argoldman

There is one problem with the Tristar....

It is restricted to grass runways

Interestingly, I ended up using the extra foam to redo the seatback. When I was doing the second side I was sloppy with the epoxy and also weighted the layup down with a piece of masonite on top of the peel ply, and forgot to use plastic to prevent a bond. Well, the masonite was pretty stuck to the seatback and cleaning it up made such a mess that I redid the whole thing.

 

So, it seems that Mr Puffer watches over me and put in the extra foam....

 

 

you just made yourself a nice layup table

The shoulder harness caused a plane to crash?

 

Sounds to me like the blame belongs a bit further upstream don't you think?

I'd like the link to that NTSB report.

Any idea of the failure mode of the seatbelt failure. Did the brackets pull the mountings out of the seatback brace or did the seatback brace separate from the fuselage?

Idonnknow,

If the seatbelts are held by the pine, or the aluminum in the Aerocanard kit or the phenolic, then why the heck put 7 layers of glass over them extending to the fuselage. Common guys, the wood has little strength in shear (especially perpendicular to the grain. The purpose of the wood, aluminum, phenolic is to try to resist crushing and to fill the concave space between the bottom of the fusealge and the flat part of the seat belt bracket and to give a flat area for the bolt heads or nuts to sit on. In the aerocanard the aluminum is tapped. How much strength do you think that the underlying foam in the center consoles (MK IV builders) gives to stop the seat belt from shearing its attachment off. It is the layers of glass on top which like the side layups distribute the load---NOT THE DIRECTUNDERLYING STRUCTURE. The overlying glass distributes the load in an acceptable manner.

Now if the bolts extended through the fuselage and bolted on the outside (using a filler block to give a perpendicular surface of appropriate size), that would be a different story in that the load would be distributed to the outside skin. That's an airplane of a different color and is not what we are dealing with here.

In an accident, although the wood/glass epoxy bond would hold somewhat the wood would split at the bolt heads were it not for the sandwich that I mentioned before. It is the top (inside) piece of bread that is the saver. It's similar to a hat section. One (I) wonder(s) if were it not for the difficulty in manufacture (the plans are written so that almost anybody with a modicum of skill can produce an aircraftoid product) if a hat section of glass, with the same dimensions, bonded to the fuselage in the same way, without the wood, phenolic etc as the filler, would yield the same strength results.(although the filler does stop it from parallelagramming and failing in that mode)

Having, had my gizzard saved by seatbelt attachments (aluminum squares, drilled tapped and bonded to the top of the dragonfly wing, by appropriate layers of fiberglass), I don't think that I would try that (especially since my attachments in my aerocanard are finished)

There is essentially no difference between the lower seat belt attachment and the seatback belt attachment. It is merely a matter of where and how you distribute the load caused by the tension of the belt (it is not explosive as the belts stretch in an accident.

Phenolic is great stuff to work with, aluminum is used in the Aerocanard kit, but don't count on the junction between either of those or wood, and the underlying glass to hold a belt on.

If you do think that that is where the strength lies, why don't you just bond 4 pieces of wood, aluminum, or phenolic to your firewall, counterbore, from the inside, till you hit the wood, or whatever and bolt your engine to that. (tongue extracted from cheek)

Something tells me that the -A200 has a built in intercom. Not the greatest, but it probably works. The units are at a good price, since Icom updated to a new model.

Just to further sing the praises of the Fein blade. You really don't have any idea of how hard it is to cut glass/epoxy when you use it since it goes all day. Take a metal cutting bandsaw, you can cut steel (slowly) and aluminum faster and repeat for a long time. Put a piece of glass/ epoxy through the blade and kiss it's metal cutting qualities good-by.

Just about the time I think I'm doing some good layups....

 

I got a nasty bubble in a bad place. I've got an airbubble in the outside seatbelt layup. I'm suspecting it was my technique. I laid up all 7 ply bid on plastic, then cut to size, then transferred to the place in one piece. Very much like I do most small layups and bid tapes. I think the problem was it was too many layup to do at once. I think the individual plies weren't able to conform to the shape. It definitely wasn't there last night, so I'm happened later during cure. The pics show that it's about a 1 to 1 1/2 inch bubble. Anyplace else I'd just inject the bubble as per plans.

