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-   -   Poll: Van's Twin (https://vansairforce.net/community/showthread.php?t=202652)

blaplante 01-08-2022 09:04 AM

Poll: Van's Twin
 
Should Vans build a twin - in the style of the Rutan Boomerang? See https://en.wikipedia.org/wiki/Rutan_Boomerang Note that design is a tractor engine, conventional tail - but the asymmetry fixes a lot of twin bad behavior. Read up on it.

Taltruda 01-08-2022 11:07 AM

It’s just so ugly.. how could anybody want to build and fly something so hideous? lol

jcarne 01-08-2022 11:12 AM

No but I sure dang wish I could afford to build and operate a Velocity V-twin!

rockwoodrv9 01-08-2022 11:15 AM

Quote:

Originally Posted by jcarne (Post 1580890)
No but I sure dang wish I could afford to build and operate a Velocity V-twin!

I dont think there is a prettier plane than the Velocity. I saw one at OSH a few years ago and my jaw dropped.

bjdecker 01-08-2022 11:43 AM

1 Attachment(s)
I'd go for something like the Wing Derringer (redux)

jcarne 01-08-2022 11:52 AM

Quote:

Originally Posted by rockwoodrv9 (Post 1580891)
I dont think there is a prettier plane than the Velocity. I saw one at OSH a few years ago and my jaw dropped.

Same! They also largely minimized the twin single engine problems that plague many others.

jimdc8 01-08-2022 01:04 PM

Quote:

Originally Posted by bjdecker (Post 1580895)
I'd go for something like the Wing Derringer (redux)

You mean like this…

https://www.youtube.com/watch?app=desktop&v=GIMVkTk26fw

rocketman1988 01-08-2022 01:12 PM

velocity
 
I actually was going to build the Velocity XLRG before I started my -10. Had an entire kit lined up, worked with the previous owner, had money in hand. The day before we were to close the deal, I get an email saying that he sold the kit...

That was a dick move, for sure...but...it pushed me into the -10 and I am happy it did.

The V Twin is nice but given the choice, I would build the TXL...250+ knots at altitude would be really nice! You are, however, going to pay dearly for that performance.

No, I really love my -10. Flies great, carries what I need, and will go just about anywhere...

sprucemoose 01-08-2022 01:36 PM

I’m with Brian. Yes to a twin, but make it conventional like the Derringer. No Bommerang type. A 14 with two O-320s would be about the sweet spot.

Biggest problem I see is that the natural tendency to want bigger engines than recommended would be a much bigger issue than say an O-360 powered -9 or a Rocketized 6, 7 or 8. If I were Van’s that would be enough to scare me away from it. But I’d love to build one.

bjdecker 01-08-2022 01:37 PM

Quote:

Originally Posted by jimdc8 (Post 1580907)

Kinda, sorta...

:)

jrichichi1 01-08-2022 03:20 PM

Wing Derringer type...
 
Make it a knockoff of the Wing Derringer. Two-seater with a larger baggage area. Retractable. Have a variety of engines available for it. O-320 up to the new IO-390-EXP119. If you really wanted it to be a high performance twin, go with two UL Power UL520T engines (220 HP). Not only are they much lighter, the turbo-normalizing gets you power up high (S.L. power up to 15,000 MSL), and they even come in a counter-rotating version (no critical engine...). However, I would never expect Van's to go with a UL Power engine. It would be an impressive aircraft if they did.

I'd make a similar to the -14 but with either doors like the -10 or a combination slider/doors (slide the canopy back, open a low-height door forward and step in). I'd probably do four tanks like a Glasair Sportsman but make them "wet" like RV's. Lots of fuel for range. You use a Facet pump to transfer fuel from the outboard tanks to the inboard tanks. How much fuel? As much as you can get!! Just like other aircraft, you can offload payload to fill up with fuel or vice versa.

No pressurization. Too complicated and too heavy. Keep it light and simple (if you can call a retractable twin simple...).

