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DLE20 - Throttle Problems

Old 08-14-2019, 05:53 AM
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hookedonrc
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Default DLE20 - Throttle Problems

This past weekend, I had an experience that I have never encountered. I have a Top Flite Cessna 182 with a DLE20 for the power, and a new carb due to a previous airplane accident. The engine runs absolutely fine on the ground and has good throttle response. It is fully tuned and no issues with RPMs and idle and at full throttle. However, once in the air, I experienced a problem that I haven't ever seen. I took off normally and the 182 flew pretty well although I did need to get some trim in her.

After a minute or two, I started to have throttle problems. The engine would run either at idle, or full speed...no in between RPM's. I pulled the throttle fully back and the engine would idle, then one click forward and it went to full throttle. It was either idle, or full speed, and even using the trim buttons on the radio (DX8) made no difference. I was lucky to even get her back to the ground, because it was either climbing or diving. I hit our tall grass area and broke off the nose gear, and tore some covering, but otherwise, the plane is fine.

I began the disassembly at home and didn't find any issues. The throttle works fine, the choke does not impede the throttle movement, nor is there any visible issue with its operation. There is an "S" curve in the fuel line from the tank with small kinks at each curve, but with the idle and top RPM working fine, I am not sure that is the issue. In fact, I am perplexed, but can believe that the fuel line "might" be the issue, but I am not convinced.

Before I go down a rabbit hole trying to assume what the issue is, is there anyone out there that could shed some light on this? I suspect the fuel line, but with the engine getting fuel, both low and high RPM, I am not sure that is the issue.

Thank you, in advance for any insight.
Old 08-14-2019, 09:24 AM
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BarracudaHockey
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Check the servo
Old 08-14-2019, 11:48 AM
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or the radio, perhaps the throttle has gone into a 'switch' mode rather than a proportional travel.....?

Check to see that your throttle movement opens the butterfly proportionally, it should and if it does...then its a very weird problem...perhaps the butterfly is not well, might check that as well...
Old 08-14-2019, 06:14 PM
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hookedonrc
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The servo was the first thing I checked and it seems fine. However, I will do more before I remove the engine from the plane. Both suggestions could be possible so I will do a more thorough testing. I did have to make a couple of switch assignments, but neither involved the throttle. Making switch changes is something new for me, and the DX8 can be confusing.
Old 08-16-2019, 05:05 AM
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hookedonrc
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Well, I spent time yesterday to check the throttle operation. I looked at the servo, the travel, and made sure no obstruction interfered with its operation. I also changed switch positions on the radio also while trying the throttle operation. Also double checked the manual choke movement and it was fine. So far no problems found.

Next step will be to remove the engine to look at the butterfly and to inspect the fuel lines. I have a 3 line system, fueling line, carb, and overflow. I may rework the tank and lines into a 2 line system to cut down on the possible failure points.

Last edited by hookedonrc; 08-16-2019 at 05:08 AM.
Old 08-16-2019, 07:30 AM
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daveopam
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Like the others I think it's a servo issue. The engine will cause a different frequency of vibration in the air than it does static. Put a new servo in and change the extension if it has one. I can't imagine an engine issue that would cause what you described.

David
Old 08-16-2019, 02:56 PM
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hookedonrc
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Thanks, that is a good suggestion and I didn't think of it. Since the Cessna 182 is scale and has an interior. If I can solve it without removing the engine it would be preferable.

The only thing I am wondering is if it is the servo, how do I test it? Last time when it started in the air, I barely got it back down. Broke the nose gear and punctured the covering.

Last edited by hookedonrc; 08-16-2019 at 04:50 PM.
Old 08-17-2019, 06:11 AM
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daveopam
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That's the $64K question. One thing you can do is once the old servo is out. Hook power up to it and thump or flick the case with your middle finger. If it has a short or a bad part many times it will jump when you hit it. Also move the extension (if it has one) around and flick it. I would also put a horn on it and see if it will hold a load by turning the horn by hand. This could point to a bad extension. I am assuming you have double checked the programming in your TX. It's unlikely the throttle is working like an on/off switch but that's easy to check. Since it worked fine on the ground it should not be the issue unless you are using a switch to idle up after take off.
I hate these kinds of problems because of the trial and error involved. If it were mine I would throw away that throttle servo no matter the test results and start with a new one.

