Return-Path: Received: from relay02.roc.ny.frontiernet.net ([66.133.131.35] verified) by logan.com (CommuniGate Pro SMTP 4.1.5) with ESMTP id 2632873 for flyrotary@lancaironline.net; Sat, 11 Oct 2003 11:48:13 -0400 Received: (qmail 3537 invoked from network); 11 Oct 2003 15:48:10 -0000 Received: from unknown (HELO frontiernet.net) ([170.215.97.8]) (envelope-sender ) by relay02.roc.ny.frontiernet.net (FrontierMTA 2.3.6) with SMTP for ; 11 Oct 2003 15:48:10 -0000 Message-ID: <3F88184E.6653C46F@frontiernet.net> Date: Sat, 11 Oct 2003 10:48:46 -0400 From: Jim Sower X-Mailer: Mozilla 4.77 [en] (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: EWP - Success at last? References: Content-Type: multipart/alternative; boundary="------------31E2BCC72A6E5A2E05A2842B" --------------31E2BCC72A6E5A2E05A2842B Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit <... The way MTBF figures work, if you have two devices both operating at the same time you're roughly TWICE as likely to have a failure ...> Which is not exactly the point. The point is the likelihood of a [complete] cooling failure. That would go up roughly infinitely if you had two units. Further, there would be no need to "change at TBO" - you could run until failure. As for check valves, I can envision a couple of ways to build a "dirt simple, dirt cheap" valve that would be more than sufficient for our purposes. Ed or whoever just bought a toy mill could start a cottage industry. With check valves, one could switch water pumps periodically in flight, thus keeping them both "exercised" and promptly detecting any failure. As for high demand moments, if the pumps were plumbed parallel, you could use them both for takeoff, climb, etc. <... can probably run this thing on battery for a bit, but you'd better have a beefy one ...> Anyone with an all-electric airplane MUST have redundant alternators or batteries. You've GOT to have at least an hour GUARANTEED after alternator failure. I regard that as a given, regardless of whether your water pump is engine driven or electrical. <... use a pump speed controller to slow it down and require less juice ...> You already have that in your temp driven controller. When you're going down, the temps cool off and the pump slows down automatically. I think parallel pumps with check valves is the "Ultimate Solution" Now listen, one and all, to my latest bran fart: ..... Build yourself a small plenum. You could use a 2" (or whatever) PVC butt connector - we'll start with that for the sake of argument. You ream out the inside for half its length so there is a small "step" in the diameter of the connector in the middle. The larger diameter end is downstream. Now, bore a small hole just downstream of the "step". Now, obtain a couple inches of Al piano hinge. Replace the pin with a smaller piece of stainless piano wire. Cut the hinge in a circle so that the hinge line forms the diameter of the circle and the diameter is smaller than the big end of the housing, bigger than the small end. Put the hinge (assembled but with no hinge pin) just downstream of the step, push the pin through the hole you drilled in the housing, close up the pin hole with epoxy and - Viola' a dirt simple, dirt cheap check valve. -- Jim Sower Crossville, TN; Chapter 5 Long-EZ N83RT, Velocity N4095T "Robinson, Chad" wrote: > > Somebody suggested two cores, one pump per core. That does tend to eliminate the flow problem, but two new issues crop up. First, now you need two cores. I know a lot of you RV folks already plan to do this, but I'm working on a Cozy and had only planned for one. =) But more importantly, this pump has a 2000 hour or so lifetime. That's not bad considering its price - I'll happily replace it as a maintenance item at TBO if it works. But it's not as simple as that. The way MTBF figures work, if you have two devices both operating at the same time you're roughly TWICE as likely to have a failure, so the MTBF is cut in half. This solution gets four timnes more expensive if you're replacing two pumps every 1000 hours, as opposed to just the one pump at 2000 hours. > > The other problem with a series hookup is that since this pump is limited to 88lpm in flow, a series hookup with both pumps operating would probably not boost flow, so its only use would be to solve the problem if one pump fails. And it might overstress a pump if another was pulling the same load - it's possible this might overspeed the motor. > > I've written to the manufacturer to see what they say, and will post their response when I get it. > > In the meantime, I'd still love to hear from anybody who might have an elegant solution to a parallel arrangement, since I love the concept of being able to double the flow for critical times, such as while on the ground on a hot day, or during climbout, then shut the second pump off and have it act as a backup in case the first fails. 2 pumps == 4lbs, and the mechanical (no redundancy) is 10. Sounds attractive to me! > > By the way - one parting shot. Somebody commented that it would be nice to nuke the belt as a risk factor. But these pumps still do draw a fair bit of power, and if your belt goes, so goes your alternator. You can probably run this thing on battery for a bit, but you'd better have a beefy one considering we're all talking about EFI and everything else that goes with a rotary... > > On the other hand, if you know that you're descending, and not using much power, you could use a pump speed controller to slow it down and require less juice. But the counter to that is that it's more workload for the pilot during a stressful time. Lots of tradeoffs. > > Regards, > Chad > > >> Homepage: http://www.flyrotary.com/ > >> Archive: http://lancaironline.net/lists/flyrotary/List.html --------------31E2BCC72A6E5A2E05A2842B Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit <... The way MTBF figures work, if you have two devices both operating at the same time you're roughly TWICE as likely to have a failure ...>
Which is not exactly the point.  The point is the likelihood of a [complete] cooling failure.  That would go up roughly infinitely if you had two units.  Further, there would be no need to "change at TBO" - you could run until failure.  As for check valves, I can envision a couple of ways to build a "dirt simple, dirt cheap" valve that would be more than sufficient for our purposes.  Ed or whoever just bought a toy mill could start a cottage industry.  With check valves, one could switch water pumps periodically in flight, thus keeping them both "exercised" and promptly detecting any failure.  As for high demand moments, if the pumps were plumbed parallel, you could use them both for takeoff, climb, etc.

