Conference vmszoo::rc

    Hi Jeff,
    Look into  Royal kit's, I think I saw one there.
                                                            Jim

    a MOSQUITO or an ME-410 ?
    
    md

    Royal does, indeed, have several twin kits...in fact, they may be
    just about the only manufacturer that does (except, of course, for
    the twin "Stiks," etc.).  However, I'm not sure they have anything
    smaller than for twin-.40's.  For your engines, you may be forced
    to scratch-build something.    

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

    
    
    	Royal does kit the Skymaster but it calls for two 40-61 sized
    engines. For the first (anything) type of plane I wouldn't suggest
    	a scale bird. They used to kit a twinstik. Like an uglystix
    but with two engines. Pica kits a twin also but I think it's for
    two .40's. I'll check RCM plans and get back to you.
    
    					Tom

    
    I checked RCM plans and came up with the following list.
    
    	# 122		Cessna UC-78       Twin .35's
    	# 551		Britten Norman		.10's
    	#744		Mosquito		.40's
    	#677		Dornier DO 28		.?
    	#628		Norman N22		.35's
    	#397		Beech C45		.15's
    
    
    					Tom

    Re: .-1,
    
    That's what I was afraid of; .25 just doesn't seem to be a very
    popular size for twins.  Check the plans listings for all the mag-
    azines and the Bob Holman catalog (Kevin Ladd and Dan Snow have
    copies).  If this fails to turn anything up, yer' probably gonna
    have to "doitcherself."    

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

    wing manufactering makes 2 semikits for twins.  their p38 looks a bit
    big for .25's but the b26 (or is it a26) MIGHT do the trick.
    theres a wing mfg b26 in the long lost 1/8 air force video hamming
    it up for the audience.  it flew great, but then, i think it was
    garland hamilton at the sticks.
    kevin                     

    Re: .-1, kevin,
    
    Roger yer' last.  Wing Mfg. kits the A-26 (B-26) as one of their short
    kits.  And, yes, the one at the 1/8 AF meet _was_ built and flown
    by Garland Hamilton.  As I recall, it had twin-.40's and seemed
    a little large for .25's but I could be wrong about that.    

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

    
    If you could get ahold of a Carl Goldberg Skylark I'm pretty sure
    that it had a twin option. A buddy of mine in NH used to have one
    It ran on two 20's so .25's might be just fine.
    
    						Tom

    Several twin conversions of popular kits have been shown in the
    mags.  The one that stands out in my mind is a Great Planes Sportster
    conversion.  How about a Sportster 40 with two 25's?
    
    Pica makes a kit called the Duellist but I can't remember if it
    is for 25's or 40's.
    
    Scott

    Hand-kit yourself a "flying boxcar"; the fuse was essentially a
    box with a 1-D taper at each end.  Should be plenty of room inside
    for servos, fuel tanks, etc.  Straight wing, two engines.  Two booms
    but they weren't tapered; they can be aluminum tubing if you want...
                              
    If you want scale, make the proto model the "film recovery" boxcar
    that snagged film cannisters ejected by early spy sattelites.  NOVA
    had some footage of it last night. (on WGBH Boston).  Now my VCR
    has the footage. :-)

    RE: .10,
    
    The Pica Duelist (designed by Dave Platt) is for twin .40's and
    up...much too big for .25's.    

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

I vote for the Wing Mfg A26 short kit.
I just checked their add and they don't describe it in the latest add
so I can't be sure that it takes 20-25s but their
phone number is (815)459-0417 at

	Wing Mfg
	P.O. Box 33
	Crystal Lake, IL 60014

I thought the A26 was the best flying twin at the 1/8 Air Force fun fly
as well.  

The guy was doing low passes and scraped the bottom of the fuselage on
the pavement.  When he landed it also had one prop cracked.  Both engines
were still running.  He painted it in Navy Colors (Olive Drab fuselage
with Chrome Yellow wings) - looked great and had retracts (for really
low - low passes!

