REFLECTOR: Fwd: Re: Still test flying...battling high CHT's (Geoff Gerhardt)
Geoff Gerhardt
geoff.gerhardt at gmail.com
Tue Sep 11 22:03:21 CDT 2012
Scott,
Thanks - that drawing makes sense. I went for a flight today. I made some
changes to the VG's for the roof NACA's. Instead of just putting a couple
right in front of the NACA, I put a whole line of them across the roof line
right about the mid-point of the doors. Did nothing. Still #3 got to 425F
on climb out. But, like other flights, in cruise at 70% power, LOP, all
cylinders were about equal at ~390F. I have another variant of VG's that I
want to try - VG's just ahead of the NACA, then a line of them right at the
transition from the NACA to the runner. If that doesn't help, I'll try the
cooling vanes, or maybe try to open up the area between the plenum and
forward cylinders as you suggest.
Geoff
On Tue, Sep 11, 2012 at 9:15 PM, Scott Derrick <scott at tnstaafl.net> wrote:
>
> Geoff,
>
> here is a crude drawing, attached
>
> The vanes for number 2 cyl, take up 1/3 of the area of the duct as
> view from the NACA side. same arrangement on the left side for #1..
>
> There are of course two ducts, left and right.
>
> Scott
>
> -------- Original Message --------
> Subject: Re: REFLECTOR: Still test flying...battling high CHT's (Geoff
> Gerhardt)
> From: Geoff Gerhardt <geoff.gerhardt at gmail.com> <geoff.gerhardt at gmail.com>
> To: Scott Derrick <scott at tnstaafl.net> <scott at tnstaafl.net>
> Date: 09/11/2012 10:02 AM
>
> Scott,
>
> So, do these vanes vertically bifurcate the flow from the runners so
> that the left half of the flow goes to the most forward cylinder and the
> right half goes to the most aft cylinder? Or, do you bifurcate it
> horizontally, the bottom going to the most forward cylinder, the top is
> then directed aft? Yeah, a picture or rough sketch would help.
>
> Thanks.
>
> Geoff
>
> On Tue, Sep 11, 2012 at 9:25 AM, Scott Derrick <scott at tnstaafl.net> wrote:
>
>> Geoff,
>>
>> I will make a drawing on how I did the turning vanes, there is no way
>> to get a picture. basically you have two rectangular feed tubes from the
>> NACA into the plenum. My two vanes start inside the feed tubes, thats
>> where they are riveted too. They are bent in a curve to end up where I
>> want them. They reach all the way down to the upper fins of the
>> cylinders. I split a small fuel line and glued that to lower edge of the
>> vane so they don't scratch or cut any of the tubes, wires or fins down in
>> there.
>>
>> Yes the gap is where the plenum comes up against the forward side of
>> the cylinders. I just silly-coned a piece of foam in between the cyl and
>> plenum to hold it out. I ended up leaving it in there, for the last 100
>> hours! I siliconed fiberglass to my lower cylinder fins to force the air
>> though them as you did with aluminum. I left those in place, don't remove
>> them! The gap causes a low pressure to form which encourages the air to
>> make the turn down through the cyl instead of going straight back to the
>> back cyls. Somebody on this list told me about this trick, he deserves the
>> credit.
>>
>> I also suffered the pusher streak! Oil breather oil on the lower
>> cowl and prop. What a Pita. I wiped that streak off for 700 hours! Now I
>> have a super clean lower cowling!
>>
>> I had Custom Aircraft weld in a 1/2 inch nipple to the left hand
>> stack which I attached the breather hose to. Now the little bit of oil
>> that can make such a nasty long streak and vapor gets partially burned and
>> thrown away from the cowling. I've attached Clinton's diagram he sent me
>> after I talked to him about it.
