Dynamic Thrust Testing

Dear All
Thank you for including me in the forum. My name is Nick, I am a 2nd year mechanical engineering student at Manchester Metropolitan University in the UK. I am leading a small group of students who are designing a model plane to take part in the 2018 BMFA Payload challenge in June. We are looking to test the static and dynamic thrust of an innovative motor/prop combination. The wind tunnel at our University can only accommodate a propeller diameter of up to 11 inches (280mm) and we would like to test up to just under 18 inches (450mm). Before I start writing the risk assessments for strapping our test rig to the roof of a car, I thought I should enquire to see whether any model plane experts are aware of the location of a larger wind tunnel which might be available for hire.
Many thanks for taking the time to read this post.
Kind regards
Nick

Hmmm....You'll need a long mounting bracket if you want to keep the test vehicle outside of the aerodynamic field of the car, so good luck with that one.

As far as wind tunnel is concerned, have you considered or looked at Farnborough? Or even considered designing your own?

Nick Try Liverpool U or John Mores U . I seem to recall one of them had a tunnel. It may have been a temporary one but could be connected to the university Air Squadron.. Might be worth an ask. Good luck John /OT

Thanks for the advice Andy. I will look at Farnborough. Certainly constructing our own is a possible solution that I have not investigated yet.

There used to be one at the Manch Uni outbuildings at Barton airfield, Eccles, not too far from where you are.
BUT - I've not been in for at least 15 years, so it may have gone by now.

Oh yes I forgot about that one. Well done

Nick
Even with a wind tunnel designing a prop is not easy as its design has to be a compromise between static and dynamic thrust unless of course you go for variable pitch but even then the actual twist in the blade itself is still a compromise between the ideal fine and coarse pitch settings.
Props for model planes have been around for a long time so the chances of finding any significant improvement must be relatively small.
I have followed several of the payload competitions and it seems many of the winners end up using a pretty conventional layout where the execution of the build (particularly its structural efficiency) and reliability seem to end up the key factors rather than any particular innovation.

My own experience in designing a plane for electric endurance showed that structural design to improve the air frame to payload ratio was more significant than simple aerodynamic efficiency but finding a 'right' balance between the two required much building and testing.

I appreciate it would be inappropriate to divulge any construction details at this stage but it would fascinating to know how you get on in the competition.

It is, of course, also a major advantage if your chosen 'pilot' can actually fly a radio-controlled model aircraft - particularly one that is over-weight, under-powered, and badly out of trim! (as many entrants are!)
[badass]

Quorneng
Thank you for taking the time to respond to my post. I am not worried about divulging any broad construction details if they lead to good advice! None of our team members are experienced aircraft modellers and while we understand the benefits of going with a tried and tested recipe, we would prefer to try something a little different to maximise our learning experience rather than try to reverse engineer a previous winner.

In terms of Powertrain, essentially we are looking at adapting an RC helicopter rotor assembly to offer a variable pitch push type set up. With limited information available we want to test our design in a wind tunnel to get some static and dynamic data. Has anyone had any experience of trying this?

Air frame to payload ratio and structural integrity are also high on the agenda. I am happy to regularly post updates on here as we progress through the project. Although the team is competitive in nature we also accept that our limitation is our experience and any pearls of wisdom would be gratefully received. If any competitors are snooping a wish to copy our design then great we must be on the right lines!

Thanks again

Nick

Wow! Using a helicopter rotor head to provide variable pitch is very innovative!
However I do fear a helicopter head is rather more complex (heavy?) as it has to provide variable pitch to control the helicopter in pitch and roll as well as 'collective' which for a fixed wing aircraft is the only bit you need but it is an interesting concept and I applaud the approach you are taking.

However don't dismiss re-engineering a previous design too quickly. It is what every aircraft manufacturer has been doing since the very beginning!
Nearly every 'great' aircraft in history, model or full size, uses existing technology. There are so many variables in designing a plane the innovative bit is understanding or (even guessing from experience) how to apply the technology in a way that creates a significant overall improvement.