Bye          --+--
Kay R. Fisher  |
---------------O---------------
================================================================================

    re .10...  Hmmm a Supersportster twin??  I could just build the
    wing then attach it to the SS-40 I have now...  Then it would look
    almost like a Ford Trimotor.
    
    As I said, I would like it to "look" like a real plane.  I am not
    planning on building a scale model (although the B-26 sounds
    interesting).
    
    Thanks for all of the suggestions; keep them coming...
    
    Side question, are 2 .25s about equal to a .40??  ie, if I were
    to do a home built, is a .40 size ship the right place to start??
    
    I was just thinking, I could do just what Piper did...  Take the
    Cherokee (Great Planes has a .40 size one), stretch the nose some
    and put 2 engines on the wings.  That would come out to be a 
    close approximation of a Senaca...
    
    Cheers,
    jeff
    

    Jeff,
    
    Engines in multiple tend to increase, power-wise, exponentially;
    that is, the power increase is _more_ than simply a multiple of the
    displacement.  For example, 2-.25's would appear to be the equivalent
    of a single .50 but, in actual practice, the power realized is
    something more than that, probably approaching a single .55-.60.  
    Therefore, yes, a .40-size ship would be a place to start, under-
    standing that, with twin .25's, the performance will be a little 
    hotter than it would've been with a single .40 or .50.

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

Not that this really belongs here, but...

I've always thought it would be neat to built a model of a really old plane, 
such as the Wright Bro's original. If I recall correctly, it was a single engine
plane with twin props. Has anyone ever put out a kit of such a plane, and would 
it be difficult to build and fly one? It certainly would be an attention getter.
The main problem in my opinion would be how to power it. No matter how beautiful
the plane looked, the whole appeal would fly out the window if the engine 
sounded like a chainsaw or a high powered mosquito.

Dave

    Dave,
    
    The only such R/C model I'm aware of was the Wright flyer built/flown
    by Jorge Vogelsang at the 1/4 scale meet in Las Vegas a few years
    back.
    
    Jorge is a wealthy west German industrialist who shows up in Vegas
    with a new show-stopper every year, e.g. V-1 Buzz-Bomb, Me-163 Komet,
    etc., etc.  He spares no expense and the technical innovations
    incorporated into his models set the R/C world on its ear regularly;
    for example the pulse-jet engines he designed/built for the models
    mentioned above.
    
    However, even with all the expertise, resources and money at his
    disposal, Jorge was unable to overcome the myriad problems associated
    with trying to harness a single model engine, via prototypical belt
    drives, to the twin pusher props of the Wright Flyer.  Finally
    abandoning the idea, Jorge resorted to installing a pair of O.S.
    .90's in pusher configuration, one at each prop location.  The engines
    were all but totally concealed in the scale gearboxes and are virtually
    unnoticeable in the pix/videos I've seen of the bird.
    
    Yes, the sound was something less than prototypical but Jorge had
    the engines well muffled and pulling enormous scale props at low RPM's
    so the sound was not offensive in the least, perhaps even sounding 
    something like you might imagine the actual engine sounding. The 
    upshot was that the replica _flew_ magnificently and awestruck all 
    who saw it fly.  

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

    The Wing Mfg. short-kit for the A (B)-26 Invader spans 68" and calls
    for .25-to-.40 engines.  If kept VERRRRRY light, it'd probably be
    OK on a pair of good .25's.    

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

    I called Wing...  They said that yes, the plane has been run with
    twin .25s in it.  But the guy I talked to was very hesitant about
    it.  He said that when they flew it with twin .25s, they were able
    to build it at about 7-1/2 lbs.  So, this is still a possibility,
    but a slim one.
    
    Actually, the more I think about it, the more I like the idea of
    using the Great Planes Cherokee as the basis for building a Seneca
    Twin.  I remember seening some article about the building a twin
    super sportster.  Their wings are almost identical.  I have seen
    it move right along with a good .40, so power should not be a problem..
    
