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Here one for all you technical flyers

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Rocker19/02/2019 16:04:31
341 forum posts

I have a Freewing Hawk and I find it hard to land with out it bouncing on landing .I have found you have to come in fairly fast and land it on it's main wheels and keep the nose wheel up .Sometimes it lands OK the next is bounces all over the place .One of our club has an FMS Hawk almost identical to the Freewing Hawk .I have flown he's FMS hawk and it lands perfectly every time with no problems .Why is that ? I have the upgraded undercarriage on the Freewing Hawk where as the FMS has them has standard .I just can not work why the FMS Hawk is so easy to land where has my Freewing Hawk is a nightmare to land ,they are identical models Anyone have any idea why ????? After flying both the Freewing and the FMS Hawk I would advise anyone who is interested in buying a Hawk go with the FMS one.The FMS Hawk is the better model but a lot dearer then the Freewing Hawk

Nigel R19/02/2019 16:30:18
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2923 forum posts
470 photos

Yours has a too long nose gear. Or possibly, several too short main gears. As in, the wing points upwards at rest.

Your "smooth" procedure is essentially doing a tail dragger 3 point landing, and allowing the nose to drop when the wing stalls as speed bleeds off. Step out of cockpit, pull off flying overalls to reveal DJ, hold out hand to receive vodka martini, etc.

If you land like a normal trike, a nice smooth wheeler, the wing is still flying, and when you get onto all three wheels, the wing is pointing up and up you go again, bounce bounce bounce.

That's my guess, anyway.

Maybe a smaller nosewheel would sort it.

Don Fry19/02/2019 17:12:12
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3726 forum posts
42 photos

No argument about your thoughts, but who the hell is DJ.

I've even made a Vodka Martini, no thoughts came with the process.

Edited By Don Fry on 19/02/2019 17:14:26

cymaz19/02/2019 17:32:11
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8530 forum posts
1150 photos

Dinner Jacket.....?

And all because

Piers Bowlan19/02/2019 17:33:47
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1801 forum posts
44 photos

That sounds good to me Nigel.

(Dinner Jacket) or maybe 'Jack Daniels' for Dyslexics?

 

Edited By Piers Bowlan on 19/02/2019 17:40:25

Rocker19/02/2019 17:42:16
341 forum posts

Well except for Nigel that was a waste of time !!!!!!!!!!!!!!

Denis Watkins19/02/2019 17:44:46
3736 forum posts
178 photos

Do you use flaps Digger? What angle e.g 25°

Does the model weigh much over 3lb?

Have you got the upgrade undercarriage fitted?

J D 819/02/2019 18:07:12
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1194 forum posts
74 photos

Could the wheels/tires fitted make a difference ? Some model aircraft wheels are sold as "low bounce".

Rocker19/02/2019 19:59:19
341 forum posts

I found on my Freewing Hawk it was better to land with no flaps ,it seem to land better with no flaps then it does with flaps but that might be me The FMS Hawk comes in with flap and lands a treat

Cuban819/02/2019 21:01:47
2564 forum posts
12 photos

Agree with JD8. A decent set of Dubro low bounce wheels can make are a big difference as I've found out by improving a couple of my models that were always a bit lively with hard type wheels. Fit Dubros to all my new models now, well worth the extra few quid.

Chris Walby19/02/2019 21:52:29
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943 forum posts
226 photos

Are the models really the same?

I enquired about a wing profile for a model and was informed (in a nice way) that almost every designer chooses a wing profile to suit the performance they want.

For one type of aircraft there were + six wing profiles and a choice of washout or not...

You could end up with two models that look identical, but have different wing profiles and hence behave very differently especially near the point of stall.

Just an idea wink

Rocker19/02/2019 21:58:29
341 forum posts

You made a good point Chris ,the Freewing Hawk and the FMS Hawk look simmer but like you point out are properly total different .All I know is the FMS Hawk fly better ,which surprised me .I am a total Freewing fan but it looks like FMS have caught them up !!!!!!!!!

