"A light Cub flies best"
The above bit of wisdom is the most offered tidbit of information provided by the crustiest of aviators on forums across the internet. Everyone who hears this sage advice nods and grunts collectively, then proceeds to bolt hundreds of pounds of extra schtuff to their airplane that they absolutely can not live without.
Redundant glass dash(s), heated seats, backup radios, backup alternators, backup fuel pumps, and forward looking infrared cameras so you don't even need to look out the window anymore:
I can't deny these systems are all uber cool, and I suppose if you live at sea level, why not?
Nothing builds character faster than flying an chubby 90HP Cub over 12,000MSL mountain passes in Colorado.
I can not stress the following enough: the mountains will try and kill you every minute of every day. Many a Carbon Cub pilot have found out the hard way in the Colorado and Idaho mountains that horsepower can not solve all problems.
Still we do what many do: we port every cylinder, compress the intake charge 50:1 on pure methanol, and bolt on every high-horsepower exhaust we can get our hands on. Eventually even the thickest skulls start asking themselves the following question:
"How can I make my airplane lighter?"
Then we start replacing every piece of fiberglass or aluminum with carbon fiber, and things start getting expensive. Really, really cool too, but still really expensive.
I quit that rat race and went in a completely different direction.
The first thing I pulled off was my starter. Then I pulled the alternator. Then I yanked off that huge ring gear. Now that there is no need for large gauge wiring, that was gone too. EarthX battery? Yes, please! By the time I was done, my nose was 40 lbs lighter. The airplane did not go any faster and the motor was still only 90HP, but the airplane flew dramatically different. Those old timers were right; lighter is better.
I flew in this configuration for six years and I will be the first to admit hand-propping a high compression finicky motor on a cold morning is no fun. Even so, that 40lbs was never going back on the nose and I found that many things I thought I absolutely-needed were not-so-needed after all.
When it came time to mount a fresh motor, the old questions led me to new ideas. Instead of a full pressure cowl, J3-style cooling eyebrows were fab'd in hopes of cooling the beast without building yet another pressure cowl. Another 15 changes later netted me one really ugly airplane but another 9lbs saved. My attention turned to my exhaust.
My Vetterman dual-pipe crossover exhaust system served me flawlessly over the years. The welds are exquisite, the slip joints and brackets are stout, and the whole system is lightweight. Clint at Vetterman is exceptional at his craft. That said, for the time being I am going to continue flying without a full pressure cowl allowing me to continue trying out new-old ideas. Would it be possible to shed some more weight up front with a slightly different exhaust configuration?
I am not going to get into engine exhaust theory, crossover vs 2-into-1 vs 4-into-1 vs 4 straight pipes, or anything of the sort here. This KITPLANES article does a fair overview of exhaust options for our 1930's air cooled tractor motors.
One image in the above KITPLANES article caught my attention:
Apparently stub stacks are loud. But, how loud? Obnoxiously loud?
Louder than this?
How much louder is a stub stack than 4-into-1 like this?
Without a pressure cowl requiring an intricate exhaust exit, I wondered how much weight could be saved with a stub stack exhaust. Would it be unbearably loud?
The answer is 12 lbs saved, and no it is not unbearably loud. The new exhaust note is not pleasant however it does not sound drastically different than my previous 2-into-1 exhausts.
My old lightweight Vetterman exhaust weighs 16.7lbs with everything and that is lighter than most Cub exhausts on the market. My new stub stack exhaust is overbuilt using 16 gauge 304 stainless, and weighs 4.5lbs.
Now that I know this idea works, version 2 of this exhaust is already being modeled:
Updates will be posted as hours are put on this version 2 of this silly yet lightweight idea.