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A Lighter RV-4

T

todehnal

Well Known Member
Okay, all of you RV-4 aficionados. First, I think that the RV-4 is the absolute best design ever, to make it?s way to the builders market: Bar none!! I have flown a 4, 6s, an 8 and a 9. For all around fun and efficiency, I?ll take a 4, any day.

As you all know, Van is working diligently on the RV-12 and my next building interest is leaning towards an aircraft that could comply with the Sport Pilot regs. Age is catching me and I must look at the fact that, down the road, passing a flight physical could start to become a stressful endeavor. I have not been real excited about the 12. Now I find out that Jay Kurtz, at the South Lakeland airport in Florida, is working to get a RV-9 to make the numbers. Wow!! That?s a heavy airplane to try to make that happen. But, what about a 4??

The 4 is only a little over 100 lbs. overweight, and that?s with 160 hp. Any thoughts about using an O235, an O200, or the new IO200. I would even consider the Jabiru 3300, with it?s 120hp. Any other thoughts about reducing the empty weight, while still maintaining complete airframe integrity?? Also, I think that the clean stall speed may need to be tweaked a bit. Anyone know what that number really is for the average RV-4, particularly at something closer to 1320 lbs?? Of course, the top end can be managed with prop.

I really want a 4 and am willing to take some risk with the project and even do a little re-engineering, with a little help. All comments greatly appreciated.. Keep them 4s coming!

Tom
 
todehnal said:
Also, I think that the clean stall speed may need to be tweaked a bit. Anyone know what that number really is for the average RV-4, particularly at something closer to 1320 lbs??
Click to expand...
The stall speed limit is 45 kt CAS, with the flaps up. I doubt any RV-4 flyers have a way to know how much airspeed error there is at the stall, so they can only give you IAS numbers.

Looking at the CAFE Foundation APR for the RV-8A - they found a stall speed of 52.4 kt CAS with the flaps up, at 1788 lb. They fitted a flight test airspeed boom, with pitot and static sources well ahead of the wing. This allowed them to find stall speeds in CAS.

The weight for a stall speed of 45 kt would be about 1318 lb. The RV-4 has the same span as the RV-8A, but a bit narrow fuselage. So, I would expect the RV-4 to have a CLmax at least as good as an RV-8A, so it should be valid to use the RV-8A data to show compliance to the LSA stall speed requirement. It is certainly a lot more valid than trying to use IAS to show compliance.

So, I think if you can get the max weight down to 1320, you should be OK on the stall speed.
 
Lightening options

Could we lose the elevator counterbalances whch would be a few pounds? We are expecting slower speeds anyway.
The -3s dont have them right? Neither do the Midget Mustangs.
Just a thought.
 
On the Lighter side...

Guys,
My friend Arvil has built 9 RV4's over the past 20 years for customers and is currently a Sport Pilot. He is seriously building a lightweight -4 as I type. His idea was to go with an 0-290G with no electrical system except a starter. He will have a ground power plug-in for starting. With only one seat, no interior, no fairings, wheelpants or radios and a wood prop with motorcycle gauges, he estimates 850 lbs empty. That leaves 500 lbs for fuel and 1 person to stay under 1350. Legal Sport Pilot cruise speeds should be no problem sans fairings and a climb prop.
I have flown an 0-290D powered RV4 that weighed 905 and flew great. If you went with an 0-235 L2C pumped up with the Cessna Sparrow Hawk conversion (125hp) it should work with a climb prop and very light construction. Low time 0-235's can be bought for under $10K.

Why not?

Rob Ray
 
If you could finish at 850lb then it could remain a two place, the trick would be keeping it in CG limits, perhaps move that light engine forward from its standard location. I happen to know who builds the engine mount for the -4 and knowing how the jig is built it would be no problem to stretch that mount buy 1? to maybe even 4? with out building a new jig. Let me know if you need some help with that.

Russ
 
More on an 825 lb RV-4

Thanks guys, for the great responses and ideas. I just may have to try this.

To answer a few commenters:
Kevin, I checked Vans specs on the wing areas of the 4 versus the 8. The 8 has121 sq.ft. and the RV4 only has 110. The stall speed still concerns me.

Pierre, Thanks, I called Jay this morning and talked with him. His empty weight is 903. Not bad for a 9.

Rob, I don?t think that an O290 is much lighter than an O320. I?m thinking more in the lines of an O235, or possibly a 120hp Jabiru 3300.

Russ, if I decide to stick with an O235, I?ll get back with you for some engine mount help.

