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gas engine reversal - is it possible ? - 6/22/2008 7:31:36 AM   
Ravivos


 

Posts: 82
Joined: 8/16/2006
From: Center, ISRAEL
Status: offline 		is it possible to reverse the rotation of a single cylinder two stroke gas engine with EI?
I know the first thing to do is to remount the hall sensor so it will be at the same angle but in a CCW insted of CW.
is there anything else to do or retiming the engine is enough ?

the engine is a 26cc gas engine, with EI.
i need it to spin CCW so i can use it as a pusher with an ordinary prop (mounting the prop backwards)

Thank you.
Raviv.
       Post #: 1

RE: gas engine reversal - is it possible ? - 6/22/2008 12:11:00 PM   
rc bugman



Posts: 881
Joined: 1/16/2002
From: Ithaca, NY, USA
Status: offline 		Just change the position of the ignition sensor and start the engine in the other direction

Have fun

Elson

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(in reply to Ravivos)
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RE: gas engine reversal - is it possible ? - 6/22/2008 3:35:12 PM   
soarrich



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From: Middletown, NJ, USA
Status: offline
quote:

ORIGINAL: rc bugman
Just change the position of the ignition sensor and start the engine in the other direction

Or you can leave the sensor where it is, but flip the sensor in the housing, then install a second magnet with the polarity reversed where it should be for reversed timing. From then on to get the othere direction you just reflip the sensor.

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(in reply to rc bugman)
       Post #: 3

RE: gas engine reversal - is it possible ? - 6/22/2008 4:22:41 PM   
Ravivos


 

Posts: 82
Joined: 8/16/2006
From: Center, ISRAEL
Status: offline 		Thank you for your answers,
It seems that the only thing needed in order to make the engine work currectly (but opposite direction) is to re-time it.

What about cooling?
in a pusher mode, the prop pulles air from the cylinder head (instead of pushing air into the cooling fins), could this be a problem?
the modified engine will be mounted as a pusher without any option for baffeling or jacketing,
further more, the plane (actually - VTOL) will spend alot of time hovering and will not have free air flow caused by straight flight.

(in reply to soarrich)
       Post #: 4

RE: gas engine reversal - is it possible ? - 6/22/2008 5:27:08 PM   
Tired Old Man


 

Posts: 11508
Joined: 2/25/2002
From: Central, CA, USA
Status: offline 		Cooling is a BIG problem with pusher configurations. If you fail to duct the air to the cylinder, fail to maintain a tight fit of a cooling duct around the cylinder, and design the cooling outlet in a manner that will force good extraction you can ruin an engine in short order. Take the time to think the cooling system through and design it with minimum obstruction. Pay particular attention to cooling the exhaust side of the cylinder. Do not use lean oil ratios!! Pusher installations are the true test of what an oil can do so stay with the upper end of the quality selections and avoid ratios leaner than 50-1.

To assist the design of a cooling system you can set up a crude wind tunnel test by using a leaf blower to push air over the airframe. Set a screen in front of the leaf blower and plane with long thin strips of mylar attached to the screen long enough to reach to the back of the aircraft. Watch how the mylar strips flow over the airframe to determine where the natural airflow runs over the plane and use that airflow to determine where a cooling duct should begin to obtain the most volume. After you build the prototype air duct perform the airflow check again to see if it's use had a negative effect on the original flow of air.

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If you can''''t fix it with a hammer, you have an electrical problem.

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RE: gas engine reversal - is it possible ? - 6/22/2008 5:37:38 PM   
octanehuffer



Posts: 693
Joined: 7/15/2006
From: Lakeland, MN, USA
Status: online 		No need to run an iar cooled engine when MVVS makes a liquid cooled 58cc. Just find a spot for the radiator in open air.

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RE: gas engine reversal - is it possible ? - 6/22/2008 7:12:06 PM   
dirtybird


 

Posts: 3031
Joined: 1/25/2002
From: Mesa, AZ, USA
Status: offline 		If the gas engine has a rotary valve like the MVVS or ZDZ you probably cannot reverse it.
Also if the engine has been run for any time in the normal direction, reversing it will create abnormal wear and might ruin it. You need to start with a new engine and always run it reverse.

(in reply to octanehuffer)
       Post #: 7

RE: gas engine reversal - is it possible ? - 6/22/2008 7:16:47 PM   
Ravivos


 

Posts: 82
Joined: 8/16/2006
From: Center, ISRAEL
Status: offline 		well, i really have no intentions of buying a liquid cooled engine (although it crossed my mined), and i want to use the engine i already have.

hi "old man", thank you for your answer.
It seems that i have a problem, isnt there any other way cooling the engine while hovering?
the plan is to build a shroud that will surround the prop, kinda like a ducted fan... a prop ducted fan,
if the walls of the shroud will be high enough to contain both the prop and the engine itself, wouldnt it be sufficient to force enough air over the cylinder and keep it cool?
p.s, while serching RCU for some VTOL information, i came across some of your threads, a lot of useful information, thank you.

