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Tony Nijhuis 72 Mosquito Build Log

Electric Version

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Allan Bennett26/08/2018 09:11:03
1524 forum posts
38 photos
Posted by Chris Walby on 25/08/2018 21:45:13:

. . . . I again agree with the slow flap transition as it can be a bit off putting with the change in pitch, I try to select gear and flaps 1/2 at the same time with the BH mossie thus hardly any change in pitch although a noticeable increase in drag (to be expected).. . . .

Do gear down and flaps down cancel each other out pitch-wise? If that's the case, might it be worth having 50% flaps on the same switch as gear? With my Taranis transmitter I can program it so that flaps respond to a dedicated flaps switch, as normal, but also respond to whatever degree I want when the gear switch is activated.

Chris Walby26/08/2018 09:23:22
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944 forum posts
227 photos

Allan, one does cancel the other out so yes its a nice idea and worth a play with my TX.

Only comment is that the full size mossie normally takes off with no flap (video of the NZ flight) or only 15 degrees,

I think I need to test it out on the PZ mossie to be comfortable that always having flap dialled into gear is a good idea.

Nice idea...and still need to have a think about aileron differential...wink

Allan Bennett26/08/2018 11:53:27
1524 forum posts
38 photos

If I do do it, it seems from what I'm reading here that the default safe value for flaps-with-gear should be around 15 degrees or a bit less. What causes the change of pitch when gear goes down, is it simply the extra drag of the gear, or the fact that it's changing the c of g because of its fore-and-aft action? I've never noticed any such effect with my LearJet or my Mustang, both of which have main gear retracting sideways.

Mixing sounds like a good idea, but my maiden flight, whenever my frame-of-mind and the weather are right, will be with manual control only so I can see for myself what the issues are.

Chris Walby26/08/2018 13:59:06
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944 forum posts
227 photos

Allan,

I would say it depends on a few factors like:

  • U/C doors installed as it will be a bit more aerodynamic when closed and more drag when open
  • Surface area of the U/C
  • Where the U/C is located in the wing
  • Whether the U/C is directly in the wash of the prop
  • Air speed when you deploy them

All said and done, I don't think it will make that much difference if you are expecting it as its all working in the right direction (C of G moving very slightly forward).

Let us know how you get on and best wishes.

Allan Bennett31/08/2018 20:14:46
1524 forum posts
38 photos

I set the model up today and measured my flaps deflection: 'Mid' flap is 15 degrees, and 'Full' flap is 25 degrees.

That sounds on the safe side to me, from what's been said above, so I'm not going to try and achieve any greater deflection. Weather forecast is good for Sunday, so I'm fast running out of excuses not to do the maiden!

Allan Bennett30/09/2018 21:30:15
1524 forum posts
38 photos

Disastrous maiden flight!

At last I got around to maidening my model today. Take-off with no flaps was a doddle, a gentle throttle-up, increasing until the tail lifted, then increasing more, with a bit of up elevator for lift-off, all within about 50m. A gentle climb and a 180-degree left turn to get into the flying area was followed by a few gentle circuits with the wheels still down. I felt a bit uneasy with the model (don't know specifically why) so decided to start my landing approach at about 2 minutes, but on the downwind leg it started getting away from me -- a bit of right wing down followed by left wing down, and I was unable to turn it back into the flying field. It went down behind a bunch of trees so I couldn't see if it was nose-down or if I'd been able to keep it level.

Still don't know how it landed, for half a dozen of us have been unable to find any sign of it sad

Chris Walby30/09/2018 21:47:15
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944 forum posts
227 photos

Allan, So sorry to hear about your loss, maidens are always (for me anyway) high pressure, tricky events where you don't get a second chance.

I have hunted for mine and others models and am still surprised as to how far out you can be + how far it can travel when out of view.

All the best and hoping you manage to find her before too long.

Martin Harris30/09/2018 22:04:13
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8675 forum posts
214 photos

That's horrible for you - even more so if you haven't found the model. I assume you've checked the trees carefully? A camouflaged model can hide in the branches very effectively.

One tip, but it doesn't sound appropriate in this case, if you have telemetry and still have a connection with a lost model is to shield the transmitter with your body and turn slowly until you get the smallest signal strength - the model should be directly behind you...range test mode can help as you get closer.

This technique worked very well for me to locate a model which refused to come out of a flat spin and ended up in a field of 8 foot tall maize.

Allan Bennett01/10/2018 08:35:58
1524 forum posts
38 photos

Thanks guys. I have a Loc8tor module in the nose, and I used the telemetry of my Taranis FrSky setup, but not a beep from either of them. It was seen by everyone disappearing behind a long line of trees, and my Taranis reported loss of signal just after we lost visual. I and the others searched all the area within about half a mile of where we thought it should be. The only place we were unable to search was a large patch of trees and brambles that's within the high fence of a nearby school. I'll be calling them today to get permission to go and look there, if they haven't already found it.

Martin McIntosh01/10/2018 09:48:14
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2874 forum posts
1062 photos

What a disappointment that must be after all the work. Sounds like you almost certainly reduced power too much on the downwind leg and stalled it, hence the wing wobble.

Fingers crossed that you recover it OK.

Allan Bennett01/10/2018 11:00:18
1524 forum posts
38 photos

Yes, too much power reduction was my thought too, though I'm not sure if it was me, or the ESCs overheating (even though they're rated at 100A and have fans on), or the batteries running down. Maximum amps draw was measured at 55A per motor, and the batteries are 5000mAh, so they should have been good for 5 minutes or so at full throttle, which I wasn't at; so it must have been me attempting my usual downwind sort of glide, even though I was repeating the mantra 'keep the speed up' to myself.

