Balancing a heli when using training undercarrige

Hi,
I've got a Mosquito basic and am really just starting off
(still on the first half of the first bottle of fuel!)

Is there any obvious way of correctly balancing the heli, it was set up properly at a shop so generally should be alright, when the training undercart is fitted.
It just seem it never really goes back on in exactly the same position, affecting the flying slightly - one day it will tend left, another right etc!
The main problem is that the skids on the model are pretty flexible so just measuring tends to get offset some by this.

Regards,

Phil

[darren_uk]

Hi Phil,

I tend to draw analogies to real life helicopters to show that things aren't as drastic as they look (e.g., landing without an engine).

Consider this: Whenever a pilot of a real helicopter takes off either on his own, with a passenger next to him, and/or with people in the back seat, his centre of gravity ("CofG") is always going to change with these different payloads.

Same with your training undercarriage: don't worry about it not being on exactly the same everytime. If you're worried about the thing change balance (changing its CofG) then have you thought about what happens during the 20 minute flight as the fuel tank goes from full to empty? Yep, the CofG is altering naturally anyway.

In models as with full-size helicopters, the important thing is to make sure that the CofG is *within limits*. If it's outside these limits, then you'll run out of cyclic to fly safely. (There's some standard calculations one should do as part of the pre-flight check called "Weight and Balance" - i.e., ensure you're not too heavy, and ensure you're within the CofG design limits of the aircraft).

An example I had when flying a real helicopter: I had an unusually large woman in the front seat. At the end of the flight when I was taxying back to the hangar, I realised I had some problems because a strong wind had picked up which was blowing from behind me (so I was hover-taxying with my nose unusually high: 1) because of the weight at the front due to the woman, and 2) because I had to tilt the heli backwards to "fly into wind").

In the end I realised I wasn't going to be able to bring the heli to a hover because I just didn't have enough back-stick (her weight and the wind combined). So instead I flew close to where I wanted then simply used the rudder pedals to swing me around 180degrees. I now had ample front-stick to maintain the hover over the same spot on the ground, and I landed. (An alternative landing that you can't do in a model is I could have sledged the heli onto the ground and slid along a bit - but room was tight so I chose against this)


Back to your flying: it's a good thing that you're practicing to fly left skid or right skid low: imagine landing on sloping ground :-) Or landing with wind coming from the left or the right (meaning the heli will be leaning into the wind in a steady hover).

So don't worry about it. As long as your training undercarriage is roughly in the middle (i.e., the CofG is certain not to be outside the limits of the heli) then you're fine.

Thanks Darren,
Hehe, just after I wrote that last night I took it outside, had a flyaround and one of the rubber bands that held it on crooked broke anyway, so now its fixed with cable ties - which don't distort the skids so much and make it way easier to centralise.
I'm looking to get some more rubber bands though since it's not so portable with the cable ties.
Kind of a moot point anyway since it just got broke in tonights flying practice - I got a little overzealous and it scooted backwards into the flying box and sheared one of the little ball links that control the tail pitch!
Tail blades look OK though - took a chunk out of the flying box though!
So I guess it's play hunt the part number tonight then get an order on for a couple of new ones of those ( I always buy 2 spares on the grounds that if I did it once I can do it again!

This is definately a hobby where you have to enjoy fixing things as much as flying them!

It's nice to see your comments about flying real helicopters, I read a few of your posts around the forum - so is it true that the models are just as difficult as the real thing?

Phil

[darren_uk]

Hey Phil :-)

"so is it true that the models are just as difficult as the real thing?"

Believe it or not, models are *harder*.

In a real heli, the pilot always has the same perspective.

In a model, the heli is going to be seen from different orientations.

I'm thinking about the following difference too, but to be honest I don't think it's that great:
In a model, it's lighter so more jittery
In a real heli, it's less so.

However, on reflection, the Robinson R22s are really quite jittery. Whereas the Bell JetRanger: they're as docile as anything!

