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Lopresti SCRAM MP increase - quick-look data


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Hi everyone

Finally got N201JX airborne today after way too long, with a new Aspen display, EDM-930 engine display and some other goodies. Took out a bunch of old stuff too and our corrected empty weight (including oil but not unusable fuel ~15lb) is 1750#. I am now FINALLY able to get some much higher fidelity data off this airplane.

One of the first things I wanted to check is the max level flight effectiveness of the Lopresti SCRAM (super clean ram air mod) at full power and low altitude. Here is the plot:

1719453376_ScreenShot2020-11-15at7_44_28PM.thumb.png.39a15e8fff48f2f841916499edc9aa0d.png

Bottom line is a 1.3" manifold pressure increase. The hp from Benchmark is 173hp before, and 182hp after. Of course there is a commensurate increase in fuel flow as shown by the blue line. 

This is an interesting exercise for air racing perhaps, but the real use would be at medium altitude once a full WOT LOP cruise is set up. That will take me a little longer, first indications are a GAMI spread of 1.0 GPH with cylinder 1 being much richer than the others (last to peak). This is at 8500', WOT and 2500 RPM and a little colder than standard day. The normal air filter intake is a little lossy, I only have 21.4" under these conditions. About 8.6 gph LOP but #1 is barely over the peak and #3 is 50 deg lean, and is on a pretty steep negative power slope at this point....meaning ham-fisted leaning might proceed to a rough engine and a nervous pilot. Can't have that.

2113469032_ScreenShot2020-11-15at7_32_40PM.thumb.png.eac798bb9788499e0c54b48bda7ce8ac.png

Note here also the SCRAM add on the top yellow MAP line after LOP, from 21.4 to 22.2 inches MAP, increase of .8" and roughly 5 hp. Again a commensurate increase in FF on the blue line, but I did not touch the mixture and the EGTs basically remained constant.

Most M20Js are ~155 to 157 KTAS under these conditions. N201JX is nicely faster than this, but I had only one on board and half fuel so pretty light. It's not going 180 KTAS guys, need a turbo or cubic inches for that.

More data later. I am thrilled to have this airplane airborne again, finally.

Edited by testwest
minor formatting fix
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Great details Norm!

Having the extra air flow, needs to be matched with extra FF... 

Or we would just add back resistances using the butterfly valve... (throttle)

Wonder if @Speed Merchant will be stopping by...

@jetdriven may be interested in the low altitude MP numbers for his race team... 

Best regards,

-a-

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16 hours ago, testwest said:

Most M20Js are ~155 to 157 KTAS under these conditions.

I really don't know how these speeds are being achieved, my J is a 140 KTAS airplane flying LOP at 8.6 to 9 GPH. MAYBE I would see 150 flying best power but I don't operate that way. Something must be wrong with my airplane...

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22 minutes ago, y2kiah said:

I really don't know how these speeds are being achieved, my J is a 140 KTAS airplane flying LOP at 8.6 to 9 GPH. MAYBE I would see 150 flying best power but I don't operate that way. Something must be wrong with my airplane...

How are you measuring TAS? Mine seemed slow and I did a few GPS 4-way tests and found that the airspeed indicator was low by about 7 kts. I checked the pitot system and found a leak at the drain. Might be worth checking. 

Skip

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19 hours ago, testwest said:

Hi everyone

Finally got N201JX airborne today after way too long, with a new Aspen display, EDM-930 engine display and some other goodies. Took out a bunch of old stuff too and our corrected empty weight (including oil but not unusable fuel ~15lb) is 1750#. I am now FINALLY able to get some much higher fidelity data off this airplane.

One of the first things I wanted to check is the max level flight effectiveness of the Lopresti SCRAM (super clean ram air mod) at full power and low altitude. Here is the plot:

1719453376_ScreenShot2020-11-15at7_44_28PM.thumb.png.39a15e8fff48f2f841916499edc9aa0d.png

Bottom line is a 1.3" manifold pressure increase. The hp from Benchmark is 173hp before, and 182hp after. Of course there is a commensurate increase in fuel flow as shown by the blue line. 

This is an interesting exercise for air racing perhaps, but the real use would be at medium altitude once a full WOT LOP cruise is set up. That will take me a little longer, first indications are a GAMI spread of 1.0 GPH with cylinder 1 being much richer than the others (last to peak). This is at 8500', WOT and 2500 RPM and a little colder than standard day. The normal air filter intake is a little lossy, I only have 21.4" under these conditions. About 8.6 gph LOP but #1 is barely over the peak and #3 is 50 deg lean, and is on a pretty steep negative power slope at this point....meaning ham-fisted leaning might proceed to a rough engine and a nervous pilot. Can't have that.

2113469032_ScreenShot2020-11-15at7_32_40PM.thumb.png.eac798bb9788499e0c54b48bda7ce8ac.png

Note here also the SCRAM add on the top yellow MAP line after LOP, from 21.4 to 22.2 inches MAP, increase of .8" and roughly 5 hp. Again a commensurate increase in FF on the blue line, but I did not touch the mixture and the EGTs basically remained constant.

Most M20Js are ~155 to 157 KTAS under these conditions. N201JX is nicely faster than this, but I had only one on board and half fuel so pretty light. It's not going 180 KTAS guys, need a turbo or cubic inches for that.

More data later. I am thrilled to have this airplane airborne again, finally.

Your data is an almost exact match to mine which I took about 21 years ago with the first Lopresti cowl.  I'm curious what KTAS you are seeing when you say yours is nicely faster.  I went from 151 KTAS to 159 KTAS after the Lopresti cowl.

