mrcoolpop

I have the 90 ARF You Can Do that I just built. This is the problem I’m having. I built the plane just as the instruction said. I am installing the O S 75 engine. Keep in mind that on this plane the engine must go upside down. When I put the engine on the stand it runs fine but in the plane it seems that it floods out and there is fuel dripping from the carburetor. What is my problem? Thanks everyone in advance.

Live Wire

What mostly causes this problem is the fuel tank is to high and the fuel syphones to the carb. Tank should be inline with the carb.

DavidAgar

My Feedback: (108)

Larry hit the nail on the head. Your tank is to high in the plane. As Larry stated, get the fuel line even with the carb intake. Good Luck, Dave

Nathan King

...AND make sure that your idle adjustment is as lean as you can make it. Most people don't lean the idle adjustment nearly enough.

JohnBuckner

My Feedback: (1)

Very common problem with inverted mounts if the fuel drips and syphons there is only one solution Lower the Tank as already has been noted. The same relative tank center/carb jet relationship must be maintained with an upright or an inverted mount or there will be runing problems.

John

ameyam

This is a very very common problem and it is unique to UCD and like designs. For example my Phoenix Topstar which is just like the UCD. I too mounted a 75ax inverted on it. What followed was a full season of engine problems, frustration, deadstick landings etc. Keep in mind these are 3D airplanes and I wanted to hover while it wouldnt even run for 2 mins no matter what we did.

Finally, I got frustrated and swapped the 75 for a FS91SI- my first 4c much against the warnings of my fellow fliers. That however was not the clincher. When I installed the 91, I sealed off the stock firewall hole and made a new one lower so that the tank centreline was in line with the carb spray bar. I changed absolutely nothing else. That did the trick. Over the last season the Topstar was the only reliably running airplane I have and even after having several near crashes (trying to do spectacular things with the new found relaibility) it still is.

Drop the tank lower, you will enjoy this airplane

Ameyam

JohnBuckner

My Feedback: (1)

Congratulations Ameyam, I remember your long frustrated threads on the subject well.

John

jaka

Hi!
Why not mount the engine on its side instead , so it comes in line with the tank!

opjose

Fuel tank height... yeah right...

The U-Can-Do does not mount the tank high enough to cause problems once the engine is running.

However when the engine is sitting on the ground fuel CAN siphon into the cylinder head flooding the glow plug and making the plane hard to start or causing hydro-lock.

You want to do the following

- You can leave the tank as it comes... remember this plane was designed for an inverted setup...

- Keep your tubing as short as possible.

- Start the plane upside down, with a heavier APC prop on it. Lean the idle as much as you can while still maintaining a reliable idle.

- Now when you start the plane normally, DO NOT prime the engine, cut fuel flow to the carb when fueling.

- Use a longer plug if possible to keep the element out of any fuel that will pool.

- Akways keep the throttle at idle cut or block flow, when the plane is sitting on the ground, UNTIL you are going to start the engine.

- Double check the idle setting with the plane upright and engine running, you want only a slight drop in RPM's at idle after a .5 sec pinch.


Do this and you'll get reliable and consistent starts and runs.

Once started the engine doesn't care which way it is oriented... otherwise our engines would shut off every time they go upside down, or nose high which lowers the tank on a U-Can-Do a full 4 inches BELOW the carb...

ameyam

Opjose,

I totally agree with all that you have written. Went through all of that and added and reduced nitro content, changed mufflers (stock and pitts), tried larger fuel lines, swapped out for tried-&-tested tanks etc etc. The only thing I didnt try was replacing the engine and changing to synthetic (I used to run castor then). The 75ax was an engine I didnt fully run-in. Anyway, with the FS91SII, I corrected all of those things, some of them basics and dropped the tank height and I got it reliably working. So much that when I tried to do a harrer roll at 50 ft and the airplane rolled half way through and headed for the ground, I was actually more concerned for the engine than the airplane (I was at 3D throws, I leveled out at full throttle just at the moment it hit the ground- actually heard a whack when it did that, was pointing at the pits, flew out first, did 1/2 circuit, landed with shaking hands and found that everything was just fine)

Ameyam

JohnBuckner

My Feedback: (1)

Sorry oppose I must disagree.

