Four engine model
 

I have a few experiences building and flying my first twin http://www.rcuniverse.com/forum/m_3862333/tm.htm. I red this forum a lot of before start to build the first twin. Also I found a lot of useful information about flying twin models.
Now I’m thinking over a next project. May be it will be four engine model.
What kind difficulties I shall meet during building and flying such model?
Nobody fly’s multi here. My model is only one. I can ask help only here.
Thanks.

RE: Four engine model
 

I have enough trouble trying to keep one engine running, and you're running two?

You are to be complimented!

Now you want to use four?

RE: Four engine model
 

Hi,

Actually i'll second Yury on his confidence level, i have just started flying Twin engined models, i have 2 twins currently and looking for third one!, i want to fly twins this season and learn from them, then over the winter i am going to build Quad engined model (4 engined)!, i feel very confident while flying my twins and don't think it would be much problem flying 4 engined model as long as all 4 engines are breaked in similarly and synked in togather properly....


Sammy

RE: Four engine model
 

Yury,

What size engines are you thinking of using?

I have a twin .25 size plane (I use .32's) that I fly a lot. I'm thinking that with 4 engines it won't be so critical if one quits. On the other hand there is more chance that an engine will quit. Getting 4 engines syncronized to an acceptable degree might be a challenge.

Glen

RE: Four engine model
 

Hi Yury!

Great that you fly twins! Multis are in my opinion very interesting planes. They get a lot of appreciation on the airfield and in the air, even if they are not built in such a high quality as a lot of other models are. Also in the air noone can stop looking at it even if one only flies some circles and slow lowpasses... it's the number of the engines and their incredible sound!

So far I have no experience with 4 engines, but I have been flying my Armstrong Withworth Whitley for 5 years now (and it still lives :)). In this time I have experimented a lot with the two at least 25 years old OS FS 40. One runs 7500, the other 9000 rpm, but the plane takes this easy, even if one of them failes (what unfortunately happens quite often....). In all this time I informed me a lot about more than two engines - on RCU, but also in some german magazines. In one I found an article from Otto Mulert (see also http://www.mulert-fotografik.de/modellbau.html ) with a lot of very useful tips. I redesigned and modified the Whitley after his tips and I am urged to say it flies very vell - and more or less safe! Also his 4engine planes, built lightweight and with a good profile (e.g. NACA2415, TNT) fly very well. After cleaning up my hangar (Which includes the finishing of a Turba Panda, also a Twin), I am thinking of realising also a 4engined "Monster" [8D]

I think, regarding some basic rules and the slightly bigger work (for nacelles etc.), building and flying Multis is realistic and provides great pleasure! Go 4 it!

regards, Chris

RE: Four engine model
 

Likewise I have been successful with twins and the prospect of a four-engine model is gnawing at me.

Finding the correct airframe to adapt to four engines appears tricky. I would like to use .40/.45 size engines that are not in use. The two possible candidates for me are a 4 Star 120 with sheeted wing or the newly released Phoenix twin from Cedar. A 4 Star 120 is a stable platform. Maybe a Phoenix build thread will be available soon.

Runway creep will probably be a concern that needs addressing. Slowing the airplane down for landing might be an issue. Four engines turning at idle might want to keep the airplane flying.

Engine out is not likely to be a problem with 4 engines. The probably of two going out on the same side is remote. Synchronization within 500 RPM doesn’t seem to bother twins and will be less important with four. However take off is difficult and erratic when the engines don’t spool up together.

Bill

RE: Four engine model
 

Guys i also think that 4 engine airplanes carry alot of grase in the sky and are very attention grabbers at the field and at contests, i got myself plans for Super Connie L-1049 "C", but i will turn it into Super "G" without much work...its not going to be big model but fair size at 80" W/S, i am thinking on powering it with 4x OS20 4 strokes or 4x OS15LAs....

This is going to be my winter project this year.....



