Tri Valley R/C Modelers
Santa Maria, California
AMA # 170

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President’s notes:

This month’s meeting place is operated by the Santa Maria Parks and Recreation Department.  We are hoping that this can be our permanent meeting location.  The recreation center is on North Railroad Street.  The map shows how to get there.

See you at the meeting,

Carl 

Notes from the September Meeting

We had a visitor, Dan Von Corbeck.

 Les Holland has negotiated with Parks and Recreation for a meeting place at 1000 North Railroad.  He has arranged this for our next meeting.  See map.  The rec. center is not right on Railroad but behind the tennis courts.

This is the year to elect a new club president. Volunteer at the meeting.  Del Wheeler has agreed to be the newsletter editor. (a non-elected position).  Jerry Miller will be the recording secretary and a new position has opened up.  The club needs a Webmaster.  Bill Korn brought a great show-and-tell.  An electric slow flyer foam Ultimate.  With a 2:1 thrust to weight ratio.  Northeast Sailplane “2Cool”.  

Safety

Use new eyes to check out your new or rebuilt plane.  Put your frequency tag on the pole before you turn on your transmitter.  Remove it when you are done.  Frequencies 38 - 42 are suspect for interference. 

Lapsed membership?

Just a reminder, if you let your AMA membership lapse you can renew it after October 1st and it will be effective for the remainder of the year and the whole next year.  I know this probably doesn’t apply to you but it does to me.  I will take advantage of the quirk of the AMA rules.

I know that this was in the last newsletter but now that October has arrived here it is again. 

Crash of the Month

Dick Washbish got his plane in the air okay but was unable to stand up to fly it.  He got away with only minor damage. 

THE ENGINE - Air Leaks

-by Clay Ramskill

Why do old engines run poorly? Why do otherwise good engines sometimes become hard to adjust and difficult to keep running? Why do some engines continually lean out badly when the planes nose is pointed upward?

There are a zillion answers to the above questions - but a good answer for any of them could be an air leak. After all, an engine is nothing more than an air pump; anything that destroys the efficiency of the pumping action will show up as poor performance, one way or another.

First, some basics - we must understand that unlike a four stroke engine, our two strokes USE THE CRANKCASE as a pump. Naturally, we have to have a good, airtight seal in the combustion chamber for good compression. But in a two-stroke engine, we also must have an airtight seal in the crankcase, also. As the piston moves up to compress the mixture in the combustion chamber, the crankshaft valve under the carb opens, and fresh mixture is then sucked into the crankcase. And as the piston moves down on the powerstroke, at the same time the intake valve closes, and the mixture in the crankcase IS COMPRESSED.

Only when the piston gets down far enough to open the transfer ports is that crankcase pressure released, squirting the fresh mixture into the cylinder under pressure.

So, not only must we have good seals in the top part of the cylinder - around the head gasket, the glow plug, and, of course, the piston itself - but we must also have good sealing in the lower part of the crankcase. This involves the seal on the backplate, on the front bearing housing if the engine has a removable one, and at the front bearing area of the crankshaft. Note that all these are relatively fixable except the last - in nearly all cases, its not the bearing that seals the crankshaft, but the fit between the crank and the housing itself that provides the seal. When an engine is "too worn out" to adjust and run properly, this area may be the culprit. But the major source of air leaks, and the first area to start looking for them, is the carburetor.

First, the carb must be sealed in its connection to the crankcase - usually an "O" ring. The barrel inside the carb must make a good fit inside the carb, or it will leak, on the low-needle side. The needles themselves must be sealed. The fuel intake fitting must be sealed, as must be the one or two screws that hold in the barrel and provide a low speed throttle stop adjustment.

Leaks around the carb are doubly bad in that they're hard to find. Only suction is involved in the carb area - pressure is also involved in the crankcase seal areas, and thus, if there's a leak, you will normally see it in the form of fuel or oil coming out. But around the carb, only suction is involved, and air leaking in will not show!

There are other air leak possibilities besides the engine. The fuel feed line is an obvious one, both inside and outside of the fuel tank. And don't forget the pressure line, and its fitting on the exhaust.

SpaceShipOne, note pilot’s hand.

September 29, 2004: At 8:13 this morning PDT, SpaceShipOne (SS1) coasted above the 100 km altitude point and successfully completed the first of two X-Prize flights. The peak altitude reached was 337,500 ft. The motor was shut down when the pilot, Mike Melvill, noted that his altitude predictor exceeded the required 100 km mark. The motor burn lasted 77 seconds – 1 second longer than on the June 21st flight. Melvill was prepared to burn the motor up to 89 seconds, which indicates significant additional performance remains in SS1.