David
Old 08-17-2019, 12:31 PM
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hookedonrc
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Thanks David,

I am going from memory, but I think I put in a low cost servo. The rest are HiTec 645 mg and are very reliable. And, what'ta ya know, the only problem one. Anyway, I started removing all the interior parts which has been pretty smooth. The darn garage is running pretty warm with our heat index around 110 Fahrenheit. Changing out the servo will follow removal of instrument panel. (Scale 182 panel, parts from I Fly Taileys.) Once out, I may just as well switch it and the extension out. The throttle in the 182 is close enough to the RX to not need one. And, I can easily have the servo checked, and even though it is new, it sat in the fuse while I detailed out the interior.
Sounds like a Viking funeral might be best for it.
Old 08-17-2019, 01:48 PM
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Truckracer
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Some analog servos have been known to have a mind of their own when mounted near ignition boxes. You might consider moving up to something like a Hitec D645 / 625mg for your throttle. Just a few $ more than the analog version and a whole bunch of difference in performance.
Old 08-17-2019, 03:02 PM
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Thanks racer.... I will check on those I already have. They may very well be digital. So adding one more is no big deal. The irony is that the ignition box is next to the servo. It's where it needs to be, but it may very well be what you suggest.

Ok, I checked and I have throughout the plane Hitech HS645 MG servos that are standard. And the throttle servo is analog ...so it looks like a suitable replacement would be the Hitech 5645 MG, the 5 designates digital.

Thanks all....not sure this is it, but it is at the top of the list after checking all of the other things. I will post if it works, so the next person will find it.

Last edited by hookedonrc; 08-17-2019 at 03:49 PM.
Old 08-17-2019, 05:45 PM
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Truckracer
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If you buy a servo, please don’t buy the 5645. Hitec has updated that servo to the D645mw that offers much better performance compared to the 5645. Frankly the 5645 was never a very good servo as its resolution and centering were in a word “terrible”! You can actually find the D series at lower prices than the 5645 if you look around a bit. The “D” series is a major improvement.
Old 08-18-2019, 05:14 AM
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Thanks, I will go to the D version.
Old 08-18-2019, 09:09 AM
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Have you ever removed and inspected the carb, throttle plate, shaft and linkage yet?
Old 08-18-2019, 11:47 AM
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Originally Posted by Truckracer View Post
Have you ever removed and inspected the carb, throttle plate, shaft and linkage yet?
LOL...now that's funny. . I will explain. The DLE20 is from a Pulse 125 that I dumb thumbed into the ground. New carb, engine dissembled and cleaned and checked. I checked the factory carb settings for Walbro on the 20. I it started and didn't even need adjustments. So it was funny that you asked.

However, I do have an update.
Got the throttle servo out, and tested. Wiggling the main wiring, or tapping the box did nothing and it has plenty of torque. The ONLY thing that I found was that during sub trim, there is a point at which it sits and flutters, but it is in the case, and the arm is not affected. Still not going to put it back in in though.

I may very well have found the problem, but that IS the 64k question. On the rear carb, the fuel intake, choke arm, and throttle are very close together with small tolerances. When the choke was open, the throttle was riding up against the open choke rod. It could very well affected the throttle operation. So I reworked the throttle travel, and choke rod was changed, and I moved the fuel inlet further away a small amount. All that, and new servo should get me back in the air.
Old 08-19-2019, 06:05 AM
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Sounds like you did find a probable cause. Best wishes for the next flight. Maybe our Oklahoma weather will get more tolerable in the next few weeks. I've got a new one I'm dying to maiden but with ambient temps over 100 I'm going to wait.

David
Old 08-20-2019, 05:34 AM
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The bounty of knowledge says do not use a high speed or high torque digital metal gear servo on the throttle. Any high quality standard servo with nylon gears is better. If available use a throttle curve and never slam the throttle.

