Using the Aileron Reflexor or T-tail on Quickie Aircraft
- Category: Safety
- Published: Tuesday, 27 December 2011 15:15
- Written by Gary McKirdy
- Hits: 21836
Using the Aileron Reflexor or T-tail on Quickie Aircraft
by Gary McKirdy
1000+hrs on several Q variants in the UK.
There is no intention to discuss here how to build either of these devices, but to provide some useful knowledge and understanding of when and how to use the facility to adjust the ground and flight characteristics of the aircraft.
There is nothing in the original Q.A.C. (Quickie Aircraft Company) supplied Quickie P.O.H. (Pilot Operating Handbook) on this as both these devices came after Q.A.C. had published the P.O.H.
The Quickie design benefits from a full span canard mounted elevator which works when the stick is back to add lift like a flap on a conventional aircraft wing. However, unlike conventional aircraft in a tandem wing you don't have the luxury of a powerful elevator with a large moment arm well aft of the C of G to force the tail up or down.
This C of G location in the case of the Quickie type with two almost equal wing area panels needs to be understood. It is located close to the trailing edge of the elevator on the canard (forward wing) or between 1/4 to 1/3rd the distance from the front of the total mean chord of the two wing panels combined. This is in the same way as the Cof G of a normal wing is usually between 1/4 and 1/3rd mean chord of the single panel. The canard mounted elevator being close to the C of G therefore has little moment arm to control the tail of the aircraft.
The aileron reflexor (often shortened to just reflexor) is so called because its original use was to reflex the ailerons trailing edge up. It came about because the GU canard exhibited a considerable loss of lift if the surface became contaminated with bugs and/or rain so a solution was sought to be able to combat the effect of having to hold significant back stick. The ailerons on the rear wing were provided with a secondary trim function which allowed them, in addition to their normal function of moving in opposite direction as ailerons, to move up or down together like flaperons. With care, this can be used on the ground to produce a tail down pitch authority which can be a significant help, both with tail wheel steering on the tail dragger, usually only after landing by increasing down force and tyre adhesion, or as a means to help lift the nose wheel on take off with the Tri Q, the Tri prefix being short for Tricycle undercarriage.
Unlike the aileron reflexor, The T-tail is not rigged through the ailerons so has no other shared function. It works directly as a mini all flying tail plane fin mounted in the conventional sense. It becomes a third entirely separate flying surface to the canard and main wing.
Both the aileron reflexor and the Le Gare T-Tail were separate developments to provide additional pitch control to overcome the loss of canard lift described. Both the mechanical type aileron reflexor and T-Tail are controlled independently of the canard mounted elevator control circuit, which is driven by the stick. They each therefore require a separate lever.
However it is important to understand that the pitch effect on the aircraft is very interdependent with the canard mounted elevator position in flight. For ease of understanding both the aileron reflexor and T-tail could be considered a second lever operated elevator control! Because of this, the most obvious, natural and safe convention for this additional control would be nose up requires lever aft, like the stick controls an elevator, as it has almost exactly the same effect.
In the tandem wing arrangement you can trim the aircraft in pitch using either the canard mounted elevator trim wheel (nose up command with elevator down) or the aileron reflexor which moves the rear wing mounted ailerons trailing edge up in the same sense as a conventional elevator on a horizontal stabilizer (nose up command with ailerons reflexed trailing edge up on rear wing). The T-Tail works in flight just like a conventional mini all flying tailplane (nose up command with trailing edge up).
It is quicker to dial in a trim change on the aileron reflexor or T-Tail than to use the canard elevator trim wheel which connects to the elevator drive arms through springs and contra rotating chord around a common shaft.
In the Qs both the aileron reflexor system and T-Tail are potentially more powerful than the elevator. They are your friend but need to be properly understood and used appropriately to remain so.
The reason the reflexor or T-Tail is so powerful in flight is simply due to the large moment arm from C of G. This easily outweighs the fact the ailerons and T-tail surfaces are smaller than the elevator.
The Q2 C of G range is from the elevator trailing edge at the root to about 4 inches aft of that measured at the root of the canard.
The ailerons used as the reflexor are 5 feet aft of this C of G location . That is a 15:1 ratio. These figures will not be far from typical for a Q (or Dragonfly). This accounts for why the reflexor is a useful but very powerful tool.
The T-tail is a smaller area than the ailerons but has nearer 3 times the moment arm of the relexor being 13ft from the C of G or a 33:1 ratio. Having flown them both the effect on trim on the ground and in the air was very similar.
