Z26 in a YT Edge 540

[Spiffy 1]

Although no stranger to fairly big aircraft, I got an Edge from YT recently over Christmas (was persuaded by the special offer price), and bit the bullet and purchased a Zenoah 26 (Magneto ignition) Petrol engine for it, which other than 2 petrol helicopters I've owned in the past, is my first aircraft gasser.

 

Started fitting it out, sorting the cowl and engine fitting, which is proceeding fairly well, cutting apertures to clear the Cyl head, plug, and a hole for the carb venturi - ( will get a better in-cowl silencer than the standard one supplied from Just Engines), the only thing I would like advice on, is the tank plumbing arrangements. I know I don't need pressure as on glow engines 'cos the carb is pumped, but presumably I will need a vent and fill pipe. What fittings do you petrol heads use to and from the tank, and the arrangement for fill and vent pipes?

[Darren 0]

Terry,

 

I've used fuel dots in the fuselage side for the filler, this sort of thing but can't remember where I got them from.

 

http://centralhobbies.com/Fuel/fuel_fittings/tetdots.html

 

The vent just hangs out in the breeze out the bottom of the cowl. Remember to plug it after use as a dribble of petrol in the car really stinks

 

As for fittings etc, I bought a replacement bung and tygon tubing from Just Engines (they may have dots too), otherwise it's standard 3 line tank setup.

[Trevor 25]

For the ignorant among us what are fuel dots?

[Darren 0]

Trevor,

 

A picture makes it so much easier, click on the link in my reply above.

 

Fuel dots are a metal ring that you fit in the cowl/fuselage side through which a piece of fuel tube pokes. You have a bung that when you fit to the fuel tube and push back into the metal ring it all fits nicely. Looks like a flush fitting alloy button.

[Spiffy 1]

Terry,

I've used fuel dots in the fuselage side for the filler, this sort of thing but can't remember where I got them from.

 

http://centralhobbies.com/Fuel/fuel_fittings/tetdots.html

 

The vent just hangs out in the breeze out the bottom of the cowl. Remember to plug it after use as a dribble of petrol in the car really stinks

 

Thanks Darren,

OK those fuel dots look neat, smaller than the BIG ones Ashtek Electronics are offering, though their petrol filler kit with pump looks good. Yes, it was the vent I was wondering about, I'll just route it out the bottom just behind the cowl to hang in the breeze. I'll have a shop around, Ashtek Electronics do some fuel dots but look huge, though I like the look of their gas tank and hand pump kit.

 

My DC3 has a Dubro Glow Fuel filler, where the fuel filler just plugs in, and seals when you pull it out, I "think" they do a gasoline one as well. I'll have a look around, long way to go yet, still working on cowl,engine, and carb arrangement.

 

Cowl on the YT Edge needs shoehorning on, but OK once it's past the "wide" point as the fuz narrows all the way from there onwards to the tail.

 

The venturi for the carb may have to stick out the side of the cowl, even with a carb bend, don't think it will fit otherwise, unless I don't fit the venturi, and use shorter carb bolts, when it will be completely enclosed.

 

That may give uneven running or slight reduction of rpm though I notice the MVVS doesn't have the venturi on the carb. However the carb on the Z26 is side facing not frontal as on the MVVS. Glen Models (Zenoah Agent) says just stick the venturi out the side of the cowl, it'll work better even if not so pretty. Any thoughts?

 

The Z26 engine goes in with the top part of the head and plug peeping out the bottom front of the cowl.

[Spiffy 1]

OK, have carb bend and standard intake trumpet fitted to Zenoah 26,, but engine set up is giving me some problems.

 

Don't seem to be able to flick start it like I do my glo engines, (not fast enough flick -no doubt- the prop is set to pass the sensor magnet when flicking) but it starts on a starter motor fine, that is, when my tired old Sullivan which is yonks old occasionally will it turn it over to start it up (This is a magneto ignition not electronic). Have ordered up a new dynatron starter which should cope with the compression better and an aluminum spinner for easier starting.

