Thread Tools
Feb 13, 2020, 12:39 PM
Registered User
kablake's Avatar
Thread OP
Discussion

Flat Twin Engine, Boxer or Not, that is the question..


Curious of the advantages of the Boxer and non-Boxer type flat twin engines??

Thanks...
Sign up now
to remove ads between posts
Feb 13, 2020, 01:24 PM
Still gassin' it.
Real boxers run a fair bit smoother and with less vibration. But they are a bit heavier, and theoretically have slightly larger mechanical losses (so less power).
Probably also slightly more expensive to build on account of the more complicated crankshaft and the split bigends. Bit harder to make them rev high because of those big ends that have the built in possibility to fail.
The "non-boxer" needs two separate carbs, which makes them slightly harder to adjust and in all other aspects is what the "true Boxer" is not….

I like them both, the sound is distinctively different, and both types can run equally well..
Feb 13, 2020, 01:56 PM
AMA 46133
SeismicCWave's Avatar
Boxers are more common type of RC engines. I believe all those Chinese gasoline twins 2 strokers are all Boxers. You will find non Boxer in some of the twin four strokers.

I only played with 2 stroke Boxers so I cannot comment on the non Boxers. This latest one I am playing with is definitely smoother when I put my hands on the plane when I run up the engine.

Bert's description seems to be pretty good on Boxers. I also did Google Boxers before and Wikipedia has pretty good explanations.

https://en.wikipedia.org/wiki/Flat_engine
Feb 13, 2020, 04:42 PM
Registered User
Quote:
Originally Posted by 1967Brutus
Real boxers run a fair bit smoother and with less vibration. But they are a bit heavier, and theoretically have slightly larger mechanical losses (so less power).
Probably also slightly more expensive to build on account of the more complicated crankshaft and the split bigends. Bit harder to make them rev high because of those big ends that have the built in possibility to fail.
The "non-boxer" needs two separate carbs, which makes them slightly harder to adjust and in all other aspects is what the "true Boxer" is notů.

I like them both, the sound is distinctively different, and both types can run equally well..
The above statements are the "conventional wisdom", I'm not aware of a non-boxer twin with a single carb but I don't necessarily think it's a theoretical necessity. This is something I want to experiment with when I get a chance, I recently acquired two Saito FT 182's, one new and another in "near new" condition.
I plan to start with a single Walbro carb with reed valves that effectively isolate the two cylinders, I think that if each cylinder has its own induction mechanism, a single carb can be used, many reed valves have two ports with flaps, isolating the chambers feeding each of the cylinders may be the ticket.
Another consideration is the installation of an electronic ignition in a non-boxer twin engine. It can be done with a single ignition and two magnets on the prop hub or two separate ignitions, one for each of the cylinders, again simplicity wins for me so I will try a single ignition first.
Feb 13, 2020, 11:30 PM
Still gassin' it.
Quote:
Originally Posted by ClippedWings
I don't necessarily think it's a theoretical necessity. This is something I want to experiment with when I get a chance, I recently acquired two Saito FT 182's, one new and another in "near new" condition.
I plan to start with a single Walbro carb with reed valves that effectively isolate the two cylinders, I think that if each cylinder has its own induction mechanism, a single carb can be used, many reed valves have two ports with flaps, isolating the chambers feeding each of the cylinders may be the ticket.
Like many things, this will work, sort of, but the issue is that the intake pulses are too close to each other.
When no air is flowing through a carb, no fuel is drawn. When the air begins to flow, it takes "some time" before actual mixture is produced, because nothing reacts instantly (if you slow down time enough, not even electricity).
So when the first cylinder starts inducing, it gets a bit of clean air first, then mixture. When the second cylinder starts to induce and the flapvalves change over, that cylinder is drawing from a carb where there is allready a gasflow, so that second cylinder will Always get full mixture from the get-go, therefore it will in total receive more fuel.
The dual carb is necessary because you will not be able to balance the two cylinders.
It is hard enough to get a proper boxer to run balanced on a single carb (Notice that BMW for their boxers Always used dual carbs) but for an odd firing twin it will be impossible.
At least difficuolt enough for Saito to never even try it.
Quote:
Originally Posted by ClippedWings
Another consideration is the installation of an electronic ignition in a non-boxer twin engine. It can be done with a single ignition and two magnets on the prop hub or two separate ignitions, one for each of the cylinders, again simplicity wins for me so I will try a single ignition first.
You mean a single ignition with two plugs firing simultaneously? Or the single ignition with two independent firing leads?
The "Boxer" ignition with two magnets will not work for several reasons: because the double magnet, it will see double RPM, therefore the advance curve will be off, and one of the cylinders will have the wasted spark at the end of the induction stroke, with a cylinder full of ignitable mixture.
But the "V-twin" ignition will work, no probs (been there done that).
Feb 14, 2020, 02:30 AM
Diesel Danny
danny mz's Avatar
Quote:
Originally Posted by 1967Brutus
>>>>>>>>>>>>>>>>>>>>>>> snip <<<<<<<<<<<<<<<<<<<<<<
The "non-boxer" needs two separate carbs, which makes them slightly harder to adjust and in all other aspects is what the "true Boxer" is not….
Actually I like the twin carbs (Saito FA-90T and Saito FA-100T) as while maybe a bit more fiddly to adjust, they allow one to compensate for minor differences in the two cylinders.

