Full Throttle Height

[Kliperoo]

Hi All,

Got a weird one for all you tonight. Im currently doing my C-Cat, and have been asked an interesting question by one of the instructors.

What is the exact definition of Full Throttle Height?

I have looked high and low (pardon the pun); Kermode, Trevor Thom, From the Ground Up and have even tried about 10 different sites on the internet, all to no avail.

It has never actually been defined to me, and yet I've used the graphs up to FTH numerous times.

Any and all responses would be much appreciated.

[currawong]

It is the altitude at which MAP can no longer be maintained by advancing the throttle.



;)

[Kliperoo]

That makes sense.... thank you very much.

[maxspeed]

depending on what MAP you are trying to maintain, but usually cruise pwr, ie. 75% and it will also the hight that the engine is at its most efficient, because the throttle bodies are wide open and the manifolds are breathing freely (no restrictions)

[blueloo]

Sorry fellas, whats MAP? Manifold somethingerother? I always thought MAP was Missed Approach Point. As with everything aviation, everything is reduced to acronyms.

[Captain Sand Dune]

Have a look at Aerodynamics for Naval Aviators.
The above posts are quite correct.
This book defines FTH as"......the increase of altitude will require full throttle to produce constant MAP and this point is termed the "critical altitude" or "full throttle height". If altitude is increased beyond the critical altitude, the engine MAP, airflow and BHP decrease"

Hope that confuses things enormously.:E

[NAMPS]

Missed Approach Point = MAPt

[Kliperoo]

Thank you all!!!

[Sqwark2000]

Blueloo

MAP = Manifold Pressure

S2K

[Atlas Shrugged]

Manifold Absolute Pressure, actually

[Towering Q]

So that's what the 'A' stands for, always wondered about that...thanks Atlas.:ok:

[Atlas Shrugged]

Ahh yes, but do you know what it actually indicates? :suspect: :suspect:

[Towering Q]

Absolute Manifold Pressure?:uhoh:

[Atlas Shrugged]

Well yes, but all the manifold pressure gauge really does is it give you an indication of the air pressure available in the engine’s intake manifold or how much air is available to be mixed with fuel. It’s just a barometer, which senses the induction manifold air pressure downstream of the throttle plate.

Actual MP varies with prop speed. As air speeds up its pressure drops, so the faster the engine is turning the lower the MP. As you reduce prop speed the air backs up in the engine and the MP increases. Increase the prop speed and the MP drops. This is why you can obtain the same percentage of power at a number of different rpm settings ie: you can get around 65% at power at SL from either 22.9”/2400rpm or 25.9”/2100rpm in most piston aircraft. Obviously, as you reduce the throttle the MP drops, but with a CSU the RPM doesn’t change until you get to a low enough throttle setting where the prop is below governing range and from there the throttle controls RPM as well as MP, but that’s a function of prop mechanics and not manifold pressure.

So, full throttle height occurs at different altitudes depending upon rpm settings. According to the power settings table for my Arrow it occurs as follows:

75% power - 2400rpm at 5000ft
65% power - 2400rpm at 9000ft or 2100rpm at 5000ft
55% power - 2400rpm at 14,000ft or at 2100rpm at 9000ft

AS