snoozer

My Feedback: (41)

What prop size and pitch would be recommended for a Webra 50GT?

Also, what is the Glow Plug of choice for the 50GT?

This is my first Webra so I'm not sure of what to expect from it. It's turning 16.4K with an 11X8 prop and stock muffler. I've got an Ultrathrust muffler ordered for it. Any comments or info on what I should expect would be appreciated.

Thanks in advance

proptop

My Feedback: (8)

I'll tell ya, if it's turning that kind of r.p.m. with that much prop and a stock muffler, you should be giving US tuning advice![X(]

Are you sure your tach is working properly? 16,400 with an 11 X 8 seems impossable... to me anyway. (unless this is one last April fools joke?)

I can get close to 14,000 with an APC 10 X 8 and Ultra Thrust on 15% and an O.S. #8 plug.

Depending on the airplane, you could use anything from a 9x8 or 9 for speed to a 12x4 for 3D.

djlyon

Yup I agree with proptop your motor is magical. His suggested prop selection is right on. I have one on a balsa nova using a modified rossi tunned muffler. The engine moves the 6lb airplane around and straight up like rocket launcher.

Denis

NM2K

My Feedback: (14)

---------------


Some tachs read high with a low battery.

Putting an 11x8 on a Webra .50 is heresay, blasphemy - well, you get the idea. It truly is not a good idea. The Webra .50 Speed and GT are meant to scream, not lug.

Anything from a 9x8 to 9x9, 10x6 to 10x8, 11x5 to 11x7 should be okay to try without running into preignition. On the 11 inch props you have to be careful when running any fuel over 5% nitro without using an extra head shim to lower the compression a bit. These engines are meant to scream. Did I say that before? <G>

I have a NIB .50 GT that is going on my Global Mach I Delta ARF. That should get it moving a bit more than the standard .46 that most folks use. When I hit the lottery I'm going to buy a Jett .76 for such applications.


Ed Cregger

DarZeelon

Snoozer,


Since you are new to RCU (Welcome!), I strongly suggest that you never 'misquote' RPM figures on any engine!

It is a sure-fire way to make your posts very unpopular.

A full length tuned pipe equipped .60-.61 engine, with a 24 mm bore and a 22 mm stroke, from the high-speed high RPM early '80s F3A pattern days, spun an 11x7 - 11x7.75 prop somewhere between 14,500 and 15,300 RPM.

The current Jett BSE .90LX R/C with JettStream LX muffler can only spin this prop size (APC 11x8) at 15,000 RPM.

...So you are basically saying your standard muffler equipped Webra .50GT makes nearly 31% more HP than a tuned muffler equipped Jett .90LX... Or making 3.2 HP (APC), or 2.79 HP (MA)...

Was that prop not a 9x8, by any chance?
Was that reading taken near a high tension line, with weak tachometer batteries?

DarZeelon

Ed,


The Jett .76 is a torquer; not a racer.
It has narrow passages for high flow-speed and high torque at mid RPM (10-11K).

The .50 is the largest high-RPM member of their .40 block engines.
It will show 17K on a 10x6 APC.

snoozer

My Feedback: (41)

Oops, I unintentionaly mis-stated my prop size.
I have a MA 10X5 prop on the engine.

I didn't think about the battery condition in my tach, so I'll put fresh batteries in and check it again.

I to thought that 16.4 sounded high, but I wasn't sure.
I'll try to post a picture of the tach reading later this evening or tomorrow.

Thanks for all the comments.

proptop

My Feedback: (8)

Ahh...10x5...O.K. that sounds more like it

The Webra .50 will rev up so 16.4K isn't in the "self destruct" zone...but it is above the practical range for most of your typical "sport" flying. I've heard of 18,000 or so being the upper limits (connecting rod might let go if it gets much above that on a regular basis?)

What airplane is it in or going to go in?

Welcome to RCU BTW [sm=thumbup.gif]

Edit: As far as plug...both of mine have always had O.S. #8's in them, with no problems.

snoozer

My Feedback: (41)

BTW, the MA is a prop I happened to have on hand but I'll swicth to an APC before flight. I don't usually use MA props which explains why I had it handy. I'll try an APC 10X6, but I may go to a 10X8 or 11X5 because I really don't want to destroy the engine. The throttle response on this Webra is fantastic.

Also, I'll double check the fuel for nitro content. This is only my second 2-Stroke as my other engines are all 4-Stroke. My other 2-Stroke is a TT .46 Pro that I've been very happy with.

I bought the engine to put into a GP Patriot that is on my list of planes to build, but I don't want to wait till I get around to building it (I build pretty slow) so I'll put it in a Nitroplanes Starlight 40 which looks to be pretty much a Patriot rip off.

proptop

My Feedback: (8)

[8D]
I would suggest an APC 10X7 with the stock muffler.

