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Saito 90-TS conversion to gas

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Old 02-23-2018, 07:35 PM
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AA5BY
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Default Saito 90-TS conversion to gas

With a little trepidation I decided to add spark ignition to my Saito 90-TS. I had the ignition because I'd wrongly bought the wrong version for the Saito 182T previous conversion which was an odd fire engine and ultimately required two ignitions instead of the dual plug ignition meant for even fire boxer engines. The Saito 90 would sometimes drop fire in one of the cylinders so it seemed to make sense to put the unused ignition to use.

What I didn't know is if the single carb engine could be tuned on gas... if not, I'd run it spark glow. With ignition installed, it was run on glow first and performed well producing 8500 rpms with a MAS 13x8 prop. Idle would go down into the mud reliably at 12-1300. On gas, rpms dropped to 7850 with idle down to 2000 but the idle suffered the problem that one cylinder was too rich and would drop out. Below 2000, inertia couldn't carry rotation through the dead cylinder.

An 8 pitch prop was really too much pitch for the Cub the engine was fitted to so it was traded for a MAS 14x6 which was heavier and that did the trick, easily allowing rotational inertia to punch through the dead cylinder and idle between 17-1800 while yielding 7600 rpm at WOT.

It sounds great and should power the 1/6 Cub without problem, given that it was over powered on glow.

Attached is video of it being tested prior to fitting the ignition into the plane and changing the fuel tank to gas. The two engine stops are me hitting the throttle kill to illustrate the restart ease.


Last edited by AA5BY; 02-23-2018 at 07:37 PM.
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Old 02-24-2018, 03:18 PM
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triumphman49
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BRAVO ! ! ! Am wondering how you mounted the magnet \ pick-up ?
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Old 02-24-2018, 06:23 PM
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Originally Posted by triumphman49 View Post
BRAVO ! ! ! Am wondering how you mounted the magnet \ pick-up ?
The timing hub is standard fare... a turned collar with a set screw and magnet mounted in it. The pickup mount took a bit more thought but was mounted to a U bracket to the engine mount.
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Old 02-24-2018, 07:23 PM
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Hey AA, Thanks for the descriptive response and pic. Haven't yet found a source for timing hub CH Ignitions or possibly a jobber machine shop. Pick-up mount looks great tho. Happy flying ! !
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Old 02-24-2018, 08:33 PM
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Am fortunate to have a lathe. Have been buying the ignitions, plugs and opto switches from Agape Racing.

Do you have an engine your thinking of converting to spark or gas?
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Old 02-25-2018, 06:44 AM
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triumphman49
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Well, do have a FA90TS still on glow ignition. Seems so many will use remote glow drivers on twins to solve various issues, while not that much difference in weight or cost for CDI.
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Old 02-25-2018, 07:39 AM
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Mine would sometimes drop a cylinder so it was add on board glow or spark. If you think you may want a timing hub I'd be happy to provide one.
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Old 02-25-2018, 01:13 PM
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AA, That's certainly a nice offer, . . . and I'm appreciative. Funny story, . . Used JB Weld once to adhere magnet to prop hub FA270T - the reaction between magnets and JB Weld was just that. May take a rain check if offer remains open. Again, Many Thanx.
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Old 03-02-2018, 10:13 PM
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AA5BY, as I posted in another thread years ago, you have proved my point, that Blade Diameter & Pitch Thrust are not equal to each other in loading an engine, meaning that more pitch does not load an engine equally to the way Prop Diameter does,

so more Flywheel Effect is what you have achieved with your larger diameter prop,

in my mind, I feel most people are Peak RPM oriented, meaning they think "the more RPM, the better" I know I can think like that because I like to fly fast for the most part, yet along with more flywheel effect a larger diameter prop also smooths out an engine (a better running engine run smoother), and a Hotter Glow plug burns more fuel at lower RPM than a Colder Glow Plug does, so a larger diameter prop and the hotter glow plug work well together,, after all, if a given prop is hard to turn it will turn easier when burning more fuel ,


also know, a given engine's peak Torque point is where that engine is most efficient. and most engines peak Torque point is below peak RPM.

so a larger diameter prop turns slower because it's harder to turn than a shorter prop, and a hotter plug burns more fuel at lower RPM because it starts the Flame Front sooner, it's a win-win for a Saito because Saito's love larger props,

so with all that I have to now wonder, just how well your engine will run with that larger diameter prop on Glow Fuel with also adding Hotter Glow Plugs than you ran before,

I'm not expecting you to do more testing, just talking, you know..

Jim
BTW, I have a Saito 100 Twin, I have not yet run it or put it in a plane, but I plan to..

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Old 03-04-2018, 09:07 PM
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Jim... good thoughts.

Converting to gas has pros and cons with the greatest negative the degradation of power. I've now flown the 1/5 World Models Cub powered by the 90TS on gas running a MAS 14x6 prop. What previously was an overpowered Cub is now a reasonably powered Cub. The plane flies slower than previous... more like a Cub. It does get airborne easily and will easily loop from level flight and pull over the top without concern due to the torque of the longer/lower pitch prop.

I'd probably not recommend converting this engine to gas on anything other than a floater such as the cub. The Cub weights 8.25 lbs... and I suspect that would be around the upper limit for the engine on gas. It requires nearly half throttle to hold altitude albeit that may change when getting the balance back. I've moved the battery back for more testing and am prepared to add tail weight if more aft balance is needed.

Floater planes generally enjoy a six or even less pitch prop because they provide more torque and less speed and they do a much better job of braking to prevent the long landings that floaters sometimes suffer, albeit a prop that will provide significant braking needs to have landing rpms dialed as too much braking action can slow the plane too much.

