Designing a glider

[facthunter]

A freewheeling drive would be ok? Centrifugal clutch. Nev

 

 

[Garry Morgan]

A freewheeling drive would be ok? Centrifugal clutch. Nev

A free wheeling prop will still have more drag, depending on what performance one wants, and what type of flying you want to do.

I find it surprising how small things can cause so much loss of performance. After flying wood gliders for over 35 years and having flown modern glass ships I now want better performance, but having said that I did two flights at christmas in my wood SF27m about 500km and did one this season at 82KPH the SF is 34-1 LD

 

 

[kasper]

If registered as an ultralight, the OP wouldn't be able to fly it as a glider by turning the engine off (unless he is a CFI).Cheers

 

John

Please quote from Ops Manual on this please, The only limit I am aware of on shutting down engine is when TRAINING and that requires that the STUDENT only operate with engine shut down by CFI for the purposes of emergency training - Ops 3.02(9)

Once you are a pilot the training restrictions are removed and there is no replication of this restriction in the Pilot Certificate area Ops 2.07 and following nor is there a specific restriction by creating an endorsement for operations in engine off situations.

 

 

[Marty_d]

There's a few interesting motor gliders here, some of which feature a folding prop for less drag.

 

ByDanJohnson.com - Ultralight Motorgliders

 

 

[facthunter]

Pulling an engine up and down just seems so er agricultural. Nev

 

 

[Marty_d]

Pulling an engine up and down just seems so er agricultural. Nev

That's why I like the idea of a folding prop - engine stays where it is, prop blades just fold so there's bugger-all drag from them. Example is the Alpaero Exel.

 

 

[Nobody]

That's why I like the idea of a folding prop - engine stays where it is, prop blades just fold so there's bugger-all drag from them. Example is the Alpaero Exel.

The thing is that as the aircraft has higher and higher performance the "little" things become more significant. Consider the example below,

 

Say you have a motorglider that is 500kg TOW and has a best LD of 25. If you as a designer have the choice of adding a tail wheel fairing that will reduce the drag force by 2kg, it will improve the best LD to 28. It's hardly worth doing.

 

If on the other hand the glider has a best LD of 45, and you could reduce the drag by 2kg by adding a tailwheel faring then the best LD increases to 55!!!! Certainly worth doing.

 

Leaving the engine where it is and faring it in is ok if your target performance is relatively low but it is a significant hindrance if the performance target is high.

 

 

[Marty_d]

The thing is that as the aircraft has higher and higher performance the "little" things become more significant. Consider the example below,Say you have a motorglider that is 500kg TOW and has a best LD of 25. If you as a designer have the choice of adding a tail wheel fairing that will reduce the drag force by 2kg, it will improve the best LD to 28. It's hardly worth doing.

 

If on the other hand the glider has a best LD of 45, and you could reduce the drag by 2kg by adding a tailwheel faring then the best LD increases to 55!!!! Certainly worth doing.

 

Leaving the engine where it is and faring it in is ok if your target performance is relatively low but it is a significant hindrance if the performance target is high.

I guess if you want really high performance then adding a motor is never an option.

 

In the future if lightweight (eg aluminium-based) batteries are available then it'd be interesting to see what low-drag designs come out. Twin small engine pushers on the trailing edges of the wings, for example, with folding props.

 

 

[Head in the clouds]

....... In the future if lightweight (eg aluminium-based) batteries are available ........

Unfortunately we're already using batteries based on the lightest known metal.

 

IIRC Lithium has an atomic weight of 7 whereas aluminium is nearly 4 times heavier, at 27 ...

 

That appears to be what has currently stalled lightweight battery development. Until a wholly new molecule with free electrons is 'created' we can't possibly see any better or lighter rechargeable battery than we already have.

 

Currently the further development of hydrogen fuel cells probably has more near-future potential. Micro nuclear cells would be much better but it may take a while to get public acceptance, I think.