<... can probably run this thing on battery for a bit, but you'd better have a beefy one ...>
Anyone with an all-electric airplane MUST have redundant alternators or batteries.  You've GOT to have at least an hour GUARANTEED after alternator failure.  I regard that as a given, regardless of whether your water pump is engine driven or electrical.

<... use a pump speed controller to slow it down and require less juice ...>
You already have that in your temp driven controller.  When you're going down, the temps cool off and the pump slows down automatically.

I think parallel pumps with check valves is the "Ultimate Solution"  Now listen, one and all, to my latest bran fart:
.... Build yourself a small plenum.  You could use a 2" (or whatever) PVC butt connector - we'll start with that for the sake of argument.  You ream out the inside for half its length so there is a small "step" in the diameter of the connector in the middle.  The larger diameter end is downstream.  Now, bore a small hole just downstream of the "step".  Now, obtain a couple inches of Al piano hinge.  Replace the pin with a smaller piece of stainless piano wire.  Cut the hinge in a circle so that the hinge line forms the diameter of the circle and the diameter is smaller than the big end of the housing, bigger than the small end.  Put the hinge (assembled but with no hinge pin) just downstream of the step, push the pin through the hole you drilled in the housing, close up the pin hole with epoxy and - Viola' a dirt simple, dirt cheap check valve.
--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
 

"Robinson, Chad" wrote:

 
Somebody suggested two cores, one pump per core. That does tend to eliminate the flow problem, but two new issues crop up. First, now you need two cores. I know a lot of you RV folks already plan to do this, but I'm working on a Cozy and had only planned for one. =) But more importantly, this pump has a 2000 hour or so lifetime. That's not bad considering its price - I'll happily replace it as a maintenance item at TBO if it works. But it's not as simple as that. The way MTBF figures work, if you have two devices both operating at the same time you're roughly TWICE as likely to have a failure, so the MTBF is cut in half. This solution gets four timnes more expensive if you're replacing two pumps every 1000 hours, as opposed to just the one pump at 2000 hours.

The other problem with a series hookup is that since this pump is limited to 88lpm in flow, a series hookup with both pumps operating would probably not boost flow, so its only use would be to solve the problem if one pump fails. And it might overstress a pump if another was pulling the same load - it's possible this might overspeed the motor.

I've written to the manufacturer to see what they say, and will post their response when I get it.

In the meantime, I'd still love to hear from anybody who might have an elegant solution to a parallel arrangement, since I love the concept of being able to double the flow for critical times, such as while on the ground on a hot day, or during climbout, then shut the second pump off and have it act as a backup in case the first fails. 2 pumps == 4lbs, and the mechanical (no redundancy) is 10. Sounds attractive to me!

By the way - one parting shot. Somebody commented that it would be nice to nuke the belt as a risk factor. But these pumps still do draw a fair bit of power, and if your belt goes, so goes your alternator. You can probably run this thing on battery for a bit, but you'd better have a beefy one considering we're all talking about EFI and everything else that goes with a rotary...

On the other hand, if you know that you're descending, and not using much power, you could use a pump speed controller to slow it down and require less juice. But the counter to that is that it's more workload for the pilot during a stressful time. Lots of tradeoffs.

Regards,
Chad

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