Once they are set and the engines are run-in they seem to hold the settings for a long time

* Danny M *
Feb 14, 2020, 02:55 AM
Still gassin' it.
Quote:
Originally Posted by danny mz
Actually I like the twin carbs (Saito FA-90T and Saito FA-100T) as while maybe a bit more fiddly to adjust, they allow one to compensate for minor differences in the two cylinders.

Once they are set and the engines are run-in they seem to hold the settings for a long time

* Danny M *
Absolutely, and several people have for that reason also fitted separate carbs to "true" boxers, but that does not take away that a single carb is easier in general.
We did a Saito 130T a while back, and getting both cylinders to run approximately the same, was not exactly an easy task, despite using telemetry and data logging to see how the system would respond to changes in throttle. We had to go as far as to discard the Original linkage rod and replace it with an adjustable one because the both barrels did not move exactly synchronous...

In fact, the more you know (the more data is availlable) the more likely you are to see differences you otherwise would not notice, the harder it gets to get everything by and large equalized.
Feb 14, 2020, 04:32 AM
Registered User
Quote:
Originally Posted by 1967Brutus
Absolutely, and several people have for that reason also fitted separate carbs to "true" boxers, but that does not take away that a single carb is easier in general.
We did a Saito 130T a while back, and getting both cylinders to run approximately the same, was not exactly an easy task, despite using telemetry and data logging to see how the system would respond to changes in throttle. We had to go as far as to discard the Original linkage rod and replace it with an adjustable one because the both barrels did not move exactly synchronous...

In fact, the more you know (the more data is availlable) the more likely you are to see differences you otherwise would not notice, the harder it gets to get everything by and large equalized.
OK, maybe I shouldn't bang my head against the wall after all...
I have a few boxer twins so I thought the odd firing ones shouldn't be too much of step up but that's not the case obviously...
Thanks for those sharing their experience and for the time and frustration you've saved me, I will keep the original twin carb setup when converting the Saito FA 182T ...
There's another challenge with the odd firing twin, the crankcase pressure is too low for a pump setup, I thought to add a pump actuated by the camshaft rod (YS DZ style) but probably give that up for the sake of simplicity...
Feb 14, 2020, 04:47 AM
Still gassin' it.
Quote:
Originally Posted by ClippedWings
OK, maybe I shouldn't bang my head against the wall after all...
I have a few boxer twins so I thought the odd firing ones shouldn't be too much of step up but that's not the case obviously...
Thanks for those sharing their experience and for the time and frustration you've saved me, I will keep the original twin carb setup when converting the Saito FA 182T ...
There's another challenge with the odd firing twin, the crankcase pressure is too low for a pump setup, I thought to add a pump actuated by the camshaft rod (YS DZ style) but probably give that up for the sake of simplicity...
You don't need a pump.... you need one of my valves and muffler pressure.