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I am pretty sure I got about what you did, this airplane has other drag reductions as well and the gains start to diminish after several have already accumulated. I will need to make some more data runs, it would be better to quote a speed at max gross and standard day conditions, and I was pretty light yesterday and it was cold.

BTW I get TAS from a couple of different sources, one from the Aspen display (but it is 2 knots optimistic on the indicated due to the Mooney's position error correction, with down path errors when computing true airspeed) and from the computed TAS from Cloudahoy. Cloudahoy uses ground speed, track angle and known winds at your 4D position to compute TAS. But strong winds aloft can make the data noisy.

Having said all that, here is a picture from Cloudahoy:

IMG_E75FD8784676-1.thumb.jpeg.0419f7e828cf8918491cac2beeddaba3.jpeg

 

Some take aways, I need to make sure the clock in the EDM-930 is set to GPS time, there is about a 5 minute delta between the engine data and the position data. Note the yellow barbs, about 35 knots of wind aloft and a bit bumpy. On the KTAS graph on the lower right, the speed was actually fairly constant but Cloudahoy's computation of this parameter falls apart in the turn downwind, so you have to let it settle. It is better to quote numbers on a calmer wind day. I was still leaning the last cylinder in the turn and then let it settle for a minute, then opened the SCRAM. The snapshot line on the graph is just a rough number at this point, and heavily caveat-ed. I was level though.

The green trace here shows the subsequent descent to the pattern at KAWO.

IMG_777C258C540D-1.thumb.jpeg.59c80a4d01a392dfb66fbbb0adf94502.jpeg

Cloudahoy is a great service. I use it all the time. Highly recommended.

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7 hours ago, PT20J said:

How are you measuring TAS? Mine seemed slow and I did a few GPS 4-way tests and found that the airspeed indicator was low by about 7 kts. I checked the pitot system and found a leak at the drain. Might be worth checking. 

Skip

I've worked it out by calculation, observation of actual ground speeds and analysis by Cloudahoy. All of them point to my lower-than-average numbers. I get about 120 indicated up at 8500. 135 KIAS down low. I would need something more like 135 up at cruise to get a true of 155.

Here is a recent snap from cloudahoy correlated to my JPI data:

image.thumb.png.3134eefb633c0334bd0e0b910d6ff408.png

image.thumb.png.d89663c9a6b300b8ffc64dfa2436ab76.png

In short, I could sure use a speed mod like the Lopresti cowl / SCRAM, but I seem to be starting from way behind the curve. I have a few hunches that bad rigging, chipped paint, badly cracked cowl, and less than perfect fairings leading to a loud humming at cruise speeds are all contributing to this. I didn't realize it was so bad though, yikes.

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Nice pireps for CloudAhoy!

My favorite app for measuring T/O runs...

Make sure you are using a WAAS resource... if you use the iPad’s non-WAAS gps... your data may get more noisy than you think...

T/O data is unusable if the resource is non-WAAS.... easily off by hundreds of feet... :)

Best regards,

-a-

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10 hours ago, testwest said:

I am pretty sure I got about what you did, this airplane has other drag reductions as well and the gains start to diminish after several have already accumulated. I will need to make some more data runs, it would be better to quote a speed at max gross and standard day conditions, and I was pretty light yesterday and it was cold.

BTW I get TAS from a couple of different sources, one from the Aspen display (but it is 2 knots optimistic on the indicated due to the Mooney's position error correction, with down path errors when computing true airspeed) and from the computed TAS from Cloudahoy. Cloudahoy uses ground speed, track angle and known winds at your 4D position to compute TAS. But strong winds aloft can make the data noisy.

Having said all that, here is a picture from Cloudahoy:

IMG_E75FD8784676-1.thumb.jpeg.0419f7e828cf8918491cac2beeddaba3.jpeg

 

Some take aways, I need to make sure the clock in the EDM-930 is set to GPS time, there is about a 5 minute delta between the engine data and the position data. Note the yellow barbs, about 35 knots of wind aloft and a bit bumpy. On the KTAS graph on the lower right, the speed was actually fairly constant but Cloudahoy's computation of this parameter falls apart in the turn downwind, so you have to let it settle. It is better to quote numbers on a calmer wind day. I was still leaning the last cylinder in the turn and then let it settle for a minute, then opened the SCRAM. The snapshot line on the graph is just a rough number at this point, and heavily caveat-ed. I was level though.

The green trace here shows the subsequent descent to the pattern at KAWO.

IMG_777C258C540D-1.thumb.jpeg.59c80a4d01a392dfb66fbbb0adf94502.jpeg

Cloudahoy is a great service. I use it all the time. Highly recommended.

My 201 is about 160 in cruise. It is an 84 model with the smooth belly. I ended up having to replace a cylinder and had to have the A/S rebuilt. It had an internal leak. I just installed a LoPresti Cowl and had paint work done. Right now I am having the panel updated. When the avionics shop gets through I will have to do some more tweaking and testing. The plane is out of rig and the the inboard gear doors don't  close very well. There may be a little more left in it. The SCRAM air valve was developed for the LoPresti Fury. At low levels we would see about a 1.7 in increase. That was due to the increase airspeed. The Fury would true out at about 217 at sea level. I am grounded for 60 days following foot surgery. I will report the results when I am airworthy again.

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27 minutes ago, testwest said:

And @y2kiah I like how you present your data! I am going to copy that shamelessly.....

No shame in that, I might have to borrow your eyes one of these days (since you are right down the street from me) to help figure out why my bird is such a lead sled.

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Good luck with the foot, Speed!

Interesting detail regarding the increased MP related to speed...

The faster you go, the more power you develop....   :)

Long X-Cs at sea level could have interesting air speeds by the time you get to where you are going... if the friction didn’t increase at a higher rate...

Best regards,

-a-

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