REFLECTOR: Updraft cooling
John Dibble
aminetech at bluefrog.com
Sun Feb 18 10:27:36 CST 2007
According to my Franklin engine manual, the measured CHT will be 50 C (90 F) higher with a spark
plug probe, located on the bottom plug, compared to a bayonet probe, located on the top of the
cylinder. Maybe the temperature difference is due to the direction of air flow. I have downdraft
cooling. The air should be much warmer after passing the cylinder. Therefore the temperature at
the bottom of my cylinders should be higher than at the top. If the bayonet probe is used and
cooling is switched from updraft to downdraft, a lower CHT may not necessarily mean the overall
cylinder temp is lower. Just a thought.
John
Dave Philipsen wrote:
> Dean,
>
> I'm in the same boat (plane) as you. I bought a Velocity that was built
> by someone else and it has updraft cooling too. But, I think that's the
> way they all were originally. The NACA scoops were introduced as
> standard a little later. I'm in the midst of working on ways to cool it
> more efficiently. At least this forum will help perhaps by providing us
> with some ideas.
>
> Unterreiner wrote:
> > I have an IO-360 in my Velocity with updraft cooling. The guy who built the
> > plane went to alot of trouble to get it to cool properly in cruise, and it
> > still needs to be modified so it will cool better during takeoff. Also, the
> > Lycoming engines are designed to be cooled from the top down. I wish the guy
> > who built my plane would have used the NACA plenum system. It's alot
> > simpler, cools the engine the way it's supposed to be cooled and is less
> > prone to develop cooling problems.
> >
> > Dean Unterreiner
> > ----- Original Message -----
> > From: <reflector-request at tvbf.org>
> > To: <reflector at tvbf.org>
> > Sent: Saturday, February 17, 2007 5:52 PM
> > Subject: Reflector Digest, Vol 33, Issue 47
> >
> >
> >
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> >> Today's Topics:
> >>
> >> 1. Re: updraft cooling (Scott Derrick)
> >> 2. Re: updraft cooling (John Dibble)
> >> 3. Re: updraft cooling (Douglas Holub)
> >> 4. Re: updraft vs sidedraft vs updraft cooling (gpoole)
> >> 5. Re: updraft cooling (Al Gietzen)
> >>
> >>
> >> ----------------------------------------------------------------------
> >>
> >> Message: 1
> >> Date: Sat, 17 Feb 2007 15:57:56 -0500 (EST)
> >> From: "Scott Derrick" <scott at tnstaafl.net>
> >> Subject: Re: REFLECTOR: updraft cooling
> >> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> >> Message-ID: <43917.63.164.47.227.1171745876.squirrel at tnstaafl.net>
> >> Content-Type: text/plain;charset=iso-8859-1
> >>
> >> Doug,
> >>
> >> I had updraft on my IO360 and it worked fine. I had to run LOP in the
> >> summer(I did all the time anyway) to keep the engine cool enough. There
> >> were times when I stopped for gas and during the following departure
> >> climbout I would have to level off at an intermediate altitude for awhile
> >> to get the oil temps back down below 230.
> >>
> >> Installing my 520 I conferred with Velocity(ScottB and Brendon) and was
> >> advised I would need to use downdraft as they had never successfully seen
> >> an updraft system work for the big six cylinder engines. So I did the
> >> conversion.
> >>
> >> I thought that using NACA intakes would "theoretically" be more drag
> >> effecient ?
> >>
> >> Scott
> >>
> >>
> >>
> >>> I can understand why Burt Rutan and Nat Puffer are proponents of updraft
> >>> cooling. From an engineering point of view, it has a lot going for it.
> >>> You
> >>> need more cooling when the airplane is climbing. If the cooling intake is
> >>> below the wing, the pressure is higher during a climb so you
> >>> automatically
> >>> get more cooling during a climb. Similarly, it would be nice if cooling
> >>> was minimized during descent. The pressure is reduced under the wing
> >>> during descent, and so there is less cooling to the engine. Also, you've
> >>> got convection working with you instead of against you with an updraft
> >>> system.
