What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Twin engine RV-6A...or not

One of a kind

Some of us will go to the extremes to have a one of a kind but this is an accident waiting to happen.
An amazing effort but don't you think Van considered building kit twins and thought better of it... I hope it ends up a static display before it becomes a deathtrap.
 
...Projects don't need to be especially practical or efficient, just fun and educational...

Ross, that is an excellent point, and there are many other gems of wisdom in your post.

However, in my thirty or so years dabbling in experimental airplanes, the cases where a builder really is experimenting, and is not interested in practicality or effectiveness are a pretty tiny minority. If this is indeed one of those cases, then it's all good. I admit to my preconceived notions about how it will turn out, but I will be as interested as anybody in the results.

I have seen too many homebuilt airplanes result in a lot of heartache in the very real sense of the word. I have seen people put a lot of work and time and money into machines that, while fascinating in and of themselves, did not nearly achieve the return on investment intended.

In the majority of the cases where I have seen unusual innovations, it is people thinking that they know of a shortcut between where they are and where they want to be, which is zooming around and boring holes in the sky. And too often those shortcuts turn out to actually be the long way around. And just as often, some critical thinking and a few flips of a slide rule would be all that is required to reveal the potential pitfalls ahead.
 
Hopefully the builder has the technical savvy or resources to ensure that it is done properly. I seem to recall a lot of adulation for an RV on floats. Surely if that was a "whatever floats your boat" effort, so can the twin.
 
This has to be one of the coolest projects yet and I don?t understand why this community is not more supportive.

Had this forum been around when John Harmon first started talking about putting an IO-540 on an RV-4, I wonder what the response would have been?

This is not an RV by any stretch of the imagination. As for the person who wondered what Van would think, if asked; Van probably would simply say it is not an RV, same as a Rocket is not an RV.

My thoughts on Twins or the multiple alternators, batteries, etc. builders put in their RV's is the same; you have twice the risk of a failure.
 
Ross, that is an excellent point, and there are many other gems of wisdom in your post.

However, in my thirty or so years dabbling in experimental airplanes, the cases where a builder really is experimenting, and is not interested in practicality or effectiveness are a pretty tiny minority. If this is indeed one of those cases, then it's all good. I admit to my preconceived notions about how it will turn out, but I will be as interested as anybody in the results.

I have seen too many homebuilt airplanes result in a lot of heartache in the very real sense of the word. I have seen people put a lot of work and time and money into machines that, while fascinating in and of themselves, did not nearly achieve the return on investment intended.

In the majority of the cases where I have seen unusual innovations, it is people thinking that they know of a shortcut between where they are and where they want to be, which is zooming around and boring holes in the sky. And too often those shortcuts turn out to actually be the long way around. And just as often, some critical thinking and a few flips of a slide rule would be all that is required to reveal the potential pitfalls ahead.

I'd say dreamers are not confined by notions like "return on investment" to any great degree and that is a big thing that separates them from the rest. Most projects don't get this far without some critical thinking being done. There will certainly be problems to solve during and after construction and that is the challenge and satisfaction of projects like this. Will it have good single engined performance? Unlikely to be much better than most other light twins out there but there are tens of thousands of those flying perfectly well.

One thing for sure, the builder will learn a LOT more than someone pulling rivets on an RV12 and following the plans. He may also learn he should have never started at some point but without exploring new ideas, nothing new is ever developed. He is doing this because he wants to, simple as that. I'll give him the nod of encouragement and be interested to see how it all turns out- safely I hope.

It's safe to say that Van's does not support this or even most minor mods to their designs as can be understood and expected in their position. Van's also couldn't support floats, retracts and Rockets using their components but we have them anyway. The builder has purposely distanced himself from Van's which is a fair thing to do.

Dreamers have a place in this world, as this is where the new ideas come from. We wouldn't have incredible designs like David Algie's LP-1 coming through the pipeline if everyone was just a drone, satisfied with existing designs.
 
