foosball_movie

Hi.

I purchased a used Twin Star at our local swap meet this past weekend. Came with two .15 OS LA engines, but no servos. Thought I'd give it a try for $70.

The servos are in and I plan on tuning the engines and taking her up this weekend.

Any advice for flying twin engine planes?

CGRetired

My Feedback: (1)

Tune the engines separately. That is, start one, tune it, shut it down. Then start the second one and tune it. Tune them both as you would if they were singles.

Hopefully, the throttles are proportional and synchronous.

If you lose one engine, you can expect it to yaw quite a bit in favor of the running (that side will lead or be more forward to the other side causing a yaw in flight). Some of this can be corrected with the rudder, but get it down as quickly as possible. A dead stick with a twin can be a bit of an experience when one engine is still running.

Good luck with that Twinstar. They do sound neat when flying. I've flown one and it was a true speedster. It had a pair of .36 Evolutions on board. A real powerhouse.

foosball_movie

I am wondering how the .15 sized engines will work with the Twin Star. I read one manual that recommended .15-.40 sized engines and I read another that stated .20-.40 sized engines were required. I'm expecting it to fly ok, but it seems like it will be significantly under powered.

bruce88123

If an engine quits:
If at all possible, avoid turning toward a dead engine. Left engine dead = don't turn left. Avoid a go-around on landing if an engine is out also and keep speed up until runway is assured. Having to speed back up is risky. Engine out? Speed is your friend. Easier to lose it than it is to get it back.

Montague

The twinstar has a ton of out-thrust on the engines, which really make engine-out flying with it a lot easier. It also has a pretty good rudder and doesn't have a bad stall at all, so it's about as easy to fly twin as you can find.

However, all the twinstars at my field have motors bigger than .15s in there. While the plane should fly fine on the .15's if you loose an engine, I don't think you'll have enough power to maintain level flight at all. With .30-size engines, I've seen twinstars fly around almost normally on one engine.

The advice above about tuning one engine at a time is right on. The guys who try to adjust the needle while both engins are running always seem to be the ones trying to fly on one engine.

chopper man

Thats funny because every time I go to recurrent flight training they make use do just the opposite

chopper man

bruce88123

And you know that in a training environment is where you stress WORST CASE scenarios. I've got a MEL ticket too chopper and you don't push it with PAX on board with an engine actually out do you? You train for the worst and hope for the best. Nothings much more fun than an engine out and the "good" engine is on fire right at liftoff.

Montague

This is one of those cases where full-scale training and best-practice for model flying are different.

In full scale, you have to be able to speed up, turn either direction, etc, otherwise you die. You can't count on being near an airport or an airport you are familiar with, so you need to be able to "keep flying". Landing off-field is a bad thing, and only done once everything else has failed. And as I understand it, full-scale planes are all flight-tested and certified to meet minimum performance standards on single-engine. Full scale pilots also have instriments to measure things like yaw, airspeed, and how close you are to a sudden snap-roll.

On the other hand, models are near a runway. The pilot probably knows the field. You can land any direction you want doing any approach you want (some safety limits here, obviously), and a slow off-field flair in to the bushes usually just results in a walk, but not damage. On the other hand, the lack of any kind of feedback through instrements or "seat of the pants", combined with the difficulty of judging things like airspeed, AOA, and yaw angle of a turning model at a distance means that you easily go from "safe" to "crash" much more quickly with much less warning than in full-scale.

So, for a model, the idea is to stay as far away from any condition that causes the plane to yaw around the dead engine and enter a stall-spin-crash situation. Cutting the other engine and going totally deadstick into the bushes is a better option with many models than trying to streach a glide to the runway. In full-scale, that isn't really an option at all.

So yeah, flying a twin in RC is more different from a twin in full-scale than flying a single in RC vs a single in full-scale.

Now, if you *want* to practice engine-out in RC, it's not a bad thing to be able to do. The more you know your model, the better. But it's really hard to practice this stuff with a model when you can't get all that high up, so you can't have several thousand feet of time/altitude to fix a mistake.

