PT20J

A few possibilities come to mind. 1. The P-51 has a wing loading of 43.4 lb/ft2 whereas the M20J has a wing loading of 16.5 lb/ft2. This means that the wing area for a Mustang is comparatively less than the wing area for a Mooney and wing area adds drag. 2. The general shape of the P-51 is relatively more aerodynamic because it is easier to form a smooth fuselage shape around a single occupant than around four. 3. Cooling drag is a significant drag contributor in piston powered airplanes. The Mustang uses a liquid cooled engine with a belly mounted radiator and inlet/outlet arrangement that takes advantage of the Meredith effect to reduce much of the cooling drag. Skip

The induced drag is a product of the generation of wingtip vortices. So, an infinite span wing would not have tips (they would be infinitely far away) so it would not have vortices and thus would not have induced drag. Obviously, an infinite span wing is an abstraction. The oft-mentioned statement that induced drag is a result of producing lift is true for a wing of finite span where vortices are unavoidable. Skip

Not peer reviewed yet https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v1.full.pdf https://www.latimes.com/california/story/2020-04-20/coronavirus-serology-testing-la-county

No. I never said that. I'm saying that this is a serious threat to life and the economy. In my opinion, we need to look at it like a war: understand the enemy, devise a strategy to defeat it, and carry it out. Just as we have military experts to wage wars, we have health experts that know how to deal with this. We should listen to them. Any suggestion that we have to trade off containment for economic recovery is, I believe, a false choice. What will really kill the economy is if we let this get out of hand again and have to shut down a second time. Skip

As I understand it, the whole idea of flattening the curve is to keep medical resources from being overwhelmed. This seems to have been largely effective (except NY). Flattening the curve has the side effect of lengthening the duration. It also can decrease the area under the curve. The various modelers (https://www.cdc.gov/coronavirus/2019-ncov/covid-data/forecasting-us.html) have continuously revised their forecasts based on new data that becomes available. For instance, the oft-referenced IHME model decreased the mortality projections when social distancing mitigations became widespread, and the current projection of 59,343-114,228 deaths is based on those mitigations staying in place "until infections minimized and containment implemented." https://covid19.healthdata.org/united-states-of-america. It is unfair to say that their initial projections of what would happen if we took no action are wrong because action was in fact taken that affected the course of events. The issue seems to be that this virus is deadly if not contained and is easily transmitted by asymptomatic infected individuals that are flying under the radar so to speak. The hard thing for most people to grasp is how fast exponential growth can overwhelm. We only had a few cases in early February; three months later we have over one million and over 57K dead even with extreme mitigations in place. Skip

A couple of fine points: 1. L/Dmax occurs at the angle of attack where induced drag and parasite drag are equal and each contribute 1/2 of the total drag 2. Strictly speaking, the induced drag is a function of wing span (b) rather than aspect ratio (AR). An infinite span wing has no vortices and no induced drag. As the span is progressively shortened, the vortices become stronger and the induced drag increases. For a given wing area (S), the aspect ratio will necessarily change as the span is changed since AR = b2/S. Skip

I have an Aspen EFD 1000. I held off upgrading because I have a lot of experience building embedded systems (including DO-178 compliant systems) and I can pretty much guarantee things like this will happen. I don't know what RTOS Aspen uses, but it takes something like a kernel panic in a Unix system to cause a reboot which is a pretty serious failure. I would feel a lot more comfortable if Aspen would explain the root cause and the nature of the fix. The whole thing has been too mysterious: If it hasn't happened to you it probably won't? This is a deterministic system. Skip

I wasn’t clear. I understand the reboot issue. I was asking what caused it and what the fix was. Engineer just wants more details. Skip

So, what was the problem? Skip

And, don't forget the SB requires pulling the suction screen every oil change also.

A lot of future plans seem to depend on testing. But widespread testing (or random sampling) in a large population with low prevalence of infection would seem to require really good tests so as avoid confusing the statistics with false positives and false negatives. Anybody know the sensitivity and specificity of available tests? Skip

I’m going to take mine apart next month and I’d like to know also. From the IPC it appears the are just stuck on with double sided tape, but it’s not all that clear. Skip

Yep. Lot's of opinions, but I've never seen any detailed studies with actual data. Since one of the often expressed concern is acid buildup, it would be interesting to take samples every ten hours and send them to Blackstone for a TBN analysis. Skip

The glide ratio is numerically equal to L/D of the airplane (not just the wing). If one airplane has a better glide ratio than another, it simply means that it has a higher L/D ratio. The lift approximates the weight. As airplane size increases, weight increases more rapidly than drag since weight tends to increase with volume whereas skin friction drag increases more as a function of area. A paper airplane has low weight and a lot of area and doesn't glide very well. Also keep in mind that best glide (max range) is different than minimum sink (max duration). Skip

