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bjnginge 06-21-2013 01:29 AM

Jetmach floating on landing
 
Well my jetmach flies :D , and it does it really well.

The only issue I have is that it seems to float right on past on landing, I think I am coming in too fast with full flap and not bringing the throttle back early enough.Very different to my aerobatic aircraft.
It seems that i will need to cut the throttle on base leg before final. I am going to get more practice next week, does anybody have any tips?

Cheers

alasdair 06-21-2013 01:47 AM

RE: Jetmach floating on landing
 
1 Attachment(s)
Check out the stall at a good safe height. I'll bet it stalls and lands at a much slower speed than you expect.
Also, make sure you have enough flap for landing, at least 60 degrees.

My own similar (but far better looking) jet trainer JayTee has quite big flaps that deflect 60 degrees. Without them it floats forever, but with full flap it lands really slowly (for a jet) with a short rollout. Using data logging I found that my typical over-the-fence speed is 27 mph, and touchdown at 22 mph. Top speed in level flight flat out on a 14 lb Wren 54 is about 125 mph.

bjnginge 06-21-2013 02:12 AM

RE: Jetmach floating on landing
 
Thanks , yeah I will get a feel for the stall speed and go from there, just coming in a bit quick I think.

FalconWings 06-21-2013 04:50 AM

RE: Jetmach floating on landing
 
You can cut the throttle all the way through downwind leg. This thing is a floater by design, no different than landing a lightly loaded Avistar.
They are awesome jet trainers.

David

limeybob 06-21-2013 05:19 AM

RE: Jetmach floating on landing
 

Quote:

ORIGINAL: bjnginge

Thanks , yeah I will get a feel for the stall speed and go from there, just coming in a bit quick I think.
Thats it, with full flap, it will fly remarkably slowly.

check out the landings at the end of the video

http://www.laser-design-services.com/jetmach60high2.wmv

limeybob

stuart_80 06-21-2013 06:45 AM

RE: Jetmach floating on landing
 
The best tip I've had as far as landings go is

"Throttle controls the height, elevator controls the speed"

So if you are landing too fast, you need to use the elevator to get the nose up on approach. This increases drag, reducing speed,, then you adjust height with throttle.

Ive been to a few jet meetings and see people closing the throttle miles out and "diving" for the threshold. The usually ends up in the model bouncing or floating miles past making a touchdown difficult

I am flying a Boomerang Élan, and land with full flap irrespective of wind conditions

Stuart

PS full flap is about 75 degrees<br type="_moz" />

FalconWings 06-21-2013 07:56 AM

RE: Jetmach floating on landing
 

Quote:

ORIGINAL: stuart_80

The best tip I've had as far as landings go is

''Throttle controls the height, elevator controls the speed''

So if you are landing too fast, you need to use the elevator to get the nose up on approach. This increases drag, reducing speed,, then you adjust height with throttle.

Ive been to a few jet meetings and see people closing the throttle miles out and ''diving'' for the threshold. The usually ends up in the model bouncing or floating miles past making a touchdown difficult

I am flying a Boomerang √Član, and land with full flap irrespective of wind conditions

Stuart

PS full flap is about 75 degrees<br type=''_moz'' />
this is true, but for a model like the jetmach it is difficult to apply because of how slow they can actually fly. On the jetmach you go to idle, leave it there, and just manage the approach with elevator back pressure down to flare...obviously if you are too far or too short, apply throttle to come back up.

A7Bldr 06-21-2013 09:20 AM

RE: Jetmach floating on landing
 
I fly a JetMach (low wing) and agree with David. I use the flaps and usually on Final the throttle is back to idle as the plane glides in.
Make sure that when flaps are lowered there is no pitch change (with mixing). If the nose is down just slightly on final it will land fine. No diving though.
Jim

highhorse 06-21-2013 09:29 AM

RE: Jetmach floating on landing
 
Look into Crow. Lots of trainers float, crow takes the float out, makes the approach more manageable, and greatly reduces the possibility of a tip stall. As a bonus, the use of crow will better prepare you for heavier jets that don't float as much.

GrayUK 06-21-2013 10:49 AM

RE: Jetmach floating on landing
 
Yep
crow braking is the way to go.
Did it on mine, worked well.
Paul G

alasdair 06-21-2013 11:51 AM

RE: Jetmach floating on landing
 
On aircraft with this configuration, putting the flaps down causes a nose-up pitch.
You need to mix in some down elevator trim to control the nose up pitch, BUT

another tip

don't trim it ALL out! Leave in a litlle nose up pitch such that the model sits on the landing approach<u> In Trim </u>at a nice slow but safe approach speed. It is nice if just putting down land flap changes the trim from cruising around trim to slow approach trim without touching the lever. You find that by experiment and practice.

