[koda2]

Still lookin for a pirep or two from folks using an MGL Extreme (or other display) coupled with an SP-5. How do they perform as a primary flight display in actual IMC?
Surely, with all that glass flying around, somebody has some experience.

Dave A.
6A build

 

[rwarre]

My experience

I have an MGL Voyager coupled with a Garmin 430W, but I also have back-ups for altitude, speed, and horizon. I flew out of Appleton last summer, couldn't get into Osh, in the clouds and watched the Voyager most of the time. I had no trouble. It is important to make sure that the SP-2 and SP-4 or SP-5 are located properly and work correctly before getting into IMC. I never plan on a lot of IFR with my RV7a but, I feel comfortable with the instrument. Hope that helps a little.

 

[Rainier Lamers]

OK, I know we have been critized over and over again for a little sentence in our manual that states "VFR only" or some such thing - but that is mainly to keep the lawyers happy.

There have been notable and heart stopping uses of our SP AHRS sensors in IMC conditions that even I am uncomfortable thinking about. One of these was the "round the World" flight of the Sling, much of it in IMC and at least one Ocean leg in real frightening conditions. All they had was two Voyagers connected to a single SP-4. That was it. They had to fly (fight) by hand, no chance of using the Trio AP. They made it. The SP-4 saved the day. Scary.
Another big one was the record breaking Cape-Town to London and return flight. Also most of it IMC. Single Voyager and SP-4, nothing else.
These are perhaps the two that stand out the most, of course there must be many more (I know there are). Up to this point we have produced several thousand of the SP-4 alone and I suspect some of them get used...
They are also used as OEM equipment in some other systems that I may not mention.

The SP-4 is pretty good but it absolutely MUST be installed correctly. It is very small and light which means a sloppy installation will cause it to vibrate or move relative to the airframe. We have seen bad installations resulting in bad performance. We have seen these things taped to airframe skins under the seat, buffeted by prop wash (the skin flexes noticably). AHRS systems don't want to see any rotation or movement other than that of the aircraft as a whole. Professional systems (Sperry systems come to mind), spend a good deal of effort on shock and vibration isolation and mounting arangements. There is a very good reason for that. Our manuals give some ideas on how to mount these things. Doing it right is the difference between a system that is so-so and a system that is near bullet proof.
Sorry for bringing this up here but I thought this a good opportunety to mention this...

Rainier
CEO MGL Avionics

Still lookin for a pirep or two from folks using an MGL Extreme (or other display) coupled with an SP-5. How do they perform as a primary flight display in actual IMC?
Surely, with all that glass flying around, somebody has some experience.

Dave A.
6A build

 

[rv8ch]

SP-4 mounting

...
The SP-4 is pretty good but it absolutely MUST be installed correctly. It is very small and light which means a sloppy installation will cause it to vibrate or move relative to the airframe. We have seen bad installations resulting in bad performance. We have seen these things taped to airframe skins under the seat, buffeted by prop wash (the skin flexes noticably). AHRS systems don't want to see any rotation or movement other than that of the aircraft as a whole. Professional systems (Sperry systems come to mind), spend a good deal of effort on shock and vibration isolation and mounting arangements. There is a very good reason for that. Our manuals give some ideas on how to mount these things. Doing it right is the difference between a system that is so-so and a system that is near bullet proof.
Sorry for bringing this up here but I thought this a good opportunety to mention this...

Rainier
CEO MGL Avionics

Thanks for bringing it up - I'm looking for more hints than I see in the documentation. With the dsub connector attached, I need about 20 cm / 8 inches of straight line space along the axis of the aircraft near the spar to mount this unit. Doesn't really leave a lot options. How far off the center axis can I place it? How far off the CG point? Is there another option on the connector? Could the software in the Odyssey re-orient the SP-4's initial position if I mount it at an angle? Do you know of any RV8 installations that are working well, and if so, where did they mount the SP-4?

Thanks,
Mickey

 

[koda2]

SP-5

Precisely the reason why I originally asked about the SP-5. It is supposedly more immune to vibration.

At least one of the forum members has mounted the unit aft of the main spar in the space below the seat floor. This puts the unit very close to the center of rotation. That area however would seem more likely to see the vibrations from the exhaust gas pulses as well as the rest of the engine/prop stuff.

The manual talks about vibration mounting, and I have thought about some ways to isolate the unit from the rest of the airframe.

Also my intent would be not to have the Extreme/SP-5 as the sole source for input in true instrument conditions and not have a single point of failure.

I am also interested how well the SP-5 would hold up over time.

Dave A.
6A build

 

[Rainier Lamers]

The SP-5 uses BAe Systems designed MEMS ring gyros. These are better than the Analog Devices gyros we use in the SP-4 as far as high frequency vibrations are concerned. These would be frequencies that interfere with the exitation frequency of the gyro and this results in bias drift.

However...

In our now very considerable experience, this matters little in an aircraft. The vibrations we have to contend with are low frequency. To the gyro this appears as rotation and linear movement and the bad thing is that this typically far exceeds the rate of rotation that the gyro can measure. This is just as bad as exceeding the maximum rates during fast aerobatic manouvers. The rotations caused by vibration may be small but they are real and there are lots of them. Similar issues can be caused by an overy loose mounting where the sensor is allowed to move relative to the airframe. These movements can also easily exceed maximum rates and are killers.

The "strapdown" three gyro system commonly used works by being extremely accurate in its measurements which happen at very fast rate (hundreds to thousands of times per second). The system has to take every tiny little bit of rotation into account with almost unbelievable accuracy or else the horizon position that it is calculating will be badly out very quickly. This is where aiding can help if you have a bad system that can only hold its own for a few seconds (but there are other potential issues with aiding, depending on how it is done - typically most aided systems don't do well in aerobatics if you do more that just a quick manouver like a roll).

You can easily see how a good mounting will tremendously improve the performance of a system and the less aided it is, the more important this becomes.

We are currently working on a FOG system which costs way more than your entire RV - completely unaided. Great system - but even here you need to be very carefull. Do it wrong and it can perform no better than a cheap MEMS system, even worse...

Regarding the mounting position - Don't put it in a wingtip or in the tail. The reason for this is the accelerometers. The rotations of your aircraft will result in the accelerometer based part of the device making incorrect conclusions about the gravity vector. That will have a negative effect to some extent.

Other than that, the mounting location is not THAT critical. I doubt if you will see a problem if your SP-4 is 6 feet from the center of rotation...

Rainier
CEO MGL Avionics

 

[koda2]

SP-2

Thanks for bringing it up - I'm looking for more hints than I see in the documentation. With the dsub connector attached, I need about 20 cm / 8 inches of straight line space along the axis of the aircraft near the spar to mount this unit. Doesn't really leave a lot options. How far off the center axis can I place it? How far off the CG point?

I am planning on the standard "behind the baggage compartment" mount. I don't have the unit yet but was going to add a little length. I will be sure to make allowances for it.
The only other place would be run aluminum angles crosswise about mid fuselage. I have seen other 8s like this. Personally, I am not going to leave the dsub connector suspended. It may put unnecessary stress on the connector that is attached to the circuit board. There may be some shorter dsubs to be found at someplace like Digikey.

Dave A
6A build