Raviv.

(in reply to octanehuffer)
       Post #: 8

RE: gas engine reversal - is it possible ? - 6/22/2008 7:23:05 PM   
Ravivos


 

Posts: 82
Joined: 8/16/2006
From: Center, ISRAEL
Status: offline 		hi dirtybird, the engine is not a rotary valve type, i know that these kind of engines need a special cranckshaft with different timing in order to spin backwards.
the engine is a normal two stroke engine , XYZ26cc.
it ran flawlessly for approximately 4 gallons, always on 1:33 synthetic oil (mobile racing).

(in reply to dirtybird)
       Post #: 9

RE: gas engine reversal - is it possible ? - 6/22/2008 9:16:00 PM   
yarom



Posts: 1120
Joined: 6/23/2005
From: Bellevue, WA, USA
Status: online
How about getting a pusher prop and running the engine in the original direction?

quote:

ORIGINAL: Ravivos

is it possible to reverse the rotation of a single cylinder two stroke gas engine with EI?
I know the first thing to do is to remount the hall sensor so it will be at the same angle but in a CCW insted of CW.
is there anything else to do or retiming the engine is enough ?

the engine is a 26cc gas engine, with EI.
i need it to spin CCW so i can use it as a pusher with an ordinary prop (mounting the prop backwards)

Thank you.
Raviv.


(in reply to Ravivos)
       Post #: 10

RE: gas engine reversal - is it possible ? - 6/22/2008 9:33:12 PM   
Ravivos


 

Posts: 82
Joined: 8/16/2006
From: Center, ISRAEL
Status: offline 		it is possible, but because this is going to be a (very) experimental model, i want to have the ability to change props without waiting two and a half weeks until i recived the one i orderd.
it seems rather easy changing the location of the hall sensor in ordr to get the timing right for a CCW rotating engine, the main problem is the heat.
using a pusher prop will not solve the heat problem.

Thank you.

Raviv.

(in reply to yarom)
       Post #: 11

RE: gas engine reversal - is it possible ? - 6/23/2008 12:52:00 AM   
Tired Old Man


 

Posts: 11508
Joined: 2/25/2002
From: Central, CA, USA
Status: offline 		The volume of air required to cool any engine is much more than most would believe, let alone the speed it needs to move at. In a hovering situation you will be forced to find a way to pump air to the engine which will present a completely different set of items to over come.

What you are doing is what modeling is all about. It's not always the easy, off the shelf, everyone does this, type of stuff where everyone has a safe haven. Someone always has to led the way and in doing so they have a lot of experimenting and research to do. You may want to look into some high volume electric mini fans. Think computer components with some specialized plenums. Better yet, brushless electric r/c motors turning fans from computer cooling systems.

Any reed valve engine is easy (easiest) to reverse running direction. Most of the piston port engines can as well. As for changing wear patterns, the only place there would be any effects would be at the bearings. Pistons and rings go in and out regardless of rotational direction.

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If you can''''t fix it with a hammer, you have an electrical problem.

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RE: gas engine reversal - is it possible ? - 6/23/2008 3:57:35 AM   
soarrich



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From: Middletown, NJ, USA
Status: offline
quote:

ORIGINAL: Tired Old Man

Pistons and rings go in and out regardless of rotational direction.

True but there are side forces which change on the piston/cylinder.


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RE: gas engine reversal - is it possible ? - 6/23/2008 6:14:34 AM   
HornetFitter


 

Posts: 82
Joined: 2/3/2008
From: Cold Lake, AB, CANADA
Status: offline 		It is never going to work . The transfer port timing (in a 2-stroke)/ valve timing (in a 4-stroke) is different when turning in reverse.

If you could redesign the engine it might be feasable, but the performance would be just plain poor.

(in reply to soarrich)
       Post #: 14

RE: gas engine reversal - is it possible ? - 6/23/2008 6:32:27 AM   
Tired Old Man


 

Posts: 11508
Joined: 2/25/2002
From: Central, CA, USA
Status: offline 		Tell that to the hundreds of two strokes currently running every day in reverse

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RE: gas engine reversal - is it possible ? - 6/23/2008 8:30:19 AM   
Ravivos


 

Posts: 82
Joined: 8/16/2006
From: Center, ISRAEL
Status: offline 		Hi "old man" (name?), electric fan is a good idea, i can use a 5"-8" diameter fan with high CFM, the noise is not a problem.
the added fan might restrict the airflow for the prop,