Sammy

RE: Four engine model
 

Hi!
I see I am not along wishing 4 engine model.
I am thinking to use four Magnum 30 4 stroke. I have two ones now.
My modest experience with bashing pattern ship into twin says that sum of displacement of engines should be the same as single one. I can compare twin US40 with two 30 4 stroke with single US40 with one 70 4 stroke in front. The models have the almost same weight(plus-minus 50 grams) . The single has a little bit more thrust as twin. The twin descents sharply as single due more drag. The single is speedy on touch down. The bigger engines adds weight only and flying speed. I guess that multi have to fly with running all engines and when one engine quits its time to landing.
I am going to use draft f3a model for 120 4 stroke as base. It has span 1.8 meters (near 6 feet). The model will be taidrager for keep weight down. I did not meet any problem with taidrager twin on take off.
I did not try to synchronize engines. Each engine was turn individually for best performance.
Now I do not see any problem with 4 engine model compare to twin from my few experience BUT I do not have enough twin and any 4 engine experience.

RE: Four engine model
 

Yuri:

Four engines? NO! Not enough! At least eight engines and then you can consider yourself a "Real" multi engine modeler.

Haw.

Bill.

RE: Four engine model
 

Yury,

Four Magnum 30 four strokes will sound great together. Good choice.

RE: Four engine model
 

Yury, I too had the same questions on Multi engine planes. One day I ran across a set of C-130 plans very simple design. No retracts, no frills foam fuse and built up wing. I cut the kit learned to cut and glass foam ect. Picked up 4 new OS 35 engines broke them in on the plane and had at it. Most fun I ever had. Never put a tach to them just turn one at a time till they sounded right. Just go ahead and do it start with something simple and get engines that run. Thinking now of a B-29. Have at it. Good Luck.

RE: Four engine model
 

Hi Yury,

about the engine size... I think it depends on what you want. If you want it fast, you can divide the total displacement by the number of engines. But if you hava a scale airplane which should be flown like the original, you always have too much power! (according to Otto Mulert, and it is also my experience; the Whitley, 6 kg of Weight, takes off with two 6,5 ccm Four-stroke engines after no more than 3 Meters!!!, and normal flying ist somewhat above idle...) Consider that the propellers of the four engines produce a constant flow over quite a big part of the wing, so you have a not too small amount of lift even at idle and in the plane standing on the ground!

There lies also the big danger in flying multis - if one engine stops, this given amount of lift is gone and the plane will drop a little to this side. And - consider that, when landing, a lot of props, especially if they are not moving any more, cause a lot of drag wich will lead to a quite steep descend.

Regards

Chris

PS: Under some Balsa rests I found some ribs and formers for a 3meter /118" Nakajima G8N1 Renzan I cut two or three years ago today... :)

RE: Four engine model
 

Yury,
I have done a 4 engine model and it was great fun. My priority was to have reliable engines so I used the OS .25 FP because it is so easy to set up. Even though it is not a strong engine it was the right choice as I never lost one during flight. Good luck on your project and post some photos when you get it done.
Paul

RE: Four engine model
 

Hi Guys,

I just blew up plans for Super Connie from 73"W/S to 100" W/S, this will be my winter project. I am looking forward to multi engine planes now, I am going to use 4 x .60sz engines or 4x .90sz 2 stroke engines. I am loving every flight i have on my B25, plus its attention grabber at my field, when it starts everybody's attention goes on my B25!!, at time when everyone is looking at it, it make me nervious and i hope nothing happens. Any how keep up your sprits high and we all have to start at one point or another.....

Rcmiket,

Your C-130 is awsome looking bird, is it a kit or scratch built or ARF?, C-130s are one of my favorites also, i woulden't mind having on of there at some point in my RC carrier...


Sammy

RE: Four engine model
 

Hi All,
I've done several 4 engine models. My last was a 4 engined Twin Star. You can get the extra cowls from Tower (they sold me mine), with cowl covers and fuel tanks too. I installed dual main gear tires for looks, and the model is still alive after four years. The first engines were MOCA .32's...and way over powered. Next re-engine was with OS .10's and now, .15's. The .15's are a perfect match for this airframe. I also installed Flap/ailerons too. She rotated on take off better with a little flap and gave you more elevator authority at round out, on your landing. NO GLIDE. Easy to bring in and land, very predictable, and she is not, a floater. Carry some power to touch down, for it is a draggy airframe with four engines...and those dual mains didn't help either. Get all the rudder you can, and I would suggest adding another 1/2" to the rudder. She will fly with three and very controlable...She will fly on two...but with two out on one side...your going to need to pull power back to at least half throttle or less, and head for the runway ASAP. When in doubt...just pull all the power off and take what you can get. You will need to hold some rudder, so get your rudder thumb used to it, and if two are out on one side, all the rudder to the live engines. Control first, then the runway, is how I look at flyng multi's. But I've always made it back to the runway...and I love this little model. The fuel tanks are small...about 4 oz. But with .15's, a good ten minute flight is a reality.

