SrTelemaster150

Please explain how plug gap would affect operating temperature as long as misfire didn't result.

Generally speaking a gap that is too wide will affect high RPM operation (missfire) while a gap that is too narrow ill affect idle.

Blair K.

I checked the Saito manuals this morning.

FG14 up to FG 21 has a spark gap of 0.4-0.5 mm for gas
FG30 up to FG40 has a spark gap of 0.7-0.8mm for gas

FG 60 has no mention other than SP2 plug being standard equipment even tho it doesn't come with one.

hpergm

SrT - indeed; plug gap cannot affect operating temps unless a misfire occurs. An ignition-induced "cylinder misfire" event will either come from limited ignition power input or plug fouling - the most usual cause-effect between gap and misfire versus operating regimes are exactly what you are saying above...

hpergm

OK, weather abated for a day, and I was able to put to the test all the (long..?!?) theory above. With good results, I am happy to say.

Set-up:
1. SP-2 plug on top cylinder (smaller gap) and Rcexl plugs on the bottom cylinders (larger gaps to avoid fouling). Made sure plug caps were 100% securely seated on all plugs to rule-out misfiring from that source.
2. Changed Klotz Techniplate to Castrol Power 1 oil to avoid carbon build-up in No.1 and the huge oily mess from the exhaust evident in previous runs.
3. Changed oil ratio from 15:1 to 20:1 to improve combustion and avoid plug fouling.
4. High needles started @ 4 turns out and low needle @ 8 turns out (previous set-up from rich WOT running)
5.Prop is still an APC 22x10.

Observations:
1. Leaning the test stand ~20-35 degrees to either side at low to mid throttle does has an effect on cylinder temps when the engine is still rich; cylinder closer to the bottom will load-up and its temp will fall (misfires due to plug fouling most probably).
2. Low needle is dominant and the engine should be tuned by that - not the high. The high is relatively insensitive in most of the throttle travel and only affects maybe the top 5% of the throttle curve. The effect of the needle on the engine takes several seconds to take hold (i.e. requires a slow tuning reaction/decision).
3. Cylinder temps will balance only when the fuel mixture is close to optimum (i.e. leaned-out). Chance misfires/fouling will occur if engine is anywhere near rich.
4. After running the engine @ WOT for at least 2 minutes, with optimum mixture, cylinder temps will be balanced within less than 10% deviation at all subsequent throttle settings, including idle.
5. The only safe way to lean-out the engine (i.e. tune the low) is by observing temperatures near the peak rpm at 50-75% throttle; there is a "peak" regime where the rpm does not change much but temps will! Why this? Because a good state of tune basically matches cylinder behavior in terms of "misfires" (= non-explosions); for example, on one case, one of the cylinders may have many more misfires (= colder) than another (= hotter) while on another case, both cylinders will have an equal amount of misfire events and thus run at the same temps. However, in both cases, the average power output of the engine (rpm) will be the same...! A further indication of optimum tune is the absence of observation #1 above - little change in cylinder behavior while leaning the stand left or right with respect to horizontal.
6. After tuning the engine just so, there will be no misfires (plug fouling) at any throttle setting, no hesitation in transition. About 6,700rpm is achievable with a 22x10.

Video(sorry for the quality and the stills - the camcorder also ran out of batt in the end...): http://youtu.be/ljXoNQvOFvA Based on my experience up to now, I would conclude that:
- The wider-gapped Rcexl plugs are perfect for this engine - avoid the small-gapped SP-2s, at least on the bottom cylinders

- Rotating the engine during initial rich running-in helps out tremendously. After lean-out, it is not really needed.

- The Castrol Oil gives out much less residue and seems to inhibit plug fouling. Also, the 20:1 ratio gives a better burn and less chance of fouling.

- The engine requires a good warm-up before achieving a perfect tune. The intake parts where the fuel is atomised and distributed need the temperature to atomise the fuel - the result will be even cylinder temps. Any rich running will cool the intake and will allow loading-up/richening and/or plug fouling of the bottom cylinders at different engine orientations. This is risky for flight. So, its good practice to run the engine @ WOT on the ground for 1-2 minutes. From idle to WOT, I found that it takes at least 30sec for cylinder temperatures to peak. The WOT running will heat-up the crankcase/inlet chamber to help good fuel gasification thereafter. Possibly also blow-out any residues from the plugs.

