Return-Path: Received: from relay02.roc.ny.frontiernet.net ([66.133.131.35] verified) by logan.com (CommuniGate Pro SMTP 4.1.3) with ESMTP id 2576583 for flyrotary@lancaironline.net; Thu, 11 Sep 2003 22:23:26 -0400 Received: (qmail 18082 invoked from network); 12 Sep 2003 02:23:25 -0000 Received: from unknown (HELO frontiernet.net) ([65.73.33.245]) (envelope-sender ) by relay02.roc.ny.frontiernet.net (FrontierMTA 2.3.6) with SMTP for ; 12 Sep 2003 02:23:25 -0000 Message-ID: <3F612076.6B7022F7@frontiernet.net> Date: Thu, 11 Sep 2003 21:25:10 -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: turbo wastegate requirements References: Content-Type: multipart/alternative; boundary="------------91C76D64BB82776D807C25B6" --------------91C76D64BB82776D807C25B6 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Rusty, <... I figure that guys can easily run 8 psi of boost on the street, so I should be able to do the same in the air ...> As you said, 8 psi is 16 in Hg boost. If 18 k ft is the 500 mb level, that's 15 in Hg. You could normalize to 30" with just 15" boost, and you can't file for FL 180 so you're at 17k ft. Now, is this 8 psi _all day long_ or in spurts? If we assume that it's loooong spurts, we might infer that 12"-14" is available all day long. That will normalize to 30" at 15k ft to 16 k ft. That will work fine for me. On a 60 F day, the OAT at 16k ft is about 22 F; on an 80 F day, the OAT is maybe 42 F. These temps would tend to reduce intercool requirements and cool the turbine which I assume (key word here) is the reason for limiting boost to 8 psi. It might follow that one could link compressor outlet temp to boost to get a map of conservative values for boost. Additionally, I would be more comfortable if there was a knock sensor that would retard timing at the onset of detonation. <... just how much normalization you really need ...> I'd say somewhat less that what we seem to have available. 30 in Hg at 15 k ft would give you upwards of 200 kts IAS which is upwards of 250 TAS. At 250 kts and 2600 rpm you need the prop from hell. It would be FULLY stalled on T/O (which would increase your ground roll to maybe 1500-2000ft ;o) and would be an interesting design problem. <... NA Lycosaur can still produce 75% power up to 8k ft ...> The 75% power at 8k ft convention is on account of the 750 mb level is about 8k ft. That means, any NA engine, balls to the wall, will produce about 75% of the power at 8k ft that it does at SL. 75% power in this context is not a throttle setting, it's ALL of what's available. <... If 6 psi is safe, then I'd be tempted to just set the relief valve there, and try to adjust the throttle for 5 psi ....> If 18k ft is 15 in Hg atmospheric, then 15k ft is close to 18 in Hg. 6 psi or 12 in hg would therefore normalize you to 15k ft. I think that's terrific. The same 6 psi would give you 42 in Hg on T/O which is waaaaay more than I would ever deliberately deliver to the engine. For my own part, I can't see myself operating at an airport that 32 to 34 in Hg wouldn't get me off with room to spare. I've heard that Greg Richter's Cozy jumps off in 1000' or so (but I don't know what his T/O MAP is. Bottom line: By varying wastegate at [about] WOT to regulate boost, I intuit that we can: A. Turbo normalize to 15 k ft staying well within a 5 or 6 psi boost limit, and with manageable (none to austere) intercooling. B. Have all of those benefits, if we use a stock turbo with no plumbing and dumb-as-a-stump wastegate control, for about what we'd pay for a muffler that would deal with the unobstructed exhaust ports of a turbo rotor housing. Sounds pretty attractive to me .... Jim S. -- Jim Sower Crossville, TN; Chapter 5 Long-EZ N83RT, Velocity N4095T Russell Duffy wrote: > Of course you're right about residual boost with wastegate > open. My 30" take off would have to be done at partial > throttle. Am