 

 

[Marty_d]

Unfortunately we're already using batteries based on the lightest known metal.IIRC Lithium has an atomic weight of 7 whereas aluminium is nearly 4 times heavier, at 27 ...

 

That appears to be what has currently stalled lightweight battery development. Until a wholly new molecule with free electrons is 'created' we can't possibly see any better or lighter rechargeable battery than we already have.

 

Currently the further development of hydrogen fuel cells probably has more near-future potential. Micro nuclear cells would be much better but it may take a while to get public acceptance, I think.

"...I'm off for a fly in my nuclear-powered glider..." - can't wait to hear that phrase!

 

I may be mistaken with the aluminium battery thing, but I recently saw an interview with an Australian scientist who was working on a new battery type involving aluminium and something else... can't think of it... bromide perhaps? Anyway this thing was meant to have greater capacity and faster charging than existing batteries.

 

 

[Garry Morgan]

I guess if you want really high performance then adding a motor is never an option. In the future if lightweight (eg aluminium-based) batteries are available then it'd be interesting to see what low-drag designs come out. Twin small engine pushers on the trailing edges of the wings, for example, with folding props.

You can have your high performance and add a motor, if fact the extra weight of the motor is an advantage as the conditions gets stronger. as adding water ballest, or the designer has a little bigger wing area for the weight of the motor.

 

 

[Oscar]

You can have your high performance and add a motor, if fact the extra weight of the motor is an advantage as the conditions gets stronger. as adding water ballest, or the designer has a little bigger wing area for the weight of the motor.

No, the analogy is incorrect.

 

Water ballast is distributed across the wing and the weight of the water is carried by the skins/spar - but NOT the root attachments. The extra penetration one gets from having water ballast does NOT come at the cost of a degradation in max. rough speed - and in 'strong' conditions', max. rough is a serious consideration. An engine is weight added to the fuselage, thus increasing the loads on the root attachment fittings, and impacting on max. rough..

 

Adding an engine to a Blanik, reduces the fatigue life by about the same as the difference between a full life of winch launches vs. aerotows, or using it as a fully aerobatic aircraft. For the Llewellyn modification Blaniks - almost the only ones flying anywhere - that reduces the fatigue life from 12K hours to around 8k hours.

 

 

[bexrbetter]

scientist who was working on a new battery type

I spent 3 years with a budget just a few years ago looking at this stuff and have seen "New battery just around the corner" more times than one could imagine. Good way to get Uni funding.

 

As HITC says, we are at known limits now with only small optimising increments possible, and only a "we don't know what we are looking for and it will happen accidentally while we were looking at something else" discovery is possible (as many great inventions have been) - of course a when and where can't be put on that.

 

After chasing my tail, I have big hopes for redox flow batteries personally, imagine a battery you can recharge by draining the old fluids out down the drain and top it up again with harmless electrolytes and 5 minutes later you're done.

 

Flow battery - Wikipedia, the free encyclopedia

 

 

[Guest Crezzi]

Please quote from Ops Manual on this please, The only limit I am aware of on shutting down engine is when TRAINING and that requires that the STUDENT only operate with engine shut down by CFI for the purposes of emergency training - Ops 3.02(9)Once you are a pilot the training restrictions are removed and there is no replication of this restriction in the Pilot Certificate area Ops 2.07 and following nor is there a specific restriction by creating an endorsement for operations in engine off situations.

The wording of 3.02(9) seems pretty unambiguous to me - it doesn't mention either student or pilot certificate holder.

 

In the absence (AFAIK) of any written clarification from Ops, I guess we'll just have to agree to disagree :-)

 

Cheers

 

John

 

 

[kasper]

The wording of 3.02(9) seems pretty unambiguous to me - it doesn't mention either student or pilot certificate holder.In the absence (AFAIK) of any written clarification from Ops, I guess we'll just have to agree to disagree :-)

Cheers

 

John

Fair enough.

