Newb - 196 mph possible in SWTA mod F ?

[garytex]

I finally got to fly my normal commute in my new F..  I was at 11,500, trying to figure out the autopilot, PC, why my GPS and encoder weren't working and doing the "if that''s Camp Wood I'm south of course, surly that's Camp Wood, isn't it?" thing.  Don't call me Shirley.

I noted some indicated airspeeds, and when home made them true, and got to wondering if I don't also need a new ASI too?

Pressure Alt 11,390.  WOT, ram closed, 19 inches MP, 7 Deg C, 35 Gal fuel, 2300 lbs, CG slightly forward.

GPH               Ind. MPH                 EGT

7.1                  147                        1350

8.0                  155                        1390 - 1440

8.3                  162                        1400 - 1450  Max power

My true airspeed would have been 196 mph, which seems way fast.  The plane has a full boat of SWTA mods.  During the pre purchase GPS 4 directions it flew 175 mph 25-25, 50 ROP 24 deg C, which seemed reasonable to me.  The plane is going into the shop Tue. for to deal with several issues, should a new ASI be on the list?  Also who makes a good True ASI.  I hate not having True airspeed.  What about the electronic ones with an encoder.  I may need a new encoder anyway.  Two birds?

Thanks and happy holidays

Gary 

[gregwatts]

That does seem very optimistic. That would make your F model faster than my 201.

[Piloto]

Before replacing the ASI verify its connection to the static line. A leak on the static line can cause an erroneus air speed indication.

Jose

[xftrplt]

Quote: Piloto

Before replacing the ASI verify its connection to the static line. A leak on the static line can cause an erroneus air speed indication.

Jose

[aerobat95]

When I plug in 147 IAS, 11300 ft, and 7 degrees C I come up with 179.3 MPH True.....or 155 KTAS.  That seems pretty much in line with what I see.  I consitantly see 156 KTAS at altitude with my F but I am typically burning around 10.5-11.3 at around 9000 ft.  The mods I have on my '74F are: oil cooler relocation, flap gap seals, wheel well liners, and a Lasar 201 windshield.

[garytex]

Ah reality rears it's ugly head.  155 kts is probably right.  I guess it does not matter how tarted up it is, it is not going to outrun gregwatts 201.  Nice to dream for a while though.  Maybe the true airspeed calculator I used suffered GIGO.  The tarting includes cowl, wing root and tail fairings, and break disc rotation.  I'm inclined to believe the burn hoever, as the gas pump and the totalizer agree. I'm going to have to find a standard sea level day and check takeoff fuel flow.

Thanks for your input,

Gary 

[Shadrach]

Quote: garytex

Ah reality rears it's ugly head.  155 kts is probably right.  I guess it does not matter how tarted up it is, it is not going to outrun gregwatts 201.  Nice to dream for a while though.  Maybe the true airspeed calculator I used suffered GIGO.  The tarting includes cowl, wing root and tail fairings, and break disc rotation.  I'm inclined to believe the burn hoever, as the gas pump and the totalizer agree. I'm going to have to find a standard sea level day and check takeoff fuel flow.

Thanks for your input,

Gary 

[Piloto]

Quote: xftrplt

True, but the ASI would then read low. 

[xftrplt]

Sorry, Jose, I still disagree--at least in practice.

Theoretically, massive static leak in the cabin, i.e., a disconnected line, just might give a slightly high indication if  the cabin were underpressurized, which, in a Mooney, I can't see happening.

Most likely, the cabin pressure would be slightly greater than at the flush static port, hence a lower A/S indication.

Theory vice practice.

[Mcstealth]

Not to start a war of words, but, isn't 50 ROP exactly not where we are supposed to run these engines, or have I been reading this site wrong?

 

Mcstealth

[Shadrach]

Quote: Mcstealth

Not to start a war of words, but, isn't 50 ROP exactly not where we are supposed to run these engines, or have I been reading this site wrong?

 

Mcstealth

[KSMooniac]

I'd have a hard time believing 155 KTAS at 8.3 GPH too.  Still sounds like a VERY fast F, though!  Enjoy.

[garytex]

I think there may be something to what Piloto says.  I had an old Cessna 170 that had the static port wide open and unconnected in the back.  It showed airspeed variences when you opened the window.  Not much, 5 mph or so.

Quote: Piloto

True, but the ASI would then read low. 

[garytex]

KSMooniac:  On the 4 way gps speed run it burned 10.3 gph at 155 kt.  The other day it burned 8.0 at 155 MPH indicated at 11,500 ft.

Mcstealth:  I concur, but 50 rop is where the seller wanted to run it, and he was flying.  I will be spending no time there myself.  I wonder if that explains the 500 hr cylinder OH times he was getting.

[KSMooniac]

155 MIAS at 11,500...sorry I gotta throw a flag on that!  No way I believe that on an F at 8.0 GPH.  Something is amiss with the ASI and/or pitot-static system.  Even with all the mods, I find that extremely unlikely.

On the GPS run, did you fly 4 headings, or 4 ground tracks?  The best way to do it is fly 3 ground TRACKS 120 degrees apart, otherwise you won't get a true reading if flying headings.

[jetdriven]

Ours wont indicate even close to that.  It does indicate 146 MPH at 11,500'.  That is just LOP and the FF was 7.9 GPH

[Shadrach]

Quote: garytex

 If the leak is on the pitot line it would read low but if the leak is on the static side it could read high or low depending on the cabin ventilation pressure.

Jose

 

[garytex]

Quote: KSMooniac

155 MIAS at 11,500...sorry I gotta throw a flag on that!  No way I believe that on an F at 8.0 GPH.  Something is amiss with the ASI and/or pitot-static system.  Even with all the mods, I find that extremely unlikely.

On the GPS run, did you fly 4 headings, or 4 ground tracks?  The best way to do it is fly 3 ground TRACKS 120 degrees apart, otherwise you won't get a true reading if flying headings.

[KSMooniac]

Years ago I heard a used airplane salesman trick was to "tweak" the static port by sticking a pin into it and bending it aft slightly, and this would create a bit of a lower pressure area at the port and cause the ASI to read higher.  Worked fine when DMEs were rare, much less GPS.    I bet you have an issue somewhere in the P-S system and/or with the ASI.

[garytex]

I was reading old posts and ran across one where someone was speaking of draining the pitot/static system, using a drain located about where the battery case vent tubes are.  He indicated that he would get all kinds of wild readings when it had water in it.  My flight was just after the first rain we have had here in Austin in months.  I haven't found the drain on my '67 F, and I have looked.  Am I blind and clueless, as my wife maintains, or do I not have said drain?

Thanks,

Gary

[jetdriven]

Scott, I dont see how altering the static can make the airspeed read higher, I don't think it is connected to static. 

Gary, on a 201 the static drain is under the battery, a small metal spring loaded pip you push on. The pitot drain is in front of the wing on the pilot side undr the belly.  F may be similar.

[xftrplt]

Quote: jetdriven

Scott, I dont see how altering the static can make the airspeed read higher, I don't think it is connected to static.

[Shadrach]

Quote: xftrplt

Instruments 101:

The ASI reads the differential pressure of (Pitot) - (Static).  Reducing Static is the same as increasing Pitot.

[Hank]

I don't recall on my Mooney, but the Slowhawk that I trained in had a small hole on the back of the pitot. I always thought the ASI measured the dfference between ram pressure in front and static from the hole in back. Being a high-wing, and having to walk around/duck under the pitot, it was easy to see, on the Mooney, not so much.

[garytex]

Jetdriven:  Thanks, I'll keep looking.  I also stand in front of the refrigerator "where'se the milk?"

Gary