Benson Blades de un Caballero

[kolibri282]

I came across a thread where a Bensen B8 is built. In post #41 of this thread
http://giroweb.mforos.com/378414/1913637-palas-de-rotor/
one sees the inner structure of the blades. The large round apertures in the trailing edge puzzled me. Is this the standard design or did the builder alter the plans?
In this thread:
http://giroweb.mforos.com/378414/4992349-autogiro-bensen-b8-mrx-de-mariano-rodriguez/
the blades are finished (post #14). There are two things that struck me:
a) the rear part of the blades is covered by aluminum sheathing which I again feel is not standard Bensen design
b) the rear sheathing seems to overlap the leading edge cover, which creates a step right at the 25% chord. This must be unfavourable or am I missing something?

I am really looking forward to the comments by the experts in this forum

Thanks,

Juergen

 

[Minnesota_Mike]

This might help...read both in English with these links:
http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=es&tl=en&u=http%3A%2F%2Fgiroweb.mforos.com%2F378414%2F1913637-palas-de-rotor%2F&act=url

http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=es&tl=en&u=http%3A%2F%2Fgiroweb.mforos.com%2F378414%2F4992349-autogiro-bensen-b8-mrx-de-mariano-rodriguez%2F&act=url

 

[kolibri282]

Mike,

thanks for the links which, I am afraid, only solve a little bit of the puzzle since the English translation is about the same quality as my Spanish (i.e. not that great...;-). Funny enough for the first link only posts 1 through 35 and 47/48 are translated on my computer, the rest is still displayed in Spanish but reading carefully again I found this in post #37:

Las palas Bensen son huecas atras y solidas adelante donde esta el borde de ataque y en la raíz.

which seems to say clearly that the apertures in the rear of the Bensen blades are standard.
As to the use of aluminum for the rear part of the blade and the strange way of letting the trailing edge cover overlap that of the leading edge I still have no clue.

 

[walternapo]

Hola a todos soy nuevo aqui y soy de argentina, tambien soy miembro del foro que usted hace mencion, esas palas no son las bensen recubiertas, son todas de aluminio extrucionado con chapas de aluminio formando el extrados y el intrados, sin relleno, y son un desarrollo de Mariano y ocho personas mas.saludos y a sus ordenes.

Hello everyone I'm new here and I'm from Argentina, I am also a member of the forum that you mention, these blades are not coated bensen are all aluminum with aluminum extrucionado forming the extrados and intrados, unfilled, and are Mariano and development of eight people mas.saludos and their orders.

 

[kolibri282]

Walter,

thank you for the information regarding these rotor blades.
The design is obviously quite advanced, which is good news
for the team who built them but bad news for me...;-)
I am looking for information on building wooden rotor blades
which seem to be best suited for my project.

Have fun in the rotary forum, a great place for rotor heads.

Cheers,

Juergen



Walter,

gracias por la información en cuanto a estas palas de rotor.
El diseño es obviamente completamente avanzado, que es buenas noticias
para el equipo que construyó ellos, pero malas noticias para mí... ;-)
Busco informaciónes sobre la construcción de palas de rotor de madera
que parecen ser mejor adequados para mi proyecto.

Diviértase en el rotaryforum, un gran sitio para afficionados de rotor.

Salud,

Juergen

 

[phantom]

bensen blades were made with a wood leading edge and plywood skins formed the trailing, they didn't have anything inside with holes like you see in the photo and there was a tapered steel spar but no metal skin.

Norm

 

[walternapo]

Kolibry Hello: I have the plans in PDF if you let me know the shipping nesecitas my project is a bit heavy for these blades, I have a Porsche 616/13 that I put two carburetors or not big turbo

 

[J.C.Casabuono]

Juergen, they are talking of diferent blades on that thread. The blades with the holes rear of maximum thickness was an idea of Mariano that he never finished, they are not by Bensen plans, he used phenolic plywood glued and the holes were to maintain the chord balance.
Later they make the Aluminum riveted blades with solid extruded leading edge spar and sheet metal finishing. As far as I know, they are similar to the aluminum Bensen/Brock blades.

 

[EI-GYRO]

Juergen, the hardest part of building the blades is scarfing the skins to get a 10 foot
length.

If you can source 10foot lengths of aviation grade ply, it is easier. The scarf needs to
be 1 in 12 or greater.

They fly great, but not as much lift as extruded blades.

 

[kolibri282]

I have the plans in PDF

Walter, thank you for your offer but I am not so much looking for the plans. I allready
have a set including building instructions and I do not intend to build stock Bensen
blades since these are not really suited for what I have in mind (see below)

they are talking of diferent blades on that thread

Juan, thank you for this valuable clarification. I was becoming quite puzzled by the
differnet descriptions of the blades. I do not want to use aluminum for my blades
since I intend to realize collective and cyclic blade pitch by Kaman style tabs or by
using fully integrated flaps at the blade tips along the lines of design that have been
investigated by Inderjit Chopra. The main questions for me are several details in
building wooden blades:

- what brand of glue has been used by Mariano.
(phenolic glues seem to have gone a bit out of fashion)

- how did he prepare the surfaces for gluing
milling, sanding, planing and did he apply any chemicals to
the surface like e.g. Hydroxymethylated resorcinol coupling
as described in the paper below:
http://www.fpl.fs.fed.us/documnts/pdf2000/chris00b.pdf

- what pressure did he apply while the parts were curing and
how did he apply it

- how long did the blades cure and at which temperature

- most of all: did these blades ever fly or has Mariano had the
idea because he was in contact with someone who had been
building and flying wooden blades

The scarf needs to be 1 in 12 or greater.

Fergus, you are absolutely right in that a wood splice should have a decent length, with 1 in 12
probably being a good balance between strength versus time and effort. Currently I my design
envisages the use of a solid wood spar about one third of the chord and plywood sheathed ribs
for the rest to give the torsional flexibility needed for blade pitch control as outlined above. In
this design the splices could be place on top of extra wide cap strips for the ribs to reinforce the
splices from below and thus a ratio less then 1 in 12 should be sufficient.

Thanks to all for the input.

 

[J.C.Casabuono]

Juergen, lets me ask Mariano about those blades, I think that he used two layers of thick plywood, say 3/4" glued with epoxy resin, carved the profile and holed as you see.

Fortunately, he didn't try to fly with them...but probably it is not a bad idea using parallel grain veneers laminated as used in early Bells and Hillers blade spars.