Cox Engines Forum
You are not logged in! Please login or register! Guests are limited to posting in the "General Questions (Guest Posting Allowed)" section only. Becoming a member is fast, easy and FREE!


Log in

I forgot my password

Search
 
 

Display results as :
 


Rechercher Advanced Search

Latest topics
» Power-Master fuel coming home tomorrow.
by Cribbs74 Yesterday at 10:03 pm

» N.E.S.T news
by roddie Yesterday at 9:26 pm

» Sam's Early Days
by londke3 Yesterday at 8:48 pm

» Couldn't help myself.
by roddie Yesterday at 8:41 pm

» Tee Dee .09 Roddie getting ready to bench-run
by roddie Yesterday at 7:25 pm

» So, The Moon Shadow Approaches...and at last, Departs!
by rsv1cox Yesterday at 5:06 pm

» The Official "International Cox PT-19 Fly It If You Got It Day!" Thread
by Kim Yesterday at 4:13 pm

» WTS: Guillows Models(B-17G, P-38, PT-17)
by akjgardner Yesterday at 2:24 pm

» Water Cooled Cox .049
by getback Yesterday at 8:13 am

» The Great American Eclipse
by RknRusty Tue Aug 22, 2017 11:41 pm

Cox Engine of The Month
August-2017
balogh's

Throttle-Dees



PAST WINNERS
CEF Traveling Engine

Tach Race 2017 Updates
Ready for Tach Race 2017?
Profile Scale Reed Speed
Gallery


Win This Engine!
The Traveling Prop
World of Aviation

Propeller deflection.

View previous topic View next topic Go down

Propeller deflection.

Post  balogh on Sat Jun 17, 2017 12:14 pm

My 5x4 black nylon COX props permanently deflect backwards after some runtime. One would expect props to deflect forward due to the thrust forces.

The straight one on the right is brand new, the one on the left has seen some hours of runtime. (Disregard the spinner now put on the backside of the prop)



Has anyone experienced the same, and knows why the prop deflects backwards?
avatar
balogh
Diamond Member
Diamond Member

Posts : 1383
Join date : 2011-11-06
Age : 58
Location : Budapest, Hungary

View user profile

Back to top Go down

Re: Propeller deflection.

Post  Marleysky on Sat Jun 17, 2017 12:31 pm

Yes, I've had the same "deflection " occur on some , older, much older Top Flight props. I'm not an engineer, but as a kid, I thought the flex was from the prop "biting" into the air and pulling the airframe forward. I know now, from this forum, NOT to use those older nylon props, for safety reasons.
avatar
Marleysky
Diamond Member
Diamond Member

I Support My Forum

Posts : 1272
Join date : 2014-09-28
Age : 64
Location : Grand Rapids, MI

View user profile

Back to top Go down

Re: Propeller deflection.

Post  balogh on Sat Jun 17, 2017 1:02 pm

Thanks. Otherwise these are my favorits on 049 size COX engines and they have never snapped. Unlike the black 5x3 props that once were on the market with visible micro cracks building on the blades and snapping if bent a little by hand.
avatar
balogh
Diamond Member
Diamond Member

Posts : 1383
Join date : 2011-11-06
Age : 58
Location : Budapest, Hungary

View user profile

Back to top Go down

Re: Propeller deflection.

Post  roddie on Sat Jun 17, 2017 2:14 pm

I've seen this too. It may be due to shrinkage.. which I think would tend to "pull'' the blades in the direction of their twist.. rather than the opposite.

Here's a pair of Cox black 6 x 2 L/H's... The one on top is NOS.. and the one on the bottom is well-used and shows this deflection.



The backward-deflection probably corrects itself somewhat when running at speed on an engine. A straight (new) prop likely deflects forward.. when grabbing air.. especially the more flexible sport-props.

avatar
roddie
Top Poster
Top Poster

Posts : 5018
Join date : 2013-07-17
Age : 57
Location : N. Smithfield, Rhode Island

View user profile http://www.stilburnin.com

Back to top Go down

Re: Propeller deflection.

Post  Surfer_kris on Sat Jun 17, 2017 2:19 pm

I have used a Cox 5x4 prop on a Norvel .061RC, but one can visibly see the plane slowing down after a extended full throttle run, the engine loves it though...

Afterwards the prop is visibly bent forward. Never seen one bent backwards, perhaps after a rough landing in tall grass?

avatar
Surfer_kris
Diamond Member
Diamond Member

Posts : 1275
Join date : 2010-11-20
Location : Sweden

View user profile

Back to top Go down

Re: Propeller deflection.

