gas throttle set up question
 

Hi,
I have a setup question with gas engines. I recently test flew a GW Sbach 68" with a dle 30. the airplane is actually sold as 20-26cc but mine required the 30 for cg. Now this isint my first gasser, but i was never comfortable with the dle20 and its airframe earlier has my 9c didnt have a proper multipoint ignition curve.

So, with the sbach I used the 12fg & multi point curve based on the rpm readings based on the onboard tach. We basically set the 75, 50 & 25 % points and edited the rest of the curve to get a smooth response by sound. But when doing a low pass, when I added a few clicks of power to maintain altitude, nothing seemed to happen & the airplane kept telling me it was losing energy, so everytime I ended up adding more power and flying out.

I am more used to the smooth response of a glow engine, this difference in thee dle 30's response makes me feel uncomfortable. Last week my buddy flew his sbach (30cc) but he tuned his curve by ear & though there was a lag in his response as well, it wasnt as pronounced as mine.

I wanted to know whether the way I set my throttle curve was wrong or is this a matter of just getting used to the gas engine setup

Ameyam

RE: gas throttle set up question
 

This was posted by Jedi Jody some time ago, and is a good way to set up your throttle linkage for more linear response, and I think works better than fooling with throttle curves.

AV8TOR

RE: gas throttle set up question
 

First, it's not the fact you're working with a DLE engine, it's the fact you're working with a gasser. Like you're finding out, they ARE different than glow.

Second, you ask a very similar question a week or so ago. What did you change? You're going to get the same answers to this question when you ask it again now - like the diagram av8tor1977 just gave you, that I gave you the last time you asked?

If you could tell us where you're not getting what we're telling you, we might be able to better help? Otherwise, all I can suggest is spend more time trying to modify the curve you're using. As mentioned previously by a couple of guys, a better plan might be to set it up best possible mechanically (per that diagram) - then trim as required electronically. -Al

RE: gas throttle set up question
 

I asked the question a couple of weeks before and was told to set the needles correctly. I have seen this diagram before when I was messing with the expo on my 9C. I couldnt figure it out then or now. Its fine to go into degrees of deflection on a diagram but how do you even measure that on the actual throttle and servo arms? What am I missing?

Ameyam

RE: gas throttle set up question
 

OK-
Forget the degrees for a minute. All of them. Those just help the digit heads that need specifics like that.

Starting with servo and throttle arms about the same length (close is good enough), throttle stick, servo and carb throttle arm all at idle position, install the servo arm so it's pointing straight at the throttle arm or maybe one tooth away from it (no more!) in the direction it will be traveling to open the throttle. Then connect your linkage. That should leave you pretty close. When you have a few minutes, zero out your radio setup and try it. Shouldn't be that hard if you already have everything in place, but positioned a little differently. Finish up with your end point adjustments, make sure you're getting full travel without binding at either end of it's travel.

This is pretty extreme linkage differential, and if you've never messed with anything like this it IS pretty hard to get your head wrapped around it the first time or 2. Once you've set it up and seen it work though, you'll probably have it conquered.

Holler if you are still not following. More help might be had if you could take a pic of your installation. Both at the carb and throttle servo.

RE: gas throttle set up question
 

How about posting a pick of your throttle linkage at both closed and open throttle. It may be the geometry is off a bit.
As noted above; Are the end-points adjusted correctly so there is no lag or overthrow in movement ?

RE: gas throttle set up question
 

With the throttle linkage geometry set as in the diagram, what happens is that the throttle moves only a little when the servo first starts moving it, then moves the throttle more and more as the servo continues in it's travel. It takes the non-linearity out of the throttle operation that is naturally characteristic of the Walbro carb and gassers in general.

It works the same as a throttle curve, except it is done geometrically/mechanically with the linkage instead of a computerized curve in your radio. Try setting your linkage up this way, but as already mentioned, clear your throttle channel of any modifications you have done first. No curve nor exponential should be required with this linkage setup; only end point adjustments to get full throttle and idle. Try to make sure that the length of your linkage is such that you are using +100 and -100 on the endpoint adjustments, or as close as possible.

