CASA Safety Notice warns against stalling Bristell aircraft - 19 Feb 2020

[Guest Bristell]

Do you regard the Piper Cherokee as an unsafe aircraft Old Koreelah? Rudder configuration looks very similar to the Bristell to me.

[M61A1]

Do you regard the Piper Cherokee as an unsafe aircraft Old Koreelah? Rudder configuration looks very similar to the Bristell to me.

With the difference being that it’s larger in relation to the aircraft and has an added strake

Gee I'm dumb. I can't see at a glance how the rudder design is likely to kill. Can you enlighten me?

According to various engineers, a rule of thumb is to draw a line upwards and aft at 60 degrees from the leading edge of the horizontal stab and another at 30 degrees aft from the trailing edge and see how much of the rudder is blanketed by the area between those two lines.

I was trying to find an online image, as the textbook that it’s in is buried.

Have a look at the difference between rudders on an Extra 300 and a Bristell. Even something like the Esqal VM1, which is a similar looking aircraft, but the rudder extends all the way down past the stab.

[Old Koreelah]

Do you regard the Piper Cherokee as an unsafe aircraft Old Koreelah? Rudder configuration looks very similar to the Bristell to me.

Good point, Bristell; they sure look similar, but as M61 points out, a subtle variation might be very important.

I've done some experimenting with my own rudder and found what a difference a small change makes.

 

... the rudder extends all the way down past the stab.

That little bit of rudder below the elevator might save a life.

[tafisama]

With regards to horizontal stabiliser,I had an aerobatic instructor show me the good design.The horizontal stabiliser needs to sit well above the wing level so that in a stall the turbulent airflow above wings does not inhibit rudder effectiveness as more smooth air is flowing to the rudder.The other design is the one pointed above where the rudder extends below the horizontal stabiliser,again letting smooth airflow past part of the rudder.These old instructors we have here are a valuable resource.Kev I will show you next time we meet at the club.

[turboplanner]

The CASA people involved in the Senate inquiry were the Director and the American legal expert.

This was a Senate Estimates Committee, not an Inquiry and these were the appropriate CASA people required for discussing forward estimates.

For anyone not sure of the difference between Senate Estimates and a Senate Inquiry, here are a couple of links.

 

They denied any knowledge of the fact the the data relied on by CASA was not right and when questioned stated that the failures attributable to fuel starvation etc had been removed from the figures. They had not.

The Senator had referenced the November 3 2014 RAA figures, and they were answering to the total (see below).

 

All this had been published well before the inquiry by "Proaviation" in an article entitled "Indecent Haste" in November 2014. The facts that CASA will now tell you are different from the facts they published before they were found out. Read the article attached.

 

Paul Phelan story Indecent Haste 28/11/14

This story is based on the press release by Peter Gibson, Corporate Communications, CASA. He based those numbers (40>12) on what RAA provided to CASA in November 2014.

Paul Phelan was reporting what he had been given, but the figures which triggered the Instrument came from years before this.

 

CASA data

• CASA referred to a batch of data from 2008 onwards.
  

 

• In December 2013 CASA offered to send staff to RAA to extract data and RAA accepted the offer. Two CASA employees collected this data on site covering January 1, 2012 to December 16, 2013. CASA provided a copy of what they had extracted to RAA.
  

 

• In August 2014 CASA requested more data, and RAA supplied data to August 3, 2014
  

 

• On November 3, 2014 RAA supplied further data (the 40>12 batch with errors)
  

 

• ATSB supplied data
  
• Jabiru Aircraft Pty Ltd supplied data
  
• Aircraft Owners supplied data
  

 

 

CASA’s Safety Systems Office (SSO) assessed the data

The assessment included allowances for debatable data.

 

The assessment was against FAA Policy PS-ANE100-1999-0006

PS-ANE100-1999-00006 Risk Assessment for Reciprocating Engine Airworthiness Directives

 

I would recommend that anyone interested in the CASA Instrument read this because it takes all the politics out of what happened.

 

The average in-flight shutdown rate of 5.8/10,000 hours from January 2012 to July 2014 was five times the FAA benchmark.