There are not many aircraft where you can pre-set and re-set the elevator authority and effective neutral position in flight using another control.
For example you can use the reflexor or T-Tail to set the neutral position of the canard mounted elevator in the approach (visibly aligned neutrally in it’s slot at the canard tip) in order to provide sufficient elevator control for the flare. This is an ideal to ultimately aim for with your set up but it is part of what you need to test during the early test flight stages whether the aircraft is a new build or new to you.
Pre test flight installation operational checks.
If you have either the Aileron Reflexor or T-tail fitted, before attempting to test fly the newly built or new to you aircraft you need to ensure 4 things regarding these devices alone.
- The limits of travel have been correctly set and that the device works in the correct sense. Refer to plans and Q-List and Quickheads source.
- You, or your test pilot, fully understand the effect of using the operating lever in either direction, and when each may prove to be useful (possibly essential!) throughout the pattern/ circuit.
- You, or your test pilot, can actually sit in the aircraft with the cushions and clothing intended for test flight and easily reach and operate the lever in full deflection in either direction just in case you are required to! This accessibility should be tested during the installation at the build phase and not left to test just before first flight.
- Neither you, nor your test pilot, can under any circumstances accidentally knock the lever whilst reaching for something else in a hurry. This requires thought as to optimum location and you must ensure there is adequate friction in the system to help prevent this.
The properly constructed and located mechanically operated reflexor is a very quick and direct means to re-trim in pitch if required. An electric driven aileron reflexor operated by a stick top or panel mounted rocker is much slower and potentially less reliable. I would not recommend this for early test flights as the ability to quickly locate and adjust this trim, for an out of rig surprise on take off for example, might be extremely valuable.
There has been some debate as to whether or not to recommend use the reflexor or T-tail on early test flights.
Nobody in my opinion should be even contemplating test flying a Q without a full knowledge and understanding and ability to operate all the controls built in to the aircraft even if, as is the case with the aileron reflexor and T-Tail, you may have heard them being described as just a trim system!
The simple reason is that to some extent the reflexor or T-tail can be used to compensate for mis-rigging of the canard or main wing found during early flight tests and so this could potentially be of great benefit here to save the day!
Fore thought, pre-planning and good cockpit ergonomics, particularly reflexor/T-Tail set up, will all help provide the ability to rescue a bad out of rig situation. Whilst on the ground, practice reaching for the operating lever until you can do it blindfolded. Whilst solo, the roll trim should also be slightly biased to the pilot side about 1/4 inch trailing edge down on the elevator to help prevent a permanent stick load. Be ready to trim this roll out to neutral once you level off at a safe height.
Control position general test flight phase.
On a new build it is not possible to predict the exact position of the contol lever for the aileron reflexor or T-Tail lever on first flight. You should therefore set it near to neutral as taxi speeds are slowly increased. Nevertheless some recommendations can be made:
- During your planned extensive taxi trials on the longest runway available, if on the tail dragger the tail starts to lift before the lift off speed is achieved, be ready to try bringing the ailerons or T-tail trailing edges up slightly and try another run. It should be possible to approach lift off speed as the tail can be progressively held down so that you know, on lift off, the reflexor or T-tail is in the right ballpark. At any point, if directional control becomes an issue, smoothly pull the power off to stop a prop torque yaw and quickly bring the trailing edges all the way up to aid with tailwheel adhesion and steering. A small glider type pneumatic tyre 200x50 is a great help here but it will require a new tail wheel fork.
- Whilst the tail dragger levitates from its ground attitude having reached lift off speed usually requiring full aft stick and neutral reflexor for minimum take off distance, the Tri will probably need not just full aft stick but some if not a lot of aileron reflexor pre-set to help initiate the rotation around the main gear. It is because you need to help force the rotation that you also need to quickly check with forward stick at the normal flying attitude to stop over rotation especially if you are already well above flying speed when the nose finally agrees to come up. On the Tri-Q, if you find yourself hurtling through lift off speed with the elevator full down try several more runs with the reflexor or T-Tail trailing edges up a little more each time. It should rotate comfortably before lift off speed. The attitude to aim for is that of the tail dragger on the ground. Some secured weight in the baggage bay within Cof G limits could also help here.
- In an emergency over-rotation on climb out, DO NOT PULL THE POWER, be ready to quickly reach for the reflexor/T-tail and dial in whatever nose down trim is needed to adjust climb out path to that desired but be careful not to over do it and reverse the climb out path! The sweet spot in between is quite large but it still may require quick reactions to find it in a new aircraft.
