12 Seconds to Pattern Altitude

[Jay Honeck]

As many of you know, we've recently transitioned to the Van's RV-8A, an aerobatic, tandem seat, 2-place high performance homebuilt. To say this is about as far away from our Cessna/Piper/Beech/Ercoupe spam-can flying as can be wouldn't be too much of an exaggeration.

We've put 51 hours on it, in just six weeks. This includes ten hours (5 apiece) of pretty intensive transition training. Both of us can pretty much thread the needle with "Amelia", now, after so much in-cockpit time.

Back to those 12 seconds. Many would argue that the most vulnerable time in-flight is the departure phase. High power, high angle of attack, low speed, long climb. Lose your engine there, and things often end badly.

Which is why I wanted to share an unexpected advantage of sport planes in general, and the RV-8 specifically -- enhanced safety during the climb out phase. So little time is spent in this critical phase of flight (as compared to most GA planes) that your odds of an engine failure during that phase are dramatically reduced.

Here's my departure procedure in the -8A, illustrating what I mean:

Full power, breaking ground in less than 500 feet.

Keep the nose down, flying in ground effect, letting the speed build until there is no more usable runway ahead. This will put me right at 140 knots indicated, at our 3600' long island airport's runway.

A firm-but-not-crazy pull will have me at pattern altitude in just 12 seconds! This is a 5000 FPM climb, with two people, full fuel, on a 90+ degree day.

I can't imagine what it would be like solo, light on fuel, on a cold Iowa day!

In addition to being great fun (obviously!), it is comforting to know that our exposure to that most critical phase of flight is so small.

So there you have it. Enhanced safety. Yet another reason to fly an RV!

 

[Jim Logajan]

Well, in theory, I've got 140+ knots to convert to altitude by then.

Landing straight ahead at that speed would be unwise, so my procedure would be the same, but with the caveat that if I can't make it to 600' AGL, I would ditch in the shallow water just off the beach, more or less straight ahead.

Why 600'? Because in my transition training, I learned that I need 500' to make a 180 degree turn, power off.

The physics says you can't convert the 140 kts kinetic energy to the needed AGL:

E[sub]kinetic[/sub] = m[sub]airplane[/sub]*V[sup]2[/sup]/2
E[sub]potential[/sub] = m[sub]airplane[/sub]*g*h

E[sub]kinetic[/sub] = E[sub]potential[/sub]
m[sub]airplane[/sub]*V[sup]2[/sup]/2 = m[sub]airplane[/sub]*g*h
V[sup]2[/sup]/2 = g*h
h = V[sup]2[/sup]/(2*g)

So:
g = 32.2 ft/s[sup]2[/sup]
V = 140 kts = 236 ft/s
h = 236[sup]2[/sup]/64.4 = 865 ft

You'd be stationary at 865 ft above your starting height. You'd want to be flying at least at stall speed at the end of the "zoom," so available V for an RV-8 would be about 90 kts (152 ft/s). Computation of h in this case is left as a simple exercise for the reader.

Since no loss of energy to air friction was taken into account, and you're changing velocity vector using a fluid, conservation of momentum means not all that kinetic energy can go into your airplane climb. Some of the available kinetic energy has to go into moving air so conservation of momentum is satisfied.

However, it may be worth trying an experiment at altitude where you are flying straight and level at 140 kts, cut the power to idle and pull back on the stick. Note the altitude gained when the speed reaches stall speed. Remember to level out and apply power - any lower speed gets into aerobatic territory.

I suspect you may be getting fooled by the power to weight ratio into thinking the RV-8 is capable of more than it is when the engine is no longer running. The great climb isn't due as much to lateral kinetic energy as it is to simply having a relatively powerful engine.

 

[Jim Logajan]

(And, frankly, the zoom to altitude is so danged much fun that I doubt I would stop doing it, even if the numbers don't show any safety enhancement...)

Practice the maneuver at higher altitude first. You could inadvertently put the plane into an accelerated stall at low altitude, ruining your whole day.

Edit: And try to avoid yanking the wings off.

 

[Jim Logajan]

I am still trying to digest the fact that Hoover can make a LOW pass at twice his take off speed... Just like Jay is twice his take off speed entering his climb.. And ol Hoover can climb, do a full roll, venture out to the edge of the traffic pattern, land safely and have enough momentum to taxi up to the announcers stand ....

And Poor Jay cannot zoom climb to a safe altitude to make the "impossible" turn....

Back in post 8 I showed that the height an object can climb with an initial vertical velocity V is given by this equation:

h = V[sup]2[/sup]/(2*g)

Notice that the mass of the object cancelled out so it isn't a factor - and that the height attained increases with the square of the initial speed. It is clear that when Bob Hoover shuts down his engines his Shrike (or P-51) is flying at the highest speed possible. He can double his final altitude by only a 41% increase in speed.

Jay could do the same maneuvers as Bob, but he couldn't do them with an initial starting speed of only 140 kts. An RV-8 and a Shrike Commander appear to have similar top speeds. So Jay would need to accelerate up to 180 kts or more. That takes time, defeating the whole point of his efforts.

 

[Jim Logajan]

Hmmm. Not sure but this appears to be a video of a Cessna Caravan flying in ground effect while accelerating and then doing a steep climb (well, steep for a Caravan) to pattern altitude; I think similar to the maneuver Jay proposes:

 

[Jim Logajan]

I don't think so...Jay still thinks we just don't get it.



http://www.vansairforce.com/community/showthread.php?p=829705#post829705

Some posters appear to have assumed Jay's misunderstanding of the physics and aerodynamics was due to a potentially fatal personality flaw. It seemed to me to devolve quite quickly into personal insults of his character, well outside any historical evidence.

At this point it seems to have become important to some to prove their original prognosis by looking for any possible confirming evidence, where ever it may appear. Mutual antagonism seems to have settled in. Personally, I find that nursing those kinds of feelings distracts from the more enjoyable aspects of life.