Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
How Does A Constant Speed Prop Work  
User currently offlineDesertJets From United States of America, joined Feb 2000, 7906 posts, RR: 14
Posted (15 years 3 months 3 weeks 6 days 18 hours ago) and read 25520 times:

Simple enough, how do they work, especially compared to the "adjustable" props that were available on early Beech Bonanzas.

Stop drop and roll will not save you in hell. --- seen on a church marque in rural Virginia
4 replies: All unread, jump to last
User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 1, posted (15 years 3 months 3 weeks 6 days 18 hours ago) and read 25493 times:

Governors. Old fashioned governors as seen on 19th century steam engines!

Enhanced by modern oil pressure systems and spring technologies of course.

Even the old Bonanza had a constant speed prop.

Depending on the engine type, oil pressure in the propeller dome is usually pitted against spring pressure working to move the propeller pitch in the opposite direction. On most piston driven single engine installations, the spring drives the propeller to fine pitch with oil pressure used to send it to coarse pitch.

On multi-engine and turbine powered propellers, the reverse is true, the spring tends to send the propeller to coarse pitch to the point of feather (necessary on a multi-engine aircraft to minimize drag if the engine fails) while oil pressure is used to send the prop to fine pitch and even reverse pitch, depending on the engine.

Once the pitch is established, then your question comes into importance. The governor will sense any increase or decrease in propeller RPM. Let's just use the multi/turbine propeller installation for simplicity.

As turboprop prop speed increases (momentarily for any reason), the governor senses the increase and restricts oil pressure to the prop hub. Restricting oil pressure causes an increase in prop pitch which in turn increases prop drag which slows the prop down. Remember that if the oil pressure is reduced, the spring tries to force the prop into coarser pitch. Conversely, if the prop RPM decreases (momentarily for any reason), then the governor increases oil pressure to the hub, driving the prop into finer pitch, decreasing prop drag which of course allows the prop to go faster.

The governor(s) work full time. The changes in oil pressure are miniscule but continuous. This is how the RPM is maintained at a constant.

Hope that answers some of your question!

Best Regards,


User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 27
Reply 2, posted (15 years 3 months 3 weeks 6 days 18 hours ago) and read 25485 times:

The variable incidence proppellers are controlled by a prop govener.

As propeller rpm increase the prop govener adjusts the blade angle by way of varying oil pressure in the prop hub to maintain a given RPM.

The prop govener contains flyweights and a valve that controll the entrance of engine oil into the propeller hub.

As engine RPM increases the flyweights swing out causing the valve to open increasing oil pressure in the prop hub driving the blades to a course pitch which in turns slows the engine down to maintain the set rpm. The same applies for a decreasing RPM.

Therefore as manifold pressure is increased rpm stays the same.

The reason piston aircraft don't feather after shutdown with a loss of oil pressure is because the prop govener is equipped with a feather lock preventing the blades from going to feather. A blade in feather is much harder to turn during starting due to air resistance. When the engine drops below 950 RPM the feather lock engages.

After the loss of an engine in flight the engine must be feathered immediately (before 950RPM) or the feather lock will engage preventing feathering.

If I remeber correctly the Beach props you actually had to loosen and adjust between a climb prop and a cruise prop which was fixed in flight.


User currently offlineCrjmech From United States of America, joined Jun 2000, 260 posts, RR: 1
Reply 3, posted (15 years 3 months 3 weeks 6 days 17 hours ago) and read 25477 times:

A couple of pretty good descriptions there! I just wanted to add to the forces utilized to change blade pitch. CTM (centrifugal twisting moment) will cause the heaviest part of the blade, the leading edge, to move inline with the plane of rotation. This serves to decrease blade angle. Counterweights on the blade roots are also used to change pitch. Most counterweights will tend to move the blades to high pitch.

Thou shalt mind thine altitude,lest the ground reach up and smite thee.
User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 4, posted (15 years 3 months 3 weeks 6 days 12 hours ago) and read 25446 times:

>>>Governors. Old fashioned governors as seen on 19th century steam engines! -Buff

Just a side note. Aircraft governor work on the same principle as other governor applications (marine diesels, lawn mowers, generators, et al): flyweights, but they regulate RPM in a different manner. Aircraft governor applications effectively change the load (wrt rotational drag) to maintain RPM with a constant throttle setting as the aircraft climbs or descends, while a marine diesel (or most any other type) governor varies the throttle position to adapt to a varying load and keep a constant RPM.

It's not much of a difference, but the concept is important. In an aircraft powerplant, it has been compared to having a infinitely variable transmission.


Top Of Page
Forum Index

Reply To This Topic How Does A Constant Speed Prop Work
No username? Sign up now!

Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)

Similar topics:More similar topics...
Constant Speed Prop Ops posted Sun Apr 2 2006 00:44:08 by Corey07850
How Does The Sewage System Work? posted Wed Jun 20 2001 04:07:39 by United Airline
GEnx Bleedless How Does ECS Work? posted Thu Apr 27 2006 01:14:40 by MesaMXORD
Air Tahiti Nui- How Does This Work? posted Tue Oct 11 2005 19:19:27 by Mirrodie
How Does An ILS Work? posted Fri Jul 1 2005 22:22:51 by Palladium
Tcas - How Does It Work? posted Sat Jan 15 2005 12:25:37 by Geoffm
Prop Condensation - How Does It All Start? posted Wed Oct 13 2004 06:43:51 by INNflight
How Does An Afterburner Work? posted Tue Aug 24 2004 18:13:52 by Dancerrada
How Does The Tcas Work? posted Mon Feb 2 2004 13:41:31 by Sfilipowicz
Beta On Propeller Aircraft...how Does It Work? posted Wed Nov 12 2003 08:59:37 by USAFHummer

Sponsor Message:
Printer friendly format