Due to the increased utility of something like this, some sort of deice would be great. Again, I wouldn't expect Van's to go out on a limb for a deice system. A "weeping wing" or a "thermal" system would be nice. Each have their respective advantages and disadvantages. If you make the leading edge "bolt-on" similar to how the tanks are attached, you can swap out leading edges with or without a deice system. It would probably be best to have the wet fuel tanks in between the front and rear spars if that was the case.

Anyway, I've wasted too much time typing about this.

Jeff

David Z 01-08-2022 07:01 PM

Jeff, I quite like where you're going with this. Nice big tail and rudder for single engine controllability. Big engines for single engine performance. It needs to be so good on one engine that the saying "second engine takes you to the scene of the crash" doesn't apply.

If we're sticking de-ice systems on this plane, then it needs big engines to keep performing when the icing gets bad too. The turbo UL520 sounds wonderful.

4 seats though, need the seats.

Would it sell? Would people build it? I'm guessing not many. Same problem as described the 6-seater thread. The plane would simply be too big and complex.

sprucemoose 01-08-2022 07:36 PM

Only too big and complex if we make it so.

2 seats
Moderate engines- O-320
Fixed gear. Retracts are a waste under 200 kts. Also improves Vmc.

Need boots or 4 seats? Go buy a Baron or 310.

jrichichi1 01-08-2022 08:23 PM

Quote:

Originally Posted by David Z (Post 1580968)
Jeff, I quite like where you're going with this. Nice big tail and rudder for single engine controllability. Big engines for single engine performance. It needs to be so good on one engine that the saying "second engine takes you to the scene of the crash" doesn't apply.

If we're sticking de-ice systems on this plane, then it needs big engines to keep performing when the icing gets bad too. The turbo UL520 sounds wonderful.

4 seats though, need the seats.

Would it sell? Would people build it? I'm guessing not many. Same problem as described the 6-seater thread. The plane would simply be too big and complex.

Yep, I agree with you David. I understand the Derringer had pretty good engine-out performance. Like you said, big engine, big tail, and you also need to be lightweight (read: high HP to weight ratio) to get good single engine performance. To help out on the S.E. performance, just don't load up with fuel and payload and stay light if you're worried about an engine-out scenario (mountains, night, etc.). Once you're out of the "danger zone" you can land, tank up and fly heavy, with a lower S.E. service ceiling.

That's one of the main reasons I said to have huge fuel tanks. So that even with half full "main" tanks you still have good range in the aircraft. You're going to want to have around 180 gallons total fuel capacity with this aircraft. 30 gallons in the outboard tanks (each tank) and 60 gallons in each inboard "main" tank. The UL520T typically burns 8-11 GPH so full tanks should give you about 9 hours before you're a glider. That's a LONG flight!!! With 30 gallons in each main tank, you're talking a 2 hour flight with a 45 minute reserve. The Derringer supposedly had a 184 kt cruise speed. I would expect with the more powerful engines you would be going faster but this still gives you about a 350 nm range with a 45 minute reserve. That can get you past a lot of "bad" territory.

Maybe a compromise on the seats would be to do what is done on the Sportsman 2+2. You have two, full size seats in the front and two aft facing seats in the back. The aft facing seats share a common seat back that can be easily removed via four bolts to make room in the back if you want to pack the back with cargo. The rear seat "bottoms" are attached to the seat back via piano hinges and are removed with the seat back (it's all one big assembly). The piano hinges allow you lift up the seat bottoms to store small items under the seats when they are installed. It's a really nice setup. The seats in the back can easily fit a couple of kids or small adults. Plus, they work great for tossing baggage on them. Just Google "Sportsman 2+2 aft facing seats" and look at the images. Some people had forward facing seats in the back but the head room was limited as was the allowable load due to C.G. concerns.

The aft facing seats have some good qualities to the design.

1) It keeps the C.G. close to the front seats when you put people in the back.

2) You get more head room for those in the back since the fuselage has a larger cross section there.

