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CHT's and fuel flows
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Wiley

Joined: 20 May 2007
Posts: 6
Location: Orange County, CA

Posted: Thu Jun 05, 2008 6:32 pm Post subject: CHT's and fuel flows

New Rocket owner here and looking for some guidance. 



The plane

io-540-c4b5  Bendix rsa

500 hrs. 



Previous owner built it and battle high cht's since new. He just redid top end at 500 hrs smoh due to low compression. The baffling looks perfect and it's obvious he's tried everything to get the temps down, cowl flaps, louvers, silicone, etc. 



I'm getting 420+ cht's on an easy climb out and it's hard to get them down until at altitude for a while. Even then I'm 380+. 



On takeoff  I'm showing flow at around 23gph. At 24sq. showing between 17 adn 22gph.  All the above up to 3000msl and oat around 75F. 



A lycoming guru said my takeoff flow was 6gph low so I had the rsa rebuilt and it came back with a report of two bad nozzles and erratic flows. After putting it back on I'm getting almost identical flow readings. I don't have a service manual for this engine. 



I have the EIS monitoring system and I can't figure out which cht reading on the screen corresponds to which cylinder. So can't tell you which is hottest but most are up there. 



Also, my manifold pressure seems to be an inch low w/o ram air. 



Each tank has a screen but I've tried both tanks and flows are same. 



Anyone have any ideas of what to check next?

jrstone(at)insightbb.com
Guest

Posted: Fri Jun 06, 2008 3:28 am Post subject: CHT's and fuel flows

I had similar problems.  What is your compression ratio.  What is your 

ignition setup.

Jim Stone

HRII

---

kahuna

Joined: 02 Feb 2007
Posts: 93

Posted: Fri Jun 06, 2008 3:55 am Post subject: CHT's and fuel flows

I recently had unexpected high cht's and it turned out to be very advanced timing.

 Somehow my mag went from 25 to 40. AHH! 

 Check timing.

 Mike

 

 

 

 [img]cid:1__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img]"Wiley" ---06/05/2008 10:43:02 PM-----> Rocket-List message posted by: "Wiley" <rdone(at)mac.com>

 

       "Wiley" <rdone(at)mac.com> 

 Sent by: owner-rocket-list-server(at)matronics.com 

06/05/2008 10:32 PM  Please respond to

 rocket-list(at)matronics.com

  
 
 
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 To

[img]cid:3__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img]

 rocket-list(at)matronics.com  [img]cid:3__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img]

 cc

[img]cid:3__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img]

   [img]cid:3__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img]

 Subject

[img]cid:3__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img]

 CHT's and fuel flows    [img]cid:3__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img][img]cid:3__=0ABBFEF3DFD372058f9e8a93df938(at)us.ibm.com[/img]    

 --> Rocket-List message posted by: "Wiley" <rdone(at)mac.com>

 

 New Rocket owner here and looking for some guidance. 

 

 The plane

 io-540-c4b5  Bendix rsa

 500 hrs. 

 

 Previous owner built it and battle high cht's since new. He just redid top end at 500 hrs smoh due to low compression. The baffling looks perfect and it's obvious he's tried everything to get the temps down, cowl flaps, louvers, silicone, etc. 

 

 I'm getting 420+ cht's on an easy climb out and it's hard to get them down until at altitude for a while. Even then I'm 380+. 

 

 On takeoff  I'm showing flow at around 23gph. At 24sq. showing between 17 adn 22gph.  All the above up to 3000msl and oat around 75F. 

 

 A lycoming guru said my takeoff flow was 6gph low so I had the rsa rebuilt and it came back with a report of two bad nozzles and erratic flows. After putting it back on I'm getting almost identical flow readings. I don't have a service manual for this engine. 

 

 I have the EIS monitoring system and I can't figure out which cht reading on the screen corresponds to which cylinder. So can't tell you which is hottest but most are up there. 

 

 Also, my manifold pressure seems to be an inch low w/o ram air. 

 

 Each tank has a screen but I've tried both tanks and flows are same. 

 

 Anyone have any ideas of what to check next?

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=186440#186440

 

 

 

 

 

 

 

 =====================================

 

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 =====================================

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 tp://forums.matronics.com

 =====================================

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nico(at)cybersuperstore.c
Guest

Posted: Fri Jun 06, 2008 6:23 am Post subject: CHT's and fuel flows

This might sound real lame, but how sure are you that your cht probes are

not faulty or the gauges properly calibrated ?

--

Wiley

Joined: 20 May 2007
Posts: 6
Location: Orange County, CA

Posted: Fri Jun 06, 2008 6:32 am Post subject: Re: CHT's and fuel flows

I'm not sure what compression I have. Data plate says 260hp if that tells you. 



