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Twin engine RV-6A...or not

jimdc8

Active Member
[Link here removed by the owner of the forums <directly competes with my own RV White Pages>. Picture posted of plane below and specs...and it's a doozey. I would be interested in reading about the engineering changes that were made on the wings and wing attach points (and landing gear) to support the extra weight of two engines! Experimental aviation!
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Ok, you've got my attention. Some questions:
  1. What engines?
  2. What is the projected performance and specs?
  3. What changes have been required to the fuselage, wings, undercarriage, etc?
  4. Who is engineering the changes and what is their educational / experience qualifications?
  5. How long has the project been underway and when is it expected to be completed?
  6. Fixed or retractable?

Cool project! Can't wait to see/hear more.
 
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Twin (was an RV-6A)

Interesting project. Looks like he's doing a good job on it. Twin corvairs for power.
Was an RV-6A that was flown for 250 hours before being used as the basis for a fixed gear light twin. I reserve judgement on how I think it will be as a twin, but 'A' for effort.

Link which I view as competing with my RV White Pages removed. Thanks, dr

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before removed the link said 110hp corvair engines.

Boy, that seems like a solid non-starter. Given the extra weight and drag of the twin engine configuration, 220 hp will make for relatively mediocre performance. And when one engine quits, all the other one can do is stretch the glide and maybe increase the number of landing options.

With a pair of 150 or 160 hp engines, it would be better, but still a not very usable airplane. It probably wouldn't be any faster than an RV-6, at least not in terms of Vne.
 
Engine redundancy

Boy, that seems like a solid non-starter. Given the extra weight and drag of the twin engine configuration, 220 hp will make for relatively mediocre performance. And when one engine quits, all the other one can do is stretch the glide and maybe increase the number of landing options.

With a pair of 150 or 160 hp engines, it would be better, but still a not very usable airplane. It probably wouldn't be any faster than an RV-6, at least not in terms of Vne.

I think it would be more for crossing ocean legs but I would have done this with a -9. Get her up a bit higher.

All sorts of concerns with this.

- Reduced wing area,
- CoG changes, that nose looks like a storage location,
- Fuel location
- Landing gear
- you would want counter spinning props of course
- How are they hung off of the spar etc

You would want a complete aerodynamic engineering assessment done by a professional consultant.

However, you have to say, who isn't impressed by the ambition and enginuity of the whole thing.

I was wondering why there aren't any exp twins out there, well none that I know of.

If the owner of this aircraft would like a moment in the spot light on this forum I think we would all give them a special thread all of his own.

What do you say Doug?
 
I think they should call Van's and see what he thinks. Perhaps ask either Ken if they have any advice they'd like to share.

A copy of the transcript posted here for all to enjoy would be appreciated :D
 
Maybe

It MIGHT get off the ground, considering all the lift that's lost because of the fairings behind the engines.

Good luck!
 
... specs on it.:)

Marshall Alexander


copied/pasted here by dr said:
This is my JAG-2 project. It started life as a completed RV-6A, which I originally built and flew for 250 hours. Out of respect for Van's Aircraft, this aircraft is NO LONGER referred to as an RV-6A. The JAG-2 is a side-by-side 2 seat twin-engine cross country aircraft. It will be IFR capable with dual Dynon Skyview EFIS. Some modifications include, but not limited to:
1. Installing 2 Corvair 2850cc 110hp direct drive with 5th bearings.
2. Custom made counter-rotating carbon fiber props.
3. Unique prop brake system in lieu of constant speed feathering props.
4. Increased wingspan by 40".
5. Installed RV-9 tail.
6. Re-designing nose gear with 4130 tubular gear & urethane dampening (similar to RV-10).
 
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It MIGHT get off the ground, considering all the lift that's lost because of the fairings behind the engines.

Good luck!

I would think the accelerated Slipstream would help with that. Anyone ever compare a Seminole wing to an arrow? I don't know if they're bigger or not.
Hope he has fun and gets what he expects out of it either way.
 