Are the rules you are working too published? or if not could you give the competition's major parameters like size, weight, power and pay load It might help us understand just how 'innovative' you might have to be to be successful.

we are looking at adapting an RC helicopter rotor assembly
I have no desire to pour cold water onto your plans, but I think this is the wrong way to go about the power system. Helicopter rotors are quite low-revving, and very large diameter, compared with a 'normal' propeller. There are commercial variable pitch props of more sensible diameters already on the market, that would be worth studying how it is done, but you also need to consider the centrifugal loadings on the prop blade hubs!
Having such a large diameter prop is going to need very long undercarriage, to ensure ground clearance, and this is going to impose considerable structural torsion loads to the airframe during the taxi, take-off, and landing, probably leading to premature collapse.
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None of our team members are experienced aircraft modellers
As I put previously - you really need someone who is already an experienced model flyer, to do the actual piloting, and guide you in the design and construction, or you are going to destroy a lot of airframes through silly mistakes! (No, I'm not volunteering!)
Flying r/c model planes looks very easy, but it is a skill that has to be learned, and cannot be done overnight, it takes many hours of practice to achieve a level of competence that can cope with a 'weird' model, with eccentric behaviour!
Any flying craft is a balance between power, weight, wing area, wing lifting section (therefore efficiency and drag), control areas, moment arms, and balance point. Alter any one of those, and it affects all the others to varying degrees.

First off, Nick, thanks for posting here and sharing your project with us. It should give a fascinating insight into modern design thinking and realisation, albeit by non-aeromodellers.

Second, a word of warning. The Forum members here have a vast practical experience of practical model flying that may provide some useful opinion....the downside is that it may not be fully correct. I'll leave it to you to decide what is good advice and what is not! Bottom line is to not take everything at face value and make sure you test the ideas before you put them into practice. Notwithstanding, it's essential that you get a competent RC Model Flyer to test and demonstrate your machine!

On a personal level, I believe you've hit on the best area for significant improvement in the model flying world - propeller efficiency. Model aircraft propellers are notoriously inefficient and any way you can find to improve that efficiency will be of interest to most duration modellers. There has been some work done in recent years in developing Larabee Propellers for models, which proved popular for a time - www.volareproducts.com/PFFT/LarrabeePropDesign.pdf . If you can improve on that formula, then you are in with a chance of significant performance increase.

I'll follow your progress with interest!

Hi Nick, sounds a lot of fun. Being a Loughborough uni man, I can't actually hope you win... But I'll give you my best advice nonetheless. As Andy says, take all advice and double check it. If its part of your course, your write up marks are more about academic rigour than project success. If you make a decision justify it, if you make an assertion, reference it, test it, or identify it as a risk.
LU Aero certainly have a tunnel big enough. They would charge industry a fortune to schedule time in it. In your case, I don't know, getting the busy academics' attention for long enough will be your biggest challenge. I recommend reading the school website then phoning the school office and go from there. If you rely on emails, don't bother.
Two other options. Coventry (Lanchester) Uni have a smaller recirculating tunnel that is between 9 and 18" iirc. But you're missing a trick in that the main point of a wind tunnel is to be able to test a scale model of the planned device to de-risk testing the full size. You may already have this in plan using your own tunnel? At half scale, you should be able to measure any 'effect' due to the novel design fairly clearly especially in a direct comparison.
Finally, to pick up a point above, a story. In 1971 the mighty Rolls-Royce Ltd declared bankruptcy because the novel carbon fibre fan blade on the RB211 delaminated under bird-strike testing. The bankruptcy was to get out of contractual obligations with customers to whom the performance benefits of the new carbon blades had been sold. Thankfully, an all aluminium version had also been designed (I suspect that was kept quiet until afterwards :ohmy: ). My point is, you could design a conventional motor prop combo that can be easily installed in the case the novel design fails in the end. You do actually want to win, bugger the 'taking part' nonsense. If you give size and weight, lots of folk on here will offer well experienced advice, including airframe design.
Good luck, N

When I had finished my metalwork projects at school I was given the run of the woodwork shop if it was free. I spent many an hour carving props .Some of them looked to be great on the bench but were crap in the air.I learned a lot but didn't take notes so couldn't evaluate them properly .It was pure trial and error stuff. However I did end up with a collection of them but I only have one left now.A rough airfield saw them off. . One consideration I found to be very important was the weight of the prop. But there seemed to be no hard and fast results I could draw conclusions with. It really was suck it and see stuff. However the very best tip I I can give you is be meticulous with balancing because vibration is a killer of performance as well as the model Anyway good luck