Rotor Spool speeds

scooter2525

Very well Member
Our room at the hospital is next to the helipad so I get to watch the Bell 407 do its thing. From the moment the starter switch is selected to when it is ready for take off, how long does that take? Why does it seem the rotors take so long to spool? Are helicopter engines directly connected to the rotor or are they like a PT6?
 

mikecweb

Well-Known Member
I'll give way to the weedwacker pilots but I know some of them can utilize a rotor brake to keep the engine running while not spinning the rotor.
 

SpiraMirabilis

Possible Subversive
The engine for the 407, an allison is a reverse flow free turbine like the PT6. It shouldn't take very long to spool up at all, I imagine the pilot is just doing checklists prior to departure.
 

scooter2525

Very well Member
The engine for the 407, an allison is a reverse flow free turbine like the PT6. It shouldn't take very long to spool up at all, I imagine the pilot is just doing checklists prior to departure.
It seemed to take a few minutes to go from initial rotor rotation to sounding like ready-for-take-off-power now...
 

jdlilfan

Well-Known Member
Maybe a minute or two to come up to ground idle. Shot in the dark, but I think they have to stabilize temps within the engine and oil temp within the gearbox/transmission. After time and temps, I assume they go to flight idle- "ready to go power" and place a load on the engine/transmission. This is why they sit for a few minutes with engines running.

Same with shutting down. I believe they have to run 1-2 minutes at idle (no load) before shutting down.
 

MikeFavinger

Hubschrauber Flieger
When the engines first start, the (throttle, power levers, condition levers, etc) are set in some sort of idle position. This gets the engines started and maintains the rotor speed below 50%. Depending on the helicopter, it will stay in idle until certain checks are done and then the throttle (levers, etc) are positioned full open and the rotor accelerates to 100%. This is what it sounds like you are hearing.

A Bell 206/406 doesn't take very long to get from start to fly, but other helicopters take a lot longer due to expensive ground checks.

The engine(s) are directly connected to the rotor, and as MikeC mentioned, some helicopters do have rotor brake where the rotors are mechanically held in place while the engine is running which is made possible by some sort of clutch mechanism.
 

USMCmech

Well-Known Member
Our room at the hospital is next to the helipad so I get to watch the Bell 407 do its thing. From the moment the starter switch is selected to when it is ready for take off, how long does that take? Why does it seem the rotors take so long to spool? Are helicopter engines directly connected to the rotor or are they like a PT6?
Some like the orrigional UH-1 are direct drive, but most are free turbines.

Virtually all of the free turbine designs have a rotor brake. This is a brake just like a car's wheel brake that stops the rotor from turning while the engine is still running.

The ususal procedure is

Rotor brake engaged
Engine(s) start
Load patient/passengers
Disengage rotor brake and spin up rotors
 

MikeFavinger

Hubschrauber Flieger
Extensive or expensive? :) What kind of ground checks?
Whoops! I guess it could be expensive if they were done wrong! :)

It's been too many years since I flew a 206 so I can't remember what you have to do in them. In my aircraft, most checks occur before engine start and after the rotors are at 100%. In the time between all I have to do is check the systems and flip a switch for our back up hydraulic pump. Doesn't take long at all. Before engine start we have to do some normal stuff like set switches and check flight controls, check avionics, turn on the APU and APU generator, and also some 60 specific stuff like check our stabilator. After 100% rotor we have to do some hydraulics checks, engine checks, and hover checks, as well as turn off the APU.
 

scooter2525

Very well Member
Whoops! I guess it could be expensive if they were done wrong! :)

It's been too many years since I flew a 206 so I can't remember what you have to do in them. In my aircraft, most checks occur before engine start and after the rotors are at 100%. In the time between all I have to do is check the systems and flip a switch for our back up hydraulic pump. Doesn't take long at all. Before engine start we have to do some normal stuff like set switches and check flight controls, check avionics, and also some 60 specific stuff like check our stabilator. After 100% rotor we have to do some hydraulics checks, engine checks, and hover checks.
Gotcha. So much different then the Baron we flew, but I was curious if because of the complexity of the aircraft the checks would more extensive.
 

MikeFavinger

Hubschrauber Flieger
Gotcha. So much different then the Baron we flew, but I was curious if because of the complexity of the aircraft the checks would more extensive.
Some definitely are - for example, our hydraulic and flight controls checks take 12 memorized steps. The initial circuit breakers and switches set up takes 19 steps. The cargo hook check takes a bunch and the engine checks are pretty extensive as well. I do miss the days of just cranking and going in a Baron!
 

badtransam97

Well-Known Member
We usually have around a 2-5min lift time from the time we are dispatched on a call. It can depend a lot on wx, day or night, and speed of the crew getting their garb and getting going. We fly B3 AStars and it's a pretty quick start. Flip the starter switch and watch the FADEC do it's magic. Usually about 1 minute from switch flip to idle. We usually preflight beginning of the shift, that way we can do a quick walk around and go.
 

The Fez

Aftplay Advocate
So for an EMS operator, how long for a 206 type aircraft to go from no pre flight to departure?
A turbine helicopter with ground power that has already been "cocked" (pre-flight inspection, pre-flight checklists, Nav systems spun-up on aircraft like the 60, hover checked, etc) can be started and off the ground in less than 5 minutes easily.
 

MikeD

Administrator
Staff member
We usually have around a 2-5min lift time from the time we are dispatched on a call. It can depend a lot on wx, day or night, and speed of the crew getting their garb and getting going. We fly B3 AStars and it's a pretty quick start. Flip the starter switch and watch the FADEC do it's magic. Usually about 1 minute from switch flip to idle. We usually preflight beginning of the shift, that way we can do a quick walk around and go.
B3 or 2B1, as mentioned, are quick with the FADEC and single switch flip. B2 is a little bit longer, but not much.

H-60.......just a ton of checklist crap that makes for a good while. 5-8 minutes if cocked......as TheFez mentioned.......is pretty quick. Much longer from a cold start.
 

The Fez

Aftplay Advocate
B3 or 2B1, as mentioned, are quick with the FADEC and single switch flip. B2 is a little bit longer, but not much.

H-60.......just a ton of checklist crap that makes for a good while. 5-8 minutes if cocked......as TheFez mentioned.......is pretty quick. Much longer from a cold start.
Cold weather control exercise anyone?! I'm glad it doesn't get cold enough at DMA to have to go through that arse pain.

On the way back from Hollister, Thad and I went from a dead aircraft to pulling pitch at PSP in 3 minutes. I was impressed.
 
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