Grier

My fourth model and its gonna be a twin =D. Ive started building it and plan to use 2 irvine 25s, is there going to be a big tendancy to yaw if one cuts? the engines are 45cm apart. Is there any specific order to starting up a twin at all?

twinman

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Suggest that you check out ourl sister site at rcwarbirds.com and the techniques section for flying twins.
The answer to your question is a bit involved, but the short answer is yes,it will yaw quickly when one engine quits. Depending upon speed, time of the flight such as take off, and altitude is the determining factor as to the trouble.
Remember the key word.....Reliability!!!!!!
As to starting order, my suggestion is to always use a helper and start the engine away from you first. DO NOT REACH OVER A RUNNING ENGINE!!!!
Let us know if you have more questions, and welcome to the multi club.
Good Luck,

Dennismate

I have had two twin's both flown on Irvine .25's and yes it will yaw if you loose one. I use a cheap gyro on the rudder to help combat the initial snap.

As regards starting, just take your time and get those motors throttling and running sweet, be prepared to start one, set it up, start up the other, set it up, run them together check they throttle up and down together if not stop them and repeat the procedure again and again until you get it right. Do this before every flight. I lost my first twin by not taking the time to check the engines again after the first flight of the day (split in the pressure line, discovered whilst pulling the rest of it out of the ground).

The Irvine .25 is a good engine, but run them in first. I put nearly an hour on each before fitting them in the plane and apart from the split pressure line have never had one die on me yet.

Hope this helps.

Stuart

Grier

Thanks guys, will each needle valve give the same rpm settings in the same place? if not, is it possible to tune 2 engines at the same time? Il look at the site now, maybe thatll answer it. How does the gyro work? is it independant of the rx or not?

glad to be in the multi club!

Grier

nevermind i saw twinmans thread on gyros The gyro is like a little sensor and fixes the rudder by itself? no extra channel needed?

anyway, heres another pic

twinman

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As discussed before, tune each engine individually. Do not worry about the individual needle valve settings being equal.
The linkage and throttle barrel rotation should be very close or the engines will not spool up together.
Remeber, reliability is the most important thing to multi engines for long life and keeping your hair.......wish I still had some...hair.

Grier

mine is gelled to my head

twinman

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You got to have something to gell!!!!!!!

kkshazzam

I have a Twinstar with OS45s.
I start the left one first and set the needle valve to my liking. Then I shut it down and start the right engine and adjust it.
Now I can go back restart the left engine without leaning over a running engine. I never try to match them in RPM.
I have never had an engine failure but I have set up a program in my 10X that will let me send either engine to idle while maintaining full control over the other. The airplane continues to fly pretty much the same on one engine. It just does it a little slower. I realize that this isnt the same as a dead engine due to prop drag but my guess is that it is pretty close.

Dennismate

I like the idea of cutting one engine back to idle whilst still having full control over the other, tell me, can you select which engine to cut back to idle on the 10X or is it always the same one.

Stuart

warbirdz1

Grier.....One thing to be aware of is Twins have a tenacity to go upside down ( Immediately) after losing an engine.......also ensure that engines are synced at approach power settings and they spool-up evenly in case of a go-around........nothing worse than being slow and one engine coming up faster than the other........thats a recipe for rekiting.......If engines aren't exactly synced at T/O power thats ok if there within a few hundred rpm......Good Luck.....Bill.......

FLYBOY

My Feedback: (11)

Don't let them scare you on twins. They don't imediately turn upside down. There is a thing called Vmc. It is the slowes the plane will fly when one engine is running at full power and the other one is off. There are more factors that apply but I won't go into it all. If you are flying faster than Vmc, the plane will have the rudder authority to keep things going. If you are below it, you will loose directional controll and yes, you will be on your back before you know it.

The thing to watch is when you loose an engine. If it is in cruise or fast flight, you will be ok, just watch the power on the other engine. If you are slow, pull the other engine back and it will stop rolling. You don't have an airspeed indicator so you won't be able to do it that way. you will have to look at it.

Just remember the key point, if you are slow and you loose an engine, pull the power off the other one and drop the nose and get the speed up or land straight ahead if you are low. If you add power to the running engine, it will cause you to loose directional control. If you are fast when one quits, it will not loose directional control until you slow down.

Have fun with it. Twins sound so cool in the air.

kkshazzam

I can select either engine. The mode switch will send either engine to a idle setting determined by a pot on the transmitter.

Regarding rolling over when an engine quits, my plane has never shown this.

snap rolls in to the dead engine are pretty cool.

warbirdz1

Gentlemen......I might be better explaining in more detail about twins and engine outs.........I mentioned they will go on their backs with an engine failure........true...but depends on type of model and more importantly "Wing Loading"........I flew a "Duelist" hundreds of flts and it was relatively docile for engine outs.....just add some rudder/aileron and you could fly fine on one...........but the wing loading was low and its designed favorably for single engine ops.........Now I'm all involved in large scale"Warbirds" and that brings a new dimension to flying.....most importantly for twins.........its all about "reliability" as stated by TwinMan over and over........the idea is to avoid in any way flying single eng. ops....... a 30lb-50lb airplane with wing-loading in the high 40's-50's is subject to new rules ......Flyboy......Stall speeds and VMC are great to know....but how can you determine those speeds without subjecting your plane to doing just that.......its easy enough with a light wing-loaded plane but would prove "interesting" to say the least with a warbird twin.......if an engine fails its most prudent to land immediately with a warbird twin......unless it has a proven single engine capability........I'm flying a "Z" B-25 and its #2.....B-25 #1 lost an engine and was inverted faster than I can say inverted....I rolled it back over pushed the nose down and parked it asap with power @ idle.........unforunately it landed on a rockpile....hence B-25 #2............so in general flying the lighter wing-loaded twins gives single eng ops good probability.....once those wing loadings go up(particularly warbird twins) now the things change.....keep your engines/systems reliable and thats the best way to avoid trouble.....Bill......