And I'm not saying "never" streach a glide with the single engine, or never turn towards a dead engine. Some models in some situations are fine with both. I had an engine out with my (overweight) Mossie, and I did both. But I also lost the engine while going pretty fast, and I kept the speed up, and landed fast with the flaps up.

chopper man

I've been flying for 27 years to include coporate and the airline. Flying rc airplanes is do different than the real thing. Rule #1 FLY THE AIRPLANE. It's always fun when I watch a inexperience pilot. When something bad happens they can't push enough buttons. I say sit back a take a look at what you got. Then push the bottons
chopper man

bruce88123

I agree completely. I've seen too many screw up simple problems and turn them into emergencies by pushing buttons too soon. One guy lost an engine and his "hurried" solution was to feather both engines. Just about tore the good one off the mounts. He was fired when the plane landed after the Capt saved the plane.

aerowoof

with the 15's on this plane it will not fly on one engine .25 is about the minimum for single engine flight.what will happen if you lose an engine is the good engine will raiise the wing and start to roll all you can do is cut the other engine to idle or kill it,if you are abl.e to stop the roll as the plane slows down and the wing with the dead engine stalls it will do the samething but you will be flying to slow to stop it without gaining airspeed,only way is to dive but hard to do while rolling.just be prepared as the plane is some distance from you due to the lag from the sppeed sound travels by the tome you hear the engine dying it has allready quit,just watch for a wing to start rising without any control input as this is a sign that an engine is going sour or quit and use rudder to correct not airlerons..for instance the right wing rises unexpectely use right rudder to correct if it keeps rising throttle back,this will all happen in a blink of an eye.the larger engines will keep the airspeed at a safer speed on one engine so that it is controllable.

bruce88123

On takeoff, keep the nose down and get the speed up. Once speed is up, establish best climb rate and circle close to field until good altitude is obtained.

Cyclic Hardover

My Feedback: (3)

I built one with a pair of .25fx's. Flew fine.

jetmech05

Never ever turn into a dead engine...props are different than a jet..in full scale you can and will feather a prop..rc we can't we're stuck with all that drag..so engine out reduce power and don't turn into the dead engine...
there was a crash at cherry point 10/75. they'd still be here, but couldn't feather due to pitch locks and turned into the dead engine then lowered the gear

acarter

Are you an ama member, if so did you get the last magazine, The whole thing was about twins, Very good instructions on tuning and flying, Good luck

Ed_Moorman

My Feedback: (1)

I am on my 24th twin and I also have a TwinStar with 2 GMS .32s. It now has larger ailerons and is on floats and I don't recommend those engines.

It doesn't have much out thrust, only 2 or 3 degrees. To cancel yaw on 1 engine to where you don't need rudder, you need 8 degrees out thrust and I have tested this on more than one plane, but not on the TwinStar (Twin Stick, Tiger 2 twin conversion, World Models Sky Raider Mach II twin, A-frame original twin).

The absolute best thing you can do is follow the advice given above about tuning each engine by itself. You do not want to peak them out. You want them leaving a nice smoke trail, otherwise, one is sure to quit.

Here's a couple of other maxims I have learned the hard way. 1. Never tune one engine of a twin with the other one running. You are sure to screw it up. Shut down, set the engine and crank the other back up. Trust me, here.

2. Next, never let your buddies tune your engines. They haven't a clue about twins and they will get your engines too lean. If they reach for your needles, yell, "NO," or shut down and tell them to keep their mitts off. Trust me on this again.

With two .15LAs, you are going to be in trouble if one quits. If other people are flying, you may not hear one engine slow down and quit. If the plane does something weird, no matter what, you have probably lost an engine. Chop the throttle back to idle and pretend you are dead stick. If you see both fans turning, then throttle up part way. If one is out, you might be able to hold rudder and get some power out of the remaining engine, but you probably won't have enough for level flight. Aim for the grass or somewhere away from trees, etc. A hard landing is better than a crash.

rcluver

I agree with aerowoof, I don't think it will fly on a single .15. I have a Twinstar, I put LA .40's on mine. If I have one quite, you barely notice it, however, the down side is reduced flying time account the small fuel tanks. I think if I were you I would replace the .15's. Good luck.

Cyclic Hardover

My Feedback: (3)

I don't have nearly the twin experience as Ed here but have set up a few and agree on dialing the engines in one at a time without the second one running. Then tweak from their.

