NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/rec/models/rc/5257

Internet Message Format | 1993-01-01 | 4.2 KB

Path: sparky!uunet!spool.mu.edu!uwm.edu!linac!att!att!fang!gator!inland!bloom
From: [e-mail]
Newsgroups: rec.models.rc
Subject: Re: First Trainer Questions
Message-ID: <[e-mail]>
Date: 31 Dec 92 08:30:48 CST
References: <[e-mail]> <[e-mail]> <[e-mail]>
Organization: Inland Steel Company; East Chicago, IN
Lines: 75

In article <[e-mail]>, [e-mail] (David Svoboda) writes:
>
> |A bushing motor like the OS .40 FP has much less power (about the
> |same power as strong .25" motor) than an equivalent ball bearing motor.
>
> I would strongly disagree with this.  The only difference between a ball-
> bearing motor and a sleeve bearing motor is the bearings.  Ball bearings
> do not have significantly less drag, they just last longer and can take
> greater stress.  But the FP is a Schnuerle ported engine, and produces
> as much power as any other 40, excepting that you cannot safely stress
> them with high nitro or tuned pipe.

In actual design, the bushing motors have less power because the
port timing is much milder than in most ball bearing motors.  You'd
have to ask the engine designer why the porting is so mild, perhaps
because the bushing wouldn't take the stress of high power/high rpm
without overheating.

>
>
> |Your trainer may not need more power than the FP provides, but you can
> |always throttle a strong engine back.  If you're short on power, you
> |can't do anything but buy another engine.  Strong engines are an added
> |safety margin on take-off.  You can make steeper climbs without stalling
> |the plane.  Weak engines are much more critical on needle valve settings.
> |If the power is marginal, any change in the needle setting may reduce
> |the power enough to cause a stall and crash.
>
> The 40FP is the single most common motor used in 40-sized trainers, and
> most of the newer trainers were designed with that engine in mind.  Older
> trainers (like the Goldberg Cardinal or Sig Kadet) were designed for
> 40's of fifteen years ago.  The 40FP is MUCH more powerful than those.
> (My reference: the old K&B 40, considered a high-powered workhorse in it's
> day, turns a 10x6 prop at about 11,000 rpm.  An FP turns the same prop at
> 12K or more.)

The only reason people stick the 40FP in their trainer is because of
cost, not performance, and I believe it is a false economy.  I put
well over a hundred flights on my own 40FP in a Skyward 40 ARF.
I also put well over a hundred flights on a Midwest Aerostar 40 using
a Magnum Pro 40 for half the flights and an Enya 45CXTV for the other
half.  The FP motor was a dog by comparison.  It certainly will not
turn a 10x6 prop 12K; yes I put a tach on mine and I seem to
remember about 10,700rpm with a MA prop.  The Magnum turns 13K and the
Enya turns 14K with the same prop.  The Enya was certainly the most
reliable of these motors with the best carburetion and power.  I'm
the chief flight instructor at our club now, and I get an awful lot
of stick time on various trainers/engine combinations.  I really do
worry more on takeoff with a 40FP whether I'll clear the trees or if
it's going to go deadstick (the needle setting on the FP is more critical
than the high power motors, too fat and you stall easy - too lean and
you dead stick).  I'm now flying our club trainer (Hobbico Avistar 40)
with a Supertigre Bullring 40, and even this inexpensive BB motor ($80)
has more power than the FP.

>
> You will have NO trouble getting off the ground with the FP.

Maybe true with some planes and some fields, but your not going to
have any power to penetrate the wind on a windy day.


> |Also, there is no more
> |messing around with ball-bearing motors than there is with bushing
> |motors.  All you do is run them dry at the end of the day, and give
> |them a dose of Marvel Mystery Oil.
>
> Which two things you do NOT have to do for a sleeve-bearing engine.
>

How lazy can you get?  If you can't spend an extra 30 seconds putting
in some oil, maybe you don't have enough time or patience for this
hobby.  I spend at least 15 minutes cleaning up the plane at the
end of the day, and I'm not going to electric motors to save time.