Peter Jenkins19/02/2019 23:43:26
1216 forum posts
132 photos

Rocker, from your description it would seem that you are trying to land your Freewing Hawk too fast. The theory of landing a trike is that as soon as the mains touch, as they are behind the CG, the nose should pitch down reducing the wing angle of attack and cutting the lift. If you land too fast, the aerodynamic lift force wins over the pitch down force and the aircraft bounces.

Many pilots are worried about stalling on approach and set too fast or steep an approach speed. When you flare the aircraft for landing the speed is too high to land and if you hold off till the speed decays to the right figure you can float the whole length of the runway. So, try landing at 50 ft and see how far the aircraft travels before it stalls. You should have enough height to recover safely.

The other issue is CG position. If you have a forward CG then you may well run out of elevator authority when slowing down for landing and then the aircraft will bounce all over the place. To check for a good CG position, from level flight, pull up to a 45 degree climb and add enough power to maintain the speed. Then half roll to inverted and relax on the stick. If the nose pitches down immediately, try moving the CG aft a little bit and repeat the test. When the aircraft pitches down slowly that's a good CG position. You can do the same test by just rolling inverted when flying level but at a 45 deg climb you are at least going away from the ground even when the aircraft pitches nose down!

With the CG in the right place, and the approach angle and speed correct, use the throttle to control the rate of descent and the elevator the speed that is the attitude of the aircraft. If she sinks, increase the throttle but keep the aircraft attitude constant with the elevator - don't use up elevator to pull up as you just end up porpoising all over the place. Similarly, if you are high, close the throttle - don't push down elevator to bring the aircraft downwards as you will just push up the airspeed. In summary, throttle controls height and elevator controls speed.

Try that and see if it helps. Oh, even supposedly identical aircraft from the same manufacturer will feel different because of manufacturing tolerances but way different when the CG is in the wrong place. CG position is the single most powerful trimming tool we have - yet few people ever think about shifting it to correct aircraft characteristics.

Good luck.

Charles Smitheman20/02/2019 08:01:17
226 forum posts
18 photos

Hello Rocker,

Nigel R and Peter J are correct.

If the nosewheel lands first, the model will go "mad" and try to go backwards. Wheelbarrowing.

Check the attitude of the model on a level surface; if it is standing nose up, then raise the mains or lower the nose.

Check the CG and main wheel placement. I find in general it is best to adjust the main undercarriage ( I am not familiar with your actual model ) so that with the correct cg it is almost balancing on the mains, and the nosewheel is just touching the ground.

It is surprising how often some small adjustments can make a huge improvement to the way a model performs.

Good luck

Andrew Ray20/02/2019 09:15:54
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699 forum posts
19 photos
Posted by Peter Jenkins on 19/02/2019 23:43:26:

Rocker, from your description it would seem that you are trying to land your Freewing Hawk too fast. The theory of landing a trike is that as soon as the mains touch, as they are behind the CG, the nose should pitch down reducing the wing angle of attack and cutting the lift. If you land too fast, the aerodynamic lift force wins over the pitch down force and the aircraft bounces.

On a nose wheel aircraft the nose will tend to pitch down on landing but the job of the pilot is to gently lower the nose or as seen when a fast jet lands the nose is held high for aerodynamic braking. The wing has lost lift but the elevator remains effective.

Furthermore if landing fast and the aircraft pitches down that will kill the lift until the angle of attack is increased, the wing will only generate lift if the nose is raised, probably by the pilot pulling back on the elevator.

This sounds more like a pilot induced oscillation and may be affected by c of g and elevator sensitivity. Excessive expo will not help in this situation.

Edited By Andrew Ray on 20/02/2019 09:16:43

Rocker20/02/2019 11:51:20
341 forum posts

Thanks ,there is some interesting stuff and I found it very useful .Thanks I will try it out and see what happens

Peter Jenkins21/02/2019 00:45:45
1216 forum posts
132 photos
Posted by Andrew Ray on 20/02/2019 09:15:54:

Furthermore if landing fast and the aircraft pitches down that will kill the lift until the angle of attack is increased, the wing will only generate lift if the nose is raised, probably by the pilot pulling back on the elevator.

