Frank Colver

THE COLVER SKYSAIL

My son Matt and his friend Ernest Feher built the bamboo and plastic glider (Richard Miller’s Bamboo Bomber) that was at the 1st Otto meet, May 23, 1971. After the meet I started designing my Skysail with inspiration from Richard Miller’s Conduit Condor. After testing a scale model (which I still have), actual construction on the Skysail started on November 5, 1971 and the wing was taken to the field for the first time on January 22 of 1972. I sold many copies of plans for a model of the Skysail but never for the full size version, due to liability worries. If someone scaled it up that was their choice.

After I quit flying the Skysail it was donated to the San Diego Aerospace Museum where it burned up in the fire that destroyed the museum.

THE COLVER HANG GLIDING VARIOMETER

The first aircraft instrument manufactured specifically for hang gliders.

A variometer is a more sensitive form of the rate of climb / decent instrument used on most aircraft. It is used for gliding aircraft to detect when rising air currents are entered and lets the pilot maneuver the glider to stay in the lift and gain altitude or to avoid sinking air to stay up longer.

Various types of variometers have been in use since the days when balloons were man’s only way to “leave the surly bonds of earth”. Most have used some method of detecting when air was entering or leaving a container. The very earliest types used “sight tubes” where bubbles could be observed as air went in or out of an insulated bottle.

Now “fast forward” to the new sport of modern hang gliding. In early 1970’s hang glider pilots were transitioning from just launching of hills or mountains and landing at the bottom to attempting to climb in thermals and stay up longer or even land some considerable distance from their launch point. They started adapting the variometers used in sailplanes with brands like Cambridge Instruments or Ball Instruments.

In the fall of 1973, to the best of my knowledge, the first ever commercially sponsored hang gliding competition was held at the Sylmar CA hang gliding site. It was sponsored by “Annie Green Springs” a maker of soda pop style white wine being marketed to the younger crowed. This was an invitational competition and my son Matt was invited to compete. He was not experienced in thermal flying and I knew he would be up against those using the sailplane variometers. I wanted to build him a vario that would beat the competition’s instruments. I had been experimenting with making variometers for RC model sailplanes using thermistors as “hot wire anemometers” to detect air moving in or out of a closed container. However, I didn’t like the delay time that the thermal mass of these devices introduced even though they were very tiny.

A “hot wire anemometer” detects the resistance change in a device heated by current passing through it when an air current cools it. I decided to use the filaments of tiny low voltage incandescent light bulbs with their glass enclosures removed. I built a sensor using two filaments positioned next to each other and placed in the air stream of air entering or leaving an insulated plastic bottle. Air flowing one way would cool the filament close to it more than the one directly behind it and my circuit would measure the difference in resistance between the two. Two tiny nozzles directed the air against one filament or the other depending on flow direction in or out of the bottle.

So, to give Matt an edge in the competition, I kluged together a variometer based on two tiny lamp filaments. I “bread boarded” my detector circuit and built a sensor. This also used a transistorized pocket AM radio for the amplifier and speaker it contained. This kluge consisted of two packages, which needed to be duct taped to his control bar, with wires running between them,.

I don’t remember how Matt did in the contest, he was up against the best that hang gliding had to offer at that point in time. What I do remember is how the other competitors recognized the superiority of my vario compared to what was being used. Other pilots begged me to sell them this kluge right off my son’s control bar. Fortunately, I had the good sense to not do that. I loaned it to Taras Kiceniuk that afternoon to fly his Icarus V. He eventually used the vario to find sink so he could get down after a long flight had tired him out.

After the meet I started to work on making a producible version of the vario. Since I was holding down a full time engineering job this meant spending many late night hours. One irony was that I had trouble duplicating that first hot wire sensor until I figured out what was different in my subsequent versions.

The rest, as they say, “is history”. I produced the variometers under the one man company name of “Colver Soaring Instruments” selling them wholesale to various hang glider manufacturers and dealerships usually in lots of five. I didn’t want to sell in bigger lots because I wouldn’t be able to satisfy the demand. After a number of years I turned the whole product over to Wills Wing who had become the prime distributer for the instrument. I still continued to make the hot wire sensors, for Wills Wing, because it took a watch makers precision and care to build.

