Duck going multi

[Turbomallard]

I did the commercial multi instrument deal. I figured I'd do the whole thing so long as I was there. Not sure if I'll ever get to fly a multi engine airplane ever again, but I have the experience, at least. Now I'll have to try and figure out what else to do. It'll have to be cheap, though... my Arrow got nailed with a prop hub AD and will likely need an engine overhaul next year.

And now if you'll excuse me, I need to go out and rob a bank to pay for it...

Oh, wait... it's Sunday.

Never mind. 

TM

[Mike]

Congrats Duck!!
I just now read through the thread again.....


Oh no! You said the "O" word!!
How much will that cost you on an Arrow??

[Turbomallard]

By the time all is said and done, about $25K. I was going to have it done in January, even though the annual is good until end of June. Then I got hit with a prop hub AD. So, I'm going to get that done in January, then fly until July (I can't afford the AD and the annual at the same time). Hopefully my 1997 Saturn will last another two or three years or I'm really screwed! But, as my friends told me almost six years ago when I decided to buy an airplane... you have to be prepared to open your wallet and smile. If you can't do that, don't buy one. 

TM

[Mike]

A wise man once said:

If god would have wanted us to fly,
he would have given us bigger wallets!

[Frank N. O.]

I was just wondering, besides the obvious of having two sets of instruments and engine/prop controls then how much more complicated is it fly a twin vs. a single prop stuck wing? Like a Piper Arrow (I think that's what it's called now, I don't know all the Piper variants) vs a Seminole?

And btw, which way should the engines rotate again to make it controllable with just one engine (opposite of what the Lightning had from the factory)?

Here's a little funny picture I found a long time ago which I just think is so funny, but I'm convinced it's not legal to do that

Frank

[Turbomallard]

It's not a big deal at all unless one of the engines quit, especially the critical engine, if the plane has one. Light twins (emphasis on light) lose approximately 80% of their performance as a rough figure when an engine quits (hence the old joke about the nice thing about flying a light twin is that if one of the engines quits the second one takes you right to the scene of the crash). So, it gets interesting, and that's what most of the training deals with.

Twins with contra-rotating props are easier to fly on one engine... to make a long story short, the downgoing prop blade on both engines (the blade that generates more thrust) is closer to the centerline of the aircraft than a twin that has both it's props turning in the same direction. On a typical American light twin with engines that turn in the same direction, the props turn clockwise, hence the downgoing blade on the right engine-- which is generating more thrust-- is even further out from the centerline of the airplane, making things that much more "interesting" if the left engine is the one that quits.

The above statements are an oversimplification and leave out a lot, but this was done intentionally to keep this from being a 10-page essay, so no need to flame me for an incomplete explanation. 

TM

[Frank N. O.]

No flaming at all, that's a fine base explanation for my question, thank you very much it was exactly what I'd hoped for. Except that it looses 80% of the performence then that really seems to diminish the idea with a twin in my book, except the zero torque from contra-rotating props of course. I'd thought twins (contra-rotating ones) would have a fair more safety in case one engine fails then you'd still have power to maneuver to a safe landing depending on where you are, and knowing energy management a'la glider pilots and Bob Hoover would of course only make it even better (although that will aid any fixed wing pilot of course). I'd actually thought the figure was a little closer to 50%, like maybe 60-65% but I guess I was wrong.

Does anyone know if Seminoles and Beech Baron's have contra-rotating props (in the safe direction)?

Frank

[Turbomallard]

It's mainly an issue with light twins. It's one thing to lose 80% of your performance on something that climbs at 5,000 feet per minute... and another to lose that same percentage of performance on something that climbs at 1,000 feet per minute. Smaller lighter twins with various characteristics (it's too late and I'm too tired to look it up) do not have to maintain a positive rate of climb on a single engine; most larger/heavier ones do. But yes, given a choice of something like a Duchess or a Malibu, I'll take the Malibu. Granted, if the lone engine quits you have a big problem, but you have a big problem in a light twin if just one of the engines fail, so you've multiplied your chance of a problem with two engines.

There's more to it than that, and I'm sure the folks in the forum here know more than me, and some may disagree, but that's my take on the deal and I'm stickin' to it! 

Plus, renting the Duchess is too bloody expensive (double the fuel rate of my Arrow and only a little faster and carries a little more weight).

TM

[Baradium]

Seminoles do have contra rotation props (an O-360 and an LO-360).   

A big reason you lose so much performance is you have to add a lot of drag to counteract the torque from a single engine beside you.   You get added lift from the prop wash (accelerated air over the wing from that engine), which you have to counteract on the other wing (more drag!) and then you have to add a bunch of rudder (which is a BUNCH of drag!).


Larger aircraft (such as a baron and up) tend to have larger engines that can take it.  A seminole will climb empty, but isn't all that great... and the problem isn't just its performance, the performance isn't what gets you, it's that if you try to get more than it's capable of it can kill you... you get behind the power curve, and then performance decreases when you increase pitch, you keep pitching back to get more performance and it gets worse until eventually you stall... not good at all when you have full rudder one way with full power on the live engine...


The biggest thing you have to train for is the idea that even at full power, "blue line"  (VYse, which is described on the airspeed indicator with a blue line and is the best climb rate you can get single engine) might not even let you maintain altitude.  It's the training to let the aircraft descend if it wants to (even if it means setting down off airport).   What gets people is the thought that they have to make an airport because they have a running engine.   Sometimes you just have to swallow your pride (and there are many such situations in aviation).

[fireflyr]

Yes Frank--the duck is right on with that 80% performance loss with 50% power loss--some are even worse (the 150 HP Apache comes to mind).   Flying a light twin is an excercise in inertia management if you lose one, your head needs to be ahead of the airplane, that's where training and plannining for emergencies saves lives.   
Unfortunately, the rate of fatal accidents in light twins with an inop engine is HIGHER than the same number of singles with a power failure because folks try to excercise more options if they still have one running.   In a single, you just concentrate on landing the damn thing successfully---in a twin, many try to get back to the airport without bending any metal----sometimes that's just not an option.   As for me, I'll bend as much metal (controlled crash) as it takes to let me walk home.   The boss can buy a new airplane but my butt is priceless!

[Frank N. O.]

Wow that's scary, but it just shows just how much is involved in flying, both the pilot and the machine must work and no matter what the vehicle can/has then the pilot still has to understand physics, limits and not take chances, similar to cars with all their advanced safety things taking promising almost nature law-breaking safety.

Frank

[mphawk]

Look out below!

here is a sticker for you

http://aero-stuff.com/flying-over-duck-fundecals-p-7195.html