Van Horn Aviation is well known for its aftermarket main rotors, especially for Bell products, but more recently it has created a tail rotor for the AS350 series. Gideon Ewers went to Tempe and Mesa to find out more.
There is a reason why the AS350 family of helicopters has been in production for over 50 years. It is the same reason why after more than 7,000 examples have been delivered the production lines in Mariginane, Columbus and soon Bengaluru are chock-full of new examples – and that is that the Squirrel, Écureuil, A-Star, AS350 or H125 (call it what you will) is a very fine aircraft.
For operators in parts of the world where regulations effectively dictate a twin-engine solution for missions like law enforcement or HEMS, the type remains top of the shopping list for operators.
That said, even being a very good aircraft doesn’t mean there isn’t room for improvement.
In the past we have seen solutions from BLR Aerospace that boost tail rotor authority using tail boom airflow asymmetrical flow.
Avionics manufacturers like Thales and Genesys have created aftermarket Stability Augmentation and autopilot capabilities.
But left alone was the tail rotor itself, which in its original form has been a pet peeve of operators – while the one-piece construction of the OEM version means that, for example, damage to a single blade has required the replacement of the whole assembly.
Likewise, among the operators and MROs, the AS350 tail rotor is notoriously “twitchy” to balance following replacement or repair.
For decades there was no alternative – it just was one of those things you’d have to accept. Machines, like people, have their fortes and their foibles. That is, until Van Horn Aviation decided to enter the fray.
The AS350 family of helicopters has been in production for more than 50 years.
Talking points
Tempe-based Van Horn Aviation has been around since shortly after the turn of the century, specialising in the design, certification and manufacture of composite rotor blades.
The original watchword for the company was to drive down direct operating costs for operators of legacy aircraft.
“For decades there was no alternative – it just was one of those things you’d have to accept. Machines, like people, have their fortes and their foibles. That is, until Van Horn Aviation decided to enter the fray.”
Part of the AS350’s tail rotor assembly, pictured in the Van Horn workshop.
Accordingly, it built its business on the design and production of main and tail rotor blades and assemblies for legacy Bell products – primarily the 206B and 206L models, as well as the UH-1.
Van Horn also operates an independent in-house Part 145 repair station providing support for its blades.
But then, conversations that company representatives had had while visiting clients or on the road at trade shows indicated that there would be a market for a tail rotor designed as an improvement on the more than 50-year-old design of the original.
So they set about designing and creating a tail rotor STC that would reach the fundamental concept goals of lowering direct operating costs (DOCs), with a side benefit of improving performance.
Modular approach
Step one in that process was creating a design that was modular – meaning damage to one part would not mean throwing the whole assembly away – that also matched the OEM tail rotor for both diameter and plane, but that used advances in materials and a rethink of the aerodynamics.
The result is a semi-rigid/teetering rotor that, while a three-part system, is actually less maintenance intensive. This is achieved because of the following primary factors.
First, the service life of the Van Horn rotor is 4,800 hours compared with 4,000 hours for the OEM version.
Second, the Van Horn rotor eliminates four Airworthiness Directives (AD) in force for the OEM rotor which call for inspections of the blade skin at the tab root, a check for trailing edge debonds of the laminated half bearings, and an inspection of the leading edge protection.
All of these have a 10-hour interval with all that AD compliance requires for not only inspection but also record-keeping. And of course, in the event of damage to one blade, only that part need be replaced.
Making savings
Van Horn says that the new design’s elimination of half bearings reduces inspections and replacements. Reduced control loading in turn reduces the wear, extending the life of pitch links, bearings and attachments, with the obvious cost benefits.
Specialising in the design, certification and manufacture of composite rotor blades, Van Horn Aviation started out by focusing on legacy Bell products such as the 206L (pictured).
Essentially the maintenance schedule breaks down as follows: an inspection of the trunnion runners as part of the pre-flight; at 300-hour intervals a visual inspection of the blades and hub components of damage as well as checking of the spherical bearings for axial play is needed; at half-life (2,400 hours) an overhaul is required that calls for a teardown of the hub, removal of paint from the metallic parts, a fluorescent penetrant inspection and a re-paint.
Overall, Van Horn estimates that compared with the original equipment its tail rotor will result in savings over an entire 4,800-hour service life of up to 25 per cent compared with the original design.
Spot the difference
Apart then from three-part versus one-part construction, how does Van Horn’s design differ from the original?
First up, while the diameter of the tail rotor is the same, the chord of the blades is increased. The partial trim tab of the original is gone, so the trailing edge is a straight line rather than having the step to the tab along about a third of its length.