 

Note that the data for this period was from the batch extracted by CASA, and the batch supplied by RAA in August 2014, not the contentious last batch on November 3, 2014.

 

I ran a check on RAA reports for July 2019 to the end of January 2020, and the good news is I didn't find any = ZERO Gen 4 engine incidents listed.

[kgwilson]

Photo of my Sierra from behind. Note horizontal stabiliser well above the wing and rudder extending well below the stabiliser. The stabiliser is a full flying stabilator like a PA28. The stall characteristics are quite benign. It just mushes and loses height. I can only get it to drop a wing by putting on power and kicking in full rudder. It will then go straight into an incipient spin which is recovered instantly by centreing controls, stick forward & power. i.e normal procedure.[ATTACH type=full]50768[/ATTACH]

[facthunter]

The strake forward of the fin is important also. It activates the air flowing over the fin and rudder. Overall size and distance rearward from the Cof G counts as well. Nev

[tuffnut]

I don't want to be a to be a Test Pilot Mum.

 

It's been my good fortune to work and socialize with a number of test pilots during my career. There has been a lot of publicity and hype about test pilots ever since the Montgolfier brothers made the first flight of an aircraft in 1783—some of it has even been true. My own perspective is that the very good test pilots tend to be quiet to the point of reticence until they get to know you, have the ability to split a second into more parts than the rest of us—which may explain their quickness of reaction and thought, and have a certain level of confidence in their abilities that comes from having the cockiness of youth knocked out of them by aircraft that made serious attempts to kill them.

 

Types of Flight Test

 

Before going further, it's necessary to point out that there are three different types of flight test: experimental, production and service. Service testing generally involves flights made after maintenance and of new airplanes that are almost ready for production but the manufacturer wants to put a bunch of time on them in a hurry to see what's going to break. As test flying goes, it's low risk. Production testing means the first flights after airplanes roll of the line in order to identify squawks so they can be fixed prior to delivery to the customer. Usually, it's low risk. However, production test pilots often wear parachutes on first flights—some have had to use them. Experimental flight testing is where high risk resides. It includes first flights of off the drawing board aircraft and exploration of their operating envelopes. Despite everything that can be done to assure that the design is safe and the prototype has been assembled with care, things have gone south on first flights and envelope exploration flights in general aviation airplanes. Two fatalities that come quickly to mind were in the prototypes of the Cessna 340 and Cirrus SR20.

 

 

A few weeks ago a friend of mine who is a retired experimental test pilot, Tom Wallis, sent me a note about some spin testing he did that moved him well along the developmental road from cocky young test pilot to the wise old pelican he became. I think his unassuming words are worth sharing.

 

 

During his career as a test pilot for Cessna, Tom made a number of first flights of new models, most notably on the Model T303, one of the very finest-handling airplanes ever built. Following his retirement from Cessna, he was a freelance test pilot for many years. He was involved in flight test programs internationally, including the certification of Wipline amphibious floats on the DeHaviland Twin Otter and the first flights of a replica of the historic Sikorsky S-38.

 

 

Tom's words are in italics.

 

 

In early 1978, Cessna decided to produce a variation of its aerial application aircraft, the A188B AgTruck, with a turbocharged engine. This was in response to requests from customers in the west, operating at higher density altitudes and struggling to haul heavy loads. The final design incorporated a slightly different version of the Continental IO-520 with a ground adjustable wastegate and a new three-blade, wide-chord propeller. It was designated the T188C AgHusky, and I was assigned as project pilot.

 

First Flight

 

The first flight went well. I liked the smoothness of the engine/propeller combination a great deal. That spring and early summer I completed all the CAR 3 (forerunner of today's FAR 23 certification regulations) Stability and Control tests, and gathered the necessary climb and cruise data for the Pilot's Operating Handbook. I thought the airplane had better low altitude performance than the A188B, and certainly much improved altitude performance, as was expected.

 

[TABLE]

[TR]

[TD][/TD]

[/TR]

[/TABLE]

 

Before starting spin testing, my flight test engineer (FTE) and I went through the available literature on predicting spin behavior—there wasn't much. We focused on the change in inertia about the pitch and yaw axes caused by the heavier engine/propeller combination. Without more data, our predictions seemed little better than educated guesses, although it was obvious that spins would be adversely affected. In addition, the installation of the spin recovery parachute system under and aft of the airframe would make matters worse.

