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Member postings for Jon - Laser Engines

Here is a list of all the postings Jon - Laser Engines has made in our forums. Click on a thread name to jump to the thread.

Thread: Calculating Washout
16/05/2018 21:26:34
Posted by PatMc on 16/05/2018 17:30:41:

Jon, are you saying that the only change you made was to increase the root incidence but you didn't alter the washout which is still at -3 degrees relative to the root ?

Yup. The washout itself, although slightly excessive, was only giving the problems it was due to the low incidence of the whole wing taking it beyond a certain threshold as -3 seems to have been somewhat of a critical angle between lift and no lift from the outer panels. I have not measured it yet but based upon my initial measurements I think I'm probably at +2 - 2.5 at the root and -.5 - -1 at the tips. Not ideal but a considerable improvement.

Thread: Seagull DH-98 Mosquito engine choice
16/05/2018 14:02:48

For those who contacted me about fitting Laser 70's to this model i have some good news.

Chris popped into the factory today with his wing/nacelle and we were able to look at the installation. Long story short its pretty simple and requires no major mods mods other than lowering the tank as shown in the photo. A small scallop should be created around the carb inlet and the mounting box needs to be beefed up (its a bit wimpy for any ic motor imo) but other than that its plain sailing.

The tank in the photo is a radio active 8oz and it just squeezes in with the nacelle over the top.

dsc_0545[1].jpg

dsc_0547[1].jpg

Thread: Who Else Wants a 63" Lavochkin La7 kit?
16/05/2018 10:22:59

ooo pretty

Thread: Calculating Washout
16/05/2018 08:47:05
Posted by Piers Bowlan on 16/05/2018 06:02:02:

I am curious to know what the 'bizarre flight characteristics' were with your hurricane Jon? -2 degrees at the tip is considered normal (for a warbird) so I wouldn't have thought an extra -1 degree would have made a lot of difference, evidently not. Are you sure it was the washout that was the problem with this model?

-2 at the tip relative to the root is perfectly normal i agree but that was not the issue. As the incidence was wrong (between 0 and - 1/2 at the root) the tips were then at about -3 in level flight. If i had a root incidence of 3 and the tips were at 0 i would have been fine.

Just to make sure we have all of our terminology straight incidence is angle of the chord line to the longitudinal axis of the model. angle of attack is the angle of the chord line to the relative airflow.

In this case, in level flight (ie, longitudinal axis horizontal or very slightly +ve) i was left with the outer wings at a negative angle of attack and hovering around their zero lift AOA. This meant that very (and i mean VERY) slight changes in this relative airflow caused massive trim changes as the wing either produced or didnt produce lift. The ailerons had a similar effect. level flight was impossible to maintain as it was continually trying to diverge either up or down.

As an example, if i went in to a loop the elevator would go ineffective towards to top and even with full up applied the model would push forward until near vertical and then stall. once pointing nose down, it would continue to tuck, even with the elevator up, until a speed was reached where it would start flying again. With the recovery in hand it would then accelerate to a point where it would become divergent in pitch and pull up almost uncontrollably. It would also do weird things like push out of a turn and was almost impossible to land. I suspected a wing incidence issue and checked. Then started packing the trailing edge down and flight tested the model. The difference was huge and while still not perfect its much improved. I would have liked to add another few degrees but it would have meant major mods and i couldnt be bothered. The flight performance in its current state is acceptable and i will fly around its remaining strange traits.

15/05/2018 22:44:16

The only time that the tips would be producing negative lift is when the model is flying very fast i.e. the wings at a very low AoA. In that case there would be -ve G force on the tips but not much if any noticeable effect on the model's handling.

I beg to differ. My hurricane was a dog until I checked my incidences. 0 at the root and -3 at the tips? oops. It had the most bizarre flying characteristics I can assure you although it was an extreme case. In any event, you want better behaviour at landing speed when the right way up given that every landing comes at a lower speed than any passes you may wish to do. Changes in section are another fix but were beyond the scope of the question asked by the op. He asked how to work out if washout is needed and if so how much. In fairness the question we should have all asked was what model he was designing before getting too into the details.

I did make one error in my edits, I did mean symmetrical and not semi symmetrical when discussing caps/extra's.

Thread: Powered by Laser, a gallery thread
15/05/2018 20:37:52

Depends which O ring is toast Ron. Give me a call tomorrow and we can sort it.

Chris, I was at Old Warden recently and they had their two hurricanes putting on a stunning display. Nothing fancy, no loops or anything, just swooping passes what seemed like eye level. it was certainly low. awesome stuff.

Thread: Calculating Washout
15/05/2018 20:33:56

Yup, just look at concorde. Although that did have all sorts of twists and camber changes going on.

15/05/2018 18:14:28
Posted by PatMc on 15/05/2018 16:24:28:

I think you're confusing "incidence" with "angle of attack"

Nope. I just read through again to make sure though.

Many aerofoil sections will still produce lift at negative angles of attack but the semi symmetrical types used on Cap and Extra models are not likely to produce much if any at all. Hence my comment about going below the zero lift angle of attack as its possible to do it when the washout angle is greater than that of the incidence with that type of wing. This is especially true if the incidence is very low in the first place as it would be on that sort of model.

Excessive washout when inverted could cause a problem at high angles of attack when inverted, but in the case of Caps and Extra's I would say that is a small price to pay for being able to land it with a minimum of fuss. Pattern aerobatic models I doubt have any washout but equally, they tend to have wing sections/plan forms that lend themselves to not needed it anyway and their routines are usually very smooth which helps keep below critical AOA.

