Trim to best glide

[BruceP]

Maybe this is a well known technique, but I just finished my BFR today in a C152. As part of an engine failure simulation my instructor told me this airplane will automatically go to best glide speed by trimming to full up on the trim wheel. So, she cut power, I trimmed full up, and lo and behold it went right to best glide speed. I thought this was a fantastic thing to learn about this airplane and had never been exposed to this technique before. I have electric trim in my 9A, and although I'm not flying yet I'm interested in pursuing this setup if I can. So, have any of you set up your airplanes to take advantage of this technique?

[BobTurner]

This works in a 152 because (1) best glide is very slow and (2) control forces are light so if you really wanted to fly even slower it doen't take much pressure on the yoke. As airplanes get heavier and faster this is no longer true. You want to be able to trim for landing approach speed, even if it's lower than best glide.
Also, especially with a -8 or -10, cg location has a lot to do with how much trim is needed.

[Kevin Horton]

Originally Posted by BruceP

Maybe this is a well known technique, but I just finished my BFR today in a C152. As part of an engine failure simulation my instructor told me this airplane will automatically go to best glide speed by trimming to full up on the trim wheel. So, she cut power, I trimmed full up, and lo and behold it went right to best glide speed. I thought this was a fantastic thing to learn about this airplane and had never been exposed to this technique before. I have electric trim in my 9A, and although I'm not flying yet I'm interested in pursuing this setup if I can. So, have any of you set up your airplanes to take advantage of this technique?

The airspeed that results from full nose up trim will depend on CG, power and flap angle. So, you'll get different results depending on whether you are solo, or with a passenger, and also depending on how much baggage and fuel you have. The speed will be different at idle than if the engine is stopped.

So, this is a useful technique in the C152 when training with an instructor. But it may or may not be useful when solo or if the engine actually fails, rather than sitting there at idle.

[Cyclone]

The 172 Skyhawk will do the same as long as the backseat is empty.

[David Paule]

Originally Posted by Cyclone

The 172 Skyhawk will do the same as long as the backseat is empty.

Ditto for a C180, but only if the flaps are down.

Dave

[flightlogic]

Bruce, it is a clever demonstration.... been around for years. As mentioned though, there are variables that will make it less than what you want to depend on during a power failure.
Memorize a few key airspeed numbers for YOUR airplane.... loaded the way you most fly it. Hit that number as you go through your failed engine checklist... and glide to the best available spot. It will be multi tasking like you have never done before. At best, it will only occur in practice... during your flying career.
At worst, it may just save you.

[rvmills]

No intent to sound preachy here, but I'd recommend to fly the airplane first, trim second. IOW, if the motor quits, fly the plane to establish best glide, and trim the pressure out. On takeoff that may likely mean lowering the nose right away. In cruise, you can probably hold altitude till you slow to best glide, and then lower the nose. You may still end up at or near full-up trim, but how you get there in each of those situations will probably require a different technique and different timing. Lots of variables, so this is just food for thought and discussion.

Cheers,
Bob

[Vac]

Lots of variables affect actual glide performance, but AOA is always the same for best range or max endurance glide. So, if there is a properly calibrated and tested system on board, you can always establish proper AOA--airspeed will take care of itself.

If you don't use AOA, the good news with RV's is the flat drag curve means relatively consistent glide performance over a pretty good range of speeds (unlike a C150 class airplane). If you've got a properly marked airspeed indicator and adjust pitch and then trim to put the airspeed at the top of the white arc plus or minus about 5 MPH/KTS, you are in the ballpark. Depending on you you prop your airplane, your glide ratio can be significantly higher than a C-150 class airplane. If you've got a controllable prop, how you adjust the prop will also significantly affect glide performance; and, of course, if the engine quits, so the prop may stop turning, also affecting performance. Once you gain some experience with your RV and establish some known energy reference points (e.g., high key/low key, etc.) you'll learn how to adjust your ground track, bank, etc. to fly through the "hoops" and keep a little extra energy "in the bank" that you can spend wisely in that base turn to a stable final.

Fly safe,

Vac

[jjconstant]

Wow...a bunch of us were just having this discussion over lunch a few weeks ago. It was prompted by my comment that when I did my transition training, the instructor demonstrated that, in that configuration (2 people, 2/3 fuel, about 10lbs of stuff in the baggage,RV7A) full aft trim yielded minimum sink. He suggested that a good use for that knowledge was in an engine failure, get yours eyes out the window looking for a landing spot while running the trim full aft. It's slower than best glide but optimizing glide while going the wrong direction is worse that staying aloft the longest amount of time, then picking a spot and then optimizing glide. The discussion around the table yielded some incredulous looks (many different kinds of planes including a Lancair ES) and the conclusion was that it is airplane and configuration specific.

Education and Recreation!

[hevansrv7a]

Originally Posted by Vac

Lots of variables affect actual glide performance, but AOA is always the same for best range or max endurance glide. So, if there is a properly calibrated and tested system on board, you can always establish proper AOA--airspeed will take care of itself.

If you don't use AOA, the good news with RV's is the flat drag curve ...

Vac

I agree about AOA. How do you support the idea that an RV has a "flat drag curve"?

Induced does not follow the rules? Parasite? I don't get it.