Tony Nijhuis 72” Mosquito – Build Log

[Allan Bennett]

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 Walby]

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?

[Martian]

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 Bennett]

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 Walby]

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

[Geoff Gardiner]

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 Walby]

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 Bennett]

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 Walby]

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

 

 

 

 

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

[Allan Bennett]

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.

[Martin McIntosh]

Sorry again that the model has been destroyed, but exactly how bad is it? Mine was a wreck after an ESC died but was repaired. Can you bring yourself to post a pic?

[Allan Bennett]

No pics! Fuselage broken in three, port wing broken in two, both nacelles smashed, multiple fractures all over. It's in the bin now.

But that's enough about my failure; let's hear more about the successes, and don't let the speed drop too low!

[Geoff Gardiner]

Well.......

I was having some issues with trying to balance using my hobbyking balancer, and wasn't convinced that I had got it right, so decided to make a Vanessa rig.

The amended AUW is 7.4kg or 16.3lbs .... hmm.

[Allan Bennett]

Yes, there must be a lot of paint on that! How much weight have you got hanging in those two bags?

[Martin McIntosh]

16.3lbs? Ouch. Be prepared for a very fast landing.

[Chris Walby]

Don't panic Mr Manwaring.... Okay the Seagull should weigh 6.4Kg and mine flies nice at 7.4Kg and I know the TN is a smaller wingspan, but dare I say it.....it has flaps.

If is anything like my BH Mossie and PZ Mossie (not tried the Seagull Mossie…bottled out) the flaps are very effective as long as you use plenty of power.

15 degrees is effective, 30 degrees and I need about 45% throttle as it becomes very draggy/more lift and the great Winkle Brown could effectively hang it on its props with a full size aircraft with 45 degrees!

All I would say from my experience is not to slow up too much as it has a sting if you tip stall it.

PS what is in the plastic bags? I did end up with some nice brass prop nuts, before I was about to turn my attention to the heavy non scale tail wheel!

[Geoff Gardiner]

I have some stick on (car wheel) weights and a couple of AA batteries in the bags.

After I took the picture above I realised that I had marked the CofG incorrectly on the wing. With the correct CofG marked it needed much less.

I have heavier (all metal) retracts and some 3d printed details but apart from that it is as per plan. Must be my covering and painting methods that need perfecting.

I have my flaps set to 45 degrees on full deflection. From reading previous comments I guess this may be too much.

[Chris Walby]

Geoff,

I suspect your Mossie is much like all others regarding flap performance bearing in mind that the flaps are both sides of the nacelles. This just means that the wash of the props has a greater effect (good and bad) when the flaps are deployed.

Could I suggest watching The Peoples Mosquito interview with Eric "Winkle" Brown when he talks about the first carrier landing of a twin engine aircraft. There are a few useful pointers when using full flap

• Full flap, very low air speed and lots of engine power, if one engine quits the aircraft inverts very quickly (<3 seconds). Eric did this at height with his "Boffin" as passenger
• Eric's comments about the swap to 4 bladed props to achieve very low approach speed to the carrier

Of course he had the benefit of being in the aircraft to feel the approaching stall.

I am sure others can assist, but my plan would be:

• Set no flap position 1
• Set flaps at 15 degrees position 2 - use this and see how it slows up
• Set flaps at 30 degrees position 3 - not slowing at all, try this, but watch for pitch up and get on the power/down elevator to keep the speed up
• Set flaps at 45 degrees position 4 - Okay you have missed 2 or 3 landing attempts (still flying like a bullet) and time is running out. Almost full power and try this flap position or
• Plan B - Gear up, flaps 2, come in real low and belly it in on the long grass. Might cost you a set of props but not much else.

If you only have a 3 position switch then:

• Set no flap position 1
• Set flaps at 15 degrees position 2 - use this and see how it slows up
• Set flaps at 35 degrees position 3 - not slowing at all, try this - Okay you have missed 2 or 3 landing attempts (still flying like a bullet) and time is running out. Almost full power and try this flap position or
• Plan B - Gear up, flaps 2, come in real low and belly it in on the long grass. Might cost you a set of props but not much else.

IMHO the number one thing to avoid is tip stalling it with no height and the U/C down and flaps as its high drag.

The thing about maidens I don't like is the quantity of things to do in a very short space of time.

PS if you can pick a day with a reasonable wind straight down the runway it will help with any swing on take off and much needed slowing on the way in.

Hope this helps

[Geoff Gardiner]

I have programmed the Taranis and set up all the control throws (and set the failsafe).

I have also tested the motors which are giving 875 watts of power and 57 amp draw, at full throttle (for each motor).

Nothing left to do except buy some rubber pants and go fly!

[Martin McIntosh]

Well, all I can do is to wish you all the best. Wind forecast for my field is fairly strong but in the wrong direction so I shall at least keep mine intact again for a little longer (any excuse is a good one).

[Allan Bennett]

Good luck Geoff. Whether you deploy flaps or not, keep a cool head and don't fly too slow.

[Geoff Gardiner]

Well, it flew.......... but not for long!

After an aborted take off, when the prop came off, I tried again.

It took off OK and trim wasn't too far out. Unfortunately, on the second circuit, it tip stalled.

I almost got it back but ran out of air and it hit the deck - teach me to build too heavy.

[Martian]

On for goodness sake all that work what a blow i am so gutted for you Geoff

[Chris Walby]

Geoff, absolutely gutted for you, it looked like a nice take off and not too much of a handful in flight.

So sorry after all that work and all the best in the future with whatever you do next.

[Martin McIntosh]

I am gutted for you as well.

I think that many of the TN designs could be over engineered resulting in a high wing loading, especially if you make the mistake of buying a plan pack which, as in the case of my 72" Spitfire, may not exactly conform with the original material specifications.

Much as I would like to fly mine again after the re build I do not wish to be the next to stall and crash so may just leave it as a hangar queen.