Phil finally building the DF

[Colin Leighfield]

Fair enough Phil, but that engine will not be on half-throttle all of the time, so be careful. What I describe to you is a known issue, if you lengthen an exhaust you need to increase it's volume along the length to minimise back pressure, the exhaust valve can overheat without the engine overall seeming to be too hot. It's too late when you find out.

I don't deny that you might get away with it, but I'm cautious on things like this.

[Phil Winks]

A very fair point Colin especially on the expansion rate of hot gases along a tube this is a point I always make when considering the airflow though a fuse on electrics that draw high amps,

I hadn't considered the fact that a valve can get hot when the head isn't, though I am in my defence taking advice from a well respected engine guru at the club, so will ask these questions when I see him next,

alterations to the exhaust duct are not impossible and won't change the asthetics to much the way I see it a simple branch to double pipes around the point this one is already joined would cover the points you've raised

[Colin Leighfield]

It's one of those things Phil, you could well be ok but you never know. I'm also influenced by experiences with air-cooled motorbike engines and our model engines are really the same technology. Also it's known that lengthening the exhaust pipe moves the power lower down the rev range, although for DF you might want that with a bigger prop. The key to exhaust valve temperature will be the combination of engine load and exhaust restriction.

I suppose I'm also influenced by thinking how good it would look to have one of those beautiful looking exhaust pipes down each side, and that would probably eliminate any risks, real or imaginary. What with Lindsay's new "DF2" coming along, this approach to vintage looking models is really interesting. About time I woke up to the fact that relaxed undramatic aeroplanes is really where I should be now.

[Phil Winks]

I've had a chance to investigate a little here Colin, the silencer efflux is a measly 3.25mm diameter according to my digital callipers and the home made duct has an internal size of 6.2 so there is fair allowance for expansion, My club expert, who really is a good source of knowledge on engines, seems to think that although this pipe is long ish its not as long as some he's seen and because the duct efflux is in the prop wash and cut to exit square into it the resultant pressure drop caused should give me little if any increase in back pressure, to quote him "if there was any significant increase you would have to lean the engine down below the factory settings to prevent it running to rich" and to be fair she seems to be perfect on the factory settings if a little lean on the bottom needle, I guess flight tests will show where the power band is though I'm running it on the prop recommended in the RCM&E review which is a finer pitch but slightly larger 10.5x5 bolly as opposed to the 9x6 or 7 thrust seems pretty impressive for a model of this size too had to put an extra 2kg weight on the portable bench as with a 1kg one it was trying to move at full chat

[Colin Leighfield]

I'm pleased that you'ved checked it out Phil and hope you don't mind me mentioning it. You can't be too careful on things like this. It can turn out expensive.

[Phil Winks]

Posted by Colin Leighfield on 01/09/2014 19:30:29:

I'm pleased that you'ved checked it out Phil and hope you don't mind me mentioning it. You can't be too careful on things like this. It can turn out expensive.

No absolutely not Colin I aint no expert on IC engines, ok I have some knowledge but more of full size and not with modifying them so every view and bit of advice is more than very welcome,

I made a start on the undercarriage this evening and ran into a couple of issues, one no captive nuts inside the bearers, I should've considered this all earlier and 2 bearers not broad enough for standard saddle clamps.

So having to make my own from brass sheet, and I'll have to be careful with the screw lengths, as the battery rests on top of the bearers, points sticking out will be a recipe for disaster, however they are progressing ok pictures tomorrow evening hopefully.

[Phil Winks]

Having stepped away for a day I went into the shed and looked for some suitable screws to mount the U/C with when I came across what had been an impulse buy from model fixings

That solved the forgotten captive nuts, Phew !!!!!!

So on I pressed with the bending soldering more bending more soldering a little drilling and finally the bolts went home

and so she is finally on her feet,

and while she was upside down I spotted how tidy the engine bay is, as you do.

the remote glow will be wired to a plug on the fuselage side just under the main wing trailing edge

[Phil Winks]

No news on the DF tonight as its our clubs mid week flyin on a wed guess what after tonight I'll be flying this and several others at Greenacres next year

[Tony Bennett]

looks smashing sir and now you have your "A" i look forward to seeing it at greenacres next year.