If you like P-51s and are ever in Salinas, CA stop by Cal Pacific Airmotive (owners of the P-51 type and production certificates) and visit with Lori Atkinson. She loves to show pilots around. You'll probably see a few restorations in progress. The other cool thing is they have completely disassembled P-51s of each model with all the parts stored in racks and cataloged so that if they need to make a part and they can't read the blurry microfiche, they can take an original part and measure it. Skip

Not sure what diameter the hole is. There is a calibrated restrictor within the body of the nozzle. The two components are a matched set so if you take them apart to clean them, don't mix up the pieces. Al Jesmer at Precision Airmotive told me that they don't actually calibrate the nozzles but they do flow fluid through each and can tell by eyeballing the spray pattern if it's good. The servos are calibrated on a flow bench. Skip

The original design was for an Allison engine and 3 bladed prop. The switch to the Merlin and 4 bladed prop moved the CG forward and a weight was added to the rudder post to rebalance the airplane. When more range was needed to provide fighter escort for bombers deep into Germany, the 85 gal. fuselage tank was added behind the cockpit and the tail weight was removed. With the fuselage tank full, the CG was indeed aft of the neutral point and the airplane was longitudinally unstable. There was a prohibition against instrument flight or aerobatics until fuel was burned from the fuselage tank which was used first. However, if all the fuel were burned from the fuselage tank the airplane would be nose heavy and prone to noseover during landing since it no longer had the rudder post weight, so the admonition was leave 15 gal in the fuselage tank to only be used in an emergency. Skip

RSA fuel injection systems meter fuel by controlling the pressure drop across the metering jet which thus controls the flow rate. The nozzles atomize the fuel and provide a restriction on one side of the metering jet. The metering systems adjusts the pressure on the other side of the jet against this restriction to adjust the flow. The plumbing between the jet and the nozzles is sized so as to be out of the picture. The RSA specification states that an 1/8" OD stainless tube with any ID between .085 and .090" is acceptable. Clarence probably got a defective tube as he suspected. On the other hand, it's probably not the best idea to mix brands. Skip

I didn't say it was. I used to work with an engineer who often said, "If you search for a rationalization, you will find one." It's the same with expert opinions. I can probably find a PhD somewhere that has data to show we never landed on the moon and the Earth is flat. I tend to go with the preponderance of the evidence, but that's just me. Skip

CDC has links to several predictive models: https://www.cdc.gov/coronavirus/2019-ncov/covid-data/forecasting-us.html

I don't seen a conspiracy. I had no trouble finding it on Youtube, or the Public Health response. https://www.youtube.com/watch?v=zb6j7o1pLBw https://bakersfieldnow.com/news/local/public-health-responds-to-claims-from-doctors-at-accelerated-urgent-care

I'm older than that: 2" quadraplex

When I was in college, I had a summer job working at a TV station. One summer I worked in the tape room. We had an entire shelf full of Scotch tapes and one new, unused Memorex tape. No one ever used the Memorex and when I asked why, all I got was a shrug. So, next commercial spot we had to tape, I picked the Memorex. It clogged a head and we had to do the whole thing over and I got chewed out. Ever since, I've been leery of trying brand X.

This mirrors my experience. I flew Beaver seaplanes commercially for several years averaging 6 hours a day behind a very noisy R-985 with no muffler. The Bose A20 is slightly quieter than the Zulu 3 but the Zulu 3 is more comfortable. The difference in noise attenuation is not very noticeable in a Mooney. You do have to fiddle with the headband in the Zulu 3 to get the tension right. If you don't have a good seal around the ears you will get the motorboating effect. Lightspeed made a big deal about improving the headband design to make the Zulu 3 quieter than the Zulu 2. What they really did was change the angle of the parts that attach the earcups to the headband to increase the clamping force and this makes them less comfortable. You can bend them back to make them fit like the Zulu 2s (Lightspeed explained this to me and told me how to do it when I threatened to send my Zulu 3s back and stick with my Zulu 2s). In the Beaver, I use the A20, but in the Mooney I prefer the Zulu 3. I haven't tried the QT. My wife uses it since she hates anything clamping her head. She's used to foam earplugs, so that doesn't bother her. Mic quality seems OK on the intercom, but it doesn't want to stay in place and she is constantly having to adjust it. The QTs are hand made and look it -- they lack a certain refinement in construction quality you would expect from a more expensive headset. I use the Bluetooth in my Zulus and Bose with the phone often for calling for clearances from airports without ATC. Skip

That was my point. The flow should be relatively insensitive to the diameter. The specification is from Precision Airmotive for the RSA injection system. They don't supply the lines -- that's an engine manufacturer's part. Might be an issue if lines from different manufacturers were mixed on the same installation. Skip