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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[Bcone1381]

A recipe for Heat

I had a 7 row oil cooler. I removed it and replaced it with a 13 row oil cooler due to 200 degree oil temperatures at 60f (15C) OAT. That larger cooler increased the cowl air temperature near the oil cooler from 125f to 150f. Now I can fly at OAT of 75 - 80F at reasonable oil temperatures.

The Vetterman crossover exhaust has attributes. It's quality and my Patrol really goes! But I've got about 8' of exhaust in my cowl. If my EGT's are 1450F those pipes are hot (guess is +900F?), and radiating heat to the rest of the cowl.

My fuel system is Bendix mechanical fuel injection. It is simple and has lots of attributes over a carburator, but it has no fuel return system, and at low power fuel travels slow through about 4 ft of lines. Fuel that heats up to 140f starts (the expert says) causing issues.

The Patrol has a smaller firewall than a side-by-side aircraft so the cowl area has less volume that any other Bearhawk.

I built my baffling very tight because air that does not cool the engine is wasted drag. This decreases air going thru my cowl than if it had a less efficient installation.

When I fly at higher power settings everything is fine. When power is then reduced fuel speed thru fuel lines slows down but engine heat starts to decrease and the fuel has time to heat up.

Larger oil cooler + Vetterman crossover exhaust + Bendix + a smaller cowl volume + tight baffling that maximizes efficient cylinder cooling = warm fuel when fuel flows are reduced.
_______________
I fabricated fittings on a lathe to let me attach a 1/4" hose on both sides to measure cowl pressures. If I know what cowl pressures are above and below the engine, then I can learn how a cowl modification effects the pressure differential betweenthe upper and lower cowl areas. For example, I'll add a lip at the cowl exit when I get this set up and see it's effect on the pressure differntial.

What I dont know....
-does the fuel in the line under the floor that goes to the firewall get heated by the tunnel?
-How much, and If so can I insulate it?
-If ceramic coated exhaust decreases temps by 25% will it fix my warm fuel issue?

Yesterday I removed the exhaust and sent it out to have it ceramic coated.

It seems to me like a bunch of what I believe are industry best practice decision making results in cowl heat. I've not seen folks talk about this. less airflow, more heat, with a injection system sensitive to it.

On the bright side...my CHT are good. Yesterday I saw 340-360F with 8F spread between them.

My next steps...brainstorming now...
-Ceramic coat the Vetterman exhaust.
-Add a lip on the cowl exit.
-change the cowl exit design...double the exit area.
-replumb my fuel supply system so the firewall exit is closer to the fuel pump to decrease the distance that the line travels in a hot cowl area by 10".
-I have two fuel lines....firewall to pump, and pump to the servo....they add 20F to the fuel temperature at the servo. If I put a shroud around one or both lines and blow ram air thru it maybe I can get some joy. But that seems like a band-aid to fix a fundamental issue.
-Take excess upper plenum air and shoot it all around the lower plenum.

I build slow. I want to fly to Oshkosh. Its okay if I don't. Time pressure makes me grumpy, removes the fun, and makes working on the Patrol onerous. So I'm not counting on it anymore.

[Nev]

I'll add a lip at the cowl exit when I get this set up and see it's effect on the pressure differential.

Brooks, do you have a cowl lip in place at present (of any size) ?

Early on, I was experimenting with different sized cowl lips while flying with a manometer. I decided to remove the lip completely for one flight and establish a base line. The result was that my CHT's temperatures increased faster than normal and to higher than I would have expected early into the flight, so I only completed a large circuit before landing and refitting the cowl lip. So if you don't have one at all, I think you will be pleasantly surprised at the difference.

[Bcone1381]

I have no lip on my cowl exit yet. My plan is to set up my manometer and get a baseline first. Then I'll fit up a lip and measure the change with the lip and what size angle and shape maximizes pressure differential.

[Nev]

I wouldn't be surprised if an exit air cooling lip resolves several issues all in one go. Might be just the biz.

[Alaskanf1]

It seems like your main concern at this point is fuel temperature? You could run the fuel lines through some SCAT hose (1"?) and have ram air through that hose. I recall seeing a certified plane that did this (C-206?) for the line from the servo to the spider. The SCAT hose went from the baffling to the servo (which also blew some cool air on the servo).

[Bcone1381]

You read my mind! You are correct that at this point fuel temperature is the concern. I now understand why Lycoming made an oil sump with a rear entry inlet for aircraft like the Piper Arrow. That makes fuel lines nice and short.

[svyolo]

I wonder how much heat the mech fuel pump itself is inputting to the fuel. I am making a couple of smaller changes (eliminating two aluminum bulkhead fittings thru the baffling) to mitigate the same thing. I have EFI feed and return lines going thru the upper baffling. I will use hogged out plastic spark plug passthru in their place.

I have always wondered why planes don't use hot air coming off the oil cooler for cabin heat. It seams much safer than heat muffs, and simpler and lighter. I removed one heat muff (for engine cooling purposes) and will give it a shot. The SCAT hoses were routed in such a way they probably detrimental to airflow out the exit.

I also moved my oil cooler hose flange 2" up on the baffling. I have a hot #2 and 6, cold #1. On average they are OK.

