Taking the Petrol Plunge

[Snorbitz]

This shows you how close things are going to be. I've had to put some countersunk holes in the wood block to accomodate the carb fixing screws.

I'll have to make a cut out for the choke lever too. Its shown here in its normal running position but when closed it clashes with the block.

[Snorbitz]

This is my routing for the manual choke lever. I think using a servo to operate it is just excesive and anyway i don't have enough channels available on my reciever for anything else. I'll support it from the 2 engine mounts with some home made aluminium brackets. It only needs operating prior to starting then it sits doing nothing.

Edited By Shuglu on 13/07/2010 09:11:44

[Snorbitz]

Ok so i've mounted the engine onto the test bed and connected all the fuel lines and electronics. I've tried to isolate the tank and the electronics as much as i can from the vibration as i'm expecting quite a lot initially. Here it the set up.

The fuel tank is sitting on some foam and the CDI unit is soft velcro'd to the table. I've used a throttle servo as i don't see the need to be messing with the levers so close to the prop if i don't need to.....it'll give me an idea how responsive it is to servo inputs too.

The rest of the switches/batteries/reciever and opto isolator are sat in the grey box which is also sat on a rubber mat.

[Snorbitz]

If anyone's got any questions on what they've seen so far please put your hands up. Likewise if you want anything photographing that you can't see or dimensional info just let me know.

[Steve Hargreaves - Moderator]

Fire it up, fire it up!!!

 

Might be an idea to put some foam under the CDI too......I believe they should be treated like receivers & soft mounted if at all possible......

 

How does the choke work? is it one of those sprung flaps that stays closed until the throttle is fully opened & then it springs open?

[GONZO]

You may wish to consider making a hole through the firewall to allow the carb to breath. From the photo it looks much too close to allow for a sufficiant flow of air.

[Snorbitz]

The First Run: Well i mixed up a 25.1 oil/petrol mix and filled the tank full. Charged all the batteries and made sure the isolator was working. A light tells you when its active which is very handy i find. Just went over the engine to make sure all the bolts were tight and the linkages were ok and following the starting procedure went for the first fire up. Closing the choke flap(manually) with the ignition off i turned the engine over by hand to draw the fuel up to the engine. I've used a full length piece of tygon of around 750mm so it took quite a lot of turns but it did draw it all the way up eventually. I then opened the choke flap fully and turned on the ignition and with my leather gardening glove on spun it over.....and again....and again. Nothing!!. I felt i wasn't spinning hard enough so i got the electric starter out. It then fired straight up. I think it just needed a good squirt of fuel into the carb by the pump which i couldn't manage on my own. Its quite a shock to hear it run for the first time. having being used to glow engines no bigger than 9cc a 26cc petrol is quite a change and this engine sounds like a completely different animal. Its very loud....maybe too loud for some i fear but it ran quite well to start with all be it a bit lumpy. It never cut out and after a few minutes i took the revs upto about 2500 and then 3000 and as it warmed up it really settled down. There is no doubt that vibration is a factor i will have to deal with when it comes to instaltion ibn the airframe but i'll cross that bridge when iget to it. After about 10 minutes running i stopped it via the TX and did a quick inspection for leaks etc. Then fired it back up...this time by hand. It more or less fired first time and the way i would describe it is like hand starting a petrol flymo. I am acutely aware that this engine is very powerfull and its not something you'd want rapping you over the back of the knuckles so i may opt for the electric starter when its finally in the plane itself.

Edited By Shuglu on 13/07/2010 10:32:30

[Snorbitz]

The choke is a single butterfly operated via the lever on the outside of the carb and latches open or closed using what feels like a d-tent (spelling?) spring or similar. I don't think its effected by throttle position and after you've started it it just sits in the open position.

[Snorbitz]

You're rite in your observation GONZO it is very close to the mounting block. On the test bed i used the nylon engine mounts that came with the model and there's at least an inch between the carb inlet and the wooden mount. The block of wood you can see in the earlier photos is what i will be using in the plane has a carb size hole in it already but i will need to open it out just a little as there will be fuel lines passing through there and maybe some electrical wiring too.

