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02 Jul 09
|I ground off the charred fiberglass and removed some of the honeycomb to provide better clearance for the exhaust. To replace the strength, I did the repair with carbon fiber and high temp resin. I'll add some Thermo Tape to protect from more heat damage and I'll replace it with a large heat barrier later.|
3 Jul 09
One of the dimmers for the LED cockpit floods is not working properly so I contacted Eric at Perhelion Design and he's sending a new one on Monday. Quick service.
I ordered tiedown rings from Van's and some Thermo Sleeve Tape (12"x24") to put on the cowling hot spot from Wick's.
I adjusted the AF3400 software so it will remind me to update the fuel computer. Also checked the audio patch cord for the video cam.
I've decided to add a trailer hitch to the golf cart so I can tow the RV to the fuel pumps. There are several other guys with them on their carts and they report good results. So, bought the stuff for that project.
4 Jul 09
Went flying in the Gaggle this morning with Orval in his Johnson Rocket. It's a neat old airplane and we were part of a 13 ship formation flyby for a local town's 4th celebration. Our flyby started the parade.
Today I modified the cowling standoff so it doesn't rub the rivets, removed material on the plenum so it's not rubbing, and raised the nose wheel and tightened the breakout force to 25 Lbs. I'm going to make only one change to the nose wheel and then test fly it for results. Then I'll make additional changes until the shimmy problem is solved. I should fly it again on the 8th and I plan to fly for 45 minutes on that day.
Photo shows how I raised the nosewheel for maintenance. Salt pellet bags are 40# each and I'll use them in place of the rear seat for CG and gross weight flight tests. Then I'll return them.
7 Jul 09 Today Hobbs - 0.4 Total Hobbs - 1.1
Got in a second short flight today. We got home late in the day and I decided to try to take a short flight to see how the cowling repair would do. I hung the lower cowling and reattached the fairings and added some ThermoTape over the patch. The ThermoTape can withstand 2000 degrees and reflects 90% of radiant heat.
Then I took it around the pattern for about 10 minutes. It really flew nice! Got up to 168 KIAS and made one landing. The cowling patch and Thermo Tape did very well. The shimmy problem, although still present, is greatly reduced, so a valid solution to nose wheel shimmy is increasing the breakout force on the nose wheel assembly to 25+ pounds. The airplane still taxied with no problem, so I plan to increase the breakout force even higher.
Here are videos of today's flight.
1. Taxi - Large File - broadband = 1 minute - all others take 30 seconds
3. 1st Flyby
4. 2nd Flyby
The engine indicates it is settling into consistent readings upon which I can now make assessments and changes. It looks like #1 cylinder needs some type of air dam so the CHT can run higher and perhaps I can redirect some of the airflow to the #3 cylinder to bring its CHT down a bit. None of the CHTs are out of range, but the general consensus is that running the CHTs as near 350 as possible is ideal.
Engine Readings from Second Flight
Takeoff at 2012 Landing at 2020 Tach 0.7 Hobbs 2.4 Todays Hobbs .0.4
Location: 7FL6 Runway 23 OAT - 79 degrees
Bus Volts - 13.5
Amperage load on alternator - 31A with everything on except MRX and CO Guardian.
Max RPM - 2560 (takeoff) Avg RPM - 2440
Max MP - 28.6 Fuel Press - 34 Oil Press - 81
Oil Temp Peak - 188 (in flight) Oil Temp Avg = 180
With RPM 2440 and MP 23" #1 #2 #3 #4
EGT 1224 1224 1215 1171
CHT 275 307 340 310
9 Jul 09 Today Hobbs - 0.4 Total Hobbs - 1.5
Short in-the-pattern flight today. Only ten minutes because the storms didn't clear until late in the day and I was able to fly just at sunset. The landing and taxi lights are great. Several comments from pilots asking about them. Once again the airplane flew very nice - no new issues.
11 Jul 09 Today Hobbs - 0.8 Total Hobbs - 2.3
First flight out of the pattern. Took off and came around for one pass down the runway. I just couldn't keep it slow and the runway pass was at 175 KIAS. I didn't intend to go that fast - just couldn't keep it slow.
