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IFR Backup: Dynon D1 or TT Gemini?

Airzen

Well Known Member
I am in the process of making decisions about my panel (RV-8). I was planning a TT Gemini as a backup EFIS, but now getting swayed towards Dynon D1.

Here are the pros that I am thinking for Dynon D1

1) Bigger screen
2) Simpler to plumb: No static or pitot lines (since all my AHARS are at the back of the fuselage, a TT Gemini would require additional routing to the front).
3) Simple to wire. Only need to connect power (and maybe a GPS antenna).
4) Dynon Firmware update seems simpler that TT Gemini (For TT I might have to send the unit in for any kind of firmware upgrade).
5) If I put a pinch mount, I can occassionaly velcro it to the backseat as an EFIS for a passenger in the back.
6) Back-up battery already installed


Some cons for D1 that I could think of:

1) I only get Ground speed instead of true airspeed (No static or pitot data with Dynon D1).
2) Not sure how good the GPS reception is (especially without the antenna). Some concern about reliability, especially if I end up in IMC with electric failure.
3) My primary EFIS is going to be a skyview, so I am really putting most of my eggs in one basket.
4) Pinch-mounted intrument doesnt feel like a real-instrument. It might feel like an accessory (this is more psychological ...)

So what do you guys think? Are there things that I am totally wrong about? (Again, this for backup EFIS for an IFR panel).

Just to add the rest of the panel will have a skyview system and a Garmin 650.
 
For an IMC backup, I would want to have real baro based altitude instead of GPS based altitude. That being said, the choice would be between the D6 and the Gemini PFD, not the D1.

I think everyone will agree that the Skyview and either the D6 or the D1 are enough different that the eggs in one basket issue would not apply.

For $200 more, the D6 offers much more value than the D1 for a real IMC backup.

While the D1 has some appeal to certified folks that want a cost effective and portable backup, do you really want to trust your life to a box velcro'd to your panel while in IMC?
 
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I like the idea of being able to Velcro it in the back for the GIB to use, but, you said you plan IFR and I think you should really go with the Gemini using air data and not GPS.

If it was VFR GPS data is fine, but not for IFR - IMHO
 
all Dynon

If have 2 SV 7" displays (front seat and rear) with 2 AHRS, a D10A and a D1 in my RV-8. The D1 will certainly be better than nothing in IMC but a D10 or D6 is far better and also much easier to update than TT. I have nearly 1000 hours on this D10A (two airplanes) and it has never failed me ever.

D1 battery life is extraordinary and while mounted low and right on my front instrument panel have had great reception of GPS satellites without the need for the external antenna. Despite this if I were in IMC with the D1 as my only remaining attitude, altitude and airspeed instrument I'd ask for vectors to VMC and/or nearest airport with an approach and keep AOB under 10 deg to preclude any possibility of blocking GPS reception.
 
also much easier to update than TT.

The TT Gemini is no harder to update than the D10A or the D6, TT has a module that connects between the PC and the Gemini that enables field updates in less than a minute or two.
 
TT update..

But dont you need to buy that module for addtional $$ in order to update TT?
 
But dont you need to buy that module for addtional $$ in order to update TT?

If you want your own you do but they also have loaners. The point though is that the Gemini can be updated in the field. Lucas did several at Airventure last week.
 
If you want your own you do but they also have loaners. The point though is that the Gemini can be updated in the field. Lucas did several at Airventure last week.

He did mine, I suspect right after yours. I'm assuming it was yours in HBC that he did Monday morning. I don't think it took a minute to update mine. My update was done in their booth.
 
The most important difference between the products that has not been listed is that the TT Gemini is a rate instrument while the Dynon D1 is an attitude instrument. The Gemini gives gyro enhanced vertical speed and turn rate info, which means if you turn it on it's side, after a few seconds it shows you level. It also does not work at more extreme pitch or roll angles. The D1 shows real attitude, so it doesn't have any of these limitations.

Your very first decision needs to be if you want real attitude or if you can accept something else. Once you make that decision, then you can look at the field of choices.

--Ian
Dynon Avionics
 
Rate vs true attitude..

Hi Ian,

Can you let me know where can find more about this rate vs true attitude comparison between D1 and Gemini?

Are you suggesting that Gemini functions as turn co-ordinator while D1 acts as an attitude indicator (for turns)? But then looking at TruTrak website they do mention that Gemini provides Bank Angle Display.

What about pitch info? I also see that Trutrak mentions that they show pitch attitude.

So I am slightly bewildered by your claims...
 
The Gemini does provide bank angle.

In the short term it provides pitch attitude that slowly transitions to vertical speed. Any change in pitch gets displayed immediately.

TT has promissed a user selectable option for a true attitude display if you prefer it over the current method. But that does not exist yet so don't count on that till it is available.

The display method being used on the Gemini has been used in the TT ADI and ADI pilot AP for years now.

Anyone that actually flys behind one will tell you that it would be very usable in IMC for backup.
 
The subject of the technical differences between the two has been discussed many, many times in the past - but - the reality is either one will functionally work just fine in a real world scenario and like Brian said, take the sales rhetoric out of it and the real world flying capabilities of both are just fine. That being said, I see the D1 as more of a backup for the flight bag...sort of like backup radio, backup GPS, etc.. and not necessarily a perfect candidate for a panel installation as a backup for an IFR panel. Firstly because the price point is such that you'd be just as well off getting a D6 for a TT PFD, secondly you have actual altitude and airspeed.

Don't get me wrong, I quite like the little D1 and think everyone should have one. I've flown it quite a bit now and it's a remarkable piece of equipment - especially for the certified folks. But for homebuilders we have access to the D6 or the TT at around the same price point so I feel that is a better expenditure of your money as an installed product.

All of the aformentioned products are excellent choices so to suggest otherwise would be dubious - you'd be happy with any of them, and any of them should keep the shiny side up in normal flight regimes.

Just my 2 cents as usual!

Cheers,
Stein
 
TT Gemini

As an aside to this conversation, if you decide on the TT, I've got a brand new in the box Gemini PFD for sale I wound up with. $1,100.00 vs. $1,300 from TT.

Thanks..
DWS
RV6-A N142DS
 
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