Thanks to everyone who has responded and I am still looking for any additional thoughts that anyone else may have to offer. By the way, one other thing that Jay offered was that he might consider titanium gear legs and lighter wheels. Think about his accomplishments so far. He built an RV-9 with a slider and an O235-C, has paint and interior, and he was still able to take 140lbs. off of Vans empty weight numbers. Van lists the RV-4 as 905 and that is with an O320. It shouldn?t be too hard to get that down to something closer to 800 lbs, considering that I should be able to drop 50 lbs from the engine compartment!! Now lets see?. Titanium gear legs, sparse panel, cloth cushions for interior, and, how about getting rid of those heavy fiberglass wingtips. It sounds like about 825 lbs. to me. Food for thought!
 
todehnal said:
To answer a few commenters:
Kevin, I checked Vans specs on the wing areas of the 4 versus the 8. The 8 has121 sq.ft. and the RV4 only has 110. The stall speed still concerns me.
Click to expand...
Originally the RV-8 was sold with the same wing tips as the RV-4, and both models had 23 ft wing span and 110 sq ft wing area. Now Van sells wider span tips that give the RV-8 24 ft span and 116 sq ft wing area. The 121 sq. ft number is for the RV-7, which has RV-8 wing panels + the new tips on a wider fuselage, so it has a longer span and more wing area (strangely enough, the conventional definition of wing area includes the area of the centre section that is in the fuselage).

The stall speed at 1320 lb should be very close to 45 kt. You could always add VGs to lower it a knot or two. The drag penalty from VGs isn't an issue, given the max cruise speed requirement.
 
Plan on being healthy

Get a RV-4 with a 320 Lyc and stay healthy. There is a guy who is 85 and still flying his RV-4. He even raced it in the last 5 years. When and if you lose your medical you can't fly a LSA either; here is the catch, if you lose your medical (the examiner denies you, documented) you can't fly a LSA either. You are also automatically grounded, if you KNOW of a reason you can't fly, doctor or not. LSA is not a free pass with no medical implications. GET A RV-4 AND HAVE FUN AS LONG AS YOU CAN.

If you do decide to transition to a LSA, sell the RV-4 and get a LSA or like a J-3 Piper Cub.

You might be able to get a RV-4 under LSA specs, but really I would not do it. It may take so long you might be too old to fly it by the time you finish it. Also you may have problems getting the FED's to believe its a LSA. They could make you prove it, which is more time, effort and money. Second it probably will be too fast to qualify for a LSA even with a O235. I think you would need no gear/wheel fairings and about 80-90 HP.
 
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What if...

I think a lighter LSA RV4 is a great idea. Who cares about whether you've lost a medical or not. What about the guys who just want a sport pilot certificate and like the RV4?
I think the RV4 could be built to fill the requirements. My RV4 builder guru friend Arvil believes the same. Having flown my RV4 above 20,000 feet and made several takeoffs from Leadville (10,469) in the summer with 150hp and a wood prop, the design is capable of amazing feats on low HP. Bob Olds and I operated our RV4's from similar 900' runways for years with no modifications. He has since installed VG's and can fly final at 50 knots and claims the stall break is non-existent. I fly final in The Bandit at 58 knots with a stock wing.
A VG equipped, very light RV4 should have no problem with the LSA stall speed requirements. As far as CG goes, restrict your back seat to kids and cute girls under 115 lbs and you'll be happy. :)

Rob Ray
1500 Hours RV4
few more in the HR2
F16 on weekends..
 
Not that light...

Van lists the RV-4 as 905 and that is with an O320. It shouldn?t be too hard to get that down to something closer to 800 lbs


There are few if any RV4s at 905. Most are 950+. My wood prop/320 is 964.
I'm leaning toward George's suggestion. Do what you have to to stay healthy. There are other benefits to that approach also.

Good luck whatever you decide.

John
 
Jabiru

With a Jabiru 3300 you will get MIN 100 lbs off, probably more in the range of 120-140 lbs because the Jabiru is 178 lbs with everything included (exhaust, carb, starter etc).
 
If you are going to shed weight off your RV-4, remember to do it from the back, not the front. Or else stretch your engine mount as was already suggested. The -4 is nice but it is tail heavy.
 
I LIKE it....!

I think a streched motor mount, Jab. 3300 powered, LSA(COMPLIANT...keep it "Amatuer built") RV-4 would be a GREAT idea! :D

Seems to be no reason it could not be done at a empty weight of 800lbs, maybe a bit less.

