Jason’s Firefly .46 Build

[Peter Wood 5Participant @peterwood5]

Hi Danny

The observations on using diamond lapping paste may be the explanation for the problems I have been experiencing. When I was trying to start the engine I noticed that the unburnt fuel that was coming out of the exhaust was black as were the residues inside the engine when dismantled.

I have read the article on making rings with interest but wonder whether I really need to go to all the trouble of annealing the ring for a simple engine like the Firefly? Why wont my approach of making the ring marginally oversize work in a simple engine like this. It just needs enough power to lift a Flair Cub into the air.

Anyway I have run out of Meehanite for the moment so will have to take stock whilst I decide whether to have another go at lapping.

Thanks for the comments.

Peter

[Martin Harris 9Participant @martinharris9]

Posted by Peter Wood 5 on 30/01/2019 16:31:21:

Has anybody modified this design to use piston rings?

Any observations why this should not work?

Peter

If you decide to give it a try, don't forget that normal 2 stroke practice is to peg the ring to stop it turning and catching the ends in any of the transfer ports.

Edited By Martin Harris 9 on 31/01/2019 11:23:50

[geoff walker 1Participant @geoffwalker1]

Hi All,

Dismantled the firefly yesterday for a winter service.

My "pilot", John, a friend and experienced aeromodeller felt that the engine was starting to labour over the few months of flying. I wasn't really surprised because it's been worked hard over the last year.

I was surprised when I opened it up and discovered the wear in the con rod. The big end hole was elongated by a good 0.010" so much so that the underside of rod had been rubbing against the crankcase. The small end was also a sloppy fit. I'm curious as to why it has worn so much. I used H15 alloy as specified and the crank and gudgeon pin were polished before assembly two years ago. Both ends had lubrication holes to feed the bearing surface. Is this sort of wear to be expected from a plain con rod with no additional bearing material?

Anyway using my new super dooper Seig mill it was a simple task to open the holes up and insert slimline phosphor bronze bearings. You can see the renovated rod in the photo. Let's hope they stand up better than the plain alloy bearing, time will tell.

Geoff

[Jeff DaymanParticipant @jeffdayman43397]

How does oil get to the rod ends? If it doesn't have a path to get there it may not, and if there's not enough lube you will get wear. Maybe you could pre-oil by hand before flights. Just a thought.

[JasonBModerator @jasonb]

"Both ends had lubrication holes to feed the bearing surface"

[Peter Wood 5Participant @peterwood5]

A photo of the two Firefly's I have built. I have had no success in getting the top one to run. I have not tried the front version as it currently contains an early attempt at the cyl /piston assembly.

Basically I don't seem to be able to get a fit of the piston in the liner to give good compression. My attempt at using a piston ring did not work (probably because I did not temper the ring).

I suspect that the venturi on the commercial carb is too large as well and the poor crankcase vacuum is not sufficient to draw fuel.

So the next (and probably final) step will be to make a new cylinder/ liner for the front version with the design carb adopting all the excellent advice I have been offered on this thread

[geoff walker 1Participant @geoffwalker1]

Hi Peter,

If you are making a new liner and presumably a new piston then it might be of interest to you to have a look at the website referred to in an earlier post by Ian Hewson

The site is Adrians model aero engines. In the technical topics section there is an excellent article by a guy called Ken Croft on cylinder liners and pistons including lapping and fitting.

I found it really interesting, maybe you will too.

Geoff

[Brian OldfordParticipant @brianoldford70365]

Posted by JasonB on 25/01/2019 07:03:48:

Does depend on the commercial carb, I have Perry and OS ones where the barrel moves the same as the firefly rather than in a helix and no remote adjustment of needle. Also no air bleed to lean off at idle.

I suppose with modern radios you could link a micro servo for the mixture to the throttle so that the mixture is adjusted proportionally to the throttle.

Edited By JasonB on 25/01/2019 07:04:23

A fairly common-place practice by the RC racing power boat fraternity.

[Peter Wood 5Participant @peterwood5]

Geoff.

Thanks for the link to Adrians Model Aero Engines. An interesting site and the article by Ken Croft was really helpful. Full of useful tips such as using Turps as a lubricant in the lapping process.

I made the cylinder lap he described but found that it tended to expand at the end as the grub screw was tightened which is exactly what you don't need so I have reverted to Adrians design which gives a parallel expansion along the laps length.

Now for several hours of patient work on the liner.

Peter

[Tajinder Khambay 1Participant @tajinderkhambay1]

Hello All

I am new to engineering and would like to build a IC engine. I am interested in the Firefly .46 but can not find any plans.

Please could I ask anyone if there is a link to where I can find these plans.

Many thanks in advance.

Taj

[andrew buttrissParticipant @andrewbuttriss48125]

hello can someone please get me the plans i would like to try and have a go at building it but i cant find any plans

[Glenn RoydsParticipant @glennroyds12911]

Sorry this is a very late response (my how the time flies)

To address anybody wanting drawings of the Firefly 46, the original website's (both mine and Alex) that hosted the PDF drawings no longer exist, however I think I still have my original AutoCAD 3D models and the PDF drawings lying around on a dusty USB Hard Drive somewhere.

Assuming there is no copyright (they were free to download anyway) If anybody wants access to these I'll try and find somewhere to permanently host them so folk have something to keep them busy in this Covid-19 Lockdown madness.

Stay Safe everybody eventually those pubs will open !

Cheers

Glenn

The Firefly46 CAD Monkey

[EmgeeParticipant @emgee]

Good news Glen, link please when you have them posted somewhere.

Emgee

[JasonBModerator @jasonb]

The plans are available from Sarik who took over the plans service including those from RCM&E.

Not sure of the exact copyright but expect the ones Sarik have are as arranged on the two sheets that were in RCM&E but Alex and Glen would still hold the rights to the originals so OK for then to do what they wish. Asking around can also probably find a set if in need of them now as a lockdown project..

[Glenn RoydsParticipant @glennroyds12911]

I originally created the various drawing sets for both Model Engineer and RCM&E along with a 32 drawing originals for the proving group who tested my drawing skills to ensure I had not dropped a bollock somewhere, you would assume myself and Alex own the rights to the originals? I cant remember the terms but it was Alex's baby.

I hosted the original plans for free I only feel it fair to let folk have access to them again especially in these mad Lockdown times. I'm working from home on my own and this is certainly tests my mental state having stuff to do would certainly help folk if I can contribute.

I will clear it with Alex first before hand but I cant see there being a problem being hosted somewhere. These would have to be the non RCM&E versions for obvious reasons.

Cheers

Glenn

[JasonBModerator @jasonb]

Glenn and Alex have agreed that making their drawings available to all again is a good idea so for those that want to have a go at building this nice little project they can be downloaded from my Dropbox account by clicking here

There may be a few additional drawings and renderings that Glenn has which I will add to the folder as they become available.

[JasonBModerator @jasonb]

I've now added the additional renderings to the Dropbox account as well as to my Firefly Album.

Just to tempt a few who may have missed it first time around and are looking for a lockdown project here is an external rendering and cross section.

[EmgeeParticipant @emgee]

Glenn & Jason

Thanks to Glenn for making the Firefly plans available and Jason for the additional pictures and hosting the plans on his Dropbox.

Emgee

[Roderick JenkinsParticipant @roderickjenkins93242]

Thanks guys. Downloaded and saved for the (not too distant) future.

Stay well,

Rod

[Anders BeParticipant @andersbe]

Thanks a lot guys. Downloaded and saved for a future dream.

[Author]

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