August 24, 2019, 06:50:18 am

RCMF Donations

Enjoy using RCMF? How about a wee donation to help us keep you in the style to which you've become accustomed?

Welcome to RCMF. Please login or sign up.

August 24, 2019, 06:50:18 am

Login with username, password and session length

OS GT33

Started by Thommo, September 20, 2013, 16:32:45 pm

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Thommo


OS GT33, stock OS 'Pitts' silencer, 45:1 full synthetic fuel.

Just Engines 20 x 8 W2   wood prop - 7,600 rpm (very noisy, howls through the air)
Just Engines 18 x 10 W2 wood prop - 8,000rpm (less noise than above but still too loud)


dogshome

肉(ròu)包(bāo)子(zi)打(dǎ)狗(gǒu) (meat+bun(2nd and 3rd)+hit+dog)
Literally: To hit a dog with a meat-bun

Thommo


Done some more comparisons today:

Menz S 18 x 10 - 7,200 rpm (MUCH quieter)
APC      18 x 10 - 8,000 rpm (quiet & most thrust)

The JE props though developing a fair amount of thrust are very noisy, even at reduced revs they
literally 'howl' in the air; APC are far and away the best albeit most expensive, Menz probably the
best overall compromise.

mase

This is not a cheap engine the exhaust it comes with should be working you would expect with OS.

Thommo

Quote from: mase on September 21, 2013, 23:12:22 pm
This is not a cheap engine the exhaust it comes with should be working you would expect with OS.


I believe that it's the choice of prop, not the exhaust at fault.  :xx

Sizzling

Quote from: mase on September 21, 2013, 23:12:22 pm
This is not a cheap engine the exhaust it comes with should be working you would expect with OS.


On this size of engine it is quite possible for prop noise to be greater than exhaust noise  :af

FrankS

at 8,000 rpm the prop tips are travelling at over 400mph on an 18" prop  :''

Thommo

Quote from: FrankS on September 24, 2013, 17:06:46 pm
at 8,000 rpm the prop tips are travelling at over 400mph on an 18" prop  :''



428 mph to be exact:

[attachimg=1]

JE 18 x 10 @ 8,000 rpm noisy
APC 18 x 10 @ 8,000 rpm quiet  $%&

Thommo


A couple more figures:

APC 20x8 @ 7,400 rpm

APC 20x10 @ 6,700 rpm - very quiet but slightly over-propped for model.

Maxster

on the 20x8 is that an acceptable noise for a club site?

Thommo


I would say so yes.  :af

Maxster

How many flights have you had? and is the muffler holding up ok?

Cant make my mind up on one of these or the new DLE35.  DLE will need a can, whereas the 33 comes with a pitts muffler.....

Thommo

November 28, 2013, 11:56:51 am #12 Last Edit: November 28, 2013, 12:02:21 pm by Thommo
The engine has been used in 2 models and so has had several hours running now. I was so impressed that I bought another one, however it's strange you should ask about the muffler....
Originally I had problems with the muffler coming loose; it's stove enamelled and this was causing the problems as paint was coming loose on the exhaust flange and where the bolt heads clamped onto it allowing it to vibrate, also paint had seeped into the bolt holes making the bolts feel tight.
I solved this by filing the paint (it's tough paint!) off the exhaust flange and where the bolts/washers locate also ran a 5.2mm drill through the holes, this cured the problem but took a while to figure out. Now I found that the flange had cracked around the edges allowing oil to seep out, whether this was caused by the vibration or is a design flaw I couldn't say so I'm currently using the muffler off engine no. 2.
Trying to repair the crack is problematic as the exhaust is brazed together so having it welded is out as the heat would probably melt all the braze; trying to re-braze the joint is difficult as it is now contaminated with oil and other crud.
The second exhaust I sorted as above before fitting and is holding up well, though has only had about 10 flights so far.
Also I found the original OS exhaust gasket burnt out quickly so am now using a Zenoah gasket which is laminated with metal layer in the middle. (This could have been caused by muffler coming loose?)

The Saint. (Owen)

I'm not convinced that you need to use a gasket at all, with glow engines, gaskets can cause the silencer to come loose and fall of while in flight.
What I do is to just use a gasket sealant compound (blue) and thread lock on the bolts and never had anymore trouble.
Electrickery is the work of the devil.
Proper aeroplanes are powered by engines.

Thommo

Quote from: The Saint. (Owen) on November 28, 2013, 14:12:19 pm
I'm not convinced that you need to use a gasket at all, with glow engines, gaskets can cause the silencer to come loose and fall of while in flight.
What I do is to just use a gasket sealant compound (blue) and thread lock on the bolts and never had anymore trouble.


I was reading an American forum and they recommended a product called Permatex Ultra Copper, it's a copper based high temp silicone sealant to cope with higher temps of petrol engines. Bought a tube myself but haven't tried it yet.