Conference vmszoo::rc

    
    Tom, my only advice about mounting the engine inverted is to bench
    test it first.  My Enya 46 idled beautifully upright but loaded up
    and eventually would quit when inverted.  It started easier upright
    too.  My solution was to add on-board ignition.  Our guess about
    why it wouldn't idle well inverted is that the raw fuel coming in
    was cooling off the glo plug.  I tried many mixture adjustments
    and different fuels but the on-board ignition was the thing that
    fixed it.  If you do have to add one it might help to know ahead
    of time, so I would suggest the bench test.
    
    Bill

I can't speak on 4 strokes but I've used Kraft Hayes nylon mounts on everything
from .20 to .61 two strokes without any problems. Haven't broken one yet. I find
that the mounts hold threads real nice so I generally tap them for my standard 
mounting screws (4-40 or 6-32). One of the benefits to using these mounts is 
that if you need more down or right thrust you just put washers in the 
appropriate places between the firewall and the mount. My feeling on fuel tanks 
is to put in the biggest one that will fit. You don't have to wait until you go 
deadstick. Drill out the mount arms on a drillpress if you have one available.

Re:<<< Note 1152.0 by WMOIS::DA_WEIER >>>
                         -< engine mounting questions >-
    
>           1. I purchased a nylon mount. It is made for 40 4-strokes.
>              Are these type of mounts sufficient for my use? Any
>              horror stories?

Should be OK. My preference is to Aluminium for extra stability and strength.
    
>           2. I am mounting the nylon mount to the firewall with 6-32?
>              Allan head bolts with blind nuts on the back. What is the
>              preferred method of mounting the engine to the nylon mount?

Provided the firewall is a hard material and will not be crushed by the nut it 
is OK. If the firewall is soft spread the load with some aluminium sheet on the 
back of the firewall suitably drilled to match the nut.

>           3. What level is optimum for mounting the fuel tank in relation
>              to the engine? The engine is mounted upright.

Top of tank approx level with the spray bar is ideal, 1/2" variation could be 
OK.
    
>           4. How long of flight can I expect with a 4 oz tank? a 6 oz
>              tank? A ballpark figure is fine.

Depends on too many things to be accurate but I  would go for a Kraft 7oz if 
you can get one. It is an excellent tank.   

>              5. How close to the fire wall can a 4-stroke be mounted and
>              still allow proper throttle operation. I assume 1/2 inch
>              is reasonable.
    
What ever distance you can get away with.

John

    
    
    	On engine mounting , I like to keep the engine as close as possible
    to the firewall if at all possible (the exception would be when
    the engine's distance needs to match a cowling that has to be mounted
    a certain distance from the firewall). The main advantage of rear
    mounting is that I like to run a little on the higher size for
    recomended engines per aircraft . The larger engine will be heavier
    and mounting it as close to the firewall as you can helps when you
    have to set C.G. for the model . Hope this helped .
    
    	Carl

    re Note 1152.3 by VERSA::TULANKO ,    

    "... keep the engine as close as possible the firewall ..."

    I mounted my OS40SF on my Kadet II so the spinner would be the right
    distance from the firewall for the cowl.  As a result the spacing is
    very, very tight, and the plane tends to be tail heavy without ballast.
    Now I'm looking for advice for the next powered plane I build.  Without
    Carl's comment I would have hung that motor way out front.

    If
        the motor is light for the plane and

        there will be no cowl to complicate the issue,


        why not mount the engine out far enough to balance the plane?


    If the answer is in vibration concerns, does this depend upon the make
    of the motor mount?  e.g.  Are Hayes mounts less vibration prone than
    the cantilevered aluminum SIG mounts?

I've been fooling around with that question myself, in my latest
design efforts.  The problem with sticking the engine out there
is that you increase the nose moment, which makes the plane
harder to handle, according to the Chuck Cunningham design
article that I'm using as a guide.

With the cardboard and pine that I've been using lately, all the
weight of the Sportster .20 at Chuck's 20% of fuse length nose
arm is insufficient to balance a moderate tail arm (40% fuse). 
I went and bought a Higley Heavy Hub (2 oz) to get the CG into
the 30% range.

    Re: .-1, Al,
    
    If not committed to engine location by cowl/spinner/etc., using engine
    placement to adjust CG is a great thing to do, within reason, of
    course.
    