- The real trick is to tune the low by temperatures and not rpm. The high just needs to be open enough to provide enough fuel to the low. It is for this reason (mistake) that the top cylinder was a temperature runaway in the first runs (tuned the high first).

hpergm

Proof of a good tune...

,

Plugs dry, tips light brown.

marksp

My Feedback: (9)

Wow...that quite a temp monitor you have! Given that your tuning approach is based on monitoring the discrete temps by cylinder, I'm wondering if it's at all possible for those of us without the bench setup, I.e. already mounted in airframe.

The changes in exhaust note when one cylinder drops is very, very subtle.

hpergm

Hi, Mark. The temperature data logger is just a nice-to-have and a bit academic if I may say so- it does not mean that everybody else who has already flown the engine and did not have this tuning approach were not successful!

But yes, dropping one cylinder is difficult to detect by ear. The even more difficult thing is that the cylinders do not drop in a binary fashon usually. They may just miss 10-20-30-whatever % of firing opportunities per second - which makes it impossible to detect by ear or tacho.. The major reason I decided to invest in the data logger is to avoid... seizing the engine during peak. Contrary to single cylinders, the engine may not bog down with one of the cylinders too lean, so it is not really easily detectable.

Anyhow, I still think the best way is to fly the engine in a proven airframe (not stress about the engine AND a warbird) and take it a step at a time. After the Saito instructions and initial lean-out, the engine IS flyable. One just needs patience, it takes a while.

Blair K.

As an exercise its good to know you can sync your cylinder temps and to record your screw settings but lets not forget tuning for actual flight is still most important.

I havent had an engine yet that was perfect on the ground and in the air.
Take mySaito nitro poweted P-51 Mustang for example, on the ground you can sneak up on that sweet spot with tacho in hand and you hear those blade tips starting to whip the air with anger, let her loose in flight and it will run very rich and subsequent flights stealing a click or two per flight and 5 clicks in on the main jet is where it performs.

Yet on Saito gas radials ive found they have a weak pump in the carby and any installation with a cowl will slow fuel delivery and they lean out.

My last Saito FG had to be 7/10 ths of a turn out from anywhere near the beginning of peak rpm to stop it dead sticking or running 6 times hotter than the sun!

hpergm

Blair +1000. As you say, it's all "an exercise" on the ground.

Real tuning does come with flight. That's... another headache approaching! Airflow inside the cowl needs some serious thought. Engine will go to a 50cc TopFlite FW190. I am conteplating a close-fitting baffle plate to keep air pressure behind the cylinders as uniform as possible and also shielding the carb stack from the surrounding low-pressure airflow. Let's see.

Blair K.

Here are some pics of my Baffling that worked well for a FG33R3, it was 2.5mm ply that I held in place with Sikaflex, I installed a rear facing louver underneath as well.

temps reduced by 50-60 degrees according to my telemetry.




I be looking forward to a build thread on your FW190, they are a fantastic example of WW11 German engineering and art as well

SJN

Thanks for all the interesting data and pictures and videos :-)
Will deffinatly use this on my yet to be started FG84.

On the weak saito fuel pumps..........would it be a good idea to install a pitot tube to the vent line of the tank so you can pressureize the tank slightly ?

marksp

My Feedback: (9)

Keleo adds a pressure fitting on the FG-33R3 exhaust ring per Ray English precisely for this purpose. Connect to tank to pressurize.

johnhi

Nice work on the baffling Blair. I've just received an email from Keleo to say the build on my exhaust is completed and now being prepared for ship so I am now very excited about this.

When I get this my plan is to clean the spark plugs check the rocker arm gaps and run the engine again on the test stand to try and do the final tune before flying, I'll also connect the pressure fitting on the exhaust ring to pressurize the tank as I'm sure this will affect the set up I already have, as Hector says 'It takes a while to set these engines up'.

