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  #1  
Old 04-13-2017, 12:33 PM
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logansc logansc is offline
 
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Default Revamping my Rocket: Questions

Rocket guys: I have a considerable difference between my old ASI and the "tape" airspeed in my new AF5600. I've flown several NTPS TAS multi-heading tests using GPS and have established (I think) that my AF5600 is reading about 10 knots high based on calculated GPS derived TAS versus the TAS displayed by the 5600 (my old ASI which I still have, is even further off---long story). Anyway, I adjusted the airspeed indication on the AF5600 calibration page down by 10 knots. Now of course, it seems too low.

1. Can anyone tell me about the 54 knot "stall speed" in the specifications of the sport wing Rocket? In further testing, I did several stalls today and was seeing 47-48 knots indicated on the tape and around 60 on the old ASI when it broke with very little difference (except deck angle) between power on, power off, and flaps up or down. Into the bargain, with these settings I am way down (as expected) on the indication at the top end. I always thought my Rocket was pretty fast, but apparently not! On a follow-on full power test, I was only seeing 195 kias or so on the AF5600 at 200' and WOT (75 degree day). I was seeing around 210 on the old ASI at the same time. If 54 knots for the stall is actually about right, it seems to me I can add around 5-6 knots back into the 5600 tape display. That won't jive with the GPS derived TAS speeds though, but I can't believe the airplane is not stalling until a real world 47-48 knots with one 200 pounder and near full fuel on board. I know airspeeds vary a bit (sometimes fairly significantly) across the range of speeds a typical airplane is capable of, but this seems like a bit more than I expected. Regardless, accuracy at the bottom end of the scale is more important to me that at the top, so...

2. My TruTrak Gemini autopilot settings have gotten all gooned up trying to follow the guidance in the 5600 manual. Is anyone flying the Sport-Rocket/Gemini combo who could share their settings with me?

Thanks very much!


Lee...
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  #2  
Old 04-13-2017, 01:26 PM
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Hi Lee, not sure this is a lot of help as my F1 has the EVO wing, but solo with 20 - 30 gallons of fuel I stall at ~57 knots, full power or full flap both drop the stall speed by ~5 knots.

With respect to airspeed, I assume you have tested your static system for leaks. I burned up quite a few dinosaurs messing with my static port but finally got it nailed - ASI is very accurate.

Here is a picture of the dam in front of the static port - same on both sides. That is a piece of .032 glued to the fuse. Static ports are behind the rear baggage bulkhead.

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  #3  
Old 04-13-2017, 01:38 PM
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Toobuilder Toobuilder is offline
 
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Lee, I wish I could go out and fly to verify, but a stall in the mid 50's is what I remember. Mid 40's is highly suspect.
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  #4  
Old 04-14-2017, 06:32 AM
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logansc logansc is offline
 
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Thanks guys; I'm confident it's now reading low on slower speeds and maybe even a bit low on the upper too. I think I'll crank it back up a few knots and see how that goes until the IFR calibration "guy" gets back here next month.

In the meantime, anyone have an answer to question number two about settings for my Gemini?


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  #5  
Old 06-21-2017, 10:35 AM
jmwigen jmwigen is offline
 
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Howdy- Flying a sport wing F-1 s/n 97, with the Hartzell 3 blade. At 10,500', 20.5" and 2170 rpm I typically true 193 knots. My panel is a Garmin G3X, Gemini A/P, with a Garmin GTN 650, an SL 40 and a transponder (Soon to be a Garmin 345 for ADS B)
My static ports are mid rear fuselage, about 3/8" diameter, and raised about .032. I used to have steam instruments and after the panel and static port change was concerned that my readings would be off. Luckily it all works swimmingly.
One test that was outlined in a previous thread was to set your altimeter, sync it with the Gemini, then fly fast down the runway. If your static ports are off you'll see a marked difference in height from that of the runway.
Good starting point.
Didn't understand your question about the settings on the gemini. Rephrase the question, please.
Hope this helps. Can send pics of my setup. Just PM me as I'm not very good at posting pics on the site.
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  #6  
Old 06-21-2017, 06:21 PM
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logansc logansc is offline
 
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No problem, Michael. I have the autopilot working better now...got the proper settings from somewhere (don't remember where---I've been traveling for several weeks and haven't had a chance to fly). Back in the air tomorrow and will try the altimeter/low pass test.

Thanks for checking in!


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  #7  
Old 06-21-2017, 08:30 PM
Mjuckes Mjuckes is offline
 
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Interesting, I have a friend of mine who flew the F100 in the 50's and he once spoke of the high speed pass down the runway to set inaccuracies in instruments.
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  #8  
Old 06-22-2017, 11:12 AM
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swaneymj swaneymj is offline
 
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Hey Lee, you can easily fly a 3 or 4 leg GPS course (several times at different airspeeds) while recording groundspeed and track from a GPS. Pop those numbers in an Excel spreadsheet and it will give you airspeed and altitude position error corrections. You can Google for the spreadsheet or download it from the National Test Pilot School website: https://www.ntps.edu/information/downloads.html

If you were certifying your aircraft to Part 23 standards, you'd want less than 3 percent CAS (or + or - 5 knots, whichever is greater) for airspeed and + or - 30 ft/100 ft for altitude.

If you use the FARs for a guideline, you could then decide if changing the static port configuration is necessary. There is a discussion of the various methods for determining position error in Appendix E of AC 23-8C.

The "low pass" in the F-100 probably refers to the classic tower fly-by method for determining position error. Granted, by just flying a low pass you can guess at your errors but for the accuracy you need for certification it really requires a way to determine your actual height above the runway. We use an observer in the old tower at Mojave and have a calibrated grid for the observer to determine actual height. Be careful flying low over the runway. It's more difficult than it may seem to fly a stabilized pass at various airspeeds. Make sure you have smooth air too.
Mark
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