abufletcher

I seem to have consistent and persistent problems getting the throttle on my models setup properly. It's definitely my Achilles' heel. So I was wondering what are your standard procedures for getting the throttle linkage and servo settings worked out.

For example, where do you have the throttle trim set when you first arrange the "wide open" position for the servo/throttle arm? Then how would you establish the "slightly open/idle" setting if, because of the nature of the engine installation you can't see the carb opening (as is the case on my Puppeteer)?

Then how do you do the "engine running" adjustments on the radio? And then finally what's your technique for doing the final engine tuning?

Whatever I'm doing now it sure as heck ain't working! [:@]

abufletcher

Some days I think I should just stick with paper airplanes and kites.

vertical grimmace

My Feedback: (1)

I will tell you how I do it on a glow engine. First I like golden rod cable with a clevis on the engine\throttle barrel end. Then at the servo end I like a dubro EZ connector. (This is the only place these should be used.)
I set my transmitter throttle trim to the center. I then set the barrel in the carb to be just slightly open. With experience you know what it should look like for your desired idle speed. Usually about 1\16". Then tighten the set screw on the EZ connector. With the TX and the RX on and servo connected, go to full throttle and chack that it opens all the way. Use your end point adjustments to acheive this without any buzzing when fully open. Cycle it back down to idle and make sure your desired 1\16" opening exists. Now set your ene kill switch to fully close the barrel when toggled. You can also kill the engine with your trim if needed. That is it.

TopShelf

My Feedback: (4)

Here is my general process based on having a computer radio. I do this all before I put any cowling around the engine.

-I use metal cable in a platic sleave for smooth operation; clevis on carb end; screw down keeper on the servo end (I can't remember what these are called right now)
-Throttle fully closed on carb
-Radio throttle full down including trim
-clevis on outer hole of throttle arm
-keeper in out hole of servo
-put the servo end of the cable through the keeper; pull out all slack; tighten the keeper
-actuate the throttle to full on the Tx and observe the carb position
-if way off, adjust the hole placement on servo/throttle arm until close to full max and min
-once close, use end point adjustment on Tx to get full closed and full open
-start the engine without adjusting trim i.e. use throttle stick
-once it's warmed up, bring the throttle stick down and the trim up to get the idle you want
-fine tune with sub-trim/end point/idle down/throttle cut as needed

I'm not really familiar with WWI planes so not sure if it feasible to run the engine without the cowl. I guess if you can't see the carb position, you could run it on the test bench and record max RPM then make sure you get that once the engine is back in the aircraft.

Probably not the only way but it's the way that seems to work for me.

Kent

Clay Walters

I'm no pro but on the last few planes I also used a cable. Once I determine the length I solder the cable ends and thread them thru EZ connectors on both the servo arm and the throttle arm. I firmly tighten the connector on the throttle arm with just a little cable poking thru so it won't interfere with closing the throttle. (4-stroke with carb at rear) Leaving the cable free in the servo arm EZ-connector I set my TX throttle to fully closed and press my kill button. Holding the kill button I tighten the EZ Connector at the servo.

Then I advance the throttle with the TX to see that the barrel fully opens. I adjust this by moving between the holes on the servo arm/throttle arm.

So far its worked fine.

Regards,

Clay

abufletcher

Lots of good ideas so far. The thing with a lot of WWI installations is that our engines are deeper than the rotary engines that powered the originals so we need to use a recessed firewall, which often means no direct visual access to the carb even with the cowl off. The photos below show some of the typical solutions.

I think I've got the linkage part of it down fairly well (in this case using a bellcrank to link the FS throttle arm and the indirectly placed throttle servo.

TFF

I think your set up is fine; older gas engines were done that way, and much more thought out than most of mine. I like either golden rod or small music wire run in a tube. The biggest thing is getting around the tank; if there is not enough anchor spots or it gets pinched you end up with one that does not trim the same. I set mine full throttle with half trim and see where it is at idle. I try to do it mechanicaly moving the clevis to different holes and use the sub-trim as last resort.

Mode One

As far as the adjustment is concerned, I base everything on setting a reliable idle and I start the adjustments, by setting this. I want the carb. opened at what I know to be a good idle position, Trim in the center and carb opened around 1/16th to 3/32nds of an inch. I have the push button kill switch on my TX, so when I push this button, I want to kill the engine, so I want to see the barrel close when I do this. As far as wide open, I want the barrel as open as I can get it without hitting the screw stop and stalling the servo. If I can't get the barrel all the way open, because I generally fly airplanes with engines from the larger end of the recommended engine size, I don't fret about not getting maximum wide open. I use the cable type push rods and the Ez connectors at the throttle servo and a ball link on the carb end. I don't use the idle set screw on th carb. as I rely on the throttle servo to hold the idle.