The Arion Lightning(Glass aircraft,3300 powered)is about 800lbs empty, and the LSA version climbs like a rocket, and performs very well.

The RV-4 should also climb very well, and cruise could be prop limited to the 138mph at VA.

C'mon guys, it REALLY is a good idea!

Pud
 
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Nah, then you would be going right back to the side by side, bubble top standard LSA look. I'd stick with the -4's sleek, tandem lines.
 
Let's be honest.....

Guys,
I've been reading all these threads about making 9's and now the -4's into LSA airplanes. Yes, it can and has been done and will probably be done to a -4 (and a -3). You guys talk about achieving the required stall speeds and that can and has been done.

Let's get to the nitty gritty. All this talk about no fairings and a flat prop to keep it under 120 knots is, in my opinion, a smoke screen, and it ain't too dark. Are you REALLY gonna keep the fairings and wheelpants off forever? Are you also gonna always keep the flat pitched prop on it too? Somehow I smell fish. As far as I'm concerned, we're heading down a slippery slope here, just like the "heavy" ultralights did.

As soon as the Feds start seeing 160 MPH (or faster) -4's as LSA's on their radar, (many have your groundspeed readouts, if not all) and other LSA's doing the same thing......putting the back seat back in, filling the tanks to max capacity.....all this to skirt the regs....new regs will come for sure.

For the older guys who mean what they say, because age and the inability to always pass a physical becomes questionable, the LSA is not an automatic answer. If you can't pass an FAA physical but you do have a driver's license, does that now make it ok to fly anyway? I know for a fact that this has been done by taking a pre-exam through your everyday Doc and when he says, "I don't think you're gonna pass this time", then you sell your airplane and go LSA because you have a driver's license and you can do so.

Let's think about this hard and do what's right so the Feds don't go on the warpath again! Flame away....... :eek:
 
No flames here

Pierre,

I agree with your view completely and share your fears. I can see the temptation of "if i just change the prop I can gain X speed" causing some real headaches. In another thread there was a discussion of FAA ramp checks. I have a vision of the fed ramping one of these "fast" LSAs and inviting the owner to have it weighed. Not going to make any of us look good.

John Clark
RV8 N18U "Sunshine"
KSBA
 
Defeatists..

John/Pierre,
I respecfully disagree. In 1500 hours of RV4 flying I have never been ramp checked, not once. In fact, in 11,000 flying hours I have never been ramp checked, ever. I don't fly around in fear of one and I defy any FAA guy (or anybody else for that matter) to determine by looking, how fast my airplane goes at a glance. I don't know of any of them who carry scales around and most of them have encouraged me more than discouraged me when we talked. ATC is too busy to try and match your N# to a type anyway. Experimental is experimental. As far as putting fairings back on and adding gas and speed, you can do that now! My RV4 is specified to a certain gross weight, powerplant and CG. Changing it by the reg, nullifies my Experimental Airworthiness. However comma, how many guys bolt a 180 C/S on RV4's now after having a 150 and send in paperwork to the FSDO? Having looked at alot of RV4's for customers, I can tell you, maybe 1%.
The experimental category by definition means "not certfied standards" and subject to an indefinite test period. How many of the "certified" LSA airplanes out there adhere to the speed limit, exactly? How do they enforce it, with a one time certification? What if the owner repitches the prop?(which is allowed) Where are the airplane speed guns posted? If the Wright Brothers had listened to naysayers 100 years back,we wouldn't be having this discussion!
I for one believe LSA is the biggest shot in the arm to GA in a long time. The more experimentals which go into the category and the more people flying them only makes it more palatable to the public and the FAA.
If someone wants to make an RV4 lighter, simpler, a bit slower and call it something else (RR-1, FU-2 etc...) SH! (that's fighter pilot for "cool") More power to them! Why discourage anyone from trying anything "outside the box"? I take "no" as a challenge anyway...
Hmmm, I have an old RV4 kit hanging around,I may do it, just because!

Rob Ray
1500 hours RV4
A few more in quite a few others
F16 on weekends...
 
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Scales

Bob,
I didn't mean to imply that the feds were going to be haunting every ramp. In my 40+ years of aviating I have been ramped many times. Mostly while flying airliners but a few in the GA world. No problems, no attitude from the friendly inspectors. I have, however, witnessed a fellow with an overloaded 182 being "requested" to bring the aircraft to an A&P for weighing with the FAA present. He made the classic error, lied on the paperwork. It just takes one interested inspector or a minor incident to bring a little "stretch" of the regs to the surface.

John Clark ATP CFI
RV8 N18U "Sunshine"
KSBA
 
Apples and...