Twin Comanche wing project??

Somewhere there was a post a while back about someone trying to mate an RV? with a Twin Comanche wing. Anyone have that story?
 
I like it. No this might not be better but maybe the next step will. Vans didn't create the perfect plane at first they evolved! This is what amateur built/experimental planes is all about. I think the RV-10 would have been a better choice.
 
counter rotating props

Maybe y'all can enlighten me, why counter rotating props? There is this old wives tale about p-factor causing yaw, but this is just a myth. Any one?
 
Maybe y'all can enlighten me, why counter rotating props? There is this old wives tale about p-factor causing yaw, but this is just a myth. Any one?

Counter rotating props removes a single engine from being the critical engine and makes them equally critical. If the P-factor is on the segment of the propeller rotation outboard of the engine, you'll need a larger rudder to counter the yaw than if the P-factor is inboard of the engine. Simple force x arm equation.

So put a clockwise rotating engine on the left side and a counter-clockwise rotating engine on the right side, both P-factors will be on the inboard side thus a smaller (RV-9 type) rudder required to counter less yaw.

Hope that helps.

-Jim

P.S. Curious why do you think P-factor is an OWT?
 
Somewhere there was a post a while back about someone trying to mate an RV? with a Twin Comanche wing. Anyone have that story?

That was me. His name is Mike Cavanagh. He now lives in Texas (of course). He started with Twin commie wings and was going to mate them on an RV4 fuselage. The drawings were good looking and he was working through some solutions regarding wing loading when he succumbed to airline captain's syndrome (divorce).
 
I all about pushing the limits of innovation to celebrate our category but I'm not even sure how to respond here. Is this actually real?
 
RV Twins

That was me. His name is Mike Cavanagh. He now lives in Texas (of course). He started with Twin commie wings and was going to mate them on an RV4 fuselage. The drawings were good looking and he was working through some solutions regarding wing loading when he succumbed to airline captain's syndrome (divorce).

Sounds like these guys need to compare notes and figure out the path forward. I also hope the negativity does not discourage the builder and providing updates. There's a heck of a lot of creative people on here who can be a great deal of help. I understand concern for safety, but a lack of free thinking is no good to the advancement of sport aviation.
 
I want to see somebody build a twin fuse RV-3,4 or 8 like a P-82...

(or Rocket ;-) )

Tailwinds,
Doug Rozendaal
F-1 EVO Rocket
 
P factor

Jim,
I do not want to hijack thisd thread, but p-factor says the downward blade has more pitch therefore it produces more thrust on the one side, The OWT forgets this is a spinning propeller so it acts in pitch, not yaw. Helicopters and propellers share the same physics.
 
This looks like a great project. This is what experimental aviation is all about. I wish the builder the best of luck!
 
Jim,
I do not want to hijack thisd thread, but p-factor says the downward blade has more pitch therefore it produces more thrust on the one side, The OWT forgets this is a spinning propeller so it acts in pitch, not yaw. Helicopters and propellers share the same physics.

I understand what you're talking about...that is when one applies a force to a spinning object, the resultant movement is 90 degree later in rotation (spinning bicycle tire proves this well)...as does rapidly raising the tail in a conventional aircraft. However, helicopters rolling left because of retreating blade stall like descending propeller blades with more angle of attack (assuming positive aircraft pitch) providing more thrust than the rising propeller, does not follow that behavior. Still not convinced P-factor is an OWT.

And to keep it RV-6A reborn as a JAG-2 related...I sure hope all these aerodynamic forces stay in harmony for this project.

-Jim
 
I'm with Peter....this just makes me go "hmmm"...I have sorta the same reaction to the Tripacer I saw with a T-Craft wing scabbed on the bottom of it a couple years ago - and yes, it still had it's top wing!

I guess I can't say too much without being sort of a hypocrite since I'm building something about the size of an RV with 500hp engine (that also hasn't been built for 50+ years) on the front!

