Operating 503 Trikes on the highveld

[tviljoen]

I have experienced problems with 503 trikes on the highveld, when operating with 2 sizable types on board (90 kg), and during warm conditions. Aiden at Solowings has confirmed the problem, and recommended 582 power for these conditions.
Typically what happens is that, after takeoff with the bar fully forward, the trike wants to stay in ground effect, rises up to 10 to 20 feet, drops a bit if the bar is brought back at all, and takes a long (nerve-wracking) time to pick up speed and climb.
The problem is to be able to predict that this is going to happen, and not attempt to fly under these conditions.
A friend of mine, who works in aerodynamics, says that taking off as we are taught to do with the bar fully forward, ensures that the trike effectively takes off with no excess speed above stall. If this happens to be near the maximum speed your plane is capable of, then you are flying under marginal conditions, and things can get scary.
If the stall speed is known for any conditions(perhaps could be measured by a short bar forward takeoff), then a better technique would be to keep on the ground until your measured airspeed is 10 -20 km/hr above this, and then push the bar forward and takeoff.
I have tried to do this but chickened-out trying to get enough speed on the ground, and took off in the normal way. Not to be attempted on short runways! Comments please!

[grostek]

What does the POH say?

Gunter Rostek

[Morph]

I have experienced problems with 503 trikes on the highveld, when operating with 2 sizable types on board (90 kg), and during warm conditions. Aiden at Solowings has confirmed the problem, and recommended 582 power for these conditions.

Have you heard of Density Altitude. Hot, High, Heavy, (Humid?) you are really looking for trouble. On a 30 degree afternoon on a 5500ft alt runway your plane quite easily thinks it is at 8500ft. Now a little 503 will happily fly at sealevel two up with two 90kg dudes but not at 8500 ft.

Typically what happens is that, after takeoff with the bar fully forward, the trike wants to stay in ground effect, rises up to 10 to 20 feet, drops a bit if the bar is brought back at all, and takes a long (nerve-wracking) time to pick up speed and climb.

The air is simply too thin and you are going to need a hell of a lot more runway to get up to speed. The plane will only take off once it has the right amount of air molecules flowing across the wing. With the heat, the air molecules are further apart, so you need to travel faster to get the same amount of air molecules as before. Additionally the thinner air results in the ASI indicating lower speed (it also expects a certain amount of air pressure to show an airspeed and thinner air/lower airpressure coming in to the pitot tube, requires faster speed to show the same speed as a cool morning).

The problem is to be able to predict that this is going to happen, and not attempt to fly under these conditions.

Simple, calculate you density altitude and then determine if it is worthwhile to take off. If it is too hot reduce weight, i.e. turf your heavy pax out, before taking off of course

http://www.pilotfriend.com/calcs/calcul ... ensity.htm

A friend of mine, who works in aerodynamics, says that taking off as we are taught to do with the bar fully forward, ensures that the trike effectively takes off with no excess speed above stall. If this happens to be near the maximum speed your plane is capable of, then you are flying under marginal conditions, and things can get scary.

absolutely, and the lower performing engine will not have enough power to maintain normal flight. very dangerous. The answer avoid these circumstances.

I would suggest to keep these sorts of flights to early and cool to cold mornings.

[tviljoen]

Hi Morph,

Thanks for the reply.
I think the problem is more one of interpretation or judgement.
For instance, if I use the density/altitude calculator, 20 deg equates to a density/altitude of 7450 ft, 25 deg to 8000 ft, 30 deg to 8534 ft. This is for an altitude of 5400ft.
So, roughly speaking, the density/altitude shows an altitude of 2000, 2500, and 3000 ft above the airfield altitude. I have flown at 7500 ft quite easily before, but not at 8000 or 85.(without a pax, though). So I could interpret this as 20 is OK, 25/30 is not? My previous experience is that 21 or 22 deg is OK with a pax, but not above. How can I judge this better?
( I have previously found tables that show increase in take-off roll also, which seem very useful).

Your reply to the 10 to 20 km/hr above stall speed question was - yes, it's a good idea. Have you used this technique before when not being sure conditions are OK with a pax?

Cheers

[Morph]

Yes, it comes down to the experience you have with your trike and your runway. If you have happily flown with a pax at 20deg at your altitude then that becomes your yardstick. Just be careful of humidity. The water in air replaces (or pushes out) the air molecules. In other words higher humidity further reduces the performance of the wing. So performance on a dry 20 deg day will be better than a wet one.

Also, different airfields can catch you out. Suddenly the airfield is shorter, or has higher trees at the end of the runway. This is particularly bad when you have done a fly away, had breakfast and are now returning. That out field can be a trap.

How does a 582 help you here as opposed to a 503. Well you can be caught out just as quickly with a 582, but your same aerie, same wing, same airfield, will get into the air much quicker with those 15 extra ponies. You have more reserve power to help you on those hot days, less critical.

