Zoom Climb

[megan]

There is an argument else where on the web about a zoom climb.

In the conversion of kinetic energy into potential energy which aircraft will climb higher, the heavier or lighter, assuming weight is carried internally?

Thanks Lads/Lasses.

[Pilot DAR]

I'm not sure that a zoom climb has much of a role in flight testing, but I have certainly explored the characteristic in some more sleek GA types. You can certainly achieve a rate of climb well in excess of normal powered performance by applying some inertia, but it takes a touch to make the most of it without incurring excess drag as well, very easy on the pitch change, and maximize it off the top. If you come off the top too late/slow, you'll throw away some of the altitude, which you cannot maintain. I remember doing ultimate ceiling testing in a normally aspirated, carburetted Cessna 185. With terribly limited climb performance, I could zoom over 21,000 feet, but I could not hold the plane up there, it would settle back. The highest I could sustain was 20,800 feet - maximum power 12" MP, stall horn steady....

[tdracer]

Unless I'm missing something - everything else being equal - the lighter aircraft should go a bit higher due to less lift induced drag at lower weights.
The 'speed' translating to 'altitude' would be the same regardless of weight, but you'll be creating less drag when you do it with a lighter aircraft.

[Vessbot]

In a simplified view disregarding drag, and we're only looking at the energy conversion, there's no difference. Mass is the same power in both energies, (mgh and .5mv^2) so it just cancels out and disappears if you're converting between them.

If you introduce drag, then it could go either way based on the particulars. If induced drag considerations predominate, (high wing loading, low aspect ratio, swept wings, high-G pull) then the heavier plane will suffer more losses. If parasite drag considerations predominate (low wing loading, straight wings, low G pull) then the lighter plane will be decelerated quicker (a=F/m, or why the golf ball will fly farther than the ping pong ball)

[zzuf]

But it is fun to accelerate to M2 at the tropopause, select an unreasonable pitch attitude, then around zero g and enjoy the ride.
Problems include required safety equipment not normally worn eg pressure jerkin, expect engine and aircraft handling issues.
More often done is Vne at dot feet, full thrust and a vertical departure, recovering a very short time later, at zero IAS possibly in a tailslide at around 30 to 40 k feet.
Kinetic energy is king, both manoeurvres are at very low or zero g.
Misspent youth!

[safetypee]

zzuf

But not overlooking important aspects at very high altitude:

1. If the objective is to look at another aircraft, best not to point directly at it - collision course, because of the reduced, sluggishness of aerodynamic control.
2. Consider the issues for the return descent, reduced control effectiveness, nose / flightpath too low overspeed, airframe heating - energy transfer, sudden trim changes.

[zzuf]

Very useful manoeuvre in day fighter tactics, which is highly dependent on a well judged zoom, is the low speed yo-yo. Used by the trailing aircraft in an air combat situation where the hassle has degenerated to both aircraft in max rate turns. The trailing aircraft can make up turn angle and distance by overbanking, sacrificing altitude for speed, continuing a max rate turn with different centre, effectively cutting the corner. The trick being: when is the correct time to fly up to the opponents 6 o'clock and a firing position?
The high speed yo-yo uses a zoom to convert overtaking speed into increased altitude and extra distance flown to avoid overshooting the target.
I would imagine that, these days, yo-yo manoeuvres are analysed and practised to "death" at fighter combat training schools.

[dave_n_s]

A zoom climb is a useful (perhaps only) way to get to the top corners of the flight envelope for engine & airframe handling testing, certainly for military aircraft. An example.... Up there surge margins are er... marginal and finding out what happens is important. A graceful flame-out is a good result; a locked-in surge, where things get rather warmer than they should, is not such good news and behaviour and recovery actions need documenting from flight test so the right guidance goes into the AFM or system behaviour is modified to prevent service pliots and their aircraft being exposed to such unnecessary excitement.

A zoom can also be used to get into position to dive onto flutter test points if the performance gurus' modelling shows that's the best way to get there.