BME 102 Question
 

I have a BME 102 that I'm thinking of useing in a comp-arf 2.6, my field requires 98DB at 9 ft. I will have to use canister mufflers to meet this requirement. Has anyone installed this combo and how is the power to weight and most important what lenth header pipe will be needed for smooth tranistion and good power.

Thanks
Mike Tango


www.tangoncash.com

RE: BME 102 Question
 

MRT1750.. go HERE:

http://www.rcuniverse.com/forum/m_55.../tm.htm#555666

This is a full buildup and review of that exact combination. Power was VERY good, and the plane flew very well and would 3D very nicely. Definitely a great combination of airframe and powerplant setup.

RE: BME 102 Question
 

Kris^
Thank you for all the help, I posted on your review, did not want to miss you seeing this.
Need more help
1 How long are the headers on your 330L

2 Where did you get the header flanges

3 Do you think the comp-arf quality has improved any and are the new planes any lighter?

Thanks
Mike Tango

www.tangoncash.com

RE: BME 102 Question
 

The "drop" on my headers, from flange to CENTER of the header tube where it goes into the canister, is 2" on the 102's, and 2 1/4" on the 106/110's. I used the flanges that DA has for the BME 102 cylinders, used the 22mm KS elbow available from DA, a 2" extension on the outlet of the elbow and expanded the outlet of the extension to a wider diameter (using heat and a pair of pliers to 'stretch" the metal a little) so that it matched the diameter of the canister coupler. The "50cc" canisters from PEFA work very well with the BME102, but for 105's and 110 Xtremes I recommend the 70 or 75cc rated canisters.

As for weight, I serously discredit the claims of 22-23 lbs planes that are floating around out there. In reality they are probably closer to 25 or so, and I've heard of weights as high as 28.5 on some planes.

As for quality??? for $995 it's a very good piece. If the price was still $1495 I'd expect much better. Best bet is to look the plane over carefully when you get it, be aware of the shortcomings, and take care of them before you beging installinghardware.

BTW, I put a 110 in my plane, and changed the exhaust to suit it. . it was such a rocket, even at 26 lbs, that I put a "bored" 102 on it, using the 110Xtreme jugs and pistons to give 106cc of displacement. It's STILL a rocket, but he dedicated 110cc engines are just a touch more powerful, and REAL animals in the air. NO SUCH THING as too much fun!!!

RE: BME 102 Question
 

Kris^
I called keith the other day with some questions, I asked him if there was some way to tell if you have a 102 or 105 he said to look in the cylinder exhaust port. take note of BDC if it is below exhaust opening then it's a 105, if even it's a 102 my engine is below exhaust opening by about .100 of an inch, is that enough to idenify as a 105. Will the header pipes be long enough to have the engine run with good transition & power. ZDZ needs about 12 inches of header pipe to be smooth and make power what makes the BME different, or am I miss reading your posts.
I ran the engine today for DB's, turned 6000 with stock mufflers 27/10 3W prop 102 DB @ 3 meters will not pass at our field need canisters, I'm looking at the MTW short 75cc from DA any suggestions.

Thanks
Mike Tango

www.tangoncash.com

RE: BME 102 Question
 

First off, a ZDZ uses a disk valve intake system, and the difference in how the engine operates versus a reed-valve induction engine is noteworthy. With a reed-valve engine, the intake pulses to the carbuetor mirror very closely the exhaust scavenging pulses, but with a disk valve engine, the valve is open at low rpm when it should not be (or a reed valve would be closed) making the scavenging and intake event of a disk valve rely on the exhaust event a bit differently, an in fact causing reversion from positive pressure pulses when the disk is open at the wrong time.

Also, remember that the BME's intake ports for the 102 and 105 are based on some very conservative "weedy" jugs, and that the combustion chamber and exhaust port are not designed with any type of "tuned" scavenging in mind. So, for the BME, having a short header, along with a free-flowing large canister style muffler, is more of an advantage than it would be for the ZDZ. Not to say that a ZDZ would not benefit from this style of exhaust, it does, but the older BME wil not gain as much from a fuly tuned system, the way a ZDZ would, but a more conservative exhaust will yield better results than a conservative setup would for the ZDZ (in theory). It all comes back to the necessity to "balance" the intake and exhaust events in the engine.

Basically, a 4-5" header on the BME 102/105, combined with the 50cc or 70cc Pefa canister muffler, will yield a decent power increase, but not at the expense of mid-range characteristics. The exhaust event is short, less than 150 degrees, and attempting to crutch it for a lot of upper rpm power will only cause it to run very poorly and have poor transition characteristics. Stick to a conservative setup, and the engine will easily wake up to the tune of 200-300 rpm, while not losing mid-range smoothness. This is true for any engine, but for the early BME's, with their limited intake and exhaust porting designs, it's a bit more important.

