Tandem Trainer

[CRAN]

Here's the question: How important is it for training helicopters to have a side-by-side seating arrangement?

It has long been known that aircraft used in a training role are preferred to have a side-by-side seating arrangement. This is important as it allows ready communication between instructor and pilot with shared instruments, maps and equipment. However, the compromise is that training helicopters have cramped cockpits and poor fuselage aerodynamics (in relation to bigger machines.)

For civil applications the primary drivers for a training aircraft are safety and cost.

Recent developments in various areas of technology mean that it is now possible to produce a 2-seat training helicopter with a direct operating cost in the UK and Europe of £60/hr and in the US of £50/hr. The performance of such a machine would be as follows:

Cruise at 75% TQ 130mph
Range at MTOW 400mi
Climb at MTOW 1000fpm

Payload with full fuel: 216 kg (2 PAX @ 235lb each)
or reduced pax weight + bags

MTOW 650kg

Purchase Price £90K

MR would be a two-blade rotor with hub spring
TR would be two-blade traditional design

HOWEVER, the design would be a tandem seating configuration.

The benefits of such a configuration would be more room for both (large) occupants, improved crashworthiness, improved aerodynamics - hence cruise speed. Additional benefits would include greatly improved CG range, traditional control layout and improved appearance.

So expanding a little, would the tandem seating configuration rule this machine out of the training market...or could instructors and schools learn to love it.......as it's dirt cheap!

I look forward to your responses!

CRAN
:8

[Blue Rotor Ronin]

Sounds good to me......although it's not my field.:ok:

[Ascend Charlie]

Obviously the instructor in the back needs to sit higher than Bloggs in the front, to get an adequate view over the meathead trying to kill him. This will add to the complexity of the canopy, which will need to be totally clear, without a sun-shading panel.

Now we need to have cooling airflow, as it will be very hot under the sun. Sliding panels? This decreases the strength of the canopy, so start adding canopy bows to hold it up.

How does one enter and exit with this canopy? Over the sill, like a Cobra? Not very practical for less nimble people than US Marines. Does the canopy hinge from the side? Or the back? Can it be opened with the rotor turning? Will it stay shut at Vne?

CG considerations will be more critical, with Bloggs's weight another 5 feet further out the front - how to balance that? Ballast in the tailboom? But that is eating up your useable weight. Twice as many instruments as with a side-by-side, adding to the weight and complexity of pitot-static runs and electrical looms. The need to duplicate some controls into the back seat, so the instructor can still control carb heat, mixture etc for an ab-initio Bloggs on a TIF who would shut the engine off if not supervised carefully.

For a big machine like a Cobra, it works well. But that is not a small, light, cheap trainer.

Lots of luck!:8

[Dave_Jackson]

A couple of points that may be of value;

I did some aerobatic training in a plane with the two seats arranged longitudinally. The instructor sat in the back. He had flight controls, but I think that he looked over the student's shoulder to view the instrument panel. He definitely took a large phone book along so he could sit up higher. :D

You may want to reevaluate the use of a Hub Spring on a rotor with 2-blades. I believe that it will cause a 2P vibration, when the tip path plane is not normal to the mast's axis*. Rotor - Hub - Teetering w/ Hub Spring (http://www.unicopter.com/0799.html) may provide some information of interest on this subject. I would defiantly appreciate feedback, if you disagree with any of this information.

Hope this is helpful.
PS. 'LZ' and "NL' are participants on this forum.

* Edited for clarification

[Lu Zuckerman]

To: CRAN

It sounds like a smaller version of the YAH-63. Tandem seating and a two blade rotor with a hub spring. The blades on this helicopter had a 41" chord. Hopefully the blades on your design are smaller.

See here http://avia.russian.ee/~star/vertigo/bell_yah-63-r.html

:ok:

[Barannfin]

in the training aspect I think that it is very important for the easy conversation between inst. student. I feel its much easier to communicate if you can easily see the persons eyes/hands. However on the other hand I have never flown in a tandem arrangement.

I do think that this setup would probably be much more popular with some other missions of v/light helicopters, that involve non-flying occupants. Observational/photo flights would negate the need to fly at odd angles to provide good view. Plus I think the tandem setup would look really cool :cool: which might prompt sales to pvt. owners as well. (visions of mini-cobras sitting on the ramp of our local airport :ok: )

[Shawn Coyle]

I'd really like to see a diagram of this before passing judgement, but my first comment is, where is the cockpit with respect to the front rotor?
How many engines?
What sort of AFCS, as tandems tend to want to swap ends pretty quickly in forward flight. CH-46 and CH-47 have some of the most complex AFCS in existance, redundant systems with sideslip ports, and a very unique arrangement for tilting the rotor heads with airspeed.
If the intention is to just tilt the fuselage for airspeed increases, the result may be less than ideal. Also, the flight control mixing units will be pretty interesting.
Will there be hydraulics?
I believe one of the early Bell tandem machines (yes, they made one) had teetering rotors, and this was not so satisfactory - hopefully the design team has looked at that for lessons learned.
And so on.
What sounds good on paper is often fraught with problems in reality.
Best wishes!