 

Spin Chute

 

As with all conventional gear airplanes, the tailwheel makes installing the spin chute a challenge. We eventually removed the tailcone underneath the rudder, and built a truss extending from its attachment to the aft fuselage, under the rudder, and ending with the parachute canister aft of the rudder by a reasonable margin. One of our goals in flight test was to keep things simple, so my choice for the spin chute "deploy" and "jettison" mechanisms (after using a spin chute, you have to get rid of it because you can't hold altitude once it's deployed) in the cockpit was a pair of ¾-inch ropes on each side of the pilot's seat, just below waist height, angling down and forward. Tied to the steel tubing of the cockpit frame under the panel, they extended back through the aft cockpit bulkhead to wire cables running through fairleads to the spin chute. Pulling a rope from aft to forward and down in what is best described as a pushing motion would activate its mechanism.

 

 

I decided that the rope on the left should be the deploy control, and the right one the jettison because I would be flying with my right hand and therefore less likely to yank the wrong rope if things got interesting. The structures people did a good job designing the truss and canister arrangement and it passed ground load tests easily. The ropes also did the job, despite their crudeness, in the ground tests. I was confident that it would all work as required in the air. We all were a little worried, I think, that we had, of necessity, made the inertia problem worse because of the spin chute. No one suggested doing the tests without one.

 

 

As was customary and cautious, we began the spin program at the usually less critical, most forward center of gravity, gross weight loading. My practice was to start the spins around 10,000 feet MSL (about 8500 feet AGL), and use the section lines for recovery inputs and for defining the length of recovery. All of the normal spins were completed successfully, as were spins with abnormal control usage in recovery and spins out of turns. The airplane was reluctant to enter in all cases. In most cases it didn't actually start spinning until at least ¾ of a turn in the entry phase. The rotation rate was rather slow. There was nothing out of the ordinary.

 

Aft Center of Gravity

 

For the first spins at the aft center of gravity, gross weight loading, our chief test pilot, Bruce Barrett, flew the chase airplane, and my FTE manned the camera. I completed the usual ¼ turn, left and right, ½ turn, left and right, and ¾ turn, left and right spins without any problem. The airplane was, as expected, more responsive to control inputs.

 

[TABLE]

[TR]

[TD][/TD]

[/TR]

[/TABLE]

Entry into a one-turn spin to the left initially looked normal; at ½ turn the airplane was steeply nose down. However, at that point it accelerated in yaw and the nose came up rapidly. At the one-turn recovery point, I could see nothing but sky and the rotation rate was very fast. I thought "uh oh," and quickly applied full right rudder and full down elevator.

 

 

Nothing happened. There were 10 to 15 pounds of backpressure in the elevator control (it took 10 to 15 pounds of force to move the stick forward). After one turn I had to look at the section line reference rather far away, since the pitch attitude had not changed—the nose of the AgHusky slopes down away from the cockpit so it had to be quite high to interfere with the forward view.

 

 

I went back to pro-spin controls for another turn, and then repeated the anti-spin inputs with the same negative results. The airplane did not respond at all and the backpressure was still there. The rotation rate was fairly fast, 90 to 120 degrees per second, and very stable.

 

 

I tried pro-spin and anti-spin inputs one more time. No change. Over the radio, Bruce was commenting on my altitude, and I decided that this flight condition would continue until the airplane screwed itself into the ground.

 

 

I pulled the "deploy" rope. There was a soft deceleration, the rotation rate slowed and then stopped as nose simultaneously came down to well below the horizon, all rather gently.

 

 

The controls worked again. I pulled the "jettison" rope, the airplane accelerated, I added power (the engine had quit in the spin, but restarted after the chute deployed) and leveled out. As I recall, recovery was complete around 5500 feet MSL.

 

 

My FTE in the chase plane counted 12 turns, which was more than I'd counted, so I'd missed a few in the heat of the moment. After seeing where the chute landed, I went back to Cessna.