This is the only thing I felt could catch out the newbie in a Tri Q in the early test stage in addition to all that has been said about the tail dragger variants. In the air the Q's fly very similar whether nose or tail wheel.
The only other thing which may already be apparent from the above is that the risk of a high energy impact in to the overshoot obstacle is greater with a Tri gear because it can be well through the minimum flying speed before it rotates enough to lift off and that takes a lot of time whilst gobbling concrete at the wrong end of the speed acquisition. You can better gain the first 10mph safely in a Tri doing a J run on to the full strip length.
Furthermore on landing you can be on the brakes much earlier and harder than in a tail dragger and so have the benefit of being able to get in to smaller strips but there in lies a trap for the unwary, YOU WILL NEED TO EXCERCISE GREAT CARE HERE BECAUSE YOU MAY NOT BE ABLE TO GET OUT AGAIN, EXPECT DOUBLE OR EVEN MORE STRIP LENGTH NECESSARY TO DEPART EVEN ON THE SAME DAY.
- On approach set the reflexor/T-tail to give the chosen approach speed and visually check the position of the canard mounted elevator is near to neutral. This is to ensure sufficient stick authority for the flare. Note that in an already flight tested, adjusted and sorted Q (which yours may not be when first tested!) if the reflexor/T-tail were set at the extremes of travel, the elevator trailing edge position would also change for any given chosen airspeed. This demonstrates the interdependence between either the aileron reflexor or T-tail setting and the position of the canard mounted elevator.
- After landing the tail dragger, ideally fully held off until it gently settles on at minimum flying speed, or once below the speed at which it could lift off again full tail down application of reflexor/T-tail will assist with tail wheel adhesion to the surface and allow the brakes to be applied harder. This can help significantly with directional control and minimum stopping distance. On the Tri Q, the benefit of the same action is reducing the loads on the nose leg, which increase under heavy braking. However, whichever type gear you have, don’t forget to re-set the lever for take off (add it to your post landing check list) in case you get distracted and forget your checks next flight.
Control Position ideal once aircraft is fully sorted.
Assuming you already have the correct reflexor/T-tail neutral position which itself may need a bit of tweeking, if we call the reflexor/T-tail range 1-4 with 1 being full nose down and 4 full nose up then expect something like the following to be an ideal set up. YOU MAY NOT HAVE THIS IDEAL SET UP WHEN IT FIRST HATCHES! A very important part of your initial testing will be to find out.
Fast Taxi tests to lift off speed when forward C of G solo light fuel 3-4
As above but heavier, with more fuel in main tank, ballast in passenger seat or baggage bay 2-3. More aft C of G is now taking the downward load requirement off the reflexor/T-tail.
On climb out FORGET THE POSITION just ease in whatever it takes to quickly trim required climb speed.
On levelling out in the pattern reduce by may be up to 1 point off what it was before so 3 to 2 but slowly ease reflexor/T-Tail lever forward until trimmed straight and level.
Descent to land at reduced power 3, (which should be at least one dummy approach at safe altitude on first flight and more goes at this if T's and P's are O.K.) or whatever it takes to trim the chosen approach speed but VERY IMPORTANT you must then check for sufficient elevator control for the flare so be prepared for whatever reflexor/T-tail position puts the stick in near neutral in pitch position. If it was a long way out you might have to hold a stick load all the way down or trim this load out on the separate elevator trim wheel if you have one.
So nothing is quite as simple as it may seem. When testing a new aircraft you are testing how close everything is to the desired parameters so nobody can really put a numerical value that means anything until the parameters themselves begin to demonstrate falling in to the desired ball park.
Only after several hours of getting used to the feel of the aileron reflexor, it is possible using the canard mounted elevator pitch trim in conjunction with the aileron reflexor to trim both aircraft flying surfaces trailing edges in the same direction, canard and main wing together by balancing a small move on each surface little by little. For increased camber used for slower flight trim both trailing edges down (think of dropping a bit of flap on both canard and rear wing). For decreased camber higher cruise speed trim both trailing edges up on the elevator and ailerons (less lift induced drag so higher speed). This has to be done carefully by balancing each wing against the other bit by bit on each control device. It is therefore important to ease in a small amount of each a bit at a time. This performance benefit is not as well defined with the T-Tail but still helps.
This is not something to attempt to do in your early test flights.
Fly fast. . . but more importantly fly safe.