On the way out and back I was having to hold left pressure on the stick as if I had a heavy wing. That was confusing because the airplane had flown hands off previously. I thought maybe I simply hadn't noticed it before. Later I realized I probably had a heavy wing due to fuel loading. Next time I fly, I'm going to top the tanks. The Princeton capacitance fuel probes are still erroneous (I recommend you buy something else). Floats aren't great, but at least they work. My fuel probes will indicate full (when I know it isn't) and then drop to near zero - causing "bitching betty" to tell me to check fuel. If they weren't so difficult to get to, I'd rip the damn things out and start over.
The plan for today was:
Soft Field TO - 10 Flaps
One pass down the runway to make sure engine was going to keep running
Climb to 4500' MSL
Check transponder operation, check MRX operation, check AOA indications
Pull 3 Gs
Compare Alternate Air MP to Ram Air MP
Do clean and configured Power Off Stalls
Check EFIS Lite GPS ground speed
Test aircraft to 180 KIAS
Check engine readings (I added a temporary air dam on the front of #1 cylinder)
Normal full flap landing
|Left is the #1 cylinder as flown on flights 1-3. #1 CHT was running at least 30 degrees cooler than the next nearest CHT and #3 was 30 degrees hotter. Right shows a temp dam added to increase the CHT on #1. On this flight, #1 CHT was only 2-3 degrees cooler than the next CHT and #3 CHT was about 10 degrees cooler than before.|
I was able to get four steady state sets of engine readings today. I had stable MP and RPM several times for periods of 2-3 minutes which gave me good data to work with. The engine readings are coming in consistent. Here are today's:
I got all test items complete except transponder check (headset plug loose and I didn't realize until after landing so no contact with approach control) and the 3 G load. The MRX worked well, but because I couldn't hear anyone, I thought it was giving me bad indications. I'll do a better check of it next time.
The soft field takeoff gets the airplane airborne quickly - so quickly that I've still not been able to get visual references at liftoff to go and measure later. The high speed pass was exactly that - 175 KIAS - faster than intended. I made the radio calls and they were being heard by others but I didn't hear anyone and assumed the pattern to be empty. The problem was I was not hearing their radios. I had a patch cord in the headset plug and that may have been the problem.
The AOA is not yet calibrated, so I didn't expect it's indications to be correct - and they weren't But, it is sensing something and giving me displays. It's also advising of error codes 11 and 23 so I need to look into those.
The difference between ram air and filtered air was significant. At 2400 RPM and 24.7 MP, the MP dropped to 23.1 when I switched to filtered air. So, the ram air seems to add about 1.5" to the MP (2500' MSL 170 KIAS 75 OAT).
Climbed to 4500MSL and did power off clean and full flap stalls. Stall is straight ahead and easy to recover. A nice little burble just before the break. Clean stall at 54 KIAS (ASI not confirmed but that matches closely with other's numbers) and full flap stall at 49 KIAS (also reasonable).
The EFIS Lite is indicating GS and it seemed to corroborate the indicated AS (no tests to confirm yet), but the EFIS designers sure picked difficult to see colors and font sizes.
During descent to pattern I hit 187 KIAS - Faster than I'd planned, but this plane accelerates so easily it's not even noticeable. That was with 2400 RPM and 22" MP and about 600 fpm descent. The GPS confirmed the accuracy within a reasonable tolerance (without indepth testing yet).
The full flap landing was uneventful but it still feels like the nose wheel is doing a bit of shimmy.
Upon return and after engine shutdown, I could hear what I think was boiling fuel in the injector lines. My fuel purge valve may prove to be very handy on long, hot cross country flights. I removed the plenum and checked for oil and fuel leaks but everything was clean. While I have the plenum off, I'm adding a bit of resin to a spot I had to grind down for cowl fit. The lower cowl hot spot issue is solved. The repair is strong and unaffected by the hot exhaust pipe. If Wicks ever gets my shipment here I'll add some Thermo Tape to the inside of the cowling. I don't understand why Aircraft Spruce can get a shipment to me in 2 days and it takes Wicks a week or more - same UPS ground shipper.
It appears the air dam on cylinder #1 is about right. I'll increase its size a little bit and make it aerodynamic so as to direct air to the aft cylinder to bring it more in line with the other cylinders.
I ran rich mixture the entire flight which is probably why the EGTs are low. Next time I'll work on leaning to peak.
Oil PSI is steady at 80 and Oil Temp is in the upper 170s with an occasional bump to the upper 180s.