I have to agree with Bob in post #47. I do laud the true spirit of "Experimental" that the builder/modifier is bringing into this project but I question the decision to use Corvair engines as that is bringing in another departure from the normal tried and tested aviation engine options that are available. Single engine aircraft have a much better safety record than light twins. Some say the purpose of the second engine is to take the aircraft to the scene of the crash. I also question the choice of airframe. Maybe cost is a factor. I would be applying my efforts to an RV-10 airframe rather than a 6A. When the project is finished what will be the resale value be? A 10 fitted with two 200hp engines would command a better resale price, have two extra seats and is a more realistic conversion IMHO.
 
...I question the decision to use Corvair engines as that is bringing in another departure from the normal tried and tested aviation engine options that are available...

That goes along with what I've heard suggested: Keep your variables manageable. If you're experimenting with engines, use a proven airframe. If you're experimenting with airframes, use a proven engine.
 
twin engine

I have to give this guy credit, he is putting the E in experimental. The tail was swapped for a -9 tail and 40 inches were added to the wings. No matter who says what.... you have to give the guy his due for doing such radical changes and wanting to fly it. I'd love to hear what changes were made as far as engineering to the airframe. BEST OF LUCK!!!!
Best
Brian
 
This sort of reminds of the Zenth twin. Only it is not ready for primetime.
ZenithAir said:
The Gemini CH 620 project is still under development and kits are not available.
AVAILABILITY TO BE ANNOUNCED UPON COMPLETION OF DEVELOPMENT PROGRAM
 
Last edited:
...The tail was swapped for a -9 tail and 40 inches were added to the wings...

Those are both exactly the kind of changes I'd expect to see for this kind of conversion.

The span extension of 20" per side gives more area and a better aspect ratio, both important for carrying the extra empty weight. Removing the engine from the fuselage and putting an engine on each wing gives inertia relief that reduces the wing bending moment at the side of body. The combination of inertia relief plus span extension probably about cancel each other out, for flight loads at least. Landing loads are a different matter, but are probably within established margins.

Putting the biggest vertical tail and rudder on it that will practically fit is also exactly what I'd expect to see. That helps keep the Vmc speed [corrected per the post below, thanks!] low. Below Vmc, if you lose an engine you have to throttle the remaining engine back until you have enough speed so that the rudder and vertical tail are effective enough to counter the asymmetrical thrust. And if you don't have altitude to trade for that speed, you're in a bad situation.
 
Last edited:
Putting the biggest vertical tail and rudder on it that will practically fit is also exactly what I'd expect to see. That helps keep the blue line speed low. Below blue line speed, if you lose an engine you have to throttle the remaining engine back until you have enough speed so that the rudder and vertical tail are effective enough to counter the asymmetrical thrust. And if you don't have altitude to trade for that speed, you're in a bad situation.

That would be redline speed, Vmc....
 
I have to agree with Bob in post #47. I do laud the true spirit of "Experimental" that the builder/modifier is bringing into this project but I question the decision to use Corvair engines as that is bringing in another departure from the normal tried and tested aviation engine options that are available. Single engine aircraft have a much better safety record than light twins. Some say the purpose of the second engine is to take the aircraft to the scene of the crash. I also question the choice of airframe. Maybe cost is a factor. I would be applying my efforts to an RV-10 airframe rather than a 6A. When the project is finished what will be the resale value be? A 10 fitted with two 200hp engines would command a better resale price, have two extra seats and is a more realistic conversion IMHO.

I'd be pretty sure that selling this aircraft and how much money he would get for it would be last on this builder's priority list. Corvair engines work just fine on aircraft if properly assembled and modified as we have seen dozens of times. POFs have been established, understood and corrected years ago now.

Using an existing RV6 airframe as the starting point seriously reduces the cost of the project as do the Corvair engines compared with using an RV10 airframe and a couple Lycomings. Proof of concept or just building the dream- this all makes sense to me.
 
It warms my heart to read your words

...
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 have so often wanted to say it but I have never quite found the words. I will not copy you but I appreciate your saying them.

Bob Axsom
 
Seems that if the wings themselves are not beefed up, the critical area might be just outboard of the engine, where the bending moment from the additional span is greater than originally designed, and the lift greater as well.