    I think fuel tank placement may be a problem...  There is not a
    lot of extra room in the Great Planes .40 size fuses.  I will have
    to dig out that article and see how they did it...
    
    Thanks!
    jeff
    

    Jeff,  Another sggestion would be to buy a supersporster 20 kit
    and scratch a second fuse.  Used two fuses on one wing for a kind
    of F82 sporty??
    
    					Tom

    here's a question.  al said in a previous note that 2 .25's has
    more power than a single .50.  why?  is it the displacement or
    the propellors.  what i'm getting at is, is a twin cyclinder engine
    more or less efficient?  also perhaps a word on fuel economy?
    thanks
    kevin

    Kevin,
    
    Understanding this relationship is easy if you'll think of it in
    terms of the pair of engines swinging, effectively, twice the prop
    blade area as the single engine, and at a similar RPM.  EX: 2-.30's
    swinging 10-6 props would be approximately equal to a single .60
    swinging a 20-6 prop.  But we know the .60 can comfortably swing
    only a little over half that amount of prop, say an 11-7 or 12-6.
    
    Of course, we don't realize a doubling of power from the twin but 
    the actual power increase is appreciable.  The "Catch-22" is that 
    both engines must be kept running at all times or we have a tiger-
    by-the-tail.  ;B^}     
    
    A twin cylinder .60 will tend to develop somewhat less power than
    a single as there is more internal weight/drag/inertia to overcome
    than exists in the single-cylinder.  Also, the 2-cylinder engine
    is heavier than the single-cylinder, making it less efficient still.
    
    Fuel economy, not my strong suit but I expect twin engines'd require
    a little more fuel than a single engine of similar total displacement,
    say two 8-oz. tanks versus one 12-oz. tank for the example above.
    I really can't speculate on the twin-cylinder engine but I'd be
    surprised if it required much more fuel that the single-cylinder.
    
      |
      | |      00	 Adios,      Al
    |_|_|      ( >o
      |    Z__(O_\_	(The Desert Rat)

    Al,
    
    A point of contention about the explanation concerning twin engines.
    I would think that what is of concern is the "area" inscribed by
    the two props, and in that case two 10-6's don't equal one 20-6.
    I figure that the area inscribed by two 10" props equals the area
    inscribed by a single 14" prop, something a little more reasonable
    for a .60 to swing.  Am I on the right track?
    
    Scott

    Scott,
    
    I'm not sure I'm following yer' rationale but, obviously, we're
    not dealing with absolutes here and the "effective" blade area being
    swung by the twin-engines _is_ something larger than what the single
    engine could swing, practically or otherwise.  If yer' 14" prop
    is closer to the truth, the fact remains that a single .60 engine
    could not effectively swing this large a prop unless the pitch was
    so low that little thrust was resulting.
    
    So, whichever one of us is the more correct, respective of effective
    blade area, my original premise holds true; that two-engines develop
    more thrust/power than a single engine whose displacement equals
    the sum of the smaller engines.  

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

    The reason why two small engines are more powerful than one big
    engine is: The smaller engines run at a higher RPM. They are therefore
    capable of consuming fuel more quickly.
    							John.

    Re: .25, John,
    
    That's certainly a portion, but not all of it.  RPM, of itself, doesn't
    necessarily translate to increased power, i.e. Cox .049's can easily
    turn upwards of 18-20,000 RPM but that alone doesn't mean that a
    pair of them could out-pull a .60.  The prop(s) must be taken into
    consideration as I've described earlier and, if a pair of smaller
    engines can swing more effective blade area than a larger single
    engine, then more power/thrust is realized.    

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

    Well, let's calculate out the mass flow rate for a quad of .049's
    and a .45...
    