I note that the whole of section 3 is titled and covers training and if you are not training but operating under 2.07 as pilot and you are not restricted by operating outside the aircraft groups and endorsements you hold (and there is no endorsement you do not hold for engine off flight) I am happy to continue flying the sapphire (when its back together) as I have with engine on/off as I choose.

 

 

[bexrbetter]

and only a "we don't know what we are looking for and it will happen accidentally while we were looking at something else" discovery is possible

Stuff like this ..

 

The most powerful proton conductor in the natural world is this jelly found inside a shark's head

 

 

[Garry Morgan]

No, the analogy is incorrect.Water ballast is distributed across the wing and the weight of the water is carried by the skins/spar - but NOT the root attachments. The extra penetration one gets from having water ballast does NOT come at the cost of a degradation in max. rough speed - and in 'strong' conditions', max. rough is a serious consideration. An engine is weight added to the fuselage, thus increasing the loads on the root attachment fittings, and impacting on max. rough..

 

Adding an engine to a Blanik, reduces the fatigue life by about the same as the difference between a full life of winch launches vs. aerotows, or using it as a fully aerobatic aircraft. For the Llewellyn modification Blaniks - almost the only ones flying anywhere - that reduces the fatigue life from 12K hours to around 8k hours.

Sorry i didn't make it clear, that Adding a motor in the design ,not adding one after the aircraft is built. Also it would have to be a retractable motor of it would have a big difference in performance

 

 

[pylon500]

Some Shawnee photos (by request)

 

 

 

 

 

 

 

 

[Oscar]

Sorry i didn't make it clear, that Adding a motor in the design ,not adding one after the aircraft is built. Also it would have to be a retractable motor of it would have a big difference in performance

In something with as much wing area as a Blanik, actually a well-faired fixed engine makes very little difference in performance - provided you know how to design the pylon. That was proven on the Riley conversion. For a Janus, big difference certainly.

 

 

[zodiacpilot]

Thanks for the reply , I,ll look into all the information you provided! all the subsections, clauses etc no doubt seems all logical to you, but I find some of it a bit difficult to comprehend, I'm probably going to have to get advise on the wing loading determination,s in regards to aircraft category's! Thanks again

I believe if you can keep a 'Goat' under 70Kg, it does NOT have to be registered & HGFA PC required to fly it. May be mistaken.

 

 

[kasper]

I believe if you can keep a 'Goat' under 70Kg, it does NOT have to be registered & HGFA PC required to fly it. May be mistaken.

Only if you can call it a rigid framed hang glider ... who is going to do the Fred Flintstone foot launch to make the powers that be happy to allow it?

 

 

[zodiacpilot]

Only if you can call it a rigid framed hang glider ... who is going to do the Fred Flintstone foot launch to make the powers that be happy to allow it?

The one in post 24 gets towed up by trike.

 

 

[kasper]

The one in post 24 gets towed up by trike.

It may well. But if you read 95.8 on powered hangliders under 70kg which is where the legal exclusion from being an aircradtvand licencing I personally would not be happy to rely on it applying to non foot launchable non foot landing aircraft without casa clarification. I'm not HGFA so do not know if they have already got this clarification so if it's out there already it would be nice to have published.

 

 

[AlanB]

CAO 95.8 no longer has any reference to foot launching. Definitions from the CAO:

 

framed hang-glider means a glider that has a maximum empty weight of less than 70 kilograms and some rigid structure.

 

powered hang-glider means an aircraft that would be a glider, in particular a framed hang-glider, if it did not have an engine attached.

 

The HGFA Operations Manual references these definitions.

 

Clarification was sought back in 2011(?) to be able to include wheeled operations like nanolight trikes, such as the Airborne V-lite.

 

The FAI (controlling body for competitions) still has a requirement for demonstrated foot launching and landing, so as long as you are not considering entering FAI sanctioned competitions it's not an issue.

 

You will require a pilot certificate issued by the HGFA.

 

Civil Aviation Order 95.8 Instrument 2011

 

cheers Alan

 

 

[kasper]

Thanks for the clarification.