AV8TOR

RE: gas throttle set up question
 

I understand what you are saying. At the beginning of the throttle arm movement, a small opening of the carb arm produces a large increase in revs. Further down the carb movement, the ratio of the two isint as much. So you set up the throttle so it is almost inline with the servo. So initial linear movement is very little and it increases as you go along.

Yes, I had tried that on the Extra with the dle 20. Just that way, except I trimmed down a few clicks before I set up. You see, there is no idle stop screw, so idle carb arm is actually throttle cut. I set the throttle up this way, then trim up till I can just get the engine to fire. Even with this, the response wasnt linear and we finally have had to resort to expo / throttle curve anyway.

I am setting up the throttle on the extra again tomorrow. Its my cheap aerobatic monsoon flier. I will post pics then. The GW Sbach is sitting under a couple of other decommissioned airplanes that I need to store away, so I can post pics of that just yet. The Sbach throttle isint set up this way, by the way mainly because I had to resort to the curve earlier with the dle20

Ameyam

RE: gas throttle set up question
 

This mechanical geometric approach looks like a great idea. Is there a similar approach for glow engines, either 2-stroke or 4-stroke?

RE: gas throttle set up question
 

RCF - it hasn't been necessary on any glow engine I've flown in a plane. That said though, I have used it on glow powered heli throttles? That's where I learned about all this. Getting the throttle synced up with the collective prior to the radios we have today was quite a trick!

RE: gas throttle set up question
 

If you were using the #4 Ignition that comes with the DL 20.You will fight the carb adjustments and the linkage untill the cows come home and will still run ratty.Use a DLE ignition from DLE 55. All of the new circuit RCEXL Ignitions The high voltage ones should be OK.
The new RCEXL Ignition does not use a internal voltage regulater,it is much more high tech then this.I may tell about it some day or I may not.The new C&H Ignitons from Adrian are fine as is the new little ignition that Ralph and Milton are selling.
BCCHI Used to be C&H.You can not no how little I care.Going flying Tomorrow Friday ,Sat and maybe Sunday after Church.
AMA 2500

RE: gas throttle set up question
 

Regarding a DLE20 (with the original 6v ign module), Bill brings up a good point, but fails to mention a lot of guys (most?) are eventually able to see their way through the tuning and setup functions and find themselves with a pretty happy little engine (even if it is a little picky on it's needle settings)? I will not deny that some people seem to really struggle getting it right, maybe to the point where they do replace the ign. module. That does make the tuning and setup more forgiving - but some continue to have trouble anyway.

I thought we were talking about a 30 though?

RE: gas throttle set up question
 

As far as the DLE 20, I don't own one, but if I did I would certainly change the ignition unit on it. Ignitions are down to around 50 bucks now, so why put up with that stupid curve and the throttling problems with that #4 RCEXL module that comes with the DLE 20. Stupidest thing that DLE ever did....

AV8TOR

RE: gas throttle set up question
 

AV8TOR, my bet is that given any incentive and a few minutes messing with it, you would have no trouble with that module? The guys having the most trouble with it are those with little or no prior tuning experience - E.G. those that might lean and lower the low speed until the engine just kind of humms along at very low rpm - not realizing a happy 2 stroke should be rambling/unsteady on the idle, even if that means raising it a little?

Still, given the choice or a proper excuse, there's no doubt I'd grab a different one!

RE: gas throttle set up question
 

I don't know why using throttle expo or a throttle curve didn't bring some relief. My old radio didn't have either and I found a work around that is so easy and effective, I've not changed methods even though now having a transmitter that will do both.

Faced with a non linear throttle and not wishing to go into the plane to mess with a mechanical fix... there is an easy adjustment that will help a lot simply in the transmitter without the more burdensome task of setting a throttle curve. Assuming that the travel throws are correct for the amount of butterfly movement, go to the travel screen and note the total percentage of travel by adding the up and down percentages. Lets say each is 80 percent for a total of 160%.

While I'm not sure it is true for all radios, for the ones I have, the lower half of the stick movement operates the low percentage and the upper half of stick the up throttle percentage. That means if the total of 160 percent is maintained, the total travel will remain correct for the butterfly movement. With that knowledge, simply change the percentages to expand the low stick resolution and restrict the up stick resolution. What I've found to work well is a value for the low of about half the upper. For the example above of 160 percent total, I'd set the lower at 50% and the upper at 110%.

