lotus



previous page: 9.4.k Strategy & Tactics: Tandems
  
page up: Model Rockets FAQ
  
next page: 9.4.m Strategy & Tactics: Optimal Thrust

9.4.l Strategy & Tactics: Helicopter design




Description

This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.

9.4.l Strategy & Tactics: Helicopter design

From Tim Van Milligan:

> I've been meaning to ask for a long time, why does everyone use front-hinged
> blades? It would seem that the struggle to pull them out against the aero
> would be enough of a disincentive that people would start hinging them at the
> back instead.

It really doesn't matter where the hinge is. The basic problem with
rear-mounted hinges is strength. That is; they need to be made
stronger than front-mounted blades.

With rear mounted blades, it is likely that the model will deploy when
the rocket is moving in a forward direction. This really aids the
deployment. But when the speed is high (like when the model is arcing
over), the forces on the blades can be very significant. This may
cause them to snap off. The higher the aspect ratio, the greater the
problem. The Estes Skywinder, which I designed, solves this problem by
having a strong hinge, and flexible blades.

I've made balsa wood versions of the skywinder (see the photograph in
the Model Rocket Design and Construction book on page 87). But when
flying this model, it is really necessary to make sure it doesn't arc
over, and that the blades deploy near apogee.

As you mentioned, front mounted blades have the opposite problem. If
the model is moving forward, the blades have a struggle to open
against the airflow that is trying to hold them down. They also need
to be flown so that they don't arc over and deploy near apogee. To
solve this problem, what I like to do is have the model separate (but
still held together by a shock cord), so that it will instantly slow
down so that the blades can open when the model is traveling slower.

So basically, it depends on your own preferences. But when you design
the model, you need to make sure that it can safely deploy when it is
arcing over.

 

Continue to:















TOP
previous page: 9.4.k Strategy & Tactics: Tandems
  
page up: Model Rockets FAQ
  
next page: 9.4.m Strategy & Tactics: Optimal Thrust