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Does the TKS system increase drag?

Ibra wrote:

A strong +/-1000fpm is barely +-/10kts

By direct unit conversion, indeed 1000 fpm is a tad less than 10 kts. However, you cannot freely exchange vertical speed for horizontal speed like that. Just try it. Set yourself in cruise at a set ground speed V. Now, don’t touch power and raise the nose so that your ground speed is V-10kts. Are you climbing at 1000 fpm (not the initial zoom climb, but the steady state)? No, you are not, you are climbing far slower than that.

The reason is that climbing requires continuously adding to the potential energy of the plane, while cruise only requires matching drag.

Last Edited by lionel at 23 Oct 07:09
ELLX

Yes you can’t convert between ASI and VSI that easily when altitude potential energy changes with well defined trend (e.g. climb)

If you plan to stay on constant altitude it is an approximate conversion for small air mouvements (if you ignore drag from trim chnages, parasit drag from additional speed and aircraft sink rate in still air) but I agree you may have to fly with full power at Vy to keep flying same hight/speed in a 50kts windsheers and defintely not with AP on ALT mode :)

I think I got it wrong, the explanation is that on constant altitude when airspeed ocilllates around some average value, average drag does increase a lot with speed variance (something called Jensen inequality: drag is convex function of speed) and hence your average power setting will increase a lot if you change power or you have to lower your average speed a lot if power is constant…

Last Edited by Ibra at 23 Oct 08:11
ESSEX, United Kingdom

Of course it increases drag, but its minimal if done correctly. I think the old TKS panels made out SS mesh were much drag inducing. I would avoid buying an aircraft with these. When damaged you can replace the whole thing wing with the newer titanium ones…Correct TAS calculations I believe have to be taken over several flights and different altitudes. I lost about 3-4 Kts with the TKS installation which is a very clean one BTW. The ruddervators are relatively thin and the TKS panels have a very good fit on it. Yes the prop was changed from a Mc three blade to an Hartzell three blade. When watching my Airspeed I sometimes see fluctuations although the aircraft flies stable at altitude. I think that there are sometimes vertical wind components even in altitude which may influence when your AP tries to maintain altitude which translated in a slow decrease, increase in IAS of a couple of knots…anyway its not an exact science. It doesn’t matter too me, cleaning up the aircraft and regaining these three knots or more will come with a big expense of moving antennas etc…If my budget would allow, go from an IO520 and install an IO550 :-), there is no replacement for displacement.. ;-)

EBST

My aircraft have a TKS.
I think it make the plane slower.
qnh 2500 feet, 20°C, 2200/20 at 10 gph 115-120 ias.
Is it normal?

LHSA, Hungary

@zozi what aircraft is this?

If it is a TB20, those power settings are not meaningful as cruise settings. They are very low power.

In low level cruise, say 2000ft, a TB20 on 23" 2400rpm and at 11.7 USG/hr (44.2 litres/hr) should be showing an indicated 138kt. This is regardless of 2 blade or 2 blade prop.

Administrator
Shoreham EGKA, United Kingdom

@Peter
This is a tb20gtfrom 2001 with 3 blade hartzell prop and TKS
i tried it to fly fast but not easy to fly over 120 kias.
the parameters when we fly from england on FL110 :
20/ 2300 -6°C 12gph 118 kias.
From the Pilot Information Manual table, this must be faster.

LHSA, Hungary

not easy to fly over 120 kias

Do you mean the aircraft is hard to handle over 120kt, or it is difficult to make it go faster than 120kt?

I suggest an airspeed indicator calibration – example with three headings 120 degrees apart. Your ASI may be reading 20-40kt too low.

Administrator
Shoreham EGKA, United Kingdom

It is difficiult to make it go faster over 120kt.

LHSA, Hungary

Something very wrong with the instruments.

What speed is indicated at say 2000ft with all 3 levers fully forward, no flaps obviously and gear UP? Should be about 165kt.

However an ASI error of this magnitude would be very obvious from the ground speed reading on the GPS.

Administrator
Shoreham EGKA, United Kingdom

@Peter!
Last weekend i could try my TB20 with professional pilot. On 3500 MSL we could fly ca. 150 KIAS not with maximum power setting. He told me that i coud not use the trim. I didn’t know that the trim can make slow the aircraft, when it is not in good position. That was the problem. I must learning…

LHSA, Hungary
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