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Quadplane tips and hints

Having recently built and flown several different kinds of Quadplanes, I thought that I would add a hints and tips page to the wiki due to some unique facets of Quadplane that are not covered currently… here is the first draft and I welcome comments and suggestions for additions for us to consider before I PR to the wiki…its in .rst format as would be added to the wiki so some of the formatting will, no doubt, be messed up(the table is really messed up here,but format is perfect in the wiki):

… _quadplane-tips:

==============
QuadPlane Tips

A few helpful hints and tips for first time QuadPlane users.

Motor Alignment

Motor alignment is always critical for any Plane’s performance, but it is especially so for QuadPlanes.
Miss-aligned VTOL motors can greatly affect basic VTOL performance, especially yaw trim and effectiveness, as well as fixed wing flight performance.

Checking motor alignment on the bench can be done by blocking the vehicle in a level position and measuring prop to table distances for all motors with props in fore-aft and side-to side positions. Measurement differences easily reveal miss-alignments. The arc-sine of the prop tip end differences divided by the prop diameter will give the tilt angles. A degree or two miss-alignment,while not disastrous for pitch or roll, can be significant in non-vectored yaw configurations with regards to extreme yaw miss-trim.

Miss-alignment can be also seen in the dataflash log RCOUT values in a hover for the VTOL motors. Yaw problems appear as large separation between diagonal motor pairs.

For vectored thrust frames, fixed wing mode alignment is also critical. Differences between motor thrust angles in forward flight will generate undesirable roll and/or pitch trim tendencies. Careful bench checking and adjustment of forward fixed-wing mode positions with respect to airframe and one another is required.

X vs H Quad Mixing

In theory, it doesnt matter which is used. With perfectly rigid mounting, no performance or flight difference will be noted as far as motor control dynamics. However, the actual implementation of the mounting can result in differences in drag and efficiency.

  • X frame mounting or horizontal H frame type mounting creates the most drag.
  • H frame mounting fore-aft (ie on the wings in line with wing chord) is the least drag, but also can result in a lot of flexing, depending on wing construction

In addition, if the mount method allows ANY twist to occur, serious performance impacts can occur. For example, a conventional style plane airframe has the motors mounted on cross members in the nose and rear fuselage. If the fuselage allows a minor twist to occur (like during yaw with one diagonal supporting most of the plane’s weight), which most foam style planes will, then if X mixing is used, the twist induced during yaw actually acts to decrease the yaw. In some cases, it can completely disable yaw effectiveness. However, the same configuration using H mixing, the twist will actually aid the desired yaw.

In general, in a Quad configuration , use H mixing and not X mixing.

AHRS “LEVEL” Trim

When you setup a Plane, the “level” calibration should be done with the plane in its normal cruising attitude (ie angle of attack of the wings). If the vertical position of the VTOL motors is not 90 degrees to this attitude, then the QuadPlane will tend to move forward or backward when hovering, requiring stick input to modify pitch.

Fortunately, there is a parameter which allows the independent adjustment of the VTOL AHRS “level” attitude. This is :ref:Q_TRIM_PITCH<Q_TRIM_PITCH> .

However, there is a better way. If mechanically possible, trim each motor to be vertical when the QuadPlane is in fixed wing “level” mode, so that using :ref:Q_TRIM_PITCH<Q_TRIM_PITCH> is not required. Usually this requires 3-6 degrees of forward tilt. This has the advantage of having the wings generate lift while hovering in the wind, reducing the load on the VTOL motors and preventing sudden pitch changes during transitions back to VTOL mode from fixed wing flight.

Battery Sag

Many QuadPlanes are targeted for duration and therefore may utilize high capacity to weight ratio, but low “C” , batteries. Battery sag in the initial phase of VTOL to fixed-wing transitions can be a real issue. Be sure to read the warning in :ref:quadplane-flying .

QuadPlane Configuration Pros and Cons

ArduPilot provides many different QuadPlane configuration options. Your specific application requirements will determine which to select.
However, the table below gives some general pros and cons of each configuration type. There is wide variations, but these are high-level generalizations.

±---------------------------------±-----------------±-------------------------------+
+Configuration Type + Pros + Cons +
±---------------------------------±-----------------±-------------------------------+
+QuadPlane +easier assembly + wing-mount: twist +

  •                              +                  +--------------------------------+
    
  •                              +                  + fuselage-mount: drag           +
    
  •                              +------------------+--------------------------------+
    
  •                              + lower efficiency +                                +
    

±---------------------------------±-----------------±-------------------------------+
+Tilt Motor Tricopter + efficient + complex mechanically +
±---------------------------------±-----------------±-------------------------------+
+Dual Motor Tailsitter + easier assembly + poor stability upright +

  •                              +------------------+--------------------------------+
    
  •                              + most efficient   + requires large flying surfaces +
    

±---------------------------------±-----------------±-------------------------------+
+Belly Landing Dual Tailsitter + stable at rest + complex mechanically +

  •                              +------------------+--------------------------------+
    
  •                              + very efficient   + requires large flying surfaces +
    

±---------------------------------±-----------------±-------------------------------+
+Copter Tailsiter +very controllable + lower efficiency +

  •                              + and aerobatic    +                                +
    
  •                              +------------------+--------------------------------+
    
  •                              + easier assembly  +                                +
    

±---------------------------------±-----------------±-------------------------------+

4 Likes

Henry,

It looks like you made another nice addition to the WiKi. For the Pros and Cons section, here are some further benefits to consider.