Cheers,
Stein
 
I've never heard my dad say ANYTHING good about his Corvair. Never heard anyone say anything good about a Corvair motor. Who would want to fly behind one? Let alone between TWO?!?
 
I'm with Peter....this just makes me go "hmmm"...I have sorta the same reaction to the Tripacer I saw with a T-Craft wing scabbed on the bottom of it a couple years ago - and yes, it still had it's top wing!

I guess I can't say too much without being sort of a hypocrite since I'm building something about the size of an RV with 500hp engine (that also hasn't been built for 50+ years) on the front!

Cheers,
Stein

Stein Please elaborate! 500HP and the size of an RV?

-david
 
p-factor last words I'll say

retreating blade stall causing a roll is also a OWT IMHO. I believe both these things are mis understood. There are other things that cause the right foot on climb out, the yaw when the tail is lifted, the reported roll with retreating blade stall (never experienced this in a heli either until I hit control limits), etc Everyone has their own ideas, I don't think I will change peoples minds, lets just leave it at that. By the way, it is only 90 degrees for helis. For a rigid attachment aka propellers, the precession force is more like 70 degrees, so there is some yaw, but a whole lot of pitch. The math is published in a book written by an old time Lockheed (Burbank) engineer.

Sorry to hijack this thread. Please start a new thread or PM me if anyone wants to discuss further.

Nice twin, I give him kudos for trying to do something different. I think we will all benefit from his experience and experimentation.
 
I've never heard my dad say ANYTHING good about his Corvair. Never heard anyone say anything good about a Corvair motor. Who would want to fly behind one? Let alone between TWO?!?

I built many of these years ago for street and track. Actually a pretty robust design if you pay attention to detail and use a few modern parts. There are many flying now and with the 5th bearing installed to take the prop bending loads properly, they have been quite reliable.
 
Good Panel guy

I'm with Peter....this just makes me go "hmmm"...I have sorta the same reaction to the Tripacer I saw with a T-Craft wing scabbed on the bottom of it a couple years ago - and yes, it still had it's top wing!

I guess I can't say too much without being sort of a hypocrite since I'm building something about the size of an RV with 500hp engine (that also hasn't been built for 50+ years) on the front!

Cheers,
Stein

Hey Stein,

Cool aircraft... if you have trouble with the Panel I know this really good panel guy you go to ;-)
 
However comma...

Man, you have to admire their ingenuity, resourcefulness and tenacity. However comma, for practicality sakes (Good Lord forbid) some very successful light twins are already out there in large quantities. They have produced some impressive numbers of their own including Max Conrad circling the globe several times in twin Comanches and Aztecs. My Dad flew F-82's and said a stock single engine P-51 could keep right up with it. I think that would apply to this aircraft as well. So, the mission of a light twin RV is, improved reliability? Redundancy? Load? Range? Prove a point? All the above? Oh well, what can I say about one-off's, I bolted a set of RV4 wings on a Six fuselage and built a Rocket :)

Having quite a few hours in a single engine engine Jet and seen twin engine counterparts alongside I noticed: We burned less gas when gas was in critical supply, more bang for the taxpayer buck, greater overall efficiency. This was Lindberg's thinking when he designed the Spirit. There are great arguments for and against but Van himself designed the RV's to provide the greatest efficiency for the least dollar. So, Why re-invent the wheel?
It is intuitively obvious that some really smart guys with slide rules have been there, done that. They even sent men to the moon without calculators or cell phones.

All that said, I still applaud their efforts.

Smokey
http://www.aviastar.org/air/usa/piper_pa-30.php


Wing Derringer designed by John Thorp
 
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Neither for or against the project but in response to the previous post: what if Van had taken that mindset. Lots of successful low-wing singles out there; why reinvent the wheel? I'm not saying this twin will be a refinement like Van's RV series has been, but just because something has been done before does not render a new take valueless.
 
Twin RV ?? Yes it's true. Pictures.

