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Hirth F-23

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13brv3

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Feb 14, 2018
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Tellico Plains, TN
Is anyone running a Hirth F-23? I've got one on an Airbike, and I'd be interested in comparing notes on exhaust length and prop sizes.
Rusty
 

proppastie

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if you have any data, prop dia., pitch, rpm, static thrust, I am sure many of us would like to see it.
 

Armilite

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Sep 5, 2011
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AMES, IA USA
e-mail Warp for there Recommendation for your Hirth, then go from there!

Prop Lenght and rpm turned sets your Static Thurst, and Prop Pitch used sets your Speed. Like, I recently emailed Warp Drive for a Prop for a Rotax 277 rated 26hp@6250rpm with the 2.0 Gear Drive. It was also rated 28hp@6400rpm. They recommended a 54" x 18 Prop. A 54" x 18 prop, turned 6250/2= 3150rpm Pitched for -100rpm = 3050rpm at 77F and using .82CF makes 171.07 lbs Static Thrust and needs 23.602 hp. Estimated flying speed = 51.5 mph or 44.7 knots! Using the same Data but changing just the Pitch.

Recommended 54" x 18, 171.07 lbs Static Thrust and needs 23.602 hp. Estimated flying speed = 51.5 mph or 44.7 knots.

A 54" x 19, 171.07 lbs static Thrust and needs 24.913 hp. Estimated flying speed = 54.4 mph or 47.2 knots.

A 54" x 20, 171.07 lbs static Thrust and needs 26.224 hp. Estimated flying speed = 57.2 mph or 49.7 knots.

A 54" x 21, 171.07 lbs static Thrust and needs 27.535 hp. Estimated flying speed = 60.1 mph or 52.2 knots.

A 54" x 22, 171.07 lbs static Thrust and needs 28.847 hp. Estimated flying speed = 63.0 mph or 54.7 knots.

Part 103 is 55 knots / 63.2 mph!

The 54" x 22 needs 28.847 hp - 26 hp = 2.847 hp you would need to find. Just a Bigger 36mm to 38mm Carb change can give you a 10+% Increase. 26hp +10% = 28.6hp! Porting the Case & Cylinder can give you 10-15% Increase. 28.6hp + 10% = 31.46hp@6250rpm! A better Exhaust Muffler can Gain you more hp also!

Static Thrust Calc.
Static Thrust Calculator - STRC
 

13brv3

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Messages
121
Location
Tellico Plains, TN
Thanks, but I'm not looking for any theoretical numbers. The goal is to find someone actually running an F-23 to compare notes.

The original log entry shows 6150 rpm static with 14 degree pitch on the prop. I had to drop the prop pitch down to 10.5 go get close to that, so either the earlier log entry was wrong, or the engine has lost power. I've been through everything now, and the engine seems to be in great shape, so I've pretty much concluded that the original numbers were just wrong. It could have been a bad tach reading, or incorrect pitch adjustment method, or something along those lines.
 

n3puppy

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Jun 25, 2019
Messages
178
13brv3
Good idea not to use those theoretical numbers. The Calculator Gives suspect numbers most of the time concerning thrust.

I would contact Dennis at Aerolite 103. When he sells a kit with the F-23 engine he supplies a 2 blade Culver Prop with it.

Good guy - I am sure he would have performance numbers for an F-23 with that prop and what exhaust he uses.
Also supplies Warp and Ivo adjustables as options and may have data for those too.
Contact email
aerolite@uflyit.com

Website
Aerolite103
 
Last edited:

Dana

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How are you measuring the pitch? Propeller pitch is measured in inches, not degrees. The angle in degrees varies along the length of the blade.
 

13brv3

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Tellico Plains, TN
How are you measuring the pitch? Propeller pitch is measured in inches, not degrees. The angle in degrees varies along the length of the blade.
The standard way to measure pitch for ground adjustable props is on the rear side, at the tip. It's measured in degrees. It's really just a reference number, and wouldn't match the effective pitch of the prop due to the twist that props have. The logs said it was 13 degrees when I got it, and that's what I measured as well, so I have to believe we were both measuring it the same way.
 

TFF

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Your degrees is only a measure of setting the blades. Pitch is a measurement of forward movement the prop moves the airplane. They are close but not the same. One is practical. One is descriptive. Each brand has their own procedures when it comes to adjusting.
 

spaschke

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Denver, CO
How are you measuring the pitch? Propeller pitch is measured in inches, not degrees. The angle in degrees varies along the length of the blade.
Warp drive propellers links a static thrust calculator on their page. It uses degrees and distance from the propshaft to measuring point. No doubt it is specific to their props. Unfortunately the link is broken at this time.
 

Armilite

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Thanks, but I'm not looking for any theoretical numbers. The goal is to find someone actually running an F-23 to compare notes.

The original log entry shows 6150 rpm static with 14 degree pitch on the prop. I had to drop the prop pitch down to 10.5 go get close to that, so either the earlier log entry was wrong, or the engine has lost power. I've been through everything now, and the engine seems to be in great shape, so I've pretty much concluded that the original numbers were just wrong. It could have been a bad tach reading, or incorrect pitch adjustment method, or something along those lines.
==================

Yes, the F-23 is rated at 50hp at 6150 rpm. What Lenght and Number of Blades are you using?
 

13brv3

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Joined
Feb 14, 2018
Messages
121
Location
Tellico Plains, TN
==================

Yes, the F-23 is rated at 50hp at 6150 rpm. What Lenght and Number of Blades are you using?
PowerFin "B" 62" 2-blade. This is what Powerfin recommends, and I think I saw 12 degrees as a recommendation.

Again though, the point of the post originally was to find someone actually running one, and compare notes about props and rpms for an actual running engine. At this point I'm pretty well satisfied that the engine doesn't have any significant issue, but the big difference in pitch between the original logs and now is a puzzle.
 

n3puppy

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Jun 25, 2019
Messages
178
Just out of curiosity went to the Powerfin website to see what they say now
You didn't say what the belt reduction was, but your 62 inch is still close to what they recommend now.

Can't find any recommendations for pitch - but in their pitch settings document says start at 14 degrees and go from there.
Maybe your original 14degree log entry was where the guy started following their guidance?

https://storage.googleapis.com/wzukusers/user-25980798/documents/589cf22d7da3cC5Y3BmI/_PITCH_Settings.pdf

E190154B-E65C-4808-BD97-E338C4B7876E.jpeg

A9B8AB19-0CDC-4997-89D1-C833E475436E.jpeg
 

13brv3

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Feb 14, 2018
Messages
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Tellico Plains, TN
2.5:1 for the belt drive. I'm not sure why the builder went with 2/62 rather then 2/63 if that was an option. The original logs say he started at 12 degrees as recommended by Powerfin, but during the break-in, the pitch was increased to 14 degrees, which gave a static of 6150. At 14 degrees now, I have about 1000 rpm less than that, which is the puzzle. I'm back to 6150 now, but at 10.5 degrees.

I've worked with Matt at RPE, and I'm convinced at this point that the engine is fine. The original 6150 rpm at 14 degree log entry must have been incorrect for some reason.
 
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