 

When it does start, idle is ok, but cuts when I go up to full rpms anything above the half throttle position on the butterfly. Dunno if this is too rich, or too lean. Have tried a 1/4 turn each way without effect on High jet. However, idle jet also seems to effect the top end also. Once I have the new bits in, will need an experienced gasser man to help me sort it probably. Any takers?

[Spiffy 1]

The reason for this is that the carb has a diaphragm that must have equal air pressure to the air intake on the carb itself.What you have done by adding a this arrangement to the carb has unbalanced the diaphragm air pressure(and yes the carb is that sensitive).

To resolve the situation you have 2 options.Firstly you can remove all articles and the problem will be solved.Secondly you will see a small hole in the back of the diaphragm case,if you remove the case plate from the carb leaving the Diaphragm inside you can then braze with a small brazing torch a copper tube as you would find in a standard glow fuel tank to the hole in the diaphragm plate.Once done,run a small piece of tygon petrol tube up to the opening (to the side of)of the carb trumpet and,keep in place with cable ties.

The carb will now be balanced and operate correctly but will still be very top end sensitive due to the new mixture of air 2 fuel,you will find you will need to run the top end on a leaner setting than specified.

Hope that all makes sense and is of help 2 you!!!!!!

 

The diaphragm balance hole on the plate (which is right at the side of the plate-not in the middle) was facing towards the front of the aircraft (in the prop wash), I have now rotated the plate only (it is perfectly rectangular) with the hole now at the rear away from the prop wash and in line with the trumpet, and drawing air from the same area. Maybe that will work, problem is, as my son has left home now, I used to use his small brazing torch, so it means buying another kit to do it, unless some kind soul offers

The other problem is if it is that sensitive, then it would change with the cowl on, as it is only possible to fiddle the mixture screws with it off !

[Spiffy 1]

No probs Joe. Take some time off from modeling, it's what I did for a time -actually it was rather a very long time off for me Real life got in the way.

 

But you do come back with renewed interest, enthusiasm does wax and wane. The problem is, once you get stuck into a new model/s, I tend to ignore everything else till it's done, and that isn't good.

 

I told myself not to get so involved, and if other chores or family commitments come up, do those, and not get so frustrated at not finishing a particular modeling project, until good and ready to.

 

The other thing to consider is good health - it's the most important of all, and I personally have had a nasty health problem recently (cancer), that really made me think where my priorities lay, and modeling isn't it - health first, family next and modeling a long way down the list. Take it easier, you can start again when you feel you are ready to.

[Lofty 5]

HEHE! Joe you looked like a whole new man at the flying field on Sunday!

 

Big boys toys = Yak 54 = Joe smiling away all day!

 

Turboprop RAVEN

 

I for can't wait to see this at the field, on the ground or in the air it don't matter to me. But there a saying "all good things, come to them that wait" or something like that

 

Something to keep me going at night :-

 

 

 

[Trevor 25]

if you remove the case plate from the carb leaving the diapham inside you can then braze with a small brazing torch a copper tube

 

Just a thought born out of ignorance more than knowledge, could the small hole in the diaphragm backplate be tapped for a small nipple like the pressure nipple on glow exhaust rather than brazing a tube on?

[Spiffy 1]

The plate is thin pressed steel (I think) and flattened dome shape and the hole is on the side of the dome, so its not a straight flush mount to use the existing hole. You would have to block this, and fit a nipple in towards the center. However a nipple would protrude through and that would impinge (big word) on the diaphragm which is very delicate -not a good idea IMO.

 

Joe would be correct is thinking brazing on a copper tube is the best solution, and I will carry out the mod when I have time, as I have seen this recommended elsewhere for best mixture control, but the following may have a more significant bearing on the matter.

