Engine

Fuel System – Firewall Forward

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Two fuel lines pass through the firewall.  One is from the electric fuel pump,  the other is gravity feed. In the picture below the right line comes from the electric fuel pump. The inline check valve ensures fuel can only flow towards the engine. 

Fuel lines at firewall
Fuel lines at firewall

After the check valve is a tee, shown below. Left side connects to the electric fuel pump check valve,  right to mechanical pump check valve and the top goes to the carburetor.  Behind the tee is the inlet for the mechanical pump.  It’s fuel line is connected to the left line in the picture above. Rest assured, the top hose now has a clamp, it was not installed when I took this picture.

Tee connecting both pumps
Tee connecting both pumps

Below you can see the mechanical fuel pump on the right.  The outlet connects to a check valve that’s connected to the tee. I wrapped some silicone tape around the check valve so won’t chafe nearby components. 

Mechanical fuel pump connections
Mechanical fuel pump connections

The outlet of the tee connects to the fuel inlet banjo on the Dellorto PHBE34BD3 carburetor. 

Carburetor fuel line connection
Carburetor fuel line connection

This is one complaint I have about the Hirth F-33, it came with the fuel pump and carburetor.  The outlet on the fuel pump is made for 1/4″ (6.3mm) ID hose but the inlet on the carburetor is only 6mm. To resolve this I ordered a new fuel inlet banjo, Dellorto part number 6273 that has a larger diameter barb.

Dellorto banjo 6475 (top) 6273 (bottom)
Dellorto banjo 6475 (top) 6273 (bottom)

Now all I need to do is fasten the fuel tanks in the wings and install the air filter and she is ready to run!

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Modify Exhaust System

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The stock exhaust on my airplane was about as attractive as Muppet Gonzo’s nose. The stock exhaust provided by Hirth looks fine on most aircraft with the muffler hanging dead center of the airplane. But the steering bar for my nose wheel would run right through the muffler so that’s not an option. I managed to make it fit but it was ugly.

Gonzo nose exhaust system
Gonzo nose exhaust system

My engine was purchased from Recreational Power Engineering so I contacted them to find out the proper way to go about this modification. Matt said the total length from engine to muffler needs to be 21″ and the pipe diameter should stay the same size throughout but could be slightly larger just never smaller. Bends are the tricky part, a regular pipe bender will slightly crush the pipe so that’s not an option. RPE sells pre-bent pieces that you can use to build your custom exhaust or you they can build it for you. I managed to make things work without needing any additional bends
The first problem I had was the 90° pipe coming off the engine does not match the angle of the fuselage bringing it too close to the fiberglass and wood. I cut the straight part at the rear of the 90° off and then cut a little off of the bend, you can see the little notch in the left picture​ below to see the small section I removed. The result is a 65° degree bend. The straight part was also rotated so the springs will be top/bottom instead of side to side. Again this was effort to get more clearance between the fuselage.

Front header 90° modified to 65°
Front header 90° modified to 65°

The muffler having a 90° elbow welded to it is not going to work so I cut it off.

Removed 90° pipe from muffler
Removed 90° pipe from muffler

I don’t have a welder here at my house so I made a template of the of the fuselage shape, marked some key locations and took this to my brothers automotive shop to weld the parts. 

Fuselage shape template made from scrap
Fuselage shape template made from scrap

He tack welded all the parts so I could take them home and verify fit, if anything needs tweaked the tack welds can be easily cut.

Only small tack welds until fit was verified
Only small tack welds until fit was verified

Back home I checked the fit and was satisfied so I created a bracket to hold the muffler onto the fuselage. The bracket was made from some 3/4″ wide steel that I shaped to match the curve of the muffler.

Fabricated muffler bracket with grommets
Fabricated muffler bracket with grommets
Muffler bracket
Muffler bracket

I used a couple large zip ties to hold the bracket in place so I could check the fit. Once satisfied I marked the locations where the new spring hooks need to be welded. Back to the shop for the final weld.

Zip ties to hold bracket to muffler until it is welded
Zip ties to hold bracket to muffler until it is welded

The result is a much better look than the stock system that came from Hirth. The only downside is when it comes time to replace it, all this customization will need recreated again. 

Hirth F-33 modified exhaust
Hirth F-33 modified exhaust
Hirth F-33 modified exhaust
Hirth F-33 modified exhaust
Hirth F-33 modified exhaust
Hirth F-33 modified exhaust

I also checked that it flexes properly when the engine moves.

I’m undecided on how I want to paint the exhaust. Black is obvious, maybe I could use red and white to match the fuselage color scheme. Maybe I’ll decide to wrap it. Need some time to think about this.

Wiring Engine Information System

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The EIS monitors the cylinder head temp, exhaust gas temp, RPM, battery voltage and air temperature. Each item can have limits set so if something is out of the ordinary the warning light on the dash will illuminate.

The cylinder head temperature probes sit between the sparkplugs and head. I ran the wires through the fins and up the side of the engine where they are held in place with a clamp. The exhaust gas temperature probe wire is also held by this same clip.

Cylinder head temperature probe wires run through fins
Cylinder head temperature probe wires run through fins
EGT and CGT probe wire secured with wire clamp
EGT and CGT probe wire secured with wire clamp

The probe wire then run to the front of the engine where another wire clamp was added.

EGT and CHT wires routed over starter
EGT and CHT wires routed over starter

The EIS harness terminates in from of the battery where the probes are connected. I kept the pair of wires for the second exhaust gas probe in the harness even tho I’m not using them. Maybe some day this airplane is updated to two cylinder and then they are needed.

EGT and CGT connected to EIS harness
EGT and CGT connected to EIS harness

The grey  tachometer wire goes to the other side of the engine and connects to the lighting coil. I spliced an extra connector into the voltage regulator wires to connect the tach input. Still need to put an end on the grey tach wire.

Lighting coil & tach connection
Lighting coil & tach connection

The EIS uses a single DB-25 connector for all the wires. I took the connector apart and removed all of the unused wires by pushing the pins out with needle nose pliers. A few of the wires exit the EIS harness just behind the connector such as power, ground, fuel sender and warning light.

EIS connector
EIS connector

The violet wire runs through the harness to the warning light with the other side of the warning light is connected to power. I made sure that the dash is easily removed by disconnecting wires as opposed to having to cut wires to remove it.

EIS warning light
EIS warning light

The last item to connect is the green wire to the fuel level sending units from the gas tanks. When it gets a little warmer I’ll roll her outside, mount the wings and tanks and then work on routing the fuel sensor wires. I’m not exactly sure where everything ends up so not much I can do with that for now.

Ignition Wire Safety

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The manual for my Hirth F-33 engine says that if it is mounted inverted the spark plug wires need to be secured so they cannot fall off​ from vibration and gravity. After inquiring on the lonesomebuzzards.com forums George and Dick gave me what I thought was the best idea.

Purchased two s-clips and a 1/4″ diameter by 6″ long spring from the hardware store. Added a scrap piece of fuel tubing to prevent the spring from chafing the ignition wires. Drilled a couple of holes in the cylinder head fins and voila, problem solved.

Hirth F-33 sparkplug wire safety spring
Hirth F-33 sparkplug wire safety spring

Engine Mounting Plate

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The engine is bolted to a mounting plate and some lord mounts attach the plate to the fuselage. I cut some aluminum spacers to insert into engine mounting plate to prevent crushing the wood. The spacers are epoxied into the mounting plate.

Aluminum spacers
Aluminum spacers
Aluminum spacers epoxied in place
Aluminum spacers epoxied in place

I drilled the heads of the engine bolts so they can be safety wired.

Drilled heads in engine bolts
Drilled heads in engine bolts

I put a washer on both sides of the plate, thread locker on the bolts and torqued them to 19 ft lbs as specified in the engine manual

Thread locker
Thread locker
Engine mounting plate bolts to engine
Engine mounting plate bolts to engine

Lastly the bolts were safety wired to ensure they can’t come loose.

Engine bolts safety wired
Engine bolts safety wired

Now the engine is ready to be mounted onto the fuselage.

Engine Cowl Continued

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Before extending the sides I drilled the hole for the starter pull string. It took a little effort to get the angle correct so the rope does not chafe on the wood.

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To extend the sides of the fuselage I stapled a straight piece of plywood along the slanted fuselage side.

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After carefully adjusting the depth on the router I used it to remove the plywood from the underlying RS-10

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Now the plywood extensions can be glued onto the ledge created by the router.

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To support the extensions two diagonal braces were added.

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Because there was little glue area I added a gusset block.

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Lastly some plywood was added on the inside so there are no ledges for debris to collect.

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Now I can start fitting the fiberglass parts.

All that remains is to fit the fiberglass parts and fasten then in place.

Hirth F-33 Arrived Today

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Just started laying out the fuselage on the workbench yesterday and my engine arrived today.

It was packed really well.

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32oz of Bluemax oil was included.

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Muffler, springs,  pipe and header included.

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NGK C8HSA spark plugs and washable maxi-flow air filter.

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Voltage regulator and starter solenoid.

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Not sure on the exact name but this piece centers the prop.

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Starter

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Belt drive
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Carburetor

imageRecoil starter

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Dual ignition
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