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DHC-6 Questions:

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DHC-6 Questions:

Old 25th Apr 2010, 23:27
  #21 (permalink)  
 
Join Date: Mar 2010
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Yes there is a published...

limit for tq in feather. It is ten pounds and it is to prevent bending the propeller blades. Says so. Try reading your SBs, because I think it is there also but I don't have it in front of me at the moment. I do have an "old book", but it is for a 300, but itĎs not in front of me either.

You do not get 51% +1-0 until you take it out of feather or its rigged wrong. I don't like sending oil pressure to change the propeller pitch until the engine is at least stabilized after start. I prefer all that oil pressure for the engine and gearbox during start.

However I don't do this anymore and I would have to refer down to ops or maint for any changes. I do appreciate your info.
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Old 26th Apr 2010, 00:23
  #22 (permalink)  
 
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Uh, thanks for your 'Word in God's Ear', as the German language saying goes.

I think you might be referring to something that may have been published 30 or 40 years ago in the TABs (Technical Advisory Bulletins), which were a DH specific predecessor to Service Information Letters. Those documents are informal. They are not controlled, nor is a revision service (in the sense of how SBs and ADs are revised) provided.

The AFM, on the other hand, is formal, it is the only document related to the aircraft that is approved by both the regulatory authority of the State of manufacture and the regulatory authority of the State of registration.

The propeller governor has its own oil pump, therefore, there is no pressure loss when oil is routed to the propeller. There is a decrease in the volume of oil, but this is of no consequence during the start process, because all of the oil should be back in the tank at the beginning of engine start.

I assure you, there is no limitation on torque when in feather published in the AFM.

I disagree with your comment about not getting idle on the governing fuel flow prior to taking it out of feather. Many (but not all) of the PT6A-27 engines installed on the Twin Otter will idle on minimum flow at ISA pressure altitude until the propeller is taken out of feather. This is an unintended consequence of Py air being bled at the Nf governor when the propeller is feathered. But, not all engines have this characteristic, nor is this characteristic by design.

Michael
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Old 26th Apr 2010, 19:08
  #23 (permalink)  
 
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All this technical talk is killing my ears!

Hej guys, I have seen a Twin Otter flown in almost every condition imaginable... Dhc-6 300 full flap t/o in 50 knots of wind, empty on both floats, wheels, and also skis. If the rnwy is short, land with full flaps and c/l max, if you run out of rudder use differential power to straighten the nose with centerline... I have had success with that method on floats, and wheels... with skis I always landed into wind if I could. Don't touch the tiller bar until you are finished flying the aircraft... I once saw an RCMP Twin Otter go all over the rnwy after touchdown because the pilot started to play with the tiller too early in a heavy crosswind - he went right off the rnwy and "staition 60'd" the nose gear. On floats, normally pitch locks are installed to keep the props in fine pitch so you have immediate thrust available after engine start... Use the doors and keep them closed... I once had to ferry a machine back to base empty because one of the engineers took the copilot's door off to repair something and another guy thought it needed to go in for maintenance and stuck it on the next flight out... not sure if there was as supplement for that .... but it sure was noisy and drafty. If you have good skills you can use the Otter like the work horse it is... if you don't and you start to push the limits, you can get yourself into trouble very quickly...
Fly safe brethern... and enjoy the Otter!
6to8
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Old 26th Apr 2010, 21:49
  #24 (permalink)  
 
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Thanks again V1....unfortunately

Iím afraid this German colloquialism went completely over my head. I have no idea what it means.
Thanks for the info. Itís certainly worth considering. We ordered new manuals from Bombardier, Pratt, and, Hartzell in 2001. Along with all the technical publications available, we also ordered and maintain subscriptions and revisions for the manuals, SBís, SIís ect.. Among the Component Overhaul Manuals were the Technical Advisory Bulletins, (TABS). If information were published and has not been amended, superseded, or deleted, then it is applicable IMO. With this and other manufacturerís published information in mind, I amended the AFM to include limits I deem in the interest of safety, or, otherwise in our instituteís interest. We have made several other changes or additions to the AFM as well. Just as we do the Maintenance program as may be applicable.
As always, I appreciate your insight.
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Old 27th Apr 2010, 11:08
  #25 (permalink)  
 
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Guys, trust me on this one (fer' Pete's sake, I'm the person who writes the AFM): There is no published limitation for torque when the propeller is feathered.

Plain old COMMON SENSE suggests that you don't want to apply more power to a feathered propeller that you would need to achieve idle +15%. Let that be your guide.

Michael
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Old 27th Apr 2010, 12:04
  #26 (permalink)  
 
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Well I was thinking....

that if Viking has the legal authority to amend, revise, or, delete the AFM and Maintenance Manuals for the DHC6-300 Twin Otter built by deHavilland, then it would seem plausible to me that Viking can publish those amendments, revisions, and, deletions.
If they have, then I'm sure we have them on file. If we have them on file then they are being adhered too. Making all this redundant. As I said before, I'm no longer directly involved with Operations and Maintenance. However I am curious as to why anyone would find it necessary or convenient to apply so much force against flat paddles spinning near their heads.
We alter our airframes extensively and have several configured alterations for the Twin Otter so Iíll see if I can bother our engineering department with the question. Thanks again V1.
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Old 27th Apr 2010, 18:10
  #27 (permalink)  
 
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Originally Posted by Spadhampton
...if Viking has the legal authority to amend, revise, or, delete the AFM and Maintenance Manuals for the DHC6-300 Twin Otter built by deHavilland, then it would seem plausible to me that Viking can publish those amendments, revisions, and, deletions.
Viking holds the Type Certificates for the DHC-1 through DH-7 aircraft - Viking took over responsibility for these TCs from Bombardier in 2005, and has been publishing all the documents (AFMs, MX manuals, etc.) for these aircraft since then.