twinman

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warbirdz1

I am soo humbled, you could not have said it better. I fly both "Bashed"twins at light wing loading and warbirds with heavy wing loading.
The light planes not only can fly with one engine relatively safely, but I have actually taken off with only one engine. (Told you twins make you nuts). It is true that there is a safe ( Relative term) for single engine flight, but as a modeler, and more so on a warbird, I would strongly suggest that it does not exist if you want to keep your plane in one piece. Yes, there are exceptions to this, but as a general rule, the warbirds are heavily wing loaded and will snap faster than you can blink or react. That is why I have done so much experimenting with gyros. They slow down the inverted death spiral to a point that you can control or at least react.
Lose and engine and get it to idle.......now!!! and land.
The closer to scale, the smaller the rudders and the bigger the problem with the inverted snap roll. The P-38 is a prime example....have wreaked three on still flying two. The rudders are very small, high wing loading, and very widely spaced engines. In most cases, it will roll over faster than you can react at almost any speed!!!!
Now having said that, there is nothing like it in the air or as thrilling to fly. ( Sorry Warbirdz, the B-25 does not do it for me..nothing personal...but then I don't own one.....yet!!!) Tee Hee

Grier

Thanks guys, i dug up some information on the wing loading...

C-160 Transall
Wingspan 1830 mm
Weight 2.85 kg
Length 1350 mm
Wing area 37.5 dm2
Wing Loading 76 gm/dm2

I have yet to venture into the part of modelling that would allow me to tell whether this is high or low!

I hope 2 irvines well run well without quitting if i give them a good run in on 4 or 5 tanks of fuel...all this flipping over malarky is scary stuff

roadtrip

Hi, Twinman. Hope your back from your Asin trip. I think you might be still out of town as I send this, while it's on my mind I better get it out. (I've been diagnosed with an acute case of C.R.S. by my miltary doc). I almost forgot what I was saying, already! All kidding aside, can any one give an opinion on the FMA C0-pilot? FMA says only one of them controls both roll and pitch, so would I need only one on my P-38, or would two still be a good idea? Also, is there a preffered on board glow system for twins that might be recommended for P-38?

FLYBOY

My Feedback: (11)

Warbirds, your right, practice and learning where the aircraft looses directional control is great to know. I had put it on other threads to do as you were saying and test it to see where it will fly on one, or not fly on one, but I didn't say that in this thread. It had just been stated earlier that they instantly go on their backs should an engine quit. That simply isn't true. That was my point. Loss of directional control which likely will flip the plane over is based on speed. If the plane is fast, it will probably not roll. If it is slow, it probably will.

I like the ideas presented about having it programmed so you can cut one to learn to fly the plane with a dead engine and being able to get it back. That is a good idea and should be done. No substitute for training. We do it in the full scale too.

TexasAirBoss

My Feedback: (22)

My experience has been that the plane does not flip over immediately, but if adequate speed isn't maintained, control will be lost. I think we have all experienced different results for various reasons. Many reasons have been stated already. One reason that I didn't noticed being mentioned, but is very important just the same, is the area of the fin and rudder. A large fin will be of great assistance with an engine failure and just looking at the photos of you r Transall, I think that plane should perform well. All twins have their limits. And all pilots do as well. I believe that you mentioned that this is only your fourth airplane. I believe it is very ambitious of you to attempt flying twins so early. Twins are very fun, but they are a different type of flying. They do require a little more planning.

twinman

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To kingwoodbarney
. Uh small misunderstanding from my explaination. This is not my forth twin, but my fifth P-38. OK so I got it bad. I have now or have had, hundred's of flights over the last ten years on twins and a few triples, and in fact do not own an "INCOMPLETE PLANE" (Sometimes called a single engine plane)
I would agree that going to the P-38 for a first twin is now good for the pocket book.
Good Luck,
Twinman

William Robison

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Twinman:

George, why do I think you've been looking at my signature line?

And this immediate rolling with engine loss will happen with any twin under the right circumstances. And in other cases you wont even notice the plane giving the least bobble.

Full throttle maximum rate of climb the plane will be on its back immediately, but full throttle screaming downhill in a dive you wont notice a thing. You just have to feel the plane out, and learn its characteristics.

Best way to handle an engine out, of course, is reliability - don't ever have one quit in flight.

Bill.

TexasAirBoss

My Feedback: (22)

Twinman:
I was responding to Grier, the originator of this thread. He says this will be his fourth model.
I thought that was a little ambitious. But I do think the Transall will probably handle OK at first when an engine dies. I base this on the large fin area of the model shown . However, it does look sort of fat and has a whole lot of wheels hanging off of it. I imagine it will slow down quite a bit on one engine. Hopefully not too slow. I would imagine he should have a good 5 or 7 seconds of relatively easy going to make his way to the approach end of the pattern. After that, it would require a little more know how.
But don't you guys think it is pretty ambitious of Grier to go for a twin on his fourth airplane? I do.

twinman

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To kingwoodbarney


Opps, my mistake..Jet lag!!!!!
Yes, if it is a highly loaded twin, I would hesitate to go to a twin so early. If it was the twin star or similar lightly loaded twin and HE CAN USE THE RUDDER!!!!!!!!, I would say go for it.

To William Robinson
Guilty..... To all, William's final line and signature is
A single engine plane is incomplete.

There is nothing I can add to that!!!!!
Twinman