Post  pkrankow on Sat Jun 17, 2017 4:48 pm

Carefully examine those for pitch. I have a hypothesis that they have permanently lost pitch so when relaxed the prop has a different shape.

Yes, a few bad landings will make a different thing happen that causes that shape. Good supple nylon props can take it to a certain extent..

Phil

avatar
pkrankow
Diamond Member
Diamond Member

Posts : 2869
Join date : 2012-10-02
Location : Ohio

View user profile

Back to top Go down

Re: Propeller deflection.

Post  batjac on Sat Jun 17, 2017 5:23 pm

I was just looking at this on a yellow Cox rubber ducky 5x3 last week. I've noticed it on several Cox props.

The Quack Mark
avatar
batjac
Diamond Member
Diamond Member

Posts : 1398
Join date : 2013-05-22
Age : 54
Location : Portland, OR, USA

View user profile

Back to top Go down

Re: Propeller deflection.

Post  getback on Sat Jun 17, 2017 7:30 pm

I don't know about grabbing the air but; have seen this and as the RRRss get up they straighten out and also flex back as the RRRs slow ,,,, i figure its a good flexible prop and don't consider it dangerous >> if they're not damaged or old. Huh...
avatar
getback
Top Poster
Top Poster

Posts : 4121
Join date : 2013-01-18
Age : 60
Location : julian, n.c.

View user profile

Back to top Go down

Re: Propeller deflection.

Post  NEW222 on Sun Jun 18, 2017 3:37 pm

Funny post. I have had a couple propellers like this myself as well and was just thinking that it was caused by the way they were stored. I never thought or looked into a logical reason why.
avatar
NEW222
Platinum Member
Platinum Member

Posts : 1046
Join date : 2011-08-13
Age : 38
Location : oakbank, mb

View user profile

Back to top Go down

Re: Propeller deflection.

Post  GallopingGhostler on Sun Jun 18, 2017 8:07 pm

The heavier mass of the prop is in the leading edge versus the trailing edge. One may want to take a caliper and measure the hub front lengthwise along the prop blade axis and perpendicular to the prop blade axis. I'm thinking that the hub may be stretching from the centrifugal blade loading. If not the hub, might be the root portion of blade that is undergoing plastic deformation (permanent stretching). It would not surprise me that you may have a slight change in prop pitch as a result, too. Fiber reinforced props would have less tendency to do this, IMO.
avatar
GallopingGhostler
Platinum Member
Platinum Member

Posts : 1155
Join date : 2013-07-13
Location : Clovis, NM, US

View user profile http://cmaswr2.org/NM/BLACKWATERDRAWGOSPELRIDERS

Back to top Go down

Re: Propeller deflection.

Post  Cribbs74 on Sun Jun 18, 2017 10:01 pm

Yep, they do that.

Cox props are not really the best props available. The grey competition ones are OK, they hold thier pitch anyway. APC are probably the best performing props for 1/2A that I have come across.

I will say that those Cox flexy props can handle a ton of abuse and they do what they are designed to do.
avatar
Cribbs74
Moderator

Trusted Seller
Posts : 9423
Join date : 2011-10-24
Age : 43
Location : Tuttle, OK

View user profile

Back to top Go down

Re: Propeller deflection.

Post  GallopingGhostler on Sun Jun 18, 2017 10:26 pm

Cribbs74 wrote:I will say that those Cox flexy props can handle a ton of abuse and they do what they are designed to do.

You certainly have an understatement there, Ron. I learned that lesson back in the 1970's. I was a fan of Top Flite white nylon props on my .020 and .049 reedies because of their cost effectiveness and durability. I tried the gray Cox competition props. Problem I ran into is they were brittle enough, that a less than perfect landing broke a prop blade. Ditto with wood props. Both were more expensive.

Most the time I'd clean the grass stains off the nylon prop and continue flying. The worst that could happen to a nylon prop was a set of nicked tips from ground strikes. That evening I could trim the blade tips, rebalance and continue flying.

It is really unnerving to run out of props because of the high rate of breakage. Sport flying is supposed to be fun, and that I had with the more durable nylon props.
avatar
GallopingGhostler
Platinum Member
Platinum Member

Posts : 1155
Join date : 2013-07-13
Location : Clovis, NM, US

View user profile http://cmaswr2.org/NM/BLACKWATERDRAWGOSPELRIDERS

Back to top Go down

Re: Propeller deflection.

Post  Sponsored content


Sponsored content


Back to top Go down

View previous topic View next topic Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum