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Under what conditions will your plane never get off the ground, even if loaded within W&B?

This accident discussion has highlighted the realistic chance of this happening, even if loaded within the W&B envelope.

With the TB20 I struggle to find a scenario, but what isn’t given is the performance with the gear down, and it has to be down until you lift off

OTOH when you lift off you are still in ground effect and that isn’t documented either, despite being a positive (helpful) factor.

Administrator
Shoreham EGKA, United Kingdom

If the airplane does not conform to the performance presented in the POH, then it is not airworthy. If gear down performance is not presented in the POH, then whether gear is up or down should not affect performance significantly during a takeoff/landing. If it does, then the aircraft is not airworthy.

ESME, ESMS

Peter wrote:

With the TB20 I struggle to find a scenario, but what isn’t given is the performance with the gear down, and it has to be down until you lift off

I am not sure what is ceiling of TB20 with gear down but it’s worth an investigation as useful data to have, my guess yours will be in the +10kft before it runs out of climb steam due to drag from gear

Many RG aircrafts POH show climb rate profile and ceiling with Gear UP but the takeoff distance is shown with Gear DN on VX until 50ft obstacle, only pilots who do not believe in slow/steep VX- climbs and like to accelerate to VY+ first in ground effect (“soft air” takeoff technique) may have that peculiar problem with Gear DN

At +4kft DA altitudes, VX & VY are the same thing for all practical purpose

The early lift off of wheels from the ground or wings from ground effect is what costs a lot of runway !

Last Edited by Ibra at 15 Sep 13:17
ESSEX, United Kingdom

My Bonanza does not list the Vx or Vy in any configuration other than the clean configuration, so those airspeeds are not actually applicable on takeoff. The old Owners manual provides the Vx and Vy data for these three configurations at 5000 feet, clean, gear down, and gear and flaps down. Example Vy is 96 knots clean, 92 Knots gear down, 68 Knots gear and flaps down. Try a go around with gear and flaps down at Vy 96 Knots near GW, you will get almost no climb at all. I wonder why the POH lists the balked landing speed at 70 Kts, might it just be this is close to Vy for this configuration? So the real Vy in this configuration is 24 knots below the POH published Vy.

KUZA, United States

Also, many aircraft don’t have published performance data. For example, my 1946 Aeronca champ, on 1943 Edo floats came with precisely nothing in relation to aircraft performance. Because you are on floats, you can spend miles trying to get airborne and ‘feeling’ out the performance.

I ended up recording the density altitude, wind conditions and aircraft weight for many different take-off runs. When I wanted to go somewhere which looked marginal, e.g. a smaller lake at a higher altitude, I would try to find a longer lake at a similar altitude first, on which I was relatively assured of take off based on prior data. Then I would go in to the big lake as light as possible, with large water jugs. Land, fill up the jugs and evaluate the performance. If take off was not possible, then that was your answer:-). Being circumspect, I never got stuck anywhere; although my partner had to leave all of his camping gear behind once :-).

At my home base, the airport was co-located with a river on which we launched. More often then not, you are going deep into the backcountry, so you are not going to leave fuel behind. After watching several of my unsuccessful take off runs, I reported to the tower that I was returning to dock. The tower said, ‘you can leave the case of beer on the dock for us!’

To be honest, I learned a massive amount about flying with that aircraft. It is very clearly quite different than the ‘structured flight school environment’. I don’t think you get the same opportunity with most land planes. I am an engineer, so I like this stuff, but it will bite you quite hard if you have to clear the trees one day and you don’t know what you are doing. Also, a headwind ‘REALLY’ makes a big difference if conditions are marginal.

Sans aircraft at the moment :-(, United Kingdom

Simple answer – if the DA is high enough. Airplane dependent, of course, but once you get into the 10k ft DA region most NA SEPs simply don’t get to flying speed. Not an issue in Europe, but a very real scenario in the western US or southern Africa.

Grass. At low DA. There is a grass configuration where you skip along the grass, sort of airborne, but hitting longer ridges which prevent you lifting clear. Pulling mixture aborted without damage as aircraft tipped when elevator lost prop airflow, then settled back on tailwheel.
Not runway grass, off runway airfield grass. And I only took control after it left the hard surface. But long grass on a runway can be unpredictable.

Maoraigh
EGPE, United Kingdom

Yes; very true. I know that 20cm grass and rough ground underneath will produce a ~800m takeoff roll on the TB20, compared with ~300m on tarmac under same other conditions (ISA, light, etc). With say a PA28-140, it will probably never lift off… and I bet that’s not in the POH

Administrator
Shoreham EGKA, United Kingdom

Maoraigh wrote:

There is a grass configuration where you skip along the grass, sort of airborne, but hitting longer ridges which prevent you lifting clear

Peter wrote:

and I bet that’s not in the POH

You mean the size of TB20 wheels are not in POH???

ESSEX, United Kingdom

Dimme wrote:

If the airplane does not conform to the performance presented in the POH, then it is not airworthy.

Do you have a reference for this, or is that an opinion rather a fact?

Dimme wrote:

If gear down performance is not presented in the POH, then whether gear is up or down should not affect performance significantly during a takeoff/landing.

The performance requirement for a baulked landing configuration is often covered by certification and it is only barely enough to safely establish a new configuration if that… For example see part FAR 23.77. (keeping in mind that aircraft are not usually updated when certification rules change so you must be aware of the rules that applied at the time for example many types are CAR 3 e.g. bonanza). I am not aware of any other certification requirement for the aircraft to climb with the gear down for these part 23/CAR 3 types.

Almost all professional flying requires some reasonable factors to be applied to POH performance data which is covered by regulation relevant to the operation. IMHO private operations should apply an equivalent buffer.

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