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Regarding the cruise missile though, I dont see why the military cannot have their own charts with terrain mapped out in GPS altitude. And the reason they are using radar maybe for speed reasons (obstacles come up fast at mach 1, 20 feet agl) and to prevent GPS signal jamming.

It is gps based but are you sure it doesnt use a radar altimeter along with gps? If not then all its charts and terrain database have GPS terrain values which would work. Basically all points on the chart or terrain database have to have gps altitude values. To Bennett's question, if you search for tomahawk cruise missile on wikipedia, it shows its guidance system as GPS over sea, then a combination of radar altimeter and gps for flying low over terrain. Heres a link: http://en.wikipedia.org/wiki/Tercom - guidance system http://en.wikipedia.org/wiki/Tomahawk_(missile)

I am pretty sure, you cannot turn certified aircraft or parts of certified aircraft into experimental. It might be some other category like research/test aircraft or show aircraft etc .. I forget the exact terminologies, but there are many more restrictions then. You cannot fly as freely as the experimental guys. You will probably need permission from the FAA for every flight if its test aircraft for example. I remember reading this a while back when thinking about going the experimental route - so might have changed now.

Forgot to mention - I think if a TSO exists - then you need to replace with a TSOd part. If a TSO does not exist - then I don't know ... things like paint come to mind - there is no TSO paint for aircraft I think - get it from autozone and patch some paint scratches

I was in the door seal replacement boat recently and the cost of the door seal was 170$ according to my AP. And the cost of the marine seal was 10-20$ (somewhere in that range). At that point as a new owner I wasn't sure what needed to be certified replacement and what didn't need to be. My AP said I had to replace with a certified door seal. I checked with AOPA - they were not sure. Checked with the forum here and the advice was to go read the Technical Standard Order (TSO). When I read that for door seals, it seemed to have a lot of specifications that make sense for aircraft. For example, flammability, how it holds up to cold etc. Its not 17x better - but just saying ... Also the marine store seal may hold up just as well to cold and fire and what not - just that its properties are not known. Whether you are willing to pay a premium for those properties is up to you.

All pricing on spruce was for each - must be a mistake though ..

Ouch - not easily swappable then Altho no sane FAA person will ever approve swapping weights on the fly - so its a moot point

That is true - except for people scud running because some software gives them an "optimistic" altitude. For IFR with today's situational awareness tools - the altitude difference is a moot point since the margins are pretty big like you said

There are radar and maybe even LIDAR based mapping from satellites that will tell you terrain rise and fall - certainly that has been mapped. But I was just saying that with pure GPS alone - you cannot get AGL - unless all obstacles and charts and terran databases also carry GPS altitudes for all terrain features

If you have a M20L - you are screwed - mounts are 1600 a piece for barry mounts at aircraft spruce heart attack time !!

Then again - this is not a problem if the terrain database has GPS coordinates for X,Y,Z values for all terrain points. But from Antares's youtube video it seems they only surveyed runway ends and nav points .. Once all obstacles etc are in GPS co-ords you can safely use just a GPS altitude to clear those obstacles

Yes that's what everyone is saying - its height measured from the center of the earth. But to arrive at an altitude value it does this: GPS alt = (height above center of earth) - (height of model's sea level) The model's sea level is not accurate because the earth has a complex shape. This is just another altitude - if everything were charted using GPS altitude we would be fine - however, stuff in charts etc is in MSL based on barometric altitude - comparing the two is when there is a problem. Your example of tractors being accurate in X Y dimensions is understandable - since the horizontal direction is never an issue. Its the vertical terrain that is an issue. You mention EGPWS - but EGPWS uses a radar altimeter to get the height above terrain directly below the aircraft. The GPS knows exactly where you are with respect to the center of the earth. It knows how far above the terrain the aircraft is from the radar altimeter and it knows GPS altitude (not MSL) with a high degree of precision. From the terrain database it gets: (height of obstruction ahead) - (height at current position) = (height of obstruction compared to current position) Say a mountain ahead is 14,000 feet MSL, height at the current position listed in terrain database is 10,000 feet MSL. Then the terrain rises by 4000 feet. Then the EGPWS gets your radar altimeter reading - say that is 1000 feet So you are 1000 feet above the ground when directly over the current position. At this altitude your GPS altitude is reading say 11,100 feet above center of earth. So amount you need to climb up by is 4000 feet terrain rise - 1000 feet = 3000 feet GPS altitude you need to reach to clear mountain is 3000 feet + 11,100 = 14,100 feet If you used your GPS altitude as your primary means of altitude clearance without the radar altimeter - you would undershoot by 100 feet and hit the peak at 14,000 feet. If you used your GPS altitude to clear the peak As I was saying, the GPS altitude has a very low error - so if you measure altitude at x and climb by 1000 feet - gps altitude will show x+1000 but it has no relation to terrain - its only a coordinate in the satellite constellation space You need the radar altimeter to tie it down to earth or you need barometric pressure altimeter to tie it down. I am curious if a GPS unit showing obstacle clearance for passenger carriers, was ever approved without a barometer tie-in.

Thanks! I thought I could only put Lord mounts on the plane - but looks like Barry mounts are a lot cheaper - 104 at spruce...