Has Slicks. Initially he put one slick w/one elect but removed the elect. thinking it might be part of problem. 



Kahuna, I read your thread on Vans about your timing issue. It's really amazing that without an engine monitor you may miss that whole issue until annual. 



One thing previous owner mentioned this morning is the area at the bottom of the air inlet where the baffling (rubber) goes under the front/bottom  of the cowl inlet lip. He thinks maybe air is going down through there and pressurizing the lower cowl. Hard to believe since I have a really big opening with the cowl flaps and louvers. I guess I'll try sealing that. 



What kind of flows are you guys getting on takeoff?

Wiley

Joined: 20 May 2007
Posts: 6
Location: Orange County, CA

Posted: Fri Jun 06, 2008 6:45 am Post subject: Re: CHT's and fuel flows

Not lame at all. We were just discussing doing that. Previous owner did check them 

a while ago when troubleshooting the problem but you never know. 



Thanks.

CNuffer(at)it21.com
Guest

Posted: Fri Jun 06, 2008 6:59 am Post subject: CHT's and fuel flows

Check for a smooth ramp transition from the air inlets to the top of the

plenum.  Make sure the ramp on the top of the air inlet is formed

properly.  We haven't done ours yet, but this seems to be an important

area with all the rocketeers. 



Chuck

www.f1rocket.com



--

kahuna

Joined: 02 Feb 2007
Posts: 93

Posted: Fri Jun 06, 2008 7:05 am Post subject: CHT's and fuel flows

a c4b5 is 8.5:1

 t.o FF for me is 25. sea level 

 IF your mixture level is operating at expected, FF is not your problem. Meaning, leaning leans, richer riches and other sensors follow expectations when you do that.

 

 

 

 

 [img]cid:1__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]"Wiley" ---06/06/2008 10:43:31 AM-----> Rocket-List message posted by: "Wiley" <rdone(at)mac.com>

 

       "Wiley" <rdone(at)mac.com> 

 Sent by: owner-rocket-list-server(at)matronics.com 

06/06/2008 10:32 AM  Please respond to

 rocket-list(at)matronics.com

  
 
 
    [img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]

 To

[img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]

 rocket-list(at)matronics.com  [img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]

 cc

[img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]

   [img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]

 Subject

[img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]

 Re: CHT's and fuel flows    [img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img][img]cid:3__=0ABBFEF3DFC18FDB8f9e8a93df938(at)us.ibm.com[/img]    

 --> Rocket-List message posted by: "Wiley" <rdone(at)mac.com>

 

 I'm not sure what compression I have. Data plate says 260hp if that tells you. 

 

 Has Slicks. Initially he put one slick w/one elect but removed the elect. thinking it might be part of problem. 

 

 Kahuna, I read your thread on Vans about your timing issue. It's really amazing that without an engine monitor you may miss that whole issue until annual. 

 

 One thing previous owner mentioned this morning is the area at the bottom of the air inlet where the baffling (rubber) goes under the front/bottom  of the cowl inlet lip. He thinks maybe air is going down through there and pressurizing the lower cowl. Hard to believe since I have a really big opening with the cowl flaps and louvers. I guess I'll try sealing that. 

 

 What kind of flows are you guys getting on takeoff?

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=186491#186491

 

 

 

 

 

 

 

 =====================================

 

 tor?Rocket-List">http://www.matronics.com/Navigator?Rocket-List

 =====================================

 FORUMS -

 tp://forums.matronics.com

 =====================================

  Site -

 bsp;          -Matt Dralle, List Admin.

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jrstone(at)insightbb.com
Guest

Posted: Fri Jun 06, 2008 7:51 am Post subject: CHT's and fuel flows

Wiley,

My hottest cylinder was 450 heading to redline the other day, I changed my 

timing on my Electroair ignition from 23 deg to 21 deg.  Now my hottest is 

375, the #2 cyl, the rest are cooler by 40-50 deg.  I have 10 to 1s, so your 

mileage may vary.

Good Luck,

Jim Stone

---

bdalporto(at)sbcglobal.ne
Guest

Posted: Fri Jun 06, 2008 10:46 am Post subject: CHT's and fuel flows

Wiley, do you have bayonet probes or the spark plug gasket type. I under stand the the  

CHT read higher under the spark plug. So if your reading it under your spark plugs your  

CHT's might not be that high as compaired to the Lycoming Spec. The Lycoming spec is for the  

bayonet location. John Deakin wrote a good artical about Leaning with CHT. See http://www.avweb.com/news/pelican/pelicans_perch_84_mixture_cht_194816-1.html 

  

Brian 

Mostly a Lurker 

Want a be 



 [quote][b]

T.gummo(at)verizon.net
Guest

Posted: Fri Jun 06, 2008 4:05 pm Post subject: CHT's and fuel flows

 	  Quote: 	
		  

 What kind of flows are you guys getting on takeoff?


