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Author Topic: 1960s Coupe d'Hiver Postal  (Read 165074 times)
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BG
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« Reply #875 on: February 21, 2021, 08:32:14 PM »

Two Beauties Archie ... looking forward to the flight reports.

BG
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« Reply #876 on: February 22, 2021, 10:10:02 AM »

Two Beauties Archie ... looking forward to the flight reports.

BG

Thanks, me too.  Building the props up.  Definately in over my head now.  Solving one issue at a time.  If anyone has single blade balancing advice, much appreciated.  Both these models have single blade props.  One has a tilted and twisted axle for folding flat against side.  I decided to laminate and wet form as I could find good enough balsa to carve them out of.  End in site!!

Archie Adamisin
Burlington, KY
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billdennis747
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« Reply #877 on: February 22, 2021, 10:37:27 AM »

Beautiful tissue work. Our fields are green and yellow - what colour are yours?!
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« Reply #878 on: February 22, 2021, 11:13:29 AM »

Beautiful tissue work. Our fields are green and yellow - what colour are yours?!

Right now they are white.  Lol.  Ya, I was thi king about that last night.  While pretty to hold, not so easy to see on ground.  Hoping there isn't any checker board grass. Lol

Archie Adamisin
Burlington, KY
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Mark Braunlich
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« Reply #879 on: February 22, 2021, 03:11:27 PM »

I don’t know about Kentucky, but here in Illinois, we won’t see any green grass before April.
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calgoddard
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« Reply #880 on: February 22, 2021, 05:44:10 PM »

Archie –

Your two coupes are very, very nice. I wish I could build as nicely as you.

You asked for information about balancing single blade propellers. If you have read my previous posts, you know that I am a bit long-winded. I endeavor to help people at all different skill levels.  Therefore, I like to include some background to give my posts some context. It’s better to know why you do a particular construction or adjustment rather than just how to do it. I will split my response into two posts.

Single blade propellers have been successfully used on rubber powered model airplanes since at least as early as the 1930’s.  One example is the Korda Wakefield.  They seem to have two main advantages.  First, in the era before plastic injection molding was available, one only needed to carve and mount a single balsa wooden blade. Aside from the savings in time and materials in making blades, obviously there was no need to match the shape and pitch of two blades on a single blade propeller. Second, the power that can be delivered by a given rubber motor can supposedly be more efficiently utilized with a single blade propeller with a larger swept area than that of a necessarily smaller diameter twin blade propeller driven by the same rubber motor.

All single blade propellers used on rubber powered models that I have seen share the same basic design shown in the attached picture.  They have a wire arm with a counterweight projecting opposite the lone blade.  The wire arm is curved rearwardly. The thrust, drag and centrifugal forces generated by the lone blade require careful static and dynamic balancing of the blade and the counterweight.  The wire arm is normally made a little longer than needed and the counterweight is typically provided with a suitable sized hole so that it can be moved along the arm, and soldered in position. The wire arm can be bent to adjust its amount of curvature.  With the single blade propeller installed in the model and the appropriate-sized rubber motor wound, the spinning propeller can be observed to see if the blade or the counterweight throws outwards. At the same time the amount of vibration can be observed.  Adjustments are then made. See my next post.
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calgoddard
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« Reply #881 on: February 22, 2021, 05:45:41 PM »

Archie -

This will follow up my previous post about single blade propellers. Lack of balance in an airplane propeller leads to inefficiency. The balancing of a single blade propeller is more involved than balancing a two-blade propeller. The process is described in an article by Brian Jackson entitled “Getting Rid of the Shakes” which was reprinted in the March 2009 SCAMPS newsletter that is available on the Internet. More technical information on this subject can be found in another article by Martyn Pressnell entitled “Single Blade Propellers the Balancing Trick” also available on the Internet. Send me a PM if you can't locate the articles and I will email you pdf copies.

I seem to recall that a single blade propeller will only have optimum balance at a predetermined RPM. Of course, the RPM of a propeller of a rubber powered model varies with the available torque.

Someday I hope to build a vintage Coupe d’Hiver such as the Barbar that utilizes a folding single blade propeller.  Several years ago, I purchased a very nice 14 ½ inch folding single blade propeller kit from Retro RC LLC. See the attached picture of the finished propeller.  I have not built it yet. I just checked the company’s website and it is currently selling the single blade propeller kit for $19.00.

Some folks will say I am crazy to bother with this finicky archaic propeller design.  But I think the look of such a propeller on a vintage rubber powered model when static and its unique appearance when climbing out both have a very nostalgic appeal.  And there is also the wow factor at the flying field when someone unfamiliar with the concept sees that such a counter-intuitive device dug up from the past works quite well.

I look forward to flight reports concerning your beautiful coupes.
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USch
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« Reply #882 on: February 23, 2021, 04:46:43 AM »

You will find Martyn Pressnell's articel in the Builder's Plan Gallery at:

https://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=4938

I've used the hints on all my last years single blade prop's, simple and efficient. If you are not interested in the math just go to the conclusions  Grin

Urs
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AAdamisin
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« Reply #883 on: February 23, 2021, 07:44:47 PM »

Archie -

This will follow up my previous post about single blade propellers. Lack of balance in an airplane propeller leads to inefficiency. The balancing of a single blade propeller is more involved than balancing a two-blade propeller. The process is described in an article by Brian Jackson entitled “Getting Rid of the Shakes” which was reprinted in the March 2009 SCAMPS newsletter that is available on the Internet. More technical information on this subject can be found in another article by Martyn Pressnell entitled “Single Blade Propellers the Balancing Trick” also available on the Internet. Send me a PM if you can't locate the articles and I will email you pdf copies.

I seem to recall that a single blade propeller will only have optimum balance at a predetermined RPM. Of course, the RPM of a propeller of a rubber powered model varies with the available torque.

Someday I hope to build a vintage Coupe d’Hiver such as the Barbar that utilizes a folding single blade propeller.  Several years ago, I purchased a very nice 14 ½ inch folding single blade propeller kit from Retro RC LLC. See the attached picture of the finished propeller.  I have not built it yet. I just checked the company’s website and it is currently selling the single blade propeller kit for $19.00.

Some folks will say I am crazy to bother with this finicky archaic propeller design.  But I think the look of such a propeller on a vintage rubber powered model when static and its unique appearance when climbing out both have a very nostalgic appeal.  And there is also the wow factor at the flying field when someone unfamiliar with the concept sees that such a counter-intuitive device dug up from the past works quite well.

I look forward to flight reports concerning your beautiful coupes.

Thanks so much for.the kind words and the very detailed responses.  I am an engineer so data and process are my candy. 
30 years ago, my dad made a 1 blade prop for a 1.5 times peanut scale 20 in Lacy M10.  I built the Lacey as my 1st indoor model.  It was a sheet formed prop with a 3/16" hub and 45deg set.  He used a wire and clay counterweight and bent it back to balance.  It flew over 70 sec consistantly and was a joy.  This was 1980.  I still have the prop.

I look forward to getting these done and using these techniques.  These are quite a bit more powerful than a 2 strand 3/16 motor. 

Archie Adamisin
Burlington, KY
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AAdamisin
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« Reply #884 on: February 23, 2021, 07:52:09 PM »

I don’t know about Kentucky, but here in Illinois, we won’t see any green grass before April.

2 days above freezing and 13in of snow almost gone.  So now a green and brown ground. 

Archie Adamisin
Burlington, KY
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