Haha somehow even that thread ran into a LOP ROP debate

Where are the charlie weights in the bravo? At the very end in the tailcone ? On a rocket that was on sale, I saw an extended baggage compartment mod by Lasar. Maybe you could extend the baggage compartment and replace charlies for baggage, unless the charlies are in a very inconvenient spot and not easily swappable for baggage

If people want to know where I am getting the cheap price http://www.aircraft-specialties.com/cart.php I should call them and make sure they have not been sitting on the shelf for too long. It might make sense to buy things like rubber etc that age from spruce because they have a high turnover

Aah crap, for some reason I said true altitude is height above terrain which it is not ... Doh I was mostly concerned with terrain clearance by looking at msl values of obstructions and terrain using charts - with a barometric altimeter you can get a very accurate msl figure which you can compare on a chart. Yes, neither altitude knows how much air is below you .. GPS is how far you are from the satellite constellation and barometric is how much air is on top of you like m201mkturbo said. For True altitude - height above mean sea level - gps altitude is still not correct for the reasons m201mktturbo mentions.

Would help if you explain why? Maybe I wasnt explaining correctly? The only way GPS altitude will be close to true altitude is if the major terrain points have been surveyed for GPS co-ordinates and that new model has been loaded into receivers. I dont know whether that has been done.

Antares, not sure whether you posted that for general education or to refute my points, but the video agrees with what I am saying. The GPS system itself cannot tell you height above ground. The video mentions that all runway ends were surveyed according to some geodetic model, which is precisely what I was saying regarding WAAS approaches - the runway height has to be brought into the GPS co-ordinate system. But the rest of the terrain is not in the GPS geodetic system because all terrain has not been surveyed by measuring gps altitude at all points on the earths surface. The video also mentions that you need barometric aiding in order to get real altitude over sea level. Sorry if you were not refuting my point but this could be a joint response for astelmaszek - maybe he can clarify why I am wrong

Having said the above - if you go to point X and your WAAS GPS shows gps altitude 1000 and then later you are flying over the point and your WAAS GPS altitude is 3000 - then you are exactly 2000 feet over point X. This is accurate because you mapped the terrain at point X and just took the difference at flying height of 3000 - which is accurate to within WAAS GPS accuracy

No that is not the case - true altitude is defined as the actual altitude above terrain regardless of temperature, pressure what not ... How does the GPS satellite constellation know where the mountains are to give you a true altitude? It doesn't. Some boxes might pretend to give obstacle clearance but they are based on data that is not as accurate as WAAS accuracy data being mentioned in this thread. What is used for this fake GPS altitude is a simplistic model of the earth - which is some sphere. GPS - knowing your point in space - calculates your height above this imaginary sphere. This altitude is very different from barometric altitude and is not accurate at all when it comes to telling how high above obstacles or ground you are - because the world is not a sphere first of all and its definitely not smooth Why you ask? How are there LPV approaches going down to 200 feet above airport elevation? That's because GPS knows your point in space very accurately - like someone mentioned the accuracy numbers are less than a meter 90% of the time, more than a meter or so some other percentage of the time. But knowing your position in space very accurately - doesn't mean you know your height above the ground. For that you will need to know the GPS co-ordinates of the terrain. Since no one has gone and mapped the entire terrain with GPS coordinates - you accuracy for height above the ground is not sub-meter accuracy ! But what about LPV approaches? Those terrain points HAVE been measured by GPS devices and their 3-D coordinates in the GPS satellite constellation space are known exactly. So when you shoot a LPV approach - the GPS box technically doesn't have your barometric altitude and hence your height above terrain. It does however know where in space you are, where in space the LPV glideslope is and where in space the runway end is.. That's how you get an accurate approach path without knowing your height above the ground. So relying on GPS altitude shown on iPads, 430s what not - is inviting disaster unless you have no other option. There was a discussion on another thread recently

I have arrived at the airport for an evening flight with the landing light out and no access to a spare bulb. Disappointing when that happens. Definitely have started doing a post-flight by checking mags, lights, alternator etc. Also clean leading edges and glass. This is technically a pre-pre-pre-flight During the winter months only, I do a pre-pre-flight when I show up to turn on the pre-heater - fuel, look around, fill air if necessary etc. During warmer months - I just do a normal pre-flight if I have done a post-flight already.

Just thought I'd check here - any cheap places you guys bought your Lord mounts from (the rubber stuff that goes between the engine and the mount) The cheapest I see is about 131 $ per shock disk Part number is J9613-40 Thanks

Make sure you make those turns very coordinated

Agreed - good points - thanks! Its good to have a plan. Its just the steps you mentioned in your first post take into account launching with a new engine AND airframe AND instrumentation AND a rusty builder pilot. With a tried and true airframe and instrumentation, I can take fewer steps - that's what probably jetdriven and me were alluding to. But I can check two of those boxes - rusty pilot and new engine installation - so definitely I plan to get some flight time in some aircraft (better than nothing) before I take my aircraft up. Also like you said, I need a plan for checking engine installation workmanship. I am thinking of visiting the installation at various steps and checking everything myself - I have some knowledge from what should happen, the quality of workmanship required etc from working on my annuals and from reading a lot of EAA builder's books