Chris Walby01/10/2018 12:31:05
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944 forum posts
227 photos

Double guessing isn't really going to help, but perhaps a process of elimination will.

  • Loss of signal - looking unlikely as you mentioned no loss of signal until it went behind the trees (how quick does it report, can that help in location assuming the signal loss was the point of impact)
  • ESC overheating where both shutdown at the same time, very unlikely and at low air speed on one motor it would have spun in
  • Is it twin lipo (one for each motor, or just one), if its one the both ESC's might have shutdown on low voltage - odd as you weren't in a high power situation. if its two lipos the changes of both cutting out at the same time is very small - again it would have spun in.
  • Had you put the flaps down?
  • I would have expected a loss of elevator authority if you were getting close to stall + loss of height, tricky to try and remember what you were doing at the time but worth a think about if its attitude (AOA) changed or not.

Might be worth asking any other TN Mosquito owners how their performs on very low power settings do they glide/spin in?

Martian01/10/2018 13:16:11
2197 forum posts
1070 photos

What a horrible blow I hope you recover quick before weather conditions make it worse. Makes me even less inclined to commit mine to the air

Allan Bennett01/10/2018 14:02:42
1524 forum posts
38 photos

Don't be put off by my experience Martian; plenty of others have flown successfully.

Chris, I agree with your elimination thoughts: Two ESCs shutting down, for whatever reason, at the same time is unlikely; and also it didn't feel to me that one motor had cut. The two batteries are in parallel but, as you say, I wasn't in a high power situation. Also, assuming my calculations are correct, I should have had at least 50% capacity remaining at that time, and the C rating high enough to supply the full-throttle amps. I took off and flew without any flaps, and I had the u/c down for the whole flight, simply because I didn't want to risk any change of attitude on my first flight. I didn't notice any change of attitude, just the left-right wings dropping, and my inability to turn it back towards the field.

So too slow, and wingtip stalls, is still my favourite theory.

Chris Walby01/10/2018 14:17:25
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944 forum posts
227 photos

Hi, you could well be right and with the gear down it will be quite draggy. No consolation but my flights I have had to drop in over trees and fly into a light/moderate wind with a long runaway so powered in all of the way.

The rudder on mine seems to have little authority so even if you had kept the wings level it would have been a big arc to get it around.

I am trying to help the best I can with working out where it is, if the school have not seen it, then it might be worth a look further afield. We had one that went a very long way assisted by its glide angle and ground sloping away others far shorter than originally thought....I am not helping am I frown

Geoff Gardiner01/10/2018 17:39:12
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370 forum posts
645 photos

Oh no - what rotten luck.

There is always hope, I suffered a mysterious loss of control when flying my Spitfire.

It went down behind trees.

I feared the worst.

Once retrieved, I found the nose had cleanly broken off at the firewall and that was about it (an easy repair).

It's now back in the air good as new.

Fingers crossed and keep us posted.

Geoff...

Chris Walby11/10/2018 06:48:52
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944 forum posts
227 photos

Allan, any news on finding your mossie as the leaves seem to be dropping off the trees around our area it might be easier to spot?

Allan Bennett12/10/2018 20:58:09
1524 forum posts
38 photos

I took another walk yesterday where we though it went down, and met a dog walker. He showed me where it was -- the other side of a motorway, about 550m from where we all saw it waggling its wings and go out of sight and out of radio contact. It was on the ground against a wooden fence. It's not repairable, but all the electronics seem to have been shielded from the rain we had last week, so I'll be testing them after they've sat around for a while to ensure they're dry. Batteries were ejected (and damaged), so there was no power on while the model was sitting there, so hopefully no electrolitic corrosion (correct term?).

Chris Walby12/10/2018 22:13:10
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944 forum posts
227 photos

Good to get the bits back and a pity its not repairable. Worth doing a careful inspection and strip down just to double check it wasn't anything else (component wise).

Apologies to ask, but you say "about 550m from where we all saw it waggling its wings and go out of sight and out of radio contact" if it was tip stall should you not have had telemetry to point of impact?

Sorry for being pedantic, but I had a model I crashed 3 times (experimental use of differential ESC control on a small twin) I sort of convinced myself it was pilot disorientation (teach me for flying in poor light and leopard spot camouflage). The last crash it didn't eject the battery and the RX was flashing (loss of signal). I have just taken it out of the naughty corner after 9 months as I found a range issue with the TX/RX combination.

Just saying its worth double checking to be sure?

PS

I think mine is repairable...honest

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Edited By Chris Walby on 12/10/2018 22:35:40

Allan Bennett13/10/2018 08:32:43
1524 forum posts
38 photos

Beyond the trees, behind which the model disappeared, the ground slopes away gently. I heard the 'telemetry lost' message on my transmitter about a couple of seconds after it disappeared from sight behind the trees, so assumed it crashed at that time. But if it had continued on, close to the ground, it would have been below the horizon so far as my transmitter was concerned, which could account for the continued loss of signal.

Everything, both physical and electrical, was connected correctly when I found the model, apart from the batteries which had been ejected. Normally there's a 'telemetry critical' message before complete loss, and I didn't hear that during the successful part of the flight, nor at the time of loss. I plan to reconnect all the electronic components in a few days, and check them for issues, and see what action the failsafe took when it lost signal.

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