[john stones 1 - Moderator]

Congratulations Phil

John

[Phil Winks]

Thanks fella's now I really must get on with those wheels this weekend, or whats left of it after saturday morning at work thankfully the airfield is closed this weekend so no temptation there but the other club airfield is open sunday morning

[GrahamWh]

I really like your exhaust work Phil. How did you attach it to the SC exhaust? I've seen your pic on the first page, but can't quite make out what you did.

Edited By GrahamWh on 04/09/2014 21:53:42

[Phil Winks]

Graham The original Idea was to bolt it on with a pipe clamp affair brazed to the pipe with a short cut in the pipe to allow it to clamp properly much the same as this joint between the front and rear pipe

However

The final detail to eliminate vibrations being transmitted down the pipe which is bolted solid to the fuse I used a short piece of silicone tube (rated at 180 degrees C) to make the join I managed to find some gun metal coloured tube so it doesn't stand out too much just visible here

Edited By Phil Winks on 04/09/2014 22:08:34

[Chris Barlow]

Looking good and congratulations on the "A" Phil! Looking forward to seeing you and the DF at Greenacres next year.

That exhaust layout is looking good & I may have to try that on something in the future!

[Phil Winks]

Thanks Chris it still hasn't fully sunk in I was thinking today about flying Sunday and thought whose likely to be about as my instructor is away, dooh I thought you don't need an instructor lol still got the silly smile on my face,

Back to the DF all I've done this evening is paint the U/C legs and prep the lathe to finish the wheel rims this weekend but every little helps as a certain supermarket would have us believe

Edited By Phil Winks on 05/09/2014 20:13:26

[Chris Bott - Moderator]

Did someone say A cert? Very well done Phil, I'm looking forward to seeing you at Greenacres already.

[Phil Winks]

Thanks Chris and nothing will stop me next year not even a poorly van like this year I'll rent one if necessary,

after all I'll have 3 yrs worth of mass build models to fly so I'll never be out of the flight line queue LOL

[Phil Winks]

A little time in the shed after work this afternoon and I've finally got my head round assembling these wheels, well the 1st wheel any way

the view most will have

and the view the rivet counters will have

I've seen better but for a stand of scale I'm pleased just need to see if they stand up to the runway at Smeatharpe

The tyre is solid nitrile chord, the rim 68mm Rain Water Pipe the hubs, custom made on my little lathe from Bright mild steel, and the spokes are steel wire

I'm leaving the construction details out here as I have no desire to inspire anyone to follow my lead only to discover they ain't up to the job, just a tad over cautious maybe. They do seem very solid

Now do those U/C legs look a tad spindly? Maybe I need to clad them in balsa or something.

[john stones 1 - Moderator]

Lovely job Phil I am impressed

Do those u/c legs look spindly ? not to me they don't..they look vintage

John

[Phil Winks]

Thanks John after a trawl through the other build blogs opinion seems to be pretty evenly split on the U/C question, so I think I may leave them as they are for the time being.

[Phil Winks]

Thanks John after a trawl through the other build blogs opinion seems to be pretty evenly split on the U/C question, so I think I may leave them as they are for the time being.

Edit

How did this double post occur Not me double tapping Well I dont think so  perhaps a kindly mod will delete this one

Edited By Phil Winks on 06/09/2014 18:36:10

[kc]

Excellent wheels Phil! What is the rim made from -plastic pipe or metal?

[Phil Winks]

Posted by kc on 06/09/2014 18:45:14:

Excellent wheels Phil! What is the rim made from -plastic pipe or metal?

Thanks Kc, the rim is from 68mm plastic rain water pipe once assembled they're not a flexible as you might think

[GrahamWh]

Thanks for your reply re exhaust Phil. I may end up doing the same on a cirrus moth in the future.

[Phil Winks]

Another nearly full days work and I'm at the point where I need to start on the tail feathers.

Both wheels assembled and fitted, plus a rocker cover guard.

the guard will protect the rocker cover in the ceratin eventuality that she noses over on the unforgiving concrete runway at Smeatharpe airfield, though the prop will take a beating

The tail skid is a simple piano wire affair

and the equipment bay is getting pretty full. the "ashlock connector" protruding from just aft of the wing seat is for the remote glow lead, and although the power switch is a little large it will handle a full 6A, more than the 5 servo's are likely to draw even if they all stall at once