>>
>> Scott
>>
>> -------- Original Message --------
>> Subject: Re: REFLECTOR: Still test flying...battling high CHT's (Geoff
>> Gerhardt)
>> From: Geoff Gerhardt <geoff.gerhardt at gmail.com><geoff.gerhardt at gmail.com>
>> To: Scott Derrick <scott at tnstaafl.net> <scott at tnstaafl.net>
>> Date: 09/10/2012 03:04 PM
>>
>> Scott,
>>
>> If you have some pictures of your turning vanes, I'd much appreciate
>> them. I'm envisioning curved aluminum bits riveted to the top of the
>> plenums that direct air flow down to the two fore cylinders.
>>
>> I've seen you mention before about opening up a gap along the side of
>> #2. On a Lycoming 1&2 are the aft cylinders, so that didn't really make
>> sense to me, but now I see that for you (Continental?), 1&2 cylinders are
>> your fore cylinders. I wonder if opening up that gap draws more air to
>> make that sharp turn. I've got my plenums up tight to the wall of my 3&4
>> cylinders. I also have aluminum extensions to my plenums that wrap around
>> the cylinders to make sure air is forced thru the fins. Perhaps I should
>> open those up a bit. I can't completely rationalize how that helps, but it
>> seems to have made a difference for you.
>>
>> One thing that may have nothing to do with this, but I've found
>> interesting...My oil vent line is in the center of the fuselage right where
>> the cowling meets the firewall. I typically see a nice brown streak
>> running up the cowling right to the furthest aft end. I've also found that
>> oil collects right under the prop extension. Initially, I thought that I
>> had a seal leak or the crank expansion plug was leaking, but it turns out
>> that the oil from the vent is turning the corner and running inside the
>> cowling and pooling right under the prop extension. Does that say anything
>> about a vacuum being created there? Good or bad? Does this happen to
>> everyone?
>>
>> I think I'm going to start by adding taller VG's a bit further forward
>> (maybe 4" like you suggest) of the NACA's. Right now I have relatively low
>> profile ones right before the NACA's.
>>
>> Geoff
>>
>>
>> On Mon, Sep 10, 2012 at 12:27 PM, Scott Derrick <scott at tnstaafl.net>wrote:
>>
>>> Geoff,
>>>
>>> I felt like my battle of the CHT's was legend!
>>>
>>> I have 5/8 VG's about 4 inches forward of the roof NACA, I thought I
>>> got 5-10 degrees better cooling from them.
>>>
>>> I have turning vanes in my plenum for #1 & #2 cylinders, those are
>>> the forward as in nearest to the firewall cylinders. Normally I've been
>>> told those are the warmest because the air has to make a dramatic turn to
>>> go through them. I have two vanes for each cylinder, one ends halfway
>>> across the cylinder, the other right between the cylinder and the next
>>> cylinder. I think that dropped the temps on those two cylinders about
>>> 5-10 degrees.
>>>
>>> I opened a gap in the plenum in front of #2(right front). That
>>> helped #2 about 5-10 degrees.
>>>
>>> I installed a cowl flap(which I didn't need when I had the IO360,
>>> that helped about 15-20 degrees.
>>>
>>> Now I can climb out full power and not hit 400 unless the oat is
>>> above 90F. In the winter I have trouble keeping the temps up, range is
>>> 290-320 in the coldest days.
>>>
>>> I cruise max throttle LOP 360-330, near max throttle ROP 390-360 in
>>> the summer. Max throttle ROP exceeds RPM redline, so I don't do that much.
>>>
>>> Scott
>>>
>>> -------- Original Message --------
>>> Subject: Re: REFLECTOR: Still test flying...battling high CHT's (Geoff
>>> Gerhardt)
>>> From: Geoff Gerhardt <geoff.gerhardt at gmail.com><geoff.gerhardt at gmail.com>
>>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org><reflector at tvbf.org>
>>> Date: 09/10/2012 07:52 AM
>>>
>>> Fred,
>>>
>>> Yes, this is a new engine, so I'm guessing that's part of the reason,
>>> but I don't like having one cylinder being that much higher than the other
>>> three. I have VG's about where you suggested putting them, an inch or so
>>> ahead of the NACA entrance. Because I'm having problems primarily on climb
>>> out, I'm thinking I should move them fore a few inches. Also, the VG's I'm
>>> using are relatively low profile (<1/2" high). I think I'll make some
>>> taller ones and see if that helps, too.
