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Wrong way round prop

Old 19th Feb 2018, 12:05
  #21 (permalink)  
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DaveRUK
Thanks for your input. I totally agree that the AB book may have some unintentional errors, bearing in mind that many Fleet Air Arm records were destroyed during the early 1950's. I just looked either side of the "possibly destroyed" aircraft to get an idea as to when they had been built and reckoned that the construction dates of some of the "possible" aircraft were post 4/5 May. X9558 was one of my suspect aircraft....
It would be nice if there was a Saunders-Roe archive somewhere!
Atb
Andy
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Old 19th Feb 2018, 13:40
  #22 (permalink)  
 
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Originally Posted by PDR1 View Post
Ahem...no!

If you install a prop back-to-front you here a prop still thrusts in the same direction, just less efficiently. If you had one "normal" and one "reverse" prop installed you'd get about 25% net thrust, and a walrus would barely get to a fast trot with that sort of thrust.

PDR
Ahem er . .
If half the pair of props was right and the other half wrong you might have a case that the reversed one only delivered half normal thrust so 75% of expected net thrust would be more like it.
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Old 19th Feb 2018, 14:03
  #23 (permalink)  
 
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True, but that isn't what was suggested. The post I was responding to suggested that it was probably one RH-rotation prop and one LH-rotation prop, with the latter therefore rotating "backwards". In this situation the RH prop would develop full thrust while the other would develop ~50% thrust in the opposite direction, giving a total of 25% of the *expected* thrust.

If you had two identical RH props with one being fitted backwards then your total thrust would be in the region of ~75% of the expected value (for any given throttle setting), but while I suspect that may be what actually happened it wasn't the scenario I was responding to.

OTOH if you had one RH prop fitted correctly, and a LH prop fitted back-to-front (so that it could rotate "forwards") bothg props would produce 100% of the expected thrust but in opposite directions, giving a net thrust of zero*

PDR

* Except that they wouldn't - the rearmost prop would probably produce slightly less thrust due to operating in the wash of the prop in front of it (the amount of reduction depending largely on the rotational speed and the solidity of the props) so there would be a (very) small net positive thrust
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Old 19th Feb 2018, 14:48
  #24 (permalink)  
 
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PRD1
That post you were responding to was so confused it seems to have confused me as well. Once it introduced the total red herring of fitting a Tractor prop to a Pusher installation I more or less gave up, as what this started from was simple incorrect assembly of correct props.
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Old 19th Feb 2018, 15:35
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Well indeed. But I think I got what he was saying, in which case my response was correct. But it's possible that I didn't get what he was saying, in which case my response was incorrect. I think.

Nurse - I think it's past time for my blue pill...

PDR
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Old 19th Feb 2018, 16:00
  #26 (permalink)  
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Wrong way round prop

Taken from my original source:
"It was later found that one half of the four-bladed propeller had been assembled in reverse and was unnoticed at final inspection"
Does that make it any clearer....
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Old 19th Feb 2018, 16:23
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As I told before it IS confusing. Not only because of tractor and pusher engines, with pushers that are Yes or not modified to run in an opposite direction, with "normal" and pusher props. Add to it that English engines run the "wrong" direction as opposed to US types and we have a Babylonian confusion!

But OK having half of the blades installed wrong, is quite an achievement from Murphy... AND no one noticed....
Luckily we are some 75 years further and comparable mistakes like this are not made any more
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Old 19th Feb 2018, 16:58
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You might like to read this......
Variable Pitch at the Cradle of Aviation Museum
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Old 19th Feb 2018, 16:59
  #29 (permalink)  
 
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Regretably as late as the 1980s someone still managed to fit a helicopter individual tail rotor blade the wrong way round, so the trailing edge was wrongly facing the rotational airflow. The remaining blades were fortunately the right way round. The pilots were alert to the extra vibration during ground taxi before getting airborne and it didn't lead to disaster (I think). All it needed at design phase was different retaining bolt diameters; rather than the ineffective outboard/inboard label. Murphy's Law.
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Old 19th Feb 2018, 17:40
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This crash took place at the Saunders-Roe flying ground near Chertsey, Surrey on the 1st July 1942.
New one on me.....
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Old 19th Feb 2018, 18:26
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Originally Posted by Planemike View Post
New one on me.....
SARO had a factory on what is now Weybridge Trading Estate/Business Park and flew completed aircraft from nearby Chertsey Meads.

Chertsey Meads - UK Airfield Guide
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Old 9th Mar 2018, 02:11
  #32 (permalink)  
 
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CFM Shadow

During my short time as a Microlight Inspector I was asked to do the annual on a Shadow microlight.
Airframe checked, now for the engine. A pusher 2 stroke with a multi bladed prop.
I cracked up laughing and had to walk away, thinking this is a send up!
Was it a test on me? Very tempted to ask the owner to taxy it for but he might overheat the motor. Yep, all the blades on backwards! He assured me it flew alright!
Had a look round his hangar, no clue so asked to see the actual prop he had been using. Then he produced the unapproved one he had been using with all the moans about the approved prop being poor etc.
Oh dear.
SFD
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