve.........

.....on this one, guys. Yesterday afternoon we flew a short XC to get Brian's -4. On the way home, we both showed 174 MPH with Brian at 2400 RPM's and me at 2300 or thereabouts, in my 0-360 powered -6A. Brian's Dynon said 7.2 GPH with his 0-320/160 HP Lyc.

His airplane has a new two bladed Catto, optimized for max cruise, so we both give up a little on takeoff and climb, although neither is slouchy....read 1800 FPM and 600' takeoff roll. Brian's -4 came in a little under 1000# and it's a delight to fly.

Regards,

I think that 4s ROCK!!!
Here is a pic of mine

Steve Sampson said:

How do you work out that the 360 will use less fuel then? On that logic a 540 would be better still!

Perhaps equal, surely?

Click to expand...

Well actually, a IO-540 is better provided you are flying at a resonable RPM and MAP. My Rocket will typically be more fuel efficient than any of the RVs in the group but that only happens if the RV are flying up to their potential. If you get too slow, the RV wins because I have a hard time staying in the air at idle RPM.

I suspect that part of the increased efficiency quoted before is due to fuel injection over carb.

My -4 has an angle valve 200hp IO-360 with an MTV-15B-183-33 CS prop, The engine uses the crank with no counterweights and a light Sky Dynamics Sump, it turned out pretty light and feels light and fun to fly.

I routinely take less fuel on cross country flights over my Dad’s O-320, wood prop RV-4, I don’t fly with him though, I just go my own pace which means I get to altitude faster and spend more time in cruse, Cruse is also faster and often higher and the flight is shorter in time, when I fly along “with” Dad I will always take a little more fuel then him.

I have asked about a new RV-4 kit and they know the market is there but they also know (think) that it will just take those sales from the RV-8 you would have bought anyway, so to them they are selling you an airplane either way so they gain nothing buy spending the money to make the new -4 kit.

It think what they don’t know is that there are builders out there that have already built one RV that would build a -4 if it where easer but since it is not they just stick to what they have, these are lost sales! I also understand there position though, this would be a gamble for them, maybe they will take it some day.

Steve Sampson said:

Tony, I am not sure if the question was rhetorical or not, so I had better answer. 10 lbs is 10lbs, but its more a frame of mind. Van had an idea when he designed the aircraft, why walk over it. If you make the 360 decision you will make a number of other equipt decisions, and end up 25lbs heavier.

I hesitate to repeat what I said before, but....

If you go for the bigger engine my thougts are these;
1. The prop will weigh a little more.
2. You will have to order the bigger lower cowl, which to my eye, doesnt look so pretty, (and presumably weighs a couple of ounces more). It must give the aircraft a slightly larger frontal area also, so is less efficient.
3. It will reduce your pax and fuel by a few pounds, which you might regret. The -4 gross is quite low.
4. As I write I see Svingen's post. The problem with running bigger engines at lower power - to my mind - is that they need to be worked hard, hence glider tugs run to TBO: full power only operation. I doubt that most 320 powered -4 get enough thrashing. Mine doesnt. Running too cool is a problem I have been working on.
5. Your point about vibration is probably true though not something I had thought about. The 320/MT/P-mags is very smooth.
6. For me, heavy is not an option because of my runway length. Recent light tailwinds have been quite character building!

Personally I can see no use for the power, but every lbs shaved off is a big help to why a -4 is such a delight to handle. (I feel really bad about the weight of the two TT servos in the AP!)

If its not fast enough I would suggest you build a Harmon Rocket. Thats a -4 designed with (I think) an O-540 in mind. Again, its a plane that is in 'balance'.

Just my thoughts, no intention to offend the 360 or 540 powered -4 drivers!

PS There is a -4 in the UK which has so many toys, paint and bondo, on board that its empty weight is close to my solo weight. The owner can never know what a joy to fly a -4 can be. The owner is quite large so for aeros to stay legal I think he has to leave the fuel out. But I bet it can exceed redline on the flat! Is that good?