	




First, let me say that my ONLY tool is a Hammer.



My engine is a IO-540 J4A5 250 HP.  It is thirty years old and rebuilt by me 

so I don't know what the real HP is.



On takeoff, I see 23 to 24 GPH fuel flow.



Hope this helps.



Tom Gummo

Apple Valley, CA

Harmon Rocket-II



do not archive



http://mysite.verizon.net/t.gummo/index.html

Lee Logan

Joined: 10 Jan 2006
Posts: 86

Posted: Fri Jun 06, 2008 5:05 pm Post subject: CHT's and fuel flows

I'm told that a good formula for the fuel needed on takeoff ((at) sea level, standard day) = .55 lb/hp/hour.  So:

  

 GPH                      HP   

   22                      240.0

   23                      250.9

   24                      261.8

   25                      272.7

   26                      283.6

   27                      294.5

   28                      305.5

   29                      316.4

   30                      327.3

  

 If you are making 280 hp, you should be seeing something like 26 gph on takeoff.  Read Deakins on leaning in AvWeb.  He is a wealth 

 of information.

  

 Lee...

  [quote][b]

psiegel(at)fuse.net
Guest

Posted: Sat Jun 07, 2008 1:26 am Post subject: 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

n395v

Joined: 10 Jan 2006
Posts: 450

Posted: Sat Jun 07, 2008 5:09 am Post subject: Re: CHT's and fuel flows

First thing is make sure your guage is calibrated and reading correctly.



You can drop the sensors in boiling water and they should read close to 212 deg F or drop them in a frydaddy filled with cooking oil if you can find a good thermometer that will read in that range. You should be able to adjust the fry daddy from ambient temp to CHT operating temps.

I fought High CHTs for the first 6 months in my F1. Checked timing and CHT guage that wasn't the problem. Finally put louvers in the cowl bottom and that solved the problem.  Now I rarely see CHTs above 380. My TO fuel flow (260HP) is same as Gummos. at cruise WOT and 2100 RPM FF is 13.3 GPH (above 10,000')



If I go LOP FF drops to 10.6 GPH at same settings and altitude and I lose about 5 KTS TAS. CHTs in the 340-360 range.



Louver install link here   



http://www.bearcataviation.com/album_frame.asp?menuID=6

_________________
Milt

Wiley

Joined: 20 May 2007
Posts: 6
Location: Orange County, CA

Posted: Sat Jun 07, 2008 7:04 am Post subject: Re: CHT's and fuel flows

Great info from everyone, thanks. That avweb article is really educational. 



I played around with the rubber bafflle at the lower entrance to the inlet and found my chts went straigth to 424 and didn't want to come down. I put them back in original position and it went to 410 but came down with lower power settings quickly to 385 (21sq)



I'm thinking this might hold the answer. I'm thinking of reworking the inlets to get the flow smoother and not letting any air escape to the bottom of cowl. 



Anyone going to the Golden West Airshow Sunday? Hoping there is  a rocket or two there to get some ideas.

smokyray(at)yahoo.com
Guest

Posted: Sun Jun 08, 2008 2:59 am Post subject: 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 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



--- On Sat, 6/7/08, psiegel(at)fuse.net <psiegel(at)fuse.net> wrote:



From: psiegel(at)fuse.net <psiegel(at)fuse.net>

Subject: CHT's and Fuel Flows

To: rocket-list(at)matronics.com

Date: Saturday, June 7, 2008, 4:14 AM






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

Lee Logan

Joined: 10 Jan 2006
Posts: 86

Posted: Sun Jun 08, 2008 5:28 am Post subject: 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(at)yahoo.com (smokyray(at)yahoo.com)> wrote:

 [quote]--> Rocket-List message posted by: Rob Ray <smokyray(at)yahoo.com (smokyray(at)yahoo.com)>

 

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



[b]

CalBru(at)aol.com
Guest

Posted: Sun Jun 08, 2008 7:36 am Post subject: 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.

  [quote][b]

fairlea(at)amtelecom.net
Guest

Posted: Sun Jun 08, 2008 10:33 am Post 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

Lee Logan

Joined: 10 Jan 2006
Posts: 86

Posted: Sun Jun 08, 2008 3:22 pm Post subject: CHT's and Fuel Flows

Great info (as usual), Tom.  Thanks for taking the time to type that all out!

  

  

 Lee...

  [quote][b]

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