RE: BME 102 Question
 

MRT- I hate to say it --but the "noise tests on the ground" - that I know of -are as worthless as teats on a boar .
They are completely unrelated to the in air sound levels - which are the real issues.
You are chasing your tail -if you hope to have any power on any large engine using these antiquated ,stupid, worthless tests.
Sorry but you are the victim in this case of "sound experts" who are counter productive to fixing the real problem.
Basically - you probably will fail each and every test - till you put a 32 x12 prop on it .
The worst of it is -- you can easily keep in air levels way down ,using a decent power prop and any decent can type muffler .--and never letting the engine unload

Probably - your field officials will insist on the ground test -so-unless you can get them to agre to a subjective in air evaluation- you are doomed.

RE: BME 102 Question
 

98dB at 9 feet is a no-brainer with that setup, Dick. . . .it's closer to 96 dB probably, especially with a fat 2-blade, like a Biela 27-10, which works well with that combination. Forget a wood prop, though, they get too noisy, even in the pits.

RE: BME 102 Question
 

You can document that?
When we used the AMA setup -tripod/flat sound surface etc., the gassers all failed .
Typically we were a little to a lot over 100 DB on anything over 2.4 cc.
The in air sound evaluations tho were entirely different.

RE: BME 102 Question
 

WOW, Dick. . a 2.4cc Gasser??? didn't know they made a .15 sized gasser. .guess it uses a really TEENSY carburetor. . ..

No, I don't have documentation, but when I get my canistered 5.8 running I'll dB it for you. . bet it breaks 93 dB at 9 ft.

RE: BME 102 Question
 

don't see how - but -go for it
Our 100 and 80 and 60 engines -even the 150and 160 stuff are all nice and quiet in the air - but that goofy 9 ft test - nope -

RE: BME 102 Question
 

Most of the IMAC planes are in the range of 92-100 dB, but they test at 25 feet not 9 feet.
According to the article on sound on the IMAC website, the equations predict that a 3 meter test will be 8 dB higher than a 25 foot test. However, these predictive equations are only valid for "ideal" cases. The real world measurements would have a lot more variability because of reflections from hard surfaces etc. That's probably the reason that ground tests have very little predictive value of in-air sound levels, when reflections don't make up a significant portion of the total energy received by the measuring instrument or your ear.

RE: BME 102 Question
 

Then there's always the "Judicious use of the left stick" .. both during testing and while flying. That one little factor can make, or break, how large a sound signature you have. I always test mine at max throttle, but I've seen guys throttle the sound tests at IMAC meets. . kind of makes the ground test a waste of time. MY planes will pass .. what is YOUR problem (what I'd like to as the other guys)

RE: BME 102 Question
 

My issue is with the 9 ft test - done by the book - we can't pass any big planes.
These planes are all very quiet in the air.

RE: BME 102 Question
 

Hi Kris,
Thanks for the notes on setup!

RE: BME 102 Question
 

MRT1750, a couple of other ways to tell if your's is a 105 instead of a 102. . first off . .BOTH exhaust ports will show that the piston is about .5-.75 mm (.020-.030") below the exhaust port. This is because the 105 crankshaft is actually a 110 crankshaft, with a 1mm longer stroke, and the 102 crankshafts and crankcases were set up to have the piston come to dead even withthe bottom of the exhaust port, or about .010" below it. The second way is to pull a jug and see if there is ahole in the counterweight. If so, it's a 110 crankshaft, because the crankshaft design was changed to facilitate balancing the 110, which have a lighter piston. It does not cause undue imbalance in a 105, since the pistons basically self-cancel when they move, but it IS a design difference.

I've enclosed a pic of the 4 crankshaft designs that BME has used. . the 110 crankshaft is in the middle, rear, and the 102 crankshaft is on the left. ON the right is the first edition 102 crank and at the bottom is the old 5.8 crank assembly.

Hope this helps

RE: BME 102 Question
 

Kris^
Thanks for the help!

mike Tango

www.tangoncash.com

RE: BME 102 Question
 

Dick
Do you know of any fields (Clubs) that have changed there 3 meter rule for something more reasonable, and if so what has happened afterwards? any noise problems etc.

Thanks
Mike Tango

www.tangoncash.com

RE: BME 102 Question
 

No I don't.
At our field we simply browbeat the noisy flyers .
If it is noisy we comment on it.
To hell with the *****footin aound
If the plane is noisy it is obvious .
No set of AMA rules will ever solve the problem.
Tell the clowns they are cutting their own and every one elses throats by creating a nuisance.
If they don't like it they can leave.
It is only the foolish and stubborn and stupid who continue to cause noise when it poses a problem.
If it poses no problem to others - well--make all the noise you want.
ANY plane can be quiet .
The problem is simply those who want their model to be noisy.
For those - our patience is exhausted.
You have no devine right to make irritating noise.
Sound rude?
yep -it is .
But - how do you feel?
Do you honestly believe AMA can make a workable rule?
Or is AMA interested in a workable rule?
AMA *****foots the noise issue because a huge voting block is grounded in the motor noises of their youth . Mufflers?
I put one on in 1949 - a tin gadget by McCoy, it fell apart.
the next time was probably in 1972.
There was always another place to go fly.
Noise has been the problem with model engines for over 50 years but AMA really has done little to solve it .
and likely never will.
Wish I had something nice to say about the "scientific rule" by AMA -but I don't .