Kalt Baron Whisper – The Ultimate Flashback

The History

KALTOne of the memories I can recall when I was a little boy was a printed brochure from Kalt Helicopters which I took home with me from our local modelling dealer. I would spend a fair amount of my afternoons studying and adoring the mechanics of the world’s first electric helicopter that was available to the mass market. It was pretty much the definition of “unreachable” to me. This was in 1990. Now, almost 25 years later, many things have changed in my life – but this love has never really vanished. This is the story of a dream finally coming true, because I decided to look out for one of those little helicopters.

I believe I used up all my luck remaining for 2014 (as well as potentially for 2015) when I discovered – after weeks of looking – that a local dealer in the Frankfurt area still had a Whisper sitting in the shelf. Supposedly a complete kit, never touched, waiting for me at least 20 years. I drove by immediately and picked up my Whisper. I still cannot believe how lucky I was:


When do you know you have purchased something really old? Two things indicate that: An invoice that says “DM” and “Pfennig”, and styrofoam packaging that has already started to dissolve.

What’s In the Package?

It was quite surprising to see the few small bags that supposedly would make a full helicopter in the end. Everything well-sorted, including wooden blades, the cut out canopy, decals, manual, and a bowden-cable – yes, a bowden-cable:


The blades come as a DIY-kit with 10gr of lead and a long shrink tube. The length is 36.5cm and the weight of the bare wooden blade is 36gr. Very light. For me, I decided to preserve them and mounted a set of Flight & Guide (do you still remember them?) 425 semi-symmetrical. They fly very well, but I suppose many others do as well for this application.


Building Up the Mechanics

The manual is a good balance between illustrations and instructions. As usual: You should read them carefully. There are steps where there is room for errors if you don’t. Let me start with some detailed pictures, I thought those are very hard to find on the net:


Single, monolithic plastic chassis, designed to host mini- & midi servos and a Mabuchi 540-sized motor.



Note this is full plastic and the central unit comes pre-mounted. This thing is not made for high-RPM:


Fully assembled rotorhead


Everything attached to the main shaft

The main shaft is hollow and is prepared to take in 2mm screws for mounting the rotorhead and main gear. There is no freewheel in this kit.

main_shaftThe swashplate is designed to hold position while changing angles. Back then there were no CCPM mixers, you were lucky to have a good reception – does anyone remember the times on the flying field when you had to ask the other pilots which channel they were using?

swash1Notice how pitch works here: There are two pieces of steel wire connected to the lower pitch slider, pushing the servo energy upwards to the upper pitch slider. Fragile, but it works. Again, not designed for heavy-duty.



This is a 2mm tailrotor-shaft, yes, 2mm. I don’t think it is hardened either. The blade grips are asymmetrical.


Fully assembled tailrotor

I had to look three times to realize that there are no ball bearings between the inner and the outer slide ring. It is designed as a plain bearing, and I have seen this in no other heli so far. When changing tail pitch angle back and forth at the fully mounted unit, you can notice some resistance because the pitch control plate is designed to bend to the outside. Also it has been quite some time since I have seen this. All in all the tail mechanics are quite free of play. This is going to work OK in the air.


This package holds the 2nd gear section as well as the side arms that would stabilize the main frame. The motor / main rotor / tail rotor gear ratio is 1: 20.6 : 4.12. All gears are 32p, which translates to module 0.8. The motor pinion is 17 teeth.

gear1Mounted with skids and frame support

The frame support really increases the stiffness of the whole unit. An interesting detail: The first gear section and the motor won’t be mounted in a 90° angle, in order to have full alignment of the tail belt to with the tail pulley.

mounted1Flybar and paddles

Very nice detail that saves plenty of time: The flybar has threaded drill holes to safely and quickly mount the two plastic paddles.

flybarFully assembled mechanics

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Of course the goal was to have a Whisper that is as close as possible to the original version. This would include electronics as well. But I decided to go for modern components instead, in order to have a more reliable and lighter system that would keep the load to the mechanics at a minimum. So Nicads and brushed motor were out instantly.


While building the Warp 360 I made particularly good experiences with a 6S LiPo setup. I am using 1400 mAh 6S packs. The measured flight time with these is 16 minutes (yes sixteen). You will feel like right after a 2 week vacation after this, I promise.

Lately I became a big fan of YGE controllers. So I went for a YGE 40 with governor function. These controllers have an active freewheel feature that will work at a nicely even at low/medium RPM situations.

A good match for a brushless motor was not easy to find. The way I approached this was to take the no-load rotor RPM, which was at around 1400 for the original RX-540VS motor. To fit with the pinion it hat to be a 3.17mm motor shaft, which narrowed the choice down even further. It is also very important to understand, that a 2,000 Watt engine would not have been a good choice, since all mechanics have been designed to work at an 150 Watt environment. It would be a short flight.

The Scorpion HKII-2221 turned out to be an excellent choice with 1630kv, there is plenty of headroom in terms of power, and the YGE keeps the RPM very constant. I run the heli at 1300-1400 RPM with around 60% of throttle input for the governor. The only challenge is to mount the motor onto the chassis. I would recommend a mounting adapter, if you do not want to dremel a lot (which is what I did in the end).


As for servos I went for HS-81 on swashplate and a HS-5084MG with a Futaba Gy401 that I happened to have laying around in my tool box.


What can I say. I was totally impressed how well this little heli flew at second flight. If you spend some time balancing everything out well, you will benefit greatly from it later on (take your time to balance out the flybar and tail blades). How does it feel? Well, after 12 years of heli flying I have never had anything like that before. It is very, very stable and relaxed. It feels really light and even at low RPM very precise and smooth. Interestingly it reminded me of a V-Bar with “Precise” style setting. The tail works like a charm, and holds very well. You can tell right away that 1300 / 1400 RPM is the comfortable headspeed for this model. Anything above will cause the heli to make weird sounds that you should take as a sign of overstressing the mechanics.

I am extremely proud to own one of these very rare helicopters, and finally go full circle with a journey that started almost 25 years ago.

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