3) Both the front and rear seats, seat belts, headset wiring, etc. tie into the same bulkhead. You don't need to make two, relatively heavy, complex bulkheads with this arrangement.

Let's face it, most of the time you probably won't be flying with someone in the back seats. If you do, they will be facing backwards. Some people won't like facing aft during the flight. For them either put them in the front seat or leave them on the ground... :)

Would it sell? Yeah, I'm sure it would sell a few. How many? Who knows. A lot of people talk. Very few take action unfortunately... If Van's had something like Glasair's Two Week To Taxi (TWTT) program, then you'd probably get more takers. With the TWTT program, you're essentially trading cash for time. Also, the people who would most likely be purchasing an aircraft like this have the cash but not the time. The people who don't have the cash for a TWTT program wouldn't be purchasing an aircraft like this anyway.

It would be nice but again, I don't think Van's would do this. Maybe someone else will...

Jeff

JDeanda 01-09-2022 11:01 AM

Nope
 
I’m not a big believer in the concept of the light twin. Universally poor single engine performance on takeoff and added complexity are too hard to fix. By the time those issues are handled, it’s not a light twin any more. As I’ve said before, I’ve seen the Comanche, Arrow, Tiger and others transmogrified into twins. I don’t think any of those became better airplanes from that, they just became multiengine trainers. Light twins designed from a clean sheet (Crusader, 310, Baron, Travel Air, Apache… ) all those, did not do much better. Worst example of course, is the Lancer (twin Citabria,) an interesting but truly useless curiosity of an airplane. I don’t see that Vans has any magic to address these problems, nor do I think a Vans twin would “pencil out” as Greg Hughes might say. I for sure would not buy one or encourage anybody else to.

David Paule 01-09-2022 02:12 PM

Quote:

Originally Posted by sprucemoose (Post 1580973)
Only too big and complex if we make it so....

Given the innate complexity of having two engines, can you imagine a homebuilder NOT loading such an airplane up with gadgets and systems?

Fortunately the poll, right now, is running 10 to 1 against the concept.

Dave

rocketman1988 01-09-2022 02:27 PM

Against...
 
Against Van's devoting resources to a twin...

Maybe someone else will step up...

MacCool 01-09-2022 02:56 PM

Quote:

Originally Posted by rocketman1988 (Post 1581140)
Against Van's devoting resources to a twin...

Maybe someone else will step up...

If I was one of the many would-be builders out there that was watching my kit and parts shipping dates slip farther and farther, I’d be a little miffed at Vans devoting resources to anything other than current supply chain, manufacturing, and shipping issues, and I include the RV-15. I can’t imagine how that theoretical airplane isn’t years away from shipping its first empennage kit.

sprucemoose 01-09-2022 04:02 PM

Quote:

Originally Posted by David Paule (Post 1581137)
Given the innate complexity of having two engines, can you imagine a homebuilder NOT loading such an airplane up with gadgets and systems?

Fortunately the poll, right now, is running 10 to 1 against the concept.

Dave

I can imagine all sorts of scenarios that would keep me up at night if I were Van’s. There is a difference between complexity added by the builder by larding it up, and complexity in the basic design (fixed gear vs retract for example) but yes, I get your point and I agree.

FWIW I don’t think Van’s will do a twin, and I’m not sure I’d want them to anyway. But for a fun little thought exercise, yes I would sure love to build one if they did!

sprucemoose 01-09-2022 04:06 PM

Quote:

Originally Posted by rocketman1988 (Post 1581140)
Against Van's devoting resources to a twin...

Maybe someone else will step up...

The practical side of me agrees with you. The dreamer on the other hand…

If Van never put a little time into dreaming and R&D then the RV fleet would consist of a few dozen RV-3s and very few of us would be enjoying this hobby. Just sayin’.

Maybe we need another poll- “which is the worse idea, a 6-seater or a twin?”

rocketman1988 01-09-2022 05:27 PM

Quote:

Originally Posted by MacCool (Post 1581148)
If I was one of the many would-be builders out there that was watching my kit and parts shipping dates slip farther and farther, I’d be a little miffed at Vans devoting resources to anything other than current supply chain, manufacturing, and shipping issues, and I include the RV-15. I can’t imagine how that theoretical airplane isn’t years away from shipping its first empennage kit.

That’s been discussed before; the R&D department has little control over parts, shipping, and supply chain issues. What would you have them do? I understand the frustration but most of the blame does not fall on vans.

Can’t say more than that as it will devolve into a political discussion and that’s not appropriate here…

rocketman1988 01-09-2022 05:30 PM

Quote:

Originally Posted by sprucemoose (Post 1581166)
The practical side of me agrees with you. The dreamer on the other hand…

If Van never put a little time into dreaming and R&D then the RV fleet would consist of a few dozen RV-3s and very few of us would be enjoying this hobby. Just sayin’.

Maybe we need another poll- “which is the worse idea, a 6-seater or a twin?”

Dreaming is one thing but that takes time, and time is money. There must be a ROI for the company and knowing what it takes to design, test, and execute a new aircraft, I’m pretty sure neither the twin or the 6 seater are viable options for the company…

emsvitil 01-09-2022 05:51 PM

The RV16 is going to be twin RV8 like the twin mustang..............


:D

David Z 01-09-2022 08:06 PM

Quote:

Originally Posted by jrichichi1 (Post 1580985)
Yep, I agree with you David. I understand the Derringer had pretty good engine-out performance. Like you said, big engine, big tail, and you also need to be lightweight (read: high HP to weight ratio) to get good single engine performance. To help out on the S.E. performance, just don't load up with fuel and payload and stay light if you're worried about an engine-out scenario (mountains, night, etc.). Once you're out of the "danger zone" you can land, tank up and fly heavy, with a lower S.E. service ceiling.

That's one of the main reasons I said to have huge fuel tanks. So that even with half full "main" tanks you still have good range in the aircraft. You're going to want to have around 180 gallons total fuel capacity with this aircraft. 30 gallons in the outboard tanks (each tank) and 60 gallons in each inboard "main" tank. The UL520T typically burns 8-11 GPH so full tanks should give you about 9 hours before you're a glider. That's a LONG flight!!! With 30 gallons in each main tank, you're talking a 2 hour flight with a 45 minute reserve. The Derringer supposedly had a 184 kt cruise speed. I would expect with the more powerful engines you would be going faster but this still gives you about a 350 nm range with a 45 minute reserve. That can get you past a lot of "bad" territory.

It's not the mountains I'm worried about. In cruise, drift down and careful diversion planning can solve lots of that. My primary concern is flying away from the trees at the end of a 3000' runway when an engine quits just after there isn't enough space to stop.

Never heard of fuel tanks being too big. However, fuel tanks weigh more than not tanks. On our planes, how much heavier is the fuel tank than the outboard leading edge? They're roughly the same physical size, yet one is thicker skins, thicker ribs, extra brackets, bolts, sealant, and weighs much more.

jimdc8 01-09-2022 09:35 PM

Already has been done…
 
A twin “RV” already exists…I just did it for me, not as a commercial venture…

https://www.kitplanes.com/twinjag/

https://www.youtube.com/watch?app=desktop&v=GIMVkTk26fw

Jim

sprucemoose 01-10-2022 07:01 AM

Jim,

That is much closer to what I envision for an RV twin. I looked at this at Oshkosh last year and even talked to you briefly, along with about a zillion others, I’m sure.

I’d love to know more about single-engine performance and controllability with your setup.

jimdc8 01-10-2022 08:15 AM

Hi Jeff!

I’m sure it was a pleasure speaking with you at OSH! The engine out performance & controllability is as predicted. It slows to 105mph in level flight and if slowed to 90mph, will climb roughly 200fpm. This was performed at a zero thrust condition. Controllability like any other light twin. Definitely adequate to divert to a nearby suitable airport!