 

But seatbelt attachment is so important that I'd like to get some outside advice. Do I inject it or sand it off and repair?

 

Sanding would likely require taking all 7 plies off and starting over. Doable, but tedious.

Bummer of a birthmark, Hal (for those far-side fans)

The picture is a little fuzzy, but it looks like the bubble is right in the middle where the attachment angle sits.

Did you use any heat while curing or adding the layup to the substructure??

Sometimes with large layups you can trap air which before cure finds its way together and gives bubbles. Or heat may create it.

If it were me, I would sand the bubble off till the top is smooth, sand the entire lay-up with 40grit, fill the defect with flox and lay another 7 ply layer over the old, now scuffed layup.

Alternately, you could go 1" or so beyond the defect and put a patch on, but the strength of this layup is critical (when needed) so spend the extra glass and weight.

This layup is sandwiched between the structure just below it, be it wood, or aluminum if kit aerocanard, and transmits the load through the plys to the fuselage. You will have two holes (mounting for the bracket) already in it, so one would think that if you just fill the defect (smoothing it out so that the bracket fits flush) would substantially reduce its strength since a major part of the glass strands will have little but cosmetic function. Perhaps Marc or other glass expert can shed more light on this, (or shoot me down)

For some reason, I am now thinking of Larson's "Boneless chicken Ranch.

It's also in EAA Sport Aviation

Ya, that's the one

Wasn't there just an article in, I believe, Kitplanes with regard to an anodized control rod snapping in a Safari helicopter which led to it's demise.

The article listed the strength degradation of the various types of aluminum treatments. A real eye opener.

I have to read it again (as most of my reading of mags is late at night while on the porcelain throne) but I walked away from the first read with the idea that any of the treatments that we use, including alodine, substantially weakens aluminum.

One of the reasons that using automotive oil is a no-no for aviation engines is the additives and the way that the detergent works. Aircraft engines (non-auto conversions) are rather loose fitting beasts and as such have more blow-by, etc. It is my understanding that aircraft oils handle this crap in a different way than automotive oils. I would assume that the automotive oils, be they synthetic or mineral have the same type of detergents in them and thus, other than the thinner lubricity, they act in an aircraft engine much like standard automotive oils do.

As a side note, Mobile 1 has been used in Rotary conversions with great success. However, there is no blow-by. I am led to believe that when oil change happens, the oil looks new.-- Perhaps that is rumor. However, on rebuild the main bearings seldom have to be replaced.

To add to Water, Anybody can do the work for the annual (condition inspection)and as he said, it must be signed off by the certificate holder or an a&P. That being said, anyone can do any kind of work on the aircraft. It does not have to be the certificate holder or a&p. There are no requirements for the person working on the aircraft. (great for those who don't build the plane). The conditional (annual) has to be done by the certificate holder or an A&P (AI is not required.) So---- If you want to, you and your neighbor's son (who may not be too bright) can totally rebuild the aircraft legally. (as long as you don't go against the original restrictions that were specified at the certification of the aircraft.

Have fun

If you get the round blade, one, maby 2 will last your whole project. As they wear (very slowly), you just rotate them. but they are $$$$$ Look on the web for better prices

Unless I read the research wrong, which is possible as I skimmed it,

The testing was on the bond between glass stuff and aluminum. In our birds this type of bond happens, for example in the aileron and elevator control tubes, but unlike many bonds in our aircraft, that bond is over a very large surface area. Perhaps that is why we don't see the tremendous problem which those data may suggest in terms of weak bonding. I seem to remember, that there is a specific anodization process which greatly increases the epoxy-aluminum bonding strength (I'm sure that it is used in many places in the aerospace industry (the Yankee(Grumman) series were totally bonded aluminum. They had some problems with this in the beginning, but that seems to have been solved before they stopped production))

There are few other places in our birds, if any, where we depend on glass to aluminum bond as a primary bond. When we sandwich a layup between a piece of aluminum (or wood) (even though we bond the aluminum (or wood) to the understructure) and a piece that gets bolted to the sandwich, ( ie seatbelt attachment on the seat-back bulkhead) we actually don't depend much on the aluminum (or wood) bond to the substrate as we count on the aluminum (or wood) to serve as a big washer transferring the stresses to the overlying glass (the PB&J of the sandwich) and where it sheds it's load.

