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Harmon Rocket, plenum
- Thread starter rogerb
- Start date
vlittle
Well Known Member
I have a CHT who is to high so I will try to install plenum on my rocket.
Is there some good or bad experience whit different manufacturers and is there some plenum who fits direct to the air inlets.
My english is`nt the best but I hope you will understand
Roger
Norway
Hi Roger. There are no commercial plena that fit the Rocket. I used one from an RV-10 that had to be cut apart and heavily modified to fit.
The inlet ramps I had to fabricate with aluminum and fiberglass.
See http://www.vx-aviation.com/sprocket/fwf.htm
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Toobuilder
Well Known Member
Roger,
It would be very unusual for a fully functional stock Rocket baffle system to be wholly inadequate for cooling. Not saying there is not room for improvement, but before you jump into a major mod like the plenum make sure the basics are covered.
It would be very unusual for a fully functional stock Rocket baffle system to be wholly inadequate for cooling. Not saying there is not room for improvement, but before you jump into a major mod like the plenum make sure the basics are covered.
I have check my baffle and can`t find any leaks.
I`m worried about my cht who can reach 440 in climb, normaly 425. In cruise 390-405F in the summertime.
There is syl. 1-2-5 who has the high temp.
oiltemp is fine (180F)
Is there some other things I can try, to get my CHT down?
I`m worried about my cht who can reach 440 in climb, normaly 425. In cruise 390-405F in the summertime.
There is syl. 1-2-5 who has the high temp.
oiltemp is fine (180F)
Is there some other things I can try, to get my CHT down?
vlittle
Well Known Member
Ignition timing is worth checking. If you have an electronic ignition it may be advancing improperly.
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Tom Martin
Well Known Member
Do you have high compression pistons? If so then setting the mags at 20 degrees could make a big difference.
How many hours are on the engine? If it is brand new it can take 5 to 10 hours for the temperatures to come down.
How much fuel are you getting at full power? You should be seeing 22 to 26 gph.
Any less could mean that you are running too lean at high power settings.
If not that, then check the inlets to your cowling. Does inlet air transition smoothly to the top of the cowling? Do you have a good seal around the inlets?
Is there something blocking the outlet air from exiting the cowling? Again, at the outlet the air should be smoothly transitioned from the inside of the cowling to the outside air.
Pictures of your cowling inlets, the baffles, and your cowling outlet would be helpful.
How many hours are on the engine? If it is brand new it can take 5 to 10 hours for the temperatures to come down.
How much fuel are you getting at full power? You should be seeing 22 to 26 gph.
Any less could mean that you are running too lean at high power settings.
If not that, then check the inlets to your cowling. Does inlet air transition smoothly to the top of the cowling? Do you have a good seal around the inlets?
Is there something blocking the outlet air from exiting the cowling? Again, at the outlet the air should be smoothly transitioned from the inside of the cowling to the outside air.
Pictures of your cowling inlets, the baffles, and your cowling outlet would be helpful.
vlittle
Well Known Member
What model of engine do you have and what compression ratio? How many hours on the engine? I think you need about 20 BTDC with high CR pistons.
Also, try to even out your CHTs by adjusting the cylinder dams on 1 and 2 and with by adding shims to the bottom fins of 3 and if necessary. If you can even out the temperatures, the hottest ones will run cooler.
Check the fin flashings between the plugs of each cylinder. You should be able to see clear passages through for the airflow. If you don't, cleaning them out with files or drills can lower CHTs by up to 35 degrees. Search the threads for this.
The Rockets are undercooled. Running LOP seems to be the best way to keep cruise temps down. There is a lot of heat to reject.
Edit: just saw Tom's post... Do whatever he says... He's helped me out a lot.
Also, try to even out your CHTs by adjusting the cylinder dams on 1 and 2 and with by adding shims to the bottom fins of 3 and if necessary. If you can even out the temperatures, the hottest ones will run cooler.
Check the fin flashings between the plugs of each cylinder. You should be able to see clear passages through for the airflow. If you don't, cleaning them out with files or drills can lower CHTs by up to 35 degrees. Search the threads for this.
The Rockets are undercooled. Running LOP seems to be the best way to keep cruise temps down. There is a lot of heat to reject.
Edit: just saw Tom's post... Do whatever he says... He's helped me out a lot.
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I adjust the timing from 25 to 23 deg. The left mag touch the firewall so I could not adjust it lower to 20 degrees.
My engine is a narrowdeck (D4A5), ly-con rebuild. lycon modified lycoming syl, (flow balance). 10:1 comp. with 155hours.
-with full power I have around 22 usg, but I will check exactly.
-one exampel: cruice at 22,5/23, fuelflow 12,8. EGT 1384 (50F ROP) I still have CHT 401F. I have high CHT in all settings, not only with full power.