On a non floater... spark ignition is a good alternative to on board glow but I'd stay with nitro glow fuel to keep the power on an engine like the Saito 90TS. If aerobatics are important... power is not something usually traded off... so stay with glow nitro fuel.

Gas has its advantages however, fuel cost are 1/10. On this plane, a flight will cost 10 cents compared to a dollar. Clean up is much easier, requiring 20 sec with a single alcohol wipe compared to several paper towels and 3-5 minutes. Fuel is readily available.and solves the problem for some areas where glow fuel is getting hard to obtain. Spark ignition is in my opinion more reliable than glow ignition. I've now about eighty flights on Saito conversions to gas with zero dead sticks.
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Old 03-09-2018, 07:34 PM
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I've now about eighty flights on Saito conversions to gas with zero dead sticks.

wow, you sure can't complain about that can you
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Old 03-10-2018, 03:59 AM
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Originally Posted by the Wasp View Post
wow, you sure can't complain about that can you
A virtue of spark ignition is the timing is fixed (excepting the desired rpm advance), whereas glow ignition has the timing influenced by mixture where a lean mixture can cause the timing to advance quite far, causing some issues with detonation, increased temperature and even a spitting a prop.

This virtue aids in providing resistance to engine flame out due to too lean a mixture. Conversely, a rich mixture that sometimes will cool off a glow plug, only causes lowered power with spark ignition.
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Old 03-11-2018, 07:29 AM
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Originally Posted by the Wasp View Post
wow, you sure can't complain about that can you
Typical to when engaging in bragging... one gets his comumpence.

After four test flights with the engine, the cowl was installed and two more flights made yesterday. All was well with the first flight except that after landing on the first flight and turning to taxi back to the pits... the engine died.

About 20 min later it was given a second flight and all went well for 4-5 min and it started to miss and progressively got worse so was brought in and it died about 10 ft altitude on the last of the landing leg. On the bench, it would not restart... even after going to the truck and getting the starter... it would not start. It would bark a little when primed by holding a finger over the exhaust stack having the muffler pressure line and forcing a prime, but it would not run.

Suspecting the carb had heated and was vaporizing the miserly amount of fuel the engine uses, upon allowing it to cool, it started and ran fine. Though the jugs stand clear of the cowl and get cooled fine, the carb was heating inside the cowl and causing fuel vaporizing.

So, a hitch needs to be worked out.
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Old 03-11-2018, 10:56 AM
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I ran into this problem on one of my conversions, a Stihl 62cc. That conversion demanded a custom intake be fabricated, and while the one I created had an insulated portion, it did allow heat to be transferred to the carb via the carb mounting bolts. This caused nasty tuning, running, and consistency issues until I remedied the situation.

In your case, I wonder if the cooling effect of the alcohol in E-85 fuel would help out if you switched to that fuel? Also, I don't remember if you had to lower the compression to successfully run gasoline in your case, but if so a switch to E-85 would allow you to raise the compression ratio back up and gain some power back.

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Old 03-12-2018, 08:09 AM
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The intake manifolds have rubber sections but the carb bolts flat against the back of the engine housing and wouldn't move much when removing the mounting screws... but I did get a thin layer of mica between. I've also increased air flow into the cowl and provided a baffle director to direct the air flow up to the carb area which sets behind the engine.

The problem didn't exist when the cowl was not installed and showed up on the second flight after it was installed. The first flight was ten minutes and it manifested about 4-5 min into the second flight but once it started, it grew increasingly worse so the plane was brought in for a landing and died shortly before touch down. It would not restart... until cooling. the jugs extend beyond the cowl so they are not heating excessively.

I will try to fly this afternoon and test the changes.
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Old 03-12-2018, 07:20 PM
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Air Dams and Cooling Air

as for your Engine's Cooling Air, because Hot Air expands the Exhaust Hole in the back of your Cowl for the Cooling Air to escape should be 1.5 times larger than the Air Intake Hole on the front of your Cowl,,example> if the Intake Hole is 2 inches square the the Exhaust Hole in the back of the Cowl should be 3 inches square, even larger, if not you will get a build up of Heat inside your Cowl,,

Note that you should not have a Cross-Cut of air interfering with the path of your Cooling Air,,

Air Dams are great, but, A) where they meat the Head and Jugs they should be as close to the Fins as you can get them, they should overlap to the back of the Jugs and Heads to force air into the Fins, B) the Intake of the Dams can be larger than the Heads and Jugs, but after the Dams Pass the Fins the Dames should end, again the Exhaust of the Hot Air should be 1.5 times larger than the Dams,,

Cool Air Intake for the Carb, it should not seal completely around the Carb's Intake, because this can force unwanted Air into the Carb at different Air Speeds and this will mess with Tuning,,

later I will try to find the site where you can read up on Air Dams

Jim

Last edited by the Wasp; 03-12-2018 at 07:23 PM.
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Old 03-13-2018, 02:22 AM
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Thanks Jim for the good information on dealing with airflow and cowls. I did not get to the field yesterday but did test run the engine at home... running it for a 6oz tank of fuel for 33 minutes continuous without problem. Noted however is that ambient temp was 56 rather than the 70 the day the problem manifest. So... maybe the problem is cured but warm weather testing is needed.

A couple of pics of the cowl.
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Old 03-13-2018, 06:55 AM
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I could not find the site I was reading about air dams, I don''t understand that no other site came up on the lists for air dams for piston powered engines, all that came up was for turbines and front air dams for autos, I don't get it !

any hoo, your engine in that photo looks so neat with the jugs sticking out

Jim
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