Any airplane that you cannot fill the tank up sitting on its gear and supposedly designed for an inverted engine, and have the fuel come flowing out the venturi is indeed a design flaw and very poorly done.

I don,t care who's name is on the label, cheezy no name arfs or the majors, there are plenty of examples of both.

This is the beginners forum lets keep this in context the reccomendation to start the airplane upside down, is dangerous and only just looking for trouble especially with folks that are relitively inexperianced. They will not even be able to sit the thing down while running without a makeshift stand or have someone hold it while some one else starts..

Fix the Problem Lower the Tank!

John

opjose

Yes we do disagree....

As I've said so often, fuel tank height is only an issue with siphoning.

Typical difference in height when inverting an engine is less than 1/2" on a U-Can-Do, which has absolutely no meaning in terms of pressure differentials.

Fuel weight is not an issue either given the small offset.

I can and have demonstrated this to disbelievers by putting engines on test stands and moving the tank height around.

Not till the tank height difference is QUITE substantial ( typically well over 10+ inches or more ) are there any effects on the engine.

Or engines would not be capable of running upside down, or stay flying on uplines otherwise when the effective differential is often close to those levels.

-

As far as upside down starting in a beginners forum.

Many of the "more experienced" set have recommended this here in the beginners forum to newbies who report inability to start an inverted engine.

It may not be the best solution, but for a grossly out of tune engine that cannot be started inverted, it permits the user to get the plane running and start tuning the engine. Once started they can flip it upright.

Ideally the plane should be on some sort of safety support but that's another matter.

-

The solution to problems running inverted engines is not "tank height" issues, it's to fix the OTHER setup or starting errors.

opjose

Ameyam

You were working with an out of tune, not run in, AX 75 and some unknown problems.

You cured things by switching to the FS91 ( which I'll bet had been previously used ).

I've fixed dozens of such problems for people who claimed the same issue w/o ever moving the tank.
Typically, pressurization, leaks, tuning, etc. is to blame.

On close to 30 of my own planes, I've never ever resorted to moving the tank no matter the differential.

Tank height did not cure your problems, something else you fixed along the way did.

I run both of those engines inverted on different planes w/o any problems what-so-ever, even though the tank height difference is greater than your U-Can-Do.

Tank height affects pre-start SIPHONING. That - IS - a problem if you do not preflight properly as I indicated above.

JohnBuckner

My Feedback: (1)

The whole point is not after the engine is running, Its before its running, I suppose you are going to attempt fuel the airplane upside down too?

To have this problem and not fix it when its so simple is just nonsense. To be someone who is supposidly a designer and designs in this problem is anal in the extreme for the majority of sport airplanes.

You can post an repeat yourself all you want it does not make the practice of being required to start a typical sport airplane upside down any less dangerous or completely pointless when the problem is so easily fixed in most cases.

To the original poster if you are still there fix the problem, lower the tank and forget it.

John

opjose

Ok, so we seem to agree it's only an issue before the plane is running.


That's not necessary if you close down the throttle or cap off the flow.

I'm not advocating that this is the proceedure they follow to always start the plane inverted... rather that they do it once or twice to get to the point they can get the engine running and tuned. That's it.

This is a beginner's forum right?

Most beginners would be faced with having to cut the formers to move the tank height up or down, thereby doing far more damage to the airframe and potentially weaken it.

If it were a simple fix I'd be the first to say go for it.

On most planes it isn't though and that IMHO is the issue.

The juice is not worth the squeeze.


The assumption is "easily".... and that's the problem it more often than not isn't easy to fix.

Better to learn to deal with it in that case.

If it is easy, I agree your right, do it.

Otherwise I'll repeat myself....

JohnBuckner

My Feedback: (1)

Shift some foam around, a hobby knife, Razor saw, Chainsaw or Class 1 explosives fix the problem, I will not argue the semantics of the word simple.

Exactly because they are beginners is all the reason to start learning right now and fix the problem. So much repetitive grief is caused by this day in and day out even when it is carefully explained.


John

opjose

Heh...

On most of the ARF's I've dealt with, the support/formers holding the tank in place are not easy to cut nor get to without performing rather extensive surgery on the plane.

Nor can you shift things around using foam, etc. as often the tank bung is designed to go through the firewall hole.