-an another example: 23.5/24, fuelflow 16.7, EGT 1342 (50 ROP) and CHT 391
I have cut a extra small pice of my air outlet, so the outlet is 70% bigger than the inlet. I will check the in and outlets so they are 100% clean and smood.
I read a tread about "Cowl Inlet Area" Maybe i should route everything so the air goes cleaner too.
I check think my cylinderfin and I think they is ok but I have to take a new look to be sure.
Maybe 50F ROP is`nt the best way to cruice but this is what I have read and what others I know doing..?
I can send you some pitures Tom but I have to do it on you email address. for some reason I`m unable to post pictures here. - [email protected]?
My engine is a narrowdeck (D4A5), ly-con rebuild. lycon modified lycoming syl, (flow balance). 10:1 comp. with 155hours.
-with full power I have around 22 usg, but I will check exactly.
-one exampel: cruice at 22,5/23, fuelflow 12,8. EGT 1384 (50F ROP) I still have CHT 401F. I have high CHT in all settings, not only with full power.
-an another example: 23.5/24, fuelflow 16.7, EGT 1342 (50 ROP) and CHT 391
I have cut a extra small pice of my air outlet, so the outlet is 70% bigger than the inlet. I will check the in and outlets so they are 100% clean and smood.
I read a tread about "Cowl Inlet Area" Maybe i should route everything so the air goes cleaner too.
I check think my cylinderfin and I think they is ok but I have to take a new look to be sure.
Maybe 50F ROP is`nt the best way to cruice but this is what I have read and what others I know doing..?
I can send you some pitures Tom but I have to do it on you email address. for some reason I`m unable to post pictures here. - [email protected]?
We see this sort of request for help all the time. Although there are clues and probables (10:1 compression and leaning to 50 ROP being good examples), there is no actual data related to cooling.
Lycoming publishes cooling charts referenced to pressure drop across the fins. A pair of pressure measurements would tell how much mass flow you actually have. In addition, a few temperature measurements would tells us how effective your installation is at actually transferring heat to that mass flow. When paired, they tell a lot. For example, a low pressure delta combined with low heat transfer indicates high baffle leakage, while high CHT with high delta and good transfer would indicate a high heat load, i.e. an operational problem.
Lycoming publishes cooling charts referenced to pressure drop across the fins. A pair of pressure measurements would tell how much mass flow you actually have. In addition, a few temperature measurements would tells us how effective your installation is at actually transferring heat to that mass flow. When paired, they tell a lot. For example, a low pressure delta combined with low heat transfer indicates high baffle leakage, while high CHT with high delta and good transfer would indicate a high heat load, i.e. an operational problem.
Tom Martin
Well Known Member
I think that there is room for improvement on your flexible baffle parts, particularily at the inlets. I suspect you are losing a lot of air on the inboard sides of the inlets on both sides.
Check the inside of the top cowling and note where the baffle material is rubbing on the fibreglass. It should be a continuous wear line with no gaps. Locations were no rubbing is noticed are leak spots.
As you noted in a prior post, 1, 2, and 5 are warm, here are some things to do.
Remove the riser on the #1 cylinder, you can try some pieces of "metal" furnace duct tape, until you get the right temperature and then cut the original piece to that size.
Numbers 2 and 5 can be helped by putting at least a 1/8" spacer between the baffle and the cylinder where the screw holds the baffle to the cylinder. This is on the outboard end of the cylinder.
You can do a search on this site for various ideas pertaining to this location it has been talked about a lot.
Make sure that you silicone around the bottoms of the metal baffles so that all the air remains in the fins until the outlet area of each cylinder baffles.
This should help both cylinders except #5 will likely still be hot as it appears that that is where you are drawing off your oil cooler air.
I have had the oil cooler mounted on either side and behind the #6 cylinder seems to work a bit better. Ideally you could draw your oil cooler air from its own inlet on the cowling. This would help your cylinder cooling quite a bit.
From your pictures it looks like I can see a gap between the cylinders 1 and 3, and 3 and 5, and the metal baffle parts.
Seal around the fuel hose where it penetrates the baffle on #1
On the left side baffles I can see some small tooling holes that are open.
These holes should all be filled as air that exits there is not doing any cooling and worse yet upsets the pressure differential between the top and bottom plenums.
All these small holes add up to one BIG hole in your system.
Try the spacers, the cut down ramp on #1, seal the holes and the baffle inlets as best you can and report back!
Good luck
Check the inside of the top cowling and note where the baffle material is rubbing on the fibreglass. It should be a continuous wear line with no gaps. Locations were no rubbing is noticed are leak spots.
As you noted in a prior post, 1, 2, and 5 are warm, here are some things to do.
Remove the riser on the #1 cylinder, you can try some pieces of "metal" furnace duct tape, until you get the right temperature and then cut the original piece to that size.