After doing so, the resolution of the low is much higher and provides far easier throttle management for landings and idle adjustment. Throttle expo should essentially do the same thing. I offer this mostly for some of those older radio users that don't have throttle expo.

RE: gas throttle set up question
 

well here goes. idle, wot, 50%, throttle cut in that order. note the engine hadn't been run to test canopy idle, so it may change a bit

RE: gas throttle set up question
 

set2

RE: gas throttle set up question
 

i have felt the #4 ignition pain. Broke my head on it for a full season before I realised the issue & got a replacement ignition. I am currently using a A03 ignition. Lets figure this out on the 20 & then I can use it on the 30 as wel
Ameyam!

RE: gas throttle set up question
 

That looks like it will work to me!

Carb arm is about the same length? End points set? Idle speed adjustment screw removed?

RE: gas throttle set up question
 

yes, yes & yes. But last time I had to add a curve (or 100% neg expo) with this same setup. Will see tomorrow how it works. Will keep u posted

Ameyam

RE: gas throttle set up question
 

Your are not going to let me get by with this are you,LOL
Youll never no how little I care.
BCCHI

RE: gas throttle set up question
 

If that works for you when you test it, great. If not, you may want to move the easy connector(ball link is safer) to the inner most hole on the servo arm. That will lessen the amount of throttle butterfly travel in respect to the amount of throttle movement from the transmitter stick.

On a side note, a guy at our club came out with a plane with a just purchased DLE 20. He asked my help in getting it running and tuned. I noticed the ignition unit was the improved version which allows up to 8.4 volts. Cudos to RCEXL for making that improvement. With a Xoar 17x6 prop, I was able to tune the high end at 8275 rpm without going into a lean setting. Pretty good for a first run. I had the idle tuned to about 1700 rpm with no hesitation when throttled up. However, the ignition module still had that curve. Engine rpm would decrease to about 2600 rpm and hold there for about 20 seconds before settling down to the 1700 mark. Did two flights that morning and the engine ran reliably.

I also noticed that the plug cap could be removed and put back on much easier than normally expected. I'm thinking DLE may have changed the tension ring on the outside of the plug cap to one that is not so stiff. That is a nice improvement also.

I would also suggest ball links on your throttle linkage, especially on the throttle arm end. I would not trust easy connectors in a gas engine setup.

RE: gas throttle set up question
 

I knew that was coming (ez link part). Those are trusted links (meaning veterans) & very reliable. In any case, throttle is now pull to open. if it comes off it will dead stick. Then, putting ball links both sides will require either full threaded rods whiich I don't have or nyrod linkage which I ant comfortable with. This setup is fairly well tested

Ameyam

RE: gas throttle set up question
 

Bill - LOL...
I'll freely admit they can be a PIA, but refuse to tell people or leave them with the impression they're junk! They WILL work - and I know you know that...

Indiomike - I don't believe the newer 8.4v module has the dreaded #4 module timing step. They learned their lesson. There is still the potential for them to do what you're describing if they're run a little lean though? Most any 2 stroke capable of the same thing, but the DLE20 with the #4 module was giving people fits because in addition to this lean condition potentially causing the problem, they ALSO had the potential for the ign. module to cause nearly identical symptoms due to that stupid step issue?

The fix for the lean condition is usually to open the low speed up a hair at a time until it will return to idle right away, or maybe with just a very brief "hang" (whatever you can put up with?). Alternatively, you can run the high speed a tiny bit richer so the combustion chamber is more easily cooled down when the throttle is chopped? That's what you're waiting for when it doesn't come right down to an idle with the 8.4 module in place. It's struggling to get rid of all the heat that WAS being generated by the wider throttle opening. A little extra fuel coming from the idle circuit speeds that process up some. It's not hurting anything as is. You're very likely VERY close to perfectly adjusted for max power there. They're just a little unpredictable on final? You can have it like that, or maybe listen to a little burble in mid range with the richer settings? -Al

RE: gas throttle set up question
 

Irecently received one of the new ignitions as a warranty replacement and I noticed the improvement right away on the throttle transition. +1 on the geometry issue, Iprinted that out years ago when it was posted and myend points are pretty close to 100/100 when done setting up. These engines are pretty much at full throttle by the time the butterfly is 1/2 open.