 

I checked all my gaskets for fit, and found that the engine to carb bend gasket was not precisely lined up to the pressure hole, and that at least a third of the hole was covered up, (probably the carb bend hole had not been drilled precisely enough) so I have opened up the gasket hole so that it gets full pressure through, as the symptoms do sound like fuel starvation at full chat as rpm rose smoothly from idle up to half throttle, but above that the engine slowed up and stopped, unless you reduced throttle again. If the hole was partially blocked, it maybe wasn't getting enough pressure through to feed the carb at high rpm. The engine wasn't hot, and not seized (plenty of oil content) so it has to be mixture.

 

We shall see, next time I start her up, whether that has improved matters.

[Jimbo 0]

I'd be happy to silver solder a tube on for you if that would suffice!

 

Not sure if thats different or the same as Brasing though

[Spiffy 1]

If you are going to club night Jim. I'll bring it along (you owe my a plug anyway)

[Jimbo 0]

okeydokey!

 

(I hadn't forgotten - its in my flight box like you said!)

[Nutz 0]

I keep coming up the field with your screw driver but forgetting to give to you Jim, please remind me next we meet as it is in my TX box.

 

I won't be at club night this month due to work commitments.

[Spiffy 1]

Knicker elastic?

 

OK, after correcting the partial blockage to the pressure hole for pumping fuel (covered partly about a third by ill fitting gasket), and reversing the mixture balance hole to be near the intake, had another go at the engine this morning - Result - SUCCESS. Now able to get full rpm at full throttle. High mixture no problem, will tach it after some running in and set it just rich of maximum revs at 300 or 400 rpm lower perhaps. It's chonking along about 8000 rpm I think, as it blew the hand tach out of my hand so it's pulling well!

 

I think it was not getting enough fuel at full power because of not enough pressure and vacuum to feed carb at high revs, because of the partial blockage by the gasket.

 

Will have to paint mark up the prop a bit to get an accurate reading.

 

Low idle is a different cup of tea, VERY sensitive, and about 1/8th turn each way can make a lot of difference to both idle and transition up to full power. Now starts easily with a new starter anyway, so will carry on some running in and tweak till I'm happy it won't quit.

 

The mixture balance hole on the carb is nearest the standard intake now, so that may have helped. It's only about an inch from the intake. If Jimbo can fit a tube it may/may not make much difference to running I think, but will take Joes word that it will. The mod would be necessary with the long high performance trumpet intake probably, whether it will help here I'm not certain but it won't hurt to do it!.

[Jimbo 0]

Did that tube work on the Carb Spiffy?

 

Just wondering how you got on...

[Spiffy 1]

Didn't seem to make much difference (on the ground), so it hasn't done any harm either!

 

The hole is for automatic balance of the mixture control for changes in air pressure, so it may be a "good thing", but until I fly it I won't know.

 

The idea is that for a set fuel mix to which the carb has been set, no further adjustment should be necessary to the mixture controls, and the engine should run reliably whatever the current air pressure, as changes in air pressure (like if you fly up high it will change) are automatically compensated for by the very thin diaphragm inside the "dome" which can press in and out if pressure rises or falls and which opens and closes a very small valve as pressure changes, which balances the mixture as required. I believe the idea is to match the intake of the pressure balancer as near the engine carb intake as possible, so that they both "see" the same air pressure under all conditions and air flow.

 

Boat and car engine versions don't have this balancer system, as of course they are usually at ground level all the time (and therefore the same air pressure), and the dome and diaphragm are replaced by just a priming bulb.

[Spiffy 1]

After my contretemps with my Z26 engined YT Edge a few weeks back landing just short of the patch and breaking off the nose (the under-carriage remained attached so it tipped the nose in hard), it's all back together looking almost good as new, mostly it was just a lot of the glue joints let go round the nose area behind the cowl, plus a couple of stringers broke, so structure was re-glued back into place, a small bit of ply to repair one former that cracked and stringers repaired in just a couple hours work.

 

Couldn't match the pro-film covering exactly but looks presentable.

 

Looked worse than it actually was, now all is needed is the engine to be set up again (it was not picking up from idle properly which is why it died short on finals).

[Lofty 5]

Good to hear.....

 

Coming back to a field near you soon, on Wednesday.....?