    As you wondered out loud, getting the engine too far forward could
    result in a spindly mount situation which could produce or aggravate
    vibration.  However, using a 4-cycle mount with its extra long beams,
    it's perfectly acceptable to mount the engine clear to the forward end
    of the beams if necessary.
    
    As to mount material: my experience has been that, from .50
    displacement and up, the glass filled nylon or other composite mounts
    contribute unnecessary vibration to the installation.  Gimme' a good
    aluminum mount every time; I particularly like the Fox mount as it's
    machined from solid bar-stock and is much stronger than the cast
    aluminum types...I've never damaged a Fox mount or seen one damaged in
    a crash.  However, I prefer even the cast aluminum mounts to the glass/
    composite varieties.  I simply drill and tap the beams for 6-32
    mounting bolts and use a flat washer and lock washer under the bolt
    heads.
    
    I hate to differ with acknowledged engine guru, John Chadd, our
    compatriot from Oz, but I always recommend that the fuel pick up line
    (usually the tank centerline) should be level with the carb spray-bar
    for optimum performance.  Lining the top of the tank with the
    spray-bar, in my opinion, puts the pick up line too low, causing the
    engine to have to draw harder for adequate fuel supply which can
    produce a lean condition when upright and a rich condition when in-
    verted.  I concede that too many trainer and sport types make this
    parameter difficult-to-impossible to achieve but I still recommend
    striving for it where/whenever possible.  Comments, John??    

      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

Re:  <<< Note 1152.6 by PNO::CASEYA "THE DESERT RAT (I-RC-AV8)" >>>

>    compatriot from Oz, but I always recommend that the fuel pick up line
>    (usually the tank centerline) should be level with the carb spray-bar
>    for optimum performance.  Lining the top of the tank with the
>    spray-bar, in my opinion, puts the pick up line too low, causing the
>    engine to have to draw harder for adequate fuel supply which can
>    produce a lean condition when upright and a rich condition when in-
>    verted.  I concede that too many trainer and sport types make this
>    parameter difficult-to-impossible to achieve but I still recommend
>    striving for it where/whenever possible.  Comments, John??    >

I will forgive you Al; no killer kolalas in the mail today. My comments on the 
center line for the fuel tank are a dislike of flooding engines by fuel 
siphoning into the engine while the model fuelled but not started. This is a 
cause of many hard to start engine problems; ie: the plug is too wet to glow. 
I know you can clamp the line but it's a pain and too easy to forget.

I really believe with muffler pressure the effect of the fuel head is 
minimised. With 4 strokes the Micro oscillating pumps work well. I use one with 
my OS90FS and the tank is a good 1/4" below the spray bar. The center line 
theory was true in the days of the open exhaust unpressurised engines but it is 
not necessary with todays engines.

I purchased a couple of CB engine mounts on my recent visit to your land. I can 
recommend the quality of the aluminium and the casting. They machine 
beautifully.

John

    I'am about half way through my first plane. It is a Bob Martin
    EZ trainer 20. The kit was really easy to build. My big question
    is the engine thrust line. I was sure to install the nose doublers
    according to the plans. It has the firewall (looking from the back
    to the front of the fuse) cocked 3/16" to the right. Does this sound
    right ? I had to get an extra long motor mount as the firewall sits
    back about 3 1/2". I'm installing an OS25FP. It appears that I'll
    be able to trim about 3/8" off the front of the mount once the engine
    is in. 
    What I need to know is this much thrust common for a flat wing trainer?
    Any comments at all will be appericated.
    Walt

    
    
    	I maped it out guessing that the fuse wided was app. 3"
    It comes out at app. 5.5 degrees of right thrust. That doesn't
    sound out of line to me. 
    
    
    Tom

    re.9.
    Thanks Tom. I fooled aroung with it last night and after getting
    it lined up and triming 3/8" off the front of the mount it doesn't
    look so cock eyed. I just love this file to keep my mind at ease.
    Walt

    I guess this is as good a place for a question as any??
    
    
    Backround.   I have to replace an OS 61 longstroke I have is my
    Speeda but as this ship will be religated to backup duties I really
    don't want to buy another OS at 180.00 dollars. 
    
    		 So, Could someone who owns an ASP61 side exhaust please
    measure the engine mounting bolt hole spacing? I'm wondering if
    the ASp would fit the OS longstroke bolt pattern. I'll need spacing
    side to side and front to back.
    
