Which throwing option (peg vs. hole) is easiest for a beginner to build?

From Don Stackhouse:

Bill Johns asks, with regard to the Chrysalis HLG:

It comes with two options: finger pegs which I understand just sorta stick out of the fuse a bit, and a way of building a finger hole into the fuse. My first thought is that external finger pegs would be an obvious source of drag and would catch on grass and such during landings, not a cool thing. Also, it seems that getting one's fingers "hung up" during a toss is a matter of high discussion in your excellent Q/A section, leading to folks having problems over stressing the wing.

I don't read anything about folks having problems with the finger hole option.

Having now introduced the topic:

Which method of construction would be easier for a newbie to fly with? Why?

Bill, this is a tough one to answer. Ultimately it usually comes down to personal preference.

Drag wise they come out about the same IF you use some sort of a cover over the finger hole. We did this on the original Monarchs back in the early 90's, we just cut a long finger hole hatch in the thin fiberglass belly of the glider, leaving it attached at the aft end. There was a balsa block glued to the inside of the fuselage at the leading edge of the hole to act as a finger rest. There were a couple of tabs glued to the inside of the hatch near the front to keep the hatch flush with the bottom of the fuselage when it was closed. Yes, there was some leakage and associated separated flow around the edges of the hatch, with an associated drag that was probably similar to that of the finger pegs. Sealing the edges of the hatch would probably give the lowest drag of all the various options, but it's a very difficult area to seal without interfering with the operation of the hatch.

The turbulence caused by a finger hole without a covering hatch undoubtedly creates GOBS of drag, probably much more than the finger pegs. Of course this is mostly based on estimates of similar aeordynamic situations, such as open cockpits in full-scale aircraft. As far as I know, there aren't any decent wind-tunnel studies of this issue on actual HLG's. If I ever get my new wind tunnel finished, this is one of the subjects I'd like to investigate in detail. Still, it's a pretty safe bet that a large, open hole in the side of almost any airframe will be a BIG drag producer.

The finger pegs were introduced to our models as a result of customer demand. At first I personally didn't like the perceived drag of those things sticking out in the airflow, but as I said above, in comparison to a typical COVERED finger hole it probably isn't significant. The pegs do have several advantages:

1. They eliminate the structural disadvantages of a huge hole in the belly of the glider.

2. For at least some folks, they seem to provide a firmer grip for throwing.

3. They keep your fingers clear of the best place on the belly for mounting a towhook, in case you like to launch from a Hi-start occasionally. The hook can be left in position for normal hand-throwing.

In a finger-hole design, the place on the belly where you would normally mount the hook is usually made of air. It doesn't hold screw threads very well! If you move the hole forward, it may interfere with radio installation. If you move the finger hole aft to make room for the towhook mount, you can have problems with big excursions in pitch during the throw, with resulting problems in getting a consistent launch, and possible problems of overstressing the wings. If you leave the towhook in place during hand-launching, it will interefere with proper hand position, and may also be the cause of an occasional case of "ventilated finger". OUCH!!

The finger pegs we use on our kits are made from spruce or plywood flat stock, and cut on the outside of the fuselage with a tapered leading edge, sort of like tiny delta wings sticking out of either side. They do not have any significant tendency to catch on grass. We specify in the plans to sand their leading edges to an airfoil shape, which helps minimize aerodynamic drag. Their position in the heart of the low-velocity flow field under the wing helps reduce drag as well.

The biggest drawback of the finger peg is the possibility of hooking your fingers over the top of the pegs during the throw, something which usually results in a downward pull at the end of the throw. This occurance is probably the biggest single cause of wing failures on HLG's. Finger holes can also be vulnerable to this problem if the finger rest inside the fuselage isn't high enough. The solution is to work on your throwing technique (rest the pads of your fingertips on the finger rest, DO NOT hook your fingers around the top of the finger rest surface), and also to laminate extra balsa on top of the pegs (or on top of the finger rest block in the case of a finger hole) to make the finger rest surface higher.

If you go with a finger hole, you need to give it a fairing or cover of some sort to minimize drag. Given this, the finger peg requires less work to achieve essentially the same aerodynamic results, plus some additional structural benefits. On the other hand, if the feel of a finger peg system just isn't comfortable for you, then by all means use a finger hole. Properly done, either system can work well.

Don Stackhouse @ DJ Aerotech
djarotec@bright.net
http://www.bright.net/~djwerks/