Phil,
A good rule of thumb would also be to keep a GOOD distance away from things like your flight box or your girlfriend's car. (remembering my training skid days) Also remember, the only thing the training skids are there for is to keep from tipping over. Once you can hover and land without incident, get rid of em. Otherwise, the'll become a crutch.
Don't get discouraged and get plenty of practice.

Remember: "The great whirlybeast has quite a bite. keep clear.

[darren_uk]

Biggie's so right in both things he mentions in his post:

- The main rotor has a nasty bite (this last week I've also seen pics and one vid of nasty cuts and bruises people have had from being whacked. With a tip speed of around 200mph, it doesn't surprise me.

- Training undercarriage: yep, lose it asap.

Here's something that helped me re the training undercarriage.


When I was out there in the field, I started to believe the heli was a sensitive thing, light as a feather, easily blown over. I started to believe the heli had to be perfectly level before landing, absolutely *zero* sideways or fore/aft movement - and if the thing started to move as I was settling down out of a hover? Up I'd go again, messing around near the ground.

This made me nervous about taking my training undercarriage off - I mean, I can't balance a pin on my forefinger, so how on earth could I land on that narrow undercarriage!

BUT: I then started to apply the thinking from my real heli flying training and experience.

There's something called "Dynamic rollover" which is when the pilot hasn't got the cyclic centred enough, and then is ambitious with his use of the collective in taking off. The sideways component of the disc's thrust is enough to pull the heli to one side, effectively tripping the heli over its skid. The pilot's natural reaction is to use opposite cyclic, and possibly try to lift into the air quicker to free the skid. Result, he topples over.

The correct procedure is to lower the collective immediately.

This brings me onto something else I learned in my training: When taking off into the hover, or landing from a hover: don't mess around. Commit yourself. I don't mean be ambitious (agressive), I mean don't hesitate when the heli's light on its skids. Smoothly, but progressively raise the collective to lift, and lower the collective to settle. To put it bluntly: don't fart around.

My landings became so much more precise and confident after this.


APPLIED TO MY MODEL: When at home, I lifted my model. It's a heavy thing. Not as light as a feather as it looks out in the field.

I then tipped the heli on the side, exploring just how far it would have to go before it really did topple over. The centre of gravity is actually quite low and it took a fair angle of tilt to get it to fall on its side rather than fall squarely on its skids; angles I've certainly never seen in my tentative attempts at landing before. I began to realise I was being unnecessarily over-cautious.


BACK IN THE FIELD: So I began to apply all this forethought: I didn't bother about getting the skids perfectly level anymore. As long as, just like in a real heli, there isn't any excessive sideways movement, the heli *will* land safely. It's natural that it will land one-skid low (wind conditions, or ground/grass not perfectly level).

Biggie is so right: as soon as you can hover over the same spot for a few seconds, lose the training undercarriage. When you want to land, and the heli's over the same spot for a couple of seconds, trust yourself, and smoothly but progressively lower the collective. Yes, the thing may start to drift sidewards a couple of millimeters (maybe a slight gust of wind? Or your cyclic isn't perfectly level?) but it doesn't matter - the heli won't pick up enough sideways speed to matter - it'll only be moving a few millimeters. The sideways movement won't be enough to cause a topple, and the angle of the helicopter is level enough. Just land the thing.


(I applied this even last weekend. I'm amazed at how robust the heli is: when things started to get a bit hairy with my side-on hovering, I just downed collective, maybe a bit too quick, but the thing settled quite happily. Even landing on the front right corner of the skids once! Didn't matter, it then fell squarely on all four corners)

It might seem odd but the main reson I bought the heli was that I had heard they were really tricky beasts to fly, sort of a new challenge and skill to master!
Well maybe not master but at least gain a semblence of competancy in!

I've never actually been airborne in a real heli, so have no idea what is actually like - noisy I suspect!