If, as A7Bldr implied, you mix in down trim so that there is absolutely NO nose up pitch then the model is trimmed to an approach speed that is too fast, and that leads to a very floaty landing. Some people correct this by applying up trim on the trim lever (the correct method), others slow down the approach speed by holding a little up (back) pressure on the stick (a definite No-No in full size flying) but getting the mix just right for the speed change is the best solution.

never tried Crow! I'll try it one day, but it goes against my full size flying background so I'm prejudiced against it. Many modellers think it's great however.

paulhat 06-21-2013 05:21 PM

RE: Jetmach floating on landing
 
Quote:

ORIGINAL: bjnginge

Well my jetmach flies :D , and it does it really well.

The only issue I have is that it seems to float right on past on landing, I think I am coming in too fast with full flap and not bringing the throttle back early enough.Very different to my aerobatic aircraft.
It seems that i will need to cut the throttle on base leg before final. I am going to get more practice next week, does anybody have any tips?

Cheers

Hi Bjnginge.

Sounds like you are just coming in too fast.
I reckon this is the hardest part about flying a jet, knowing how fast you should be going on that base leg.
For me I find it hardest to judge when there is no headwind. Where I fly its often dead calm so altitude and speed on the base leg have to be just right otherwise it just floats past you :)
When there is some headwind its easier to manage the approach speed with throttle. Well that's what I find anyway.
I think its just a matter of practice and getting to trust your plane. No point coming in too slow though. Better to have it float past than stall 3 meters above the ground.

Stuart_80 said -
Quote:

Ive been to a few jet meetings and see people closing the throttle miles out and "diving" for the threshold. The usually ends up in the model bouncing or floating miles past making a touchdown difficult
Well to be honest I kind of use this technique on both my jets (UF and Reaction) because I find it the best way to slow the aircraft down when there is no wind. My version goes like this... Downwind leg = whatever throttle setting is making it fly nice (I don't want it feeling mushy). Base leg, lower the throttle a little and get the altitude set to what you want on final. Final, Throttle to low. It takes probably 5 seconds in any case for the turbine to spool down to idle. This works well for me and I reckon most of my landings are greasers :)

Have never flown a "hard to land" plane and I am sure that throttle management is essential with these. If you look at the F-18 vids the guys seem to be on the throttle right to the ground. I think "my easy to land" plane technique would not work with and F-18 for example.

In any case...Get out there and practice :)

Paul.

edwarda10pilot 06-21-2013 05:31 PM

RE: Jetmach floating on landing
 

Quote:

ORIGINAL: bjnginge

Well my jetmach flies :D , and it does it really well.

The only issue I have is that it seems to float right on past on landing, I think I am coming in too fast with full flap and not bringing the throttle back early enough.Very different to my aerobatic aircraft.
It seems that i will need to cut the throttle on base leg before final. I am going to get more practice next week, does anybody have any tips?

Cheers

I too have Jet Mach and it flies well but as you say it floats on landing. What I have found that works for me is on the upwind pass I lower the flaps and make any trim adjustments. I then turn downwind and begin to bring the throttle to 1/4 or less. I turn base and when I do that I am at less than 1/4 throttle. Once I turn final, I have the engine at idle. I have found the secret to be to put a lot of flaps in for landing. For landing I use about 60-70* of flaps. With all of this drag, the plane will slow dramatically when you get out of the throttle. I can get the plane down and stopped in about 150-200 ft. on hard surface runway (this is when no one is watching) :D

Ed

rctech2k7 06-21-2013 06:22 PM

RE: Jetmach floating on landing
 
Paul,
You're so humble, you're the guy who can easily learn to land a "hard to land" plane...

bjnginge,
Seems you've got plenty of good tips already. IMO that should be normal to float at excessive speed so that means you can still slow it down. It's a forgiving characteristic of a trainer. Also you're earning turbine experience and becoming use to land at higher speed. This is a good preparation for landing a havier jet.