Perhaps my engineering background gives me an over developed sense of 'balance'.

Click to expand...

I appreciate it! The question was not rhetorical, I want it light, but certain things I am going to cave on, like a CS prop. I sorta assumed it'd be the same prop for the 320/360. I didn't know they used different cowls and all the like, I literally thought it was like the same engine exterior dimensions between the two, and essentially the same price, so what I thought before was a no brainer is a little more complicated. I'm used to 160hp 172s, I'm sure a 160hp rocket with a CS prop is going to feel like an animal. Part of me even wants to keep it carbed, if carb proves to be a lot lighter I will do exactly that. I have to search the archives discussing FI Vs Carb in terms of weight. Nimble handling and short field performance/climb/aerobatics is more important to me than a few kts on top.

Tony, the cowl on the carb'd O-320 only just goes under the air box. The IO-320 injector, or an (I)O-360 requires a deeper cowl. Props need to be stronger to transmit more power.

My own view is a prepunched -4 would provide additional sales, but the firewall and u/c are the weakness in the design to my mind and would need a redesign....which probably makes it much more complicated.

What's weak about them?

The -4 seems to get a bad rap for a weak fire wall and or under carriage, this is in my view totally unfounded (Bogus) I have landed my -4 very poorly on occasion, I think you would need to about crash the airplane to bend the undercarriage or firewall or mount. As for fatigue cracking of the attach brackets, this has been adequately addressed.

FYI any RV with landing gear/engine mount

For our information, any RV with the landing gear part of the engine mount which is connected to the firewall (RV-3, -4, -6, -7) has this potential for damage. Whether it be from the landing gear itself shaking on take-off/landing (hence gear stiffeners to help) or rough landing fields that transmit harsher loads to the engine mount/firewall, the potential is there for cracking attach points/firewalls. As alluded to in previous post, the engine attachment points in the -4 have been beefed up to address this and mostly this problem is over. But it is something to keep watch for but not of major concern to a well kept RV-4 et al. My 1st -4 had the original mounts with the short gear and at over 1,000 hours, still not problems. A friends -4 at our local airport had to remove/replace his for the problem but spent most of its first years on a rough grass strip.

I wouldn't call it a 'weakness' anymore really. Just an item of interest to watch for during inspections.

Another Opinion For You

I have only flown the RV3, 4 and 6. I have flown several examples of each. The RV3 gets my vote hands down for flying quality. The RV4 is a close second when flown solo and the RV6 as an also ran. I have flown several hundred different types of aircraft in my career and currently fly a 1500 HP, turbine powered, 16,000 pound tail dragger that has a single seat. 200+ knots cruise, excellent in every way, but 1.2 million dollar price tag and 80 gallons per hour. We also fly a Beech Baron and a Cheyenne II is on the way. Your wallet gets alot thinner each time you walk away from the fuel pump.

I recently sold my Mooney and wouldn't you know it, we bought another business that is 70 nautical miles South of my house. It is a two hour drive by road and a 24 minute flight in a RV4. My search began and I looked at all the options and settled on an RV. Then I had to decide on which model. The RV3 is the most bang for the buck, but the fact that I have a 15 year old son eliminated the 3. The RV6 and 7 got passed over because I have other turbine powered options for transcontinental travel. The RV8 was what I really thought I wanted, but was two times the money. Having flown five different RV4s in the past and a little market research sealed the deal. An RV4 would be in my future.

My wish list included a well-built and safe airplane, (I did not want a show plane because I would be flying it daily and in the rain if necessary.) O-320, 160 HP with FP Sensenich prop. Tall gear (I thought I wanted.) Basic panel (I didn't want to pay for a 10 year old panel that was what someone else wanted and not what I wanted.)