Dave
 
I have so often wanted to say it but I have never quite found the words. I will not copy you but I appreciate your saying them.

Bob Axsom

Thanks Bob. Really just saying that while the modern Van's prepunched kits are truly a marvel, they take away a lot of the creativity of original or highly modified designs. Paint and panels are are main places we see some self expression these days.

I don't want to take away or minimize what Vans has done for fast, easy construction or giving us safe, fun aircraft. What they have done has made them #1 and satisfies most builders but at the same time this has resulted in a cookie cutter mentality where many can't appreciate something different.

In my view, building an experimental is all about building what YOU want. If that is a standard 8 with a Lycoming and Hartzell up front, that is absolutely fine with me but so is an RV on floats or a twin engined one.:)
 
<snip>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<snip>
Thanks, Bob K.
The weight you quoted for an IO360 is NOT all up flying weight. I weighed my O360 bare with no accessories, and it was 240lbs. Add all the accessories, fluid lines, everything to make it ready to fly, and it will be over 400lbs.
8-22-08-003w.jpg


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 works 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.:)
Best post in this thread IMHO...
Some of us will go to the extremes to have a one of a kind but this is an accident waiting to happen.
An amazing effort but don't you think Van considered building kit twins and thought better of it... I hope it ends up a static display before it becomes a deathtrap.
Jim has the experience to make this work. Lots of engineering work done (three years worth), and lots of twin engine experience (97% of Jim's 15,000 hours of flight time are multi-engine hours).

This has to be one of the coolest projects yet and I don’t understand why this community is not more supportive.
Because it's not an RV...well, it was an RV, and now it's modified to be something else, and it just "doesn't fit". Too bad...it's one of the most interesting projects out there right now that I know of. And I know of A LOT of them now. ;)
When the project is finished what will be the resale value be?
I can personally guarantee you that resale value is not even on his radar. Besides...it's not your dollars he is spending, so who cares, really?

:cool:
 
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 works 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!

Thank you!
 
I can personally guarantee you that resale value is not even on his radar. Besides...it's not your dollars he is spending, so who cares, really?

:cool:

To be honest Chad mate, I do not care who's money he is spending as long as it not mine. Seems your telling me to mind my own business. I was just trying to put a valid point across with what information that was available to me at the time. As I said in my post, I laud (admire) the spirit of experimentation that this guy is bringing to this project. I wish him all the very best for a successful conclusion. However fron MY point of view (and everyone is entitled to one of those) this is.not my cup of tea.
 
To be honest Chad mate, I do not care who's money he is spending as long as it not mine. Seems your telling me to mind my own business.

Not at all Anthony...more of a general statement of 'to each his own'. Sorry about that. Internet talk...hard to convey how I was actually "speaking". :)
 
They finished both engines for it at Corvair College#31 late last year. Jim said his time line is to fly the twin back to Barnwell this year, fully flight tested and proven.
 
Why would a link to the site describing this cool RV based Twin project not be acceptable? In reviewing the posting rules, I don't see any of the restrictions related to posting links of RV derivatives.



[ed. Hi Russ,

If memory serves (it was over four years ago) the project in question was listed here initially by the person who had started a competing homebuilt aircraft site, and this airplane was his. His *click here for more info* initial post took readers to his site (with RV forums/classifieds/directory/etc). I never had any issue with pictures and discussion in my site at all - just someone using it to promote their competing site! I'm sure any small business owner who has bet everything would appreciate my feelings on this!

Having said all this, I think there are many pictures of the plane in this thread, and I look forward to learning more about it. I hope there are updates using this site down the road - it seems very interesting.

v/r, dr]
 
Last edited by a moderator:
COOL!!!

? I think it was a big mistake to remove the original engine as it was already
in place, and working. An R/V twin, not so different, but an R/V Tri-Motor, now
your talking!..:rolleyes::rolleyes:
 
I thought it was going to be like the twin Yak that Jack Links flys out of our airport. This looks pretty nice. I would be interested in the performance numbers and how the engines worked. I guess it is time to search!
 
