IMAC781

My Feedback: (2)

Guys,

Recently my 33% Pitts had an airborne deadstick engine failure from which I was able to successfully land. The engine is a DA100 on which DA had installed a new carb and reed bank last summer, so I think these are OK. When I replaced the engine in the Pitts after it returned from DA I also replaced the DuBro fuel tank with a new RotoFlow and made two or three uneventful IMAC style flights. When examining the airplane immediately after the deadstick I noticed that the fuel head was slightly below the center of the RotoFlow tank which is where the outlet communicates with the mechanical pick up inside the tank. At home I disconnected thee fuel line from the carb and was easily able to reverse pump the balance of fuel from the RotoFlow and noted no bubbles. Refueled and defueled the RotoFlow from the carb line again with no bubbles, so the new RotoFlow seems to be "off the hook". Still I am putting the Rotoflo aside and going back to a convention DuDro two line tank. I am NOT flaming the Rotoflow in this post; I found no evidence it malfunctioned. But the fact is that prior to it's installation the DA100 had operated flawlessly for eight years with careful use and service as needed with a DuBro tank; in flight number four with the RotoFlow a deadstick. So much for the fuel side.

The throttle servo is an obsolete eleven year old Futaba S9101 which was used on one large gasser with the same DA prior to the plane in question. Both use(d) throttle servo mounts on the engine box. This always looked suspect to me because of placing a servo signal wire close to the electronic ignition and servo mechanics in a high vibration location. However after many uneventful flights in the Pitts and it's predecessor with the throttle servo so configured I stopped worrying about it. Maybe went hard over to the low end? Naturally it works perfect now in the shop. However I will change out this servo to a new digital, coreless motor and NON ball bearing servo and replace the ignition switch and harness just for good measure; The switch is installed in the nose just aft or the engine, an area also vulnerable to vibration. Perhaps rumaging through my collection of old servos for one to use on the throttle of a 10 HP motor flown at a crowded club field is not a good idea.

Examining the plugs showed no tan OR grey coloration of the ceramic elements so maybe it was running a little lean although there was no sagging in vertacal flight.

Please suggest a modern standard size Futaba servo for use on ignition mounted on the engine box of a 100cc airplane. I would greatly prefer Futaba but will consider a standard size JR but not a HiTec.

Any other suggestions are welcome!

Chris in Miami, FL

AA5BY

The effort to avoid another dead stick is obviously very detailed and gets a kudo. An item not mentioned is fail safe setup. Guys seem to be divided in the way it is done with some setups to kill the engine and some to go to idle... which is yours? If you temporarily lose signal, do you have an opto coupler that kills the ignition? If transmitter fail safe is in play on the throttle, to kill the engine or go idle?

IMAC781

My Feedback: (2)

Mine is good old trottle trim/Tx kill switch. In many years I have not had a total throttle servo failure or engine mount failure but a fiber optic servo switch on the ign. battery is the only way to be sure. I actually own an updated (higher intensity light/sender marked with white dot; returned for upgrade) Jomar unit. I weighed my experience against introducing another point of potential failure and stuck with the throttle kill. Yes, I know, this logic may be nearly as flawed as any defense of cigarette smoking.

Before anyone mentions it, yes, cleaning the carb screen is on my to-do list. Crap Trap on fuel dispenser and Crap Trap in fuel line from tank to carb but the carb is recently replaced so why not take a look?

-cmh

AA5BY

Can you rule out that signal wasn't lost for a moment, causing the opto to kill the engine? Also, was a fail safe set on throttle? If so, was it set to go to idle or full closed to kill the engine?

IMAC781

My Feedback: (2)

At the time I had no fiber optic engine kill installed. Your question is one reason why not even though I own one.

Yes, one of my first thoughts was "did I accidently hit the engine kill switch?" Before retrieving the plane I checked the engine kill switch and it was still in the run position. On my radio (Futaba 10C) I believe the engine kill function only operates at idle. It is a 72 MHz radio (I'm such a relic and the fail safe setup is surfaces neutral, engine idle. The engine quit in midrange and not while operating the throttle, just cruising along; did not quit hard like no spark, sputered briefly like fuel starvation.

-cmh

IMAC781

My Feedback: (2)

Would someone please suggest a standard size digital coreless motor NON BB servo for throttle? I prefer Futaba and JR.

-cmh

AA5BY

As gas fliers know, dead sticks are not common. Given the evidence points to a fuel issue, what about a kinked tank vent line? A gas engine with its pump and less fuel consumption will run much longer into a flight than a glow engine with kinked vent line. I had a dead stick a couple years back for that reason and it was about 4-5 minutes into the flight and as was as you described... slight stuttering and then dead.
Normally a hard kink will be noted when filling the tank as when unhooking the fuel dot the tank will push the fuel back but in my case, the vent line vented out but not back in.

IMAC781

My Feedback: (2)

My feed line is supported with rubber grommets at two locations between the tank and carb and no longer than neccessary so I think that is unlikely. Thank you for your reply.

