Microlighters

I recently enquired about a set of plans for a scratch build project, and asked some technical questions.

The one answer I got confuses me a bit, beeing that only approved aviation engines may be used.

Say I want to build an aircamper, and plan to use a vw polo 1.4 tdi engine.

Will an a.p. pass it?

Will caa issue authority to fly?

Will I get a test pilot to testfly it?

The other question I have is regarding the VNE rating, how is it determined?

Does it have to do with the structural strength of the aircraft,

the maximum safe RPM of the engine fitted,

or handeling caracteristics of the design?

Hi Smallfly,

Since no one responds, I'll start voicing a few of my conceptions (misconceptions)

Being a scratch built project, you should be able to use just about any engine you fancy bar that it falls within the design weight and below the max design hp. (After all, it will be registered as an "Experimental"!

No one can guarrantee the services of a test pilot, but if built safely and to normal standards, I'm sure someone would be willing to act as test pilot.

VNE is normally calculated - your wings WILL come apart backwards at a certain speed regardless whether this is caused by too much power (RPM) or too steep a dive.

Please note, I'm in no ways an expert on any of the above, but maybe this will start the different opinions flowing.

Keep well,

Henni

This is an EAA project. Tailspin on this forum is very active with them.

My thoughts
Are you currently a pilot?
Have you built before?

If the answer to these questions are no then I would be very hesitant to even think of test flying or AP'ing the plane (Am am not either but If I was). This is where I believe the EAA come in to it, they can give advise, set you up with a list of AP's, approved non-aviation engines, design criteria etc

smallfly wrote: The one answer I got confuses me a bit, beeing that only approved aviation engines may be used.

Not neccesarily avaition. VW engines and BMW bike engines have been known to be used. You do have a risk. Aviation engines should hve dual ignition systems, i.e. two full sets of ignition, points, plugs everything. So they will typically have 2 plugs per piston. Automotive motors don't.

Say I want to build an aircamper, and plan to use a vw polo 1.4 tdi engine.

Why this engine, how heavy is it.

Will an a.p. pass it?

Not easily unless built under the direction or auspices of something like EAA

Will caa issue authority to fly?

Building a completely new model has a lot of red tape involved including strength tests which could mean physically testing the airframe to destruction by loading it with airbags to get the g-ratings

Will I get a test pilot to testfly it?

If built under EAA's direction and is approved at every step of the way by an AP then I suppose yes.

The other question I have is regarding the VNE rating, how is it determined?

I am sure there are scientific methods of calculating this without having to fly an aircraft to destruction. It is determined by the design, build, covering, farbics used, techniques used on building it etc. If you build using plans of a well known design and build it exactly according to their direction and specification then you can use their specified VNE as a guideline

Does it have to do with the structural strength of the aircraft

absolutely

the maximum safe RPM of the engine fitted,

depends on the size and pitch of the prop to be fitted and whether or not a gearbox is fitted. A prop generally cannot spin at more that 2300 to 2500 rpm. (This depends of which prop, what length etc) Anything faster than that and you stand the risk of the tips going through the sound barrier and the prop self destructing.

Your motor's peak power and torque is perhaps at 4500rpm and you would want to run in this power band. As a result you are going to have to use a reduction drive. If you don't the motor will be labouring at 2300rpm at low power. An aviation engine is designed to run at 100% rpm for take offs and climbs and 75% rpm for extended periods of time. Will this motor be able to handle the load. Also, aviation motors need to be able to compensate for sudden changes in altitude. Take a car from Jhb to Dbn and see how suddenly it starts running rough and 'pinging'. That's just going from 5500 feet to 0 feet in 6 hours. Now try to use this motor to climb from 0 feet to 12000ft in 15 to 20 minutes. Even VW motors undergo significant engine modifications before being used in planes. Finally automotive motors are too heavy for the power they produce.

or handeling caracteristics of the design?

You will only know this if you have other models to compare to.

Why the polo engine?

The aircamper was originally designed to fly using a model A Ford Bakkie

engine, I don't think the 3 cylinder polo engine could outweigh that.

The aircamper flies happily on a 2000 vw boxer engine producing in the

region of 150 nm on a direct drive, the 1400 turbodiesel produces 165 nm

@ 1900 rpm, and have a beatifull flat torque curve, wich means it will be

very happy to operate between 1900 and 2500 rpm.As a bonus diesel is

that much cheaper than mogas, and the consumption of a diesel engine is

so much less than a petrol engine.

