Hi,

strictly speaking, this is a radio setup question. But I couldnt find a radio support forum so I am posting it here. I have a 9CAP with 2.4GHZ module setup with a DLE20. Now my problem is that, at landing, even if I add one click of power, the airplane just zooms off back up i.e. its producing too much power at too low a stick position. This is a classic case for a throttle curve. However, I couldnt find the setting anywhere on this TX. When I read through the manual (actually, I searched for throttle curve in it), the only references are in the HELI mode. Doesnt the 9CAP have throttle curve in ACRO mode? If not, it plain @&$%#%.

Does some one here have an answer to my problem?

Ameyam

Did you try the FUTABA FAQ page on their website?

No.

That radio doesn't support TC's in ACRO mode.

The good news, is that you can can run a basic single servo heli program on most airplanes, though the terminology is different but if you're not doing any strange mixing it should work fine.

Guys are doing that on that radio that are running variable pitch props.

Should I simply moveon to my 8FG now? I got that in October on a hunch I would need it soon. Also, I needed a second TX after my original 6EX 72mhz started having inteference issues (I lost my prized trainer to that). I havent opened up the 8FG much because I am not yet as adept with its controls as with the 9C

Ameyam

Just use mechanical differential on the throttle / servo linkage. A good description of this has been presented on this forum and was authored by Jedijody. Very easy to do and every bit as effective as an electronic curve. I've been doing this for years to prevent what I call "toggle switch" throttles.

If I had an 8FG my 9C would be on a table at a swap meet in about 30 seconds.

So yes, if you want throttle curves on your plane, its time to bust out the 8

Now wait a minute ...... I'm an old titewad and even though I own and use (2) 8Fg radios I'm not about to retire my trusty 9C. I'm not about to change out perfectly good radio equipment in old planes.

More accurately it's the DLE20- (#4 Ign module) odd ign curve issue, discussed here in the Gas Engine section a bunch of times already.
That occurs around abouts 2200-2400 rpm, then it suddenly jumps up way higher.
Primarily it's a poorly set idle, so reset your idle to 1700-1800 rpm.
NOT a big issue when the idle is properly set.

As others have stated the first generation Futaba 9C didn't have a throttle curve in 'ACRO' mode, but the "Super 9C' does, and the 8FG, 10c, etc.
What you can do & many others have as well, is program some 'expo' into your throttle, found under "D/R, EXPO" on your 9C.

Also, some fliers use a 2-idle setup off a switch on their tx's. Setup one for taxiing/ground running (low idle) and a second one (higher idle) for flying. When ready to touch down you'd flip to the lower setting. Similar to setting throttle trim lower, but on a switch.

Btw/fwiw....RCU does have a transmitter/radio section PLUS one just for Futaba radio support....
http://www.rcuniverse.com/forum/forumid_157/tt.htm

That timing curve isn't helping a darn thing, but you can work around it, negating it almost completely using differential and/or throttle curve.

ameyam -

The sticky at the top of the gas section (http://www.rcuniverse.com/forum/m_8673009/tm.htm) go to that and scroll down to near the bottom of post #20. You'll see a diagram there you would do well to study for a minute. It deals directly with the problem you're experiencing. Take a few minutes and set your throttle and servo arms as close as you can to the figures as illustrated. Then try your new setup - I think you'll find your problem has been minimized or is gone completely.

Yep, but I'd put setting the idle as first, throttle linkage geometry second, and any throttle curve/expo next.
Like I said, getting that idle set correctly cures most of it. It certainly has on both of mine!

Better make that Post #21

ameyam.....

For an example of what ahicks speaks of regarding that Post #21, look over my photo showing the throttle linkage. The servo arm originally had 4 holes, but I connected my linkage closer to the shaft - cutting off the outer 2 holes of that servo arm. The throttle shaft arm on the DLE20 carb has the included fiber arm extension on it. End result - closer at the servo....farther out at the carb to get a more linear throttle response.

Ok, Thanks guys, I will check that post a bit later. I am at work right now and last night and this morning I didnt have the time (and the strength) to take my airplane down to reset the throttle geometry. Right now my DLE20 is running as it came out of the box.

I havent even touched the needles. My ears are not good enough to note the difference in the sound in doing this, so I had one of the more experienced club fliers set the engine up and he and a few others were ok with the needle positions. So I am not sure how to set the ignition timing etc. It doesnt hesitate, cut etc so I should be close to ok. May be you guys can enlighten me / point me to the thread / post where the procedure is given.

