Simulating High DA/ Weight Takeoffs

How do you demonstrate High DA/Near Gross Weight T/O?

  • I don't do this / I haven't done this -- Should I?

    Votes: 4 26.7%

  • I reduce MAP.

    Votes: 5 33.3%

  • I reduce RPM.

    Votes: 5 33.3%

  • I have the student load up the airplane.

    Votes: 1 6.7%

  • I have an anvil in my headset bag.

    Votes: 0 0.0%
  • Total voters
    15
dmccormack

dmccormack

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Dan Mc
Chime in if you use a technique to simulate High Density Altitude and/or at/near gross weight takeoff conditions with your students or if you practiced this as a student.

(Two Big guys in a 152 with full tanks doesn't count)
 
I've done this as a student in a sea-plane, not so much as simulation of high DA, but as a way to force the student to seek the proper low drag attitude through the water (i.e. "on the step"), and not let excess power mask inefficiencies. It's a little easier to do in a sea-plane, because you can ensure "plenty long" runway on a big lake.

But I think it's an exercise that can be done safely on land, with preparation and care.
-harry
 
I haven't done anything with regard to DA but I have done simulated partial power loss with possibilities being a broken throttle cable or carb heat cable. I may bring it back to allow them to return to an airport or it may be just enough to assist in a longer glide.
 
Wait for some prominent instructors (who, btw, live nowhere near high DA areas) to suggest NEVER reducing RPMS.

That's how we did it when I was a student. That's how I practice when the season's coming. That's what I'll do should I ever become a student.
 
SkyHog said:
Wait for some prominent instructors (who, btw, live nowhere near high DA areas) to suggest NEVER reducing RPMS.

That's how we did it when I was a student. That's how I practice when the season's coming. That's what I'll do should I ever become a student.
Click to expand...

I'm sure some will, but like others, I am a Disciple of the Church of Kershner.
 
When we were early in my PPL, (April in MD) my instructor had me note the time and distance it took to reach rotation speed. Later on (August), he had me do it again - same runway, close as far as wind went, density altitude 3000+ feet higher. I saw the difference in runway required. It always stuck with me. A flight early in the morning and mid afternoon could have similar effect.
 
I regularly have student pilots bring friends to get us near MGW before their checkride. For high DA we do Big Bear checkouts 6700' plus it gets hot there in the summer.

Joe
 
We never practiced any density altitude simulations while I was a student, but before I flew near any mountains, I tried some low RPM takeoffs. It was an eye opening experience and taught me patience waiting for the right time to rotate as the runway slips by, and learning how slow you climb out. I think my plane handled better in actual conditions than in these simulations but it was helpful.

Barb
 
Never really had to simulate, when it was time to cover high DA issues, we went to Big Bear in the summer, and we had high DA. You could partially simulate it by reducing power at sea level, but it doesn't really do justice to the experience bcause you don't get the handling/aerodynamic difference.
 
I haven't had to simulate it ;), but the reduced RPM (or reduced MP for a constant speed prop) is about as close as you are going to get. Bear in mind though that the airplane will still fly a little better in the simulation than in real d-alt conditions since higher d-alt afects not only engine power but generated lift, TAS, and propeller slippage.
 
I can see using reduced power to simulate high DA, but I'd need a real, not simulated, very long runway to do it, and it wouldn't take much for me to abandon the effort and shove the throttle to the stop.
 
Reduce RPMs. Like Dan says.

The grain silo at the end of the short runway 18 (now closed) in Iowa City got very very big, very ver quickly.
 
BTW, the way to do this is to throttle back. In a fixed pitch prop plane, that means reducing RPM's; in a constant speed prop plane, that means reducing MP. It would be unwise to reduce RPM's via the prop control while leaving the throttle full up in a CS plane, especially a turbocharged one. Just be very careful about making your 70/50* check and aborting or throttling up if you aren't there.

*70% of liftoff speed by 50% of runway.
 
We jump out of the 185 and get into a tailwheel 172.:D
 
Seems to me that a lot of the reason people are nervous about high density altitudes isn't so much the reduced performance and higher groundspeeds required to get airborne, although these definitely factor in.

The biggest reason appears to me to be the fact that nobody knows just how much runway it's going to take. "Performance charts are based on a new airplane, test pilot, yada yada yada."

Two things, IMO, would solve a lot of that particular problem. First, calculate takeoff and landing distances, and compare them to your actual distances on a regular basis.

TMetzinger said:
When we were early in my PPL, (April in MD) my instructor had me note the time and distance it took to reach rotation speed. Later on (August), he had me do it again - same runway, close as far as wind went, density altitude 3000+ feet higher. I saw the difference in runway required. It always stuck with me. A flight early in the morning and mid afternoon could have similar effect.
Click to expand...

Second,...
Ron Levy said:
...making your 70/50* check ...

*70% of liftoff speed by 50% of runway.
Click to expand...

For my Maule (which has no performance charts), I've determined appropriate numbers to use with my T.O.P. Computer, and the resulting calculations are very accurate. I've gone so far as to compute a nearly-MGW takeoff on an 80-degree day from my 1500-ft strip (uphill 2% average) as requiring 1300 feet, and making the takeoff. Granted, I had nice rollout/clearway off the end, but my halfway marker told me I was on target, and I lifted off about 200 ft from the end.

While I'm not advocating planning on lifting off with minimal runway to spare without some solid alternatives, I don't think this type of accuracy is beyond the capabilities of the vast majority of pilots. They just have to learn to do it. Then, when you get to high density altitudes, you have confidence in your knowledge of what is actually required.

Fly safe!

David
 
Don't forget to take advantage of the same method test pilots use. Take off on a 10000 foot runway, and measure the distances (the runway markings will get you close enough). Do NOT try it on a short runway until you've gotten consistent on a long runway.
 
RPM reduction to take off on long runways (engine out sim optional) and mandatory aborted take off with reduced RPM on shorter runways.
 
TMetzinger said:
Do NOT try it on a short runway until you've gotten consistent on a long runway.
Click to expand...
And do not forget to take the difference in performance between a sealed and a turf runway into account, either! (I presume your 10,000' runway is sealed! :yes:)
 
Last few FBOs I've been to, the CFIs like to invite extra pax during check outs. Basically ppl that are sitting around the FBO. If I ever before a CFI I might do this too.
 
I've got an idea. Just fly to Phoenix on a July afternoon when its 116 degrees F. It's already mother-scratchin' hot out here and its only May...just did an afternoon flight today, and had to get that off my chest. Sorry...back to the experts.
 
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