This ad space is available now!

Your Reviewer

My Credentials
So who's doing this reviewing then?

Well I've been building and flying or driving radio controlled models for over 40 years and during that time I like to think I've built up a reasonable amount of knowledge.

I'm also a qualified electronics engineer who has worked in radio frequency, analog, digital systems and software for more than three decades. In fact I designed and built my first RC set back in 1969.

For the past nine years I've also been involved in the design and manufacture of some rather sophisticated engine technology and UAV flight control systems.

So, chances are I've been there, done that and have a huge pile of tee shirts to prove it.

Right now I'm heavily into 3D flying and enjoy all aspects of the RC hobby. I may be old but I don't feel it.

In the Pipeline

Here's just a little bit of what's to come on this site...

RC explained: Demystifying terms such as PCM, PPM dual conversion, single conversion, full-range etc., this feature will explain it all.

Cheap Chinese Engines: Just how good are those cheap Chinese glow and gas engines that sell for half the price of their "brand-name" equivalent? I put several to the test.

Build your own radio gear?: Back in the old days, building your own RC gear was not uncommon and now the arrival of 2.4GHz has made it practical again.


Review: The FY21AP FPV system


Updated: 27 Jan 2011

In its barest of forms, FPV (first-person view) flying requires just a camera, a video link and some kind of display for the pilot.

However, those wanting to get even more enjoyment from the hobby, or who wish to fly further away will find a system like the FY21AP well worth considering as a way of improving the capabilities and safety of their model.

What is it?

In this review I'll be looking at the two products which make up the FY21AP system.

These products are the FY21AP itself and the AP117 onscreen display (OSD). The FY21AP can be purchased without the OSD if you already have one but if you don't then I highly recommend the AP117, or some form of OSD for serious FPV flying.

In essence, the FY21AP is a clever box which contains a set of gyros and accelerometers that can be used to give your plane added stability -- thus making the job of flying your FPV model much easier.

Also included is a GPS system and barometric sensor which add the extra feature of allowing the system to return the model to its launch-point on request, or should you fly out of RC range. The barometric sensor also provides for an "altitude-hold" facility that allows you to fly your model without having to constantly worry about whether you're gaining or loosing height.

The OSD box overlays the video signal from your camera with a raft of extra information such as altitude, airspeed, heading, battery consumption etc. This kind of telemetry further adds to the safety and practicality of long-distance FPV flying.

This video shows the component parts and how they interconnect.

Quality of construction

The construction seems of acceptable quality, plastic moldings being well made and finished, plugs and connectors typical for RC products.

Both the FY21AP and the OSD units are encased in lightweight moldings for protection and the system comes with a little "cradle" with rubber suspension so as to reduce the effects of vibration.

Installing in the HK EPP FPV model

To be honest, I was a bit concerned that the installation and setup would be a complex and time-consuming task. After all, there are lots of wires, plugs cables and connections -- with the manuals offering all the information you need but being in rather small print for an old man like myself.

I was however, very pleasantly surprised at just how quickly and easily the whole thing went together.

The FY21AP itself simply sits between your RC receiver and your rudder, elevator and aileron servos, with an extra lead going off to the OSD box.

Power for the FY21AP comes from the RC receiver so there's no need of a separate connection, which is good. Power for the OSD comes from the same battery which is used to power the camera and video transmitter (a 3S lipo in this case).

Some soldering was required to connect the OSD box between the camera and video transmitter but this was all very simple and not at all difficult to work out. If you only want video then there are only three wires to worry about: red (the power), yellow (the video) and black (the earth/negative).

You will also have to solder power leads to the current sensor that is part of the system. If you're not confident then perhaps getting someone with reasonable soldering skills to perform this task would be a good idea -- although it's not hard.

Actually mounting the FY21AP inside the HobbyKing FPV model was much easier than I had expected because the anti-vibration tray was just the right width to slide firmly between the sides of the model -- allowing it to be positioned so as to be "straight and level" with no drama at all.

The OSD unit was attached to the inside of the fuselage using velcro.

Here's what the full OSD video overlay looks like, as you can see there is a lot of information being displayed here but, as you'll see later, it does not obscure the actual video picture that is returned from your camera.

Setting it up

The system requires up to three RC channels to control all its options.

One channel will determine the state of the stability system, allowing you to switch between no-stability (regular RC flying), stability-on, and stability on with altitude hold.

In the latter case, the model can be simply "steered" around the sky using just ailerons to set the direction. The system will automatically ensure that it doesn't climb or descend beyond the height it was at when you switched into that mode.

A second channel determines the autopilot mode. It can be off (normal RC) or in either a "circle current position" or "return to launch" (RTL) mode.

In the RTL mode, the model will turn around and fly back to the point of launch, whereupon it will continue to circle at the same altitude until you switch the autopilot off.

The third RC channel is used to control the onscreen display. This offers three modes: off, low-clutter and full-data. Being able to turn off the OSD is quite handy if you want to collect aerial footage for making videos and don't want all that extra information included.

It took just a few minutes to set up my JR9XII (9303) radio to control all aspects of the FY21AP's operation and everything worked just like the book said it would.

The next stage of the setup was to ensure that the stability system was proving the right corrective inputs. By holding the model and pitching it nose down, the elevator should go up (so as to level the model). Likewise when rolling the model, opposite aileron should be given by the stability system. Fortunately I didn't have to change a thing -- it worked 100% straight out of the box, although the instructions describe how to make those changes, by turning the small pots on the FY21AP unit.

Does it work?

Having already tested and trimmed the model without the FY21AP installed, I was confident that the test-flights would be largely uneventful and indeed they were.

As I earlier demonstrated in this video, the HK EPP FPV model has no roll-stability so will remain in a tight turn (descend at quite a rate) if you simply release the sticks during such a turn.

With the stability system enabled however, the plane suddenly became incredibly stable. Releasing the sticks with the model in almost any attitude would result in an instant return to straight and level flight. Yes, it works as advertised.

Switching to the altitude-hold mode, the FY21AP clearly ensured that the model neither climbed nor sank, even when the throttle was varied between quarter and full throttle. Of course you must be very careful in this mode not to remove all power because this will cause the model to stall, as the FY21AP attempts to maintain altitude simply by controlling the elevator and so will precipitate a stall if the motor is not providing enough thrust.

All this time, the OSD was delivering a clear indication of altitude, heading, ground-speed, the amount of battery consumed and even the temperature inside the model (which, I might add, climbed to over 42 degrees C at one stage, as can be seen in the above picture).

In order to test the RTL I decided to fly a long distance away, while flying full FPV using the FatShark video glasses.

At a distance of several hundred yards, something very odd happened.

Suddenly, I no longer had any control of the model and it performed a 180-degree turn, heading directly back towards me.

Initially I was confused and wondered what had gone wrong -- until I noticed that the OSD indicated the autopilot was now in RTL mode. The model was coming home -- but why?

Well, as you can see in this video, a faulty transmitter antenna meant the model had actually flown out of range and because I had the foresight to set up the failsafe correctly, it immediately activated the RTL so as to bring the plane back into range.

To be totally honest, it's hard to say anything bad about a system that saves your model from loss or damage in the way the FY21AP did. And, just to further demonstrate how valuable this function is, I experienced another heart-stopping moment during another flight when the battery for my video receiver disconnected itself and the video-link was lost -- while the plane was beyond visual range!

What did I do?

Well I flicked the transmitter switch to RTL and, while I was busy trying to reconnect the video receiver battery, the model flew back and began circling overhead, just as it was supposed to.


Well the FY21AP certainly does work as advertised, I can vouch for that.

It's also surprisingly easy to set up, for a unit that does so much.

However, it's not cheap -- costing over US$300 for the configuration that is the subject of this review. You can fly FPV without a system like this but, as my own experiences prove, it sure can save you a lot of money if/when things go wrong.

If you're planning to invest any serious money in an FPV model, and that's pretty easy to do, with HD cameras costing up to $300, airframes, motors, batteries and video gear easily adding another $200 or more -- paying a fraction that for the peace of mind that the FY21AP can deliver seems like a good investment (to me).