 

Change the Inertia

 

[TABLE]

[TR]

[TD][/TD]

[/TR]

[/TABLE]

 

It was obvious that the inertia effect of the heavier engine and propeller along with the spin chute installation had overcome the airplane's basic stability and aerodynamic control power. In discussions with structures folks, they thought they could lighten the spin chute attachment assembly, and proceeded to do it. Engineers in flight test, aerodynamics, and advanced design groups began thinking about an aerodynamic fix for the elevator back pressure, a positiv indicator that the tail was completely stalled—elevator and rudder.

 

 

The second flight at the same heavy, aft loading was conducted with a lightened spin chute attachment structure, and a careful re-weighing and loading of the airplane. I decided to start at 11,000 feet MSL for a little more altitude cushion. I performed the ¼ turn. ½ turn, and ¾ turn spins as before. The airplane seemed to respond a little better in pitch and yaw, indicating that the lightened spin chute installation was a good idea. However . . . the one turn spin to the left had the same result as before with the same backpressure and perhaps a little slower rotation rate—kind of hard to tell.

 

 

I tried the normal anti-spin input—nada. I the experimented with ailerons with and against the spin in successive tries, going back to pro-spin for about a turn between tries. I then tried an elevator first technique. Then several normal anti-spin inputs with very rapid control inputs. Nothing worked. I went to the trusty deploy rope at about 4500 feet MSL.

 

 

Happily, it worked. After stabilizing in a steep descent I pulled the "jettison" rope. It didn't release. I tried again—same result. Now I was going down really fast. I finally thought to slow the airplane down as much as possible to lower the tension load on the release hook. I put the flaps down and pulled the stick back until I thought it was as slow as it would go, and then pulled really hard on the rope. It released, and full recovery was obtained at about 700 feet AGL. This time chase counted 32 turns. I took their word for it . . .

 

Why Didn't the Chute Release?

 

Post-flight examination of the spin chute attachment hook showed that the D ring on the end of the chute riser had slightly damaged the hook, preventing its free travel. Sadly, a year or so later we heard that a Piper test pilot had died when, after having his airplane go flat and successfully recovering with the chute, he flew it back to shore (they apparently did their spin testing off the coast near Lakeland) to save the chute. The chute D ring had enough time to damage the hook to the point where it didn't jettison, and he was then too low to bail out.

 

 

The lesson was to ensure that the Brinnell hardness of the D ring and the hook were the same, and to jettison the chute as soon as possible.

 

 

We began to work on an aerodynamic means to unstall the tail, since it wasn't feasible to modify the inertia any further. Several things were tried. I went on two weeks active duty (Tom retired as a colonel in the U.S. Marine Reserve) and Bruce Barrett filled in.

 

[TABLE]

[TR]

[TD][/TD]

[/TR]

[/TABLE]

 

When I returned, I found that the team had developed small delta-shaped strakes ahead of the horizontal tail. At high angles of attack, the delta shape would not stall, but would shed a strong vortex off its leading edge. This high-energy airflow would help to keep the flow attached to part of the rudder and elevator to provide enough control power to overcome the inertia effects.

 

 

I re-ran all the longitudinal stability and control tests successfully, and repeated the forward gross spin tests without any problems. I then flew the aft gross loading, and again had to use the chute (right away, this time) in a one turn spin to the left—again—when it didn't recover at the one turn point. That was a surprise. Investigation showed that the airplane had been loaded measurably aft of the aft center of gravity limit. After fixing that, I completed all the normal spins at aft gross successfully.

 

 

So this cocky test pilot (now somewhat less cocky), learned that what Ernie Gann had written was quite true: that sometimes an evil genie is going to piss all over a pillar of science, just for the hell of it.

 

Tom Wallis is a retired test pilot, now living in Oregon.

 

Learn and Live!

Tuffnut.

[Yenn]

I have a photo in front of me in Australian Flying, which shows 3 Bristell aircraft, in two of them the fin is ahead of the horizontal stab. far enough that none of it would be shaded.

I have never been close to one and don't know how the size and shape would go in theory, but I don't think shading is a problem

[M61A1]

I have a photo in front of me in Australian Flying, which shows 3 Bristell aircraft, in two of them the fin is ahead of the horizontal stab. far enough that none of it would be shaded.