Numbers 2 and 5 can be helped by putting at least a 1/8" spacer between the baffle and the cylinder where the screw holds the baffle to the cylinder. This is on the outboard end of the cylinder.
You can do a search on this site for various ideas pertaining to this location it has been talked about a lot.
Make sure that you silicone around the bottoms of the metal baffles so that all the air remains in the fins until the outlet area of each cylinder baffles.
This should help both cylinders except #5 will likely still be hot as it appears that that is where you are drawing off your oil cooler air.
I have had the oil cooler mounted on either side and behind the #6 cylinder seems to work a bit better. Ideally you could draw your oil cooler air from its own inlet on the cowling. This would help your cylinder cooling quite a bit.
From your pictures it looks like I can see a gap between the cylinders 1 and 3, and 3 and 5, and the metal baffle parts.
Seal around the fuel hose where it penetrates the baffle on #1
On the left side baffles I can see some small tooling holes that are open.
These holes should all be filled as air that exits there is not doing any cooling and worse yet upsets the pressure differential between the top and bottom plenums.
All these small holes add up to one BIG hole in your system.
Try the spacers, the cut down ramp on #1, seal the holes and the baffle inlets as best you can and report back!
Good luck
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Tom Martin
Well Known Member
I would also, most definitely, change that magneto timing. You could modify the firewall where the magneto contacts it, or try a different style mag. Slick mags are smaller then Bendix, for example.
Perhaps the mag that can not be adjusted could be changed to an electronic ignition.
You should fix this.
Perhaps the mag that can not be adjusted could be changed to an electronic ignition.
You should fix this.
vlittle
Well Known Member
AHA! Running 50 degrees ROP puts the CHTs into the danger zone for detonation. That's the biggest issue right now. richer than 100 ROP or LOP are your two choices, never operate between these two unless operating at 65% or lower power.
vlittle
Well Known Member
The problem with commercial plena is that the HRII cowl curves tightly around the engine and a 'flat' plenum (RV-10) style won't fit.
vlittle
Well Known Member
The three things we have, as a group identified:
-meticulously seal and adjust your baffles
-get to 20 btdc timing
-run 100 degrees ROP or go LOP.
I have been facing higher than desired CHTs. It seems that they have been creeping up over time. I spent several hours poring through my SkyView datalog and found out that my electronic ignition didn't seem to be advancing or retarding the timing properly. I have been seeing 380 to 400f temps in High power operation recently. LOP is a lot cooler. Last year, temps were about 10 to 20 degrees cooler.
It turns out that my timing was not going below 23 to 25 degrees BTC, spec is 20.
I just cleaned out my MAP restrictor and I am waiting for the eye of Hurricane Ana to pass overhead to go fly. My expectation is that my temps will be better... Because I can get back to 20 degrees. I can also disconnect the MAP sensor to fix timing at 20. I will report back.
Timing matters!
-meticulously seal and adjust your baffles
-get to 20 btdc timing
-run 100 degrees ROP or go LOP.
I have been facing higher than desired CHTs. It seems that they have been creeping up over time. I spent several hours poring through my SkyView datalog and found out that my electronic ignition didn't seem to be advancing or retarding the timing properly. I have been seeing 380 to 400f temps in High power operation recently. LOP is a lot cooler. Last year, temps were about 10 to 20 degrees cooler.
It turns out that my timing was not going below 23 to 25 degrees BTC, spec is 20.
I just cleaned out my MAP restrictor and I am waiting for the eye of Hurricane Ana to pass overhead to go fly. My expectation is that my temps will be better... Because I can get back to 20 degrees. I can also disconnect the MAP sensor to fix timing at 20. I will report back.
Timing matters!
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Yep. I tried that - cut it into pieces to try to make it fit but in the end decided it would be easier to make one from Al.
vfrazier
Well Known Member
Here are a few photos that might be useful for curing the heat woes:
http://vincesrocket.com/Engine and Prop.htm
Also, I have found that it is very easy to overlook a very large air leak that is often behind and below the #4 cylinder (#6 on a Rocket) near the cylinder base. Take a flashlight and mirror and double check that area.
http://vincesrocket.com/Engine and Prop.htm
Also, I have found that it is very easy to overlook a very large air leak that is often behind and below the #4 cylinder (#6 on a Rocket) near the cylinder base. Take a flashlight and mirror and double check that area.
vlittle
Well Known Member
Did they paint it? I thought they went with a vinyl wrap.
Regardless, they hopped up the engine and added inverted systems. It was a great airplane before. Now, I'd probably wet myself.
I saw it in pieces, assumed it was being painted but could have been wrapped.
Another topic... Dialing back my timing by 3-4 degrees dropped my CHTs dramatically... 10 to 20F. Timing matters.
