This probably isn't a tru beginners question, but a new to me anyway. I just couldn't control myself any longer and bought a P61 from Hobby People yesterday. It was on sale and it has been wiggeling it finger and saying "come on, you know you want it" . Turns out that a couple months back, when they had that super sale on Mag 52 four strokes, I picked up two and this bird just happens to use that engine. They delivered it today. NOW comes the big question, can I fly it. I've been flying for almost three years, I've crashed my share and some, but I'm almost a year now with out a crash. I've flown trainers, and 3D planes, as well as a couple 4*60's. Even a quicke500. Twin engines though are going to be a completely new experience.

I'm starting with a pair of new, never run engines, so things should be equal on the power side, once I get them tuned right. I'm wondering though if I should setup with a slave to the throttle servo for the second engine vs just a Y harness. I'm flying from a Futaba 9C supper, so channels arn't a problem yet. I was just wondering if it would be easier to balance out the throttle response with two channels or not.

The other thing is retracts. The ARF kit is designed around their own retracts, but also gives the option of fixed gear. My thoughs are to use the fixed gear at first and then add the retracts latter. I'll know more once I've started the build if this will work or not, but I think it should looking at the construction manual. I'm wondering if I could use the lado electric motor retracts and make my own struts.

To many projects on the bench now. I've got to finish up the 1.20 pattern that I'm refurbishing. I just got the head for the engine back from Clarence Lee today, he put in at new set of glow plug thread for me.

After my rambling, the quesiton is flying a twin engine, espically this bird. What do I need to look out for. I would like to have it ready for our club fun fly just before Memorial day, but I'll not rush it.

Don

Unfortunately, there's no way to get into twins slowly. You gotta run with the big dogs or stay on the porch.

There is really no difference at all flying a twin... Until one engine quits [X(]

IF that should happen, you'll want to drop the throttle, add rudder to the side with the good engine and start planning your landing ASAP

You'll need to hold a lot of rudder and avoid turning toward the dead engine. If you're the praying type, go for it. If you're not, this is a good time to start

I perfer to keep the throttle simple and get the engines in sync manually. Here's how I do it:

Put a pin inside each carb barrel and close the carb on the pin - now you know that both carbs are in the exact same spot. Make sure that both servo arms are exactly the same. Note: If you're using Futaba Servos, the 6-point star shaped servo arms can be rotated from one arm to the next with slightly different positions to make it easy to match them.

Now with the throttle at idle, adjust both throttle linkages so they align with the throttle arm on the engine (While they are still closed on the pins).

Now they should be mechanically in sync.

Start both engines, go to full throttle and adjust the high ends until you can hear that they are in sync (Or use a tach if you can't hear it)

Go to idle and if they are not in sync, see which engine transitions better, then adjust the low end on the OTHER engine.

Mike great input, exactly what I was hoping for. Thanks a bunch. I know I'm not ready for this bird, but at my age, ability and experience are on conflicting curves. So I might as well make the jump now. It anin't going to get better. By the way, I'll use a tach with the hearing being on the curve with ability [&o]

Don

Mike reading your post for the third time, I am amazed at the good info included. There is stuff that really doesn't directly apply to the twins but is useful for a lot of other things. IE the futaba 6 point servo arm for one. I always assumed that it didn't matter which arm you worked with, but now I know that wasn't correct. Great input. It will apply to something else along the line I'm sure. IE aileron setup, and for this bird flap setup. WOW. Thanks again.

Don

Don,
If you have'nt already seen this, here's some good info on the plane, I'm working on their A-26 right now.

http://www.rcuniverse.com/forum/m_5364231/tm.htm

Yes, this is a feature that I really like about Futaba servos

Don:

What Minn had to say is dead about twins is dead on point: as long as both engines are running, twins fly like singles. But having flown (and lost []) two twins, and with a Wing B-25 that should be finished in the next 3 months, a few things to consider.

1) The Magnum 52 is a great engine... once it's broken in. One of the guys at our field has one in a trainer, and until he'd run about 1/2 to 3/4 gallon of fuel through it, it was pretty finicky. Now it's his favorite engine. So I wouldn't fly the P-61 until you've convinced yourself that both of your 52's will idle and transition properly.

2) Your P-61 is a beautiful bird, and it would be a shame to lose it on a twin maiden. Prior to flying the Widow, you might want to find one of the cheap ARF twins (A Twinstar or Dual Ace), and use all the servo's, receivers, batteries, engines, etc. for the P-61 and get some time on on a milder twin before going to a warbird. Yes, this costs $$$. But it might save lots of grief. (Also consider that if your radio will provide individual throttle control, and you get really brave, you can try "engine-out's" in a controlled fashion.)

3) There's a ton of info on flying twins over on the RC Warbirds sight, and in the Twins forum here.

Good luck with it,

Fred

Yup, just put your Big Boy pants on and go have some fun!

Fred,
I have a Mag 52 that I started with on my trainer. I later ran across a couple O.S 52 in new conditiona and Switched the trainer over to one of them. It was not a finicy as the Mag. I traced the mag idle issues to the carb and Hobby People replaced it, but it still didn't run as well as the O.S. engines did. I checked the carbs and the O.S. is a bolt on replacement for the Mag. I've now got an O.S. carb, curtiosy of a crash, that I'll put on one engine, and I'll pull the carb off the O.S. Im flying now. That should help with the problems I had before. Humm, I've got my little funstar with the other o.s in it , I' should be breaking in eingines now, I never even thought to use it as a break-in airframe. If I switch carbs, the mag is a bolt in replacement for for the o.s. in it now. Beter than setting in the back yard listening to an engeine run for hours.

Stuntpplot, thanks a bunch for that link. I'm sure I'm going to be reading and re-reading it as I go along.

I really want retracts in this guy, but they seem to be on back order for ever, one part or the other. I've been considering making a set with motor drives to fit. I'm hoping that I can used the fixed gear until I get the retracts done.

Back to work.

Don

Sort of related question I had but didn't really want to start a new thread...

I have a 46AX with a full season's use on it and have been thinking about using it for a twin. Can I buy a new 46AX, break it in with a few tanks of fuel, and use them both for a twin engine plane? Or is it strongly recommended to buy the two engines together, new?

Sure, even two engines bought at the same time might not be exact

you can use twin sync to help with the engine out scenario and a gyro on the rudder would be a big help also

Don:

Your idea of using an older Funstar as a breakin platform has merit. That's what I'm doing with a pair of Magnum 70 4s' for the B-25, flying them in an older 46 sized airframe. But between running them inverted, starting problems with a glow driver, seemingly low power delivery, and deadstick problems, my confidence level is not what it needs to be for using them in a twin. Just make sure whatever combination of Magnum/OS parts you use is performing reliably enough that the engine is the last thing you think about when you go fly.

Aerowoof has a good idea about the Twin-sych... I'm considering one of those with their on-board glow option. But between the cost of the Twin-sync, and possibly a gyro, you now begin to see the other problem with twins: they get expensive, and fast.

I seemed to have not posted the response to a couple other post.

Aerowoof, I played with a gyro on my first tail dragger. It really helped keeping it pointed straight down the runway on take off. It did effect the turns though as I don't use rudder in turns. I may have to learn to do that
I'll look into the Twin sync, It sounds like a good idea

FallDown, I've been flying a 70 for a couple years. It was an absolute nightmare to get running, until I read the manual and started over. The carb is different than most as the mix needle screws out to a stop vs screwing in. Once I read the manual, and set things to it's start point, the engine fell right into place and has been rock solid since. I crank a 13x4W prop with it and it pulls like a tractor. Mine only took about three tanks before it was in the grove. My Mag 52 though was a royal pain.

I peaked a bit deeper into the box today. Boy are the engine booms light weight stuff. I' suspect this will be a crash once plane, although the wings look well constructed. Time will tell.

Don

Don:

I appreciate the info on the '70's... think I'll go re-read the instruction manual, as turning the low-end screw outward to lean the fuel/air mix is 180* out of phase with all the other Magnum carbs I've used. Wonder why they did that?

Fred

Fred, it still turns in for lean, it's just that the stop you reference from is fully rich vs fully lean. Set the start points up per the manual, I think it is starting with the head of the Idle Mix flush with the throtle arm, but I don't have my manual near. Once you set the start points per the manual, it will adjust like any other carb.

I found that running the first three or four tanks on the ground with it really rich on the top end and keeping the idle about 3000 or faster got my breakin going OK. OH yes, I mixed 6 oz of drug store pure castor to a gallon of Omega 15% for my break in fuel.

The method I use to setup a four stroke is after the break in adjust the high speed for peak, then back off at least 600 RPM. Then with the TX to as slow as you can and keep the engine running. At this throttle setting slowly lean out the idle mix for maximum RPM. Now go back and peak the top end again. Back to the idle again and this time you should see it drop to around 2400 or so. Again find the slowest speed that it will keep running at and again adjust for maximum RPM at that throttle setting. It wouldn't hurt to do this sequence one more time. The 70 should idle very well at 2100 to 2200. With fresh fuel, mine will idle at 2000. Now for the transistion, run the engine up full throttle like you were clearing it our just prior to take off. Now go to full idle and let it set for 15 seconds or so then punch full throttle as fast as you can move the stick. If the engine coughs and dies, the idle is to lean, open it up 1/16 turn at a time to where the engine jumps to life on full throttle. If it sputters and either doesn't gain RPM or very slowly gains RPM, it is to rich on the idle, so now 1/16 turn at a time until i jumps.

Of course all this assumes a clean fuel line setup with no air leaks anywhere.

The Magnums some times have kind of loose tolerances on cutting the mix needle Oring Groves. If the mix needle isn't slightly hard to turn, you may have one of these under cut needles. The Oring should be very snug and a bit stiff to turn. One other Magnum tip I found and it proved correct is that the Highspeed needle is the same PN for all four strokes and most of their 2 strokes. However the needles in the engines when they are new are not all the same. My Mag 52 had a quite stubby taper, and I replaced it with a new needle which was close to 2mm to 2.5mm longer with a finer tip. This made finding the sweet spot a lot eaiser. It's a $3 fix if you need to try it.

Good luck. Let me know how the engines wordk. You know, I just remembered. The Mag 70 recently had a problem with weak Valve springs. They were replacing them if you had a bad one. I ask them how to check as I have a 70 NIB that I didn't want to start yet. The instructioins were, take off the rocker cover. Push on the valve end of the rocker. If it hurts your finger to put the valve open, they are OK. If it is easy to push them open, they need to be replaced. It is an easy check and probably would be worth your effort just for the peace of mind.

Don

Don, I could have saved you some typing...

The pair of Magnum 70's I'm working with are both a couple of years old, and were pretty much broken-in as you suggested (the only thing I didn't do was add the extra castor, which is a trick I learned last fall breaking in an OS75AX). I'd also heard about the valve spring problem. After lots of difficulties (no top end rpm and a couple of fatal dead-sticks) last fall, I finally got so PO'd I sent 'em both back to Global with a letter that said (short version!) "... I can't make these run, maybe you can." Three weeks later, both engines show up in the mail, repair papers included that show about 10K rpm top and 2200 idle; they replaced the valve spings on one of them and added new head gaskets. All at no charge; I can't say enough good things about their service department.

Finally got enough of the snow off the ground last week that we got airborne again. I flew one of the reconditioned Magnum's, and once it was running it seemed stronger. I still have starting and idle problems (it wouldn't start using the onboard glow, and the idle was too fast), but those are probably more related to the inverted mount (idle's probably too rich) and the glow driver (battery?) than the engine. At least I hope so. I have yet to check the actual RPM with a tach, and the engine died after about 6 or 7 minutes airborne. That could be related to the idle problem, and I also need to dig the tank out and make sure all the internal lines are the right length. But at least it didn't die two feet off the ground during take off.

The plan now is another try at the inverted mount operation. If that doesn't work, I'm gonna side mount the engine and see if performance and reliability improve. Also went from a 12x6 to 13x6 prop, which should give me little more "umpfh". Whether that shows up as vertical pull or horizontal speed, I'm not sure.

Now if the sun will just stay out for the weekend... !

Fred

Fred, I've got an O.S. 52 mounted with the head at 7:30. Not fully inverted, but almost. That enginge runs awful for the first two minutes or so from cold. It won't spool up right, sometimes quiting at more than 1/4 throttle. The strange thing is that once it is warmed up, it is solid as a rock. Once it cools of, it is back to it's bad habbits.

I pulled the rocker cover to check the gap a while back, and about a half teaspoon of oil poured out. My guess as to what is going on with it is that the rocker cover, and the piston are collecting a load of oil after running. The crank vent is now on top, so what ever collected around the cam, can only drain into the rocker cover. My theory is that this oil is screwing things up untill it gets heated up well and vaporizes again. If I don't wait to long between flights, or it is a hot day, the first start of the day is the only troublesome one. I've just come to accept this and I let the engine run for at least two minutes at over 1/2 throttle prior to the first flight. I'm wondering if you may have some of the same issues.

Don

Well, the sun's in hiding, and the wind's blowing, but since it hasn't snowed... yet...

Put the Magnum up again today. Went to a 13x6 prop, and first flight of the day the on-board glow got it lit. Leaned out the low end by about 1/8 turn total. Take off was shaky, but once airborne the engine ran fine. However, most of the flight was at full power, and my flying partner thought the plane didn't fly as well as last week, with a 12x6. And wonder of wonders! no dead stick. So I had to land under power, and dinged the end of the prop.

So I changed to a 13x8 I had in the flight box. The Magnum wouldn't start with the on-board glow, but we used a normal glow ignitor and it lit right off. Put the plane out on the runway, hit the throttle, and the thing just jumped off the ground! Much better throttle response, and a bit more speed in the air. Loops, hammerheads, and humpty-bumps were much better. Still not as smooth as with a .46 2s, but I think that's the difference in 4s vs. 2s power delivery. The only real problem was landing... the plane wanted to balloon (maybe if I wasn't flying in 20mph wind!), and that prop thingy wants to dig holes in the ground. Sometimes I think deadsticks are easier: you get one shot so it's total concentration and you do everything right!

So, at least some positive progress. Next step is to see if I can slow down the low-speed idle, and to figure out why the high-speed needle is so finicky... one click either way drops engine rpm. I'm going to have to check out the length of my needle valves per your tip.