I have never been close to one and don't know how the size and shape would go in theory, but I don't think shading is a problem

Looks to me as virtually the whole rudder is blanketed......

[ATTACH type=full]50775[/ATTACH]

[Old Koreelah]

Possible fixes:

-fitting a distinct strake forward of the fin;

-extending the rudder so a small part if it is below the tailplane.

 

I note that the F4U had a similar design, but the rudder was huge and not slanted back, ensuring it caught plenty of air during a spin:

 

Edited February 25, 2020 by Old Koreelah

[Jabiru7252]

M61A1, Try as I might I cannot pry the image from your post!

[M61A1]

M61A1, Try as I might I cannot pry the image from your post!

It was there before. I can’t get the image now either.

[Student Pilot]

There were lots of Corsairs on the 70's TV series Black Sheep, was pretty lame storylines but had lots of footage of Corsairs

[M61A1]

M61A1, Try as I might I cannot pry the image from your post!

I have reposted it as it seems to have disappeared.

[M61A1]

There were lots of Corsairs on the 70's TV series Black Sheep, was pretty lame storylines but had lots of footage of Corsairs

Yep, I loved it as a kid. I have some of the series now. It's interesting to watch just for the F4U and actual gun camera footage, but the acting is over the top. Robert Conrad's flight suit was so tight I reckon his scrote must have been damaged.

Funny watching cockpit scenes where they yell into the throat mic over the noise, but that tach is on zero as is the ASI and VSI while they're "manoeuvring" all over. Some serious over acting.

[Jabiru7252]

Wow, that Bristell looks like a Sport Cruiser. I wonder how the sport cruiser recovers from spins...

[Downunder]

So.....is it the rudder or fin that is important not to be shaded?

[M61A1]

Wow, that Bristell looks like a Sport Cruiser. I wonder how the sport cruiser recovers from spins...

Maybe???

https://aviation-safety.net/wikibase/144489

[M61A1]

So.....is it the rudder or fin that is important not to be shaded?

What I was told (from memory) by a well known design engineer was that at least 30% of the rudder needed to be outside those lines to be effective to stop spin rotation. There are other fixes like limiting CoG or elevator authority and strakes or combinations of any of these, but a good design is a better starting point.

[kgwilson]

The Sport cruiser and the Piper Sport were the same aircraft. It was rebadged by Piper & AFIK the relationship between Piper & Czech Aircraft Works went South for some reason & Piper stopped rebadging. There is a striking resemblance between the Bristell & Sportcruiser which may be a bit like the reason the Zenith & Savannah look the same.

[SilverWing]

The Sport cruiser and the Piper Sport were the same aircraft. It was rebadged by Piper & AFIK the relationship between Piper & Czech Aircraft Works went South for some reason & Piper stopped rebadging. There is a striking resemblance between the Bristell & Sportcruiser which may be a bit like the reason the Zenith & Savannah look the same.

The reason the Piper Sport, Sport Cruiser, Roko and Bristell look similar is because they were all designed by the same person - Milan Bristell. In an earlier job he was to some extent also involved in the design of the EuroStar/SportStar/Harmony but this aircraft has a distinctly different fin, rudder and tail plane configuration - and has been fully spin tested for EASA Certification.

[Downunder]

Piper sport was many tens of thousands of dollars more....for the same a aircraft.

Went the way of the Cessna Skycatcher and the Dodo.....

Probably a good private aircraft but nosewheels didn't hold up as a training aircraft...

[Thruster88]

Lots of good advice in this video for all pilots.

 

 

Marking the ASI is simple and a constant reminder, not that we should need it but we can all get distracted.

[M61A1]

Lots of good advice in this video for all pilots.

 

 

Marking the ASI is simple and a constant reminder, not that we should need it but we can all get distracted. [ATTACH type=full" alt="Resized_20200227_101019_2614.jpg]50860[/ATTACH]

I saw that video just the other day, but I had similar advice over ten years ago.

During a simulated engine fail n the circuit, the instructor was reminding me that if I maintain XX knots then I'm good for steep turns if I have to, while at Best Glide speed manoeuvring was quite limited.