Ace Aviation Redrive: New model

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davidjgall

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Joined
Oct 7, 2010
Messages
131
Location
Northern California, USA
...It looks like a four-bladed prop might be worth it at VP speeds.
Don't go there. The one thing most prop design discussions in this horsepower range neglect is Reynolds' number; by the time you carve four itty-bitty blades, all the assumptions about the airfoil that were built into the prop design software or input from TOWS are not valid anymore and your resulting performance disappoints. Two blades is the maximum number of blades you should consider for an airplane in this speed/horsepower range unless you're "doing the math" to account for the reduced Reynolds' number.
 

EzyBuildWing

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Joined
Sep 23, 2009
Messages
335
Location
Sydney NSW Australia
GK makes an 800cc 2-cylinder 2-stroke Aircraft Engine (derived from their Snowmobile).......100 hp at 6500 rpm. 35 kg. 12.3 : 1 Compression. EFI.
If we de-rate this engine to 15 cc per hp for great reliability, we're talking 54 hp at 5500 rpm continuous (same hp/cc as Cuyuna).
How to de-rate? ...just add an extra Head Gasket to lower the compression!
With the John Perry-Evans belt re-drive, might be better than the 503.
 

103

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Joined
May 2, 2015
Messages
389
Location
Wauwatosa WI
GK makes an 800cc 2-cylinder 2-stroke Aircraft Engine (derived from their Snowmobile).......100 hp at 6500 rpm. 35 kg. 12.3 : 1 Compression. EFI.
If we de-rate this engine to 15 cc per hp for great reliability, we're talking 54 hp at 5500 rpm continuous (same hp/cc as Cuyuna).
How to de-rate? ...just add an extra Head Gasket to lower the compression!
With the John Perry-Evans belt re-drive, might be better than the 503.
I think two strokes are complicated and need a exhaust system tuned for the task at hand. I would think just turning it slower may make it work I do not have enough 2 stroke experience to count on. Likely a big research project. With ROTAX pulling out hopefully someone steps in the gap.
 

mm4440

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Joined
Jan 14, 2012
Messages
288
Location
LA area, CA
Increasing the squish band height is a bad idea. It can make it ineffective and the engine more prone to detonation rather than less than the decrease in CR would indicate. Dropping the red line 1000 rpm would do it. When you see high nominal CR in a two stroke, they are calculating it based on full stroke. It is more informative to base it on exhaust port closure (when compression starts) to TDC. You will find the 12.3 : 1 is actually about 7.5 : 1 and needs no reduction.
 

Armilite

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Joined
Sep 5, 2011
Messages
3,613
Location
AMES, IA USA
GK makes an 800cc 2-cylinder 2-stroke Aircraft Engine (derived from their Snowmobile).......100 hp at 6500 rpm. 35 kg. 12.3 : 1 Compression. EFI.
If we de-rate this engine to 15 cc per hp for great reliability, we're talking 54 hp at 5500 rpm continuous (same hp/cc as Cuyuna).
How to de-rate? ...just add an extra Head Gasket to lower the compression!
With the John Perry-Evans belt re-drive, might be better than the 503.
====================

With that high of CR, you would want to burn 100LL. The EFI should have a Computer and Knock Sensor for the Engine. [email protected] and if you dropped the CR to 9.3cr you would only lose about 3hp. You have the extra weight to contend with, is there a Redrive (Cost) for it? If so, got a photo of the Redrive on the Engine? Then you have an Exhaust (Cost) to fit on your Plane. What is the Engines Cost, does that include the Computer & Wiring Harness? The trouble with these Newer Sled Motor conversions with EFI is most have a Limp mode built-in, which you don't want for Plane use!

800cc turning 6500rpm using 12.3cr making 100hp:
At 6250rpm = 97hp
At 6000rpm = 93hp
At 5750rpm = 89hp
At 5500rpm = 85hp
At 5250rpm = 81hp

800cc turning 6500rpm using 9.3cr making 97hp:
At 6250rpm = 93hp
At 6000rpm = 89hp
At 5750rpm = 86hp
At 5500rpm = 82hp
At 5250rpm = 78hp
 

Armilite

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Joined
Sep 5, 2011
Messages
3,613
Location
AMES, IA USA
The Gk1000 drive John made for Kevin Armstong 800cc variant is 2.32:1 the ideal for these would be 2.6:1.

Look Kevin up in youtube he was under proped but just installed a new prop. 160kgf static on the 800cc

This has high potential for all type 1 applications to loose some weight and pickup a larger diameter prop for better climb. Don't know if I am ready for fuel injection inam sure it could be switched to carburation with carb heat....
======================

6500rpm/2750rpm = 2.36 Ratio. What the O-200 used for rpm. Is Kevin turning it 6500rpm?

6500rpm/2.32 = 2,801.7rpm
6450rpm/2.32 = 2,780.1rpm
6400rpm/2.32 = 2,758.6rpm
6350rpm/2.32 = 2,737.0rpm
 

n3puppy

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Joined
Jun 25, 2019
Messages
259
====================
800cc turning 6500rpm using 12.3cr making 100hp:
At 6250rpm = 97hp
At 6000rpm = 93hp
At 5750rpm = 89hp
At 5500rpm = 85hp
At 5250rpm = 81hp

800cc turning 6500rpm using 9.3cr making 97hp:
At 6250rpm = 93hp
At 6000rpm = 89hp
At 5750rpm = 86hp
At 5500rpm = 82hp
At 5250rpm = 78hp
Hp to compression ratio changes are usually figured on Percentages because of the compression curve.

100hp at 12.3 to 9.3 will be about 92hp (not 97)
91.9hp - per cr chart (91.9%)
93hp per generic calculator

C9733642-FBF3-47D3-B031-3C8F0861D8C7.jpegB5B4E6EE-2B63-4E31-BE00-6C3D29CB20A5.jpeg
 

mm4440

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Joined
Jan 14, 2012
Messages
288
Location
LA area, CA
You are thinking 4 stroke. The engine in question is stated to be a two stroke. Read my post. No need to drop CR. Lowering red line will do.
 
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