QuadPlane:

  • Can carry or drop payloads
  • Can assist hover or forward flight modes
    Q_ASSIST_ALT
    Q_ASSIST_ANGLE
    Q_ASSIST_SPEED
    Q_VFWD_GAIN

Cheers!

Hi Henry, very usefull hints. But one comment:

I do not agree with your efficiency assessment. The Quadplane is the most efficient VTOL type (!)

The reason is very simple: since most of us do not have variable-pitch propellers, the selection of the motor-propeller unit in tiltmotors/ bellysitters / tailsitters are always a compromise between either optimization for cruising-speed or optimization for hovering.

Not so in quadplanes. The quad motors/propellers can be absolutly optimized for hovering and the propulsion motor/propeller combination is optimized for a designed cruising speed .

In my expirience this advantage far outweighs the disadvantages of more weight and higher air resistance.

Another advantage of the Quadplanes is that you can easily use two different batteries for hovering and cruising. A high C-rated battery with small capacity optimized for hovering and a low c-rated with high capacity battery for cruising. The battery for cruise-speed can be flown almost empty, since the high-rated c battery is used for the VTOL landing.

I myself was surprised at how much more efficiently a quadplane is compared to a tiltrotor or bellysiter.

Rolf

Thanks, Rolf, but I have to continue to disagree…both intuitively and with apples to apples data …assuming you are talking forward flight efficiency…the only thing I would think that really matters in a quadplane…if you are looking for an efficient hovering copter flight, then a copter would be better :wink:

Intuitively: take an efficient flyer like the Minitalon…
–add four engines and booms and escs…whose only purpose is VTOL action…contributing nothing but drag and weight in forward flight
now take the same plane and convert to tilt tricopter quadplane:
–replace the forward propulsion motor with three motors, two of which are not wasted in forward flight and roughly the same weight as the single forward motor…10g more total… and only have a slight increase in weight due to small rear tricopter motor (sized ~ 1/2 than the two tilt motors up front )…so “dead” weight in forward flight has increased only 35-40g…plus another 20g for the tilt servos…so instead of 300-350 extra grams, its only 50-70g…in addition, since their are no booms, not much additional drag and no vertical motors side-on into the airflow with additional interfering propeller disks to increase drag like in the quadplane…pretty easy to see why of the two configurations on the same basic airframe, tilt-tri is a lot more efficient for forward flight duration…

actual data:
all using 4s 5200mah 10C Lipos

Minitalon std…1800g range cruises at 4.5A at 32mph (mine and data correlates with others)
Minitalon Quadplane… 1800g cruises at 8-9a at 35mph (mine…removed gimbal to counter added weight…which also decreases drag even) with optimized forward tilt…10-12A cruise with free-wheeling prop disks…
Minitalon Tilt Tricopter…1800g cruises at 5.5A at 32mph (Mark Q’s)…I am about to convert to it also…

PS agree with basic qplane advantages of forward assist and that you can use different batteries for VTOL and forward…but was trying to distinguish BETWEEN the Qplane types to help someone who know they want a VTOL plane as to which is best for their application…

1 Like

Forgot to add that equal forward tilt to cruise AOA also fully “feathers” that draggy prop disk to minimize drag…also to set brakes on copter motors not used in forward flight…a “free-wheeling” prop creates tremendous drag…feathering them by correct forward tilt also reduces or eliminates the free-wheel…

Hello Henry, still disagree :wink:

I think there is a lot to optimize !
Mine: 2320 g 4s 5200mah 10C only for forward propulsion
Prop: Aeronaut 10x8 / Cobra C-2814/16 Kv 1050
(You can’t do a hand launch with this combination)
90 Watt at 65 km/h (40 mph) Airspeed
75 Watt at 61 km/h (38 mph) Airspeed

Every gram is important in copter modes. As an airplane additional weight is not so important - it increases the stall speed somewhat. But it is much more important for the efficiency that the CG is correct and the engine / propeller runs efficiently at cruising speed. With the VTOL we do not need to pay attention to minimal stall speed or enough thrust at zero speed for the hand launch. Under these assumptions, the quadplane is more efficient in case of long duration/distance flights with only 2 short copter-phases. It would be different, if we use pitch adjustable props.