Hehe - if I was flying it near a girlfriends car that would be the least of my worries - getting caught by the wife would be tops on that list - but I take the point though!
The stupid thing was that the flying box was just about the only thing it could have hit, what I was doing was trying at a low level to sort of hover a loop around an apple tree in the garden, stupid here swung the tail around just as it decided to move sideways (ground effect I guess) an just clipped it, an inch more and it would have missed entirely.
Live and (hopefully) learn from that one I guess.

There was a certain degree here of running before I could walk, so once its fixed it's back to hover practice for a while longer and no more "try this" until I'm better at it!

I agree entirely about ditching the undercarrige as soon as possible, but keep in mind I'm still only 1/3 down the first bottle of fuel right now, so really still an absolute novice.
I'll get there though!

I understand exactly what you mean about the tipping point and the weight distribution pulling it level, I would guess the centre of moment would be around the swashplate or slightly higher, above that there is really just the weight of the rotors, pitch adjusting gear etc, whereas below is the weight of the rest of the heli - the tipping angle is going to be quite high as you say.

So if it is leaning sideways then leaving the rotor angle alone and letting the weight of the main part of the heli pull it level is a lot more sensible.

One thing I would say about the Mosquito design that I consider a little poor is the tail skid, just a loop of wire, I had one problem a while back in that it was pretty wet underfoot and when it landed the wire just went into the ground resulting in the tail rotor digging a little trench and snapping the tail drive belt. I'm going to improve on that design wehn I get time!

I must say though, those tail rotors are tough little things even after choping a segment out of the flight box there is no visible damage or marks on them!

I guess I'll be playing with another toy over Easter, there's no way I can find time to go to Hinkley to collect a new bit in the next couple of days - if I don't sort out the garden soon the wife is going to get aggresive with me!



Phil

[darren_uk]

Hi Phil!

"I've never actually been airborne in a real heli, so have no idea what is actually like - noisy I suspect!"

Earphones are mandatory :-) In a fixed wing you can get away with not wearing them (in Germany I was flying fixed wing and they don't tend to wear them - well, not in the Cessnas I was flying).

However, you're right: helicopters are very noisy. I've lifted my earphones a couple of times - the difference is remarkable!

But I had seen people try to have a telephone conversation on the mobile whilst in a heli :-) (my examiner for example !!!)

" So if it is leaning sideways then leaving the rotor angle alone and letting the weight of the main part of the heli pull it level is a lot more sensible."

Yeah. As long as the disk is roughly level, then that's OK. But if it's at a significant angle (whatever significant is!!) then there'll be enough horizontal component in the thrust to pull the heli over to the side - trip the skids if you like.

Sloping ground landings: Agh! They were the one thing that had my palms going sweaty. You have to *slowly* lower the helicopter towards the ground (and you really do need a rock solid hover) until one of the skids touched - then it was a balancing act because you're now hinging around that one skid. Then slowly lower the collective....and you're leaning over !! But all the whilst you have to keep the disk level (using progressively more and more sideways cyclic). Eventually the other skid will touch, but it seems like a bottomless pit...

10degrees slope. And because helicopters hover/land with one skid low (tail rotor blowing so you're leaning into that) then doing sloping ground landings change depending on what side you do them on. I had to do 30 minutes constant of them whilst my instructor stood outside and watched. Boy were my palms sweating!

Just another anecdote: Another teacher (who eventually examined me) asked me to recite "Mary Had A Little Lamb" whilst doing a sloping ground landing! You know what? I just couldn't recite that damned rhyme!


I'm waffling again.

Hey, you manage to get into Hinckley? Midland Helis? Cool! I like them. They fixed up my Shuttle back in 1999 and it hasn't needed anything done to it since. Have you seen that gas turbine machine? Apparently they've now begun to sell it in kit form, but it's something like ?8000 :-/ (I was raised in Hinckley, and my mum and sister now live close by).