Is anybody aware of delaminations happening in the control surface/torque tube interface????

I used acetone on polyvinyl esther resin, when fixing some swimming pool chairs.

But with epoxy is that good too?

Be really careful with the acetone (spelled don't use it!!!!)

Almost all of the lay-ups are over foam of some sort. Although we like to think that all of our lay-ups are impermeable to any outside influences, many are permeable and the small amount of air inclusions will wick any fluid to the foam which underlays.

Put a little acetone on some polystyrene and see the results. PVC etc may not react the same way, but if you dissolve the foam from under the layup you have squat!! You may never know it until the part fails, or a careful inspection shows what will seem like a delam.

Use clean water after sanding to get the sanding dust off. Peel ply is good. Jeff Russell suggested to always lightly sand the peelply (my guess is to activate the surface electrically. In the dragonfly world, we just wiped it off and bonded to it. I am not aware of any separations that were the result of that.

Don't use acetone....

Sorry for the troubles on Tuesday/Wednesday 27/28 January. I am in the process of moving the server to a new environment.

 

I'll also be upgrading the software, so we can get our calendar working again along with some other improvements.

 

Thanks for your patience and support.

 

Jon

Thanks for your efforts, Jon:)

Depending on where you like to place your elbow when flying, the expanded strakes may or may not give you more room.

However, the expanded strakes make the interior of the aircraft feel much larger which may be more important than the actual room, especially for the GIS or BIS. If desired, they also give you room to stow a hand held com, fire extinguisher, or lunch in easy reach.

Yep, that's what I was referring to. I read Marc Zeitlin's account of his total immersion instrument training and it seemed so much more efficient than dragging it out through a traditional school approach. While all the expense gets compressed I believe that it would be a great savings in calendar time and total cost over traditional. I also think the quality of instruction may be better too with a dedicated instructor.

I'm all for immersion training. When I did my instrument training [in the late '60s:irked: ](with the precursor to American Eagle), I flew, only on Saturday's and spent all day Saturday for about 2 months. I got my ticket in 40 hours. 20 hours of it were in actual conditions (which I consider a must). My first solo flight was actual IFR and I felt, and did well (at least I survived).

There is one problem with doing it so rapidly, and that is that unless you specifically go for additional dual, you will be flying in only one, or possibly on the cusp of only 2 seasons, with an instructor. In our part of the country we have 4, and if you use your ticket for travel, even though you may, personally, have only one season, you will ultimately be traveling through 4 of them.

The gremlins are different in each of the seasons, so if you do immerse, get some additional dual in the other climes.

Getting the ticket is just one step in staying safely.

Get the ticket and fly safely.

If this jest is over, I am ready to get out my slide rule (used to be pretty fast on the draw) or my chess set and challenge any of you to a duel !!!

WTJohnson

If you get out your slide rule I may have to start cursoring

First of all, delta V is the change in velocity, which is not the same as acceleration. Acceleration is dV/dT. If you are travelling at 20mph and reduce speed to 19mph your delta V is the same as if you decrease velocity from 10 to 9mph. The time taken is the same - assuming constant deacceleration - but the distance is doubled. If you limit the distance (as in a crash situation) then the time is not constant.

 

Perhaps my braking example was confusing. I was referring to emergency stopping distances, where the acceleration is (approximately) equal at all speeds and limited to a fixed proportion of the acceleration due to gravity. If you have a coefficient of friction of 1, the largest deacceleration you can maintain without skidding is 10m/s/s. Typically cars seem to manage 0.5-0.8 of this value. There are caveats (sports cars can produce downthrust at high speed) but at lower speeds it's basically correct.

 

I obviously wasn't claiming that a car couldn't brake gently, or that it's harmful to land an aircraft at high speed even though it can dissipate the energy in the brakes. We're talking about crashes and accidents here.

You, of course are right about delta V. It seems like we are really talking about the same thing. It was a pleasure sparring with you. Perhaps others benefited from our clarifications.