I correct in my inference that gradually closing > the wastegate as I go higher and higher will minimize > intercooler requirements and wear and tear on the turbo? I'm > counting on not needing an intercooler using this same logic, > so I guess we'll find out if my engine blows up. It would > also seem like it would save some wear on the turbo bearings > by bypassing as much exhaust as you can, but I'm not sure how > significant this would be. > Additionally, I have put a 36" or so limit on MAP to safeguard > the engine. Does the turbo also have a boost limit? If the > turbo has, say, a 10" boost limit, then as ambient pressure > dropped off, I would reach my turbo normalize limit at about > 20" ambient or around 10k'. What would the boost limits be on > the Mazda stock turbo? Are they a factor in normalizing to > 15k' - 18k'? Take it away, Ed :-) Yes, turbos have limits, but > this is the part of the turbo class that I'm not qualified to > teach. As I understand, each turbo unit has a "compressor > map" that shows it's efficiency range as a function of > absolute pressure, and airflow. Absolute pressure is > basically the boost that the turbo produces above ambient > pressure, which is why I maintain that a traditional boost > gauge is handy to have. My (over)simplified way of looking at > this is- I'm using the same turbo as Mazda sized for this > engine, so airflow, and boost needs to be kept in the same > range that's been proven to be durable in the cars. The > difference is the duration of the boost, and the extremely > free intake and exhaust systems that we have compared to a > stock car, though many modified cars are in about the same > situation. I figure that guys can easily run 8 psi of boost > on the street, so I should be able to do the same in the air. > 8 psi gives me about 16 inches of mercury, which is 15-16 > thousand feet of normalization. That's plenty for me. Another > thing to consider is just how much normalization you really > need. I don't think too many people are planning to cruise at > full sea level power. If you do, I hope you're flying a fuel > tanker :-) Let's just say that we'll use 75% like you would > with a Lycosaur. A NA Lycosaur can still produce 75% power > up to 8k ft, so our turbo only needs to make up the difference > between 8k and whatever our max cruising altitude is. Even at > 18k ft, that's only 10k ft of normalization for cruise power, > or 5psi (roughly). I really wish I knew how much boost the > 9.7 rotors would tolerate. If 6 psi is safe, then I'd be > tempted to just set the relief valve there, and try to adjust > the throttle for 5 psi. I suspect this will still be with a > fully open wastegate. Did I mention that I can't wait to > actually try some of this stuff :-)Rusty --------------91C76D64BB82776D807C25B6 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Rusty,
<... I figure that guys can easily run 8 psi of boost on the street, so I should be able to do the same in the air ...>
As you said, 8 psi is 16 in Hg boost.  If 18 k ft is the 500 mb level, that's 15 in Hg.  You could normalize to 30" with just 15" boost, and you can't file for FL 180 so you're at 17k ft.  Now, is this 8 psi _all day long_ or in spurts?  If we assume that it's loooong spurts, we might infer that 12"-14" is available all day long.  That will normalize to 30" at 15k ft to 16 k ft.  That will work fine for me.  On a 60 F day, the OAT at 16k ft is about 22 F; on an 80 F day, the OAT is maybe 42 F.  These temps would tend to reduce intercool requirements and cool the turbine which I assume (key word here) is the reason for limiting boost to 8 psi.  It might follow that one could link compressor outlet temp to boost to get a map of conservative values for boost.  Additionally, I would be more comfortable if there was a knock sensor that would retard timing at the onset of detonation.

