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Drooping helo blades


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Hi all,

      I need to droop the blades on my Hobby Boss Mi-17. Any suggestions? I've tried using a blow dryer over a plate, but all it got me was one deformed blade that I'll be lucky to salvage. Thanks, Fred K.

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The method I read several times is as follows:

  1. Secure the blades in their bent configuration with 3 supports, 2 below at the ends and 1 above in the center - This guarantees that they all have the same drop
  2. Put in warm water for some time (I guess 30' is largely enough)
  3. Check, if the bend is not enough increase the diameter of the end supports

I hope this helps,

 

Arnaud

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A lot will depend on how brittle the plastic is, or isn't...

....I use the time-old method of applying gentle pressure between fingers and thumb, starting at the root and working outwards...

....apply a liitle pressure to bend short sections in stages along the length of the blade, then go back to the root and start again...

....repeat as many times as necessary to achieve the amount of droop required, but each time stop a section shorter than before...

....because blades usually exhibit more droop along the inner third or so than along the rest their length, especially the outer ends.

 

I've successfully used that technique on all my helicopter builds when drooped blades were required - and yes, there have been a few mishaps...

....but none irrecoverable - a snapped blade is far easier to repair than one deformed by heat; done carefully, even brittle blades can be shaped.

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One new technique that I saw somewhere on youtube recently goes a little something like this:

 

  • Prepare a solid flat surface, like your work bench top, with a soft cover, like a towel, laid out flat. You might need to fold the towel twice to get a soft enough base. The base that the blade will be worked on needs to be soft but not overly soft. A softer cutting mat might even suffice.
  • I reckon this method will work better when the blades are glued to the rotorhead but not yet painted. 
  • Place the blade you want to work on down on the cloth or towel with the rotor system upside down.
  • Get a solid tube of a suitable circumference (paint spray can, shaving foam can, other tubular shape of a suitable size) and gently press down on the underside of a rotor blade and roll out ONCE from the rotor hub towards the centre span of the blade or a little further. The inner third of each blade is where most droop occurs on a real rotor blade.
  • Stop and inspect the blade for droop. Do you need to roll it again? Do you need to roll it again with increased downward pressure? 
  • Continue working the blade until you have the amount of droop you require. Don't over do it. Work the blade over slowly.
  • Keep a note of how many times you have rolled your first blade!!!! Also make a mental note on the portion of the blade you have been manipulating.
  • Repeat this for all the other blades until you have an equal amount of droop on each blade. 

I have tried this on a 1/144 scale AH-64D main rotor and I was happy with the result. It is a method I will use again. Heat is a great way to impart droop into a blade but I think this method that I have described above might give better overall control of the "drooping process". I hope this proves to be useful.

 

I wonder is there a way to straighten out a blade that comes moulded with too much droop?

 

LD.

 

Edit: I have just read Andy's tip and the technique I have described is basically the same one but with the finger-bending being replaced with the pressure from the can/tubular shape instead. 

Edited by Loach Driver
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Here's a quick and easy method I used last week:

 

In-Progress-16.jpg

 

Clamp blade to steel rule using a clamp and magnets. Dunk in near-boiling water for 30-60 seconds.

 

Result:

 

In-Progress-19.jpg

 

This is for 1/48 CH-46 blades.

 

Jon

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Be sure to consult photos, not all types have the same type of droop.

That's based on rotor type and blade construction.I

Some blades arch up Before drooping.

Others, notably the Robinson don't "droop" the entire blade angles down in a straight line like it's on a hinge.

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You may also consider twisting the blades. Like propellers, helicopter rotors have approximately 18 degrees of twist and for the same reason. Washout (the official term) equalizes lift across the span of the rotor (or length of a propeller). Since the blade tip is traveling through the air faster than the root, it requires more negative twist (incidence). You’ll want to twist the leading edge of the rotor blade down at the tip. Most airplane wings also have washout (most easily seen on A/F-18s). On airplanes, it’s typically used to ensure the wing tips (and ailerons) stall last giving the pilot roll control as the airplane enters a stall. 

 

Mig

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Hi modellers,

 

My request is to get Phantoms contact information. I am an active RCAF Flight Engineer about to retire and looking for some models I've maintained or flown over my career. Also I have a model that has been damaged in my recent posting move and looking for guidance for repair or replacement and pricing. 

 

If anyone has any way to contact Shawn, please along any info you may have. Appreciate the assistance.

 

Bernie

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  • 3 weeks later...
On 10/16/2022 at 12:54 PM, JohnEB said:

Be sure to consult photos, not all types have the same type of droop.

That's based on rotor type and blade construction.I

Some blades arch up Before drooping.

Others, notably the Robinson don't "droop" the entire blade angles down in a straight line like it's on a hinge.

It's also worth knowing what type of rotor head the a/c has e.g. blades fixed to a rigid head will display very limited blade droop, if any. Similarly, CH-47 blades, especially those attached to the forward head, tend not to droop per se, as 'bend' where the blade root meets an elastomeric bearing

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