It is largely semantics. Acceleration is what does the damage, but in a crash situation the accelerations are likely to be approximately proportional to the kinetic energy.

Ai, there's the rub The acceleration (in this case a negative number or deceleration---Delta V) is not directly proportional to the kinetic energy in that the more of the KI the more deceleration must happen over a constant time frame. The other and equally important factor is the time frame in which the KI must be disipated to zero. A relatively small KI when forced to zero over a very short time will yield damaging results, whereas a huge KI forced to zero over a long period of time will yield nothing but heat. Said differently, the same KI will have different results when forced to zero depending on the length of time it has to go to zero.

Take your car at 50 mph, drive it into a concrete wall or take the same car, at the same speed and apply the brakes until stoppage. The KI is essentially the same in each situation, however the delta V is radically different.In the case of the concrete the KI is dissipated by some heat, some metal bending (heat) and some bone breakage(heat). In the gentle braking scenario, the KI is dissipated into heat, mainly by the brakes with some possible straining of the passengers on the seat belts and the physiology necessary to resist that with it's attendant production of heat as well as other factors. We may see this phenomenon in softening of gear legs if they are not shielded properly.

To see why this is true without doing the maths, consider car braking distances. Drivers should know that braking power is limited to a fixed deacceleration.

No, Braking power is definitely not limited to a fixed deceleration. It may have a fixed maximum. The deceleration of braking is, to the point of maximum, determined by the nut behind the wheel. You can stop gently, with only smiles on the faces of your pax, or you can slam on the brakes and suffer the comments of your pax as well as possible injuries caused by our friend delta V.

If you double your speed your braking distance quadruples. To stop within the same distance, you have to quadruple your deacceleration also.

 

I can see an argument that if you're moving faster you're likely to have a longer distance to deaccelerate, provided you don't hit a cliff. For example, if you fire two bullets into water, a high velocity round will penetrate deeper. If you land and hit a hedge, perhaps you'll penetrate further through and the acceleration will not be quite proportional to the square of the velocity.

 

Essentially my point, only if the braking force is constant (we won't consider brake fading here)

On the other hand, if you land with a high sink rate or nosedive into the ground, most of the deacceleration will be provided by the landing-gear and aircraft structure, rather than the ground. There's a fixed amount of structure, whatever the change in velocity.

 

Yea, However in a three dimensional world you must consider deceleration in three dimensions. Vertical deceleration is as important as horizontal. ie crushed spines, etc. With the vertical deceleration, the landing gear and aircraft structure merely serve to decrease the delta V by their abosorbtive qualities. Put a similar landing gear setup on the nose of the aircraft, with the same (identical)mechanical properties and attachments, if you hit something with the same KI, the resultant effect to the fuselage on the horizontal axis will be the same. (of course when flying, those bull horns sticking out into the breeze might be a detraction.)

It's also absolutely clear that if you have a given amount of kinetic energy and you reduce this to zero by stopping, all that energy has to go somewhere. Conservation of energy is a fundemental law of nature. Ideally it will all be dissipated by the airframe, hedge and by digging up earth or heating water during a water landing. In the worst possible scenario it all gets dissipated by mashing the pilot to a pulp, leaving the rest of the world intact.

 

Yea, and in a normal landing it is transformed harmlessly to heat by the brakes. (of course there is wear of the pads and the disks)

This isn't an entirely theoretical problem - early protective paragliding harnesses were rigid carbon fiber, and could survive just about any paragliding accident unscathed. They actually increased pilot injuries though.

 

Again exactly my point. Greater delta V

Actually---it is the KE---and it is the items that you pointed out. .......

So lessee-- if it is the KE that causes the damage, while I am flying at touchdown speed, where the KE is identical, why don't I feel the need to count my limbs.

The KE only exhibits itself harmfully when there is the delta V where the KE is converted to crunched metal/glass and bent bones. With a slow delta v, such as in a normal landing, since it happens over a long period of time (relatively) we feel it as deceleration, faster the deceleration the more chance of injury.

Perhaps we are just talking about semantics

Perhaps I have the wrong nutplate. If I had the one pictured at the start of this thread it might work....