Of course, for all its strengths, the FY21AP is not without a few problems.

Firstly, the way the altitude-hold and RTL work can end up causing serious grief. That's because the system has no control over your throttle and only maintains height by adjusting the elevator. This means that if you have initiated a "return to launch" and your motor shuts down due to a weak battery, the model will stall and could well crash, as the system attempts to maintain altitude.

The lack of ability to control the motor's throttle setting also means that when you set up the failsafe on your RC system, to use the RTL you'll also have to set the failsafe on throttle to a high enough power-level that the model will be able to maintain altitude without stalling.

It would be far more desirable if there was an airspeed indicator that could over-ride the altitude control so as to ensure the model never stalled, or if the altitude-hold was linked to throttle rather than elevator.

Secondly, because it only supports a single aileron channel, you can't use your transmitter's flaperon mix to provide that functionality. Nor can you set up aileron differential to help produce coordinated turns on some airframes.

Watch out for more video coverage of this product on the RCModelReviews YouTube channel including this flight-review video. Pro's:

  • It really is a model-saver!
  • Works exactly as advertised
  • No complex calibration required
  • Not affected by environmental conditions
  • Lightweight and easily installed
  • Very nicely integrated


  • RTL and altitude-hold can cause problems
  • RTL failsafe setting requires motor-on to avoid stalling
  • Doesn't support flaperons (useful for slow FPV flying)
  • Not cheap
  • It's really not cheap
  • Product: FY21AP and AP117 FPV system
  • From: FeiyuTech
  • Website:
  • Price: around US$340
  • Overall rating: 4.5/5


The FY21A system was provided without charge by FeiyuTech for the purposes of this review. However, if it sucked, I'd have told you.

Once all the FPV articles are completed, the system will be given away to some lucky RCModelReviews reader/subscriber -- in accordance with my policy of not keeping "free stuff" -- so as to ensure all reviews are unbiased and objective.

Related links

Fresh Articles:

Privacy Policy




Join the Forums!

Discussion Forums


The Blog

Updated: 20 Sep 2012
Here's a blog that will keep you informed just what's going on behind the scenes at RC Model Reviews and also tells you a little more about myself.

How compatible are 2.4GHz RC systems?

23 Mar 2010
How come there's no compatibility between different brands of transmitters and receivers? Why can't you use a cheap Chinese receiver with your Futaba FASST radio?

How to get a product reviewed here

4 Mar 2010
Since this has become a very frequently asked question, I've posted this simple guide to getting your product, or a product you're thinking of buying reviewed here at RCModelReviews

How servos work

Useful information on what's inside your servos and how they work.

The Good Oil

Important facts you should know about the oils that are used in our model engine fuels.

Heads-Up: 2.4GHz RC systems tested

How well do five different 2.4GHz systems stack up when hit by interference? The answers are here, with more to come.

Review: Bushnell's $80 Speed Gun

Yes it does work on model airplanes but there are some limitations involved with this bargain-basement radar speed gun.

Review: TowerPro MG995 servo

These are possibly the world's worst servos, find out exactly why you should avoid these boat-anchors at any cost.

Review: SK90


It's cheap but can it really stack up against other glow engines in the .90 market? Find out in this review.

Review: iMax 9X 2.4GHz radio

How does this cheap 9-channel 2.4GHz radio system perform when compared to big-name systems that can cost two or three times as much? Have the Chinese finally developed a real contender with the iMax 9X?

2.4GHz Explained

Does all this 2.4GHz stuff have your head spinning? 2.4GHz

I've done my best to demystify the whole subject so if you feel like a bit of learning, this is the stuff for you!

Fix That Engine!

How can you tell when your engine needs new bearings? Who has the best prices and service on replacements? Just how do you change them? Get all that information and watch a great video tutorial anyone can follow.

Chinese Servos - How do they stack up?


The Chinese are now churning out a huge number of very reasonably priced no-name servos. But are they any good?

Baffled by batteries?

Batteries Nicad, NiMH, Li-Ion, LiPoly, LiFePO4, A123... the range of different battery types has never been greater. So how do they differ and what type should you be using?

Possibly useful: