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Post  Dizzyman2011 Wed Feb 13, 2013 8:35 am

Maybe the small shim
Makes a
Difference because the exhaust ports are then opposed and air flow over both are equal other than that I'm not sure just experimentation I think that and I got lucky
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Post  John Goddard Wed Feb 13, 2013 8:37 am

Are we talking a cylinder shim here Phill?
If so don't forget as well as the ignition
Timing you're also altering the port timing
Induction etc.
In the olden days at the track some of the
'experts' used to stick an extra one or two
Base gaskets (paper) under their X7 cylinders
Don't know if it make any difference cos they
were always behind me. Till I fell off of
Course Very Happy
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Post  Dizzyman2011 Wed Feb 13, 2013 8:47 am

Yes cylinder shims not head shims mmm interesting I wonder if it also makes a difference as this is an oldie with fully open exhaust ports must get better flow surely ?
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Post  John Goddard Wed Feb 13, 2013 8:48 am

I gotta do some work today so can't tinker
But if you can wait till tomorrow I'll do
A tached back to back with the extended Bee
Avec et sans muffler.
There's no two ways the Cox mufflers
Murderise revs, my 09rc is about 3k down
With.
The analogy I'd use perhaps is we're attempting
To make a BSA Bantam run like say an RGV
Perhaps we shouldn't be surprised when they don't
Want to. Goodness knows I've tried.
lol!
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Post  pkrankow Wed Feb 13, 2013 8:51 am

If you shim the cylinder up then the head should be shimmed less so the compression ratio remains the same

EGR isn't all bad, case pressure gets boosted.

I know there is a maximum allowable SPI for cox engines, but can't find the reference.

Phil
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Post  John Goddard Wed Feb 13, 2013 9:37 am

pkrankow wrote:If you shim the cylinder up then the head should be shimmed less so the compression ratio remains the same

EGR isn't all bad, case pressure gets boosted.

I know there is a maximum allowable SPI for cox engines, but can't find the reference.

Phil

Don't forget chaps it's the Oxygen burning with fuel where we get our 'go' from.
With spi and a muffler the spi ingests Oxygen scarce gas into the combustion process.
So less 'go' and perhaps more erratic running.
Very Happy
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Post  Dizzyman2011 Wed Feb 13, 2013 9:51 am

True true and surely then that part in burnt fuel in a hot state is not what you want mixing with your next charge of f to a mix especially as the burn is more efficient when cold maybe this also has an effect reducing efficiently while a positive of increased crankcase pressure as was said is a good thing perhaps the hot gas negates the added pressure mmm got me thinking now
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Post  Dizzyman2011 Wed Feb 13, 2013 9:53 am

Out of interest has anyone made an air intake scoop to raise crankcase pressure ?
Think I might start another thread with this on !!
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Post  RknRusty Wed Feb 13, 2013 12:12 pm

Diz; our forum thinking man, not afraid to tinker. Wink lol!

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Post  Dizzyman2011 Thu Feb 14, 2013 2:11 am

Thanks rusty might write a book one day
"101 things u have never thought about thinking about"
Could be the next best seller or could be aflop like my ram air idea
I shall change my avatar you have really made me laugh with "the thinking man not afraid to tinker"
I think it should be "Phrase of the month"
1st prize to rusty

lol!
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Post  Dizzyman2011 Thu Feb 14, 2013 4:47 am

Well the fuel provider has dried
And drum roll ........ I've finished a project
Celebration time " alt="" />
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Post  Dizzyman2011 Thu Feb 14, 2013 4:48 am

Alternate pic ...." alt="" />
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Post  John Goddard Thu Feb 14, 2013 4:57 am

Can I be the 'Tinkering man afraid to think'?
Very Happy

Ps
Love that cowling, just like the FF5 but done properly.
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Post  Dizzyman2011 Thu Feb 14, 2013 5:30 am

Cheers johnnie just a shame that the fuel proofing decided to take some paint off while drying !!! Might have to touch it up but then ... Paint over fuel proofing ? Then more fuel proofing ? Think I'm fighting a loosing battle
The tinkering man afraid to think ... Lol I like it !! lol!
Now I'm gonna have to look closely at your ff5 cowl
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Post  Dizzyman2011 Thu Feb 14, 2013 5:32 am

Weighs in without fuel all up at 126g with a 17" span mmmm still wondering about performance yes it will fly prob quite quick but stunts maybe not !!
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Post  John Goddard Thu Feb 14, 2013 5:46 am

Have you got one of the old 3 bladers?
Just input on the thrustometer I reckon it would strangle
it sufficiently.

