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Re: 748 Queries
Posted: 23 Mar 2013, 20:19
by Viscount Cornbank
The rasping is caused by the sudden air resistance as the propellers move into the constant speeding range, 10500-11500 RPM, dependant on mark, and into the flight fine range and there is a momentary pause or even reduction of rpm despite the power increase. Generally the bigger the propeller diameter the more pronounced the rasping sound. Depending on the pilots technique you could hear as many as three separate power bursts and rasps before the engine and propeller harmonised at take-off RPM.
[EDIT]
Keith;
The fine pitch stop setting was at 25' blade angle approx on Viscount 810's, plus the additional cruise or high stop at 38' ish
The difference in prop diameter is well illustrated by comparison to the lock settings on the FH-227B; 16' and 28' respectively
Happy days
cheers
Fraser
Re: 748 Queries
Posted: 23 Mar 2013, 22:20
by Tomliner
Thanks for that explanation Fraser.The reduction in rpm that you mention is clearly audible in the Vanguard sounds.
EricT
Re: 748 Queries
Posted: 24 Mar 2013, 10:10
by Dev One
Thanks Fraser, you saved me rummaging in the garage!!!
As you say Happy days!
Keith
Re: 748 Queries
Posted: 30 Mar 2013, 17:59
by Motormouse
Viscount Cornbank wrote:The rasping is caused by the sudden air resistance as the propellers move into the constant speeding range, 10500-11500 RPM, dependant on mark, and into the flight fine range and there is a momentary pause or even reduction of rpm despite the power increase. Generally the bigger the propeller diameter the more pronounced the rasping sound. Depending on the pilots technique you could hear as many as three separate power bursts and rasps before the engine and propeller harmonised at take-off RPM.
[EDIT]
Keith;
The fine pitch stop setting was at 25' blade angle approx on Viscount 810's, plus the additional cruise or high stop at 38' ish
The difference in prop diameter is well illustrated by comparison to the lock settings on the FH-227B; 16' and 28' respectively
Happy days
cheers
Fraser
16 and 32 degrees on the Fokker 27's I worked on.
Different prop again.
Ttfn
Pete
Re: 748 Queries
Posted: 30 Mar 2013, 19:14
by NigelC
Whose F-27s did you work on Pete?
Re: 748 Queries
Posted: 31 Mar 2013, 14:30
by Motormouse
Company I worked for at the time, not AirUK or JEA! PH-FFF,PH-FGE, & PH-FEY.
There's a paint for one of them in the VA Fokker 27 thread in the members section of forum.
Aeroplanes were ex Icelandic with full power rated Dart 7's, unlike UK registered ones which had
derated ones.
Ttfn
Pete