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Van's over-engineering compared to certified aircraft

I was reading through some older threads last night about how the RVs are significantly over-engineered when compared to other certified aircraft. Vic made reference specifically to a comparison between an RV and a Cessna. I'd be curious to know, does anyone have pictures, drawings, etc. that might show to what degree these airplanes are over-engineered?
 
I don't have a drawing, but I've looked inside some airplanes structures and said "thats the wing spar?!?!?!" Or "that's the engine mount!?!?!?". Same for hinges, brackets etc.

Stuff on RV's does seem to be beefier that alot of certified stuff.
 
I was reading through some older threads last night about how the RVs are significantly over-engineered when compared to other certified aircraft. Vic made reference specifically to a comparison between an RV and a Cessna. I'd be curious to know, does anyone have pictures, drawings, etc. that might show to what degree these airplanes are over-engineered?

I don't know that they are as over-engineered as some would think. There has been mention of the spar and motor mounts, for example, but comparing those on an RV to a C-172 is not really appropriate since the typical two seat RV is stressed for +6/-3G while the C-172 is a utility category aircraft only. Moreover, the C-172's wing spar isn't carrying the load in the same way since it is strut-braced and not a cantilevered design.

The only accurate way to know if something is "over-engineered", as used in this context, is to understand the design specifications and then compare them to the actual design. If the design spec says +6/-3 but the design will handle +12/-6, then saying it's over-engineered is probably fair. But to say that one design implementation (an RV) is over-engineered to another design implementation (C-172) is specious at best.
 
I don't have a drawing, but I've looked inside some airplanes structures and said "thats the wing spar?!?!?!" Or "that's the engine mount!?!?!?". Same for hinges, brackets etc.

Stuff on RV's does seem to be beefier that alot of certified stuff.

This is the kind of stuff I was referring to, hoping someone might have some pictures. I wonder if the beefiness of the RVs is because of the aerobatic capabilities or just generally more solid construction?
 
I don't know that they are as over-engineered as some would think. There has been mention of the spar and motor mounts, for example, but comparing those on an RV to a C-172 is not really appropriate since the typical two seat RV is stressed for +6/-3G while the C-172 is a utility category aircraft only. Moreover, the C-172's wing spar isn't carrying the load in the same way since it is strut-braced and not a cantilevered design.

The only accurate way to know if something is "over-engineered", as used in this context, is to understand the design specifications and then compare them to the actual design. If the design spec says +6/-3 but the design will handle +12/-6, then saying it's over-engineered is probably fair. But to say that one design implementation (an RV) is over-engineered to another design implementation (C-172) is specious at best.

I can appreciate this, and I did contemplate prefacing my post with an apples-to-oranges disclaimer. I have never taken the time to really look into the construction of a 172 (or Archer, or whatever) because before I started building my 14 I really didn't care. Now that I know what the inside of mine looks like it makes me curious about others!
 
Show me the data

I was reading through some older threads last night about how the RVs are significantly over-engineered when compared to other certified aircraft. Vic made reference specifically to a comparison between an RV and a Cessna. I'd be curious to know, does anyone have pictures, drawings, etc. that might show to what degree these airplanes are over-engineered?

My Diamond DA40 had a 26G "cocoon" for the passengers and crew, plus airbag seatbelts. The fuel tanks were welded aluminum placed between two beefy composite wing spars. My 1650 pound DA20 had a nose gear design more like the 2050 pound RV-14A.

Accident data would seem to indicate that these Part 23, factory built airplanes are a lot more "over-engineered" than the non-certified, garage-built RV's.

I for one am not convinced that the RV's are over-engineered compared to certified planes.
 
My Diamond DA40 had a 26G "cocoon" for the passengers and crew, plus airbag seatbelts. The fuel tanks were welded aluminum placed between two beefy composite wing spars. My 1650 pound DA20 had a nose gear design more like the 2050 pound RV-14A.

Accident data would seem to indicate that these Part 23, factory built airplanes are a lot more "over-engineered" than the non-certified, garage-built RV's.

I for one am not convinced that the RV's are over-engineered compared to certified planes.

I take it you've reviewed the design specifications for both then in order to make this comparison? And what's the max load factor for a DA40 again?
 
I've heard people exclaim about Van's being overbuilt :eek:...but it's just not true IMHO.

My -7 is NOT over engineered, far from it. It's a great aircraft but the total performance comes from the light weight design. Some Beechcraft's may be considered over designed...they're built like a tank.
 
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I take it you've reviewed the design specifications for both then in order to make this comparison? And what's the max load factor for a DA40 again?

Kind of difficult to do. I do know that all of the Diamond's meet Part 23. No idea if any of the RV's meet any spec.

This link provides a bit better perspective

https://www.diamondaircraft.com/en/private-pilots/safety/

Other than a couple of drop test videos, not much from Van's as to their design criteria.

The Diamonds are normal/utility category, same as some of the Van's designs.

My issue is with blanket salesman-like comments with very little data to back them up.
 
No idea if any of the RV's meet any spec.

Sure they do - Van's specs. Don't assume that because it's not published in the federal register that it's not a design specification.

My issue is with blanket salesman-like comments with very little data to back them up.

I agree, which is why I take issue with blanket salesman-like comments with very little data to back them up. For example:
Accident data would seem to indicate that these Part 23, factory built airplanes are a lot more "over-engineered" than the non-certified, garage-built RV's.

You are judging all RVs by a part 23 design standard, but not all - in fact most - were designed to that standard. Conversely, I might say that DA40 is under engineered, since it's not stressed for aerobatics, has relatively high stick forces, low roll/pitch rates, and excessive takeoff and landing distances compared to some RV models.

Both are fine airplanes and we can infer that they both have proven to measure up to their design specifications. But the DA40 fails to measure up to the same specs as an RV-4 (for example), and the -4 wouldn't meet part 23.
 
Sure they do - Van's specs. Don't assume that because it's not published in the federal register that it's not a design specification.

Agreed. What I should have said was that I can't determine what FAA or EASA spec(s) any of the RV series meet, other than the LSA RV-12.

You are judging all RVs by a part 23 design standard, but not all - in fact most - were designed to that standard.

And we know that how? At least with a certified airplane you can be pretty confident that not only was it designed to that standard, it was tested and proven.

Conversely, I might say that DA40 is under engineered, since it's not stressed for aerobatics, has relatively high stick forces, low roll/pitch rates, and excessive takeoff and landing distances compared to some RV models.

Sure, different airplanes for very different missions. The 9, 10 and 12 weren't designed for aerobatics either. I'd still prefer to be in an accident in ANY Diamond versus ANY RV.

Both are fine airplanes and we can infer that they both have proven to measure up to their design specifications. But the DA40 fails to measure up to the same specs as an RV-4 (for example), and the -4 wouldn't meet part 23.

Hardly a reasonable comparison. Maybe a better one would be a 10 and an SR22?

Yes, I know my RV-7 and under construction 10 will outperform my DA20 and 40 in handling qualities, speed and runway performance but I am not willing to accept that RV's are over-engineered in comparison.
 
And we know that how? At least with a certified airplane you can be pretty confident that not only was it designed to that standard, it was tested and proven.

My error. I meant to state the opposite actually of what I wrote - the "not" that I omitted originally is important :)
You are judging all RVs by a part 23 design standard, but some - in fact most - were not designed to that standard.

I think we're on the same page. "Over engineering" is used in a vague way and having spent my previous career in engineering I'm perhaps a bit sensitive when terms like that get thrown about :)
 
Over Engineered?

Just my $.02 after 40+ years of maintaining and repairing light aircraft. The RV line is well engineered for the intended mission and price point. There?s no magic, they are light and clean with a good power to weight ratio. The lightness comes from using just enough metal and fiberglass to get the job done so I wouldn?t consider the RVs as durable as a similar certified aircraft. A good example of this is the landing gear. If it was built like a Cherokee it would perform like one. We just accept compromises to get the fabulous performance for the dollar that we all love so much.

Don Broussard A&P IA ATP
RV9 Rebuild in Progress
57 Pacer
 
Probably not

I'll open by saying I'm not too big a fan of the term "over-engineering". It implies the design engineer did not have a clear reason for the design specifications; like using .032 everywhere .025 meets spec just because "a bit thicker has to be better right?" The problem with that is that design is a series of compromises and making any part of any aircraft "beefier" than it needs to be based on the design criteria would adversely affect some other characteristic of the aircraft (cost, useful load, handling, etc).

I think it is very likely that the designer considered the variability in the workmanship of the builders, construction materials, and the intended use of the aircraft as they determined the design specs and safety margins. One good example is the nose gear. Cessna clearly intended the 172 to be flown by low-time pilots and designed a nose gear that would take a least a bit more abuse than an "A" series RV will. The nose gear RVs are just as clearly not intended to be the first plane you fly. It is just as likely that Vans designers built more-than-customary safety margins in other aspects of the design to account for builders with less skill than the average Cessna worker.
 
If you want over-engineered, look at a Navion. But then, it is thought that it was designed to land on a carrier (and did) so maybe not over-engineered after all. I would never put an -A model Vans aircraft through what I have put a tripacer through. If Vans is over-engineered then a tripacer is over-over-engineered.

They are what they are - total performance. But I would argue that they are just enough to accomplish the mission. We know that it is possible to rip the wings and tails off these things. How many 172s out of all the thousands flying have ripped their tails off in flight over the past 5 or 6 years (or however long it?s been since the -7 driver went down)?

Saying they are over-engineered May lead some zealous and foolish pilot to over-load or over-fly their over-engineered plane.
 
This is like the argument I hear all the time that Boeings are built "stronger" than Airbuses. It's total BS. No designer builds an aeroplane (especially a commercial one) any stronger than it need to be to be able to do the job and meet the appropriate legal design criteria. A heavier or beefier Boeing is going to have a commercial disadvantage when it comes to payload/range capability.

It comes down to appearances. Having flown both commercially I can compare. Boeings have bigger, chunkier switches. They have control yokes rather than side sticks. Big, moving thrust levers rather than small fixed ones etc etc. The whole impression is "beefier" - American design against European. Nothing to do with being stronger or over-engineered.
 
Personally I would prefer that they at least slightly over-engineer their design vs under-engineered!

I'm sure there are examples of perfectly built RV aircraft but would much prefer some "safety margin" and expectations that some builders take longer to get to the top of the learning curve. Based on what I have seen on some of Vic's slides I would subjectively say that our aircraft are at least slightly forgiving. That doesn't mean you ignore bad rivets or skip bolts in your build, counting on this margin. :)
 
This is like the argument I hear all the time that Boeings are built "stronger" than Airbuses. It's total BS. No designer builds an aeroplane (especially a commercial one) any stronger than it need to be to be able to do the job and meet the appropriate legal design criteria. A heavier or beefier Boeing is going to have a commercial disadvantage when it comes to payload/range capability.

It comes down to appearances. Having flown both commercially I can compare. Boeings have bigger, chunkier switches. They have control yokes rather than side sticks. Big, moving thrust levers rather than small fixed ones etc etc. The whole impression is "beefier" - American design against European. Nothing to do with being stronger or over-engineered.

Hate to start an off-topic Boeing versus Airbus war, but as a former Boeing engineer and long time Boeing pilot, I'm going to push back a bit.

China Air 006, 747SP, pulled about 5 G's during a recovery from loss of control at 41,000 feet. Aircraft was damaged, some injuries occurred, but the airplane stayed (mostly) intact and landed safely. As you know, transport category design load factor is 2.5G's positive, with ultimate load limit of 3.8G's. I'm not aware of any early Airbus models that have "accomplished" anything similar.

Of course, the FBW Airbus models should never depart controlled flight and can't pull more than 2.5G's in normal law. So I suspect (but have no proof), that Airbus can design their FBW models with a little less margin. Whether they do or not - I really don't know.

Boeing's implementation of Fly By Wire incorporates soft and hard limits, giving pilots the ability to pull 2.6 G's (or more) if needed and aerodynamically available.
 
Compared to factory

I recently disassembled a 1946 Cessna 140, down to the individual fuselage frames and skins. I saw no deburring and prep to the standards that the RV assembly instructions specify. Sheared sheets with edges that catch a fingernail, etc. I even found pencil markings used at the factory 73 years ago to mark rivet locations.

FWIW.
 
"Over-engineering" is a rather vague term. To some it means over-strength and to others, it approaches the infamous "paralysis by analysis," excessive use of engineering time.

Are the RVs over-strength? Apparently not, from all I've read. They seem to be adequately designed for their mission, without a whole lot of margin. Remember, their mission includes being built by amateurs.

Has Van's wasted excessive engineering on them? Probably not, because they are still in business.

Dave
 
The Vans aircraft (edit) ARE certified and designed for aerobatic category load factors. Cessna's are certified and designed to normal and utility category load factors (which are lower than aerobatic).

Van's aircraft are not "over engineered" or assume you mean over built or stronger than a Cessna. RV's are well designed for intended purposes if flown within limits.

Big difference is in control forces and speed. RV's have very light controls and are very fast compared to a Cessna... so a pilot could overload an RV easier than a Cessna if they are careless or ignorant RV's build speed very fast when pointed down hill and can exceed Vne quickly. The control forces are very light. if the pilot is incompetent or careless, say botched Aerobatics, excessive loads are possible and more likely than a Cessna. Cessna you can't legally do aerobatics, except in an C150/152 Aerobat.

Cessna's are more forgiving and in many ways are a little more robust as well for "abuse loads". An airplane is only as strong as it's weakest structural link. Cessna, can take the pounding of student pilots year after year. The nose gear on RV trike models is not as robust as a Cessna to be sure.... for example.

RV through wing main spar carry through is stout. However a Cessna typically has a strut, also strong.

One is a fast sport kit-plane and the other is a Cessna. Apples and Oranges. Are RV's falling out of the sky? No. Are Cessna's falling out of the sky? No.
 
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I recently disassembled a 1946 Cessna 140, down to the individual fuselage frames and skins. I saw no deburring and prep to the standards that the RV assembly instructions specify. Sheared sheets with edges that catch a fingernail, etc. I even found pencil markings used at the factory 73 years ago to mark rivet locations.

FWIW.

Which kinda makes one wonder.......why do RV builders obsess over these build techniques?

2019-1946 = 73 yrs

2019 + 73 = 2092 AD

How long do our RVs need to last? :)
 
One thing I found interesting when researching my first RV purchase was how well the RV6 seems to hold up and the complete lack of any reports of inflight structural failures. They may have been some but I could not find any during my research. The RV7 and to a lessor extent the RV8 have had issues however most appeared to be outside the design envelope of the airframe with possible the exception of the Utah accident a few years ago. The six was probably designed with a slide rule but you would expect the seven to be a improvement.
G
 
If there was ever an example of "over engineering" by Vans (defined here as a part stronger than it needs to be) it is the RV-6 spar carry through. They took the -3/ -4 style of spar attach and just extruded it out a few feet. Made for a clumsy, hard to install and probably over-strong spar center section. Look at a 6 and 7 side by side and you'll see what I mean.

This may or may not have anything to do with the higher rate of in-flight failures of 7s vs 6s, even though they are in all other ways very similar.
 
engineered vs implementation

While I was building the tail on my 7A a very experienced AI visited me and immediately saw a crack in a part.

I called Van's and got it replaced. My AI helper pointed out that the part's alignment was not correct as to the "grain" in the sheet from which is was cut. He had been my instructor in a metal 101 class at a local aero school so I knew what he was saying. Cracking like that can result from the alignment issue.

I discussed that with the Van's tech and he brushed it off by saying they are not falling out of the sky. There cannot be any question that properly aligning the intended load on the part with the grain in the metal is how you do it best. But that doesn't mean it is necessarily faulty if you don't. It depends on what loads it is intended for and how well you can predict its strength if you don't align. Van's is getting as many parts as they can from a sheet of aluminum without, apparently, regard for grain in this context.

Add that the the well known problems with the 7A nose gear.

I love my 7A but I don't think that "over engineered" is a particularly accurate assessment.

As for Cessna landing gear, I've abused some of them pretty awfully and with no obvious damage. I would not want to do the same to my 7A, especially with regard to the nose gear. Yes, I did make the SB mod AND added the anti-splat device from a 3rd party. But I stopped using grass strips, too.
 
Offensive language...

In my profession, accusing someone of over-engineering is, at best, accusing them of neglecting their professional responsibility (which is against the law for a Professional Engineer in most states). That term is highly offensive to a structural engineer. The primary goal of structural engineering is to arrive at a design that can resist the required loads with an optimal structural system. What defines "optimal" can vary (least cost, fastest speed of construction, lowest weight...)

I do not think the OP was in any way intending to denigrate the Engineers at Vans. I believe he used the term over-engineered in reference to the perceived robustness of the design. I think many of the replies have very aptly discussed the dangers of exaggerating the capabilities of any design. My whole point in posting this is so that people without this perspective may gain some insight into why there have been some testy responses to the topic.

There are many places in an RV structure where having stress risers (nicks, scratches, burs, etc..) will not cause any problem over the life of the aircraft. However there is not a reasonable way of evaluating and communicating which ones are and are not a problem to such a vast manufacturing base. I would assume, in an area with any significant shear flow in a Cessna you will find nicely deburred and smooth surfaces.

I have no problem shooting for the level of quality that Vans describes in the first five chapters. I just hope I don't hold myself to such a standard that I never finish...
 
Interesting Read

Really enjoyed reading through this thread.

Interesting points to think about.

Worked several years as an AutoCAD technician for a group of Civil Engineers.

To me "Over Engineered" means a group of engineers trying to accomplish what one could do in less time.....

Best regards,
Mike Bauer
 
...and

"...I would assume, in an area with any significant shear flow in a Cessna you will find nicely deburred and smooth surfaces..."

...and that would be a faulty assumption. Having owned many different Cessnas and Pipers over the years, I never found that to be the case...
 
"Over-engineering" is a rather vague term. To some it means over-strength and to others, it approaches the infamous "paralysis by analysis," excessive use of engineering time.

Are the RVs over-strength? Apparently not, from all I've read. They seem to be adequately designed for their mission, without a whole lot of margin. Remember, their mission includes being built by amateurs.

Has Van's wasted excessive engineering on them? Probably not, because they are still in business.

Dave

My vote: Best answer.
 
We all know what assumptions do...

Well I am glad I stated it as an assumption. I have not had the opportunity to see under the skin of light aircraft. For what it?s worth, the certified aircraft I see in production have extremely high standards for edge preparation, but those are all made for operations in the flight levels. Thanks for setting me straight Bob.

Of course, if the stresses are sufficiently low, the stress risers are a non issue.
 
I remember seeing a horizontal stabilizer from a Luscombe that was de-skinned for restoration. The ribs looked like bananas, none had been fluted. The AME said that Luscombe didn't flute the ribs, they just bent them into place and riveted them.

Regrading the difference between a -6 and a -7, the -6 was designed as someone said "with a slide rule" which may be an overstatement, there were probably hand (electronic) calculators involved as well. But more calculation was done longhand, i'm sure, and those calculations would be done at discrete points in the structure. In between those points, the loading and structure sizes would be some kind of average. That could lead to slightly oversized parts in places.

On the other hand, the -7 was designed with a computer, and as such could be optimized at every point on the aiframe to meet the mission, with safety factors, and no more. There are practical considerations as well, such as reinforcing for wing-walks, that probably aren't factored into the (flight) structural loading, but are necessary for human interaction.
 
Slide rule

I wouldn’t knock that slide rule...look through aviation’s past and you will find some really impressive design work that was done...you guessed it...on a slide rule...:D
 
Well said below

Just my $.02 after 40+ years of maintaining and repairing light aircraft. The RV line is well engineered for the intended mission and price point. There?s no magic, they are light and clean with a good power to weight ratio. The lightness comes from using just enough metal and fiberglass to get the job done so I wouldn?t consider the RVs as durable as a similar certified aircraft. A good example of this is the landing gear. If it was built like a Cherokee it would perform like one. We just accept compromises to get the fabulous performance for the dollar that we all love so much.

Don Broussard A&P IA ATP
RV9 Rebuild in Progress
57 Pacer
 
Two biggest concerns with RV designs

I have two main concerns over the RV engineering.

First is the location of the fuel tanks which can easily impact a post or tree and rupture during an off field landing. Other designs put the tank behind the main wing spar providing better protection.

Second is the tendency of the fuselage to buckle behind the cabin but in front of the shoulder harness anchor point during a hard landing causing the occupant to be more likely to impact the glairshield.

I love flying my -9a. It is an amazing machine. Those are the only two design details that give me some pause when contemplating an off field landing.
 
Hate to start an off-topic Boeing versus Airbus war, but as a former Boeing engineer and long time Boeing pilot, I'm going to push back a bit.

China Air 006, 747SP, pulled about 5 G's during a recovery from loss of control at 41,000 feet. Aircraft was damaged, some injuries occurred, but the airplane stayed (mostly) intact and landed safely. As you know, transport category design load factor is 2.5G's positive, with ultimate load limit of 3.8G's. I'm not aware of any early Airbus models that have "accomplished" anything similar.

Of course, the FBW Airbus models should never depart controlled flight and can't pull more than 2.5G's in normal law. So I suspect (but have no proof), that Airbus can design their FBW models with a little less margin. Whether they do or not - I really don't know.

Boeing's implementation of Fly By Wire incorporates soft and hard limits, giving pilots the ability to pull 2.6 G's (or more) if needed and aerodynamically available.

I was going to cite exactly this same case. I saw the airplane at the United depot at SFO after it survived that flight. A whole bunch of people lived because of Boeing's conservative design approach.

A second example to cite is the A-300 that shed its vertical tail in a high sideslip overshoot that was arguably pilot-induced, but the politics glossed over the fact that the incident occurred at a speed lower than V_a (maneuver speed) and the fin should have stalled before exceeding any structural limit at that speed. Designed to meet the narrow letter of the regs, but failed to meet the spirit and intent of the regs, and a whole bunch of people died.
 
I have two main concerns over the RV engineering.

First is the location of the fuel tanks which can easily impact a post or tree and rupture during an off field landing. Other designs put the tank behind the main wing spar providing better protection.

Second is the tendency of the fuselage to buckle behind the cabin but in front of the shoulder harness anchor point during a hard landing causing the occupant to be more likely to impact the glairshield.

I love flying my -9a. It is an amazing machine. Those are the only two design details that give me some pause when contemplating an off field landing.
The tendency to buckle the fuselage has been noted in several accidents in Australia...

RV-3 VH-BEM, RV-6 VH-TXF, RV-6 ZK-VBC and likely RV-6 VH-OAJ as well.
 

First time I've seen this, quote from the linked accident:

"Examination of the failed propeller blade

A fatigue crack had initiated near the leading edge of the blade 216 mm from the blade tip. Crack growth had occurred as a result of alternating thrust loads, and had propagated along the thrust face (rear surface) of the blade. The characteristics of the crack indicated that it had grown under constant amplitude loading. There was no evidence of flight by flight striations. The propeller material was of the correct type and no damage or other reason for the crack to initiate was found.

The pilot fitted a new engine and propeller to the aircraft during construction. The engine was modified to improve and balance the airflow through the valves of each cylinder to enhance engine performance. In an apparent further attempt to improve engine performance, the pilot replaced one magneto with an electronic ignition system that was capable of varying the ignition timing in response to changes in engine RPM and manifold pressure. That variation contrasted with the fixed timing ignition provided by the other "standard" magneto fitted to the engine."


"All propellers are subject to alternating thrust loads during normal operation. Propellers are designed so that those loads will not exceed the design value, thus preventing the development of fatigue cracks during operation. The firing of each cylinder in a reciprocating engine produces torsional vibrations. That means that the crankshaft momentarily speeds up at each firing stroke, and then slows down again prior to the next firing stroke. The vibration leads to alternating thrust loads in the propeller.

Examination of the engine connecting rod big-end bearings revealed distress on the bearing surfaces. That distress was indicative of firing loads exceeding the designed capacity of the bearing lubrication. For optimum operation of spark ignition engines, the peak pressure developed by the combustion of the fuel air mixture should occur approximately 15 degrees after the crank has located past top centre.

Ignition timing was a critical factor, influencing engine power, fuel economy, and the operating condition of the engine. Timing depended on the rate of propagation of the flame front through the fuel-air mixture. Increased or advanced ignition timing resulted in increased combustion chamber pressures. Magneto timing was fixed and was optimised for the operating range of the engine. If the response of the electronic ignition system to reductions in manifold pressure created by part throttle opening was to advance the timing of ignition, that could increase cylinder head pressures and increase the magnitude of torsional vibration."


Did they just say that the prop and engine bearing damage was because he was using an electronic Mag with a standard one?

Will start looking closer at my Catto prop during pre-flights. Have an EMAG and a Slick.