[Snorbitz]

So back to the running-in. I ran the engine for 20ish minutes at around 3000rpm....thats about 1/3 throttle on the TX which is about right. Then turned off and let it cool down naturally. Then after wiping the black spots of oil/soot off my neighbours garage door and my ankles which i hadn't noticed before started it up again by hand. I think the 25.1 mix has something to do with the spots of mess (i must add its nothing compared to a glow engine's goopy splodge). Even after just one heat cycle the engine is a lot smoother with a reduction in vibration and maybe its just a bit quieter... its still way more than a glow but getting better. You can tell just from the way the fuel is jiggling about in the tank.

So i repeat the process for run No2, Starting after just a couple of flips and taking it up to 3500 for 25/30 minutes. Its barely used just over half a tank after 45mins which is around 230ish mls,  which ok is unloaded and low revs but i'm very excited at the prospect of the fuel savings to come. It will have paid for itself in no time.....thats what i'm telling SWMBO and to be honest i think i'm right.

Run No3 went ok an i have to admit i did blip the throttle a couple of times before i turned it off. Anyone who says they don't is lying!!!. I'll be honest with you....its awesome....it sounds very powerfull and really wants to rev....there is no lag in throttle response whatsoever. I would say its comparable to the F1 engines i work with for response and thats saying something!!. The noise will quite literally shake your fillings and your neighbours will hate you while you run it in but hey they should turn there telly up. I admit to having a little tingle of excitement down my spine to think i'll be flying it soon. I've stopped at 3 runs for now as i've ordered an 18" prop to replace the 16" i've got on it at the moment. Then i'll continue with the running in. So far i'm very happy with the whole package. Its used around 600mls of fuel and hasn't missed a beat. Fingers crossed its a good omen!. The noise factor may be an issue to think about but i won't do a noise meter check until its fully run with an 18" prop and is in the plane. I'll stay with the supplied silencer too until i know for sure what the final Db reading is. 

Edited By David Ashby - RCME Administrator on 13/07/2010 12:14:16

[GONZO]

Great stuff!! Looks like its going to be lots of fun in the plane. A few observations:

with no velocity stack on the carb you will get fuel spit back at low revs and although low oil content be sure to fuel proof the inner edge of the hole.

Vibration, use servos with metal gears and have a look HERE

[GONZO]

Almost forgot about the noise. One of THESE  may help if you have room.

[Snorbitz]

Do you really think a pitts muffler would reduce the noise?. There's nothing at all in the can section of the exhaust that it comes with it so its not surprising its so noisy.

[GONZO]

I think the original exhaust is best described as an exhaust deflector. I think that the pitts is only slightly better otherwise it's make your own time or go to JE for a custom made item.

[Snorbitz]

Has anyone ever used these for engine mounts. AV MOUNTS ?

[Steve Hargreaves - Moderator]

I'm no expert but I would avoid these....you are relying on the bond between a rubber block & a steel washer to retain your engine from what I can see

 

The solution from Gonzo looks much better to my jaundiced eye....you have a positve retention of the mounting bolt behind the firewall & the rubber bushes isolate the motor to prevent any vibration reaching the airframe....

[Snorbitz]

It was just a thought as i've got access to these at work. Never mind.

Edited By Shuglu on 13/07/2010 14:43:37

Edited By Shuglu on 13/07/2010 14:44:53

[Ultymate]

Don't use those mounts I've seen them used and they're not up to the job far better to hard mount the engine to the firewall. As for the Pitts silencer some are better than others.Cannister type silencers are best for noise but a lot of models are not can friendly ie there's not enough room for a can in the fuselage.

         Don't judge the noise until you get the engine out in an open field environment, if you're running it in or near to hard structures ie buildings the noise will be magnified 

[Snorbitz]

Just a little update as to where i am with things. The engines now done 2.5 hours of bench running and i now have (after a short delay) my 18" prop to fit. I'll do another couple of 20minute sessions then i think it'll be time to mount it in the plane. Hopefully all in and plumbed up by the end of the weekend.

I purchased an "Easy mixing bottle" which incidently i've seen offered on some popular model web sites with the oil fuel ratios marked on the side so you don't have to measure it out so acurately and the first time i used it i poured a measured amount of fuel and oil in only to discover that its quite a bit out in its calibration so i double checked my measuring jug and 50ml syringe. They are fine but the mixing bottle is at least 50ml out which is miles out so when you consider the small difference between a 25-1(40ml) running in ratio and a 40-1(25ml) normal running amount per litre.