> >>>
> >>> That all adds up to more drag with down draft cooling, because the NACA
> >>> scoops have to be large enough so that there is adequate cooling during
> >>> climb out, when the pressure at the NACAs is at its minimum.
> >>>
> >>> But the down draft is a lot simpler to implement, and that's probably
> >>> going to be the deciding factor for me.
> >>>
> >>> Doug Holub_______________________________________________
> >>> To change your email address, visit
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>> Visit the gallery! www.tvbf.org/gallery
> >>> user:pw = tvbf:jamaicangoose
> >>> Check new archives: www.tvbf.org/pipermail
> >>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>>
> >>
> >> ------------------------------
> >>
> >> Message: 2
> >> Date: Sat, 17 Feb 2007 15:04:56 -0600
> >> From: John Dibble <aminetech at bluefrog.com>
> >> Subject: Re: REFLECTOR: updraft cooling
> >> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> >> Message-ID: <45D76DF8.5468770B at bluefrog.com>
> >> Content-Type: text/plain; charset="us-ascii"
> >>
> >> I assume that updraft simply refers to the intake air coming from below
> >> as opposed to downdraft where the air comes from the NACAs above. I
> >> think the way it passes the engine is the same. It would be inefficient
> >> to pass the air past the exhaust pipes first.
> >>
> >> John
> >>
> >> Chuck Jensen wrote:
> >>
> >>
> >>> I've not seen the layout of an updraft cooling system, but does the
> >>> air get preheated from passing by the exhaust pipes before it every
> >>> gets to the cylinder heads? If it does, that would greatly increase
> >>> the volume of air required because of the reduced delta T across the
> >>> heads. By comparison the top NACAs provide clean, cool air directly
> >>> to the CHs. Too simple--I must be missing something?
> >>> Chuck Jensen
> >>>
> >>> -----Original Message-----
> >>> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
> >>> On Behalf Of John Dibble
> >>> Sent: Saturday, February 17, 2007 2:41 PM
> >>> To: Velocity Aircraft Owners and Builders list
> >>> Subject: Re: REFLECTOR: updraft cooling
> >>>
> >>> I think the amount of air going past the cylinders will determine the
> >>> degree of cooling, so it's a matter of making the NACA or armpit scoop
> >>> and ducts big enough for sufficient air.
> >>>
> >>> John
> >>>
> >>> Ron Brown wrote:
> >>>
> >>>
> >>>> And, the downdraft NACA cooling for some unexplainable reason, runs
> >>>> about 40 degrees cooler than the updraft cooling. Mark Machado
> >>>> converted what is now the factory trainer from updraft to downdraft
> >>>> and says the heads ran 30-40 degrees cooler. My 173 Elite RG runs
> >>>> 360-370 max on a long climb out and 320-340 degrees during a 2600
> >>>> rpm/155 kt cruise. I highly recommend the NACA cooling system.
> >>>>
> >>> ----------------------------------------------------------------
> >>> _______________________________________________
> >>> To change your email address, visit
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>> Visit the gallery! www.tvbf.org/gallery
> >>> user:pw = tvbf:jamaicangoose
> >>> Check new archives: www.tvbf.org/pipermail
> >>> Check old archives:
> >>> http://www.tvbf.org/archives/velocity/maillist.html
> >>>
> >>>
> >> -------------- next part --------------
> >> An HTML attachment was scrubbed...
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> >>
> >> ------------------------------
> >>
> >> Message: 3
> >> Date: Sat, 17 Feb 2007 16:13:01 -0600
> >> From: "Douglas Holub" <doug.holub at tx.rr.com>
> >> Subject: Re: REFLECTOR: updraft cooling
> >> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> >> Message-ID: <007e01c752e0$ca67f130$6a01a8c0 at Workshop>
> >> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> >> reply-type=original
> >>
> >> "I thought that using NACA intakes would 'theoretically' be more drag
> >> effecient ?"
> >> -------------------------------------------------------------------
> >> I was just comparing updraft to downdraft. It looks like I could put one
> >> big
> >> NACA underneath the rear seat. I was thinking of using that spot for ram
> >> air, though.
> >>
> >> I'm a little confused about the benefits of a NACA scoop. I need to read
> >> up
> >> on them some more. I think that if the cowl lip were extended up a little
> >> to
> >> catch the air it might be more efficient than the NACA scoops. But even
> >> if
> >> it were more efficient, you would be making it a little harder for air to
> >> flow to the propeller because the cowl would be getting a little taller.
> >> But
> >> then, you lose some head room in the back seats with the NACAs. Decisions,
> >> decisions.
> >>
> >> Doug Holub
> >>
> >> ----- Original Message -----
> >> From: "Scott Derrick" <scott at tnstaafl.net>
> >> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> >> Sent: Saturday, February 17, 2007 2:57 PM
> >> Subject: Re: REFLECTOR: updraft cooling
> >>
> >>
> >>
> >>> Doug,
> >>>
> >>> I had updraft on my IO360 and it worked fine. I had to run LOP in the
> >>> summer(I did all the time anyway) to keep the engine cool enough. There
> >>> were times when I stopped for gas and during the following departure
> >>> climbout I would have to level off at an intermediate altitude for awhile
> >>> to get the oil temps back down below 230.
> >>>
> >>> Installing my 520 I conferred with Velocity(ScottB and Brendon) and was
> >>> advised I would need to use downdraft as they had never successfully seen
> >>> an updraft system work for the big six cylinder engines. So I did the
> >>> conversion.
> >>>
> >>> I thought that using NACA intakes would "theoretically" be more drag
> >>> effecient ?
> >>>
> >>> Scott
> >>>
> >>>
> >>>
> >>>> I can understand why Burt Rutan and Nat Puffer are proponents of updraft
> >>>> cooling. From an engineering point of view, it has a lot going for it.
> >>>> You
> >>>> need more cooling when the airplane is climbing. If the cooling intake
> >>>> is
> >>>> below the wing, the pressure is higher during a climb so you
> >>>> automatically
> >>>> get more cooling during a climb. Similarly, it would be nice if cooling
> >>>> was minimized during descent. The pressure is reduced under the wing
> >>>> during descent, and so there is less cooling to the engine. Also, you've
> >>>> got convection working with you instead of against you with an updraft
> >>>> system.
> >>>>
> >>>> That all adds up to more drag with down draft cooling, because the NACA
> >>>> scoops have to be large enough so that there is adequate cooling during
> >>>> climb out, when the pressure at the NACAs is at its minimum.
> >>>>
> >>>> But the down draft is a lot simpler to implement, and that's probably
> >>>> going to be the deciding factor for me.
> >>>>
> >>>> Doug Holub_______________________________________________
> >>>> To change your email address, visit
> >>>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>>
> >>>> Visit the gallery! www.tvbf.org/gallery
> >>>> user:pw = tvbf:jamaicangoose
> >>>> Check new archives: www.tvbf.org/pipermail
> >>>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>>>
> >>> _______________________________________________
> >>> To change your email address, visit
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>> Visit the gallery! www.tvbf.org/gallery
> >>> user:pw = tvbf:jamaicangoose
> >>> Check new archives: www.tvbf.org/pipermail
> >>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>>
> >>>
> >>
> >>
> >> ------------------------------
> >>
> >> Message: 4
> >> Date: Sun, 18 Feb 2007 09:29:29 +1100
> >> From: "gpoole" <gpoole at zeta.org.au>
> >> Subject: Re: REFLECTOR: updraft vs sidedraft vs updraft cooling
> >> To: "'Velocity Aircraft Owners and Builders list'"
> >> <reflector at tvbf.org>
> >> Message-ID: <00b801c752e3$1725de40$4deb64cb at gregb97b7132b4>
> >> Content-Type: text/plain; charset="windows-1250"
> >>
> >> I have been making the same deliberations as Doug for quite some time.