I'll agree with ya on the throttle response
I've had both of my .50's (a few subtle internal mods done to ea.) in a World Models Dago Red...with the U-T muffler and APC 10X8 and 15% Powermaster I got 13,500 with one, and 13,800 with the other. For a .50, it hauls the Dago Red around quite respectably.

DarZeelon

Snoozer,


That is quite a bit more probable.

However, Master Airscrew limit the RPM of their props to 160,000/diameter in inches, which for a 10" diameter means 16,000 RPM.

If you run that prop at this RPM, or fly it (which causes RPM to increase due to unloading), you would be risking disaster from a thrown blade...

I agree a warm plug, such as the OS #8, Enya #4, Novarossi C-6S, or K&B-1L are appropriate.
The lowest cost plug is the TowerPower, which is very similar to an OS #8.

djlyon

You really shouldn't run that engine on more than 5% nitro unless you have added a shim to the head to increase the squish band clearance. Best is to just run it on 5%.

Denis

Test005

APC 12X4
OS #8
Byron 5%

...Good engine!

4dogspete

Another issue on a Webra 50GT
I'm running an 11 x 5 prop using 15% nitro and a Tower plug.
Starts and runs fine, but if I crank it up, it gets to top rpm then quits immediately.
May be getting too hot. Not sure about that?
I'm thinkinng the piston and cylinder is too worn.
This engine was in a previous profile model that lost battery or signal and went straight into a pond. Broke the crankshaft which I replaced and it's now in a new profile model that I cannot get flying due to the unreliability of the engine..
Any thoughts anyone?

MJD

My Feedback: (1)

What happens when you richen the top end?

turbo.gst

My Feedback: (8)

Webra's don't need 15% nitro. I actually like the fact that run well on FAI ( 0%/ 20% Castor oil ) to 5% nitro. They throttle fantastic! Try some lower nitro or add some head shim to run the higher nitro fuel.

4dogspete

With a bit more rich on the needle, it just seems to blubber and when it gets cranked up, it just dies to apoint I can't save it.
This engine seems to have good compression, but I ordered a piston and cylinder to be sure.
FYI - I've been running 15% or 20% nitro on this engine previous to the crash and never had problems.
Maybe the shim is the right answer?
I typically use 20-20 fuel for all of my 2 and 4 strokes.

DarZeelon

Pete,


Nitro solves very few problem, if any at all.

Running any engine on more nitro than it was initially intended for; even if one shims-up the head, is not a solution either.
It just changes the problem to a slightly different problem.

This engine was originally intended to be run on 0%-5% and can be coerced to run rich on 15% (as the manual allows).
Trying to run more than that will just give you trouble - the engine might become a 'rabid dog' and bite you.

MJD

My Feedback: (1)

You've had the engine apart.. this couldn't be something related to the disassembly/reassembly process could it? A rotated liner, an air leak, some such gremlin? Just reading the part about replacing the crank and wondered if something crept in during that process.

Are you getting anywhere with it?

4dogspete

Thanks so much all for your thoughts and suggestions.
Right now I'm on a vacation and have no time to fiddle with it for the time being.
The first thing I'll try is to try some 5% fuel to see if that does anything.
After that, if it doesn't do a fix, I'll take it apart to see if anything's amiss. I don't think so as I've rbuilt quite a few motors in the past.
I did order a new piston and cyslinder set, so may install that and try again if the fuel thing doesn't work.
Thanks again everyone.
Pete

jaka

Hi!
11x6 or 11,5x6 APC for low winged sport planes and 12x4, 12x5 or 13x4 for slow flying high winged planes or 3D types.
9x7, 9x8 APC for smaller (130cm in span Q-500 planes) .

A good fuel is: 5% nitro and 15% all syntetic oil like Aerosynt 2 or 3 or Motul "Micro" and the rest methanol. No more than 5% nitro is required for perfect throttling ability.
I use 15% all synthetic oil like most pilots do over here, but 20% Castor oil works good too.

Nova Rossi 4 or 4A is a good plug, but as usual OS 8 or Enya 3 works good too.

Kmot

My Feedback: (24)

I have a Webra 50GT, that is completely stock, out of the box, and has been broken in and flown numerous times on Powermaster 15% nitro fuel without a single problem.

FWIW..........

NM2K

My Feedback: (14)

Our "problem" is that there are probably differences between the Webra .50 GT, which I suspect has been westernized somewhat (lower compression) and the more familiar Webra .50 Speed (actually the .40's of long ago), which entered the US with their European hymen intact.


Ed Cregger