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Eng Questiom

Old 01-12-2017, 05:19 PM
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dlpjr
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Default Eng Questiom

The plans of the plane I am building suggest using two .40 eng. I want to use two 4 stroke engs on it. What would be the size of 4 stroke I need to buy.

Thanks
Old 01-12-2017, 06:11 PM
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rcjetflyer0718-RCU
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If the plans call for 2 stroke 40 engines then a 4 stroke 52 should work.
Old 01-12-2017, 08:48 PM
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JohnBuckner
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dlpjr What is the airplane you are building?? and if it is an unknown what is the wingspan, projected weight and type performance expected. Knowledge of these factors will provide a better basis for engine recommendations especially so with a twin.

John
Old 01-13-2017, 03:06 AM
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I agree with the 52
Old 01-13-2017, 05:43 AM
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dlpjr
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Thanks everyone.....

John,
The wing span is 85", total weight of the plane should be 16 to 17 lbs. I was going to use .46 instead of the .40. The plane is a Seneca Piper II, its not going to be doing anything crazy, I am building it to scale.
Old 01-13-2017, 05:49 AM
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A pair of 52 4-strokes doesn't seem enough power for a 16 lb plane to me (IMHO), even for scale flying. At least a pair of 70 4-strokes maybe.
Old 01-13-2017, 06:16 AM
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RCFlyerDan
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Originally Posted by hsukaria
A pair of 52 4-strokes doesn't seem enough power for a 16 lb plane to me (IMHO), even for scale flying. At least a pair of 70 4-strokes maybe.
+1
Old 01-13-2017, 06:21 AM
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JohnBuckner
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Originally Posted by dlpjr
Thanks everyone.....

John,
The wing span is 85", total weight of the plane should be 16 to 17 lbs. I was going to use .46 instead of the .40. The plane is a Seneca Piper II, its not going to be doing anything crazy, I am building it to scale.

What a diff a little information can make

I can think of no other way to express it, that combination (I suppose weighted down with retracts and big holes in the bottom of the wing/fuse too) with the 52's in my opinion would be a dangerous dog. A great deal of your flying around may actually be close to stall and even more important below the actual VMC.

My preference would be a pair of OS 15cc two stroke gassers. Now whatever you choose please install the engines with plenty of 'outthrust' if you want the airplane to survive a long time. Now many complain that outthrust is not scale, well I think you will find with research that many general aviation light twins do in fact use outthrust and for the same reasons we model flyers would benefit by it. Simple three views do not usually show this but its there with the PA-28 series twins and the PA-23 series twins.

John
Old 01-13-2017, 07:13 AM
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Originally Posted by JohnBuckner
What a diff a little information can make

I can think of no other way to express it, that combination (I suppose weighted down with retracts and big holes in the bottom of the wing/fuse too) with the 52's in my opinion would be a dangerous dog. A great deal of your flying around may actually be close to stall and even more important below the actual VMC.

My preference would be a pair of OS 15cc two stroke gassers. Now whatever you choose please install the engines with plenty of 'outthrust' if you want the airplane to survive a long time. Now many complain that outthrust is not scale, well I think you will find with research that many general aviation light twins do in fact use outthrust and for the same reasons we model flyers would benefit by it. Simple three views do not usually show this but its there with the PA-28 series twins and the PA-23 series twins.

John
John, that was wise of you to ask that question.
Old 01-13-2017, 07:45 AM
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Another major consideration using two engines would be fuel consumption
You will need to start one engine first and have it run while you start the second and then have enough fuel to fly for a given amt of time
The four cycles will use less fuel than the two cycles and should give you more time in the air with the same size fuel tank
Engine weight is another consideration
Do not put to much engine weight in the plane ( nose weight ) as you will kill the wing loading and have a hell of a time coming to the runway
Very important to me after many years of flying to have an excellent landing and bringing the plane to your feet to tie up a wonderful flight and impress you pears
A good flight with a poor landing just dosen't do much for me
The boys are watching LOL ! !
Old 01-13-2017, 07:52 AM
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Originally Posted by tony0707
Another major consideration using two engines would be fuel consumption
You will need to start one engine first and have it run while you start the second and then have enough fuel to fly for a given amt of time
The four cycles will use less fuel than the two cycles and should give you more time in the air with the same size fuel tank
Engine weight is another consideration
Do not put to much engine weight in the plane ( nose weight ) as you will kill the wing loading and have a hell of a time coming to the runway
Very important to me after many years of flying to have an excellent landing and bringing the plane to your feet to tie up a wonderful flight and impress you pears
A good flight with a poor landing just dosen't do much for me
The boys are watching LOL ! !
Yeah, the peanut gallery at the field is always watching!!
Old 01-13-2017, 10:42 AM
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I wouldn't even waste my time with glow. Every glow twin I have watched fly, including H9 B25 that was powered as per H9 that I maiden for a student of mine, usually end up auguring ground. Glow engine are too temperamental and usually there is one of the engines that either didn't get broken in correct, over heats, doesn't get the same carb airflow, etc and fails. There is an electronic devise that detects rpm and the loss of one engine, and brings the other running engine to idle. I recommended to my buddy, and of course he didn't listen, so we loss the plane. Otherwise, I would go gas or I even hate to recommend electric, because I am not an electric guy. But if you build it glow, don't put the loss of rpm sensor on the plane, your plane won't last long. I have flown the Seneca and Aztec, both considered trainers in the full scale life, are not hot rods, and if you loose one, unless already in cruise, it will be questionable if the other engine gets you back around the pattern. I don't recommend those .15 cc Chinese junk engines either. A student of mine had one, and it had no power, and didn't last long.