You can configure your trainer depending on your preference or next jet to fly but most trainers are not enough to simulate landing experience of a havier scale jet, so for me I believe that would be helpful. Try to use crow and raise the nose up slight on the approach. Also move CG forward, these will make it stable on the approach as well as on the ground and though you might still have control of your ailerons it keeps you from going back in the air. Usually a moderate flaps can give you enough drag and lift while in high alpha but you can determine the best for you. You might need to carry power to compensate for drag depending on your sink rate. With that configuration after flaring and touchdown the aircraft absolutely has lesser lift to airborne again because its wings are level down with a lot lesser lift and higher static load caused by change in CG.

toolmaker7341 06-21-2013 07:04 PM

RE: Jetmach floating on landing
 
Do you have plans for your JT?

edwarda10pilot 06-21-2013 07:14 PM

RE: Jetmach floating on landing
 
Deleted

alasdair 06-22-2013 12:54 AM

RE: Jetmach floating on landing
 
1 Attachment(s)
Quote:

ORIGINAL: toolmaker7341
Do you have plans for your JT?
The short answer is "No, it's a one-off"
However, for years I have been promising a drawing to Tony Stephenson, boss man of Traplet Publications who publish Jet International and R/C Model World.
I really must get on with finishing the drawing and writing an article to go with it. I am sure Traplet will do a laser cut wood pack if, or rather when, I get round to it.
I will start a thread on RC Universe to celebrate (didn't mean to hijack this one, sorry).

P.S. it looks good and flies well on floats too.



bjnginge 06-22-2013 01:50 AM

RE: Jetmach floating on landing
 
Thanks for all the tips, I just need to get time to get some practice now. I think I will try your approach edwarda10pilot and see how it behaves.

Cheers

Rob2160 06-22-2013 04:19 AM

RE: Jetmach floating on landing
 

Quote:

ORIGINAL: bjnginge

Thanks , yeah I will get a feel for the stall speed and go from there, just coming in a bit quick I think.
As a Full size aerobatic Instructor.. may I recommend, get a feel for your elevator position when your plane stalls...

This position will be constant every time it stalls, even high speed stalls.

Speed is really irrelevant as stall is a function of angle of attack and your elevator control is really an angle of attack control device....Try it... You will see what I mean...

Once you know how much elevator deflection produces the stall you will be able to "Feel" your aircraft much better and on approach you will actually feel that you are flying too fast on final (because your elevator becomes an angle of attack indicator by its position that you can feel and if the angle of attack is low on final you are flying too fast)

Its a lot to digest but I just summarised a 1 hour Pre Aerobatic Lesson on Angle of Attack control Briefing into a few lines - Hope it helps..

Some extra reading if interested...

thecfiguy.com/student/aerodynamics/AOA.php

avstop.com/ac/1-14.html

aeroexperiments.org/seeforselfairplane.shtml



Rob2160 06-22-2013 04:50 PM

RE: Jetmach floating on landing
 


I now have time to explain the above a little deeper...</p>

</p>

Consider your elevator stick on your Transmitter... it is spring loaded to return to centre...</p>

</p>

Lets call this centre position 0% deflection..</p>

Lets call Full back deflection (UP Elevator) 100% deflection</p>

Full forward would then be -100% deflection But we can forget about that for this discussion..</p>

Exact numbers will change for each aircraft type but the theory is the same for all...</p>

If your aircraft is trimmed to fly level at full throttle with 0% elevator deflection - The angle of attack of the main wing is approximately 2 to 3 degrees in normal level flight..</p>

The more you deflect your elevator, the greater the angle of attack on the main wing..</p>

Assume that 100% deflection gives you 20 degrees angle of attack..</p>

It follows that 50% deflection will give you 11 degrees (half way between 2 degrees and 20 degrees)</p>

Any aerodynamic text book will tell you that an average aerofoil will stall at 16 degrees angle of attack</p>

at 15 degrees it will be unstalled and at 16 or more it will be stalled..</p>

</p>

In this example, you would reach 16 degrees with about 78% deflection of the elevator joystick</p>

So regardless of speed or attitude, if you don't pull more than 78% elevator, your aircraft will not stall..</p>

</p>

Again, regardless of speed or attitude, pulling more than 78% elevator you WILL stall.</p>

:When landing a real aircraft you aim to approach at 1.3 xthe 1 g stall speed in the landing configuration.</p>

In this example.. this would require an angle of attack approximately 12-13 degrees during the stabilised landing approach (disregarding flaps)</p>

Which means, flying a stable final approach at the correct speed, you should be holding steady back elevator of about 55 to 60% deflection..</p>

If this amount of deflection produces a pitch up or zoom climb then you are approaching way too fast..</p>

</p>

These figures are just for explanation purposes and any number of factors can change the actual figures / stick position for the stall on your aircraft...</p>

EG, dual rates, how much elevator deflection you have set up with your servos, C of G changes etc etc.. but the theory is solid...</p>

For your aircraft there will be an elevator position that produces the stall.. without changing your rigging or CG significantly this position will remain the same..</p>

