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Old 05-12-2007, 11:22 PM
RVadmirer RVadmirer is offline
Join Date: Dec 2006
Location: Kalifornia
Posts: 466
Default Does anyone have one of these or want to build one?


I would love one of these to go with my pitch trim.
A friend that builds a lot of electrical things says it's as easy to build several as it is to just do one, and the price of the boards goes down with quantity. The fellow that designed it quit making them.

From his web site:

Altitude Hold Unit

Description & Specifications

What is it?

The Ez-Trim is a small low cost unit that provides basic altitude hold function for homebuilts. I wanted a economical unit for my E-Racer canard. I could not find one, so I started designing my own. After several months and over half a dozen different test units, I had a unit that worked. It has been used and tested with a MAC pitch trim servo attached to the PTH trim lever and the Strong pitch trim servo. It will maintain the selected altitude very well in smooth air conditons. In turbulence it will keep trying but you may prefer to fly manually. The key is getting the unit adjusted to the plane properly using the response adjustments provided. It has front panel adjustment screws to allow you to adjust its response to your particular homebuilt.

It is intended to provide missing altitude hold when used with a wing leveler like the Navaid Devices unit. It sends control to the relays that control the electric pitch trim servo. The unit is designed to provide altitude hold function using a pitch trim servo through relays. The unit does not have the current capacity to directly drive the servo.

Since the unit controls using the pitch trim it is easy to override if there is a malfunction.
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Old 05-12-2007, 11:38 PM
SteinAir SteinAir is offline
Join Date: Feb 2005
Location: Minneapolis
Posts: 2,474

Best advice I can give you is don't waste your time. If you want altitude hold, the best solution is to just go buy a TruTrak ALTRAK unit or Trio EZ1.

These types systems have not performed well in RV's or other high speed aircraft at all. The trim tab is always behind the control surface movement, which ends up leaving your plane "hunting" a bit.

These have been discussed to death before (perhaps on the RV list instead of here...I don't rightly remember) and tried without much success in RV's.

Just my 2 cents as usual!


Flying behind an Altrak and loving it!
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Old 05-13-2007, 02:41 AM
matt matt is offline
Join Date: Nov 2005
Posts: 125

There are several RV's that use them and are happy with them. "rv6ejguy" on this forum used it in his RV-6A before, you might drop him a line and ask him if it worked ok?
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Old 05-13-2007, 05:26 AM
gmcjetpilot's Avatar
gmcjetpilot gmcjetpilot is offline
Join Date: Jan 2005
Posts: 4,326
Default It's a nice toy, I'd like to play with

Originally Posted by RVadmirer
I would love one of these to go with my pitch trim.
I have looked into it. They work "kind-of-sort-a. As an altitude hold its no where near a rock solid like what we now have available with the TruTrak or Trio EZ1. It only moves the trim. The true altitude holds have a dedicated pitch servo that moves the elevator.

If you are a hobby electronic guy you can build one. Even if you are learning electronics, its not impossible but its not simple either. You pretty much are on your own if you can't get it to work.

There was a used one on eBay a few weeks ago. I was going to bid on it for fun, but the bid got to hundred and half, which more than what the raw materials would cost to make one. The main thing to get is the PCB.

These guys in Europe offer PCB and parts kits and pre-built units ($410 euro) $554.

Be aware there have been improvements; known errors in the original design have been corrected. The big thing is getting a PCB (etched circuit board). The other parts are very standard. The europe guys sell just the PCB for $70 euro, but you could have one made locally for less. Ideally you would have a batch made to get cost down.

The EZ trim is not a set and forget altitude hold. I would not say its a waste of your time, but I would say its more for fun, for learning how to make a little microprocessor controlled device and make it work as best as you can in a RV. Don't count on it to being a rock solid altitude hold.

Personally I have flow RV's long cross country coast to coast with out any autopilot and don't find it hard. Usually my knees do a pretty good job of pointing it. With a wing leveler and trimmed in smooth air the X-C work load is even lower.