> >> There are compromises with every option ..sigh! Scoops vs NACA ducts...
> >>
> >> If pinching air before the prop with a scoop on the belly is considered to
> >> affect prop efficiency then perhaps (surely?) Al G's & several other's
> >> approach of putting radiators in the wing is the way to go. I like the
> >> idea
> >> of being able to tailor the amount of air to the radiators to balance the
> >> compromise between drag and amount of cooling required by having variable
> >> inlets. Only problem is that the air needs to do several sharp turns to
> >> get
> >> to the cylinder heads....which would should slow it down considerably....
> >>
> >> Would be interested in this thread continuing to see what others think....
> >>
> >> Greg in Sydney.
> >>
> >> gregpoole at saaachapter11.com
> >>
> >>
> >> -----Original Message-----
> >> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> >> Behalf Of Douglas Holub
> >> Sent: Sunday, 18 February 2007 9:13 AM
> >> To: Velocity Aircraft Owners and Builders list
> >> Subject: Re: REFLECTOR: updraft cooling
> >>
> >> "I thought that using NACA intakes would 'theoretically' be more drag
> >> effecient ?"
> >> -------------------------------------------------------------------
> >> I was just comparing updraft to downdraft. It looks like I could put one
> >> big
> >>
> >> NACA underneath the rear seat. I was thinking of using that spot for ram
> >> air, though.
> >>
> >> I'm a little confused about the benefits of a NACA scoop. I need to read
> >> up
> >>
> >> on them some more. I think that if the cowl lip were extended up a little
> >> to
> >>
> >> catch the air it might be more efficient than the NACA scoops. But even
> >> if
> >> it were more efficient, you would be making it a little harder for air to
> >> flow to the propeller because the cowl would be getting a little taller.
> >> But
> >>
> >> then, you lose some head room in the back seats with the NACAs. Decisions,
> >> decisions.
> >>
> >> Doug Holub
> >>
> >> ----- Original Message -----
> >> From: "Scott Derrick" <scott at tnstaafl.net>
> >> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> >> Sent: Saturday, February 17, 2007 2:57 PM
> >> Subject: Re: REFLECTOR: updraft cooling
> >>
> >>
> >>
> >>> Doug,
> >>>
> >>> I had updraft on my IO360 and it worked fine. I had to run LOP in the
> >>> summer(I did all the time anyway) to keep the engine cool enough. There
> >>> were times when I stopped for gas and during the following departure
> >>> climbout I would have to level off at an intermediate altitude for awhile
> >>> to get the oil temps back down below 230.
> >>>
> >>> Installing my 520 I conferred with Velocity(ScottB and Brendon) and was
> >>> advised I would need to use downdraft as they had never successfully seen
> >>> an updraft system work for the big six cylinder engines. So I did the
> >>> conversion.
> >>>
> >>> I thought that using NACA intakes would "theoretically" be more drag
> >>> effecient ?
> >>>
> >>> Scott
> >>>
> >>>
> >>>
> >>>> I can understand why Burt Rutan and Nat Puffer are proponents of updraft
> >>>> cooling. From an engineering point of view, it has a lot going for it.
> >>>> You
> >>>> need more cooling when the airplane is climbing. If the cooling intake
> >>>> is
> >>>> below the wing, the pressure is higher during a climb so you
> >>>> automatically
> >>>> get more cooling during a climb. Similarly, it would be nice if cooling
> >>>> was minimized during descent. The pressure is reduced under the wing
> >>>> during descent, and so there is less cooling to the engine. Also, you've
> >>>> got convection working with you instead of against you with an updraft
> >>>> system.
> >>>>
> >>>> That all adds up to more drag with down draft cooling, because the NACA
> >>>> scoops have to be large enough so that there is adequate cooling during
> >>>> climb out, when the pressure at the NACAs is at its minimum.
> >>>>
> >>>> But the down draft is a lot simpler to implement, and that's probably
> >>>> going to be the deciding factor for me.
