Outside Loops
 

Hi Guys,

I'm having a little trouble with my engine dying when doing outside loops. I enter the manoeuvre from the top at about 1/3rd throttle and the engine starts play up just before the bottom (about 4 o'clock) of the loop. The engine dies either at the bottom or just after the bottom when I'm starting to open the throttle right up to complete the loop.

The engine I'm using is an OS 1.60 FX with a Perry pump. The tank is a 16 Oz two line set-up with a standard clunk. The tank is mounted on the CG.

I suspect the fuel is dropping to the front of the tank leaving the clunk out of the fuel. On a full tank the engine appears to do outside loops fine. The engine seems to do all other manoeuvres fine although I haven't tried an outside loop from the bottom while inverted...

I'm considering trying a few things like a heavier clunk, more flexible clunk line or even a header tank.

What are people's thoughts and have others seen this problem?

Cheers
Jason.

RE: Outside Loops
 

I think you've answered your question already.
The fixes you are proposing sound reasonable. Definitely go for the most flexible line you can get for the clunk as well as a reasonably heavy clunk. A header tank is often a good idea. What plane is it on?

RE: Outside Loops
 

Hi AussieSteve,

I see you're in Tianjin... I worked there for two years back in the 1990's. I can only imagine what the polution is like now.... In all the time I was there I only saw a blue sky once! What surprised me was the RC equipment the locals had up there... They had better gear than me!

To answer your question, the model is a 73" QQ Yak. I used it at my last pattern comp for the first time and outside loops presented this problem. My Pinnacle is currently under repair due to a landing mishap/brain fade.[&o]

I had another thought just now about using two clunks... One for the back of the tank and one for the front with a T piece joining the two lines. I'm not sure it would stop air being sucked through though. I think air from the rear clunk would pull through faster than fuel from the front clunk.. Not sure about this one. Might be a good experiment candidate.

Cheers
Jason.

RE: Outside Loops
 

Oh yes - Nothing has changed, the sky is still Grey. (I first visited here in the late eighties) and there's a lot more cars on the roads these days. They are doing thier best to clean it up though and we have had a lot of blue skies this year (even able to see stars at night - without too many Tsing Tao's required:D). Sure makes me appreciate the Perth Skyline and quietness when I go back there for leave. The gear the locals use is certainly good. I've seen almost as many 14MZ's here as I saw in the US while I was there. They're a great bunch of guys to fly with as well.

I wouldn't advise the 2 clunk with "T" piece setup - it's almost guaranteed to give you air when you least need it.

RE: Outside Loops
 

This is not an uncommon problem. Y.S users are very familier with this problem. Most likely your engine is sucking air. Perry pumps don't work too well that way. O.S. sells a special clunk, the O.S. Bubbless clunk. p/n 71531000 for this problem. It is listed on the 1.60 parts listing. Or you can use the DuBro filter clunk. It works fine on my 1.60. Before I installed it I had exactly the same problem.

BillB

RE: Outside Loops
 

I had a similar problem with an O.S. 91FX in a 3D plane, where the engine would die if I did a blender with the tank about half full or less, or an outside loop with about 1/3 or less. Got the O.S. Bubble-less clunk and the problem disappeared. Runs the same in all attitudes, even with a very small amount of fuel remaining in the tank.

RE: Outside Loops
 

Thanks for your help guys.

I have just ordered one of the bubbless clunks and will give that a go first. I will install a very flexible pick-up line at the same time. If that fails then the header tank will be tried..

I'll make sure I report back my findings so others can learn/troubleshoot.

Cheers
Jason.

RE: Outside Loops
 

I used a OS160FX / OS'F' Plug / Perry VP30 pump / Hatori Header / Aeroslave Carbon Pipe all last year in Pattern.

Ran standard tank over the CG with basic clunk and dubro medium fuel tubing right through. All I did was richen the pump half a turn and it never missed a beat all year.

Had a small issue with the needle turning in flight, but stretched a small piece of dubro fuel tubing over the needle and 'ratchet' finger to hold the finger against the needle and it was fixed.

I am thinking that it may be a simple fix like flexible clunk tube and/or heavier clunk, but I doubt whether it will take much . . It's a GREAT combo . .

RE: Outside Loops
 

I am wondering if anyone has tried a bladder tank. These are pretty much standard in pylon.

RE: Outside Loops
 

Is this happening in any particular maneuvre or just outside loops, and also, outside loops from the top or the bottom?


P.s. Dreadnaut: ShOcK HorOr! Gasp! Amaze!, Tetra, the pattern tank masters have had 16-20oz bladder tanks since the 90's.

I think the only reason they went out of vogue is their colour changed or perhaps the wind shifted or some other reason....


...plus is sucks to fill a 20 oz tank with the tetra syringe, actually, I find it suckworthy to fill a 8 oz tetra these days.


is that lazyiness or do I need a bigger tank in my planes?

RE: Outside Loops
 

Hi Rendegade,

It's happening in outside loops from the top. I have not tried it inverted from the bottom yet. I think it would be an issue in any manoeuvre where throttle is being used in a vertical downline. When the tank is full it does outside loops fine. It's only after using about 1/3 rd of a tank that the issue shows up. In the sportsman sequence I would have used ~ 1/3 rd of a tank by the time outside loops comes up.

I suspect that on a vertical downline the clunk is completly out of the fuel. If I was at idle it would probably be ok because it would be sucking less fuel. The more I think about it the header tank may be the best solution however I will try the OS clunk first.