-cmh

AA5BY

Not the feed line... the vent line.

speedracerntrixie

My Feedback: (29)

Have you checked all the electrical connections to the ignition? The ignitions come with Anderson Power Poles and I have seen them fail several times. The wires tend to break right at the crimp.

IMAC781

My Feedback: (2)

Yes that's possible. From the tank vent nipple my vent line is secured to the top rear strap holding down the tank, NOT under it bit with a loosley fit second small zip tie under the main strap, then to a Jersey Modeler fitting on the fuselage. The fitting was not capped. As an incredible aside, I once completed an entire 10 min + flight with the JM vent line accidently capped. I may have been saved by having the fueling line accidently uncapped (I put the cap on the wrong fitting even though they are different colors).

I just inspected the carb screen and found an unexpected amount of crud in it which I cleaned out after removing the screen. I first removed the wrong side of the carb (fuel inlet diaphragm) and am not sure I re-engaged the diaphragm fork with the inlet needle when I put it back on (looks like you can't put the plate on without the fork enging the inlet needle). Can you remind me how to check if the inlet needle is operating? I put a short piece of fuel tubing on the carb nipple and blew gently in it, I think I hear the diaphragm/needle popping).

-cmh

IMAC781

My Feedback: (2)

Good spark on both sides when the removed plugs are grounded to the cooling fins and the magnet rotated quickly past the switch. I use Deans super connectors not Anderson power poles. I've always thought the most vulnerable part of an ignition system is the power switch located in a high vibration place. Thank you for your reply, I remain convinved the problem was on the fuel side. It did not quit hard like when I turn off the ign with the engine running but sputtered like fuel starvation or as AA5BY said a clogged vent.

-cmh

AA5BY

I've had hard crimps in the vent line and those are easily detected when filling as when pulling the fill line off, the pressure build up in the tank will immediately come shooting out the fill line. The soft crimp that allows filling but then wont vent back into the tank is the one that goes unnoticed and will kill the engine with fuel starvation well into the flight.

But... if you found crap in the screen, that could very well be the cause. I'm personally guilty of not running a three line tank because it is so easy to put a tee in the carb line to the fuel dot but when doing so, a filter gets put between the tee and the carb. I guess it is really better to use three lines where the felt klunk filters everything going to the carb. Might go back to that although I've liked the idea that filling it with two lines, gets fuel to the carb when filling for easier choking and starting but that might be a misguided thought.

IMAC781

My Feedback: (2)

Gee AA5BY this was the very first time I didn't use three lines and just put the finishing touches on a two lines with a T set up. SO much easier to get the stopper in the bottle. I used three lines in the past to eliminate possibility of air leak from tee (mine in large metal from Central Hobbies) or filler (mine capped with fitting by [link=http://www.jerseymodeler.com/index.html]Jersey Modeler[/link] Their stuff is awesome, their web site doesn't do them justice. I think with a Crap Trap on the gas dispenser and one before carb two line will be OK.

Now...Can anyone recommend a standard size digital coreless motor w/o BB servo for giant scale (mounted on engine box) throttle use?

Dick T.

My Feedback: (243)

You aren't likely to find a digital, coreless servo that doesn't have ball bearing. All I have encountered have at least one ball bearing but that one does not have a coreless motor (Futaba S3151).

IMAC781

My Feedback: (2)

Thank you Dick I was afraid that it was so. I guess my fear of engine box mounted throttle servos with BBs is without merit. No one else is complaining about them.

-cmh

speedracerntrixie

My Feedback: (29)

If there was debris in the screen then you may want to rethink the filters you are using. I have stopped using hobby filters on my gassers and use filters intended for lawn equipment. They seem to do a much better job.

IMAC781

My Feedback: (2)

Agreed but all too soon they deteriorate and become debris sources in their own.

-cmh

Uncas

My Feedback: (1)

Eight years is a long time. Many things could be worn out. However - What did you change? The tank. I would fly it again to se if it would repeat then start changing things out. The first thing would be the new technology rotoflow tank.

IMAC781

My Feedback: (2)

One more thing: I will never fly a new carb without inspecting the inlet screen. I suspect most of the debris I found came from the factory. This carb was almost new.

-cmh

IMAC781

My Feedback: (2)

I will not opine on the RotoFlow and can find no defect in it. However I am going back to the simpler DuBro as a personal preference.
This plane is not a platform for experiments.
-cmh

dignlivn

I had a couple dead sticks this summer. The culprit was the
screen on the carb. been running great after cleaning.


Bob

sensei

I use a JR D-368 mini servo mounted inside all my G/S motor boxes with no issues to date, also I do not run an on board fuel filter, I filter the gas going in my clear soda pop tanks.

MX240

My Feedback: (4)

If your plane is eight years old you need to replace the on/off ignition switch on the side with a JR heavy duty slide switch. I have seen that problem a lot this last hot summer with people useing outher brands.

IMAC781

My Feedback: (2)

The DA is eight years old, in the Pitts (with new Futaba heavy duty ign switch) on third season.

-cmh