RE: BME 115 Any Field Reports?  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Gas Engines >> RE: BME 115 Any Field Reports?
Page: <<   < prev  8 9 [10] 11 12 13 14 15 16 17   next >   >>  

Login
Message << Older Topic   Newer Topic >>
RE: BME 115 Any Field Reports? - 5/1/2007 5:23:44 PM   
dick Hanson



Posts: 10268
Joined: 12/12/2001
From: slc, UT, USA
Status: online 		pont40 -is describing a different type of carb than we use in the model engines
no bowl in these -and the discharge hole is even with the bore - no low pressure bump. so -the little bugger which makes these holes work is the diaphragm (not the pump diaphragm-t' other one with the little vent that screws up the bottom/side port engines .) This one is doing a fine balancing act all th time --it is known as a "demand regulator -and when the bore pressure in the carb bore drops enough -it lets fuel flow thru the passages to the low/high speed discharge ports . the location and sometimes the shape of the throttle blade ( some have a wee cutout) lets the low speed hole flow then the high speed hole flows as it sees low pressure .
all very simple yet can be all very screwed up .
changing pressure at the inlet of the carb -or- the vent on the diaphragm can knock this balancing act on it's ear.
the pressure changes with the AOA of the fuselage. not from air blowing on the diaphram -but from the ambient pressure change as air flow changes in the cowl (or over the cowl). In many cases -it all works just fine -on some setups tho - bad news

On engines with relatively larger bore carbs - this all gets more sensitive -if all is working as intended, the carb works -if not --- bad news
for example -small engines (25-26 use small bore carbs -- 60-100 use larger bores - and 100-160 large bores .
put the big carb on the small engine and you likely get not enough vacuum (the low pressure needed to make it all work correctly.
here comes the rub
in all of the bore sizes - there are a jillion discharge hole/ throttle blade / etc., variations - all lovingly done by Walbro and Bing and Tillotson - to match a particular engine and engine task .
For guys who run their engins at full tilt and turn left -- the problem is different -as compared to guys trying to slide/twist flip the planes as they juggle the power . so as frightening as it sounds -if you really want to get the best results --be prepared to do some swapping and adjusting to carbs, needle settings - prop sizes - exhaust systems . if not
stick to flying a computer sim .
BTW-- the early ZDZ80 is a 6 port -open port - but six channels . the Super 80/160 has paired angled ports blowing inward n upward . different ideas -they all can work extremely well when properly setup.


< Message edited by dick Hanson -- 5/1/2007 5:41:26 PM >

_____________________________

I am watching you
Libby

(in reply to RTK)
       Post #: 226

RE: BME 115 Any Field Reports? - 5/1/2007 5:32:28 PM   
Pontiac_40


 

Posts: 117
Joined: 4/25/2002
From: Fairfax, VA, USA
Status: offline 		I guess we (as in high performance seekers and high performance engine manufacturers) are mating components that are off the shelf with a completely different use in mind to a 6 port high performance engine...not a good mix. There is so much you can get out of the basic Walbro design, on the other hand BME has introduced some radical changes in the 115 to boost performance and reduce weight. I think an electronic fuel control unit just like OS engines came out with for there 160 is in order here.

_____________________________

Fly and let fly

(in reply to Tired Old Man)
       Post #: 227

RE: BME 115 Any Field Reports? - 5/1/2007 6:01:34 PM   
RTK


 

Posts: 4089
Joined: 4/20/2003
From: CENTRAL , CA, USA
Status: offline
quote:

ORIGINAL: dick Hanson

pont40 -is describing a different type of carb than we use in the model engines
no bowl in these -and the discharge hole is even with the bore - no low pressure bump.


Same principle. Some of my other carbs have a low pressure bump, SDC 80's I believe.

I agree that these carbs are not really designed for our intended use, but like you have said Dick, with a little trial and error we usually find what we need.

(in reply to RTK)
       Post #: 228

RE: BME 115 Any Field Reports? - 5/1/2007 6:02:37 PM   
Herby 1


 

Posts: 10
Joined: 4/26/2003
From: Northern Arizona
Status: offline 		Part of the dreaded bog might be the ignition....An electronic ignition works by varyi8ng the timing according to the rpm...The tail is wagging the dog...The spark advance occurs when the rpm changes...If the low needle is too rich the crank doesn't accelerate very fast and the igntion stays retarded...It happens in microseconds, but if you purposely set the low needle very rich you will see what happens...Slow crank acceleration, slow spark advance, bog.....
You could test this with an ignition that has fixed timing...Unfortunately all the collective wisdom says you NEED electronic advance ignitions, so no one makes fixed timing any more....The bog problem was not as pronounced when we made mechanical advance, or no advance at all....My 26s have fixed timing....
All magneto engines are mostly fixed, with the possible exception of the Fuji with the magneto....

(in reply to RTK)
       Post #: 229

RE: BME 115 Any Field Reports? - 5/1/2007 6:23:31 PM   
dick Hanson



Posts: 10268
Joined: 12/12/2001
From: slc, UT, USA
Status: online 		to add-
some use an advance which comes on (hopefully) out of phase with the bumpt/bog transition in the carb AND the inherant out of balance phase on singles.
some come on early -I checked out the new 3M 53--that engine had one small vibe at 2200- very low - then smooth runnin right on up. Not an endorsement -just noting .
most of my single engines have the "vibe at 2900-3000rpm -and no bog . the new ZDZ40F3A has a very very low vibe node -but it is at 3300 . --fascinatin--

Everone has their own idea as to which and when and to whom-

swapping prop LOAD -big prop --little prop - will change the whole darn character - the vibes stay the same place but engine transition and "bog" moves and/or improves..
if you think there is a magic setup which eliminates these problems - guess again - yo just shift em around.

