Flew the hawk today and had a really great time. It grooves and tracks with ease. Soon discovered that it does not like landing flaps applied during the downwind leg of the landing approach. It rolled over and nearly died. Missed the ground be mere inches!!! It is highly recommended that full flaps not be applied until you are set up for approach with wings level. At that point flaps were added to a point beyond what is recommended with no apparent harm. Procedure for me will be takeoff flaps on the downwind leg, and landing flaps applied once over the runway with level wings. Skymaster also will be sending me the wing fences, which will enable the hawk to slow down about 6 to 8 knots more than it does now. The new procedure and added stall strips will make a great plane even better.

The General

Note: If you apply full flap on this model at any kind of speed the model will pitch down and the flap will override the elevator no matter how much mixing you have. We advice to everyone is to take some time during the first flights and following flights to get used to the flaps and how they interact with pitch. We suggest getting some height, slowing the model down into wind and as the speed decays gradually applying more and more flap. This way you can monitor any pitch change and get used to the feel of the model.
When deployed correctly the flaps can be left down and the model flown perfectly happily. We only concern is with either too much speed or too much flap without the correct up elevator mix.

Another point to remember is that you want to set your mix from flap to elevator so that the elevator is a progressive as the flaps. We fly a hawk recently where the customer had set the flap and stab mix so that he only got his 15mm of up elevator when full flap was deployed. Not Good. He had a model that wanted to pitch down until he hit full flap and then it would shoot back up again.
With the correct flap set up the model will sit perfectly for landing,

I don't mean to try and teach you how to !QUOT!suck eggs!QUOT! But this is what is written in the Skymaster instruction manual.
it is just as important to get the elevator mix set up correctly as it is not to deploy the flaps at the wrong speed. I am also experimenting with a little bit of crow (up defelction on both ailerons) with good effect.
Regards Al

Does this mean that if you shoot a missed approach (leaving the flaps fully deployed) and throttle up to go around, that as you gain airspeed, at some point the Hawk will pitch down and simply dive into the ground as the flaps over-ride the elevator?

You will have to gain a lot of speed to get this effect but I guess so Yes! But I dont think it will be too hard to remember to put the flaps away?

I have had no problems with the flaps on my hawk.

But, I need to point out that that as a full scale pilot, the real planes have very explicit gear and flap speeds. The toys are no different than the real ones it is just harder to judge air speed on the toys! Exceeding these speeds causes bad things to happen and is not the aircrafts fault.

I have done several practice go a rounds and a few for real also, with no problem. I always take a notch of flaps out on climb out as the gear is coming up them remove the approach/takeoff flap setting on cross wind turn out, or about 1/3 of the way on a vertical climb-out that is where the P-120 is a lot of fun!

I would go up high and fist stall your plane to see what it does then circle back around and extend the gear then some flaps fly one circuit then extend full flaps to get a feel for the plane. If it is rolling your flaps may not be coming down equally, better to find this out at altitude then in the pattern.

Stick with it until you get your plane set right and don't be afraid to use the flaps.

You can see where they are set in the pic below on a go a-round.

May I suggest you gentlemen take a look at my review article on the SM Hawk in RCJI . I made some suggestions, and flight tested them and my Hawk is totally docile., throughout the flight envelope. My suggestions were based on fullsize practice and the experience of Duncan Simpson during early flight test of the real Hawk, when control was temporarily lost during stalling trials with flaps extended.

In short, :

Use two powerful servos on the stab.

Mass balnce the stab.

Limit flap angle to no more than 1 inch of depresssion at full flap, half that for take off and approach.

Set the stab. trim slightly up about 1/8th inch for take off/ approach flap , about 3/16th inch with landing flap.

Set up like this the model is a delight to fly.

The results of early problems with the Hawk can be seen by the deletion of about two feet of the outboard section of the secondary flap.

The problem was the strong downwash created by the flaps on the tailplane. In addition flap extension caused a nose down pitch, (probably due to C of P shift) which required uptrim on the stab. the result being a stalled satb.

The model seems to replicate this extremely well !

Regards,

David Gladwin.

Does that minor amount of flappage at full down (1 inch?) do enough to be worth having flaps? It does not seem like it would add much drag to offset residual thrust.

Mine is set up as David and others has suggested. and the model flys as he and I have described. Very docile.

The flaps do not look like much but some drag is better than none!

Don

OK, you guys have flown them so you must know. Its just that I am used to having HUGE (14" x 3-3.5" ) split flaps on an Isobar deployed at 70 degrees or more. Compared to that, the Hawk's flaps look almost not there!

But I guess that's all ya need!

Apparantly that's all the Hawk need. When John Wright and the WREN gang did an AMD version, they found the same thing....DON'T use too much flap.

Greg

as for our hawks, larry and I have redesigned the flaps, when the flaps are down, there will be about 1/2 inch, in the gap between the trailing edge of the wing and the leading edge of the flap.

our thinking is, there will be more air flowing over the elevators, giving us a little more control at full flap

mark

This mean only trim up the stab from neutral position to get the correct AOA? The travel of the stab shoul remain as recomended?
Though, in my Jr9303 I have to use a 3pos. switch to make the mixing. 1 for takeoff, 1 for regular fligth, and the last for approach and landings. Did I understand correct?

Thanks,
Alejandro

My Hawk is powered by a Jetcat 160 derated to 120 standards so the idle thrust is unchanged. There is no problem with excess thrust at idle on approach, in fact, power is required.

The Hawk flaps are small but effective, but do produce strong downwash on the stab. and it is possible to stall the stab. If this happens and the machine pitches down I guarantee the pilot will KEEP the stick back until impact so the stab is never unstalled. Include the mods. and settings I quoted and I doubt you will have a problem, they have been flight tested. Although they are small the flaps DO make a worthwhile contribution to lift and drag and it should not be forgotten that they also "wash out" the wing, making flight at low speeds safer. If you want more drag just use aileron upset as Ali suggests (crow), that also adds to safe flight at higher angles of attack at low speed.

I use flight modes and the flap system on the 10X. This allows the flap angle and stab angle to be set to maintain trim. This trim can be fine adjusted in flight using the normal trim switch and the flight mode system will memorise them, makes life very easy.

Two more points:

Limit max stab. travel to 15 degrees to protect agianst stab. stall. (I will measure mine when I get my transmitters back from calibration)

Set the Tx so that flap movement is slowed, giving you more time to correct if things go wrong. If an uncontrollable pitch down ocurrs retract the flaps immediately.

Redesigning the flaps on the SM Hawk MAY be exactly the WRONG thing to do. The problem is not the amount of air over the stab. but the angle at which it flows onto the stab. with flap deflection. A slot may re-energise the boundary layer over the flaps increasing the downwash. Without putting the thing in a wind tunnel there only one way to find out, good luck !


Regards,

David Gladwin.