<... just how much normalization you really need ...>
I'd say somewhat less that what we seem to have available.  30 in Hg at 15 k ft would give you upwards of 200 kts IAS which is upwards of 250 TAS.  At 250 kts and 2600 rpm you need the prop from hell.  It would be FULLY stalled on T/O (which would increase your ground roll to maybe 1500-2000ft ;o) and would be an interesting design problem.

<... NA Lycosaur can still produce 75%  power up to 8k ft ....>
The 75% power at 8k ft convention is on account of the 750 mb level is about 8k ft.  That means, any NA engine, balls to the wall, will produce about 75% of the power at 8k ft that it does at SL.  75% power in this context is not a throttle setting, it's ALL of what's available.

<...  If 6 psi is safe, then I'd be tempted to just set the relief valve there, and try to adjust the throttle for 5 psi ...>
If 18k ft is 15 in Hg atmospheric, then 15k ft is close to 18 in Hg.  6 psi or 12 in hg would therefore normalize you to 15k ft.  I think that's terrific.  The same 6 psi would give you 42 in Hg on T/O which is waaaaay more than I would ever deliberately deliver to the engine.  For my own part, I can't see myself operating at an airport that 32 to 34 in Hg wouldn't get me off with room to spare.  I've heard that Greg Richter's Cozy jumps off in 1000' or so (but I don't know what his T/O MAP is.

Bottom line: By varying wastegate at [about] WOT to regulate boost, I intuit that we can:
A.  Turbo normalize to 15 k ft staying well within a 5 or 6 psi boost limit, and with manageable (none to austere) intercooling.
B.  Have all of those benefits, if we use a stock turbo with no plumbing and dumb-as-a-stump wastegate control, for about what we'd pay for a muffler that would deal with the unobstructed exhaust ports of a turbo rotor housing.

Sounds pretty attractive to me .... Jim S.
--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T

Russell Duffy wrote:

 Of course you're right about residual boost with wastegate open.  My 30" take off would have to be done at partial throttle.  Am I correct in my inference that gradually closing the wastegate as I go higher and higher will minimize intercooler requirements and wear and tear on the turbo? I'm counting on not needing an intercooler using this same logic, so I guess we'll find out if my engine blows up.  It would also seem like it would save some wear on the turbo bearings by bypassing as much exhaust as you can, but I'm not sure how significant this would be. 
Additionally, I have put a 36" or so limit on MAP to safeguard the engine.  Does the turbo also have a boost limit?  If the turbo has, say, a 10" boost limit, then as ambient pressure dropped off, I would reach my turbo normalize limit at about 20" ambient or around 10k'.  What would the boost limits be on the Mazda stock turbo?  Are they a factor in normalizing to 15k' - 18k'? Take it away, Ed :-) Yes, turbos have limits, but this is the part of the turbo class that I'm not qualified to teach.  As I understand, each turbo unit has a "compressor map" that shows it's efficiency range as a function of absolute pressure, and airflow.  Absolute pressure is basically the boost that the turbo produces above ambient pressure, which is why I maintain that a traditional boost gauge is handy to have. My (over)simplified way of looking at this is- I'm using the same turbo as Mazda sized for this engine, so airflow, and boost needs to be kept in the same range that's been proven to be durable in the cars.   The difference is the duration of the boost, and the extremely free intake and exhaust systems that we have compared to a stock car, though many modified cars are in about the same situation.  I figure that guys can easily run 8 psi of boost on the street, so I should be able to do the same in the air.  8 psi gives me about 16 inches of mercury, which is 15-16 thousand feet of normalization.  That's plenty for me. Another thing to consider is just how much normalization you really need.  I don't think too many people are planning to cruise at full sea level power.  If you do, I hope you're flying a fuel tanker :-)  Let's just say that we'll use 75% like you would with a Lycosaur.  A NA Lycosaur can still produce 75%  power up to 8k ft, so our turbo only needs to make up the difference between 8k and whatever our max cruising altitude is.  Even at 18k ft, that's only 10k ft of normalization for cruise power, or 5psi (roughly).  I really wish I knew how much boost the 9.7 rotors would tolerate.  If 6 psi is safe, then I'd be tempted to just set the relief valve there, and try to adjust the throttle for 5 psi.  I suspect this will still be with a fully open wastegate.  Did I mention that I can't wait to actually try some of this stuff :-)Rusty

 
 
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