Dc2LightTech

I am unable to upload the pics of my twin, it was 50% my own design so I had no idea how it would perform on the first flight. After geting the engines all tuned up, i got in in the air and kept it high over the field at all time just in case i had a engine die. As luck would have it, the fuel line came off in flight (see my gallery). i only had 3 flights and did not want to deal with thrust issues so i killed the good engine as it was in a good position to glide in. I made 2 mistakes that day, first i let my friends tune the engines and then i set the idle too high and the landings passes were so hot i found it easer to kill the engines after i was set up to land[X(]

fling the twin is a real adrenalin rush!

foosball_movie

Ahhh, success.

First off, I was wrong about the .15 OS LA engines. They are actually .25 sized. I was pleasantly surprised when I was asked at the field, "What sized engines are those?" and I doubled checked to find the 25 on the side. So I knew I had enough power to fly comfortably.

I had originally decided to use a Y-harness on the throttles, because I couldn't figure out how to program my DX7 transmitter to work with the two throttle servos. But once at the flying field, one of the trainers was able to show my how it's done (here's a hint, when setting up the mix for the AUX2 --> Throttle, be sure to put 100% in both rates. The servo will act like it doesn't work if the rates are at 0%).

So after about an hour of tweaking the mix, I fired up one engine and tuned it. I was very happy the engine started right away, because the plane and engines were purchased at a swap meet. I shut down the first engine, then started and tuned the second. I set both so they were fairly rich. Then I started them both.

The sound of those two engines singing together put a big smile on my face. They sounded fantastic. I actually preferred the sound of them idling to the WOT. I did have a problem however. The mid-range of the RPM were way off. At half-throttle, the right engine was nearly WOT, while the left engine was correctly opened. The RPM difference was around 2000. The idle and WOT were almost exactly the same RPM, but I knew the mid-range was important so I didn't take her up. I did taxi for a couple of minutes. I thought I had perhaps put the servo arms on incorrectly, so I packed everything up and went home to investigate.

Turns out I had adjusted the idle location of the right engine with the sub-trim on my TX instead of using the mix rate. I don't even know what sub-trim is supposed to do (I'll be starting a new thread in a little bit), but I used it to tweak the idle to match the right engine. I returned the sub-trim to 0% and used the mix rate to match the right engine. Problem solved.

Back to the field on Sunday. Fired up the engines, a little tweaking of the idle, mid-range RPM were within 200 of each other, looked good. Taxied to the runway with the props trimming the top of grass along the way. I may need to replace the small stock wheels with some larger wheels to give me a little more space between the props and the ground. Full throttle. She used up almost the entire runway but finally lifted off. About 5-6 right clicks on the aileron and she was trimmed. Flies great. Reminded me of my Hobbico Hobbistar trainer. Very stable with some quickness. Sounds fantastic during low-highspeed passes. I felt she was a little loose at slow speeds, but not too bad. Inverted, rolls, loops and my attempt at a knife edge went very well. Probably one of the easiest planes to land; however, I've only had four planes.

The four-ounce tanks are a big downside. I gave myself 5 minutes on my timer. By the time I taxi and take-off, that leaves me around 4 minutes of flight and I had better get the landing right the first try. Tanks were practically empty when I landed.

A great plane. Highly recommend. Another pilot had his Dual Ace with two .45 engines at the field Sunday too. That's a good looking twin as well.

Dc2LightTech

I have 4 tanks in my twin. I run 2 in series for each engine. a 4oz in the necel and a 6oz in the fus.
the exaust tube runs into the vent line of the fus tank and the fuel output runs into the vent of 4oz necel tank. the fus tanks are located as for forward as possible. i don't seem to have any fuel flow problems going vertical.

bruce88123

Congrats Foose - you're a multi pilot.

aerowoof

as you found out on the take off roll the 15's would have been very marginal.Congratulations on a successful flight but always be rady to cut the power any time the plane does the un expected.

foosball_movie

Interesting. I have plenty of room in my fuselage. Can you post some pictures of your set-up?

Dc2LightTech

I hope the pics upload as it did not work last time...