172driver wrote:
In the real world taking ff from Big Bear (L35, FE 6752ft, TORA 5850ft) on a really hot day you would probably make it, but the cows at the end of the rwy might get quite big in the windshield ;-)
Been there, done that. Given the relative power required to fly versus roll (assuming a paved runways) it is not so much the length of the takeoff roll that matters as what happens once you are airborne. In this case it’s fortunate that there is a large flat lake at the west end of the runway.
Peter wrote:
What would it take to make a TB20 not get off a tarmac runway (assuming infinitely long)?
Field elevation inxs of 8k ft and OAT inxs of 30C.
In the real world taking ff from Big Bear (L35, FE 6752ft, TORA 5850ft) on a really hot day you would probably make it, but the cows at the end of the rwy might get quite big in the windshield ;-)
What would it take to make a TB20 not get off a tarmac runway (assuming infinitely long)?
Old aircrafts have “placards limitations planted in the cockpit” and that’s it, pilots had to make their own numbers and judgement 
Placard limitations are those in TCDS limitations, these get incorporated in AFM that goes into some POH sections
No point talking about airworthiness or legality by sole reference to full POH, better call it “good POH airmanship”
If one is going to wet long grass in an IFR tourer, take the biggest ground roll in POH and multiply by 5 and see if that works, if one is going to a dry tarmac with no obstruction, take the lowest POH number and see if you can beat it by a factor of 2
Dimme wrote:
f 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.
US aircraft do not require a POH, they require an AFM, for which the GAMA standard POH satisfies the requirement. Section 2 of a GAMA standard POH lists the limitations and is approved by the FAA. For most GA aircraft, the rest of the POH is not approved by the FAA and does not determine airworthiness. My Bonanza came with an AFM that is about 15 pages of information on an 8 1/2 inch paper document. The entire AFM performance section is one page and only covers a very limited set of conditions.
§23.2620 Airplane flight manual.
The applicant must provide an Airplane Flight Manual that must be delivered with each airplane.
(a) The Airplane Flight Manual must contain the following information—
(1) Airplane operating limitations;
(2) Airplane operating procedures;
(3) Performance information;
(4) Loading information; and
(5) Other information that is necessary for safe operation because of design, operating, or handling characteristics.
(b) The following sections of the Airplane Flight Manual must be approved by the FAA in a manner specified by the administrator—
(1) For low-speed, level 1 and 2 airplanes, those portions of the Airplane Flight Manual containing the information specified in paragraph (a)(1) of this section; and
(2) For high-speed level 1 and 2 airplanes and all level 3 and 4 airplanes, those portions of the Airplane Flight Manual containing the information specified in paragraphs (a)(1) thru (a)(4) of this section.
With say a PA28-140, it will probably never lift off…
Would agree that not a high DA performer, but the slab wing PA28 is a perfectly acceptable farm strip animal as long as conditions are not soft and no fences along the runway. In fact it is one of the reasons the Arrow II has a nice following, the slab wing being happier on shorter strips than the, arguably more aerodynamic taper wing.
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.
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???
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
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.