The way I set up the throttle is I held the carb arm physically at approx middle of its motion range and then adjusted the stud servoside at neutral to get the position. I had seen Jedijody's geometry post but I am still not sure how you can measure the angles accurately. Should I get out a small protractor from a shool geometry box and check it?

Regarding the 9C, I bought it second hand couple of years ago. (Now I think I know why that guy wanted to sell it). It was fairly cheap (about $150) for the TX. It came with a 72MHZ module and I put in a 2.4ghz module. Otherwise its a full featured TX and I wouldnt want to give it up because I am familiar with it and because I have spent a bit on it. May be I should fly glow with it and port my gas models to the 8FG. In this case, should I replicate my trims one by one to the 8FG as they are from the 9C? Also, are there any user guides to using the 8FG in video or so? I wish someone would 'teach' me to use it atleast to the point that I understand what to press at which time and I am sure I am not doing anything wrong

Ameyam

Hi,
Problem is not with TX. The problem is the timing curve on the DL 20 Ign. It jumps to full retard and full advance all at once.If you Ign has a No#4 on the case,it has the screwey timing.You need a RCEXL Ign for a DL30 ot 55.
You about have to put a timing light on the Ign to see this.RCEXL nos this is not right but this is what DL wanted. Not RCEXL fault. I am flying two DL 20s.But I build my own ignitons.You can use expo on the throttle will help some but will never ovrcome the timing problem.
BCCHI

And don't let any of the forum "experts" tell you otherwise

How do you check the number on that ignition (where is it written)?

I could get a replacement ignition for the engine.

http://www.himodel.com/engines/Rcexl..._90degree.html

I noted one week on the last flight, the sudden increase in power didnt happen and I was able to land scale-like with a constant 10% power whereas the next week it kept happening time and again.

I already have expos of the throttle, almost 90% but that will only soften the center, it cant do anything regarding the sudden surge at the end of stick movement

Ameyam

It's not the sort of ign timing you can set like moving the hall sensor. What we're discussing is the timing 'curve' built into the ign module itself.

Go back to my other post with the photo of the throttle linkage, and re-read my description. It's not about "middle of motion range" but rather the linkage as mounted to the servo arm (closer to the shaft) and at the carb arm (farther out on that arm).


On mine it's a tiny round stick on in the lower right hand area on the face of the ign module. It states "4#"
Just above the dle web address.

True, but why spend the extra on an issue that's NOT really an issue?

Get your throttle geometry correct, set the idle to 1700-1800 rpm, and be done with it. IF you like, setup the 2 idle off a switch as I mentioned earlier. You can set the idle with a basic tach.

True, but you asked about a throttle curve on a tx that doesn't have such, so I mentioned the next best thing.
Going to your 8FG won't cure the issue, it'll only give you a throttle curve.

Correct the idle, fix the throttle geometry, and (optionally) set up a 2 step idle off a tx switch (IF you like).....problem solved!
Now, go fly the daylights out of it!

I've been flying an old Goldberg Obsession 120 weighing near 14 lbs powered by a DLE 20 and controlled by a 9Cap for about a year now. Overall I've been very impressed with the performance of this engine. Other than not having unlimited vertical or the ability to hover at will, this little gasser does a good job yanking this tank around. My only gripe has been that darn timing curve issue, which always shows it's ugly face when attempting to grease a landing using throttle mangement to control the attitude of the plane just before touchdown.

I've tried tuning it out, played with the geometry of the linkage, applied expo, modified the throttle curve, etc, etc to no avail, the RPM surge, followed by a slow return to idle is still there.

One thing I have observed tho is this. This surge is not so pronounced on the ground (ie. blip the throttle holding the plane). However, when on final for landing with a nice smooth glidepath established (throttle control at idle), you will hear the engine return to full idle suddenly as the plane airspeed reduces to a certain point. My conclusion is that on the ground, the prop is "loaded", but in the air it's "windmilling" to a certain degree which causes it to hang up on the high side of the curve longer.

The first few landings with this plane were interesting to say the least, but now I understand (thanks to observations of others on RCU) what's going on.

OK, there's 2 very different things going on here. They're addressed separately, but must be combined to smooth out what's going on.

