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Armilite

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Sep 5, 2011
Messages
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Location
AMES, IA USA
Rotax 912 A/F/UL From Rotax operators manual

Max rpm = 5800
75% power = 86% rpm (5000)
55% power = 74% rpm (4300)

Use your tach and published engine data to set 75% power.View attachment 102884
=========================

Dude, for these Honda/Clones there is No published Data! A few months ago you was against turning them 5000-5500rpm when I suggested it, now you say use Published data from a different Type of Engine that says 5800rpm. You're comparing a 460cc Single Engine to a Certified 1211.6cc Engine.

There MAX Continuous Rating hasn't been established. So No, we can't use the 912 or your VW Engine Data, you have to use the Engine in Question.
 

n3puppy

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Jun 25, 2019
Messages
286
Dude, for these Honda/Clones there is No published Data!

There MAX Continuous Rating hasn't been established. So No, we can't use the 912 or your VW Engine Data, you have to use the Engine in Question.
A Small V Twin making just 50hp at 5000rpm could turn a 46" x 16 Direct Drive.
Some people can use published data to develop general guidelines.
Some people use online calculators for specific data.

Previous suggestion was that a [email protected] industrial engine could swing a 46x16 direct drive prop

Per often quoted online calculator for a 46x16 prop
100% power = 50hp = 5000 rpm
75% power = 37.5 hp = 4543 rpm

4543 rpm = 91% rpm NOT 75% rpm

Prop load on any engine will follow similar patterns
It is about how props work - NOT engines

Any engine build for aircraft use should keep these parameters in mind
Cruise HP - 75% Takeoff rating (heat load )
Cruise RPM - 90% take off rating (mechanical reliability)

BFA90997-2303-46BE-A8FE-51999B94DE12.jpeg9FD8EF41-F791-42B6-8FA4-B1BE05533BB7.jpeg
 
Last edited:

simflyer

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Joined
Sep 24, 2015
Messages
238
Location
Moravia
Some people can use published data to develop general guidelines.
Some people use online calculators for specific data.

Previous suggestion was that a [email protected] industrial engine could swing a 46x16 direct drive prop

Per often quoted online calculator for a 46x16 prop
100% power = 50hp = 5000 rpm
75% power = 37.5 hp = 4543 rpm

4543 rpm = 91% rpm NOT 75% rpm

Prop load on any engine will follow similar patterns
It is about how props work - NOT engines

Any engine build for aircraft use should keep these parameters in mind
Cruise HP - 75% Takeoff rating (heat load )
Cruise RPM - 90% take off rating (mechanical reliability)

View attachment 102904View attachment 102905
RPM over 4500 are too high and time of small V-Twins - reasonable power is up to 40hp, without higher compression. Bigblocks are heavy.
 

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,674
Location
AMES, IA USA
Some people can use published data to develop general guidelines.
Some people use online calculators for specific data.

Previous suggestion was that a [email protected] industrial engine could swing a 46x16 direct drive prop

Per often quoted online calculator for a 46x16 prop
100% power = 50hp = 5000 rpm
75% power = 37.5 hp = 4543 rpm

4543 rpm = 91% rpm NOT 75% rpm

Prop load on any engine will follow similar patterns
It is about how props work - NOT engines

Any engine build for aircraft use should keep these parameters in mind
Cruise HP - 75% Takeoff rating (heat load )
Cruise RPM - 90% take off rating (mechanical reliability)

View attachment 102904View attachment 102905
===================

Until a Continuous [email protected] rating is figured out for these Engines, you're just throwing Numbers at a wall.

For Part 103:

At [email protected]:
46" x 16 (CF.822), 2 Blade 5000rpm 77F
246.70 lbs req 50.008 hp
Est Speed (75.7 mph).

At 75% hp: 50 x 75% = 37.5hp
46" x 16 (CF.822), 2 Blade 4543rpm 77F
203.66 lbs req 37.511 hp
Est Speed (68.8 mph).

At 75% rpm: 5000rpm x 75% = 3750rpm
46" x 16 (CF.822), 2 Blade 3750rpm 77F
138.77 lbs req 21.097 hp
Est Speed (56.8 mph).

At 84% rpm: 5000rpm x 84% = 4200rpm
46" x 16 (CF.822), 2 Blade 4200rpm 77F
174.07 lbs req 29.640 hp
Est Speed (63.6 mph). Part 103 Max Speed 63.3mph

50hp x 12.4cc = 620cc Van Guard 627 V Twin.

45hp x 12.4cc = 558cc

40hp x 12.4cc = 496cc 500 Clone

35hp x 12.4cc = 434cc 440 Clone

30hp x 12.4cc = 372cc GX390

28hp x 12.4cc = 347.2cc

26hp x 12.4cc = 322.4cc

GX270 (77mm x 58mm) 270.1cc / 12.4 = 21.8hp. The GX270 with 1 in PTO Shaft is the Smallest useful Engine if Big Bored.
BB (87mm x 58mm) 344.9cc / 12.4 = 27.8hp
BB (85mm x 58mm) 329.2cc / 12.4 = 26.5hp
BB (83mm x 58mm) 313.9cc / 12.4 = 25.3hp Rotax 277UL Dynoed 25.4hp.
BB (81mm x 58mm) 298.9cc / 12.4 = 24.1hp
 

n3puppy

Well-Known Member
Joined
Jun 25, 2019
Messages
286
===================
Until a Continuous [email protected] rating is figured out for these Engines, you're just throwing Numbers at a wall.
Like I said, take off at 5000rpm 2-3 Min, then throttle back to 75% Power. 5000 x 75% = 3750rpm! You don't have a hp Gauge, you have a Tach! 5000 x 80% = 4000rpm, 5000 x 85% = 4250rpm. 5000 x 90% = 4500rpm.
You are right - until these engines are actually tested with a prop or wood bar dyno - we are simply developing general guidelines based on typical aircraft parameters.

Likewise, without testing, saying every industrial 4 stroke engine ever built can reliably produce 1hp /12.4 cc in aircraft use is just throwing numbers at the wall.

But I am glad you finally agree -
75% power does not equal 75% rpm
In fact, as shown on multiple charts and calculator
75% RPM = approximately 45% power

Per your numbers
5000 rpm = 50hp. ...100% power = 100% rpm
4543 rpm = 37.5 hp. ...75% power = 91% RPM
4200 rpm = 29.6hp. ...59% power = 84% RRM
3750 rpm = 21.1 hp ...42% power = 75% RPM

F668EF7A-D1BE-4C45-8BF0-77346457A6D3.jpeg
 
Last edited:

pictsidhe

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Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Just found this on the Loncin site. They make v twins up to 803cc. If Briggs stops making engines, they are an avenue to explore. It's likely that this PTO is the same for similar size industrials. They also have a 1 3/8 straight shaft option.

B轴 (1).png
 
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