There's no arguing that drag reduction becomes more significant the faster you go, it's part of the drag equation (v^2) but when comparing two low-drag airframes with the same power one would expect similar results.
Found this in an article on the Mooney M20J at flying.com A published flight test evaluation made by the Mooney Aircraft Pilots Association (MAPA) produced 162 knots true airspeed at level flight at 7,000 feet with full throttle and 2,500 rpm, burning about 11.5 gph.IIRC the MTOM of the M20J is about 1250 kg, so similar to the Panthera but still worlds apart according to the performance specs. That's some serious drag reduction to achieve more than 40 knots speed increase.
I think "we" are conditioned to thinking it makes little difference, but most of the clear evidence for that is at low speeds - say 120kt. At these higher speeds it will make a huge difference. Admittedly the TB20 gear has no cowlings but I lose 20kt the instant I drop it. I recall from a PA28-140 POH that cowlings are worth about 7-10kt and that is at about 100kt. The gear could easily be worth 20kt+ at a TAS of ~ 180kt.
Totally agree. I fly mainly the C172RG and recently the C182RG and a gear-drop results in about 20-25kts loss in airspeed. As both a/c ave a gear-down speed of 140kts, this gives you a great braking action when flying the approach to an airport with jet traffic behind you. You can really keep your speed up till very close to the rwy.
While the Cirrus wheels are tiny, I also don't believe their claim of a loss of 'only a few knots'. Just doesn't square with experience in all other retractable a/c. Fairings, however, do make a difference!
Cirrus POH says 10% loss in airspeed when flying without wheel fairings. 10KTAS loss when flying without the nose wheel fairing.
Cirrus POH says 10% loss in airspeed when flying without wheel fairings
That shows the hugely increased drag at those speeds. On a PA28 is it just 1/2 that amount.
So I absolutely don't buy the "5kt" (or any similar) claim.
162 knots true airspeed at level flight at 7,000 feet with full throttle and 2,500 rpm, burning about 11.5 gph.
I would have thought a M20J would do better than that, according to legend. That is only very slightly better than a TB20 and the M20J is a smaller cockpit. However I would say Mooneys are especially "aerodynamic"; their advantage seems to come from the cockpit being just squashed a bit 
Thread picks up a Q from here
are the pre-GT models really that much less good, or is it more of a perception thing?
I have never come across a document which lists changes by airframe S/N (even though many people ask for it, and I asked Socata a number of times) but:
A good Q is which pre-GTs had the capacitive fuel gauges. These are obviously not essential (most piston GA has useless fuel gauges, and a totaliser is a must for any serious flying, and doesn’t cost much) but they are “nice” because you can switch fuel tanks accurately, and you do get a confirmation of what is in the tanks. I looked in the IPC and it looks like the crappy ones ended with S/N 1512 and the good ones start with 1513 although some earlier numbers had them too as you can see.
What I don’t know is whether the FUEL LOW warning is accurate on the models without the capacitive gauges. It is very accurate on the GT and I use it on long flights to run a tank down, by waiting for it (it comes on with 8 USG left in that tank) and then I time say 30 mins (say 4 USG) before switching to the other tank. I don’t have the balls to run a tank dry and it is poor risk management IMHO in a SEP anyway.
Peter wrote:
go for the latest one you can afford
Any special reason for that or just to get the most recent airframe you can to avoid corrosion and aging issues?
Peter wrote:
I don’t have the balls to run a tank dry and it is poor risk management IMHO in a SEP anyway.
I would say that depends on which plane, it can be good to know how much fuel you have left and it can also be a total non-event.
Any special reason for that or just to get the most recent airframe you can to avoid corrosion and aging issues?
See the serial numbers in my post, but other than that, just as you say.
it can be good to know how much fuel you have left and it can also be a total non-event.
You need to be cutting it awfully close to need to know the difference between approx 4 USG and zero
Also nothing is going to be a non-event if you are above water or mountains… and I am one who doesn’t get scared easily
Peter wrote:
You need to be cutting it awfully close to need to know the difference between approx 4 USG and zeroAlso nothing is going to be a non-event if you are above water or mountains… and I am one who doesn’t get scared easily
The problem is, landing with, say, 8 USG in both tanks is ok if you have a totaliser but how do you know you will have exactly 4 USG in each tank? My totaliser only shows how much I have in total, not how much is left in each and if I had to, I’d rather run one near enough empty, knowing I have 8 Gallons in the tank I’m currently on than have the engine sputter when I’m on short final, just as I need a dose of power.
I’ve only ran a tank dry once and that was because I was diverting around storm cells on a return flight from Denmark. I knew I would be ok for fuel but decided to empty one tank until the motor started spluttering. My decision making was that If it occurred further than 20 minutes from my destination, I would land immediately and refuel as obviously the totaliser could have been defective. As it was, the engine spluttered 5 minutes from my destination so I quickly switched tanks, boost pump on – it was a non event because I was expecting it.
You would wait for the FUEL LOW indication, at which point you have 8 USG in that tank, and then you glance at the fuel flow (on the totaliser) which will show say 8.5 USG/hr (typical for a TB20 at FL150, 140kt TAS) and then you run on that tank for 30 mins. Then you have 4 USG in there, plus or minus very little. If you had bigger balls you would run for 45 mins
Instead of the watch one could use the totaliser. If at the FUEL LOW point it shows 56.5 USG, you would fly till it shows 52.5 USG, etc…
The problem is that you might not have noticed the FUEL LOW light for some time………. especially if there is sunlight on the instrument panel. But working together with the capacitive fuel gauges, which are very accurate, this works well.
FWIW, more on the GT vs. pre-GT TB20’s is also on EuroGA: https://www.euroga.org/forums/hangar-talk/674-tb-20-are-the-newer-gt-versions-better
Putting this here in case someone finds this thread but not the other, for whatever reason.