The reason you can't duplicate that "drop" when you're on final, while on the ground, is because of the amount of heat in the cylinder/combustion chamber. It's hot from the flight, and it's either got to run rich enough to cool more quickly (my preference), or you can pull the power back soon enough to let that "drop" happen sooner on your flight path. The problem with that plan is that "drop" can be unpredictable. Jim and I have said repeatedly that the engine's low speed needs to be on the rich side, with idle speed trim adjusted to compensate. This is the problem we're addressing talking about this.

The other piece of this is the ballooning tendency when trying to use throttle to flare for a landing. That's where you need to know full power from the gassers are typically nearly all in by time the throttle is half way open. The last half of the throttle movement produces very little extra power! That engines power IS NOT linear when compared to the throttle opening! The first quarter of that throttle travel needs to be spread way out on your stick! That's the reason we're talking about having the throttle and servo arms placed the way they're suggested in the drawings posted earlier (go back a couple of posts).

In short, the most important piece of those illustrations is the fact that the SERVO arm is pointing nearly straight at the engine when on idle. Set up like this, there is going to be very little THROTTLE arm movement at first, even though the SERVO arm (and throttle stick) are moving much further.

When both of these problems have been addressed, that step in the ignition module's timing curve is not a big deal. It's not even apparent. It does take some screwing around, and the knowledge that the engine's power output does not match up with the throttle opening. It's not even close.

Put that DLE20 on an AW PROX260 "Freestyle" and at 7 lbs you can hover easily & pull-outs are like a missile.
Hovering is all about the thrust to weight ratio......but you knew that.

ahicks gave a very good overview of what's happening.

A little more about my previously mentioned 2-stage idle off a tx switch;
The pro fliers we see at events like Joe Nall, Tuscon Areobatic Shootout, FG Huckfest's, and other events, often fly such extreme maneuvers that they found sometimes the engine could die, or nearly so. Since the normal eng idle was too low & really meaningless while in flight, they came up with a 2-stage idle off a tx switch.

When taxing around, during takeoff, and on final ready to land, a lower idle setting is preferred. On these DLE20's I set mine at around abouts 1700-1800 rpm for that portion. For in flight/flying I set mine slightly above around abouts 2000-2200 rpm. Some adjusting to suit YOUR preferences may be needed. But the end result is the lower switch/idle setting forces the throttle to come down below the odd #4 ign curve issue, and the 2-stage idle off a tx switches just plain eliminates the odd ign curve issue. It still exists, but is no longer any concern.

One thing that has not been mentioned is getting rid of a throttle with the conventional detents and going to smooth friction such as used on heli transmitters. I did this years ago for most of my radios. I firmly believe in a good mechanical throttle curve (differential) but even with that, with a course detent on the throttle stick, one click more or less throttle can be way too much. With a smooth throttle you can put it exactly where you want it. It would be nearly impossible to fly a heli smoothly with a ratcheted / detent throttle and collective stick and the same logic applies to an airplane throttle. Try it, you might like it.

Yea, I've converted quite a few airplane flyers into smooth throttle after flying one of my planes with a heli transmitter with the smooth throttle.

My 8FG is a heli transmitter. But much on that later.

My work schedule and the rehab I am undergoing to prevent that hamstring pain I am gritting from over a month did not allow me to even touch the airplane today. I also received an Aeroworks Extra 300 30cc I had ordered and just finished inspecting it. It already 11.30pm and I really dont have the patience left to work out my throttle today

I will be having rehab tomorrow as well but on Thursday I hope I can take the airplane to a more experienced flier to set the throttle geometry right. I still need to workout the logistics tomorrow though.

I read through the post and I am not completely sure I understood it fully. It will take me some time to revert on this problem. One thing is for sure- I am going to open up my 8FG and setup my next two airplanes- GP Reactor Bipe/ FS91SII and AW Extra / OS GT33 with that Tx

Ameyam

Good point there too. Ex heli pilot here as well. I hadn't even considered sharing that thought.

The solution to your problem is really easy. First of all you have an excellent TX. The 9CAP have two mixes with curve, i think they are mix number 6 and 7. You can set the throttle as a master and one aux channel (7,8) as a slave, you can connect your throttle servo to the slave channel and program that curve. This trick works perfect to me.

Javier

Thats super, Javier. I will try that on the model this weekend. Should I rely on the onboard tach to set the curve? i.e. I can get readings from idle through WOT and then plot that on a graph. Then mirror the curve about the linear to get a negative curve that I need to set for throttle and then set the corresponding points on the slave by changing the pecentage while the engine is running

Ameyam

Yes!