It will change slightly if your aircraft has flaps, but again there will be a new position that causes the stall when flaps are extended and this again will be constant for a constant flap position..</p>

Its almost impossible to get a feel for the stall speed with an RC aircraft because you are not in the aircraft and you don't have an airspeed indicator, temperature and wind can change the appearance of actual speed anyway.</p>

But it is very easy to get a feel for the stick position of the elevator when your aircraft stalls, and once you understand this concept and develop the muscle memory of knowing exactly where your aircraft stalls you will be able to fly it much more accurately during tight aerobatic manoeuvres and during landing approaches.</p>

I hope my humble attempts to explain this in text will help, usually this is something best demonstrated practically..</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

</p>

hooker53 06-22-2013 06:51 PM

RE: Jetmach floating on landing
 
Just flat good stuff right there and thanks for taking the time to type that.

Roy

alasdair 06-23-2013 01:24 AM

RE: Jetmach floating on landing
 
Rob2160

You make a good and very valid point, that a particular elevator angle places the aircraft in trim at a particular angle of attack and hence a particular speed.

Two follow-on points though
  1. when flaps are deployed the principles remain exactly the same, but all the numbers change, and how much (i.e. the new trimmed AoA or airspeed) depends on pitch coupling which varies from aircraft to aircraft.
  2. All the full size flying instructors I've ever met said "re-trim, re-trim, re-trim" whenever you change anything, power, speed, flap angle,socks, whatever
    I hope you teach the same. I assume that you advocate that the aircraft should be in trim at 1.3*Vs on the approach??? In which case please explain further the following quote

    "When landing a real aircraft you aim to approach at 1.3 x the 1 g stall speed in the landing configuration.
    Which means, flying a stable final approach at the correct speed, you should be holding steady back elevator of about 55 to 60% deflection.."

In full size flying we are constantly taught that the secret to a good landing is a good approach, in trim at the correct speed (1.3*Vs as you said).

That is what my posts above were trying to get at. You set the elevator trim to the angle which, with full landing flap, will AUTOMATICALLY lock the angle of attack and trimmed airspeed at the optimum approach speed, 30% above stalling speed (in landing config as you said).
Carrying more airspeed than this (due to not enough up elevator) is what causes excessive float on landing.



<br type="_moz" />

rctech2k7 06-23-2013 06:55 AM

RE: Jetmach floating on landing
 
If we consider 1.3 is 100% then the room for error for an additional 30% airspeed is approx 25% which means 5% safer than coventional factor. Good to know that light and heavier aircraft are carrying more than enough safety during landing.

I've been in practice before landing models in steeper decend by nosing down even with full flaps is very hard to determine the right speed for touchdown.

Applying priciples above for aircraft with full stab such as F-15, 16 & 18 is much easier because at any given angle for elevator is equivalent to the AOA considering airspeed is enough to level the elevator in relation to the airflow. Also at slightly more than 12 deg for hornet on touchdown is very close to tail strike. Very good point by Rob and thanks for the link, I will try that ground effect for short grass takeoff.

Oh I forgot that ground effect is also causing that JetMach to float easily...:D

Rob2160 07-03-2013 06:08 AM

RE: Jetmach floating on landing
 

Quote:

ORIGINAL: alasdair

Rob2160

You make a good and very valid point, that a particular elevator angle places the aircraft in trim at a particular angle of attack and hence a particular speed.

Two follow-on points though
  1. when flaps are deployed the principles remain exactly the same, but all the numbers change, and how much (i.e. the new trimmed AoA or airspeed) depends on pitch coupling which varies from aircraft to aircraft.
  2. All the full size flying instructors I've ever met said "re-trim, re-trim, re-trim" whenever you change anything, power, speed, flap angle,socks, whatever
    I hope you teach the same. I assume that you advocate that the aircraft should be in trim at 1.3*Vs on the approach??? In which case please explain further the following quote

    "When landing a real aircraft you aim to approach at 1.3 x the 1 g stall speed in the landing configuration.
    Which means, flying a stable final approach at the correct speed, you should be holding steady back elevator of about 55 to 60% deflection.."

In full size flying we are constantly taught that the secret to a good landing is a good approach, in trim at the correct speed (1.3*Vs as you said).

That is what my posts above were trying to get at. You set the elevator trim to the angle which, with full landing flap, will AUTOMATICALLY lock the angle of attack and trimmed airspeed at the optimum approach speed, 30% above stalling speed (in landing config as you said).
Carrying more airspeed than this (due to not enough up elevator) is what causes excessive float on landing.

Yes please excuse that I didn't differentiate between real and RC control systems...