The Colver Vario’s internal components were also used inside the “Chad” hang glider instrument dash board.

I estimate that over the product lifetime about 5,000 units were sold. Still to this day I occasionally hear stories of epic flights made possible by my varios. The variometers on the market today have far surpassed my product in smaller size, weight, and features, but absolutely none have the sensitivity and fast response time of the “Colver vario”. I challenge any of them to respond to the pressure drop in a room when a toilet is flushed and the water goes down the hole. Or to react to the pressure changes when someone bounces up and down on a wooden floored room. If the “Colver” was moved up or down an inch or two it would indicate the rate of change in atmospheric pressure, due to that altitude change.

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My intent is to build a glider so easy to ground handle with good roll control response in flight and good pitch damping + slow flight and landing, that we almost return to the days of the rogallo but without the bad characteristics of that flat flex wing design. Many people taught themselves or took lessons with gliders that were easy to ground handle and fly but lacked the good parts of the fixed camber airfoil (battens) and reflex of today’s flex wings. This is strictly a “training hill” or “dune gooning soaring” glider.

Shooting for a all up weight of less than 40 lbs using thin wall 7075 aluminum tubing and thin light sail material.

I’m assuming a low sink rate with a glide ratio somewhere between that of the old standard rogallo and today’s single surface flex wings. Maybe the L/D will be in the neighborhood of a large paraglider.

There will be three main design stages:

1) Test the flight performance in a 1/5 scale model. Make any changes needed from results there.

2) Decide on tubing sizes and cable bracing methods, where used.
At this point I will need to evaluate the tubing size/weights for “complexity vs benefit”. It may be that with the short span that 1-1/2″ x .049 6061 cable braced may not be much of an advantage over 2″ x .032 7075 not cable braced. BobK suggested this evaluation. Although I have an inclination to trust more the structural integrity of the cable braced approach.

3) Design detailed junctions of folding components and other hardware components. Probably going to be some physical full scale modeling done here.

Next will be the construction of the full scale airframe and getting battens made by WW. At this point it won’t be complete with control bar or king post. Just a lay on the floor airframe. Now beg, conjol, plead, with Steve at WW to make me a sail for it. Actually before the battens ar made I hope to get some input from him on the exact cut of the trailing edge curves for distribution of loading and airflow without flapping edges.

One reason for the design’s short span is to lessen the effect of the spanwise weight. For every foot I bring the tips inward there is the corresponding reduction in the effect of the weight of the tip portion. The short span also makes the pilot’s sideways weight shift more effective as a greater portion of the span. Another stated goal of the design is to reduce the sail cloth weight which will further reduce the spanwise weight since I’m trading span reduction for chord increase (keeping sail area about 300 sq ft). Then of course there is the goal of keeping the whole mess to under 40 lbs. 

The other reason for the design’s short span is for easier ground handling.

If successful, this glider will not be for getting from point A to distant point B it will be for getting from easy launch to easy landing with well damped pitch and quick roll ability along the way, traveling at a slow speed and low sink rate.

I envision the sail tension along the LE’s to be a grommet with a line extending out to the corners with the tips to pull tension outward. The ends of the tips could be done the way it is done on current glider wingtips.

REPLY TO A LETTER ASKING: “WHY DO THIS”? 

Thank you for contacting me regarding your conversation with Jim about my “HG Basic Trainer” project.

I agree that hang gliding is diminishing and the general age of the pilots is getting older (I’m about to turn 84). The whole purpose of my project is to try and make it easier to get new pilots trained. You ask what am I doing that hasn’t been done over the past 40 years, so ‘ll try to answer that question. I’ll give a more detailed answer below, but the short form would be that I’m going back to over 40 years and not taking the branch that hang gliding followed to the good performance gliders we have today.