I rejected the first four airplanes for condition and safety. I found N934RV in Texas and Jim flew it over to our shop for a pre-buy. The airplane passed with flying colors. I flew it three flights that day and one week later, it was paid for and in my hangar. I think that the RV4 is a tremendous buy in today's market. N934RV is a great airplane with 525 hours total time, 2 owners, no damage history or corrosion. It was built with a factory new engine and has about 60 hours on a new Sensinich metal prop. I did not get the tall gear and I am in the process of upgrading the panel to suit my needs. The airplane needs a little tweaking to fly perfectly straight and eliminate a slightly heavy right wing. After 15 hours of cross country and some loops, rolls and cuban eights, I couldn't be happier. It cruises at 195 mph at 23"MP and 2550 RPM and 185mph at 2450 RPM.

In my opinion, the RV4 flies the best when it is built and kept light and powered with the O-320 160 HP, Fixed Prop. I am delighted with the Sensenich FP. I climb at 150 mph indicated and get between 1300 and 1500 FPM. Take off in 350 feet and land in under 1000' ( two of our runways are under 1600' long and I am still getting used to not having reversing prop.)

I have flown RV4s with IO-360, CS prop, a truck load of instruments and other stuff that made them HEAVY!!! Everything is a trade-off. I am still thinking of an RV8, but I know that the extra fuel, extra room etc. will mean a heavier, less nimble aircraft that may do some things better than this RV4, but will also not do as well in other areas.

You can't go wrong with an RV, no matter which model you choose. Pick one, fly it often and be happy. Don't worry about what the other guy is flying. I can make my little 140 nautical mile round trip in 52 minutes or less and burn less than 9 gallons of fuel total. It takes me a little over 4 hours in my chevy tahoe and burn more fuel than in my RV4. If you buy it, find a light one and if you build it, keep it light. 10 pounds here and 10 pounds there can easily add up to 100 pounds. Adding 10% to the empty weight of any aircraft will always have consequences.

Jeff
N934RV

wickedsprint said:

What's weak about them?

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Well this has partly been answered since I wrote that.

Historically two related problems. They have suffered from the corner weldements fracturing resulting in a very difficult repair, and they have also suffered from the stainless steel of the firewall itself cracking at the right angle bends.

The problems are a result of the design in my view, although you can argue they are just a function of poor landings. What you cant deny is that the -4 has suffered far more of this sort of damage than the rest of the RV range.

The first of the problems was fixed by throwing more steel at the weldement in two or three iterations. The final version is the one in the pictures at the first link above. Is it a complete solution? Personally I doubt it. Stronger yes, and I am sure the newer -4 will suffer less of this problem, but when they have as many hours of the ones that have suffered my bet is some will show the same symptoms.

I am not aware that VANS has ever proposed a fix for the second problem, though in the plans somewhere, I did see mention of a heavier grade of stainless from the one they actually shipped to me. I presume their hope is that by fixing the weldements, the dimensional stability of the frame around the firewall will be increased, resulting in less stress being transmitted into it. I should perhaps add that I believe the engine frame has been beefed up also with gussetts at some of the corners. This must also help.

The problem with the firewall is the right angle bends around the part where the rudder pedals & your feet go. As momentary dimensional changes occur due to the shock of a heavy landing, instead of any transmitted load being absorbed by a large flat area it is concentrated at a point in the right angle, resulting in an eventual tear. The firewall should of course not be stressed in this way (poor design), but the tears are the proof it is. (The -6-7 and -9 dont have the step in the firewall, and have diagonals to handle the stress, so don't suffer from the tearing, to my knowledge. I know nothing of the -3 but it is of course a lighter aircraft.)

Clearly the less weight hanging on the engine mount the better since this is a source of a lot of the stress.

The ultimate cure is to make sure 100% of your landings are perfect, something I can only aspire to!

PS Despite that because of its flying qualities it is still the one for me!

I will have to respectfully disagree with Steve. This is the sort of bad rap I am talking about, my -4 has proven to be very durable over 26 years and 2150 hours of operation, the last 1100 or so hours with the 200hp IO-360, it lived on a grass field for about 1000 flight hours. I have personally landed the airplane like a C-150 during primary training and with the rap the -4 has I have looked for damage and on a couple of occasions I was surprised and pleased to find none.