> >>>>
> >>>> Doug Holub_______________________________________________
> >>>> To change your email address, visit
> >>>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>>
> >>>> Visit the gallery! www.tvbf.org/gallery
> >>>> user:pw = tvbf:jamaicangoose
> >>>> Check new archives: www.tvbf.org/pipermail
> >>>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>>>
> >>> _______________________________________________
> >>> To change your email address, visit
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>> Visit the gallery! www.tvbf.org/gallery
> >>> user:pw = tvbf:jamaicangoose
> >>> Check new archives: www.tvbf.org/pipermail
> >>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>>
> >>>
> >> _______________________________________________
> >> To change your email address, visit
> >> http://www.tvbf.org/mailman/listinfo/reflector
> >>
> >> Visit the gallery! www.tvbf.org/gallery
> >> user:pw = tvbf:jamaicangoose
> >> Check new archives: www.tvbf.org/pipermail
> >> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>
> >> --
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> >>
> >>
> >>
> >> ------------------------------
> >>
> >> Message: 5
> >> Date: Sat, 17 Feb 2007 14:52:30 -0800
> >> From: "Al Gietzen" <ALVentures at cox.net>
> >> Subject: Re: REFLECTOR: updraft cooling
> >> To: "'Velocity Aircraft Owners and Builders list'"
> >> <reflector at tvbf.org>
> >> Message-ID: <000001c752e6$4ecd94c0$6400a8c0 at BigAl>
> >> Content-Type: text/plain; charset="us-ascii"
> >>
> >> Subject: REFLECTOR: updraft cooling
> >>
> >>
> >>
> >> I can understand why Burt Rutan and Nat Puffer are proponents of updraft
> >> cooling. From an engineering point of view, it has a lot going for it. You
> >> need more cooling when the airplane is climbing. If the cooling intake is
> >> below the wing, the pressure is higher during a climb so you automatically
> >> get more cooling during a climb. Similarly, it would be nice if cooling
> >> was
> >> minimized during descent. The pressure is reduced under the wing during
> >> descent, and so there is less cooling to the engine. Also, you've got
> >> convection working with you instead of against you with an updraft system.
> >>
> >> Doug;
> >>
> >>
> >>
> >> I'd think that both climbing and descending are high AOA, and would have
> >> similar air pressure under the wing; and given the strake configuration,
> >> it
> >> is not clear that there is increased pressure during climb. I also think
> >> that the main reason for difficulties with the stock armpit scoops and
> >> updraft is they are poorly designed scoops. Need to have ever increasing
> >> x-section after the entrance, and possilby placing them a bit further
> >> outboard from the strake/fuselage intersection would be helpful.
> >>
> >>
> >>
> >> I have an 'armpit' scoop for my radiator which is very effective.
> >>
> >>
> >>
> >> But the down draft is a lot simpler to implement, and that's probably
> >> going
> >> to be the deciding factor for me.
> >>
> >>
> >>
> >> And since it seems to work well, why not? The amount of natural
> >> convection
> >> driving force is likely overcome by a few knots of forward speed.
> >>
> >> Al
> >>
> >>
> >>
> >>
> >>
> >> Doug Holub
> >>
> >> -------------- next part --------------
> >> An HTML attachment was scrubbed...
> >> URL:
> >> http://www.tvbf.org/mailman/private/reflector/attachments/20070217/bff4b314/attachment.html
> >>
> >> ------------------------------
> >>
> >> _______________________________________________
> >> Visit the gallery! tvbf:jamaicangoose
> >>
> >> End of Reflector Digest, Vol 33, Issue 47
> >> *****************************************
> >>
> >
> > _______________________________________________
> > To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
> >
> > Visit the gallery! www.tvbf.org/gallery
> > user:pw = tvbf:jamaicangoose
> > Check new archives: www.tvbf.org/pipermail
> > Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >
> >
> >
>
> --
> Dave Philipsen
> Velocity STD-FG
> N83DP
>
> _______________________________________________
> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>
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