>>>
>>> Thanks for the suggestions.
>>>
>>> Geoff
>>>
>>> On Mon, Sep 10, 2012 at 9:23 AM, Fred Anderka <fred at holohil.com> wrote:
>>>
>>>> Geoff:
>>>>
>>>> Had similar CHT problems with the IO-550, particularly cylinder #2.
>>>> There are deflector plates between the cylinders that can be bent to
>>>> change the air flow, have not messed with them though. Trying to put
>>>> deflectors on top of that engine would be a nightmare with all the plumbing
>>>> that is on top of that engine. Is this is a new engine? I have been told
>>>> that the CHT's will decrease as the engine breaks in. This is also a scary
>>>> portion of your flight testing if you follow engine manufacturers
>>>> reccommendations. The engine manufacturers recommend that for proper break
>>>> in of the engine it should be operated near maximum power for the first
>>>> 20-25 hours. Continued low power operation will glaze the cylinders
>>>> resulting in high oil consumption. I suppose 25 hours of touch and go's
>>>> might qualify.
>>>>
>>>> Place a pair of VG's 1 1/2" ahead of the start of the slope of the
>>>> NACAs. You will see a dramatic decrease in the CHT's to the point where I
>>>> am trying to figure out a way to reduce the air flow in the winter or when
>>>> flying at very cold altitudes. Scott suggested making the ramp of the
>>>> NACAs adjustable to reduce the size of the air intake. The VG's pressurize
>>>> the plenum to a point where I have also noticed an increase in manifold
>>>> pressures during climb out. The Continental gets it's combustion air from
>>>> the back of the engine plenum.
>>>>
>>>> Fred
>>>> XL-RG (620 hrs.)
>>>>
>>>>
>>>> Date: Sun, 9 Sep 2012 20:08:51 -0400
>>>> From: Geoff Gerhardt <geoff.gerhardt at gmail.com>
>>>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>>>> Subject: REFLECTOR: Still test flying...battling high CHT's
>>>>
>>>> All,
>>>>
>>>> Just an update on my test flying. I've got just over 9hrs in now. I
>>>> have been battling high CHT's, making a few changes. I had a fuel flow
>>>> imbalance that was causing some problems (hot #2) - I think it was a
>>>> partially blocked injector. I took all the injectors/lines out and cleaned
>>>> them and balanced the flows (mixed and matched injectors until all
>>>> injectors were putting out the same flow. Now, in cruise, all cylinders
>>>> are pretty close and reasonably cool (or, I guess, not overly hot). Once I
>>>> get to cruise, they all sit <380F. But, on climb out, #3 gets way too hot
>>>> (420F) forcing me to reduce power and bring the nose down so I'm
>>>> climbing at <500FPM at ~60% power, 100kts. But, once I get to cruise and
>>>> can bring the nose down and get the speed up, it behaves. Still the
>>>> hottest, but it'll sit around 380F. So, I'm thinking I have to work on my
>>>> cooling plenums. #4 will get hot too, but it doesn't get much over 400F.
>>>>
>>>> Has anyone had success putting deflectors in the plenums to direct air
>>>> flow to cyls 3/4? Or, maybe VG's in the entrance of the runners to keep
>>>> the airflow better attached to the bottom of the runner so it can turn the
>>>> corner down to cool 3/4 (I have VG's before the NACAs)?
>>>>
>>>> Part of the issue may be my cruise prop - I need to keep full power on
>>>> to get a decent climb rate.
>>>>
>>>> Thanks.
>>>>
>>>> Geoff
>>>>
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>>>
>>>
>>>
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>>>
>>> --
>>> What the superior man seeks is in himself; what the small man seeks is in others.
>>> Confucius
>>>
>>>
>>
>> --
>> What the superior man seeks is in himself; what the small man seeks is in others.
>> Confucius
>>
>>
>
> --
> He who knows others is wise;
> He who know himself is enlightened.
> Lao-tzu
>
>
>
>
>
> _______________________________________________
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