A chainsaw or explosives may work, but that may be beyond the scope of a beginner's forum.

geeter

My Feedback: (110)

hi , anytime you mount an engine inverted ,get a pair of hemostats. you'll need them. the fuel always leaks into the carb. had a tai -ji pattern plane the same way. clamp the fuel line off. also they have permenent fuel shut off clips that stay right on the fuel line. they cost about 1.99 at tower hobbies or LHS. these are plastic and just need to pinch them on or off. a real time saver ,not to mention engine saver. you can route the fuel line on the outside of the cowl if you have one ,and put it there.................... worked for me...........RON

opjose

Yeah I've used them. They work quite well and prevent damage to the tubing.

I believe they were designed for Helis.

HighPlains

My Feedback: (1)

I see you guys are back to tank height again. While ONE guy claims it makes no difference, people with decades more experience say it does. The rest of you make up your own minds, and consult engine manufacturers if you can. Since you can't hear any of engines run, it might be difficult to know which keyboard warrior to trust.

JohnBuckner

My Feedback: (1)

Hemostats were designed for bloodvessels not Heli's.

Yes they are in fact ideal for use with bubbless tanks and of course I use them for all my airplanes so equiped.

There is a magic tool for lowering fuel tanks to a level where you can fuel the ordinary sport airplane airplane without all the needless drama and added complexity of hemostats where there is no need. The magic tool is called a dremel.

Lower the Tank


John

mrcoolpop

I am truly thankful to all that responded to my post because I am truly a beginner. This I my first plane that I have built. My other planes have been built by a club member and I want to start building my own. Now one more question. It appears that I am getting too much gas by the engine being inverted. Most of the posts suggest that I lower the tank. How about if I add more fuel line and loop the one that goes to the carburetor, will this work?

HighPlains

My Feedback: (1)

No, the problem will still be there. Much of the problem of starting an inverted engine is that oil and fuel tends to collect on the plug. You can help this somewhat by the way you store the model. Some glow engines are tough to start for the first flight of the day when mounted inverted, but subsequent flights usually have no problem. Starting with the model inverted does help, but is very unsafe unless everyone helping knows exactly how to handle the airplane when turning it back over and putting it on the wheels. Even then, if you do fire it up inverted for the first flight, you might consider killing the engine once it is warmed up and then turning it over to restart.

mambarider

A couple of years ago, I helped a visiting gentleman break in a os 55 on a 40 size u-can-do. He said the trick was to have hemostats on the fuel line going to the carb at all times except when the engine was running or the tank was empty. He had several u-can-do's and this one was going on floats. I can say that after 3 tanks, this plane was running real nice. This man had experience with inverted engines and had it adjusted to run that way. I know that the air frame was stock, but don't know if anything else was changed.

David

JohnBuckner

My Feedback: (1)

Agreed it won,t help and a syphon can still occur. One of the more heinous situations that can and does occur. Lets say you arrive and fill your fuel tank on a nice bright glorious morning and you have done this fuel line looping band aid fix.

The airplane is sitting there on its wheels and you dicide to go over and BS with the boys a bit. Well heck great conversation but it starting to get hot so ya,ll get on back to you own pit so ya can go flying.

You pull out the trusty starter, push the button and Bang! That prop is locked up solid and you may have even damged you engine (usually a bent connecting rod).

Whoa you say it was not leaking when You filled it! Yup but that cool fuel after heating up in the sun has expanded and started a syphon despite the band aid fix (fuel line loop). Now if the prop just happens to be in the right position this syphoning fuel can now flow right through one of the transfer ports and completely fill the combustion chamber with non compresable fluid (fuel). You come along and hit it with a starter, bang goes the weasel.

Operation of an inverted installation even one with the proper fuel tank center/carb jet relationship carries many additional. procedure that you will be required to learn and practice without fail to be successful.

Actually Jaka presented an excellent idea earlier in this thread with the suggestion for a sideways mounting which raises the carbs to eliminate most of these problems. However I understand that most are not going to be willing to do this especially with an ARF. So the most practical thing I highly reccommend for anyone with a tank mounted to high is to simply lower the tank. This even if it requires a little surgery.

If you are completely new get on of the old timers in your club to help you with this most are most willing to help for only just the asking.

John