David Bathe

You have some strange geometry going on there Abu' with that bell crank solution.
Might be a dinky piece of hooby engineering but...
Why not just put a simple servo on that wood plate you have that bell crank thingy attached to?
Sure save yourself the headache of getting the servo arm action parallel and proportional to the throttle arm.
And thats the key to good throttle stick feel and throttle response.

Regarding throttle trim. On my radios it only effects the situation at throttle stick idle possition.
I set the trim middle, and mechanically ajust the servo linkage so it gives a good general idle at mid trim. Max low trim: Engine cut off and higher trim: increased idle (usefull for different weather conditions, prop choices and different fuels.
When setting the general engine throttle action Max to Low, use the servo arm possition premerily to get the same movement/arc of movement at the servo as on the throttle barrel.
And remember to set the servo ATV at 100% at each end before doing this. When thats fine, use the ATV to do MINOR tweeks at each end, cerntainly not more than plus/minus 5%.
Anything more starts effecting the proportional action of the throttle stick and engine response if you know what I mean.

Regarding carb adjustments... Now you know why the scale 4 stroke engine of choice, Laser place their carbs in a position thats more friendly for scale applications.
Rocket science.

Mode One

(I drew up a nice BMP file, that isn't supported here for some reason; so, I can't upload it).

The following throttle cable set-up has worked well for me over the years:
I run the cable through an innner Golden Rod tube, attaching the cable to the servo arm with an EZ Connector. I use a ball link with a threaded stud soldered to the cable at the throttle arm. A short peice of the outer tube of the Golden Rod will slip over the plastic portion (Socket) of the Ball link. I rough up the inside of this piece of outer Golden Rod where it will come into contact with the Ball Link Socket and do the same to the Ball Link Socket, where it comes into contact with the outer Golden Rod tube and epoxy the two pieces together.

This outer Golden Rod telescopes over the inner and provides a fairly good seal against fuel creeping down the cable and getting to the servo and inside of the airplane. It also stiffens the unsupported portion of the cable a bit. Mind you, the telescoping portion is only in the engine compartment, and no further. It is a balancing act to determine how long the telescoping portion can be without causing interference and the method needs a straight cable run where the telescope is located. Becasue the carb. is in the back on four strokes, it may not be a usable method if the throttle cable is very short in the engine compartment.

This idea is not mine and I found it in the "For What It's Worth" column of RCM many years ago. It is far easier to make, then to explain!

If the above is not clear and you would like clarification, PM me with your email address and I can send it to you as an attachment.

Mode One

Abu, I don't see anything wrong with using a bellcrank to get the proper action from your throttle servo. I have used them myself for four strokes, as the carb. in the back makes it difficult to find room coming from behind with the throttle linkage. Every thing looks Ship Shape and Bristol fashion to me (Old Sailor's Term). I like your choice in radios! You will wrap the RX and battery in foam, won't you?

abufletcher

David, first you're right about the somewhat funky (non-parallel with unequal arm lengths) geometry but the response seems fairly proportional as it. I hadn't thought about the idea of putting the servo itself on the engine mount. I've seen people mount a throttle servo forward of the firewall but haven't ever done so myself. I guess I'd worry vibration and also how to protect it from all the gunk.

The problem with any direct cable connection from the current servo location is that it would actually have to run through the tank box. It's possible but it's a bit of a messy solution. I had seen bellcrank operated throttles and wanted to give that a try. Anyway, I think I have the mechanical part figured out and thanks to everyone's advice here I think I have some ideas to try during my next tune up session.

The hard part is not being able to see the carb opening at all with this installation. I'd have to cut a whole through the left side of the model and then through the fuse doubler and even though the bottom of the tank box to be able to see the carb. There's not even a way to hold a mirror in there.

TopShelf

My Feedback: (4)

Perhaps a fiber optic video camera is in order

kdc

Isn't it a pity engine manufacturerers don't incorporate a mini servo onto the carb so all we have to do is plug in the servo.

Note to Mr Enya, Mr Saito and Mr OS you can have this idea for free if you send me one each of the engines that use it!