Best regards,
Mike Bauer
 
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Did they just say that the prop and engine bearing damage was because he was using an electronic Mag with a standard one?

No, that's not what they said. Look at the factual statements, versus the leading statements, and one critical factual statement that was left out. There was a fatigue crack on the prop blade, which CAN be caused by torsional vibrations, that's true. There was an electronic ignition fitted on the engine, that's true. The timing of an electronic ignition (some models anyway) can vary depending on the manifold pressure and rpm, that's true. Bearing distress was found on the engine indicative of exceeding the stresses of the bearing lubrication - that's a fact.

Now the leading statement that is NOT necessarily true - that advancing the ignition point causes increased chamber pressures - that statement is only partially true. If the advancement occurs at full manifold pressure, then yes it is true. Most EI's will not go to full advance at full manifold pressure - because doing so puts you into the detonation "red box" where you can damage the engine. If the manifold pressure is lower, such as at altitude in cruise, then you can advance more on the timing and you are still outside the detonation area, so you are fine. At lower manifold pressures, advanced timing does NOT produce a peak cylinder pressure greater than the standard full manifold pressure levels with standard timing - so the logical leap that advanced timing automatically means exceeding cylinder pressure limits is faulty. The finding is worded to point at torsional vibrations from the EI firing as a suspect cause.

Now the critical factual statement that is not mentioned - that bearing distress evidence indicating excessive cylinder head pressures is commonly caused by detonation, rather than torsional vibration. Torsional vibration can easily cause the propeller blade fractures, if it's bad enough for long enough - but it likely did not cause the bearing damage on the engine connecting rod - that was almost certainly caused by detonation.

Now the key part of this is taking the anectodal apart from the factual - we know the electronic ignition was installed, but we don't know what model/manufacturer it was, and we don't know what the timing map looked like versus the manifold/RPM on that unit. If the user had played with the factory maps and gotten the engine into a detonation area, that would explain bearing damage and MAY explain the torsional vibration producing the propeller blade crack. Without knowing what the installed ignition map looked like, and the operating conditions at the time, there is no reason to assume the EI is at fault (no matter what brand it was) - and it may very well be a case of the operator taking the EI outside its normal parameters in a hunt for more power, and finding the limits of doing so.
 
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I have two main concerns over the RV engineering.

First is the location of the fuel tanks which can easily impact a post or tree and rupture during an off field landing. Other designs put the tank behind the main wing spar providing better protection.

The location of pretty much all newer Cessna and Pipers as an example, have the fuel tanks forward of the spar, typically for weight and balance reasons. Back in the 90?s Vans modified the forward tank attachment point to allow the fitting to pull away from the fuselage as the wings bent in a crash. This reduced the possibility of the root rib being torn out introducing a large leak. Aft of the spar is typically a weight and balance problem with moving CG during full burn. Bigger a airplanes can sometimes put the tank behind the spar because the CG range allows it.
 
Propeller testing done in conjunction with Van's, by Hartzell has produced empirical data that shows that advanced ign. timing can have a detrimental effect on fatigue life of propellers in certain operating modes.
There is info on Hartzels web site.
Detonation could definitely have an impact as well (consider it to be an order of magnitude worse than just highly advanced ign timing).

The issue with this case is that there appears to be no evidence to indicate what amount of timing advance the engine may have been operated at. Only that there was evidence of engine damage that could have been caused by extreme combustion pressures, and the non standard ign system is the only thing to point a finger at as a possible cause (though they don't seem to do that directly).
 
I have two main concerns over the RV engineering.

First is the location of the fuel tanks which can easily impact a post or tree and rupture during an off field landing. Other designs put the tank behind the main wing spar providing better protection.

Second is the tendency of the fuselage to buckle behind the cabin but in front of the shoulder harness anchor point during a hard landing causing the occupant to be more likely to impact the glairshield.

I love flying my -9a. It is an amazing machine. Those are the only two design details that give me some pause when contemplating an off field landing.

My biggest concern (by far) when contemplating an off field landing in my RV7A is the very high probability of the nose gear collapsing leading to the aircraft tipping over and me being trapped inside, possibly injured, and with fuel leaking. To be honest I think that the chances of not ending up inverted in an off field emergency landing are not good. As I?ve said before, I love flying my RV7A...but I?d much rather crash a Cessna. ;)
 
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