I have repaired bent and broken motor mounts for pilots that said they never made a bad landing in there -4, I know there is a problem when they tell me that. Based on my experience with my old -4 I think much of the mounts I have repaired where basically crashed. Credit where credit is due, most of the pilots come right out and tell me there final landing was very bad and it was there fault.

I will admit it is probably not as durable as a C-150 but is plenty durable compared to it?s reputation, remember it?s the ones that broke for whatever reason we always hear about, seldom hearing about the ones that keep right on with no problems witch is the majority.

I have to agree with Russ. The early -4 had problems in the lower engine/gear mount area. It was addressed. I'd be willing to bet that problems after the fix are probably due to engine/prop combinations that are heavier than recommended.

If I'm reading the right sources, it seems the carbed 320 might be a lot less weight than the same in FI. It does seem that less props are available for the 320 than the 360, and the sensenich has a 2600rpm limitation, that is a dealbreaker. I like the idea of the WW151 since it is pretty light, but the stuff I have read scares me about them...but a metal hartzell 7663(for the 320) is something like 51;bs, and I don't know if that even includes the spinner. I was pretty sold on the Composite Hartzell for weight savings with the 360, but it doe snot appear that it will fit a 320.

Bingo...

...what Jeffs550 said! and one more thing. The Sensenich FP metal prop with the 160hp is THE combo for the -4 IMO. For all the the typical and known reasons plus this... It helps to keep CG in limits. I've flown three different pax who each weighed around 230lbs. No problem. Not every -4 out there could say that.

Sensenich 70CM series is good.

wickedsprint said:

and the sensenich has a 2600rpm limitation, that is a dealbreaker.

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Even though I prefer wood or composite props, the Sensenich metal is extremely efficient. I can't imagine why the 2600 rpm restriction would be a problem. When would you want to turn more than 2600 rpm? You certainly won't turn that kind of rpm on take-off, and for cruise, this kind of rpm would be quite noisy.

another opinion

My plane spends most of it's time between 2500 and 2700 rpm. Don't fly cross country, rarely fly straight and level, have 160 hp with a wood prop. The metal one just won't cut it for my flying style. ;-) (mostly solo, occasional kid in back) Ordering an MT and adding a landoll harmonic balancer to be installed before summer. MT for rain, Landoll for prop inertia and smoothness.
Can't say enough good things about the four. Flown probably 100s types of planes over the years but this one is near the top of the fun meter...

DM

Mel said:

Even though I prefer wood or composite props, the Sensenich metal is extremely efficient. I can't imagine why the 2600 rpm restriction would be a problem. When would you want to turn more than 2600 rpm? You certainly won't turn that kind of rpm on take-off, and for cruise, this kind of rpm would be quite noisy.

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ProCoach said:

...what Jeffs550 said! and one more thing. The Sensenich FP metal prop with the 160hp is THE combo for the -4 IMO. For all the the typical and known reasons plus this... It helps to keep CG in limits. I've flown three different pax who each weighed around 230lbs. No problem. Not every -4 out there could say that.

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A Hartzell CS is only 20lbs more, and a WW151 is probably 10lbs less. If the Sensenich did not have the rpm restriction I'd strongly consider it...but it has two strikes against it, one it weighs 40lbs(heavy side of available props, especially FP), and two being the restriction.

I think the notion that the -4 is some kind of icon that is somehow purified by doing so and so is completely false and serves no good. The -4 is designed as a tandem two-seater, +- 6g, 150 to 180++ HP, MTOW 1500++ lbs. It can be built light and simple and cheap (O-320 FP prop), it can be built like an aerobatic machine (simple with injected/Ellison 180++ HP and CS prop), it can be built like a cruiser (IFR, autopilot etc etc), it can take you round the world several times, it can be used as a bush plane, or it can do everything in between.

But, no matter how it is built, you will always end up with high performance aircraft that also has the distinct iconic looks of a high performance aircraft. No other RV has this. It is like a Porsche 911, there simply is nothing else like it.