I'm hope you found and fixed your problem. I saw a similar case with a loose engine mount and broken firewall.
Old 08-20-2019, 07:11 AM
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Thanks kmeyers, I did remember that I did not use a throttle curve, which I am going to add. I do not slam the throttle as a general rule to avoid torque rolls, or similar. Especially on a maiden, which this was, I advance the throttle slowly. However, on this, all I did was advance the throttle 1 click resulting a change from full idle to full speed. I have other servos that I can substitute if needed.
Old 08-20-2019, 07:42 AM
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“Bounty of knowledge”? Not sure where that came from. I agree there is no need for a high speed servo on throttle but what does high torque have to do with the issue? Speed and torque are relative to what? In many cases just another servo in a product line such as the Hitec 625 / 645 neither one of which are overly fast or torquey. Metal gears are recommended far more than plastic these days but there is nothing wrong with a high quality plastic gear servo for throttle, if you can still find one. The number one thing that is important to me is position accuracy and you don’t get that with any so called standard servo. I’ve seen too many examples of idle speed being either too high or dead on landing with cheap servos. A better quality, higher resolution servo resolved the issue. This is especially important with a small gas engine where even a tiny bit of servo movement at idle can affect the speed so much.
Old 08-20-2019, 02:43 PM
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Originally Posted by Truckracer View Post
“Bounty of knowledge”? Not sure where that came from. I agree there is no need for a high speed servo on throttle but what does high torque have to do with the issue? Speed and torque are relative to what? In many cases just another servo in a product line such as the Hitec 625 / 645 neither one of which are overly fast or torquey. Metal gears are recommended far more than plastic these days but there is nothing wrong with a high quality plastic gear servo for throttle, if you can still find one. The number one thing that is important to me is position accuracy and you don’t get that with any so called standard servo. I’ve seen too many examples of idle speed being either too high or dead on landing with cheap servos. A better quality, higher resolution servo resolved the issue. This is especially important with a small gas engine where even a tiny bit of servo movement at idle can affect the speed so much.
Thanks truckracer, I was hoping I would get another opinion. I have never given any thought about type of servo for the throttle. In any of my gassers that I have all servos match the torque and speed. That way, I can swap them out across same size planes that I have. Don't use much nylon, or karbonite gears, just metal geared ones.

Old 08-26-2019, 09:11 AM
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Besides the servo you could also have a receiver problem. I had a receiver that worked great on everything but the ailerons. Didn't end well. I've also had transmitter problems as well. Like others, I think your problem is electrical, not engine.

carl
Old 08-26-2019, 03:38 PM
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Thanks Carl. I have completed all of the changes, and fixed the hole in the fuse bottom. New throttle servo, new throttle arm configuration, new manual choke config. These changes added room at the carb to make no interference between them. Minor rework of the throttle pushrod, and minor changes to the fueling and overflow lines. No servo extension needed as the throttle servo is close enough. The last thing will be the throttle curve entered on the trans, but I will not make an rx change until another test flight before Sending it back to Spektrum. I am just waiting for Sierra to remill the main nose gear strut and return it.

Then it is test time.

Last edited by hookedonrc; 08-26-2019 at 03:41 PM.
Old 10-25-2019, 04:13 PM
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Just an update.

After repairing all damage, and having the nose wheel strut re-milled, got the plane back together. This time, no interior until testing and flying are successful. Got to the first test run of the engine just last weekend. Well, after doing all modifications recommended here, and some of my own, I started the engine for a ground test. This time, the idle is perfect, but upon acceleration, the engine quits. Without the engine running, all mechanical components work well, with no interference.

I think ink I have only 2 possibilities left. One is the fuel line and the other is the EI control box. However, I will test the fuel line first. When doing a visual check, there is a small bend in the line that may be providing enough fuel at idle, but is too kinked for high RPMs. Will update thread when I find the issue.
Old 10-25-2019, 06:35 PM
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Have you tried richening the low speed needle until the engine will transition normally to full throttle. This needle feeds fuel through the whole throttle range.
Old 10-27-2019, 04:45 AM
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"This time, the idle is perfect, but upon acceleration, the engine quits."

Truckracer's question is legitimate. Don't assume for any reason that this carb is not going to need adjusting. Factory settings assure only that it's going to start. They do NOT provide any assurance it's going to run right after starting. That part is on you!

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