    
    						Thanks in advance
    
    
    						Tom

    
    
    		Tom ,
    
    			I measured as well as I could my ASP.61
    		last night . It came out to 51/64" on the sides
    		and @2 1/16" between the mounts . The @ is because
    		It may have been 1/64" more ( looks like all the
    		mounting holes may be metric ).
    	
    
    			Hope this helped ,
    
    
    				Carl

    Thank's for the info. I have found out that the ASP 61 mounting
    is identical to the OS FSR 61 an that the OS61 FSR is identical
    to the OS Long Stroke 61.
    
    
    Tom

	Further on this topic...

	I have a need to be able to mount two different OS engines
	on the same plane [no....not at the same time 8-)]. Anyone 
	come across a single mount that that will accept the two 
	engines (OS46SF-ABC/OS61SF-ABC) ?

	I don't have the spacing for the 61 handy but my ST61ABC will
	not share a OS46 mount - no can do. 

	Options so far are:
	
		1. different mounts on seperate plates bolted to airplane.
	           This is OK but space on the firewall is not great.

		2. Cutting slots in mounts to allow common bolts to
	           attach either.		
		
		3. Mount that will accept both engines.

	Any thoughts ?

	Eric();

    Why not take a lesson from the Japs! plan to install the 60 sized
    mount however install it app. 1/8" below the cenetrline. To install
    the 60 make two 1/8" plates to be used as shims under the 60 engine
    mounting lugs. When it's time to install the 46 make two more shims
    but this time make the so that the 46 gets mounted to the 1/8" stock
    and then you mount the 1/8"stock to the 60 sized engine mount.
    
    
    Tom

I've done this by swapping firewall mounts that share the same hole pattern 
(If they don't, drill 'em ;^)

	Thanks for the suggestions. I think I will opt for Tom's suggestion.
		
	Eric();

    I am in the process of building the Balsa USA Taube, a .40 sized
    "scratch built kit".  That phrase applies well to this plane because
    the instructions are really BARE BONES when it comes to spelling out
    the details.  For example, there are no instructions on engine
    mounting and the only place where the engine shows up is on the side
    view where the outline for a K&B .40 is shown.  But, there are no
    engine mounts supplied with the kit, nor any directions on how to mount
    the engine.
    
    What I have done therefore, is to construct two maple mounting rails,
    and simply epoxy them to the 1/4" balsa side walls.  These rails are
    about 3" long and I should have no trouble mounting an OS .40 FP
    between them.  My only question is one of structural integrity.  Will
    hardwood mounting rails epoxied to balsa stand up under the constant
    vibration?  Am I asking for trouble with this setup?  What other
    alternatives are there for mounting the engine?  
    
    Oh, another thing.  Since the bottom of the engine compartment is
    closed, I am not sure I'll be able to get blind nuts under the
    mounting rails.  Can I use wood screws to attach the motor?  What are
    the possible drawbacks of this vs. machine screws/blind nuts?
    
    Thanks for any advise.
    
    Regards,
    Joe

    Most hardwood mounting systems I've seen go through the tank
    compartment so they connect/tie in with two bulkheads. In the situation
    you've described, I probably would have mounted a nylon engine mount
    direct to the firewall. I've been very successful drilling and tapping
    these mounts to accept 4-40 or 6-32 bolts with no blind nuts. I'd be
    somewhat concerned if the engine mounts are only glued to the sides and
    don't pass through at least one bulkhead.
    
    I've successfully used the threaded brass inserts for wing holddown
    bolts. I would think that they could be installed in the maple mounts
    from the top to act as captive/blind nuts.

    Here's an update to how I am solving the problem discussed earlier.
    
    Since the hardwood rails don't go through the firewall, I decided to
    add some additional thickness to the firewall such that it surrounded
    the two rails.  The materials available to do this were plywood and
    aluminum.  I chose to go with aluminum for maximum strength, and built
    it using 1/8 inch thick aluminum bar stock available at the hardware
    store.  I cut it out using my band saw, providing tight-fitting notches
    that fit snuggly around the rails.  I then used both epoxy AND mounting
    screws to hold this extra piece in place.  Came out very strong.  Now
    the rails will not be able to tear loose from the sides.
    
    I also doweled the front of the mounting rails to the fuse to further
    add strength and prevent them from pulling loose.  All in all, I
    believe this combination will work, and will start flying it in this
    configuration.  If, after multiple flights it seems to be getting
    loose, I will bite the bullet and perform surgury.  
    
    First flight will probably occur in early July.
    
    Regards,
    Joe