I'll be fitting the engine to my trusted Hanger 9 Carden Yak 54 and try and copy the baffling set up that Blair has used in the P47, I'll post pictures when I do this.

hpergm

Blair, thanks a ton for the pics - this is EXACTLY how I plan to baffle the FG-60 in the '190.
But, with a couple of "twists": first, I will try to copy/paste fake Saito cylinders in the blank areas of the black baffle (a color image or even mould a "facade" off them with silicone??) to make it look "busier".

Second, and after some search (and a lot of luck) I found something to help with cooling even further. And its' scale!

Pics speak louder below.

The only thing that really needs good attention is the balance of airflow and pressure inside the cowling - too much suction or positive, the Saito carb may de-tune. Means perfect tune on the stand but then go fly and ending up with a surprise...

I suspect this is why Ray recommends the pressure tap - so one can thenset the carb in a way which is less prone to pressure/density changes due to airspeed (fuel would be already be pressurised). The FG-60 Keleo does come with a pressure fitting. Isn't this a fire risk, though??? Are there any flame arresters for the tygon lines?

marksp

My Feedback: (9)

I also copied Blair's design for the baffle (thanks again). Significantly brought down temps. Next step is to apply paint and re-install, then I can optimize tune.



WRT to the vent line, I used the Horizon 'FKM' tubing which is designed for high temps and is fuel safe.

http://www.horizonhobby.com/products/EVOA102

Cheers

slither

It looks like the Spal fan part number is partially obscured in the photo. Can you tell us more about it? Where did it come from and how much? This might look fairly scale on the Yaks...

marksp

My Feedback: (9)

what part/picture are you referring to?

SJN

va22-ap11/c-50s

http://www.spalautomotive.com/eng/pr...A22-AP11_C-50S

hpergm

OK, now I got you.. SNJ gave you the link. The FW190 spinner from TopFlite is 100mm or 4" and will hide the boss completely. Only downside with this fan is that the blades have the right angle of attack for a CCW engine (looking from the front of the aircraft towards the tail) but the blade airfoils will be reverse when mounted this way (i.e. behind the spinner backplate); they will travel TE-first. But no biggie, the fan will just have somewhat smaller blowing force.

It does need some lathe work to fit (remove part of the the center boss and open mounting holes to the spinner backplate) plus I have not tested it @ 6.5k rpm to see if the Fiber-reinforced nylon will hold-up. OEM fan turns @1,6k rpm... Costs about 50-60 Eur or $70.

Blair K.

Which pressure fitting are you referring to? I am only aware of the crank case breather.

You can use a pressure line but I would like to suggest at least one flash arrestor in the line before the rank. Petrol plays by different rules to glow, is rather pump that fuel by other means myself.

Also i found those flat aluminium louvres tend to loose surface area when you bend them to suit your cowl, let me know how you get on.

For flow you should acheive about 1:3 ratio. Takes some time to work out but it works.

marksp

My Feedback: (9)

Keleo includes a pressure fitting on the top aft of the exhaust ring to pressurize the fuel tank (similar to glow applications). Ray determined that the FG-XXR3 benefits from fuel tank pressure so Keleo adds this to the Saito gas radial exhaust rings.

Blair K.

Now i got you, have you actually put a low range guage on that pressure tap?

just wondering how much pressure is available.

slither

OK, it looks like they have two versions of this fan... puller and pusher. Can't quite tell if they just reverse the leads on the DC motor or if it is actually a reverse blade set up. If they are airfoil shaped, then I would guess the latter, so you should be able to get either direction you need... no? I saw them for $50... might be able to source just the fan to save $$.

Running this at 6.5Krpm might be pushing the limits of the material... any ME's out there with practical experience in fan design/strength of materials that could comment? This is a cool idea!

hpergm

The 2 different versions have the same motor rotation sense - the fan blades are reversed both in AoA and LE-TE. THis is why one has to accept reverse blade profile travel (TE-first).

A 6.5k test will be done on the stand to see if it blows up. Imagine the carnage in a close-fitting cowl...

slither

Why not swap it out for the correct rotation version? I did not see where replacement parts are available, but it would be good if you could buy the fan as a part separately... no need for the rest of it.