I agree completely with your follow on points..

1. Stated perfectly and I agree 100%
2. Absolutely, yes the aircraft should be in trim at 1.3Vs during the landing approach..

You quoted two of my lines but left out the one in between that said "disregarding flaps" Yes, flaps do change the equation.. but for my explanation of that specific comment, it was disregarding flaps..

We practice flapless landings in the Hawker 900XP simulator each year for recurrent and yes.. when on final at 1.3 Vs (clean) the control yoke is WAY back during the final approach.. right into your stomach.. IE much further back than it is in a normal landing with flaps 45.

The Hawker is a great pilots plane because it has good old fashioned pulley and cable flight controls and no hydraulic assistance.. You fly it and you feel it flying.. Pure aerodynamics at work.

As you described there are numerous variables and I was over simplifying the explanation.. Most RC aircraft trims do not operate in the same way aerodynamically as a full size trim system.

IE.. in a full size aircraft.. if you change speed / power etc... your elevator position will change to achieve straight and level for example. Trimming in a full size aircraft does not change the elevator positon, it simply releives the pressure required to hold the elevator in that position.

In an RC aircraft the trim works by simply changing the neutral position of the servos..and you can never feel how much control force is being applied back to the servo, so the use of trim in RC aircraft is not to releive the force on the servo but to give the desired flight path with stick neutral. This may actually result in continual force required by the servo. Very different to a trim in a full size aircraft where you are always trying to remove this control force your hands are experiencing. (the organic servo if you like)

In RC flying you are trimming an RC aircraft so that it will fly essentially straight with all the RC gimbals centred.

I have never seen anyone who constantly re trims elevator on an RC plane every time he climbs, descends or lands.

It is actually a slightly different technique....

My comment was confusing and for that I apologise, it was in the context of an RC aircraft that is trimmed for normal straight and level flight at normal power settings.

When reducing power and speed in the RC aircraft you will need to hold back elevator on final approach as the aircraft is "trimmed" for higher speed and power.. and will therefore naturally want to drop its nose unless you compensate with more elevator..

In a real aircraft the trimming and re trimming is constant during all phases of flight and on final, yes your elevator will be generally further back than it would be if flying faster in the same configuration, but the trim is aerodynamically assisting this elevator deflection and therefore there is no pilot force required to hold the elevator in this position. the trim is doing so..

The difference really is because an aircraft gives you feedback.. you can feel control forces change with speed, power etc etc.. the RC transmitter simply has springs that try to centre the joystick and the tension on the spring never changes regardless of the speed or power setting in your aircraft.. So you don't have any real feedback as you do in a real aircraft.

The only real feedback in an RC aircraft is Visual and perhaps aural.

On a side note.. I found it very interesting learning to fly RC collective pitch helicopters.. in the early days it was all visual feedback, but now, I would say 50% of it is aural, every single minute change in collective stick position creates a different blade sound and you learn to recognise the subtle differences and play the sounds during manouvers. I found it fascinating when I realised I was actually responding to the rotor sound more than the movement of the helicopter.




alasdair 07-06-2013 02:16 AM

RE: Jetmach floating on landing
 
Sorry Rob2160, I overlooked the "(disregarding flaps)".

In my defence, my JayTee, like the Jetmach we were discussing, is most reluctant to land without flaps. With idle power they just float and float and float......

You are also right that most modellers do not constantly retrim, because we seldom fly jets straight and level for more than a few seconds. We are constantly turning, looping, rolling etc. The only times when it pays to be in trim "hands off" are<ul>[*]on climb out[*]On a fast low pass[*]on a slow low pass (1/2 flap)[*]on approach[/list][I remember my instructors on Chipmunk or Pa28 were always saying "take your hands off" to check whether or not I had trimmed. Do you do that?]

I try to take off in trim for a safe climbout. I then add down trim to trim out for fast straight and level flight, which covers the fast pass and does for all the aeros.
When I back off the power for slower flight at circuit speed I retrim by adding a little up trim. Thistrimmeans that if I go to full power it will climb, if I go to idle it will descend (as I'm sure we all know).

Now I come back to the point I made earlier. When I put down takeoff flap I mix in enough elevator so that the nose comes up very slightly to trim at a slower speed, and when I put in land flap I mix enough elevator so that the model is in trim at approach speed. I don't trim out ALL the pitch-up-with-flap. I leave a little of the pitch up again so that ity is trimmed to approach slowly and land. Then I leave the trim there for the next takeoff. On full power with that trim it will climb out in trim with T/O flap, or even flapless.
<br type="_moz" />


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