 

Of course a larger washer might work, or I have some extra 1/8" 2024-T3 available.

there are nut plates with smaller dimensions between the rivet holes. Look in ACS

No, really it means you should build a light pilot. Small, light people are significantly more likely to survive car crashes (automobile wrecks) than obese 6'6" people.

 

What you would want out of your aircraft is for it to limit the maximum deacceleration in an accident to a level that your body can withstand. Cars (automobiles) do this by using a space-frame that crushes gradually, absorbing energy as it goes. But there are some small cars that will withstand ridiculous accidents and still keep the passenger compartment intact, but through failing to limit the deacceleration the occupants may still be killed.

 

To some extent adding weight to the aircraft will also increase the structure available to absorb it's energy, and assuming the pilot mass remains constant the ratio of sacrificeable mass to non-sacrificeable mass will increase. How effectively this happens is a matter of design. To use an extreme example, paraglider harnesses typically only weigh a few kilograms but provide relatively little protection for the pilot, in comparison with an aircraft airframe.

 

For any given design, lightening the aircraft will give you a lower stall speed which will give you a lower landing speed, which is obviously good. But as Drew pointed out lowering the landing speed, even by a little bit, is far more significant than lowering the mass by a similar proportion.

But then again, it's not the kinetic energy that is the killer, it is the Delta V (rate of change in velocity from touching down speed until stopped) as well as the various things that can penetrate the cockpit, and perhaps our flailing about due to lack of restraints. Glass seems to have a great ability to make that delta V more lifestyle manageable than metals. ie smaller delta V. modern craft of the road persuasion have foam or liquid filled bumpers and crumple zones built into them so as to reduce the delta V as much as possible in the case of a collision. Perhaps this approach could make our, and other craft more survivable in the case of a less than successful landing.

then why is the survivability in an ez been so much better then a LSA or a ultalight or C- 150 type

Agreed, that is the topic of another monotribe. When I get time I will talk about that. As I said there are many factors which enter into the equation.

My point was not to say that the ultralites or C-150s are safer, as a matter of fact what is still in my head is the answer to that, however I must get away from the computer. It was only to say that when comparing accident/survivability, etc we must play on as level field as possible, which statistics don't.

I agree...

 

 

 

All aircraft are equally safe..? No way.

 

 

Safety of an aircraft has many factors which must be taken into account (including type of pilot) when trying to compare one to another.

Our aircraft have a relatively high lading speed, higher, in fact than many high performance store bought types.

Higher than ultralights also.

Part of the increased risk in the e-z types is that speed. VGs tend to bring the landing speed down to that of a Bonanza, Mooney Cirris or Cessna's glass.

An engine out experience at a similar altitudes will yield interesting results.

If a low altitude, the ultralites and trainers will do better. As the landing speed increases the safety of the aircraft with engine out decreases.

At 1000' with no engine, would you rather be flying a weedwacker or a lear jet?

At 2000' same question

At 3000' the answer changes quite a bit. We just had a successful landing of an airbus just yesterday under these circumstances. (certainly not a low landing speed aircraft)

At 5000' chances are, with equal piloting skills most of the aircraft would be able to land safely (assuming appropriate landing areas available)

At 10,000' All aircraft would have the opportunity to land safely independant of their landing speed.

I will never forget William Wynne (of Corvair conversion fame), at a Dragonfly fly-in musing about how the higher landing speed of the D-fly approx 70 is so dangerous, and that we should all be flying pietenpols (some liberty taken with the misquote) and we would all be much safer. Good thought, except he almost perished in a Piet accident and subsequent fire shosrtly after that. (fortunately he is now OK)

If you are going to compare aircraft, you must compare apples to apples.

Perhaps comparing all aircraft with similar landing speeds would be a good start.

It would also be more significant if the altitude of the engine failure/ reason for the less than goo landing is taken into account.

The real question is that with an engine failure or other forced landing situation in aircraft of similar landing speed, at similar altitude, What is the compairative damage/fatality rate. Other data points although interesting seem to be somewhat trivial.

Until we change the laws of physics (as we know them) if we want a high performance, economical(?) aircraft, we must compromise by the higher landing speeds. If we are unwilling to compromise, by all means get/steal/build one with much lower landing speed and the increased safety that MAY be gained.