According to builder/pilot the performance, except fuel burn, is pretty much same as an RV-6A he started with, just now have two engine redundancy. Of coarse the performance he was only interested in was cross country and not over all Vans sport aircraft performance.

I would be interested in wing attach as the carry through forward spar had to have moved forward to balance with the weight of the two engines. the spar had to have moved forward to the firewall to keep it out of the way of the leg room and rudder peddles.
 
Last edited:
Fair Warning

For you thinking about using Corvair power, the front bearing is not adequate to support the prop, and the thrust bearing on the crank is at the back, away from the prop. At a minimum, the Corvairs need a prop bearing add on, which puts this in the realm of the Subaru auto conversion. Really dangerous to fly without an added prop bearing. And Corvair parts are hard to get. Everytime we looked at Corvair power, it seemed a Lycoming out of a Cessna 150 was cheaper.
 
Last edited:
For you thinking about using Corvair power, the front bearing is not adequate to support the prop, and the thrust bearing on the crank is at the back, away from the prop. At a minimum, the Corvairs need a prop bearing add on, which puts this in the realm of the Subaru auto conversion. Really dangerous to fly without an added prop bearing. And Corvair parts are hard to get. Everytime we looked at Corvair power, it seemed a Lycoming out of a Cessna 150 was cheaper.
The engines have a 5th bearing.

https://www.youtube.com/watch?v=DvjECeDnS2M
 
If Piper can turn a Cherokee 6 single engine plane into a Seneca Twin engine plane... a RVt6 can become a twin...

Remember the The Wing D-1 Derringer

1c6c56a7507773790ad319be86ee54ed.jpg
 
Wing D1

There is a Wing D1 based very near my home field in NC, and the first time I saw it fly in, I was sure it had to be an RV derivative, in fact when it was still aways off I thought it was a flight of 2 RV's based on sound. After careful inspection on the ground, I was very impressed with the design and quality. Im quite sure a twin RV would perform well, though like the D1, its going to be a 2 place twin, and twin complexity/cost. In reading about the D1 history, its been around since the late 60's and somewhat of a production experimental built by different assemblers, some still around unfinished. I look forward to following the twin RV derivative and see where it goes.
 
Misinformation alert!

For you thinking about using Corvair power, the front bearing is not adequate to support the prop, and the thrust bearing on the crank is at the back, away from the prop. At a minimum, the Corvairs need a prop bearing add on, which puts this in the realm of the Subaru auto conversion. Really dangerous to fly without an added prop bearing. And Corvair parts are hard to get. Everytime we looked at Corvair power, it seemed a Lycoming out of a Cessna 150 was cheaper.

Stop misleading people with misinformation….the TwinJAG has 5th bearings with dedicated oil lines and high volume oil pumps. This setup addresses thrust and gyroscopic loads on the crankshaft. BTW, Corvair aircraft engine parts are VERY easy to obtain.

I am the designer & builder of this aircraft and reading posts by misinformed internet armchair quarterbacks like this makes you lose faith in fellow so called “builders”. To all so called experts, please put down your keyboards and come see me at my aircraft at Oshkosh and would be glad to inform you on how it was really built.

BTW, C-150’s use Continental Engines
 
Last edited:
For you thinking about using Corvair power, the front bearing is not adequate to support the prop, and the thrust bearing on the crank is at the back, away from the prop. At a minimum, the Corvairs need a prop bearing add on, which puts this in the realm of the Subaru auto conversion. Really dangerous to fly without an added prop bearing. And Corvair parts are hard to get. Every time we looked at Corvair power, it seemed a Lycoming out of a Cessna 150 was cheaper.
Oh no someone is going to accuse you of "misinformation"... Ha ha.

Stop misleading people with misinformation….the TwinJAG has 5th bearings with dedicated oil lines and high volume oil pumps. This setup addresses thrust and gyroscopic loads on the crankshaft. BTW, Corvair aircraft engine parts are VERY easy to obtain.

I am the designer & builder of this aircraft and reading posts by misinformed internet armchair quarterbacks like this makes you lose faith in fellow so called “builders”. To all so called experts, please put down your keyboards and come see me at my aircraft at Oshkosh and would be glad to inform you on how it was really built.