My friend told me he saw it with his own two eyes and I didn't believe him. So we flew into Mattituck and I saw it for myself. I'm sorry I forgot the builders name, I'm sure he'll chime in here, but I figured I'd post a couple of pictures. It was a flying 6A that is being modified. It is not flying, yet but the work is progressing.

This not my RV, I have no idea about the engineering of this thing, I just took a couple of photos. Interesting for sure. I don't know that it's something I would want to build, but then again to each his own.

twinrv2.jpg


twinrv3.jpg
 
...what if Van had taken that mindset. Lots of successful low-wing singles out there; why reinvent the wheel?...

Here's one thing to consider regarding that line of thinking: Van has always taken a very measured approach to sizing and configuring his airplanes.

Where we see this most directly is in the way they are designed for decently sized engines. All of the RVs are designed from the get-go to accommodate somewhere between a reasonable amount of power and lots of power, and still balance reasonably well. They may not accommodate the great gobs of raw brawn that the Rocket crowd demands, and they may not balance as well as someone with an RV7 and light prop would like, but they've all been in the ballpark.

What we haven't seen is a new RV design that comes out with a small engine, and then goes back to the drawing board for a power upgrade just to give it decent performance. Many airplane projects, the Wing Derringer included, have been there and done that.

I think that if Van were to dabble in a twin engine airplane, it would have a lot more horsepower on a side than the airplane we're talking about here. What I'd sort of guess at is that he'd start with the RV10 airframe, and mount 200 hp IO360s on a side. But that is a speculation for a different thread, and maybe a different forum.

For the twin we're talking about here, I think we will see that 2x110hp won't really be enough. According to www.flycorvair.com, the installed weight for a single 110 hp corvair motor ready to fly is 215 lbs or so. So for 220 horsepower worth of them, it is 430 lbs of weight, versus the single IO360s 300 lbs or so for 200 hp. And let's not forget that it has two engine mounts, two sets of fuel plumbing, two cowlings, two propellers, two sets of engine controls (cables, wires, etc). It also has about half again as much frontal area as an RV6. What it adds up to is an airplane with a bit more power than an IO360-powered RV6, but a lot more empty weight and a handful more drag. It will require greater workload to fly, but won't reward that workload with better performance or better handling.

And let's not forget that the usual selling point of the light twin is the improved safety of having an extra engine. At least that's what the brochures say, it too often does not work out that way. But anyhow, I don't see this airplane holding altitude very far above sea level on one 110 hp engine. I guess you can say that the extra engine gives you a lot more landing options, but I don't think that is worth the trouble.

Thanks, Bob K.
 
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My friend told me he saw it with his own two eyes and I didn't believe him. So we flew into Mattituck and I saw it for myself...

I have to say, from what the pictures show it looks pretty impressive. It looks like a lot of thought and work has gone into it.
 
I think many people here are simply missing the point of this project and perhaps the essence of true experimental aviation. For many, they simply want to do something different or they have a dream. Projects don't need to be especially practical or efficient, just fun and educational.

Really, building a hole matched RV with a Lycoming up front, while still being a truck load of work and hours, isn't very "experimental" other than by category.

While many might question the practicality to add retractable gear, floats or another engine to RVs, I personally think these are all pretty cool mods because they are so different and involve a lot of independent thought and design/ fab work.

Dare I say, too many here have almost taken on a "sheeple" attitude, criticizing projects that stray very far from the flock. I say let's let the dreamers dream and build something unique that satisfies their desire for something different.:)

I seriously looked at doing almost the same thing before buying my RV10 kit. I was planning twin 130hp Suzuki 1.3 turbos with gearboxes on a modified RV7 airframe. I ran into design issues mounting the nacelles over the fuel tanks and couldn't get past not being able to source suitable full feathering props so I called it quits there.

I briefly considered a push/pull design like the Do 335 WW 2 fighter using RV7 wings and tail feathers and the same Suzuki engines until the design realities with the rear engine driveshaft system and a complete custom fuselage brought me to my senses!
 
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