No worries John, However your overloaded 182 incident and building a light RV4 are unrelated events. Once an experimental is weighed for inspection, it's weight watching days are effectively over. To quote my FSDO neighbor (former chief) "Experimentals don't exist as far as the FAA hierarchy is concerned, like military aircraft they aren't TSO'd, therefore can't be totally regulated." As far as building a light RV4, the data plate on mine says Rob Ray RV4. If it were an LSA it would say Rob Ray One. (of one)

Experimental brother, that is why we do it!

Rob Ray
 
LSA -4

Hi guys,

It could be done, and not too hard either. My -4 with 180 and FP wood prop stalls 43-45kts CAS at idle (some residual thrust). This is solo with full fuel, ~1340lbs (610kg). Build it to plans, but lighter, and you have LSA with partial fuel and a light pax.

In Australia, the LSA rules don't specify the 120kt speed limit, and the ASTM design standard is just one to choose from. Maybe, just this once, our Regulator was a little more enlightened than those in the US!

The problem with all this, is insurance. Yes, you will be able to get it, but if something happens will they pay out? A -4 crashed here recently with two fatalities, and I know the insurer was analysing the circumstances with a view to not paying if the aircraft was being operated illegally.

In the end, you must do your own risk analysis, and then manage the risk.

Grant Piper
VH-PIO
 
0-235 RV-4

I was reading this thread from over a year ago and was wondering if anyone has actually tried a 0-235 in a RV-4? Russ if you are still out there,I would really appreciate more info on the engine mount.
 
I?m still out hear, what did you want to know about the mount? At this point no one has contacted me to modify one so, at this point we have only ever built stock mounts for Van?s, they are Conical and Dynafocal type 1 & 2 for Lycoming engines.

Russ
 
0-235

"Russ"
would I be able to buy a modified mount directly from you and would it come with the gear legs drilled for alinement?
 
Don't forget that the new Lycoming 233/Continental O-200 have recently been lightened up for LSA use. But... neither would be as drastic of a weight/W&B difference as changing to a Jab.

I am still planning on building a 12... not because I need an LSA... but simplicity in build/pulled rivets, etc. But I must admit that NONE of the LSA's stir my loins (can we say that?) like a 4 or 8.

What I'd LOVE to see is Van's take the RV-4 and re-engineer it as a pre-punched, pulled-rivet, open cockpit LSA version of the PT-19! I think that'd be COOL. :D

DJ
 
I don?t do the legs, so no, the best plan would be to buy one from Vans ready to go and have me make the alterations on your mount. For an LSA you might try to get an old mount or the old gear legs and have me build you an old mount, the smaller old gear legs are probably lighter.

Russ
 
Restart an old thread with a new spin on it...

I am interested in a custom built experimental category, amateur-built RV-4 that meets the definition of a light sport aircraft.

I know this has been discussed quite a lot in years past, but as far as I can tell, there aren?t any RV-4s (or RV-3s either) out there that have been built to meet the definition of an LSA. Or at least none that have publicly declared so.

In the early days, there were few people that understood the different aspects of the LSA rules (myself included) and as a consequence, there was a lot of misinformation out there (although I suspect, not intentional). Most misinformation has centered on meeting consensus standards which isn?t required for an experimental category, amateur-built aircraft. Even today, most people are unaware of the possibility of building many of the existing kit aircraft in a manner to meet the definition of a light sport aircraft. I feel this has intimidated some that were initially interested in the RV-4 or RV-3 as an LSA compliant aircraft.

The reason for this post is to open the discussion again. What makes it different this time is that I would like to discuss doing this as an experimental category, amateur-built aircraft, not an ELSA. I suspect Van will never turn the RV-4 into an LSA and frankly, I understand why he wouldn't. What I a referring to is one that is custom built for me, by me. I believe it can be done, safely and legally.

I have chosen this old thread because some good points have already been made. I would like to expand on those instead of re-inventing the wheel.

I realize that many people will be skeptical, and some will never believe it?s possible or legal. I welcome discussion from any and all that?s interested in the subject.

My question(s) at this point are:

1) Are there others that have done it? Has to be?
a. If so, how did you go about it?

2) Are there others that are in the process of doing it? Has to be?
a. How do you plan to accomplish it?

3) Are there others still interested in this subject? Has to be?