If the full size cub has washout that is fair enough, most model cubs don't however and don't need it either.

15/05/2018 13:38:05
Posted by David Mellor on 15/05/2018 13:20:28:

Not all wings require washout, it depends on type of plane, wing aspect ratio, wing loading and specified flight envelope.

Some designs cannot stall, even at AoA values of 45 degrees. However, these are specialised LAR designs.

Totally correct.

To clarify, piper cubs, spacewalkers, astro hog's and so on dont need anything. WWII fighters, scale civil aircraft and certainly aerobatic jobs like Extra and Cap would get 2 degrees if i was to build one.

In general, the longer and thinner the wing (thickness and chord) the more it is likely to see washout help it. That said, i still wouldnt exceed 2 degrees.

One thing to be careful of is not to give yourself washout that takes you into negative incidence at the tip. If you only have 1 degree incidence at the root 2 degrees takes you to -1 at the tip. Depending on the aerofoil used this could be below the zero lift AOA and you may even get lift on the under side of the wing. Needless to say that would make it exciting to fly!

15/05/2018 12:49:36

I have always worked on the principal that washout is usually in the order of about 2 degrees. Too much makes the model fly funny. 

This generalisation is for essentially straight wing sport/scale stuff. 

Edited By Jon - Laser Engines on 15/05/2018 12:50:39

Thread: Powered by Laser, a gallery thread
15/05/2018 08:28:09

I think you will be surprised. My Hurricane was 10lbs when i first flew it and the 80 brutally over powered it. Time and prop selection will tell!

14/05/2018 23:35:55

An unusual subject for a Laser but looks good. As for the 100, I cant build without parts. Alas its out of my hands.

Thread: Fuel tank setup
12/05/2018 19:26:00

one way valve? whats that doing in there?

Thread: Flying a Turbine
12/05/2018 12:17:42

Percy I never assumed you were targeting me, I was just noting that the systems in place are only as good as the person looking after them. Your man seems to have not been up to the task on many fronts.

Capt, we had a situation recently at my club where a chap had been repeatedly noted by several members as being a bit of a liability. Working out how to proceed was difficult as its not easy to tell an established pilot 'sorry mate, you aint any good and we fear for our lives when you turn up'.

We were as diplomatic as possible but he still was not a happy bunny and took great offence.

12/05/2018 10:10:16

I agree in principal Bob but I have seen many many B cert pilots who cannot land to save their lives, especially in a crosswind.

To touch on Percy's comments about the man with the turbine, all of my models have a single battery/switch/rx setup with no backup. The oldest of these models is now in its 8th season and looking further back I have never lost a model to battery/power failure.

I do however keep an eye on battery capacity to try and head off any cell failure etc. It it possible this chap did not? did he use a battery of too low a capacity for the model? we don't know and its possible he was caught out. Equally, he could have suffered 'radio failure'. Bob is quite right though. I have a fleet of 9 airworthy models comprising sport, scale, and largeish scale (80'' warbirds). To keep them airworthy and in a condition I am happy with is almost a full time occupation and certainly my winter deferred maintenance list took me most of the winter. The more complex the toy, they more it needs to be looked after.

But this brings us right back to square one. Be it flying standard, maintenance of the model and its systems, or technical understanding of the model in question, there is no way to test a person adequately and completely in one sitting. This is why I believe that it is better for clubs to make a judgement of a persons ability over a longer period of time and that is what I push for at my club.

11/05/2018 19:10:49

Percy is right, most clubs will recommend a B cert for turbine pilots.

I personally think this is a bit daft as you can have a pilot who has got his B with a foamy acrowot but has never flown anything else. Equally you can have a pilot who has flown every model under the sun but has no B cert to his name.

Tell me which one you would rather have flying the jet.

The problem is that while a B certificate is not a true representation of the flying ability of any given person it is also the only means available to try and ensure that at least some standard has been achieved. Its an imperfect system to say the least.

In essence though, if you can demonstrate sufficient aptitude and understanding of the aircraft, and have sufficient experience then there is nothing that should stop you flying a jet.

Edited By Jon - Laser Engines on 11/05/2018 19:11:17

Thread: WANTED hangar 9 P-51 60 Bluenose wing panel
11/05/2018 08:30:44

If you carefully sift through the debris you may be able to piece together the missing ribs. You could alternatively use the other wing and make templates to replicate the missing ribs. The leading edge is easy enough and splicing some sheet should not be too hard either. DO you have a photo of the damage?

Given that i think it was discontinued (as usual with H9) a while ago a rebuild might be the only option

10/05/2018 22:46:28

is the old wing beyond repair?

Thread: Balsa USA Sopwith Pup 1/6 scale
10/05/2018 12:14:03

With the tail down the tank will effectively be lower than with it level so the worst that will happen is that the engine will go rich. In practice, the effect is not worth getting worried about.

If the engine was going lean in flight raising the tank and rotating it the other way round will make it worse as you are increasing the possible change in the fuel head. But, if the tank was falling about in there its possible it was pinching pipes and all sorts so continue as you are for now

Thread: Another banking scam
10/05/2018 09:12:19
Posted by Martin McIntosh on 09/05/2018 20:11:01:

Paul Marsh,

I have just looked at this and why do you say that Norton is a virus in itself please? I have been using it for a few years with no problems.

Norton brings even fast pc's to a crawl. Hopeless

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