(half joking, half serious: you really do NOT need a pump, not even on the Original carbs. One of my clubmates has proven that beyond the shadow of a doubt. With AND without the solenoid valve).
Feb 14, 2020, 04:59 AM
Registered User
Quote:
Originally Posted by 1967Brutus
You don't need a pump.... you need one of my valves and muffler pressure.
Yes I know, you keep teasing me Bert...
That requires a PhD in setting up throttle curves on the transmitter..., too much info for my simple mechanical brains...
One day my curiosity will get the better of me, I know it..., do you still have some in stock?
Feb 14, 2020, 05:07 AM
Still gassin' it.
Didn't mean to push a valve on you (but I do actually have 4 in stock that are not yet claimed ).

But if you simply use the Original carbs, you'll have a slightly rich midrange, but in all other aspects a very usable and reliable engine. Trust me, it'll work.

Don'need no stinkin'pump, mate!
Feb 14, 2020, 05:26 AM
Registered User
Quote:
Originally Posted by 1967Brutus
Didn't mean to push a valve on you (but I do actually have 4 in stock that are not yet claimed ).

But if you simply use the Original carbs, you'll have a slightly rich midrange, but in all other aspects a very usable and reliable engine. Trust me, it'll work.

Don'need no stinkin'pump, mate!
OK I better take at least one of them solenoid valves while they're still available, otherwise I may regret it when they're gone ...
I'll stay in touch offline, can't remember if we discussed it before.
Feb 14, 2020, 06:10 AM
Still gassin' it.
Quote:
Originally Posted by ClippedWings
OK I better take at least one of them solenoid valves while they're still available, otherwise I may regret it when they're gone ...
I'll stay in touch offline, can't remember if we discussed it before.
There's the one with your name on it...
At the moment, there's 4 (nay, now 3) full kits availlable, and I have still 30 valve housings left, so there will be a few availlable in the near future.
If enough demand, I will have another run of housings made, and that might happen sooner than expected if things continue like this.
It actually goes faster than I expected, I started out with 54 housings, 8 destined for my own planes, which means at this point 16 units sold.
Last edited by 1967Brutus; Feb 14, 2020 at 06:19 AM.
Feb 14, 2020, 06:20 AM
Registered User
Quote:
Originally Posted by 1967Brutus
There's the one with your name on it...
At the moment, there's 4 (nay, now 3) full kits availlable, and I have still 30 valve housings left, so there will be a few availlable in the near future.
If enough demand, I will have another run of housings made, and that might happen sooner than expected if things continue like this.
It actually goes faster than I expected, I started out with 54 housings, 8 destined for my own planes, which means at this point 16 units sold.
Good man, thanks Bert...
Feb 14, 2020, 06:29 AM
Still gassin' it.
Just shoot me an e-mail whenever you're up to it, and I'll send it to you


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Old Rossi 40;To run it or not to run it, that's the question! Sam Ehab Engines 247 Feb 20, 2020 02:18 AM
Discussion To varnish or Not To Varnish? That is the question. wmetcalf Electric Plane Talk 13 Sep 12, 2017 12:33 PM
Discussion To LiPo or not to LiPo that is the question GaCrossRider Batteries and Chargers 6 Mar 14, 2017 04:36 AM
Discussion To V-tail or not to V-tail . . . THAT is the question! muffcook Sailplane Talk 52 Nov 18, 2016 10:12 AM
Discussion To part out or not, THAT is the question! lovetoflyco Fuel Plane Talk 21 Apr 08, 2016 01:56 PM