News: Added Links For Twin Commander and Facebook Pages

Login  |  Register

Author Topic: Jetprop Environmental Systems-- Sundstrand  (Read 13934 times)

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3260
Jetprop Environmental Systems-- Sundstrand
« on: October 20, 2015, 11:31:25 pm »
I have the Sundstrand ECU in my 980 (which was the original ECU design from the factory), along with a Keith freon air conditioner. I think it's the best system available for the Jetprop Commanders (840/980/900/1000).

The Sundstrand got a terrible reputation when new for early failures. However, the recommendation for checking the oil was something ridiculous, like every 300 hours.

Per Bob Mays' recommendations, I check the oil (add, really, since that's all you can do) every 25 hours, and change it completely every 300 hours. Furthermore, there is a service bulletin from the 1980s which adds some ducting to give the unit additional cooling.

Finally, never, ever, ever, use the MAX FLOW switch. It's fine to use it in a 690/A/B, or an enviro-equipped Jetprop, but not with a Sundstrand.

Adam Frisch

  • Administrator
  • Hero Member
  • *****
  • Posts: 1673
    • Adam Frisch FSF
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #1 on: June 17, 2017, 08:54:24 am »
Why is it not good to use MAX FLOW on a Sundstrand?
Slumming it in the turboprop world - so you don't have to.

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3260
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #2 on: June 17, 2017, 12:28:56 pm »
There are a couple of reasons. First of all, Twin Commander did a poor job in labeling the switch. The 690s also have a switch labelled "Max Flow" and it's fine to use it-- in fact, on a 690 with a leaky cabin, you almost have to turn it on leaving FL180 to keep a reasonable pressurization differential. In the 690, it just increases the flow into the cabin.

On a Sundstrand, however, it's more akin to the late, lamented "Ground Cool" switch that 690As had (before most of them were disabled)-- it increases the flow of air through the ECU and spins the ECU faster. At low power settings or high altitude, you don't have a lot of air and that might be fine. At high power settings (such as climb power), it just spins the little ECU faster and faster and faster... and that's not good for the life of the bearings. Not good at all.

The late Hugh Davis described it better than I could:

Quote from: Hugh Davis
In addition to the restricted use of Max Flow during takeoff and landing, Max Flow should not be used below Flight Level 200 on the JetProp-series 840 and 980 aircraft. The Max Flow valve increases bleed-air pressure from 21 psi to 37 psi to increase the speed of the air-cycle machine turbine. Due to the limited lubrication of the bearings in the turbine, many service center maintenance personnel recommend that Max Flow not be used at all.

http://flightlevelsonline.com/issues/spring11/article/control-column.html

I think the summary is that the big old air cycle machine in the 690 (Hamilton Standard, maybe?) was just much more tolerant of higher speeds and pressures than the little Sundstrand in the Jetprops.
« Last Edit: June 17, 2017, 12:39:14 pm by donv »

Adam Frisch

  • Administrator
  • Hero Member
  • *****
  • Posts: 1673
    • Adam Frisch FSF
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #3 on: June 17, 2017, 12:57:42 pm »
Good info, Don.

Think it's a Fairchild in the 690's.
Slumming it in the turboprop world - so you don't have to.

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3260
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #4 on: January 30, 2018, 04:33:31 pm »
I learned a lot about the Sundstrand during my recent recurrent with Barry Lane. Although, in the end, it boils down to the same two things:

1) Add oil every 25 hours

2) Never, ever, ever, ever use MAX FLOW

He did teach me some things about departing from hot, humid environments (which I rarely encounter)-- climb a bit more slowly, and maybe crack the heat.

I also learned about the importance of the anti-ice valve, which I never really appreciated. Finally, I learned that, yes, you can get one overhauled, and it's not the end of the world.

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3260
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #5 on: March 13, 2018, 02:48:36 pm »
Incidentally, I was going through the AFM looking for some other information, and in the Handling, Service, and Maintenance section I discovered that it recommends (requires?) adding oil to the Sundstrand every 25 hours! So it's actually an official thing, not just a "best practice."

Adam Frisch

  • Administrator
  • Hero Member
  • *****
  • Posts: 1673
    • Adam Frisch FSF
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #6 on: March 13, 2018, 09:01:21 pm »
Out of curiosity, what kind of oil should go into my old Fairchild or the newer Sundstrand's?
Slumming it in the turboprop world - so you don't have to.

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3260
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #7 on: March 13, 2018, 10:27:42 pm »
I can't remember-- actually, it's probably in the AFM. I think it's normal turbine oil.

You probably have the Hamilton Standard... at least, that's what the 690s have. On those, you can actually check the oil-- on the Sundstrand, all you can do is add some until it spills out ("Fill to Spill" is literally what the AFM says).

donv

  • Administrator
  • Hero Member
  • *****
  • Posts: 3260
Re: Jetprop Environmental Systems-- Sundstrand
« Reply #8 on: September 19, 2020, 05:51:11 pm »
I heard an interesting theory about the Sundstrand recently. The theory is that you should start with the bleed valves turned on. This makes the start a few degrees hotter, but spins the Sundstrand up more slowly, as opposed to opening the valves once the engine is running and hitting it with full force of bleed air.

I'm a bit skeptical of this, but open to thoughts.