Michael
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Old 27th Apr 2010, 21:27
  #28 (permalink)  
 
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Thanks V1....

...but yes I know this already.
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Old 28th Apr 2010, 09:40
  #29 (permalink)  
 
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Thought the best Angle of climb (altitude gain per unit ground distance) was 87 kts.
so Its not "rate of climb'' we should be talking about.
Vx is always lower than Vy and Climbing at Vy allows pilots to maximize the altitude gain per unit time.
So for obstacle clearance Vx would always be the the speed we concerned with....

Back to the bunker...fire away
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Old 28th Apr 2010, 23:53
  #30 (permalink)  
 
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Originally Posted by tickler
...So for obstacle clearance Vx would always be the the speed we concerned with....
See the elaboration of that in my post (above) of 26th May 2008, 11:30.

Michael
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Old 3rd May 2010, 09:57
  #31 (permalink)  
 
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With the prop gov having its own pump, is there a reason to start in feather rather than full fine all the time?

Our twin otters operate in a tropical environment and also idle in feather at about 48% Ng and require full fine for ballpark 52% Ng.
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Old 3rd May 2010, 11:36
  #32 (permalink)  
 
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Engine start in fine pitch

Smitty, we used to start up with the props in fine pitch only because pitch locks were installed and it was used to bring immediate thrust up while on floats. You don't want to have foward lurch on a closely parked dock when you bring the prop out of feather....
Others may know more.... I just drove the "Dienst Pferd" (Work Horse)!
Cheers
6to8
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Old 3rd May 2010, 11:50
  #33 (permalink)  
 
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The prop gov has it's own pump....

It don't start pumping till the engine starts turning.....and the "pump's" speed, (thus it's efficiency), is directly related to engine speed up to idle.
Think about that for a second or two.

PT6A-27 48% NG idle in feather, with 52% NG in full fine sounds quite normal to me and that is what they taught at Flight Saftey. It is what is in the book also, (unless it has been changed recently).
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Old 5th May 2010, 01:13
  #34 (permalink)  
 
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I'm not trying to hijack this thread, but I've posted this question elsewhere with little luck. This thread is obviously active with folks that know there away around a Twin Otter.

I'm looking for operating costs for a Twin Otter on amphibs (300 series with -27 engines). Salt water ops.

Real world hourly operating costs would be very helpful! Any advice for someone looking to purchase and operate one (I know this last question is vague)? Part 135. I'm trying to run the numbers as a very early start to a business plan.

Thanks in advance!
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Old 6th May 2010, 20:46
  #35 (permalink)  
 
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Twin Otter Inprovements

Would love to see the exhaust system on the DHC-6 400 improved or modified not to blow directly over the leading edge of the wing. Creates lots of mess and heat and in time corrosion. Maybe a Dash 7 design would be better. Also landing lights should be positioned on outside of the wing fence to get away from the exhaust gasses. Pilot's seat needs better leg support, just not long enough. On long trips, ferries etc very uncomfortable. And hopfully those dreadful fuel pumps will be more reliable... Just a thought.
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Old 6th May 2010, 22:42
  #36 (permalink)  
 
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Reebs

Very Good Ideas and not to difficult to bring about either. As well, I for one would like to be able to order new Twotters with any of the old deHavilland modifications, such as the camera bay, wing hard points, and, 250 amp electrical system. Even a higher amperage electrical system than 250A would be more desirable. It would also be nice if the fuel tanks were integral rather than bladder.
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Old 6th May 2010, 23:00
  #37 (permalink)  
 
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New Twin Otters CAN be ordered with any of the previously available de Havilland special purpose modifications (cameras, scientific survey, etc.).

Why anyone would want bigger generators is beyond me. The Series 400 aircraft only consumes about 50 amps of power with all avionics working, and it already has two 200 amp generators installed. One generator alone is more than sufficient to support every electrical load operating at the same time, including full de-ice with the heated windshield, hot props, every single light bulb in the aircraft turned on, etc.

The new avionics in the aircraft draw far, far less power than the old avionics, and all of the lighting (excepting the two wing inspection lights) is either LED or high intensity xenon discharge.

Michael
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Old 7th May 2010, 18:21
  #38 (permalink)  
 
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V1

Research aircraft Michael. To power more research payload. More power available, means a more valuable aircraft. NOAA, NSF, NRL, British Arctic Survey etc..

NSF recently bought a new G-5 with 30 million in added structural modifications to add to their research aircraft fleet. How many Twin Otters is that? For low altitude research, slow airspeed means higher particle resolution. The Twin Otter has proven itself extremely valuable in terms of payload utility, reliability, and, operational cost efficiency, though a little lacking in mission endurance or loiter time.

More wattage available means more science equipment. More science equipment means more missions. More missions means MO MONEY.

We all know what mo money means.
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Old 7th May 2010, 18:58
  #39 (permalink)  
 
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Well, there are 350 amps of additional (surplus to needs) electrical power available now on every Series 400 aircraft produced. If a customer needs more power than that (perhaps they plan to run an electric-arc blast furnace installation in flight) , we can provide higher amperage generators, because this is consistent with what I said earlier: All of the "special options" that de Havilland ever offered - this includes additional electrical capacity - are available from Viking on new build aircraft.

Seriously, though, electrical power needs on aircraft (of all types) to run comparable types of equipment have been steadily declining over the past 30 years. My guess is that an aircraft fitted with survey, photographic, or research equipment today would require far less electrical power than an aircraft fitted with similar capability equipment 30 years ago.

Michael
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Old 7th May 2010, 22:02
  #40 (permalink)  
 
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V1.....

The more power the better Michael.
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