If you want true altitude hold get a commercial units ($1,800). People are very happy with their commercial altitude holds. I never heard of one being removed, but I have heard people that took their EZ trims out. Check out the canard Forums. Those guys are more likely to know about the EZ trim.
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Last edited by gmcjetpilot : 05-13-2007 at 05:36 AM.
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Old 05-13-2007, 08:00 PM
RVadmirer RVadmirer is offline
Join Date: Dec 2006
Location: Kalifornia
Posts: 466
Default Thanks George

Thank you for, as always, a well thought out and detailed opinion on my topic. I talked to the fellow again and he eventually improved his software to work pretty well, contrary to Steins' opinion. Not a fly & forget, but not $2,000 either! I have flown cross country with a Navaid that does a good job once it "hooks up" which takes a few tries. But it takes me 20 minutes or so to get the trim to smooth out and stay within 100'- 200' either way of assigned altitude. It can wander more than that and I like to fly more accurately anyway without having to spend so much time nudging the stick back and forth. That's what I think this gadget will work well for.
You are right about the board costs. My electrical guru has ordered boards from this company before and the first one or two are $100 or so and the next ones are much less. Hence my postings here and the canard forums looking for interest, if not for the whole unit at least for the boards to build their own. It seems many RV builders are putting very nice stuff in their planes. I've got other things to spend money on and I think this will do me just fine and will post the results if anyone is interested.
Thanks again George, I much appreciate the time you take to provide great input. I have a CHT question coming up and look forward to your thought on that.
Dave V.

Last edited by RVadmirer : 05-13-2007 at 08:02 PM.
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Old 05-13-2007, 08:25 PM
SteinAir SteinAir is offline
Join Date: Feb 2005
Location: Minneapolis
Posts: 2,474

I'm not saying it won't work at all, I'm saying that my opinion is that it probably won't work as well as you think it will. Canards are entirely different animals than our planes. They are lifting surfaces and react quite differently than our elevators and horizontal stabs which are loaded the other direction.

Sure, you may only have couple hundred $$'s in parts, but I'm guessing you'll end up with quite a few hours of time invested (count yours and your friends). While you can sometimes consider your time is free, in reality it's not. Everyone building a plane should assign some sort of value for your time.

Anyway, I'm all for experimenting, and will encourage you to try it. It's been tried before, and like I said it has worked....just not that well in the RV's. Perhaps it works great in the Canards, but again, they are entirely different animals. There are over 5,000 of these thing flying, and almost every succesfull gadget out there has grown in relative popularity in direct proportion to the fleet - this one didn't. I'm not the most experienced RV'er out there, but I have been around the pumpkin patch for awhile and have seen quite a bit regarding these planes.

Most of us are as carefull as anyone when it comes to bucks and believe me if there were an $100 or $200 altitude hold available that worked well I can guarantee you that there would be not just dozens installed, but probably hundreds or even thousands. Heck...I'm one of the cheap skates that built a $30K RV6 - and that wasn't done by buying all kinds of fancy stuff.

Like George said, all of us have rarely heard of people removing their altitude hold AP's, but we've heard quite frequently over the years of people removing their "trim" altitude hold. Now I have to admit that was before any newer fixes you refer to which may make the system work much better...I don't know. What I do know is that historically they haven't worked well in RV's.

If you are indeed successfull in creating something that works well, you can expect them to be quite popular and I hope you succeed - I might even buy one....but not before I see how the modified/fixed system works. I just want you to take a real world look at it. Read carefully what George said:

"I would not say its a waste of your time, but I would say its more for fun, for learning how to make a little microprocessor controlled device and make it work as best as you can in a RV".

That's basically the same thing I'm trying to say here. I truly wish you the best with this project and do indeed look forward to the results. Perhaps you'll find the next great gadget we all need!

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