_____________________________

I am watching you
Libby

(in reply to Herby 1)
       Post #: 230

RE: BME 115 Any Field Reports? - 5/1/2007 6:28:38 PM   
Tired Old Man


 

Posts: 12356
Joined: 2/25/2002
From: Central, CA, USA
Status: online 		The ignition "bog" problem was one we experienced with RTK's 115 when it still had the original carb. Once everything else was dialed in with regards to airflow disturbances, baffle designs, and carb tuning, what was left was a hesitation that appeared to be caused by the ignition timing. Everything else was about as peachy as could be. Believe that anything that could be experienced in the beginnings of the 115 have been experienced by RTK. I was there and got to watch along with him.

Ralph, I agree. All the wisdom that went into the electronic advances have left us in the cold in some areas. The mechanicals were very nice and easy to work with.

_____________________________

If you can''t fix it with a hammer, you have an electrical problem.

(in reply to Herby 1)
       Post #: 231

RE: BME 115 Any Field Reports? - 5/1/2007 6:50:25 PM   
RTK


 

Posts: 4089
Joined: 4/20/2003
From: CENTRAL , CA, USA
Status: offline 		As of now (on the ground, haven't flown with new carb/block) There is no hesitation from any throttle setting. You can stab it from any throttle setting and it will instantly respond. The mid range has almost no detectable 4 cycling, just when backing down. We will see this weekend.

(in reply to Tired Old Man)
       Post #: 232

RE: BME 115 Any Field Reports? - 5/1/2007 7:53:25 PM   
Tired Old Man


 

Posts: 12356
Joined: 2/25/2002
From: Central, CA, USA
Status: online 		You still have that Falkon or did you make the change to the CH?

_____________________________

If you can''t fix it with a hammer, you have an electrical problem.

(in reply to RTK)
       Post #: 233

RE: BME 115 Any Field Reports? - 5/1/2007 7:59:07 PM   
RTK


 

Posts: 4089
Joined: 4/20/2003
From: CENTRAL , CA, USA
Status: offline 		Falcon until it quits again, or causes problems, then CH.

(in reply to Tired Old Man)
       Post #: 234

RE: BME 115 Any Field Reports? - 5/1/2007 9:01:01 PM   
Tired Old Man


 

Posts: 12356
Joined: 2/25/2002
From: Central, CA, USA
Status: online 		I put that Falkon right up there with your servo operated choke. It's not an if, but a when...

_____________________________

If you can''t fix it with a hammer, you have an electrical problem.

(in reply to RTK)
       Post #: 235

RE: BME 115 Any Field Reports? - 5/1/2007 10:12:43 PM   
dick Hanson



Posts: 10268
Joined: 12/12/2001
From: slc, UT, USA
Status: online 		there is a problem with servo operated chokes?
ok --what?

_____________________________

I am watching you
Libby

(in reply to Tired Old Man)
       Post #: 236

RE: BME 115 Any Field Reports? - 5/1/2007 10:26:36 PM   
RTK


 

Posts: 4089
Joined: 4/20/2003
From: CENTRAL , CA, USA
Status: offline 		Although I have never killed my engine in flight with it (close), Silversurfer has done it more than once

(in reply to dick Hanson)
       Post #: 237

RE: BME 115 Any Field Reports? - 5/1/2007 10:41:56 PM   
dick Hanson



Posts: 10268
Joined: 12/12/2001
From: slc, UT, USA
Status: online 		problem not the mechanics --
problem - the mechanic.
A local friend who was recently doing hi low n slow hover -- hit his throttle position /cutoff switch -with his big ol 40%
KABOOM--
I use retract switch as choke switch - on all models-- back is ON so I can't pull it accidently wif my finger.
so far so good
same reason I use no switches in flight - just lots of throw and lots of expo and lots of practice .
I have flown with guys who are constantly clicking switches - good flyers- but I would never remember what was on -off.
I can barely remember my way home --
(one woof for right turn -two for left )

_____________________________

I am watching you
Libby

(in reply to RTK)
       Post #: 238

RE: BME 115 Any Field Reports? - 5/1/2007 10:59:15 PM   
Pontiac_40


 

Posts: 117
Joined: 4/25/2002
From: Fairfax, VA, USA
Status: offline 		Here is an interesting read. If only this system could be redesigned to be light-weight to work for our gassers it would be great.... Keith check it out.

http://www.envirofit.org/files/publications/BAQ%202003%20Development%20of%20Direct%20Injection%20Retrofit%20Kit.pdf

_____________________________

Fly and let fly

(in reply to Pontiac_40)
       Post #: 239

RE: BME 115 Any Field Reports? - 5/1/2007 11:46:32 PM   
Tired Old Man


 

Posts: 12356
Joined: 2/25/2002
From: Central, CA, USA
Status: online 		I use 3 switches fo flight. Dual rate switches for aileron, elevator, and rudder. Any more than that and I can't remember what was where and why. RTK tosses in a servo operated choke switch and about a zillion different conditions. It's usually very close to where one of my rate switches are with a different make transmitter. I killed the engine twice, he almost did it with his own transmitter once. Me, I use a very simple mechanical (read that as human) operated choke rod. If I'm really in deep doo-doo in flight and desperately need to kill the engine I figure the elevator is still funtional and the ground is still hard. That engine is GUARANTEED to stop!

Being a simple guy I figure if I need more than a couple of rates it's time to sit down at a ground control station and let the auto pilot do all the work