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

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


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