I was just thinking about the sound of boiling fuel after landing. I've noticed that about 5 minutes after each landing I started having some engine surging where it wanted to quit and had to be nursed along to keep running. I'd originally blamed it on the fuel selector "Both" setting drawing air from one tank, but as I think about it, it makes perfect sense that the fuel is vaporizing in the injector lines causing the surging problem. I'll look into covering those lines with a reflective covering to see if that will solve the problem.
So, for the next flight:
Clean up plenum repair and upper cowling repair (small crack along edge of honeycomb)
Pull EFIS 1 to check for GPS antenna connection
Top the tanks
Determine how to measure TO roll
Adjust the redline and caution lines for the fuel pressure
Ensure Headset is functioning before TO
Plan to get a transponder check
Check ASI against GPS
Check on AOA error codes and plan to calibrate AOA
Do power on stalls - clean and flaps
Install cowling Thermo Tape
Add silicone rubber to seal air intakes
Work on an air dam for #1
Plan for close up video of landing to check shimmy
Trim cowling standoff to avoid rubbing on rivets
Check Oil and Fuel Filters
Top oil to 7.5 Qts
Lean to peak
Insulate fuel injector lines
15 Jul 09
Today I ground and reshaped the fiberglass and resin I added last week. The latest work should make clearance all around for the plenum inside the cowling.
I removed the temporary tape installed to increase the #1 CHT and replaced it with a metal air dam. I've never like the blunt force air dams on aircraft engines to control CHT. Since aerodynamicists say that much of an airplanes drag is cooling drag, I can see no reason to use un-aerodynamic air dams to control air flow. So, I made a "ski jump" air dam to direct air past cylinder #1. I made it a little higher than the temporary tape was and I will file it back down as necessary to get the CHT where I want it.
To lower the #3 cylinder CHT to match the other cylinders, I've added a removable deflector that will direct air to the front side of cylinder #3. I'll fly with this configuration to see if #3 CHT drops and monitor the oil temp to make sure I haven't diverted too much air flow away from the oil cooler.
Wicks is so slow I don't know how they stay in business. They must not keep anything in inventory. Of all the things I ordered, they shipped the one item I really don't need now and back ordered everything else. Even Van's shipment from Oregon got here first.
|The air dam I made to fit in front of #1 cylinder.||I'll flight test it and refine the shape and size to optimize temperatures, then I'll clean it up and smooth the edges and add RTV on the backside to keep it from touching the cylinder fins.||On the same side, the #3 CHT is a bit too hot (in relation to the other cylinders) so I'm adding a deflector inside the plenum to force air onto the front side of cylinder 3. I'll shape and smooth to get best CHT and oil temp.|
16 Jul 09
|I trimmed down the #3 cylinder air dam a bit and mounted it. I'll fly with it and make adjustments as needed.||To help solve the boiling fuel and vapor problem, I wrapped the injector lines with Thermo Tape. It reflect 90% of radiant heat, so maybe it will help.||By wrapping it from the front, I was able to give a bit more aero shape to the lines. Other that a flat plate, a round surface is the next worse drag producer.|
|The exhaust pipes are close to the engine mount and the fairing between the pipes. The paint on the fiberglass fairing was bubbling a bit and I saw no reason to not go ahead and protect the engine mount from heat.||So, I added some Thermo Tape on the engine mounts and on the fairing.||
The ADC oil filter had some green rubber-like residue on it. There were only a few tiny pieces of bright metal on the filter.
I haven't pulled the fuel filter yet because the manufacturer recommends cleaning it after 5-10 hours. I have to buy a 1.5" wrench and It's going to be very tough to remove for cleaning due to the tight location.
17 Jul 09
Started up this morning for a flight, but couldn't get radio reception, so decided to taxi to warm the engine. I did an engine runup and decided to do a high speed taxi down the runway - nose comes up at 49 KIAS (same as dirty stall speed). As I exited the runway, I noticed the brakes were very weak and spongy. I suspected overheating brakes, but that didn't make sense since I had only taxied about 12 minutes at 84 OAT. When I cracked open the canopy, I could smell hot brakes and asked Pat to check the wheel pants for smoke. None - and that was a good thing because I'd decided to not bring along the fire bottle today. From now on, I'm going to take along the fire extinguisher and tow bar every time. I should have had them today for safety and I could have towed the airplane back to the hangar.
