Sponsor: Jim Brown

Description: To design a release mechanism for the tow plane of a sailplane or glider

Completion Date: April 24, 1998

Team Members: Eric Gano, Team Leader

Angel Moreno, Research

 

  What's In Store What's In Store

Our Project Problem Feasibility Issues

Failures Pictures

Scope Specifications

Solutions to Problem

 

Links

 

 

The Problem with Release Mechanisms

Executive Summary

Sailplanes initially gain altitude while attached to a tow-line that is pulled by another airplane. A release mechanism allows the line to be disconnected by the sailplane pilot or the tow-plane pilot. The tow-plane pilot will release the sailplane only in the event of an emergency.

 

In the past there has been a problem with the tow-plane release mechanism currently in use. When the tow hook latch is loaded beyond a certain angle, the tow-plane pilot can not release the towline. Recently an amateur sailplane pilot was to be towed u p for a flight by a tow-plane. As reported to the design team, shortly after take-off the plane in tow was taken aloft by unpredicted thermal activity. This put the sailplane at a higher altitude than the tow-plane. The difference in altitude made the load angle on the tow hook latch much larger than normal. Reportedly at this point the tow-plane pilot proceeded to try to release the sailplane in tow but was unable. The severe angular load on the release mechanism made it impossible for the tow-plane pilot to release the sailplane. This caused the tow-plane to nose towards the ground. Shortly thereafter the tow-plane crashed into the ground killing the pilot. The towline broke allowing the sailplane to land safely.

Our design team is going to design a new latch/release system that will not have the problems the old system has. The new release mechanism will operate reliably and safely under all modes of operation. The team will also try and achieve FAA approval so that the new latch/release system can be installed and used on commercial tow planes.

 

 

This is what's happening to the latch the sailplane increases its height over

the tow-plane.

 

 

 

Failures

NTSB Identification: LAX95LA183. The docket is stored in the (offline) NTSB Imaging System.

Accident occurred MAY-11-95 at PEORIA, AZ

Aircraft: PIPER PA-25-235, registration: N7403Z

Injures 1 Fatal.

 

A WITNESS STATED THAT THE TOW PLANE ENCOUNTERED A "DUST DEVIL" BETWEEN 100 AND 200 FEET AGL. HE THEN SAW THE GLIDER ENCOUNTER THE "DUST DEVIL" AND GAIN ALTITUDE ABOVE THE TOW PLANE UNTIL THE TOWROPE FORMED A 30- TO 45-DEGREE ANGLE. THE NOSE OF THE TOW PLANE THEN DROPPED AND THE AIRCRAFT DESCENDED TO THE GROUND. THE TOWROPE WAS FOUND TO HAVE SEPARATED AFT OF THE TOW PLANE TOW RING. THE ROPE, WITH THE TOW RING ATTACHED, WAS LOCATED NEAR THE AIRCRAFT. THE REMAINDER OF THE ROPE, WITH THE GLIDER TOW RING A TTACHED, WAS FOUND BACK ALONG THE FLIGHT PATH. AN INSPECTION OF THE TOW PLANE HOOK RELEASE MECHANISM FOUND IT TO BE IN THE OPEN POSITION. THE MECHANISM OPENED ON IMPACT BASED ON THE SEPARATION OF THE TOWROPE AND THE PROXIMITY OF THE ROPE TO THE TOW PLANE HOOK, AS WELL AS THE APPARENT SNAP BACK OF THE REMAINDER OF THE ROPE AWAY FROM THE CRASH SITE.

Probable Cause

The pilot's in-flight loss of control due to his delay in releasing the glider after the towed glider experienced an unplanned altitude gain on takeoff when it encountered dust devil.

More Related Accidents by NTSB (National Trans. Safety Board)

 

 

 

Feasibility Issues

Feasibility Issues

The tow-plane latch/release mechanism that is currently in use is very simple, inexpensive, and it requires no maintenance. Since the crash mentioned in the Executive Summary, there has been a simple modification made to the existing latch. Most people in the sailplane community believe that this modification has solved the previously mentioned angular loading problem.

 

In order for the newly designed latch/release mechanism to be accepted and put into use, it too will have to be just as inexpensive, maintenance free, and simple as the current latch/release. Ease of installation will also be very important; the release will not be used if it is difficult to install.

Unless it can be shown that the modification to the existing latch doesn't make the latch 100% safe under any possible angular loading, it could be difficult to get the new latch mechanism accepted and used. Analysis will have to be done on the existing modified latch in order to see if the problem is truly fixed. There could be other possible design flaws that could still cause the problem.

 

 

 

 

Pictures

! Our Fearless leader! Sailplane in action

 

 

Tow Plane, which has the release mechanism to pull the sailplane

 

Tow Plane doing its job! Release Mechanism attached to Tow Plane

 

Another Look from another view, and hooked to the chain.

 

Scope

Design Scope

Design Deliverable

Working prototype to be installed on a tow-plane

FAA approval, minimum goal of waiver for a single tow-plane

Ultimate goal of total FAA approval

Fully documented paper design

Fully documented test results

Test stand for operational demonstrations

 

Specifications

Specifications

Minimum life span of 15 years

+ 60 operation rang

Tow pilot release effort 20lb maximum

1500lb strength, F.S. 1.75

Must fit within 10" x 10" x 10" spatial cube

15lb max latch weight

Must use existing 1/2" mounting bolt

 

Our team is working very hard in coming up with a solution to this overlooked problem. In the meanwhile enjoy the art of gliding.

 

 

 

Solutions

The team's solution is an attachment to the existing latch. This allows current sailplane flyers to continue the use of their existing latches. The attachment provides the tow plane pilot the ability to release the sailplane at any angle. This design will safely prevent the occurrence of future accidents.

 

Actual Specifications

 

No moving parts, life span practically infinite

+33 operation range

Used existing release tension

Factor of Safety = 1.78

Fits within a 7 in. cubical space

7.5 lb. total weight

Attachment to Design

 The attachment : Demonstrating how it reduces the angle of projection.

 

 

 

 

 

 

Actual Picture of Design

 

  

Links

 

College of Engineering

Doctor David Hartman