[Bcone1381]

I wonder how much heat the mech fuel pump itself is inputting to the fuel. I am making a couple of smaller changes (eliminating two aluminum bulkhead fittings thru the baffling) to mitigate the same thing. I have EFI feed and return lines going thru the upper baffling. I will use hogged out plastic spark plug passthru in their place.

I have always wondered why planes don't use hot air coming off the oil cooler for cabin heat. It seams much safer than heat muffs, and simpler and lighter. I removed one heat muff (for engine cooling purposes) and will give it a shot. The SCAT hoses were routed in such a way they probably detrimental to airflow out the exit.

I also moved my oil cooler hose flange 2" up on the baffling. I have a hot #2 and 6, cold #1. On average they are OK.

Fuel Pump......The fuel pump indeed heats up fuel. My pump has a cooling shroud fed air to it by 1" SCEET fed from the upper plenum. On the ground at idle after I land the fuel is moving slow due to idle fuel flows so I doubt much air flow. Normal cruise temp rise thru the pump is about 9F. Fuel temp rises from 107F at the in fitting to 134F at the out fitting. At 20"/2250 and 5 gph the temp rise thru the cooler was 17F. At 23"/2300rpm and 9 gph temp rise thru the cooler was 5.5F. Moving Fuel doesn't have time to heat up. I visualize a hotter engine that is trying to cool and lower fuel flow going slower in the hot pump soaking up heat.

Heat Muffs....The shrouds (not the muffler) is getting Ceramic coated along with all the pipes. Then I'll take my temp data sample, then remove one shroud and take another data sample.

Fittings......You are right to remove mass in the fuel lines by removing the bulkhead fittings. Your Aluminum bulkhead fittings transmit heat efficiently, and they soak up the heat from the baffles if they are hot. The Red Cube is another heat sink. I had mine on the firewall. That firewall gets hot. The cube soaks up the heat.

I am asking myself "If the Red Cube has a positive head pressure of fuel and if it fuel flows to meet the 125% then why cant I move it into the cabin? Today I did a fuel flow test and it flowed 25 gph with the cube. I only need 20gph. So unless EI can tell me why its a bad idea (I asked them this morning) it is getting moved.

Oil Cooler Heat....I know of a gifted fabricator/builder who built a Harmon Rocket. He did used the cooler as his heater and it worked out well for him. I happen to know my engine need no oil cooler at 30F. Burrrrrrr. Gotta keep my wife warm on a cold day.

[Nev]

Brooks I would install the cooling air lip first before moving the Red Cube. Reason is, they get quite inaccurate when installed aft of a fuel pump (or between fuel pumps) - I found that out the hard way. There are a number of references on the forum that show the transducers installed aft of the firewall. I did the same in good faith, not realising that several of those weren't working reliably. A phone call to the manufacturer resolved the issue and mine is now mounted on the engine mount, and the issues immediately resolved.

[svyolo]

I am also going to Fab a SS mount (vice AL) to reduce heat transfer to an EFI version of the Bendix flow divider. I don't know what is used to mount the Red Cube. This is unique to SDS and doesn't exist in the EFII type.

What I will say now might make me a heretic on a GA forum. Flame suit on. The best way to improve a Bendix style MFI system is delete the engine driven fuel pump, and just install 2 electric boost pumps, in series.

Hot start problems reduced or eliminated. Fuel heating problems reduced. Fuel pump replacement cost is 120$ instead of 1500$.

But, I know, electrically dependent.

I think overall it is a reliability improvement, and cheaper. And Bendix works really well other than that.

[Bcone1381]

Thanks for your feedback Nev. I'll follow your advice and hold off moving the Red Cube.

[Bcone1381]

It seems like your main concern at this point is fuel temperature? You could run the fuel lines through some SCAT hose (1"?) and have ram air through that hose. I recall seeing a certified plane that did this (C-206?) for the line from the servo to the spider. The SCAT hose went from the baffling to the servo (which also blew some cool air on the servo).

Welcome to the Forum, Alaska!! I had not visualized the installation you saw on the C-206. I had in mind putting the SCEET around the hose from the pump to the servo. I fit up the C-206 today with some 1" SCEET and boy is the fit nice and simple. Very Nice!! Thanks so much for your collaboration.

[svyolo]

Brooks, I just checked my fuel temps. I have EFI with a 1/2 gallon header under the right front seat. I probably have 3-5 times as much fuel line North of the firewall than Bendix FI. I have both electric fuel pumps, fuel pressure regulator, feed and return lines. All firesleeved Aeroquip hoses/AL hose ends. My pumps are flowing 43 gph continuously, so the fuel is making 3-4 passes thru the engine compartment, and back to the little header tank. I can feel the temp of the tank right next to me. In flight, I don't think I am getting more than a 10 deg F increase in fuel temp at the header tank. And that is with 3-4 round trips thru the engine compartment, that has probably 15 feet of fuel line.

Extended ground running, I am probably seeing 30 deg increase. But slow or fast cruise, 10 over ambient.

My attempts at improving cooling and MAP were in vain. Looks like cowl flaps are in my near future.

[rkennell]

Svyolo do you have a cowl lip installed?