Any Part 103 with >650 pound MTOW?

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n3puppy

Well-Known Member
Tim -

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.

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Armilite

Well-Known Member
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

Well-Known Member
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

Well-Known Member
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.

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Armilite

Well-Known Member
"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).

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

Well-Known Member
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

Well-Known Member
HBA Supporter
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

Well-Known Member
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.

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Armilite

Well-Known Member
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

View attachment 106646
==========================

This ATV Engine you're talking about as far as I know has never been used on a Plane in Continuous use for Hours! Can a Belt/Gear Drive even be attached to it? For long Service Life, these Engines should not be turned more than 6500rpm. R&D took the Stock 277UL that was rated 26hp@6250rpm, but actually Dynoed 25.4hp@6000rpm and with just a Bolt-On Tuned Pipe it made 30.4hp@6250rom! Going from Max 6500rpm to 75% Cruise Power is usually lower than 1000rpm.

In reality, probably anything more than 36hp will Push/Pull most Part 103's over the 55 knots Full Power Speed!

You can at least see, even some of the Small Engines can make 26hp to 36hp for Part 103!

They say, but I have never seen it proven that a Reed Fed Engine makes about 20% more hp than a Piston Port Engine and that a Rotary Valve Engine outperforms a Reed Fed Engine! The 292 Single Class was the most popular Class in Sled Racing. 32 different Brand Name Engines, 31 were Piston Port, 1 was a Reed Fed Yamaha which did win the most Races. Once again, were they all using the Same Size Carb, using the same CR, using the same Tuned Pipe, using the same rpm, using the same Porting, I seriously doubt it.

ATV 244cc/7cc= 34.8hp @6500rpm if perfectly Built!
ATV 244cc at 93% VE at 6500rpm = 35hp!

277UL 268cc/7cc= 38.2hp @6500rpm!
277UL 268cc at 93% VE at 6500rpm = 38hp!

There are many Variables between these two Engines ATV/277UL that affect hp made.
Carb Size/CFM 36mm vs ??mm?
CR 11.8cr vs ??.?cr?
Port Sizes
Exhaust used!
268cc vs 244cc!

This 397cc EFI Single made by Arctic Cat for 2021 may be a Game Changer at 65hp. I haven't seen the PTO Side yet.

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n3puppy

Well-Known Member
==========================

This ATV Engine you're talking about as far as I know has never been used on a Plane in Continuous use for Hours! Can a Belt/Gear Drive even be attached to it? For long Service Life, these Engines should not be turned more than 6500rpm.
You have completely misinterpreted my posting.

I am NOT recommending that Polaris ATV engine for airplane use. The ATV engine was an EXAMPLE of an engine with multiple pipes available based on usage
Sorry I confused you by not stating it was an example

The post was about warning Tim that pipes designed for snowmobiles and other other usages may have power curves that do not match the requirements of aircraft use.

That is especially true if trying to reach very high HP outputs at low RPM

The 38hp RACING ATV Pipe was at approx 7350rpm NOT 6500
The "torquer" style produced 27hp at roughly 6125rpm

Based on INTENDED USAGE pipes are tuned for different power outputs
ATV Torque 244cc@27hp@6125 = 117 BMEP (close to R&D 277)
ATV RACE 244cc@38hp@7350 = 138 BMEP
And
ARMILITE 268cc@38hp@6500 = 142 BMEP

Clearly- A piped 277 @ 38hp (7cc/hp) is in RACE territory for a piston port engine and likely requires a peaky pipe to obtain the high HP at low rpm

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Armilite

Well-Known Member
You have completely misinterpreted my posting.

I am NOT recommending that Polaris ATV engine for airplane use. The ATV engine was an EXAMPLE of an engine with multiple pipes available based on usage
Sorry I confused you by not stating it was an example

The post was about warning Tim that pipes designed for snowmobiles and other other usages may have power curves that do not match the requirements of aircraft use.

