When you launch a hlg is it best to climb as steep as possible or to climb gradually?

From : Joe Hahn

Interesting and good question, Jerry.

Don and I have been discussing this very issue recently. Our conclusion to date is that it really depends on what you are trying to accomplish, ie., maximumum altitude is obtained with a launch as close to vertical as possible, with a properly timed and smooth pullout at the top. This would of course yield the best still air times and the most altitude for searching for lift. Is this ALWAYS the best way to launch? Generally yes, occasionally no.

Contest situations as well as your air reading ability may dictate the need for a launch that is flatter, allowing you to cover more ground(turning your launch energy into more distance than altitude) which gets you into a known lift area more quickly. I personally will sacrifice a bit of altitude in order to get to an area in which the air is going the right direction (UP!). This is a very common tactic I use in contests. I have the confidence to know that if I can send the ship to an area producing lift, even if it means arriving there at a low altitude, I can find lift, center in it, and go up. The plane I fly is no small part of that confidence-the Monarch is exceptional at exploiting weak lift at low altitudes.

The answer is to practice, and get comfortable using, both techniques.

Joe

From : Don Stackhouse

I just had a few additional comments to add to Joe's response.

Assuming you're trying for maximum altitude in your launch, the basic requirement is to use as much of your initial kinetic energy from the throw for lifting the weight of the model to altitude, and therefore the minimum amount of energy wasted as aerodynamic drag loss. The energy lost to drag depends on how fast you're going, the length of time you spend doing it, the amount of lift you're generating, and the aerodynamics of the model. If none of the other factors get in the way, the way you can minimize your drag loss and maximize your altitude is by spending the shortest time possible in the climb. This would suggest a nearly vertical climb path.

Unfortunately it's not that simple. First of all, in order to get a good follow-through on your throw and put the maximum possible kinetic energy into the model, you have to end the throw with the model moving almost horizontal at the moment of release. So how to transition into that near verticle attitude? Well, when you pull up you are making lift, which also means you are making more drag (usually, but there are exceptions I'll discuss in a moment). If you pull up too fast you kill off energy with excessive induced drag. If you pull up too slowly you lose too much speed while you're still moving horizontally. Without getting into it too deep, the best pull-up will happen when the wing is working at around the lift coefficient for best glide angle. If you have the c/g on your Monarch set in the forward part of the recommended c/g range and set the elevator trim for that flight condition, the model will probably do a close to optimum pull up by itself right after you release. If you set the c/g near the aft end of the recommended range (like most of the experienced competition flyers) your pitch stability will be low, and you will probably need to use a some up elevator right after the throw. Just make it quick but smooth. You might want to ballast your model with a forward c/g, trim it for best glide angle, then try a few throws that way just to see what it should look like. Then re-balance and re-trim with an aft c/g for performance and try to manually fly it along a similar flight path at the beginning of launch.

The next complication involves the airfoil. Some airfoils (like the Monarch 'C's) are great at high lift coefficients for slow speeds, and may do well at best l/d and penetrating speeds, but have problems with the flow on the lower surface when you get to the near zero lift coefficients encountered during the initial high speed part of launch. This type of airfoil will also have drag problems if you push over too abruptly at the top of the climb. On this type of wing you do best if you try to keep some load on the wing all through the launch, to keep the wing producing lift. Pull up firmly right after the throw, but only pull to about 40 degrees above horizontal, then ease off into a more gradual pull up to about 50 - 60 degrees. Hold that climb angle till you get close to best l/d airspeed, then use a smooth pushover to level. Be careful not to push too hard, or you will start to make negative lift with the wing, with the resulting high drag. Remember, the idea is to keep the wing producing some positive lift at all times throughout the launch. This is the technique I would use on a Monarch 'C'. The timing here is critical. If you push over too soon you make negative lift and kill off speed, but if you wait too long or push too gently you don't get leveled off soon enough and you'll stall. Either way you don't get maximum height. Just like landings, the solution is practice, practice, practice.

On the Monarch 'CX' you can use a little negative flap (about 3/32" to 1/8") to reduce the camber during launch and avoid this situation. On this one I would recommend a little negative flap (just enough to flatten the underside of the wing), smooth but quick pull to vertical right after the throw, and a vertical climb with a smooth push to level at the top. As the model approaches level, bring the flaperons back down to neutral (or to about 3/16" positive (downward) deflection if you're in a thermal or in dead still air). Once again, you want to pitch over at the top gently but smoothly along a more-or less ballistic flight path, so that you aren't making negative lift. Just don't do it too gently and stall.

The Wizard works well with pretty much the same approach, but you need even less negative flap deflection at the beginning. We spent a lot of time on the Wizard and Chrysalis airfoils making sure they don't have drag problems at low lift coefficients. The Chrysalis also likes a vertical climb. Of course on the Chrysalis you don't need to worry about the flaps. Just pitch over smoothly at the top.

Once you get to where you can do a max height launch consistently, re-read Joe's answer and start practicing launches that attempt to put the model at a particular spot in the sky, in terms of both height and location. You should also be developing your ability to read the lift conditions at the same time, as well as practicing downwind and crosswind launches when the winds and your skill level allow. When you finally master all these skills you will be able to spot where the lift is, throw the model towards the lift, and have the model reach the peak of the lauch right in the middle of the lift zone. Then, after beating Joe Wurts at the Nats, you can come by my place and teach me how to do it!

Don Stackhouse @ DJ Aerotech