David Bathe

I wouldn''t worry to much about the vibrations. They're just the same ones directly behind the firewall, as they are in front of it!
Here's something, illustrated on the G'D' awful sketch that I've used in the past.
Basically it's a separate, removable fire wall that includes the engine, mount, servo and in some cases, even the tank and plumbing.
Having it as a separate complete unit really helps engine set-up, and the entire unit can be bolted to a stand and bench engine set up run/tweeked.
When happy, then bolted as one unit directly back onto the airframe.
It's a classic set up. I used it for the first time back in the 70's. It's also what Byron/IronBay recommend on some of their models. My Cessna 195 for example.

Try it next time.

Mode One

Abu, can you get a small mirror in there to see what is going on with the barrel of the throttle?

abufletcher

The Flair Puppeteer kit makes use of an integral tank box/engine mounting beams system that is intended to make getting the engine thrust right a no-brainer. And it does seem like a pretty well thought out design. However, the one drawback is that the carb of a 4-stroke is completely obscured within the forward end of the tank box.

But I think this is bound to be a problem shared by by a number of scale models were the engine needs to be deeply "buried" in order to maintain a scale appearance. I guess all that can be done in such circumstances is to get a sense of the carb opening from the movement of the throttle arm.

TFF

One reason I like the music wire is because once I clear the tank I can make a joggle to the carb. Also a little bit of "engineered" slop can help with some odd placements; a little flex at the ends can help prevent a bind in tight quarters.

abufletcher

OK. I just frickin' give up! [:@][:@][:@][:@][:@][:@][:@][:@][:@][:@][:@][:@][:@][:@][:@][:@] There is just no way that I'm going to get this engine tuned. No matter what I try, I can't get it running the same frickin' way it was running just a week ago.

I'm an idiot.

abufletcher

OK. So it's been a couple of hours for both the engine and me to cool off. I removed the Saito 56 from the Puppeteer and mounted it on the test stand. And I'm still getting about the same thing. I can't get more than 9,100 with the carb wide open. I started the engine with the needle value open about 2 1/2 turns but that seemed way rich and was only running at about 7,000. To get up to the "sweet spot" around 8,800-9,000 I needed to close the needle valve down to about 1 1/2 turns open. But there's nothing I can do to get the 9,800-10,000 I had on this engine last Sunday (which is the same range I get on my other Saito 56 and my Saito 72). I suppose the bright side is that I now know it wasn't a problem with the radio/servo setup.

Two observations: First, I notice that there seems to be a awful lot of darkish oil that pooled on the test stand from just two runs with a smallish tank. Second, there seems to be some smoke rising from the outside of the muffler (rather than exhaust puffs) after the engine shuts down. I wouldn't describe it as "thick smoke" or "black smoke," but it seems a bit more noticeable than with my other engines.

So what do you guys think?



PS. I'm very tempted to buy a new Saito 62.

Sandmann_AU

Lots of excess oil and slow max speed sounds to me like it's running rich (duh) and obviously you've tried to tune that out without success. If you can't lean the mixture out with the needle valve I'd be pulling the carb apart to find out why. I once spent four days trying to get a super tigre .61 to maintain a constant tune, pulled out at least 1/2 of my hair in frustration, picked the brains of everyone I could find at the club etc. Took it home and pulled hte carb apart to find out the barrel retention screw had come loose. It's often the simple things we overlook.

cyclops2

Only 1 important thing to remember. IF you are not electric.

THE ENGINE MUST NEVER STOP RUNNING !

So I ALWAYS set the idle speed & mixture to be the MOST reliable. WOT means very little compared to a reliable loww speed.
Battery on, finger choke of 1 slow turn over. Fires up on the second real flip.

abufletcher

On a recommendation by TFF I checked the feel of the bearing and there may be some roughness there. I opened the crankcase but there doesn't appear to be any obvious rusting. Nevertheless, I think the engine is due for an overhaul.

cyclops2

abu.

You really need someone to help you on the first couple of setups.

If you have no help. It is a long, long day.
Were the engines originally bought new by you ? or used ?

abufletcher

I bought the two Saito 56's new a couple of years ago and both have been used in other models. Generally low runtimes. Sorry to sound (and be) so clueless here but as I said in my initial post, engine setup is absolutely my Achilles heel. I've gotten to the point that I hear the changes in RPM pretty well and know the sound of a "sagging" engine (though I almost always use a tach as well). But some of the guys at the field have an absolutely magical thumb when it comes to tuning up engines. There's one "Saito guy" who has always been able to perfectly tweak any engine, but he hasn't been around.