Any Part 103 with >650 pound MTOW?

[n3puppy]

Tim -

Just for fun - you might want to read this article too
http://www.bridgestonemotorcycle.com/documents/do_you_really6.pdf

It is by Gordon Jennings - the guy that wrote the Two Stroke Tuners book.

Fun part is that he wrote about his own "Real Life" experience building a motorcycle expansion chamber from ideas in the book!

Turns out even he hadn't expected all of the cutting, testing, changing involved.
Would have been really hard without a Dyno.

 

[Armilite]

Exhaust Calc, if you READ the Info says:

A simple 3 stage two-stroke exhaust calculator based on formulas of G.P. Blair (The other Guy) from the book: The Design & Simulation of Two Strokes.
You can also save and load the data by using the provided functions.

Note:
This coefficient Kh is called the Horn Coefficient, with typical values between 1.0 and 2.0. Small values of Kh are best suited to Grand Prix engines with narrow power bands, larger values are for wider more flexible engines. This means 2.0 (WideBand) for Snowmobiles, ATV, Jet Skies, Off-Road karts, Ultralights, and Kitplanes, etc.

Some Tuned Pipe Software lets you pick which Formula to use, Jennings or Blairs.

Most BAD Tuned Pipes are a result of People not taking proper Cylinder Measurements, or Recording them Measurements, too not Cutting the Parts right and then Welding them together, or just asking it to make more % of hp than it can provide. Every engine has it's limits at a Specific rpm used. Like a Super Stock Race Engine might turn 10,000rpm and use 16.0cr. You can use Spec's from other Engines.

Like a Stock 2004 Skidoo 380F using 9.6cr was rated 36hp@7000rpm with a Muffler. A 2004 380HO with a higher 11.2CR and a Factory mild Tuned Pipe was rated 48hp@7000rpm a 35% Gain, a 380HO with a better aftermarket Tuned Pipe Dynoed 57.26hp@7000rpm. 36hp to 57.26hp = 59% Gain in hp using a Higher 11.2CR with a Good Tuned Pipe.

277UL 268.8cc/26hp= 10.3cc to make 1 hp with their Muffler Exhaust.

277UL with R&D Tuned Pipe 268.8cc/30.5hp= 8.8cc to make 1 hp with their Tuned Pipe.

377UL 368.4cc/35hp= 10.5cc to make 1 hp with their Muffler Exhaust.

447UL 436.7cc/40hp= 10.9cc to make 1 hp with their Muffler Exhaust.

503UL 496.9cc/50hp= 9.9cc to make 1 hp with their Muffler Exhaust.

503UL with R&D Tuned Pipe 496.9cc/62.3hp= 7.9cc to make 1 hp with their Tuned Pipe.

Simonini Victor 1 Super with a Tuned Pipe using 9.5cr and 6500rpm, 400cc/54hp= 7.4cc to make 1 hp! Bump the 9.5cr to 11.5cr = +2.0 hp. 400cc/56hp= 7.1cc to make 1 hp!
400cc/7cc= 57.1hp if it was Perfect.

 

[n3puppy]

Tim - sometimes it helps to visually see some of the stuff we are talking about

Olaf Aaen is one of the premiere two stroke engine modification people in the world.
Worked as a design engineer in OMC's snowmobile division until they shut down

He offers an off the shelf set of modifications for the piston port air cooled 244cc Polaris Trailblazer ATV. Sold in stages, they include a pipe and porting for increased power.

He makes two types of pipes for the same ATV engine - wide and narrow band.
They are based on the actual usage the purchaser has in mind not just "ATV"
One he calls one the Torquer - Nice wide power band
The other he calls the Top End - Higher output -Narrower band

Stock 244cc engine is 22hp@5250rpm
His Stage 2 ports plus "Torquer" is 32hp@6750rpm
His Stage 4 ports plus "Top end" package is 38hp@7250 Rpm

Now imagine you are flying behind one of these engines.
After Full Power climb out - you throttle back 1000rpm for cruise
Stage 2 "Torquer" - 32hp@6875 and 28hp@5875 12.5% reduction
Stage 4 "Top End"- 38hp@7375 and 31hp @6375 18.4% reduction
Without actually flying one - I wonder how a fixed pitch prop combined with these engine packages would react to the greater reduction of the narrow band pipe.

Here is an another interesting observation
His Stage 2,3,4 packages for a 244cc engine are all in the 30-32Hp range at 6500rpm
Very similar to the 30ish HP for the R&D piped 277UL at 6250rpm

 

[n3puppy]

Tim - Another set of performance packages from Aaen illustrating
pipe/porting differences.
This time for the single cylinder 400cc Liquid cooled reed valve Polaris ATV

You can see how he varies the packages for the intended use of the ATV.
Not just highest horsepower possible.

Look at the curves marked "Torquer" and "Top End"
Those curves just the pipes on stock cylinder with no porting.
Notice how the Torquer pipe has a very flat curve around the 40hp line compared the "Top End" in the same rpm range.

Its wide and flat on both sides of peak power. Another common trait of wide band pipes.

 

[Armilite]

"I've been looking around. I'm a Sasquatch sized person 6'5". . Needs to be able to take a 275-ish pound pilot, fuel, helmet etc."

I would be looking at the Legal Eagle XL and if it needs any real mods. I don’t think there is a difference between it and the two seat spar, so it should be plenty strong. If built to the T, there is a little weight left to change up. I doubt there is any strength problem, but you probably start getting into legal stall speed problems, not flying problems. If you are wanting to pack stuff around, you are just not going to be able to and be in the spirit of the law with any 103.

