stunthanger.com
Engine basics => Engine set up tips => Topic started by: frank mccune on October 15, 2018, 04:46:16 PM
-
Hello All:
One of my flying mates has the above problem that he would like to solve. The engine breaks into a 2 cycle at the top of the maneuver too late to give any help to get any additional power. Perhaps it would help if you know some details about his setup:
Plane: Old Big Tudor
Engine ST G51
Fuel 11-11-5
Prop Wooden 12-5
Lines 60'x.018
Stock engine
Tank Uniflow
The engine runs like a well oiled sewing machine in a 4 cycle mode.
Suggestions/comments?
Tia,
Frank McCune
-
Hello All:
One of my flying mates has the above problem that he would like to solve. The engine breaks into a 2 cycle at the top of the maneuver too late to give any help to get any additional power. Perhaps it would help if you know some details about his setup:
Plane: Old Big Tudor
Engine ST G51
Fuel 11-11-5
Prop Wooden 12-5
Lines 60'x.018
Stock engine
Tank Uniflow
The engine runs like a well oiled sewing machine in a 4 cycle mode.
Suggestions/comments?
Tia,
Frank McCune
Well, I work on sewing machines for a living now, so I know what that should sound like. I would try this:
1) APC 12.25-3.75 prop
2) longer lines, probably 63' or so eyelet to eyelet.
3) Turn the needle in to anywhere from 9500 to 10,000 RPM.
You are probably running way too rich for so much pitch. You are probably running so rich because you are on 60 foot lines and trying to slow it down to a comfortable lap time. The G-51 will want to run more RPM than that. That is my educated guess from experience running ST. G51's since 1994 or so.
Type at you later,
Dan McEntee
-
Hi Dan:
Thanks for the tips. My friend is a perfectionist and he is really frustrated! Are all Stunt people high strung?????Lol
Be well,
Frank McCune
-
Are all Stunt people high strung?????Lol
Given that Stunt is about doing the same thing we've been doing since 1952, only a little bit closer to perfection than the last best guy -- yes. Yes we are.
-
Hello All:
One of my flying mates has the above problem that he would like to solve. The engine breaks into a 2 cycle at the top of the maneuver too late to give any help to get any additional power. Perhaps it would help if you know some details about his setup:
Plane: Old Big Tudor
Engine ST G51
Fuel 11-11-5
Prop Wooden 12-5
Lines 60'x.018
Stock engine
Tank Uniflow
The engine runs like a well oiled sewing machine in a 4 cycle mode.
Suggestions/comments?
Try shaving the LE flat at the tips - just a little , make it about 1/32" thick over the last inch or so. Alternatives include going down to 2.5% nitro, and reducing the pitch slightly (like .1-.2" over the last 3 stations) at the tips. You need to make the engine either weaker, or the prop draggier. It should take only a very subtle change, in fact, given your other post about cold weather, you are probably getting a hair too much power for the conditions.
Brett
-
Frank,
There are various ways to set the break point on our engines. Load on the motor (as Brett suggested) is one way, here I would try a prop with either some undercamber (the RMS props have 0.020", or just sand some in at the tips) or one with thicker or wider blades (BTW, Zinger props come with the flat leading edge). Another option is to open up the venturi size say one #drill size at a time, this reduces the suction and can increase the point at which the engine will switch. As you do this you could get tad bit more power and burn more fuel.
You didn't indicate if muffler pressure is being used, if so, he could try running open uniflow venting (make sure the vent line is to the inside and pointing into the free air stream about 1/4" off the fuse side. You may need to combine a couple of these (i.e. open vent and bigger venturi) to get the break you want.
Another option is to change the run style from the 4-2-4 break to a high rpm/low pitch. In this setup the prop is pitch down to 4 or below and the rpm is brought up to a solid rich 2 cycle. On many ships is pretty close to constant speed as the low pitch allows the ship to drive through the maneuver with minimal lose of speed and hold back when being pushed by the wind.
In either case you may need to adjust the line length to get the lap time you are confortable with after you get the engine run you like.
Best, DennisT
-
I'd suggest "your friend" read and study the three pinned articles by Randy Smith at the top of this "Engine Setups" forum. My recollection (haven't run a 4-2-4 engine in some years) is that higher nitro content or larger venturi will make it switch sooner, rather than later, or at least harder, rather than softer. Note where Randy says that a bigger muffler outlet acts much as a larger venturi. This makes sense, because either will improve the "pumping" action.
I'd bet that more prop load would also make the switch quicker, as Brett points out, but I'd suggest getting a better prop, rather than making the existing prop less wonderful. The RSM 12 x 5.5 would probably work, tho I haven't run it on a G.51. I have run a 12-5 APC and a 12.25 x 3.75 APC (as Dan suggested). I had some nice results from the 12.5 x 5 TT Cyclone and the 11x6 Graupner. I may have tried the 11-6 APC, and know I have an 11.5 x 6 APC (a stock size), but didn't ever get around to trying it. I'm looking forward to trying out my G.51 ABC's, hopefully next Spring. ;D Steve