X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.2.15) with ESMTP id 3760646 for flyrotary@lancaironline.net; Wed, 15 Jul 2009 18:09:43 -0400 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (sv1-1.per.aanet.com.au [203.24.100.68]) by poplet2.per.eftel.com (Postfix) with ESMTP id CB16A1738F6 for ; Thu, 16 Jul 2009 06:09:02 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id EF6D8BEC031 for ; Thu, 16 Jul 2009 06:09:01 +0800 (WST) Message-ID: From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Intake velocity, stack lengths. Date: Thu, 16 Jul 2009 08:09:07 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_002B_01CA05EC.B114EDC0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 090715-0, 07/15/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_002B_01CA05EC.B114EDC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 =20 > runner tubes out of carbon fiber. My question is regarding length of = =20 > the velocity stack. Does the length make a difference? Could a =20 > velocity stack be more or less the entire length of the tube? =20 > Meaning, if I have a 12" intake tube, could the entire length of the = =20 > 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? =20 > Aerodynamics is not something I have a very good handle on, and am =20 > 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 =20 > 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.=20 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.=20 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.=20 On takoff you would want to have say 6,500 or 7,000 available. Where = would you tune for that?=20 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.=20 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.=20 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.=20 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.=20 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.=20 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.=20 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.=20 Lynn E. Hanover =20 ------=_NextPart_000_002B_01CA05EC.B114EDC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 Lynn,
I've often wondered how the air flow is = affected by=20 joined tubes, with a slip tube outer. My concern is tripping the = boundary layer=20 and causing turbulence enough to restrict flow. Is there any really good = way of=20 achieving a nice consistent flow with such a join.
I thought of rounding off the inner = facing edges,=20 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=20 idea of trying to make intake 
> runner tubes out of = carbon fiber.=20 My question is regarding length of 
> the velocity stack. = Does the=20 length make a difference? Could a 
> velocity stack be = more or=20 less the entire length of the tube? 
> Meaning, if I have = a 12"=20 intake tube, could the entire length of the 
> tube be a = gradual=20 taper to the diameter of the block opening? Would 
> that = mess=20 with the speed the air is traveling in the tube? 
> = Aerodynamics=20 is not something I have a very good handle on, and am 
> = hoping=20 someone out there in Fly Rotary land can shed some = light.
>
>=20 Thoughts???
>
> BTW,  Any reasons why carbon fiber = should not=20 be used for intake 
> tubes? May make the velocity tubes a = mute=20 point.
>
> Thanks for any thoughts.
>
> Ben=20 Schneider
 

It would take the rest of your life to read all there is to = read=20 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=20 interest. In actual operation just about anything works prety close to = just=20 fine. I just reviewed some formula Super Vee stuff and note that a = number of=20 intakes were tried. Super Vee was a class where a 1600 CC VW (Rabbit) = engines=20 were used in race cars. The stock parts had to be used but could be = modified=20 by machining, The intake runners could be up to 32MM, and the = mechanical fuel=20 injection (probably from the diesel I think) could be used.
 
HP well above 180 was the result, from VW parts. A straight 32MM = tube=20 with a bellmouth. Not very exotic.
 
The tuned length of any system has many harmonic peaks. They look = like=20 the primary frequency but are removed from it by a factor of = 4. So=20 you have harmonic peaks at multipals of 4. So, 4,8,16 and so on. So = there are=20 secondarys that show up to either side of the primary, and some of = those are=20 reenforced by combinations of the secondaries, so the 16th harmonic = can be=20 quite clear and easy to find on a scope.
 
The outcome is that it would be foolish to build an intake with = one=20 primary frequency in mind. Say you want to cruise at 6,000 RPM, and = built=20 tubes to peak at that frequency. If you cannot keep the engine at that = RPM=20 exactly, the effect is lost. Then you find the engine in a null = between peaks=20 and performance is now less than that of the thrown together mess on = that=20 plane in the next hanger. 
 
On takoff you would want to have say 6,500 or 7,000 available. = Where=20 would you tune for that?
 
So I drop back to what works in most situations. In general long = columns=20 of air operate at lower frequencies. Short columns at higher = frequencies.=20 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=20 seen due to complexity of construction, but if you want to talk=20 ideal.................
 
The horn shape at the end of the tube is to prevent a vena = contracta that=20 reduces the effective diameter of the tube. A short rounded edge that = turns=20 back 180 degrees is the very best and works well in confined spaces = like a=20 plenum. For carbs, not so good. At harmonics of, and just off peak=20 frequencies, you will get a ball of fuel standing in space just = outside of the=20 horn. In those cases, a longer tapered horn works better to cover up a = number=20 of frequencies and make the ball less obvious.
 
The tuned length thing works less well in bent systems, and since = the=20 nearly best length will involve runners over the top of the engine, = there is=20 at least a 180 turn involved, and for side port engines, two turns = involved.=20 So, to start off we are in tuning trouble with a bent system that = tends to=20 null our best math picture of ideal.
 
Round runners are ideal for efficiency in moving air through the = smallest=20 cross section. However, in a turn
the "D" shape takes over from the round, in that the mass of the = airflow=20 tends to move along the outer wall, and at some speeds may be seen = moving=20 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=20 may have slightly less cross section than the original round runner. = Also=20 there may be improvements should a slightly course or rough surface be = left=20 along the flat of the "D" so as to keep flow attached and reduce the = higher=20 velocity along the outside. Uniform velocity is better than a number = of=20 velocities or even reversed flow.
 
The taper............
 
Large tube diameters have lower velocity and small higher for any = fixed=20 depression. If you imagine the rotor as a blade and the intake flow as = a=20 sausage being pushed through the blade, then you are one sick=20 puppy.............
 
However, it works for me.
 
So would high velocity at the port face, (where the rotor cuts = off each=20 chunk) be better than low velocity?
 
The higher velocity for any unit of time means more sausage (or = fuel air=20 mixture) entering the chamber.
 
Yes high velocity is better. But drag in the runner develops at = the=20 square of velocity, so if the runner is the same diameter for all of = its=20 length, drag will be high, the boundary layer will be thick and easy = to upset.=20 Suppose then that the taper was only in the last several inches of the = runner.=20 Or if you want the ideal, the taper starts at the horn and runs the = length of=20 the runner tightening to the port size at the manifold face. Less drag = overal.=20 Thinner more stable boundary layer, and the highest possible = velocity at=20 the port face.
 
Another thought..........
 
The primary and secondary ports feed just one rotor each set. The = primary=20 ports are those in the center iron, and are smaller than the secondary = ports=20 in the end irons. The engine operates for most of its life on the = primaries,=20 as little HP is called for in normal driving. The primaries are small, = so as=20 to maintain high velocity, and crisp throttle response. 
 
I would join the two intake ports and run a single runner for = each rotor=20 housing. Less volume consumed.
Lighter intake system. Smaller plenum. Probably no loss of = performance.=20 The molded part then could be tapered, have the "D" shape, the rough = inside=20 turn, a length of straight tube to mate to a slip tube to "tune" = runner=20 lengths. 
 
Lynn E. Hanover  
 
 
 
 
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