Received-SPF: pass
 receiver=logan.com; client-ip=66.147.249.2; envelope-from=jslade@canardaviation.com
DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=default; d=canardaviation.com;
	h=Received:Message-ID:Date:From:User-Agent:MIME-Version:To:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding:X-Identified-User;
	b=hml0PbXrireAc4LM9u9F8pFLE3APMS/+qPtR4CQLj5HQm/b86nsqe4zyGSoAdTWEVf+cPTWz8nOyMHoMbUHNVN4DGfB7PNFce+DSn7pZElEGSHkelIIDStrs9th7OPGh;
Message-ID: <4A5E8402.8010007@canardaviation.com>
Date: Wed, 15 Jul 2009 21:36:02 -0400
From: John Slade <jslade@canardaviation.com>
User-Agent: Thunderbird 1.5.0.14 (Windows/20071210)
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Intake velocity, stack lengths.
References: <list-3760648@logan.com>
In-Reply-To: <list-3760648@logan.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Ben,
If you're thinking of making a tube out of carbon fiber, this product 
may be of interest:
http://www.fibreglast.com/showproducts-category-Carbon+Fiber+Fabric,+Tapes+&+Tow-15.html
Scroll down to Braided Biaxial Sleeves.
I used the Vinyl Ester product from this firm. Their customer support 
was excellent.
Regards,
John Slade

George Lendich wrote:
>  Lynn,
> I've often wondered how the air flow is affected by joined tubes, with 
> a slip tube outer. My concern is tripping the boundary layer and 
> causing turbulence enough to restrict flow. Is there any really good 
> way of achieving a nice consistent flow with such a join.
> I thought of rounding off the inner facing edges, but then wondered 
> if that minor diameter increase would disturb the continuity of velocity.
> Probably all a trade off.
> George ( down under)
>
>      Fellows,
>     >
>     >  I have been thinking up this crazy idea of trying to make intake 
>     > runner tubes out of carbon fiber. My question is regarding
>     length of 
>     > the velocity stack. Does the length make a difference? Could a 
>     > velocity stack be more or less the entire length of the tube? 
>     > Meaning, if I have a 12" intake tube, could the entire length of
>     the 
>     > tube be a gradual taper to the diameter of the block opening?
>     Would 
>     > that mess with the speed the air is traveling in the tube? 
>     > Aerodynamics is not something I have a very good handle on, and am 
>     > hoping someone out there in Fly Rotary land can shed some light.
>     >
>     > Thoughts???
>     >
>     > BTW,  Any reasons why carbon fiber should not be used for intake 
>     > tubes? May make the velocity tubes a mute point.
>     >
>     > Thanks for any thoughts.
>     >
>     > Ben Schneider
>      
>
>     It would take the rest of your life to read all there is to read
>     about intake (tuned) lengths. So here is my view on it.
>      
>     The pipe organ idea is in play, but in my opinion is gifted too
>     much interest. In actual operation just about anything works prety
>     close to just fine. I just reviewed some formula Super Vee stuff
>     and note that a number of intakes were tried. Super Vee was a
>     class where a 1600 CC VW (Rabbit) engines were used in race cars.
>     The stock parts had to be used but could be modified by machining,
>     The intake runners could be up to 32MM, and the mechanical fuel
>     injection (probably from the diesel I think) could be used.
>      
>     HP well above 180 was the result, from VW parts. A straight 32MM
>     tube with a bellmouth. Not very exotic.
>      
>     The tuned length of any system has many harmonic peaks. They look
>     like the primary frequency but are removed from it by a factor of
>     4. So you have harmonic peaks at multipals of 4. So, 4,8,16 and so
>     on. So there are secondarys that show up to either side of the
>     primary, and some of those are reenforced by combinations of the
>     secondaries, so the 16th harmonic can be quite clear and easy to
>     find on a scope.
>      
>     The outcome is that it would be foolish to build an intake with
>     one primary frequency in mind. Say you want to cruise at 6,000
>     RPM, and built tubes to peak at that frequency. If you cannot keep
>     the engine at that RPM exactly, the effect is lost. Then you find
>     the engine in a null between peaks and performance is now less
>     than that of the thrown together mess on that plane in the next
>     hanger. 
>      
>     On takoff you would want to have say 6,500 or 7,000 available.
>     Where would you tune for that?
>      
>     So I drop back to what works in most situations. In general long
>     columns of air operate at lower frequencies. Short columns at
>     higher frequencies. Large diameters at lower and small diameters
>     at higher, and so on.
>      
>     The ideal shape for intake runners is tapered. Yep, thats it. not
>     often seen due to complexity of construction, but if you want to
>     talk ideal.................
>      
>     The horn shape at the end of the tube is to prevent a vena
>     contracta that reduces the effective diameter of the tube. A short
>     rounded edge that turns back 180 degrees is the very best and
>     works well in confined spaces like a plenum. For carbs, not so
>     good. At harmonics of, and just off peak frequencies, you will get
>     a ball of fuel standing in space just outside of the horn. In
>     those cases, a longer tapered horn works better to cover up a
>     number of frequencies and make the ball less obvious.
>      
>     The tuned length thing works less well in bent systems, and since
>     the nearly best length will involve runners over the top of the
>     engine, there is at least a 180 turn involved, and for side port
>     engines, two turns involved. So, to start off we are in tuning
>     trouble with a bent system that tends to null our best math
>     picture of ideal.
>      
>     Round runners are ideal for efficiency in moving air through the
>     smallest cross section. However, in a turn
>     the "D" shape takes over from the round, in that the mass of the
>     airflow tends to move along the outer wall, and at some speeds may
>     be seen moving along the inside wall in the wrong direction, and
>     also may
>     slow and upset the flow along the outer wall. In most cases the
>     "D" shape may have slightly less cross section than the original
>     round runner. Also there may be improvements should a slightly
>     course or rough surface be left along the flat of the "D" so as to
>     keep flow attached and reduce the higher velocity along the
>     outside. Uniform velocity is better than a number of velocities or
>     even reversed flow.
>      
>     The taper............
>      
>     Large tube diameters have lower velocity and small higher for any
>     fixed depression. If you imagine the rotor as a blade and the
>     intake flow as a sausage being pushed through the blade, then you
>     are one sick puppy.............
>      
>     However, it works for me.
>      
>     So would high velocity at the port face, (where the rotor cuts off
>     each chunk) be better than low velocity?
>      
>     The higher velocity for any unit of time means more sausage (or
>     fuel air mixture) entering the chamber.
>      
>     Yes high velocity is better. But drag in the runner develops at
>     the square of velocity, so if the runner is the same diameter for
>     all of its length, drag will be high, the boundary layer will be
>     thick and easy to upset. Suppose then that the taper was only in
>     the last several inches of the runner. Or if you want the ideal,
>     the taper starts at the horn and runs the length of the runner
>     tightening to the port size at the manifold face. Less drag
>     overal. Thinner more stable boundary layer, and the highest
>     possible velocity at the port face.
>      
>     Another thought..........
>      
>     The primary and secondary ports feed just one rotor each set. The
>     primary ports are those in the center iron, and are smaller than
>     the secondary ports in the end irons. The engine operates for most
>     of its life on the primaries, as little HP is called for in normal
>     driving. The primaries are small, so as to maintain high velocity,
>     and crisp throttle response. 
>      
>     I would join the two intake ports and run a single runner for each
>     rotor housing. Less volume consumed.
>     Lighter intake system. Smaller plenum. Probably no loss of
>     performance. The molded part then could be tapered, have the "D"
>     shape, the rough inside turn, a length of straight tube to mate to
>     a slip tube to "tune" runner lengths. 
>      
>     Lynn E. Hanover  
>      
>      
>      
>      
>