If i'd just gone by the bottle readings i'd have ended up with somethng like a 13-1 ratio and a very black spark plug!!

So i'll have to look into that some more to see what can be done but theres a warning there...if you're going to get one of those types of jugs try to have it measured accurately before you use it regularly. Don't go borrowing the wifes best pyrex measuring jug caus you ain't going to be her best friend for a while if you do.

It would explain why so many folk can't get their petrols running nicely though!!

I'll be back with some piccys on Monday and tales of how smoothy the engine fit went. or not!.

[Steve Hargreaves - Moderator]

In a recent column in the mag Brian Winch told us about a measuring syringe that has the different ratios marked up the side...25:1, 40:1 what ever...you select the correct ratio....suck up some oil....squirt it into your petrol & away you go.......I'm just trying to find it on Google......

[Snorbitz]

I've just been talking to a friend who "knows" his 2 strokes and he says that when the time comes to change to synthetic oil i should treat the engine as if i'm running it in all over again. Interesting thought. Sometimes a sudden change to synthetic can be very damaging. I ran the engine to max revs just briefly over the weekend prior to taking it off the test bench and was pulling 7500 rpm with the 18x8 Master Airscrew. Surprising how anything thats not bolted down tends to blow around in the draught!!!. Its still early days yet but the idle is very good now with just a little vibration. Our club is invited once a year to fly at a local event which is on the 8th August so my mission now is to get the plane finished for that. I'm on holiday next week so progress should be quite quick after the weekend. I'm aiming for a maiden on the Thursday/Friday to iron out the bugs.

[Steve Hargreaves - Moderator]

I've said it before, that I'm no expert, but I can't see why a change in oil should be "very damaging".....there is nothing mystical or magical about petrol motors...they are mechanical components with bearings & metal to metal fits that require lubricating with oil at the correct ratio. I can't see the manufacturers (who after all should know a bit about their product) warning that a change in oil would be very damaging.....!! Not enough or the wrong grade oil would cause problems but other than that....

 

As long as you use a 2 stroke oil designed for air cooled engines in the correct ratio I'm sure you'll be fine. Personally I would use a synthetic oil as I think they are generally better than mineral based oil but I would have no concerns about swapping from one to the other. Since the amount you will use will be miniscule I would splash out on the best racing oil I could find!!!! I think our learned colleague Brian Cooper suggested Bel-Ray...?

 

What did your friend say when you asked him why it should be so damaging?

 

I found the article by Brian Winch too...about the Miz Mizer oil measuring syringe.....it was in the August 2009 issue so a bit further back than I thought......check out thearticle in the mag or if you're a subscriber look up the digital issue.

 

Good luck with the maiden...

[Snorbitz]

I asked my friend about the oil situation and his explanation comes from Kart engines which rev to extremely high numbers and what he said was over time oils build up a glaze on the inside of the cylinder and to change straight to another oil even from one different mineral to another requires a process that he calls "re-washing" which is effectively a way of slowly washing away the old build ups and replacing them with the new. He has known folk change straight from one to another and they have siezed their engines as a result. It kind of makes sense to me but then maybe i'm being overly careful.

I think i still have the copy of the magazine you mention so i'll look that out later. I'm afraid i don't subcribe any more....still buy it every month though..

[Snorbitz]

Its been a while since i last updated you on things so this lot should bring you right up to date. The engine fit has gone very well. I dummy fitted everything first which is a lot of work but worth it in the end. So for starters i fitted the spacing block supplied with the model but needed extra spacing so i used the models nylon engine mounts as they were the correct thickness as well as the actual engine mounts to get the correct firewall to prop-driver face distance. You'll hopefully get my drift from the photo.

[Snorbitz]

I drilled the wooden block to allow the fuel lines to pass through it for tidyness. Breather and filler lines come out the sides and the carb line out through the top. The ignition module fitted snuggly into some vibration protection and into the gap at the bottom of the engine bay all secured with a cable-tie. The opto isolator was mounted on the other side of the firewall and no extensions were needed.