That is especially true if trying to reach very high HP outputs at low RPM

The 38hp RACING ATV Pipe was at approx 7350rpm NOT 6500
The "torquer" style produced 27hp at roughly 6125rpm

Based on INTENDED USAGE pipes are tuned for different power outputs
ATV Torque 244cc@27hp@6125 = 117 BMEP (close to R&D 277)
ATV RACE 244cc@38hp@7350 = 138 BMEP
And
ARMILITE 268cc@38hp@6500 = 142 BMEP

Clearly- A piped 277 @ 38hp (7cc/hp) is in RACE territory for a piston port engine and likely requires a peaky pipe to obtain the high HP at low rpm

View attachment 109218View attachment 109219
====================

I've not misinterpreted your posting! You gave a 244cc ATV RACE Engine turning 7350rpm as an Example which isn't suited for Airplane use! It has never been used on any Airplane yet. But with the right Tuned Pipe Designed for 6500rpm it might be useful depending on the PTO Size and it's total Weight. ALL 32 different brand Name Snowmobile Engines ever made that used a Tuned Pipe is out of Spec for Airplane use account their ALL rated at 7000rpm to 8000rpm Stock, so not for Airplane use! The Industry Standard across 5 different Engine companies that make Engines for Plane use today is 6500rpm.

A 277F Race Engine would be turning 7000 to 10,000+rpm making up to 55+hp!
 "VINTAGE 292 RACE PIPES" from Aaen.​ We have two pipes available for the popular 292 Yamaha single engine. The full race pipe is developed for modified Oval racing and delivers 70 HP at 9000 RPM with Full Race Porting, Reed Valve intake, and a larger Carb. We also have a milder pipe that is turned for 7500 RPM and delivers 50-55 HP depending on Cylinder Porting."

For Aircraft use at 6500rpm, 38hp is the max, which also equals 93% VE for 268cc.

As I said, either way you Approximate the hp made for 6500rpm:
ATV 244cc/7cc= 34.8hp @6500rpm if perfectly Built!
ATV 244cc at 93% VE at 6500rpm = 35hp!

277UL 268cc/7cc= 38.2hp @6500rpm!
277UL 268cc at 93% VE at 6500rpm = 38hp!

How much Heat the 277UL can take in Continuous use would have to be determined after you build it! I'm not too concerned about BMEP as long as you stay below 145, I'm more concerned about BTU's made. With the Engine Coatings and burning 100LL I don't think it will be a problem. With the Coatings at 38hp@6500rpm, it will be equal to the R&D 30.5hp@6250rpm BTU Heat and that's just for take-off 2-5min.

After looking at some Prop Numbers, I think anything more than 36hp will Push/Pull most Part 103 over the 55 knot Full Power Speed.

n3puppy

Well-Known Member
====================
 "VINTAGE 292 RACE PIPES" from Aaen.​ We have two pipes available for the popular 292 Yamaha single engine. The full race pipe is developed for modified Oval racing and delivers 70 HP at 9000 RPM with Full Race Porting, Reed Valve intake, and a larger Carb. We also have a milder pipe that is turned for 7500 RPM and delivers 50-55 HP depending on Cylinder Porting."
After looking at some Prop Numbers, I think anything more than 36hp will Push/Pull most Part 103 over the 55 knot Full Power Speed.
I am sorry , you are correct, you are not misinterpreting my post.
You are changing the subject away from pipes.

As I stated - 142 BMEP @ 6500 is high output for a piston ported engine and will likely require a peaky pipe. Aaen CLEARLY STATES his Yamaha 292 pipes are for the REED VALVE 292 not the lower performance piston port version. (You missed that part)

If you don't know how a reed valve works to improves performance I suggest you go back and read some books and watch some videos. No sense me spending any internet bandwidth trying to help you learn something you are having trouble with since you only seem to believe books.

Good news is you do seem to have learned something from the smart people who discussed the relation of speed vs power in this recent thread

You even created your own new "Rule of Thumb" that ultralights need less than 36hp or they will break the 55 knot Part 103 rule.
That rule of thumb will help you someday in future when you finally build your dream 38Hp 277. After you build/prop/test it and you find out it makes less then 38hp you have a built-in excuse. You can say:
"I purposely kept the output below 36HP so my T-Bird didn't break the sound barrier"