To me at reef altitude a 582 is the better choice, especially if you are going to fly often with a pax.

Here at the coast we often do fly away's to Swellendam, Oudtshoorn, Tanqua, Carnavon..... and all of these require climbing from sea level to as much as 9000ft to clear these mountains. None of the 503's carry PAX's on these trips. The 582's do this easily.

[Morph]

Your reply to the 10 to 20 km/hr above stall speed question was - yes, it's a good idea. Have you used this technique before when not being sure conditions are OK with a pax?

Sorry missed this one. I had a nice short wing fixed wing Challenger with a 503 motor. The shorter wing gives better speed at the cost of climb. So when two up, especially heavy, I would accelerate along the runway with the wing neutral, i.e. not pulling back on the stick (this gives minimum drag) then at the normal rotation speed would pull back quickly to pop her off the ground and instantly release the pressure and fly her in ground effect again with the plane fairly neutral (not as in the case you mention with the wing in maximum attack). The plane now accelerates much quicker since it no longer has the drag of the wheels on the ground and the wing being neutral has less drag. Then at about 10-15 mph above normal climb out, pull her up into a max rate of climb. Works very well on short rough runways when you need to get off the ground quickly but have enough room to fly out in ground effect.

You could apply the same principle to a trike. I would not take off with the wing in maximum attack. The plane will take off before the 1.3 X stallspeed, the higher drag will have to be counteracted by higher thrust, needing more power from the engine, just to keep you in the air. You will be close to the stall, close to the ground, and if you manage somehow to get out of ground effect, the you will not have enough power to sustain flight and you will go in.

Did you ever see the story of Brian Milton, who tried to fly non-stop across the Atlantic in a Trike. He tried to take off from a GA airfield in Canada that had a lovely long smooth runway. He was hopelessly overloaded with fuel and luggage, took off and stayed in ground effect all along the runway and crashed.

BTW Approach and take off speeds should never be below 1.3 times your stall. You should know what your stall speed is, it should be documented, if not measure it, or get an instructor to measure it for you. Remember your stall speed is higher 2 up. On my Challenger it was 38mph solo, 43mph dual, so my minimum takeoff speed clean solo was 50mph and 55mph dual. The same for my approach speeds.

[REDROMAN]

Hi tviljoen

I have a Raptor with 503 on.In Aliwal North out alt is 4400.Performs like a dream with two up +-180kg.Just concider not to fill up all the way and most inportantly choose the right time of the day to fly - early mornings,late afternoons.At the right time she will perform excellent.

[Morph]

most inportantly choose the right time of the day to fly - early mornings,late afternoons.At the right time she will perform excellent.

Exactly.

And if you are caught away on a hot afternoon with a pax and the runway is marginal rather try a circuit on your own to get an idea of performance. You should also know the difference between solo and dual takeoff run. Let's assume your normal takeoff solo takes 40m and dual takes 100m, i.e. 2.5 times the distance. Now do a circuit on your own and estimate the distance of extended takeoff roll, let's say 75 meters. Expect then to run a minimum of 75 X 2.5 = 187.5 meters dual on the hot day. Do you have enough runway length to safely do this?

If it is marginal then rather arrange alternative transport for the pax or get him moved to another, longer field where you will pick him up. Rather safe than sorry.

[ICEMAN]

Hi tviljoen


Your performance described is approx the same as we have on a scout with a 503- i have had it with my previous windlass and also aquilla each with various cuts and sizes of wing.

Be very very careful of flying the stall with the bar fully foward on take off with a 503....... my typical take off with the highveld 503 has an initial climb off the runway, then on climb out i get a "levelling" of period despite being at max RPM- this sometimes even includes a brief period of descent ......... then the wing "bites" again and off we go with a rate of climb of approx 300f/min.

The technique that i use is to start the ground run with the bar neutral to get maximum ground speed, then to get airbourne (it usually takes approx 250meters of runway to this point) with a quick bar foward and then back to neutral position. Now i fly straight and level down the runway (bar slightly in, max RPM) building up speed (energy).

Once i have plenty of energy i start to trade it off for climb out........ i work on approx 1000meters distance from my starting point on the ground to get to an altitude of approx 350ft agl .......

Choose your weather, D/Alt, fuel and pax loads carefully with the 503 on the highveld and you will be ok........

[Biggles]

So in your guys opinion would ibe able to fly a 503 with a Spirit15 (high lift wing) at 4300m? That is where I work and wondering if i would get off the ground.

I can expect a 30% decrease in power from the engine... would have to increase the pitch on the prop, change jets, and fly with minumum feul and go on a diet.

[aeroden]

Hi jviljoen,
We are three instructors at Aeroden. We all do training on 503 and no problem at all. All 4100 and get in the air
with student 100kg.Talk to Fred in Springs 0832561873 he only use the 503 for training and his a big bloke.
It's a "kan nie dood engine".
Aeroden Flight Training Centre
Basie