    The .049's (we can assume) are turning 20Krpm, so that's 
    
    	.049x20,000= 980 cu in of air/minute throughput PER ENGINE
                   = 3920 cu in/min for the array
    
    The .45 (we will assume) turns about 8.5 Krpm (not a DF engine :-))
                                                                    
    	.45x 8500= 3825 cu in of air/minute throughput PER ENGINE
    
    
    So, very roughly, one .45 sport engine ought to pull the same ship,
    at roughly the same airspeed, as four .049's...
                       
    -----
    
    What about weight?  Do 4 x .049+prop weigh more, less, or the same
    as 1 .45 plus prop?
                     
    -----
    
    Don't forget "annoyance factor"; the probability that one engine
    out of 4 will decide to be ornery on any given day and refuse to
    start...
    

    I can only comment on my experience with boats.  Two engines is
    definately less efficient than one of twice the power rating.
    This is mostly due to the extra drag of two props and lower units,
    but I would expect the same to be true for aircraft engines.  Also,
    fuel consumption is much greater for two engines than one.  The
    main reason many people put two motors on a boat is increased
    reliability.  They can get back in if one engine runs and an engine
    out situation is not as serious as it is for an airplane.  The other
    advantage of two engines on a boat is torque cancelation.  Most
    setups use counter rotating props which reduces torque steer.
    
    
    Charlie
    

    Re: a few back, FYI's-
    
    I pulled out the WD40 and sprayed my algebra, brushed off the rust
    and came up with the following re: effective sizes of props:
                          
                            2                                  
    Area of 10" prop:	PI R  or 3.14*100 = 314 sq in 
                                         2            
    	   therefore:   2 props =  2 PI R  = 628 sq in
                                          2
    A single prop of the same area:   PI R = 628
                                          2
                                         R = 628/3.14
                                          2
                                         R = 200 sq. in.                       
    Radius of a single prop equal to                      
           two props of 10" diameter:    R = 14.145  in.
    
    
       
                             |                      
   \	       	         ____|____                      /   Regards,
    \________________________O_________________________/    Frank.
   

    Whoops, I used Diameter instead of Radius... should still work out,
    Yes??
    
                             |                      
   \	       	         ____|____                      /   Regards,
    \________________________O_________________________/    Frank.
    

>    Whoops, I used Diameter instead of Radius... should still work out,
>    Yes??

But you can't count the center of the props and there are two centers on a
twin.  Also you can't count the whole prop.  The percent of thrust given
by each part of the prop is not the same - for instance the section just 
outside of the prop nut probably has very little thrust and also I assume that
the very tip where the pitch flattens out to near zero again probably 
has very little thrust (at least the last 1/16 inch of it.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
================================================================================

    In the base note, the Cessna SkyMaster was mentioned.  Is that by
    any chance the plane flown by "Bird dog" in the film BAT21?
    
    If so, did anyone locate any plans for a small (500 to 600 sq. in.)
    version?

    I'm pretty sure that's the one. The only plan/kit I know of is from
    Royal Products. I think it takes two 40's.
    
    
    						Tom

    Yes the Cessna Skymaster also called the O-2 "oh 2" or the Cessna load
    master (I think) is the one they flew in BAT-21.

    
    About the Skymaster plans/kit:
    
    Royal has a kit; Span = 76+ in.
                     Area = 754 sq. in.
                     Power= twin .35 - .60
                     Scale= 2" = 1'
    
    Royal Products
    790 W. Tennessee Ave
    Denver, CO  80223-2875
    
    I don't know any more about it, just got this info from
    a 1986 catalog.
    
    john

    If you want to build one smaller you could buy a set of plans fron
    royal. Send the plans out and have them reduced. The reduction would
    cost you about 40.00 .
    
    
    Tom

    Reduction is no problem.  Modern photocopiers take care of the tricky
    stuff, and then you can fill in the straight lines.
    
    Any idea what Royal would ask for a set of plans?

    More about the Skymaster,
    
    According to my 1986 catalog, plans for the Cessna Skymaster,
    Cat #K79-396, plan only @ $8.95   
    
    Funny, nowhere can I find their phone number!
    
    john