With a header tank I assume it would still suck air into the header when in a vertical down line. Not sure if this would present an issue or not.

Cheers
Jason.

RE: Outside Loops
 

I would submit that you pump and or low speed settings are too lean. If you increase the pump pressure (richen it up). Then you can much better control the fuel flow with the carb adjustments. I would submit that you are the edge of being too lean on the pump and you needles are opened up further rich to compensate, however when you are needing the pump to provide fuel it is not there.

I seriously doubt it is the fact that you are getting a big gulp of air due to your tank clunk setup.

However what do I know I run YS. On the YS DZ engines they are very senstive to air bubbles in the fuel. This is why we use the "foam clunk" pickup. Well you don't have to run the foam clunk, you can runa regualr one and the engine will run fine. Its just when it gets low on fuel in the tank it will start to get air bubbles. The engine will surge and could quit. This is why we use the Bubbless type of clunk pickup. If you don't use this bubbless pickup on the YS DZ enigne you don't get the problem you describe...instead in violent manuevers like a snap roll or hard corners the engine will get the air bubble not in a smooth outside loop.

I would also submit that the fuel is likely not running to the front of the tank like you thing it is. I personally think the fuel tends to stay in the rear of the about 90-95% of the time. Or maybe more. In things like stall turns and violent snaps and such I think it can go forward but in most cases even a downline I don't think the fuel is sitting in the front of the tank.

I think you should richen your pump a bit to increase the supply pressure to the carb. Then re-set your mixture and I would bet the problem goes away.

The perry pumps in my experience with them don't seem to hold their settings too well especially over time with lots of flying. Personally I think you would be better off with a demand pressure regulator like the cline or the Iron bay regulator. I know Iron Bay is not in business anymore but I think the cline is still available.

Then again I don't know much about it I fly YS

Troy Newman
Team YS

RE: Outside Loops
 

Thanks Troy,

I will try adjusting the pump and low end so they are richer this coming weekend. I did try leaning the low end, richening the top end and leaning the pump last Sunday only because I thought my fuel consumption was too high and it seemed rich on the low to mid range. That problem turned out to be that the overflow tube had rotated only allowing the tank to be 3/4 filled.

I must say that this model and engine has performed faultlessly until a few weeks ago when outside loops were performed.

I'm sure that I will get to the bottom of the issue by a process of elimination. It's been a good learning experience anyway.. It really gets you thinking!

Cheers
Jason.

RE: Outside Loops
 

If it has only just appeared,have you changed anything?
Maybe it is a simple as a pinhole in the fuel pickup tube in the tank.
I had a model once where a similar thing happened, I opened the tank, changed the internals and messed around with all sorts of stuff. I eventually found a pinhole in the aluminium tube for the pickup piep just near where it exited the stopper inside the tank.

RE: Outside Loops
 

Hi Steve,

I have only just started to do outside loops with this model. It seems to be fine with other aerobatics. The fuel lines and pump pressure lines were the first things to be replaced. Been caught by that before too..

I fitted a new tank this afternoon and have also adjusted the pump to provide more pressure. Fingers crossed...

Must be brass monkey stuff up in Tianjin now... I remember standing outside the Sheraton for my ride in -13 C.. lol The coldest I experienced was -16 in my office when the reverse cycle aircon died.

Cheers
Jason.

RE: Outside Loops
 

That makes sense. - good luck with the new settings. Let us know how it goes.

It is a little frosty now down to about -6 degC. It's due to snow (actually - it's late - the official report said it should snow on the 10th:D). for those in places where that is normal, for us Aussies - anything below 5 deg C and a clear blue sky is "extremely" cold.

As a hobby business, I import to Oz a few excellent F3A planes and IMAC planes made here by small volume manufacturers - the quality is exceptional. I've taken advantage of my time here to make some excellent contacts with some quality manufacturers. Did you get involved much with any of the RC guys here? There's a very strong F3A crowd nowadays as well as the long standing Helicopter guys.

RE: Outside Loops
 

Hi Steve,

I was working there in 1993 - 1995. It wasn't until late in my sentence (felt like one.. lol) that I met a guy who worked for Otis and he was putting together a trainer in his hotel room. He had never flown RC before and he asked me to test fly it. We went out to an area where people flew. I'm not sure it was an official field or not but it was next to an old hanger with a big concrete slab out the front and fruit orchards in the surrounding area. There were a few people there and if memory serves me correctly, an F3A ship was there. We flew the trainer for a few flights and then decided to do a few basic aerobatics (loops etc) and the wings folded. I don't think he had the fibreglass bandage on the centre section from memory. The guy that took us out to the field was named Mr Chen. He apparently worked in a factory that made models including RC blimps.

That was my only contact with the local RC scene unfortunately. It surprised me that the locals were able to afford to fly RC... At the time, the ARF industry was only just starting to get going in China.

Do you have a website or details of the models you're importing?

Cheers
Jason.

RE: Outside Loops
 

Hi Guys,

Flew quite a few outside loops on the weekend in between the rain showers... Yes we finally have some rain here in Sydney!

The motor performed far better with the pump re-adjusted to provide more fuel and mixtures tweaked. I think more adjustment is needed because the engine did burble a little at the bottom. It didn't cut out once though which is much better. I'll probably adjust the pump another 1/2 turn in to provide a little more fuel.

Thanks to all for your help.

Cheers
Jason.