BTW, C-150’s use Continental Engines
Don't get upset. This is a cool project and appreciate you sharing. Everyone is going to have opinions. Get ready. :D Clearly you are a proponent and passionate about Convair power. I have seen at least one RV (single engne) with a Convair. It was for sale cheap. Just saying. I have seen the Convair booth at Airventire a few times.

You indicate the Convair engine in stock form is inadequate for aircraft use as-is and requires modification to make it more suitable. That is great. I like the fact it is like a Lycoming, Horz opposed air-cooled direct drive, so a PSRU and coolant radiator is not required. With that said I would never use one. Personally I think the best ENGINE CONVERSION is to convert $28,000 bucks into a Lycoming. Ha ha.

The C-150 Continental O-200 is a great engine. That would be ideal for the twin RV or two Rotax 912 or 915 (may be). Not a Rotax fan but I have to admit they are here to stay. The price, PSRU, liquid cooling are things I don't like. It looks like you need or want 100-120HP.

What about UL Power UL520iS or other alternatives. I don't know much about the UL company (Germany I recall) and the reputation of their engines. The DarkAero guys are using the UL engine on their new design. UL power has a wide range of power outputs. They use the same cylinder and add more jugs or boost compression etc. I can say it is expensive and a Convair with FlyConvair parts would be cheaper.

If a single 160HP engine can make an RV scoot along, a twin RV with two 100 to 120 HP engines will result in good performance. Single engine performance? Well what people might not know, twins under 6000lbs only have to demonstrate single engine rate of climb for certification. Demonstrate does not mean positive ROC. You just have to demonstrate it, which can be negative ROC. Yes you can have a zero single engine service celling. It is just the regulations for light twins. Once you get over 6000lbs you have to climb single engine.

In a Jet you lose an engine in high altitude cruise, you start to DRIFT DOWN. You can't hold altitude. Same with a light twin you need to drift down to SE service ceiling. SE operations can extend your range before the ground comes up, but given conditions you may be able to maintain altitude. People think two engines is great. It is great, but with serious limits unless you are in larger heavy twins.

All light twins I flew can climb slightly below say 5000 ft DA. When I say slightly I mean 50 FPM. I can tell you my beloved Piper PA-23-160 (Apache) did well single engine, solo, half fuel sea level conditions. Two people, full 108 gal, baggage, high density altitude, loss of engine means pulling the good engine back and making a forced landing. Trying to fly it would result in loss of control.

You also have to worry about Vmc as I am sure you know. You can have too much power from the standpoint of single engine operations. The whole problem is asymmetric thrust. Reducing that helps control. Also adding more yaw stability helps. Did you consider a bigger Vertical Stab/ rudder or ventral fin? Have you estimated Vmc? Vyse (blue line). I think keeping it light (O200 or Rotax) is goodness. I don't think a Convair is heavy but guessing (forgive me no time to research) it is not lighter than a O200 and Rotax. I know the Convair is claimed to make 100 to 120HP. With non feathering prop you will lose more performance and have even higher Vmc.

Cheers

I see there is a twin RV6A or TwinJAG N622JG with Convair engines... COOL!!! It is at Oshkosh 2021
https://www.youtube.com/watch?v=GIMVkTk26fw
 
Last edited:
Don't get upset. This is a cool project and appreciate you sharing. Everyone is going to have opinions. Get ready. :D Clearly you are a proponent and passionate about Convair power. I have seen at least one RV (single engne) with a Convair. It was for sale cheap. Just saying. I have seen the Convair booth at Airventire a few times.
And yet, not familiar enough with it to spell Corvair correctly.
 
I would be interested in wing attach as the carry through forward spar had to have moved forward to balance with the weight of the two engines. the spar had to have moved forward to the firewall to keep it out of the way of the leg room and rudder peddles.

I was looking for pictures because I wanted to see how he handled the nose gear (looks like an RV-10 style gear on the old firewall) and it looks like the wing attach is stock. I did not see early pictures that showed how he carried structure forward for the new firewalls. Impressive project.
 
Back
Top