Luke,
 
seriously building a lightweight -4

smokyray said:
Guys,
My friend Arvil has built 9 RV4's over the past 20 years for customers and is currently a Sport Pilot. He is seriously building a lightweight -4 as I type. His idea was to go with an 0-290G with no electrical system except a starter. He will have a ground power plug-in for starting. With only one seat, no interior, no fairings, wheelpants or radios and a wood prop with motorcycle gauges, he estimates 850 lbs empty. That leaves 500 lbs for fuel and 1 person to stay under 1350. Legal Sport Pilot cruise speeds should be no problem sans fairings and a climb prop.
I have flown an 0-290D powered RV4 that weighed 905 and flew great. If you went with an 0-235 L2C pumped up with the Cessna Sparrow Hawk conversion (125hp) it should work with a climb prop and very light construction. Low time 0-235's can be bought for under $10K.

Why not?

Rob Ray
Click to expand...

Smoky,

I was sad to hear about your friend Arvil. I know it was some time ago, but you have my condolences.

I was wondering , is anyone finishing his project? Do they intend to finish it in the same manner?

I think you are right on the money as far as the 850 lbs. The 0235 also seems a good choice.

Oh yea, your RV6X is very cool!

Regards,
 
LSA 3

I am building an LSA RV-3 with a six-cylinder Jabiru. I already have the engine. A friend and I have completed the construction of wingtips that are patterned after Steve Wittman's Tailwind. If I would get on the ball and figure out how to post pictures, I could further enlighten you.
I had Van's send me a conical engine mount, figuring that it could be lengthened. I never thought of asking Russ to do this because I didn't know who Russ was. Now I know.

Bill NEWKIRK
Prather, CA
 
I'll give you one more engine to think about...TCM IO240. 125 horse and fuel injected. I have one on my Rans S-16. Pretty simple installation.
 
LSA RV-3

Bill,

Good to hear from you and thanks for the response. Would you be willing to share details about your project?

As I mentioned, I am interested in the 4 which requires careful attention to weight in order to retain the ability to carry a passenger. Smoky said it best; "limit the rear seat to pretty girls". I weigh 188lbs fully clothed and my wife weighs 114 lbs. I believe the weight can be managed, at least for me. It will be a tradeoff but worth the handling qualities that the RV-4 has. I am convinced I can build an RV-4 that weighs 850 -875 lbs depending upon engine choice.I am curious about your plans for the other two design obstacles we must each manage:

Stall speed - I am unfamiliar with the RV-3 but I understand the NACA 230XX series airfoil respond particular well to the use of vortex generators. With the 4, simply limiting the gross weight to 1320 gets me close. I have used vortex generators previously with great success and am convinced they will reduce the stall speed to 45 knots clean. My experience with them is that the performance results are highly variable based upon size, height, spacing, angle, and location in relation to wing chord.

Max speed with max continuous power - For me, I have decided that an underpowered aircraft will not meet my requirements. With that said, my plans are to build a custom engine from a proven design such as Lycoming. What do I mean by custom? Flow porting, moderately high compression pistons and maybe even cold air induction with light weight components and such. I also plan to burn a mixture of 100 LL and 93 octane Mogas in order to provide maximum service life for this engine. This will require careful attention to operating limitations to avoid detonation and valve seat recession. The point is, it will truly be experimental, and as such, I will determine the maximum continuous power rating. I imagine it will be time and condition based, such as max cylinder head temp restrictions to prevent detonation.

It has been done by a few already. I realize the burden of proof will be mine. Built as described, I feel it is not only provable, but also justifiable. We all know a couple of well know aircraft companies doing this very thing.

If memory serves, an experimental category, amateur-built aircraft is for the purpose of research and education.

I have no illusions; it will be a lot of work but well worth it to me in the end.

Regards,
 
TCM IO240

SpyderMike said:
I'll give you one more engine to think about...TCM IO240. 125 horse and fuel injected. I have one on my Rans S-16. Pretty simple installation.
Click to expand...

Thanks for joining the thread?

I have read about this engine but haven?t flown behind one yet. From what I read, it?s a really nice package.

I mentioned a Lycoming for my plans simply as a matter of practicality such as engine mount, cowl, exhaust and such. All readily available for the RV-4. I am not getting any younger and need to simplify the build as much as possible. I already have the components mentioned so it?s also about $$ for me.

Regards,
 
Happy to share

Sorry to take so long to reply, but there are some places where wireless or cell service is not available. Go figure.
Yes I would be happy to share any info.

Bill Newkirk
[email protected]
1-559-430-7220
 
Vortex Generators

Luke;
Could you contact me again. I'm interested in your experience with vortex generators.

Bill Newkirk
559-430-7220
 
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