Four engines are a lot of fun...and a lot of work too. I spent one day running and adjusting my engines for each day flying. If I could not get them to run reliably...I didn't fly...and why I still have a flyable model. By the way...I've a two engined verson also of the Twin Star. It's a good solid flying model, with two, three or four engines. I've never seen one with five engines, but Twinman is nuts enough to do it...he did it to a perfectly good flying 4 engined B-17. It looks like some guys will do anything for a little attention.

There is an inexpensive Twin Stick ARF available (Ceder Hobbies), it's a good flyer too, and would convert to four engines easily. I've built the old Midwest version of the Twin Stick from a U-build kit, to four engines. Four K&B .19's flew it really well.

Weight is the factor in all of this...and with four of everything...keep it all in focus. But it sure is a lot of fun...and the sound of four turning...is about as good as it gets.

Soft landings,
Bobby of Maui

RE: Four engine model
 

Well guys if you don't mind me chiming in. I have two bashed twins one is an electric version of a C-47 converted to glow OS 26 fourstrokers and a tower Voyager coverted to a twin also with OS 26 fourstrokers:D. The Voyager I've been flying for about two or three years now and have had a couple engine out situations ( learning curves) and have had to do some repairing. I did finally decide to increase the rudder:eek:. On the C-47 flys like a dream and lands even better. I am currenly working on a Wing P-38. It will have Mag 52 fourstrokers on it. So far the weight is about 15lbs. I also have a Wing B-17 with the fuse and wings sheeted and waiting for me to get back to her and finish. I also have a B-24 under the bench waiting for me to get in gear and start on her. Again the B-17 and the B-24 will either have OS fourstrokers or possibly some LA 15 or 25s not sure just yet. Two sound great but four sound even better.;)

RE: Four engine model
 

William Robison
Why not in future. Single – twin – 4- 8 – 16 …… Who knows?
On Russian we say one – two – a lot of. On modeler’s language it sound as single – twin – multi. Real multi starts from 3 engines. Twin is not multi engine model.

Multimaniac
I tried your link but I don’t understand German. I’m thinking about sport model no scale one. May be in future I’ll be build Pe-8. The effect from flowing air over wing from engines I noted on twin. I understand that on four engine model this effect will be bigger.

ps2727
Can you write the specification of your model? Wing span, weight ets. 25 fp is close to 30 4 stroke. Thanks

RE: Four engine model
 

Hi Yury!

Give me some time.... I will post an abstract of his tips here, together with a little summary of my experience (sorry, I didn't think about the language!)! - The tips may be valuable for every twin or multi engine plane, no matter if scale or not scale!

regards
Chris

RE: Four engine model
 

Yury,
My model was 86 in span, 18 pounds and built to 1/16 scale ( douglas DC-6 ). It was rather heavy with a wing loading a little over 50 oz/sq ft. Still it handled well just a bit sluggish like the real one, I suppose. Try to keep it light but don't be put off by a higher loading than what is considered "normal". I used a small tank in each nacelle as well as a small servo on each throttle. That way the wing went together as four separate fuselages rather than share fuel tanks and throttle linkages. The inner engines required homemade fuel tanks because of the tires when the gear was retracted. Also, I set all engines up at 0 degrees -- no out or down thrust mainly because I didn't have access to rcu to ask the pros!
The other guys here probably have much good advice for you - my way may not be the best or easiest way to do things! Good luck on your project.
Paul

RE: Four engine model
 

Here you are...