1 Like

i’m going to wade into the efficiency debate and say that you cant classify one type of VTOL as more efficient than another, the fine points of the design make much more difference than tilt-rotor vs quad-plane vs tail-sitter. A well designed tail-sitter is more efficient than a badly designed quad plane and a well designed quad-plane is more efficient than a badly designed tail-sitter. There are just too many variables to boil down to a single bullet point. I think its best just not to comment.

true, true…but that is not apples to apples…if Rolf removes his quad motors and arms and escs and VTOL battery, and then bungee launches, it will have much longer flight times

if he converted his optimized quad configuration to an optimized tilt-tri or a belly landing tailsitter on the same airframe with the same weight, it would fly longer and farther…

The problem with a focus on pure efficiency is that you start to leave the world of practical application. I would have to agree with Peter on the aspect of efficiency being less relevant, especially in commercial use. You don’t see any tailsitters carrying a significant payload so the choice of efficiency seems irrelevant when you go from theory to many different practical applications. Perhaps using some examples in each category might provide a better choice of direction for the user looking to decide which type of configuration to use in various applications, climates, and, conditions. The user may want to map 15 Hectares or drop a First Aid kit along a mountain side or simply fly a small foamie indoors.

@Rolf re my Qplane’s efficiency…no doubt it can be further optimized, I only have three flights on it…only thing I have done so far is adjust the motor angles…I am using looooong horizontal cross sq carbon tubes with no fairings and BIG VTOL motors (ss2216-1250) lots of flat plate drag…
I went with Mozzie style cross tubes because several reported problem with wing mount twist…just didnt want to mess with it…also the motors will be changed to low profile 2212/950s since the ss2216 is way overkill…all should help, but will never get to that of a tilt tri on this airframe at that weight…

Greg,I agree that this has too many variables to help someone with choosing…and will just eliminate that section…btw re tailsitters not carrying payloads : https://wingtra.com/
99w for 1 hour on a 4.5Kg plane with 800g payload…not too shabby

I had not seen the Wintra before…very cool, thanks!

Even if I’m not convinced - maybe I’ll buy another Mini Talon and upgrade it to a Tritilt.
Until then I am looking curiously forward to datas of our reverse tritilt ( Reverse Tricopter-VTOL Plane - https://vimeo.com/369415229 ) . Thanks again to Peter for implementing the firmware for this kind of tri to master: Both rear motors are only active in copter-modes and have to carry most of the load. So that the center of gravity can be further to the rear, we have chosen a swept wing. Only the single front motor tilts forward, efficiency is not designed to hover, but rather for forward-propulsion. Unfortunately in the past few month the weather here has either been wet, cold, stormy or a mixture of all three - We are eagerly waiting for better weather to be able to test and measure.

I would like to focus another more practical aspect: batteries.
In VTOLS, the aging of lithium ion batteries is very fast, since at the end of the battery capacity we need full power again. - and there is a great risk that the drop in battery performance is too big at the end of a flight for hovering. That’s why I became a friend of the 2-battery concept. When flying as a plane I don’t have to worry about an empty battery no. 1, as long as there is enough power for landing with battery no. 2. After a prang due to a weak battery, I look at the aging of the batteries by comparing BAT.res from flight to flight. How are your experiences ?

I havent taken a Qplane to the end, except for a Convergence and it had a 60C so was not a problem…the MT Qplane Iv’e flown to 4000 out of 5200 mah on a 10C Multistar and had enough to hover and land and still had >13.5V during landing…of course, I fly the plane down to 10-15 feet and 60ft out in FBWA ,and then switch to Qloiter and land as soon as it stops, so its quick…

Am rebuilding it today…nosed in this morning…I had swapped out my 2814/9x6prop forward motor for 2216/8x6 to allow me to get rid of ballast up front (I had removed the gimbal and just had FPV cam and HD cam so had to add some lead), but forgot to raise THR_MAX back to 100% instead of 65% that I used with the 2814 to avoid going over the 10C limit…so when I switched to CRUISE after flying a bit in FBWA, and trim throttle dropped to 25% actual instead of 45% … it promptly stalled ,rolled over on its back and nosed in from 60ft before TECS could raise the throttle …crushed the forward section…hot glue gun is already in action…wont be pretty but will be straight-enough…had not gotten to trying ASSIST yet which may have prevented my super-stupid regarding the TECS target throttle percent…

hello Greg,
yes, wingtra is cool but the best one is


look at their video and you will be fascinated.

Yes, that is very cool, thank you! It reminds me of my Ares V-Hawk X4 VTOL which was originally designed by Graupner. Only the motor pods tilt but the concept is similar. I still fly mine today.

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