===================

Handles his Weight but under Powered!

Legal Eagle XL ™ Specifications The new design handles a 275 Lbs Pilot Seat is bigger, taller, and longer. Weight 246 pounds (dry), Wing Span 315 inches, Wing Cord 55 inches, Wing Area 120.3 Square Feet, Wing Loading 4.7 Pounds per square ft at gross weight of 575 Lbs. The engine is the Better Half VW ™ ~ 30 HP @3400 RPM. for a 275 lb Pilot you need 33.5hp! Can a 1/2 VW be built for 35hp, 40hp, Yes! A Rotax 277UL (28hp) Fan Cooled is 65 lbs Complete. Lighter than a 1/2 VW. The 1/2 VW comes in Suited for ultralight use and single-seat light sport aircraft, the engine weighs 86 lbs and produces 40 hp (30 kW). 86 lbs- 65 lbs = 21 lbs. 246 lbs - 21 lbs = 225 lbs. 225 lbs + 30 lbs + 275 lbs = 530 lbs needs 32.2 hp. A 277UL can be upgraded to make that hp. and more with a Tuned Pipe.

1/2 VW Engine(40hp).

Mosler 1/2 VW / Mosler CB40 / Global Motors 1/2 VW / TEC ½ VW / TEC CB-40 / TEC CB-35

all this about aviation, airplanes, helicopters,

all-aero.com

MTOW 575 lbs - 246 lbs = 329 lbs - 30 lbs Gas = 299 lbs for Pilot & Bags.

575 lbs = 260.8156 kg / 10 kg = 26.08156 kw needed = 34.97595 (35hp) needed for MTOW.

 

[TFF]

Rockiedog isn’t 275 but he is 6 ft and some change and his regular LE is all over YouTube and seems to be just fine. Having helped build a LE XL, it’s as solid as a Baby Ace. A forth fuselage longeron and a steel tail, it pretty much would be one. If I was to go crazy and throw an A65 on one, I’m not worried about the wing, I’m worried about the tail fluttering going faster. Miracles is what everyone wants; getting the job done gets snubbed.

 

[BTCrenshaw]

Tim
Sorry if I caused some confusion

The goal of the CVT in a Snowmobile is to maintain a constant engine RPM regardless of load/mph/throttle setting. The graph below shows how a good snowmobile transmission can be tuned to maintain the same maximum output rpm at any speed.

I also should have been more clear by saying constant speed propellors. With a constant-speed propeller as power requirements vary, the pitch automatically changes, keeping the engine and the propeller operating at a constant rpm If the rpm rate decreases, as in a climb, the blade pitch is lowered and the crankshaft rpm can increase to optimum RPM. The constant-speed propeller thus ensures that the pitch is always set at the most efficient angle so that the engine can run at good constant rpm regardless of altitude or forward speed.

In either case- Snowmobile or propellor -the goal is the same - Keep the engine at its optimum rpm.

Snowmobile Pipe manufacturers understand how that CVT works and design pipes counting on the help it gives them when they produce peaky pipes with high outputs over a very small rpm range.
Motocross race pipes are what are called "Wide Band" Because motorcycles don't have the advantage of CVT - they need a pipe that produces good power over a wide RPM range dictated by the manual transmission

The trade-off is a wide rpm range pipe produces less hp than a peaky Snowmobile pipe tuned for a narrow range.
Rotax has been making Snowmobile engines for years - They know how to make High output snowmobile expansion chambers. Yet they CHOSE wide range tuned exhausts tailored to aircraft use.

Since Fixed pitch props don't give the advantages of a CVT or constant speed prop they need the wide range lower power output characteristics of a Motocross pipe not a Snowmobile pipe

. View attachment 106621View attachment 106622

I think I understand what you're getting at. Being a long time and former dirt rider we called what you're describing as the power band on our two stroke engines. This is the area of RPM where the engine would rapidly increase in power. Go under that RPM range and the bike was sluggish. Go over that rpm range and there was a loss of power, but not as much as going under. If in the power band the engine made gobs of power. Our exhaust was tuned for this area and most of the time we raced trying to keep the engine in that RPM range. If that's done in an airplane then there could be a large portion of the RPM range that's pretty useless. I've heard small aircraft engine builders (mostly Polini) discuss how they tune their exhaust to give a broader power band. This works but is at the expense of a higher potential power output in the best RPM range for the engine. It's a trade off from the way I understand it. Smooth, wider power band but overall a lower max HP output or not as smooth, narrow power band but when the engine gets into ideal RPM range - hang on.

Good discussion going on and I'm enjoying the different points of view.

Todd

 

[n3puppy]

It's a trade off from the way I understand it. Smooth, wider power band but overall a lower max HP output or not as smooth, narrow power band but when the engine gets into ideal RPM range - hang on.

You pretty much got it .
Any flying you do with a fixed pitch prop is going to be a compromise of some sort.
I used to fly my Aeronca with a climb prop because with my passenger and full tanks we were near max useful load. Sacrificed MPH for that climb performance from the grass strip we flew out of. Other guys got away with cruise props.

There are no doubt flying styles that can benefit from lots of power even if peaky- Aerobatics, STOL competitions, glider tug, etc. Firewall the throttle for max power and pull it back to land.
Lot different than a cross country flight with max take off power followed by an extended period of say 75% power or lower.

Even though less peak power, a wide power band simply smooths things out, so you are not constantly jockeying the throttle in flight as conditions change.