P.S.

I don't fly yet nor have I built anything, but I won't even try to build

anything unless I am absolutely sure it will be safe.

Smallfly

There are some interesting topics (or mentions) on this forum, concerning the use of auto engines and more specific diesel. Read them and consider your options.

The power to weight ratio is the most important as to "will it fly". Safety is the most important to us all. You'll find that some a/c perform better with a 582 than a higher HP 912, because of the 912 weight. And remember the centre of gravity issue. Some guys fit a higher HP, heavier engine just to add 6 or 8 kg of lead in the rear to get it balanced

There are gentleman in the aviation circles who, for good and valid reasons, prefer auto engines and more specifically diesel.

Have a look at http://www.eco-motors.com/

I can't wait to look back in 10 years time! There are a few projects around the world (some in SA).

To put it briefly, diesel has less that can go wrong (no ignition, no plugs etc.) more torque.

Engine management is a valid issue, but it has been done before. After all, it's software.

{Makes me think of the proprietary software VS OpenSource issue, but don't make me go there. The guys in the lead will always fight to stay in the lead, even if it's dirty or irrelevant}

Mmmm... seems like no-one has raised the TBO issue yet? I'm sure we'll get there.

Google "diesel in aircraft"

I seriously suggest you contact someone from EAA to assist you. They are a great nunch of guys, have chapters everywhere and are active.

Smallfly wrote:The aircamper was originally designed to fly using a model A Ford Bakkie

That might be true but there are no versions of these still flying because they very quickly realise that the engine is not an automotive engine.

There are folks looking at the Smart turbo diesel as well, but these motors are very heavy when compared to aviation motors. Remember any model has a specified maximum all up weight. Lets assume for purposes of comparison the max all up weight is 450 kg and using a rotax 582 gives you an empty wight of 250kg. This leaves you 200 kg to share between 2 people, fuel and luggage.

Now use a VW engine. Suddenly your empty weight is over 300kg. Now you have only 150kg to play with. You second person can only be an infant and you are limited to 40liters of fuel.

Hi All

Ok there are a lot of good andswers already put in the pot, almost all are correct, as long as themotor HP does not exceed max HP for the aircraft, you can even use a lawnmower engine. To get a test pilot i could suggest a few who would be very willing to test fly her for you.

Remember the aircraft needs to adhere to the standards set by the CAA and as long as you stick to those guide lines there should be no problem. You can contact me direct with a PM or E-Mail and i will give you the specs on how to determine VNE and the rest.

Thanx for the replies gents, I am always eager to learn from the

experience or knowledge of others.

Of course I will considder things like AUW and the comparative C of G

issues, but then again is the aircamper not PPL as it is?

Engine management should not be a problem as a diesel engine has

mechanical feul injection, wich is preset and does not advance or retard

during operation like petrol engine timing.

There is also no mixture of feul and air issue as the airflow is never

adjusted, just the quantity of diesel injected.It therefore seems to me like

diesel should be the aviation engine of choice anyway, after al the

Junkers flew on radial diesel engines, and that was during WWII!

The only danger is the tendancy of diesel to gell (freeze) at very low

temperatures, but that can be countered by running the feul line through

the haeter pipe as it is done succesfully by the newer generations of

Isuzu.

I beg to difffer: those running with mechanical diesel pumps are older engines and does not produce the same amount of power /cc or power/weight. That Polo tdi will most propably be electronic injection. The injector pump only produces high pressure diesel while electronic valves determine the exact timing of the diesel injection (the diesel burns immediately when it is injected - under high pressure onto a hot, high pressure environment) - Diesel Injection timing and Petrol spark timing has the same effects.

The elctronic map ambient pressure, tubo pressure, RMP, EGT, CO etc. etc. to have the right timing and amount of diesel to be injected. What is good news is that you'll propably be able to squize a bit more out of a diesel if you map for maximum power and not best CO (Carbon Monoxide).

Anyway though I'm an electronic engineer, I don't want any crutial electronics in my 4x4 NEVER MIND MY A/C

T

As far as I know most of the new generation petrol and diesel motors have electronic sensors that determine the timing and amount of fuel injected after messuring things like ambient temp. alt etc. You dont' have to set the timing when at the coast as the comper advances or retards the timing as nessecary. I think the biggest challenge would be the remapping of the electronic system as all the sensors like abs etc are disconnected on an aircraft and that buggers the comper around. My 2c