Let me add that this project is to prove a design concept and not to sell gliders or make any money (it’s going to cost me a lot). I’m open sourcing all of my thoughts and design ideas, on Hangliding.org, US Hawks.org, and USHGA.aero, in the hope that if it proves to be a beneficial trainer glider, that schools might build their own or that a manufacturer would make it a break-even product to grow the sport and ultimately sell their standard line to new pilots. All I want out of it is credit for any of my ideas used or for having provided inspiration to other ideas.

This is a training hill only glider but it could also be good for “dune grooming” coastal dune soaring because of a tight turning radius and slow low sink flight. The glider will use light construction so it would not be certified for general utility glider use (similar to the WW Condors).

OK, let’s go back more than 40 years. Thousands of people were either teaching themselves to fly a hang glider or with the help of a friend (who also loaned them the glider). The glider that most learned on was what came to be known as the “standard Rogallo”. It was light for carrying back up the training hill, it was easy to ground handle in wind, it was relatively slow flying and big flair, stand up landings, by new trainees, was common. Launches, in my opinion were actually a little more difficult than a modern single surface glider in that the angle of attack had a narrower margin. A little too high and you never reached launch speed unless you were on a very steep hill, and a little too low and it went negative, leading to a nose-in crash on the side of the hill.
Now to my personal experience of 49 years ago.

After the Otto Lilienthal meet of May 23, 1971, in which my son Matt flew a bamboo and plastic Rogallo, I set about designing and building a rigid all wing hang glider I called the “Colver Skysail”. I first built a scale flying model and then completed the full scale glider in January of 1972. I then started teaching myself to fly it and probably benefited a little bit from many years of flying RC gliders most of which were my original designs. The reason I went with a rigid design was because I didn’t have the ability to make a sail. Had I gone with a flex wing sail I would have had, in the beginning of 1972, a glider planform much like what is flying today.

My experience on the Skysail was much different than my son Matt’s. He could fly my glider right from the get-go because of his Rogallo training which had changed from the bamboo of the beginning to aluminum tubing and poly plastic and then to an Eipper 17’ Dacron sail Rogallo. It took me over a year before I could make a good launch, flight, and landing. The performance of my glider was very good but that made the whole process of learning on it more difficult. I tell people it was like learning to drive using a hot Italian sports car.

So, now the flight schools are either using newer single surface gliders, that are commonly seen flying today or a slower version of those gliders like the WW Condors (I have a Condor 330 and a Condor 225) which are both take-offs on their Falcon models.
Back to the Rogallo that all those early day new pilots were learning on. As you well know, it had some bad characteristics and a very poor glide ratio. Bad characteristics like a tendency to go pitch divergent into a full luff dive and its steep turns tended to lose a lot of altitude. The poor glide forced trainees to use steep training hills which meant that things could go bad very quickly on a blown launch.

So, here’s my premise: Design a glider with the good characteristics, but with vast improvements over the less desirable characteristics of the “standard Rogallo”. This would be a glider that weighs less than 40 pounds, is easy to ground handle in turbulent winds, has slow launch, flight, and flare landing characteristics, and a better glide than the Rogallo but glide probably won’t be as good as a good modern single surface hang glider.

My “Basic Trainer”, which I have now named the “PUFFIN”, (suggested by someone following my design thread on Hang Gliding .org) because of its short squat design, is a low aspect ratio, short span (27 feet), with large area (278) and a high cambered airfoil (WW Condor 330) for low sink and slow flight. See photo of the 1/5 scale model in free flight (actually soaring the bluff without control) at Dockweiler Beach, which will give you the general idea of what I’m building. The model was rigid but the full scale glider will have a floating cross spar and deep keel pocket. The keel area incorporates the “Swallowtail” design for reflex there to reduce the tip twist needed to give it good pitch damping for beginners. Design CG is at 25% of MAC. I’ll adjust tip twist and center reflex to trim to that CG location. Cross spar runs from tip to tip and can be used to adjust sail billow by the haul back cables.

Sincerely,
Frank Colver Feb/01/2019

PLEASE NOTE:

This project is on hold for an indefinite period of time. Due to space limitations in my shop and some difficulty in getting some materials, plus still not having someone to layout and make the sail, and other projects taking up my time, I’m not currently proceeding with construction of the full scale glider frame.

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