Sunday, May 07, 2006

Vern Raburn has enough hot air to float all the balloons in the Albuquerque Balloon Fest

Don't let the following frivolous comments detract from major issues discussed in the first three posts, especially the April 11 post, but last month Vern went to the European Business Aviation Convention in Geneva, and proclaimed the Eclipse to be an environmentally friendly airplane.

According to Vern, people living near the airports will love the Eclipse, it hardly makes any noise. When your engines only have 900 lbs of thrust you can have a pretty quiet airplane. My wife's vacuum may put out more than 900 lbs of thrust.

And cabin noise lower than the Challenger 604 and Hawker 800. Vern, these are real jets flying at real jet speeds. Noise is energy, it goes up with the square of the velocity. If your airplane was as fast as theirs, it would be noisy. Or slow the 604/800 down to Eclipse speeds and you will find these airplanes to be even quieter.

The Eclipse is going so slow, it hardly qualifies for jet speeds. In fact, your airplane is so slow, it will be a real pain-in-the-ass for Air Traffic Control because the Eclipse can not keep up with the air traffic (mostly regional jets) that use the same airspace above 29,000 feet.

And I have not read where the Eclipse will be doing any bird strike tests. It may not be necessary because this airplane may be most vulnerable by getting struck from behind!

6 comments:

mouse said...

Check out the wing leading edge design relative to a bird strike. The leading edge is all fuel, with no bulkhead separation. Other than the aluminum skin which is/was less than .032 and a rubber deicing boot, there is nothing to keep the fuel in the wing, or ram air out of the wing, if there is a penetration. The scenario is a bird strike or rock ricochet that could pierce the wing skin and at cruise speeds the wing could be inflated with ram air as the fuel pours out.

Stan Blankenship said...

mouse,

Interesting comment and it begs the question, why put fuel in the wing leading edge?

So I went to the library today to check the Eclipse specs in an earlier Jane's All the Worlds Aircraft.

When the a/c was powered by the Williams engine, the max fuel load was 1,330 lbs with a 36 ft wing span.

To accomodate the more thirsty Pratt engine, fuel was boosted to 1,540 lbs, span was increased to 37 ft 4.75 in, which probably represents the original wing plus tip tanks.

Somewhere I read the tip tanks were not really used for fuel but rather just provided the 2% expansion space as required by Part 23 regulations.

So one might conclude the fuel ahead of the front spar was part of the mod for the Pratt engine.

Stall speed with the lighter Willaims configuration was 62 knots. V stall with the Pratt 67 knots.

During the 24 months or so it took Pratt to design and produce the new engine, Eclipse should have scaled the wing up 10%. If my calculations are correct, the wing area would increase 21% and a 62 knot stall speed could have been maintained, and the wing volume (fuel capacity) would increase 33%.

The weight increase would be minimal since the thicker wing section would make the structure more efficient.

This is precisely, what Air & Space was refering to in their statement, "small aircraft are penalized by the pitiless exponential mathmatics of scaling down."

Conversely, scaling up helps in exponential manners and could have helped the Eclipse immensely.

You had two years Vern, why didn't you make the change?

Thanks mouse,

Stan

Doug said...

What I find amazing is that the aircraft certification office they are dealing with will let them put "tip tanks" containing fuel vapor on at all. lightening tends to strike the extremities of aircraft. No one has certified an aircraft with true tip tanks in many years. If fuel in a tip tank is a bad idea, how about fuel vapor. Sounds concerning to say the least. I am confident no such design would gain type certification in Wichita.

Stan Blankenship said...

Doug,

Thanks for your comments and bringing up the certification issue.

The "Hot Jobs" page on the Eclipse website has listed engineering job openings for the past several years. Among the listing have been DER's in about every discipline.

Are the DER's buying off the certification items?

Considering the number of aircraft programs in work around the country plus a shortage of qualified FAA engineers, one might wonder how much FAA involvement there is in the Eclipse program.

How would you like to be a DER trying to persuade Vern a system does not meet the regulations?

Raburn has boasted of his newly developed automated computer controlled systems. If one were to get a TSO on such a system, you would be years doing testing and writing reports. It is one thing to show how a system works...it is quite another to show what happens in every conceivable failure mode.

Most companies steer clear of doing too many clever things and are "fossilized" to use Vern's own words.

Thus far, I have not commented on Eclipse certification because I do not have knowledge on what the FAA procedures are today nor how Eclipse is approaching certification.

Perhaps one day, more information will be forthcoming.

Stan

ps. Correct me if I am wrong, but I believe Wichita is the lead FAA region for business jet certification.

Albuquerque would be covered by Fort Worth.

Stan Blankenship said...

More on the terms DER and TSO for the casual reader.

A DER is a Designated Engineering Representative for the FAA. The individual can work directly for a company like Eclipse or work as a consultant on a contract basis.

There are about a dozen different flavors of DER's, structures, powerplants, systems, electrical, noise,etc etc.

To receive a DER appointment from the FAA, one must demonstrate knowledge and experience in the discipline being applied for.

I am not sure of a DER's authority. Do they just recomend approval to the FAA or can they actually buy off on certification items? Does their authority change with light aircraft vs air transport category aircraft? Perhaps a reader can shed more light on the subject.

There are hundreds of contract DER's. Some are probably good, some not so good. Some that can find compliance with the regulations easier than others.

With regards to TSO's, lets assume there is a company that wants to develop a new autopilot and sell it for various installations on certified aircraft. The certification basis for that autopilot would be a published Technical Standards Order.

The TSO will cover in great detail how the a/p should work and how it should not work. For instance, if the pilot is flying a coupled approach in bad weather and a diode fails, you don't want a false command for full nose down trim.

Some of this is like trying to prove a negative and TSO certification is time consuming and expensive.

Vern Raburn has talked about automating several of the cockpit functions to simplify the workload for single pilot operations. Again, somebody correct me if I am wrong but I believe these systems are covered under the basic aircraft certification issues and would not undergo the rigors of a TSO evaluation. All Eclipse would have to show is how they work, not necessarily what happens in all conceivable failure modes.

hrr said...

Stan,

A DER has authority to recommend approval to the FAA. The FAA still has final authority to sign off. Also, DER authority is Part specific. That is, a DER must be granted authority separately for Part 33, Part 23, Part 25, etc.