I pulled the wheel pants and the brakes were hot, but not smoking hot. The clear plastic hose on the brake lines was not melted or deformed, so apparently no damage. The wheels are so tightly cowled by the pants that there is little chance for the brakes to cool unless you takeoff. So, in previous situations I may have been getting hot brakes each time, but they rapidly cooled when I got airborne and didn't heat up much on landing.
I believe the cause today was my inadvertent riding of the brakes during taxi. I'd heard about RV brakes overheating during taxi, but thought I'd addressed the problem by adding rudder pedal extensions on the bottom of the pedals. I was probably riding the brakes during taxi instead of resting my feet on the floor and using the extensions. I will use more caution in the future.
Now, I have to solve the headset issue and taxi test the brakes with the wheel pants off. So, back to work.
Well, the headset issue was non-existent - I must have bumped the volume knob with my knee and the volume was down. The brakes were solid after cooling and I am more careful about accidental brake use during taxi.
Flew late this afternoon. Today's Time - 1.2 Total Hobbs - 3.5
During taxi out, the EFIS 1 tumbled and the EFIS Lite was locked up and displaying garbage. I had to reboot them four times to get them to function. It looks like the BMA products may be junk and have to be replaced. I'm still trying to give Greg the benefit of the doubt, but with the loose airspeed sensor, the early freezing, and now this, I don't know if this equipment is anything more than boat anchors.
They may have been affected by power cycling during start. I decided to start the engine today with the EFIS 1 and EFIS Lite already on to see how they would handle the situation. They both rebooted due to voltage drop during start. It is obvious they CANNOT be on during engine start. So, for now, I'll assume today's problems were due to the power fluctuations during start. The engine was sluggish starting today. I decided to try a different start technique (not putting the mixture in idle cutoff) and that turned out to be a poor technique. So, I'll be using the "I need four hands" start procedure with mixture in cutoff.
After getting the EFISs operating the takeoff was no flap and it was airborne in about 300' and accelerated quickly to 100KIAS for the climb. Two passes down the runway to make sure the engine was going to keep running and then departed to the south at 1000 feet. Got a transponder check with Daytona Beach Approach and their radar readout matched my altitude, so at least the BMA encoder is working okay. The climb to 4000' at 130 to 150 KIAS took about 3 minutes and then I did some GPS speed readings on three different headings. I'll put the data into a spreadsheet and check the accuracy of the airspeed indications. I couldn't stop myself from doing several whifferdills and aileron rolls even though they weren't on the agenda. I had planned to calibrate the AOA, but it requires a zero G maneuver and a slowdown to final approach speed at both flaps up and flaps down. Sunset was approaching and I ran out of time to get it done. So, that will be a task for later.
I leaned the engine but I'm still not sure how to determine peak and LOP settings. With a rich mixture and 24 square, the fuel flow is about 16 GPH. I can lean to about 12 GPH, but going beyond that caused the EGTs on cylinder 1 & 2 to exceed redline. (update: the engine monitor EGT redline was set too low, thus giving me a false exceedance). So, I enrichened to 14 GPH and left it there until RTB.
Had my worst landing today - feeling for the runway and carrying the power too long. I was a little fast on final - 78 Kts - and that combined with carrying the power too long caused a long touchdown and hunting in the flare for the runway. It's hard to tell how much the nose wheel is shimmying now but the brakes were strong and did not overheat.
The engine readings follow and they indicate my #3 cylinder air dam did not do its job. So, I'll have to give this more thought. I'll also contact Lycoming about the differing CHTs to see if they are normal. Maybe I'm worrying about something that's not important.
The air dams did not affect the oil temperature. Oil consumption is very low thus far.
Engine readings for today
I flew today's flight using the both position on the fuel selector and I'm happy to report the tanks fed evenly. So, the extra plumbing we added to equalize the distance fuel travels from each tank is working as designed. Switching tanks every half hour will not be necessary.
I do have a heavy right wing. Today I took off with both tanks full and the heavy right wing is still there. So, I'll have to attack that problem now. It may be a matter of adjusting the rod ends on the push-pull tubes. It's certainly flyable and I'll have to think about a solution.
Here's a video of a high speed pass and one of the landing.
|A couple of panel shots during the
flight. At left with 24 Square, 600 FPM descent, OAT 82 and 1480'
MSL the IAS was 180 Kts.
To right is 26/2400, level at 910', OAT 83, the IAS was 161 entering the pattern.
|A couple of out the window shots.|
The GPS speed readings were:
4000' MSL IAS - 161 Hdg - 011 GS - 177
4000 MSL IAS - 156 Hdg - 153 GS - 172
4000 MSL IAS - 157 Hdg - 220 GS - 155
Thus, calculations indicate the wind was 250 degrees at 17 Kts. TAS = 170
I plan to reaccomplish the TAS readings on another flight to confirm all numbers.
24 Jul 09 Today's Time - 0.8 Total - 4.3
Takeoff at 1718 Landing at 1746 Location 7FL6 Runway 05 Runway OAT - 85
No Flap Takeoff - Rotate at 49 - climb at 85 to 1000'
Set power to 25 Square and accel at 1000'
Climb at 110-120 to 7500'
Chk Filtered MP vs Ram MP
Operate engine at high power for breakin
Evaluate the heavy wing situation
Expand flight envelope to 200 KIAS
Check CHT and EGT Readings
Fly initial to RW 05
Normal Full Flap Landing focusing on holding 75 KIAS
I'm having one heck of a time getting a good video with audio. Today, I got a reasonably good video and talked to the video during the entire flight only to discover I didn't get any audio. I'm not sure what the problem was, but I'm going to focus on a good video on the next flight.
I topped the tanks before takeoff and each tank took exactly 5 gallons, so the both setting on the fuel selector is perfect - rather the fuel plumbing is perfect.
The EFIS One froze at the EOR when I tried to insert a flight plan waypoint and then delete it. Arrrggghhh! I had to reboot. It worked okay afterwards.
I still don't have a TO distance measurement, but it is short. Rotate at 49 and it flies off within a second. Climb at 85 is a fairly steep angle and took 38 seconds from liftoff to 1000'.
A downwind departure to the south with 25 Square and speed was about 160 KIAS.
The climb to 7500' was averaged about 1000' FPM at 110-120 KIAS. CHTs rose a little during the climb, but the hottest (#3) got no higher than 370. I leaned as I climbed but still haven't figured out how to best lean the engine.
I still have a heavy wing and it is more pronounced at higher speeds. It is not rudder or yaw related. I tried countering the roll with rudder without success. As I cruised, I checked the elevator position and noticed that at 7500' and about 160 KIAS, the left elevator balance arm is flush while the right one is slightly above the horizontal stabilizer. I'm going to check the elevator again on the next flight to see if my observation was correct. So, the saga of the heavy wing continues.
I ran the engine at high power during most of the flight - even the descent. I reached 198 KIAS during the descent.
Flew initial to RW 05 with pitchup mid field. Tough to get the airplane slowed down even in a climb. Held 75 KIAS reasonably well on final but held it too long in the flare and floated.
Engine Readings for this flight
|RPM||MP||FF||OAT||Oil P||Oil T||1||2||3||4|
|RPM||MP||FF||OAT||Oil P||Oil T||1||2||3||4|
|RPM||MP||FF||OAT||Oil P||Oil T||1||2||3||4|
25 Square at the top, 23/24 in the middle, and 29/25 on the bottom - yet even with different OATs and fuel flows, the CHTs don't vary much. The EGTs vary a bit with leaning. It looks like, for now, the CHTs are 311, 311, 345, & 316. The only odd one is still #3 and next I will try adding an air dam behind #3 and in front of the oil cooler duct. I'll start small and increase the size until CHT drops without driving the oil temp too high.
Anyway, off to fly in the Gaggle Flight tomorrow.
25 Jul 09 Today's Time - 1.0 Total Time - 5.3
Flying in the Gaggle was interesting, but not productive as far as aircraft analysis goes. I was number 5, number 4, or number 3 depending on the particular moment of the flight. The formations here are "flexible." If someone wants to leave the flight for awhile and then rejoin, then everyone accommodates.
|This was my Gaggle Flight formation
"Alpha Flight." Two RV-8s O-360s and a Harmon Rocket
Right are the displays during the flight.
Here is video of the flight.
I got more engine readings and these are the last I'm going to post before making changes to the cooling. Upon returning, I pulled the cowling and plenum to examine everything and I discovered several things.
First, my use of Thermo Tape on the fuel injector lines did not work. The adhesive on the tape is not sufficient to hold with the high heat and air flow in the plenum. So, I'll look for another solution. I also used the tape on the engine mount and a fairing near the exhaust pipes with the same results - poor adhesion and shredded/missing tape. So, Thermo Tape has limited usefulness.
Secondly, I may have discovered the reason why the #3 cylinder is running hotter than the others. There is a rather large opening in the baffle aft of the #3 cylinder. I hadn't noticed it before. I did some research on the net last night regarding the causes for high CHT (mine aren't high, just uneven) and the engine experts said it was almost always due to poor sealing of the baffles. In particular, they referenced the baffle seal that fits against the cowling, but their point was that multiple leaks in the baffle can add up to several square inches of leaks. So, after spotting my large leak, I suspect part of the solution to even CHTs will be closing the hole.
Third, the air dam I added inside the plenum (which I intend to remove) was partially blocking the purge valve movement.
The nut which secures the push button locking control cable for the ram air was loose. It doesn't have any flats to fit a wrench on, so tightening it is challenging. I guess I'll have to accept some scratches on it and use pliers to grab it tight to tighten.
After this flight I removed the EFIS One and front seat back and packed them for shipping to the manufacturers. The EFIS One airspeed sensor is broken and it is occasionally acting up in other ways. The front seat back has a puckered place and the manufacturer says it needs to be repaired. So, the airplane is down for awhile until everything returns. While it's down, I'll change the oil (recommended at 5 hours), clean the oil filter and fuel filter, mod the plenum and baffle, prime and paint some bare metal parts, and work on streamlining the cowling exit air flow.
Engine Readings for this Flight
|RPM||MP||FF||OAT||Oil P||Oil T||1||2||3||4|
|RPM||MP||FF||OAT||Oil P||Oil T||1||2||3||4|
|RPM||MP||FF||OAT||Oil P||Oil T||1||2||3||4|
Analysis: FF is higher than expected - but, I haven't figured out leaning yet and most flying has been at low altitude and high power. Florida OATs don't seem to bother the engine much until after landing and then the heat buildup in the plenum apparently causes the fuel to vaporize and the engine to surge. After engine shutdown, I can hear what sounds like a tiny leak somewhere with pressurized air and liquid mixed escaping. But, I examined the engine numerous times and I can find nothing leaking. There is nothing showing up inside the cowling and nothing on the engine. The EGTs at full rich have settled into a pattern - #1 is hottest (11F above #2), #2 is next and it is 15F above #3, #3 is 40F above #4, while #4 is the coolest at about 1145. The CHTs are also exhibiting a pattern - #1 is 2-3F below #2, #2 is 30F below #3, #3 is hottest at about 330-335, and #4 is 25F cooler than #3. So, #1, #2, and #4 are evenly matched. I'll work on bringing #3 CHT in line with the others.
After pulling the cowling and studying the situation and making a prototype air dam to fit behind the #3 cylinder, I may have come across the cause for the higher #3 CHT. I discussed it with Nelson when we were building, but I didn't do anything about it at the time. The scat duct from the heat muff to the cabin heat selector valve largely blocks the exit air flow for cylinder 3. The other cylinders aren't blocked. So, I think I'll remove part of the duct, tape off the end, and see if that solves the problem. If so, then I'll devise another way to get heat from the muff. I'm going to press on with the air dam to fit behind the cylinder because it will improve air flow to the cylinder and close off the large air leak behind the cylinder.
|Left shows how #3 cylinder exit air is
blocked by the duct.
Right shows the #1 and #3 cylinders and #1 is not blocked
|Likewise, #2 and #4 are not blocked.
Since #1, #2, and #4 all have mostly equal CHTs, it follows that #3 exit
air being blocked may be causing the higher CHT.
Right shows the current routing of the heat muff duct. I'll have to find another way to route it. For now, I'll cut it in half (to avoid having to remove all of the adel clamps) and tape it closed. Not much need for cockpit heat right now anyway.
Unfortunately, I have to wait for the seat to be returned before I can do a flight test to see the results.
29 Jul 09
Lots of thinking today. Smelled like wood burning in the hangar.
I added some fiberglass and filled holes on the plenum with resin. I had several spots where air was leaking. I've set a goal to close up the air leaks and I'll do all I can with fiberglass and metal and then do the fine work with RTV. I'm going to reduce the cooling drag as much as possible. I gave a lot of thought to fairings to improve the cowling exit air flow and I think I may have some workable ideas. I'd like to make the fairings out of fiberglass, but I can't get in the tight spots to work, so I'm using sheet metal.
I added nutplates to the plenum so it's easier to install and remove. Next I'll work on the #3 cylinder air dam.
|Why is it always the corners?!? It doesn't matter what you're working on, the corners always cause the most work. The plenum aft corners have air leaks that need to be closed.|
30 Jul 09
I got the air dam made for cylinder 3, but it took most of the day. I added some resin slurry to close more leaks in the plenum and to strengthen the glass added yesterday. Here's a page on cooling drag. Here's an excellent EAA article on cooling drag. Cooling drag analysis on a Lancair.
I made a fairing for one of the engine mount steel tubes and installed it. The aerodynamics folks on the net indicate that the length of a fairing for a cylinder (tube) should be 3.5 times the diameter of the cylinder and should be slightly concave aft of the cylinder for pressure recovery. So, that's what I attempted to do. I'll make another one tomorrow for the other side and then start making them for other locations in the lower cowling.
I removed the heater duct so, that along with the air dam, should drop the CHT on #3 cylinder on the next flight.
|With the heater duct removed, the path for air flow is much less restricted.||The area below #3 cylinder is more free of obstructions. I believe cooling will improve.||I added an air dam behind #3 cylinder to capture more air and force it along the aft fins and underneath. I believe the oil cooler will still have enough air - the next flight will tell the story.|
|I used a 1x4 and sanded it to the airfoil shape I wanted, cut a piece of 7x7 inch .032 and wrapped it around the shape.|
|It took a lot of trimming to get it to fit
and one of the holes I drilled for screws was impossible to reach because
of the exhaust pipe. But, for a prototype, it should be good enough
to prove, or disprove, its usefulness.
Right shows the right fairing in place and the left side without one. I need to polish the exhaust pipes again.
31 Jul 09
Well, the cooling air exit fairings are complete. We'll see if they do any good. I should know if there is any improvement in airflow if the CHT on cylinders #1, #2, and #4 drop. I'm not trying to lower the CHTs, but that is the result I expect. If there is improvement, I'll do additional air flow changes.
Here are a bucketload of photos of the fairings.
|Making the second tube fairing took 1/4 the
time the first one did.
The goal with the initial cooling drag reduction is to make the cooling air exit look prettier to the air. The next step is to convert this bracket from flat plate (worst aerodynamics) to something better. It is not a welcome sight to air on either the front side or the back. The aero guys say the engine cowling exit air must accelerate to match the outside airflow and meet the outside air as close to parallel as possible for least drag.
|I made paper templates to check for problems. The drawback to paper templates is the bends can be tight whereas with metal, the radius must be larger.||The is the aft side ramp that will let the air coming off the fairing above it smoothly ramp down to rejoin the exit air flow.||It's easy to see the ramp in this photo.|
|This is a wrap around to improve air flow on the front side of the bracket.||For strength, I had to add some L brackets on the ramp. There are two nutplates that protrude through the ramp, so that seemed like a good place to put the L brackets.||The aft fairing is held on with three screws - two in front and one at the trailing edge. The front fairing is attached to the aft one with two screws. The bends are too tight and caused small cracks in the metal. Later I'll fill those spots with JB Weld to keep them from cracking more.|
|Here are all of the fairings installed.||The aft view shows how the air will drop off the fairing above and ramp into the slipstream.||A closeup of the fairing shows the L brackets and where the nutplates protrude along with the attachment screw.|
|Closeups of the exit area fairings.|
|The "upwind" side of the fairings looks better. It appears there is less space for air to exit, but that is only slightly true (the thickness of the .032 metal) and the surfaces are much cleaner.||To my amateur eye, it looks more aerodynamic.||The tube fairings are very close to the exhaust pipes. Should they touch or rub the pipes, I'll either trim them as needed or find another solution.|
|Side views of the changes make me think the air flow must be more aerodynamic.|
|I bought some "Cowl Saver" silicone rubber with imbedded fiberglass to close air leaks where movement must be accounted for. Here it's used for the oil cooler flex connection. I'll also use it for the ram air intake and the cooling air intakes.|