The core of the blade is formed mainly of Rohacell foam, plus high-density GEE-F material.
Another obvious difference at first glance is the slight rake to the swept tapered blade tip, as is the greater area of the nickel abrasion strip – especially out toward the tips.
So what’s happening under the surface? The core of the blade is formed of two materials – the majority Rohacell foam, with high-density GEE-F material at the root leading edge block and forward and aft close outs.
This sees the leading edge block and forward close outs forming the basis of the housing for the titanium root doublers.
Also added in this layer are tip GEE-F leading edge and tip close out blocks. These provide additional resistance to tip damage
The second element is a spar constructed of unidirectional carbon which encases the blade to the mid chord, as well as the root doublers. This is then encased in a carbon fabric skin and then the nickel abrasion strip which, as mentioned above, has significantly greater coverage compared with the original equipment.
Moving on to the hub, the assembly is fabricated from stainless steel and results in considerably reduced wear compared with the original equipment.
Performance gains
So what does this all deliver in practice? We’ve already discussed the improvements to be found in life extension and inspection reductions compared with the original equipment.
The service life of the Van Horn rotor is 4,800 hours. This compares with 4,000 hours for the OEM version.
Moving on to performance, the proof is as always in the pudding, and I was able to have a sortie in the Van Horn test aircraft in the company of Chief Test Pilot, Terry Tyner.
It’s important to keep in mind that I don’t have enough time in AS350s to make a value judgement of the tail rotor authority improvements of the Van Horn tail rotor versus the original, but the response was certainly crisp even in the higher density altitudes found in the Arizona summer.
I was assured by Tyner that to the experienced AS350 pilot the difference is immediately noticeable and invariably remarked on early in a demonstration flight.
Reviewing the data from the flight test programme leading to the STCs, which encompassed 150 test points – including aggressive pedal turns, sideways flight, speed sweeps in turns, pedal pulses and autorotations at a number of altitudes – it was clear that critical factors like tail rotor shaft torques were lower than the original equipment. Likewise, boom bending loads were also clearly and consistently lower.
Another performance gain was hover performance with an aircraft ballasted to maximum gross weight (MGW), where gains were made especially at higher density altitude (9,400 feet).
A key data point that underscores Van Horn’s claims for wear reduction is to be found in the pitch link loads, which show significant reductions in both hover and forward flight manoeuvring.
An unexpected although always welcome improvement was in noise reduction.
The obvious conclusion is that, thanks to the rake of the swept tips, the energy of the tip vortices is reduced, thereby delivering the improvement in emissions.
Setting aside my amateur aerodynamics, the net result is that with the aircraft ballasted to its test weight of 5,140 pounds, the noise produced by the Van Horn tail rotor was 0.9 dB(A) lower than that of the original equipment – boosting the margin versus the Stage 2 limit of 86.5 dB(A).
Getting the balance right
Thanks also to the positioning of chord and span weight to inboard ends of the blades, the issue of the AS350’s notoriously twitchy tail rotor balancing has also been addressed.
Van Horn estimates that its tail rotor design will result in cost savings of up to 25 per cent.
Experience to date reveals that the static balancing carried out at the factory has transferred well to the field, with no static balancing required, while dynamic balance at ground and flight idle has also been shown to be straightforward and noticeably easier.
But since this is aviation there is a price to be paid and it comes in the form of a weight increase of 1.8 pounds over the OEM design – so following installation an update of the weight and balance is required.
This diagram shows the composition of the AS350 tail rotor assembly. Image: Van Horn
As of now, the FAA STCs have been granted for the AS350 B/BA/B1/B2 and B3, the STC for the B3e (or H125) is in progress, and Van Horn expects to complete the FAA’s requirements by the end of October and receive approval around six weeks after that.
For operators outside the United States, an EASA STC is something that remains in the future – with the timeline for starting the approval process still under consideration.
What then is the bottom line? A complete kit will set operators back USD 57,000 – but if an existing tail rotor is getting close to its life limit or has sustained non-reparable damage then the Van Horn solution starts to make a lot of sense.
If you factor in the time it takes to secure a new build replacement part, given that Van Horn prides itself on its agility in responding to customer need, it begins to make even more sense.
Recall too that one blade getting damaged doesn’t mean an entire replacement tail rotor.
Well, that might just be the whole ball game.
This article “Tweaking the tail” was published in the October/November 2025 issue of RotorHub International. To read more articles like this, apply for your complimentary subscription today.