On takeoff, I have a self-imposed limit of 3500’ runways. I adjust that based on GW, density altitude & obstructions. If either engine fails during this critical phase, I simply pull both engines back and land straight ahead.

Not ALL twins should be treated equally…it’s all how you fly them! Anyone that spurts out the “good engine will take you to the scene of the crash” line, is not taking this into consideration!

Jim

sprucemoose 01-10-2022 05:49 PM

Jim,

Good info. I agree with your dismissal of those who criticize all light twins and cite old saws. They strikes me as very similar to the misconceptions that surround tailwheel aircraft. Misconceptions which, incidentally, Van's designs have probably done more to rectify than any other aircraft in the modern era. But I digress.

A few follow up questions if I may.

You cite 90MPH as Vyse. How did you determine the zero thrust condition? Have you flown it with one caged? Under what conditions was this number determined?

What kind of Vmc testing did you do? What were the results? As I'm are you know, this is the thing that is most likely to bring a light twin to grief if not done correctly.

David Paule 01-10-2022 06:06 PM

Is that 200 feet per minute based on sea level standard conditions? Here at my home field, in the summer, the density altitude of frequently around 8k', which would degrade that. That would be a limitation to the utility of your airplane, wouldn't it?

Dave

jimdc8 01-12-2022 11:52 AM

Quote:

Originally Posted by sprucemoose (Post 1581412)
Jim,

Good info. I agree with your dismissal of those who criticize all light twins and cite old saws. They strikes me as very similar to the misconceptions that surround tailwheel aircraft. Misconceptions which, incidentally, Van's designs have probably done more to rectify than any other aircraft in the modern era. But I digress.

A few follow up questions if I may.

You cite 90MPH as Vyse. How did you determine the zero thrust condition? Have you flown it with one caged? Under what conditions was this number determined?

What kind of Vmc testing did you do? What were the results? As I'm are you know, this is the thing that is most likely to bring a light twin to grief if not done correctly.

My “zero thrust” setting is not a true number since I cannot feather the prop. It was performed with engine shutdown (prop locked…no rotation) at 3000’ with myself and 30 gallons of fuel. OAT was 62F. I did both my Vyse & Vmc testing at this time…both kind of crude numbers, but gave me an idea of what to expect.

Vmc…82mph
Performed with above conditions…raised nose and decreased speed until lost rudder authority.

Vyse…90mph
Maintained roughly 105-110mph at level flight. Raised nose to 90mph to get max ROC. (100-250fpm)

Once again, wasn’t looking to build “spaghetti charts” but just getting rough crude numbers. Performed at 3000’ back in Long Island during phase I knowing I would be moving it to North Georgia with a field elevation of 2700’.

Jim

Snowflake 01-13-2022 07:58 AM

Does anyone know what happened to the Wing Derringer design? Surely someone owns it or has the drawings or something? It seemed to be a great design.

jrs14855 01-13-2022 01:57 PM

Derringer
 
John Thorp designed the Derringer in 1958 as a development of the Sky Scooter. It was "taken over" by George Wing/Hi-Shear Corp. It was developed and certified with help from North American engineers. originally powered by Continental 0 200's with fixed pitch props, all but the first example were powered by Lycoming IO 320 B or C series identical to the Twin Commanche.
Hi-Shear has gone thru various name changes and owners and is still in business. It seems likely that Hi-shear owns the rights to the Derringer.
Both George Wing and John Thorp have been gone for many years.
I saw the 0 200 powered prototype at Rockford EAA in the 60's.
The reality is that most did not want a two place twin. A Miller Conversion Twin Commanche with additional speed mods with outperform the Derringer but the horsepower goes from 160 to 200.

jrichichi1 01-13-2022 05:58 PM

Wing Derringer plans
 
Probably about 15-20 years ago I saw a Wing Derringer up for sale. In addition to the aircraft, the seller supposedly had a set of the production drawings for the aircraft that was included in the sale. Looking back I wish I had bought it. I was relatively broke at the time so no way could I afford it. Not sure how I would have made it happen but it would have been nice.

I thought that maybe someone could try to contact the owners of the Derringer aircraft out there and see if they have a set of plans for the aircraft. You'd pay them just to make a copy of the original plans so you can have them. Not that you'd make an exact duplicate of the aircraft but it would be a good starting point. A lot has changed over the years and using modern aerodynamic and structural analysis to the design along with CNC production of parts could yield some benefits over the original.

Again, not sure if it would sell or not. Most likely not...

fixnflyguy 01-20-2022 04:59 AM

Derringer construction complexities
 
A side note on the Derringer ,( there is one based near me), and my curiosity got me researching. It was designed/built by some airliner guys with resources consistent with big jets(as mentioned in earlier post). It used chemically milled skins that were also hydro pressed.not a cheap route. The aircraft was never really certified, and best I can understand, most were hand built by the design team, although some partially assembled "kits" were finished by individuals. Seeing the one fly into our airport and smoking it over, I was impressed, however, its much of a 2 seat retractable hotrod with twice the basic RV operating cost. When I first heard it coming, I thought it was a 2 -ship RV formation...a cool concept, but I question kit sales numbers vs. design/test/production cost.

jrs14855 01-20-2022 09:15 AM

Derringer
 
Where does this stuff come from?? See post 33. John Thorp was not an airliner guy. He designed a number of homebuilt airplanes, some of them intended for production, some strictly homebuilts. The Thorp T18 probably the best known.

abwaldal@gmail.com 01-20-2022 09:32 AM

My real question is WHY?
I can't order a new RV-14 kit and expect to receive it in much less than a year.
With a backlog like that and orders coming in every minute why take the time to do anything except build kits all ready sold.
My business sense opinion.
Art

jrs14855 01-20-2022 09:36 AM

Derringer
 
The Derringer that I saw at Rockford/EAA in the 60's was powered with Continental O 200's with fixed pitch metal props that were custom modified for the airplane. Those props did have problems as the prop concept did on many other airplanes. From the second airplane on the engines were identical to the Piper Twin Commanche. The props were Hartzell full feathering constant speed.
Thorp left Lockheed in 1946. His involvement at Lockheed with large airplanes was the P2V Neptune. NO AIRLINBERS.
Thorp did the preliminary design on the Piper PA28 Cherokee which was a four place derivative of the Thorp Sky Scooter.
The Thorp T18 was the first EAB aircraft to fly around the world.
Thorp was the first recipient of the EAA August Raspet Award, an award still sponsored by EAA.

jrs14855 01-20-2022 09:58 AM

Derringer
 
Derringer was type certified in 1966. Sir or seven production airplanes we5re completed depending on source. Seven unfinished airplanes were later sold. Nine Derringers remain on the US registry.
The statement about stretch formed chemically milled skins is correct. That was a process that Lockheed used dating to the Constellation and used on the Electra's and probably other Lockheed aircraft.
This information is widely available from multiple sources. Comments such as the "Derringer was never certificated" are hogwash.

rocketman1988 01-20-2022 10:05 AM

Quote:

Originally Posted by abwaldal@gmail.com (Post 1583428)
My real question is WHY?
I can't order a new RV-14 kit and expect to receive it in much less than a year.
With a backlog like that and orders coming in every minute why take the time to do anything except build kits all ready sold.
My business sense opinion.
Art


Yeah, no. The R&D guys have nothing to do with the building and shipping of previously ordered kits. I think vans is doing everything they can to catch up on the backlog while also looking to the future.

PhatRV 01-20-2022 10:08 AM

There is one builder extraordinaire who built a twin engine RV6



Here is the article of his endeavor. It can be done but even the builder thinks it is a crazy proposition to try. He probably grafted the RV7 tail to his RV6-T

https://generalaviationnews.com/2021...-engine-rv-6a/


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