N62588 Phase 1 Flight Testing

[Nev]

My firewall was drumming early on. I added several beads of RTV to adhere it to the airframe. This made an audible difference. Also the lightweight carpets reduced the drumming on the aluminum floor panels.

[TJ_Slice]

I used this product on the face of wall studs when I was building a theater room 15 or 20 years ago. I wonder about marking the tubing locations on the floorboards, and then sticking the tape on the floorboards: https://www.greengluecompany.com/noi...cts/joist-tape

I also plan on doing carpet.

[rodsmith]

I placed 1/16th rubberized cork strips over the tubing before installing the aluminum floor. Can't say how much it helped. I used 5/8th open cell foam on the backside of the firewall and on top of the exhaust tunnel, and the grey insulated blanket material on the inside of the boot cowl. That is the extent of my sound proofing and even at full power I can talk on the radio and hear responses ok. My entire front doors are covered with .100 lexan and skylight is .125 lexan.

[svyolo]

The tunnel and Firewall are definitely going to get something.

[Bissetg]

Hi Brooks, I too had horrendous ambient noise levels. I was running straight exhaust pipes, no muffling. After trying all sorts of things and worrying about not hearing traffic calls I bit the bullet and got MotorSport Solutions to custom build me a 4 into 1 tuned exhaust.

Thats what made the real difference, I could dial back the volume on the radio 25% and still hear it better than before.

Soundproofing and going to Bose ANC headsets all helped but the big win for me was the exhaust.

Good luck, noise is annoying, fatiguing and a safety issue.

[Bcone1381]

Acoustic Noise:

The source of noise on my ears ended up being mitigated by Bose A20 headset without earplugs. I did not immediately identify that the noise overpowered the intercom using the David Clark One-X. The easy way to test this is to unplug the mic and experience quiet. I suppose one might blame my intercom manufacturer for not having a mic gain adjustment.

The Bose A20 with no ear plugs and max engine power is satisfactory. It seemed negatively effected with headset+ear plugs which I don't understand.

Additionally, I tested the noise source by controlling the drumming with a felt covered board then acoustic foam. I pushed it against each window, the floor, the sidewalls, and firewall to stop the drumming while I monitored the noise on an iphone acoustic sound app that measured Hz, and dB. There was no change heard or recorded.

Hot Fuel:

My engine has an issue running smooth when returning home from a flight and it's not cold outside. I experienced it in the traffic pattern and idling on the ground at 60F (15C). It's been diagnosed as hot fuel in the fuel lines (Bendix Fuel Injection system.) The fix is to get better airflow to the fuel pump cooling shroud and change the fuel injection plumbing so fuel lines are shorter. My tight baffling resulting in little extra airflow in the lower cowl may be a contributor also. We need more data after we fix those two items. Vetterman Crossover exhaust also has a lot of hot tubing plumbed in the area. We'll see. This is experimental aviation!

[Nev]

Brooks, regarding the hot fuel, when you notice it in the traffic pattern, is it with the engine at idle or under power ? Mine runs rough at idle on the ground when hot, but runs smooth when I increase to take-off power. In other words I've never noticed an issue inflight. Just a data point for you.

[Bcone1381]

I notice it shortly after I bring the power back to 1800 RPM when the OAT is not cold. I reduce power abeam the runway threshold on downwind. It seems the fuel flow decreases, so the speed the fuel travels through the system slows down and gives it time to cook. My firm data points are a heat soaked fuel pump that was hot to touch, and the Fuel Flow transducer mounted to the firewall that was hot as well. Those are Heak Sinks. One fix moves the transducer into cool air.

I would guess your issue of rough idle on the ground when hot is the same as mine, but not to the degree.

[Bcone1381]

Hot Fuel:

I moved the Red Cube Fuel Flow transducer off the firewall and re-designed the fuel line route to reduced the length of line going thru the cowl area. The Red Cube now resides in the cool high pressure side of the cowl between cylinders 1&3 surrounded in cool air when we are flying. I have fixed the hot fuel issue in flight at 60F OAT. I will stay vigilant as summer heats up.

You can see that my Patrol IO-360 installation has vertical induction and Vetterman crossover exhaust. This setup is not ideal. The best practice with Bendix is to keep fuel cool. So keeping the fuel injection lines short prevents heating up the fuel as it travels thru the engine cowl.

To have minimum length in my installation requires the lines are threaded them between the exhaust and oil sump. If you look for my red arrows you will see the issue. I avoided this installation in version 1 which had the fuel line exit out the back of the servo to the firewall mounted red cube. Then the fuel traveled up the back of the cowl area thru the aft baffle at cylinder 3 and to the flow divider. The hot firewall communicated heat to the red cube, and long lines soaked up more heat.

What you see here is typical industy best practice for the fuel line route and I am managing the risk of threading the fuel line thru the exhaust - oil sump pinch point. The exhaust shield is covered with fiberfrax and reflective aluminum tape to limit heat from radiating aft towards the sump. The fuel line is wrapped in fiberfrax to insualte and protect it. The line is extreamly secure and has clearance there. it cant touch anything (but its tight). I then installed a cooling tube to keep air flowing into the pinch point during flight.

How hot does it get there? We need that data to feel safe. It stabilized at 153F running 75% power and 1500F EGT. We gathered data using thermocouple placed in this choke point. One arrow points to one of the five thermocouples I installed on the fuel line fitting at the servo input.

Red Arrows below point out the modified heat shield, an example of a thermocouple (white/blue wire) , Loop Clamp for securing the line, and the cool air supply line.



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[rkennell]

Brooks: For some reason the photos did not download correctly.

[Bcone1381]

I like data. Gathering heat data is easy and inexpensive. I never touched a thermocouple before last week. My thermocouples look like a 3 meter long single strand of 20awg wire. One end plugs into a meter and the other wire end is put in a specific place in the engine cowl to display data on the temperature meter. I took heat data from five points in the engine cowl during a 40 minute flight and learned a lot. I learned from Arborite (who is active here) to go gather data, and the common error is to try see the data while I collect it and or try to do something about the data while I fly, or change things while I fly to make data confusing. So we made up a flight plan and I stuck to it. Results were good data points now exist.

I learned that my concerns about cowl heat were from heat data I felt on my fingers after the engine cowl soaked up heat after a flight. I learned that my cowl temps during flight (OAT was 60f/15c) were about 125F. I saw fuel temp data as it entered the cowl area, passed thru the fuel pump, and to the servo. I saw the temperature at the area where the fuel line is pinched between the exhaust and oil sump. We figure that the fuel temp issue in flight is possibly solved, and the trend on the engine oil temperature will be unsat as summer time temperatures arrive.

The last attachment has a graph of the temp data that Arborite put together.

I built a Patrol. But what do I know? It seems like decisions I made when I built were backed up with data I gathered and were not just made up. I thought building was complete when I performed my condition inspection in January. ha! Nope, I'm still building. We build, we fly, we learn and make adjustments to perfect our craft. That is experimental aviation. Maybe we don't stop crafting and adjusting our ship, trying to make it a bit better....something you cant do with a type certificated production design.

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