[Spaced]

I had a similar thought to you in this reguard.
I managed to track down a few Cobra and Apachie pilots who were unanimous in telling me that the Tandem arangement was far from ideal. The general consensus was that due to the fact that even passing a peice of paper became a chore and it was difficult to communicate.
The current way in the Apachie is through a mail slot type arangement for passing stuff between the two flying.
I still think the disadvantages are outweighed by the coolness of the apearance.:ok:

[Lu Zuckerman]

If the Apache has some type of slot to facilitate the passing of messages between the gunner and the pilot it is a major modification. The main purpose of the transparent armor is to protect the pilot or gunner when a high explosive round goes off in the cockpit or the gunners’ station. Having a slot cut in the armor would compromise its’ structural integrity and allow high velocity gasses to flow from one cockpit to the other when the HE round went off.

:confused:

[Spaced]

Good point Lu, I was only repeating what I was told by a few mil boys. Having not seen the inside of an Apachie I cant varify it myself.
The description was of a draw type arangement.
Again Im only going off what I was told. However I am prepareed to bow to your experience.

[CRAN]

Shawn,

Thanks for you valuable contribution, however I think you may have misunderstood me. When I loosely refer to 'tandem', I am refering to tandem seating i.e. Pilot in the front passenger directly behind him. Otherwise it is the single MR and singe TR standard configuration.

A tandem rotor configuration is clearly not going to give a viable low cost training platform. Well thats my view anyway, not necessarily everyones....

www.lafhelicopters.com

Thanks again for you input.

CRAN

[Genghis the Engineer]

An interesting discussion. I come at this from this largely from a FW perspective - my only flying hours in helicopters are down the back as Flight Test Observer in larger military types.

However, I've flown right / rear seat (in the same role) in a number of 2-crew fast jets which are certainly not less complex than a helicopter. I can't honestly say that I found the side-by-side configuration of the Hunter easier to live with than the tandem configuration of the Hawk or Jaguar, and the RAF seems very happy with the Tucano as a basic trainer (from that perspective at-least !). What it clearly does is mandate clear verbal communication between crew, I'm not at-all convinved that's a bad thing. (Also, you need duplicate sets of checklists, approach plates, etc. but I can't honestly say that ever troubled me either).

As a pilot, I did my first PPL in a Shadow, which is a tandem FW trainer, and had no problem at-all; in-fact I enjoyed the feeling of detachment from my instructor when they weren't talking, and suspect that it made me less mentally reliant upon them baling be out in the earlier stages of my training. I have heard FW instructors in various types complain about lack of forward visibility during approach and landing - how relevant that is to RW issues I'm not qualified to judge.

As for dual controls, speaking as an Engineer I can't really see that as being a huge technical challenge - certainly no worse than numerous tandem FW trainers. The controls may work differently, but at the end of the day it all comes down to pushrods, hydraulics or cables, and they can always be either split or combined with various well-established devices.

G

[Shawn Coyle]

OOOPS
I obviously need to slow down my reading...
Sorry. Hope this affects my 'demi-god' status negatively.
Other comments on tandem seating are quite valid.
For helicopter training, one of the things is to be able to see where the student is looking, to make sure he is using good and appropriate cues.

[Ascend Charlie]

Shawn is absolutely right here - the instructor wants to see where the student is looking, particularly when learning to hover. It is also nice to be able to use hand signals instead of yapping on the intercom, and for the student to see that the instructor's hands are not on the controls. Sure, they might be being used to cross himself or pray, but at least Bloggs knows that whatever happens, he is responsible for it.

In F/W, such as the Macchi, forward vis from the back seat was dismal and flapless training at night was fraught with apprehension. Not so critical in a helo, with slower speeds and more reliance on lateral cues.

[bugdevheli]

Tandem Helicopter. what about a three place machine P1 in front P2 or 2 passengers in rear, sitting under centre of mast the machine is almost ready for its first ground run. it is called the RAPTOR

[slowrotor]

Cran,
The CH-7 Kompress built in Italy has tandem seating.
The instructor sits close behind the student and shares the students cyclic (the cyclic has two hand grips about 3 inches apart).
The foot pedals have about 16 inch extensions for the instructor.
I think I would prefer this to the odd bar used in the R22 that makes transfer from instructor to student very awkward.

slowrotor