ABSTRACT OF O. MULERT'S ARTICLE ABOUT MULTIS IN "MOTORFLUG SPEZIAL" IN THE LATE 1980IES

About the design of multis:

- The bigger the model is, the better it flies because it becomes more stable
- Build as light as possible! The lower the wing loading is, the better the model flies
- Profiles like the good old NACA 2415 or the TNT are superior to e.g.the Clark Y in terms of flight behaviour
- About engine size see picture below

About the engines:

- Each engine mount shout be one part with a rib. This provides best force transfer into the wing.
- One tank per engine, and as close as possible to the engine!!! In general you don't need an acro tank
- Mount the engines horizontally resp. in the axis of the wing. This helps avoiding resonance of the wing/engine system because the forces of the pistons are moving in the axis of the wing. Otherwise, if you adjust all engines to maximum power, the vibrations can loose the engine mounts/engines!!! And - the exhaust is on the lower side. Abundant fuel can easily flow ot of the exhaust and will not block the engine at the starting procedure.
- One channel for all engines - either all are running or all can be stopped by moving one single stick or switch on the radio!!! In flight you don't get out wich one stopped exept flying very low, but then it's over anyway!
- Mount the engines with 0° downward angle compared to the FLIGHT AXIS (You always have too much lift, so it will climb anyway, if you add some downward angle or not!), and, very important for easy flying, give them 3 to 5 degree outward direction!! (Look at the original Ju-52, the side engines have 5° (five!!!) outward angle!) This leads to 1: rpm-differences up to 1000 rpm do not matter! maybe, if there is no wind, the whole plane drifts slightly towards the stronger side; 2: in case of engine failure, this drift becomes a little more impressive but the plane is still controllable.
- It does not matter if you use engines of different types or differen age. Adjust throttle so that the thrust (measure with a spring balance) is about the same. E.g. you can power a twin with a .40 and a .60 engine, you "simply" need to reduce the throttle way on the .60!

About the most important: Flying

- Let yourself time for preparing all engine before the starting procedure! Chech all tanks, glowplugs etc.
- run the engine 10 to 12 times by hand whitout heating the plug before starting
- The starting procedure of up to 6 engines should not take longer than one minute! Begin (in the sight from the starter) on the left side and move to the right.
- Adjust the engines only approximately to the same (full) power
- For Starting: give throttle only until the plane begins to roll. Slowly give more throttle until it takes off (more or less without the use of the elevator!)
- Fly multis using the rudder and the elevator. Use the ailerons only for correrctions.
- In case of one (ore more) engine stops:
1. reduce throttle to idle or, if necesary, stop all engines
2. hold direction only (and O N L Y !!!!) with the rudder --> you will generally get back to the runway. If you begin to move uncontrolledly with every flap on the plane you will promote some form of stalling, then it is definitely lost. In case of stalling, let it dip and get some speed before you do anything else!


Most of those tips mentioned above apply with my experience! I built my first twins about them, and until now I really had little problems. Sure, there are points to discuss... [8D]
regards,
Chris

RE: Four engine model
 

Yury,
I forgot to say that I had a .25 sized trainer that I used to break in each engine with it's custom muffler. It gave me something to fly while building the plane and was also part of the project. I would never recommend you use a brand new never-been-flown engine on a multi.
Paul

RE: Four engine model
 

...Sorry coulden't upload tiff file....

RE: Four engine model
 

Multimaniac
Thanks for information. My twin has all your wrote except thrust of engines and foil. They were installed 0-0 and the wing has original symmetrical foil. I can’t tell that it’s overpowered compare to single one.
I know a lot of Switzerland’s are multi languages. Some years ago I spoke to Francua in Neon on English. At the same time he spoke to staff in the office in French and by telephone in German.

Paul
Thanks. It’s very useful information. I also made breaking procedure on stand. Each engine had at least 2 hours working time.

RE: Four engine model
 

Here is my "test" plane.
I have flown twins for years and
wanted a lot of stick time before going to huge b-17.

Bigstick 410
4 o.s. 10's bigstick 40 kit

I have about 40 flights. Patially filled tank(s) to have a engine(s) out drill.
Flys great on 4
Flys well on 3
Flys ok on 2.
Major handful on 1. I had one engine throttle stick wide open
made it fun,scary, to land so I went high throttled to idle and waited till engine died
powered up the 3 and landed

Tips
1)Remote glow a must
2)Reliable engines
3)patient ground crew takes 4 times as long to set up and
tach engines etc........
see 1st few test flights @ www.baxterfield.com

RE: Four engine model
 

After many hundreds of multi engine flights over many years including a model like Mosert's my advice can be summed up in just 2 words:

GO ELECTRIC

The B-29 has 2 x 40's & 2x20's, the B-36 6 x geared 400 electrics on 24 cells. - John.