Last edited by RCFlyerDan; 01-13-2017 at 11:10 AM.
Old 01-13-2017, 11:05 AM
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Originally Posted by RCFlyerDan
I wouldn't even waste my time with glow. Every glow twin I have watched fly, including H9 B25 that I maiden for a student of mine, usually end up auguring ground. Glow engine are too temperamental and usually there is one of the engines that either didn't get broken in correct, over heats, doesn't get the same carb airflow, etc and fails. There is an electronic devise that detects rpm and the loss of one engine, and brings the other running engine to idle. I recommended to my buddy, and of course he didn't listen, so we loss the plane. Otherwise, I would go gas or I even hate to recommend electric, because I am not an electric guy. But if you build it glow, don't put the loss of rpm sensor on the plane, your plane won't last long. I have flown the Seneca and Aztec, both considered trainers in the full scale life, are not hot rods, and if you loose one, unless already in cruise, it will be questionable if the other engine gets you back around the pattern. I don't recommend those .15 cc Chinese junk engines either. A student of mine had one, and it had no power, and didn't last long.
I witnessed a scary multi-engine event about 3 years ago at our club. A guy had a giant B-17 with 4 Zenoah G-38s (with the magnetos). Soon after takeoff both engines on the same wing quit. It was a scary scene and he had to violate some club safety rules, but he landed that monster without damage. But if it could happen to those engines, it could happen to any other type of engine. Heck, you might get a bad Lipo if you are using one for each motor too, less likely but possible. That's why I have not tried multi-engined planes yet. Maybe someday.
Old 01-13-2017, 02:39 PM
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Anything can go wrong with anything, I've had just as many dead stick with gas motors as Glow. Glow Twins are not going to be more prone to cutting off if you know how to tune and don't abuse the motors,, I think anything between 70-91 4 strokes would be great for that plane.

good luck
Old 01-13-2017, 03:42 PM
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Originally Posted by scale only 4 me
if you know how to tune and don't abuse the motors,
good luck
There in lies the problem! Most don't know how to tune, and the art of tuning glow engines is going away. The owner/pilot needs to understand and use a tachometer and be patient for the changes in what has been adjusted. Understand that on the high end, with a pressurized tank, it may take a minute or two for the tank to be pressurized. This leads to miss tuning and engine failure.
Yes, we all have had dead sticks on single engine planes/jets, no matter what we are flying. The issue is that it is difficult for an r/c pilot to recognize a dead stick on either one of the engines on a twin. By the time the pilot recognizes the loss of an engine, the plane is already below Vmc. The pilot is then too late to pull the throttle back to idle and treat it as both engines have quit. Most try to be hero's and fly it out, but it normally doesn't end well.
This is an old thread....so watch if you decide to post, but good info.

http://www.rcuniverse.com/forum/twin...r-support.html
Old 01-13-2017, 04:00 PM
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My experience with tuning is the same for glow or gas. There were greater variations of tuning between 2 and 4 stroke glow than between gas and glow. Gas also requires tuning skills, it's no free ride.
Old 01-13-2017, 05:20 PM
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dlpjr
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Just spent the last hour or so reading about outthrust...... I should have keep a more accurate count, but i would say 1 in 5 say it makes no difference. The plans of the Seneca I am building were in RC Mag, I think back in the late 70's early 80's, they show no outthrust, in fact no thrust angle at all. I have to look into this deeper. I have build many kits, never a scratch build, and never a twin. Am I on the right page to say that the outthrust would be better to have when one eng dies, making it somewhat easier to fly with one eng, but not impossible.
Old 01-18-2017, 01:08 PM
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Hi!
I must ask! What flying characteristics do you want? That's important because it means powering the airplane according to how the plane will fly, or is supposed to fly.

If the twin is a scale model, let's say a DC-3, B-25, B-17, B-24 all of them should fly in a slow way, acting graciously in the air. A Cessna or Piper twin should also fly in that way.
16-17lbs (around 8kg )is heavy for a 85" span (215cm) twin. I built and flew a Marutaka Cessna 310 with a span of around 165-175cm 35 years ago, powered by two Enya .40X two strokes and the power was just simply to much for that plane. It flew too fast! I was in those days a keen pylonracer competing frekvently but when I flew a scalemodel I wanted it to fly in a scale like maner, not like a pylon racer.
Years later having both constructed, built and flown many models I built a Marutaka DC-3 model (210cm in span). I wanted that model to fly real slow and I knew to accomplish that I had to build it light so I choose two OS FS .26 four strokes aiming for a weigh of around 3kg (6 lbs). I did not reach that goal but the plane finally came around at 3,6kg ready to fly. At that weigh it has the same flying characteristics as a large sailplane, behaving just like the full size DC-3 in the air.

Soo! If you want a good flying scale model or any twin (or any model), build it light and power it with small light engines and prop it right. The fault many newcomers to twin-airplane flying do is to powering the model with too large and heavy engines. This results in a model that flies too fast, that lands to fast and that probably does not last too long...

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Last edited by jaka; 01-18-2017 at 01:11 PM.

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