Today's Message Index:
----------------------
1. 03:59 AM - Re: CHT's and Fuel Flows (Rob Ray)
2. 06:28 AM - Re: CHT's and Fuel Flows (Lee Logan)
3. 08:36 AM - Re: CHT's and Fuel Flows (CalBru@aol.com)
4. 11:33 AM - Re: CHT's and Fuel Flows (Tom Martin)
5. 04:22 PM - Re: CHT's and Fuel Flows (Lee Logan)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: CHT's and Fuel Flows |
I have a 13 year old HR2 with the stock Harmon cowling and a LyCon flowed 10.4:1
comp engine. Summer temps reached 400 CHT in extended climbs with oilreaching
245.Cruise was 350-380 and 210 oil. I have read thatcowling outlet area should
slightly exceed inlet area by 10%. I measured my HR2's cowling and trimmed
6 inches off the bottom lip of the cowl.Now my CHT's at altitude running at peak
range between310 and 348 with 180-190 oil temp. I have experimented with LOP
and see 288-315 with oil at 170. During extended climbs in 90+ degree FL weather
I never exceed 380 CHT (oil has reached 230 butquickly cools to below 190
when level).
Lycon frowns on LOP operations for the 10.4:1 comp engines, but it cools all temps
another 20 degrees with a 5% FF reduction.
I have found even with my RV4 and 2 other Rockets I have helped with that cowling
exit area needs to be opened up. My Dos Centavos...
Rob Ray
--- On Sat, 6/7/08, psiegel@fuse.net <psiegel@fuse.net> wrote:
From: psiegel@fuse.net <psiegel@fuse.net>
Subject: Rocket-List: CHT's and Fuel Flows
On one of my early cross country flights, I had to pull back the rpm's a
bit when I noticed one of the CHT's was getting close to my personal upper
limit of 400'.
Back home after pulling the cowl and plenum, I noticed that some of the paint
on the cylinder heads had flaked partially blocking air flow, particularly on
the hot cylinder head.
I took great care to completely clean out all the cooling fins of any paint
flakes or casting flash and I was amazed to see a dramatic drop in the formerly
hot CHT!
I am also amazed at how operating lean of peak in economy cruise ( I NEVER run
LOP at high power settings) drops CHT's! Bart did a nice job right from
his shop on my fuel flows to each cylinder...I sent my data to GAMI and they
responded that my numbers were so close with the stock injectors that there was
nothing they could do for me!
A good rule of thumb with the IO-540's is at full power, take your fuel
flow in gph and multiply by 10 (add a zero at the end of the fuel flow) and
that will give you a pretty good idea of the horsepower you are getting. So
depending on compression ratio, it is normal to see takeoff fuel flows at sea
level in the 26 to 29 gph range.
Paul Siegel Evo N4XU
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: CHT's and Fuel Flows |
Rob: Do you know what the "official" measurements are with a Rocket cowl?
What is the inlet area and standard outlet area with the lower cowl trimmed
to the "factory" trim line? Did you end up with something like a 1 to 1.1
ratio with your inlet/outlet?
P.S. Don't know if you know it or not, but Festus is building both an RV-8
and a Pietenpohl!!
Thanks,
Lee...
On Sun, Jun 8, 2008 at 6:54 AM, Rob Ray <smokyray@yahoo.com> wrote:
>
> I have a 13 year old HR2 with the stock Harmon cowling and a LyCon flowed
> 10.4:1 comp engine. Summer temps reached 400 CHT in extended climbs with
> oil reaching 245. Cruise was 350-380 and 210 oil. I have read that cowling
> outlet area should slightly exceed inlet area by 10%. I measured my HR2's
> cowling and trimmed 6 inches off the bottom lip of the cowl. Now my CHT's
> at altitude running at peak range between 310 and 348 with 180-190 oil temp.
> I have experimented with LOP and see 288-315 with oil at 170. During
> extended climbs in 90+ degree FL weather I never exceed 380 CHT (oil has
> reached 230 but quickly cools to below 190 when level).
> Lycon frowns on LOP operations for the 10.4:1 comp engines, but it cools
> all temps another 20 degrees with a 5% FF reduction.
>
> I have found even with my RV4 and 2 other Rockets I have helped with
> that cowling exit area needs to be opened up. My Dos Centavos...
>
> Rob Ray
>
>
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: CHT's and Fuel Flows |
Does the theory of a 10% larger exit area vs. cowl inlet hold true for ships
with pressure plenums?
Thanks, Cal
F1
**************Get trade secrets for amazing burgers. Watch "Cooking with
Tyler Florence" on AOL Food.
(http://food.aol.com/tyler-florence?video=4?&NCID=aolfod00030000000002)
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | CHT's and Fuel Flows |
Opening up the trailing edge of the cowling, or adding louvers will lower
engine temperatures. I have confirmed this on a observations that I have
made on my rockets. This allows more air to go through the system. In my
experience this increased airflow is directly related to a decrease in
airspeed. A three to four knot decrease in speed is what I have found when
trimming back the lower cowling.
I was not satisfied with reduced airspeed and an article in the
august 2003 sport aviation helped me to gain back the lost speed and improve
cooling. The key to the system is in the inlets. Not so much the actual
size but the internal shape. The inlets need a straight or gradually
increasing diffusion zone and then a smooth transition to the plenum. The
seals between the inlets and the plenum need to be as tight as possible.
Although I have no personal experience with the round cooling air inlets
they have two main advantages. Number one is that they are usually located
further forward and this allows a longer smoother transition zone. Secondly
it is quite a bit easier to seal the round inlets than it is the rectangular
style. By improve my inlets I noticed an immediate improvement in cooling.
The decrease in cylinder temperatures was to a degree that I was able to not
only return the aft cowl opening to the original size but I was able to
extend the aft ramp and close the opening from stock. The lost speed has
been gained back, plus a little (maybe) but the engine now runs where I want
it;330 to 380CHT depending on OAT and power settings. Oil temps are in the
190 range.
The conclusion that I have come to with my experiments is that there
is not much in the way of speed gains to be made with the stock cowlings but
significant improvements in cooling are attainable. I believe the stock
rocket cowlings are quite efficient. Some day I will try some round inlets
just to see if there are any improvements to be had there. I suspect that
if you have a good stock system then there probably is not much to be
gained, but I would like to confirm that suspicion. Currently my combined
inlet size is 37" and my outlet area is 48". I do have a cowl flap but have
found that it is really only useful in the cold winter months in keeping the
engine warm during descents. This is the second plane that I have installed
a cowl flap on and both instances I could find no speed benefits. (It looks
kinda cool, and that must be worth something!)
Tom Martin
C-GEVO The EVO 1, 230 hours
Checked by AVG.
AM
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: CHT's and Fuel Flows |
Great info (as usual), Tom. Thanks for taking the time to type that all
out!
Lee...
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|