This sounds more like a pilot induced oscillation and may be affected by c of g and elevator sensitivity. Excessive expo will not help in this situation.

Edited By Andrew Ray on 20/02/2019 09:16:43

Andrew, I have to disagree. If you land a tricycle u/c aircraft too fast, it will bounce. Even jet fighters bounce as do airliners. We don't need to go to the extreme some pilots of jet fighters do of keeping the nose up to increase drag from the wing as our aircraft slow down pretty quickly in comparison, especially on grass. Light aircraft types like the Cessna 150 can also be bounced when landing too fast. If you have the speed right, and full size pilots have an advantage over model pilots as they have a read out of their airspeed, then the impact of landing generally knocks the speed back to below stalling speed - or else you use lift dumpers to kill the lift as most modern airliners do. With little lift from the wing, the weight takes over and pitches the aircraft nose down.

I think it most likely that Rocker is trying to land with too much speed on his aircraft. It could then develop into a pilot induced oscillation as the bounce starts and you then push down elevator into another bounce now with up elevator to encourage the bounce etc. The best solution, if there is room on the runway, is to level the aircraft while adding a touch of power and make a second approach. If you don't have the room, or it just doesn't feel right, overshoot and have another go at landing - always assuming you have the fuel / battery capacity available.

Chris Walby21/02/2019 05:43:36
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943 forum posts
226 photos

Only flow one EDF (PZ Habu) and was advised by a club member with more experience to follow reduced power circuit technique.

It has small wheels so suffers high drag and performs a bit like a mad ground squirrel on take off - giving the impression it needs to be going quick to fly.

It then cuts a very nice quick path across the sky and so I get used to it flying quickly (fun) which confirms my mind set.

When I want to land throttle back a for complete circuit as its quite a slippery model and it will fly slowly given a chance, its just I get used to how quick it can go in usual flight.

Result, if I bleed the speed it will land perfectly, just as it touches down the grass kills the speed and it stays put...come in too fast and it will bounce (best just go around), but if I try and land the bouncing gets more a more violent sometimes ending it finally leaping into the sky nose up at almost no ground speed!

What is quite surprising is just how slow it will fly before it stalls and how many fast low passes it takes before I remember that laugh

PS - The great thing with this hobby is no two flights are ever the same, not with me at the sticks!

PPS - The Habu is a great model, its just I can make a right dogs dinner of landing it sometimes

 

 

 

 

Edited By Chris Walby on 21/02/2019 05:45:18

Piers Bowlan21/02/2019 06:34:25
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1801 forum posts
44 photos

The advice from my flying instructor (C150 Aerobat) 41 years ago, is still ringing in my ears, 'the main gear is for landing on, the nose wheel just for taxying'. The other things he used to say is 'the landing hasn't finished until you stop', and 'you land at landing speed, for if you touch down at flying speed you will just bounce back into the air!' This is all sage advice and just as true for models as full sized aircraft. You only have to watch a few videos of model aircraft with tricycle landing gear to see where some people are going wrong. Landing with excessive speed, not holding off to allow speed to decay, and having touched down, just relaxing the back pressure on the elevator so that so that all the weight is transferred to the poor old nose wheel after touchdown. The moral of the story is 'don't land flat' maintain the elevator back pressure throughout the landing roll, particularly if the landing strip is rough. Be kind to your nose wheel, that way it might remain attached to your aeroplane!

Full sized aeroplanes like the old C150 have a nose oleo strut that is nicely damped but none the less will still do a very good impression of a kangaroo, catapulting the aeroplane back into the sky after a flat landing. With our models they only have simple undamped springs for nose wheel legs, so good landing technique is even more important.

Finally, if the nose wheel leg is too long, as Nigel pointed out earlier, this will only exacerbate the problem. Rocker's Freewing Hawk maybe just poorly designed and the above is not necessarily a criticism of his landing technique, I hasten to add.

 

Edited By Piers Bowlan on 21/02/2019 07:01:57

Roger Dyke21/02/2019 07:19:30
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195 forum posts
10 photos

Hi Rocker,

From my experience from flying light aircraft my guess would be that it's nose heavy and landing too fast.

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