PS
I couldn't find a 5 4 but have dug out a 5.5X4 for this afternoons 'tale of the tape'.
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Post  RknRusty Thu Feb 14, 2013 8:28 am

If it won't stunt, add an inch of faux flap to the trail edge. That'll lower the wing loading plenty enough to turn a loop.
Pardon me, but isn't your fuel tank a bit behind the CG?

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Post  Dizzyman2011 Thu Feb 14, 2013 8:44 am

Hey rusty good peepers am having balancing issues with this nose heavy models I realise that cg will alter as the fuel runs low which isn't ideal to say the least but don't really want to add to much weight to the tail bad practice I know when I balanced it initially I forgot to take into consideration the solid cowl bad news on my part coz now she balances about 1cm in from the leading edge good idea about the Te though might even make it useable and put flaps on it yet oh and I thought this project was under my belt !!!! Maybe not
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Post  Dizzyman2011 Thu Feb 14, 2013 8:46 am

So you think a 3 blader is the way to go with this never had or used one will have to punch it into the machine and go figure might be buying one while I'm away yet !!
Am awaiting vids johnnie will be very interesting
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Post  RknRusty Thu Feb 14, 2013 9:02 am

Dizzyman2011 wrote:... she balances about 1cm in from the leading edge good idea about the Te though might even make it useable and put flaps on it yet oh and I thought this project was under my belt !!!! Maybe not
Nah, working flaps are too much trouble for this plane. I'd say wait and design another one for that. If you extend the TE, it will it not only make it more maneuverable, but will aid with the nose weight problem with something useful. And if you still have to add weight to the tail, remember, it only takes a tiny bit back there to shift the CG back to where you want it. You could have the flaps glued on today and painted, a tad of tail weight and get that baby in the air.

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Post  Dizzyman2011 Thu Feb 14, 2013 9:47 am

You could be right although to stick 1" on would be a bit messy I think as I have rounded the tips so either butcher it and stick some on or working flaps might just see how she flys without and then make a decision more thinking from the man that does lol!
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Post  John Goddard Thu Feb 14, 2013 11:05 am

Bearing in mind I was always a disappointment to my Mum as well......!

No Vid I'm afraid I was loosing the light for the tach (I used 2 btw)
so cracked on without but'-

It is a new engine with only 25 cc through it before so who knows...

Bit of a surprise really
Without muffler topped out at 13260/13200 on second tach
happiest around 12500 on both tachs
With muffler topped at 12700/12600 other tach
happiest at around 11,300 where it sounded as if it would buzz till the end of time fuel permitting.

Very Happy

PS
30% one gasket
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Post  Dizzyman2011 Sun Feb 17, 2013 2:50 pm

Hey John mmm interesting maybe it needs rinning in a bit more not as much of a drop in revs as I thought though which is good we're u using the 51/4 prop ? Don't have any 3 bladers but that might be the way to go nowhere seems to have them but will keep looking out for them what engine were u using ? The tach never lies but it seems a little slow on the rpm front no ? Normally get around 19 k on some of mine with 25%
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Post  John Goddard Mon Feb 18, 2013 1:13 pm

I dunno Phill, the engine has only had 2 tanks through it but if we cross ref the thrustometer and the
bee review sticky 13,000/13200 at 41 watts is right on the money with a 5.5X4.
Very Happy
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Post  Cribbs74 Mon Feb 18, 2013 1:41 pm

Bernie has the 3 blade props brand new. I have a couple used as well if needed.
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