Aerobatics with the Whisepr

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RudiCronje

Aerobatics with the Whisepr

Post by RudiCronje » Sat Aug 30, 2008 9:53 pm

Hi all. Was wondering since the whisper is a glider, basic aerobatics should be possible. Obviously the engine should be off, but will inverted fligt not cause oil and fuel problems even if engine is off? I was thinkin the Jabiru 85HP engine seems to be a real good contender for the Whisper. R60000 cheaper than the Rotax, but probably more relyable than a Vw option?
Blue skies

RudiCronje

Re: Aerobatics with the Whisepr

Post by RudiCronje » Wed Sep 03, 2008 6:36 pm

Anyone out there with some advice?

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Re: Aerobatics with the Whisepr

Post by whisper » Thu Sep 04, 2008 10:45 am

Hi Rudi
The aerobatic manoevres possible with a motorglider are limited to looping and other pitching type manoeuvres such as wing overs and chandelles. Because of the span, all rolling type manoevres are out of the question. This cuts out most aerobatics. An inverted system on a motorglider would therefore in my opinion be rather a waste of time.
Whilst the Whisper has demonstrated it has the strength (static testing) for most possible manoevres we don't market it as an aerobatic aircraft. I have looped mine (during the controlled flight testing process) and often do wing overs but we do not suggest you see it as an aerobatic aircraft. After all in the right hands even a 747 is probably mildy aerobatic :D

If you fancy some gut wrenching, eye popping inverted stuff I have just the plane for you....see pitts for sale under "market place"

rgds
R

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Re: Aerobatics with the Whisepr

Post by speedy » Thu Sep 04, 2008 11:42 am

Because of the span, all rolling type manoevres are out of the question.
Hmm, why should the span inhibit rolling manoevres?
I think aerobatics with engine off should only be limited by:
- strength of spar / construction (positive and negative)
- agility
- VNE / flutter
Off course a motorglider will never be a dedicated aerobatic plane, but RF-4 and RF-5 show us that it's possible to have some nice diversion during a boring straight long flight 8)
Interesting to know in this question would be something about the spinning behavior of the Whisper?

Greez,
Christian

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Re: Aerobatics with the Whisepr

Post by whisper » Fri Sep 05, 2008 9:23 am

An RF4 can do a reasonable roll but it has a relatively short span and large ailerons designed with the intention of doing rolling manoevres.
I have not seen an RF5 do a roll yet ....(longer span)

On our airshow circuit we had a single astir flown by karl heinz hirsch that did rolling manoevres. It apparently had modified ailerons and aileron travels to allow this. They were however very lazy rolls flown cleverly by a very experienced pilot.

Visit your local gliding club and ask one of them to show you an aileron roll in their 16m gliders and see the look you get :D

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Re: Aerobatics with the Whisepr

Post by speedy » Fri Sep 05, 2008 11:15 am

8) 8) Hmm, I just went to my local glider club and questioned myself: "Is it possible to roll a glider, especially the heavy double-seaters with more than 15 meters span?"
And I answered myself: "Yes, why not, if it's permitted by the manufacturer. I roll the ASK21 (17m) a couple of times nearly ervery weekend and have done this with a Twin-Astir (17m) also. Ok, with these two ships you can nearly have a coffee while completing the roll (~5 sec.), but it works pretty good and we even use these gliders for aerobatic training. It's obvious that you can't use the open-class ships like Nimbus for doing rolls, but nearly every single-seater (15m) is capable of doing rolls. Unfortunately most of them are not allowed to due to insufficient strength of the construction especially for negative G's."
And yes: I have seen RF5 doing rolls, even from inside the plane :D
So, I'm not calling for a whisper as a perfect aerobatic plane, but everthing what's not limited by factors I mentioned above should be possible?

Christian

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Re: Aerobatics with the Whisepr

Post by whisper » Fri Sep 05, 2008 11:53 am

The ASK21 was designed and tested for aerobatics. I assume the twin astir that you roll is the "acro version". I am not aware of an aerobatic version of the RF5 though??

Anyway the bottom line is that the Whisper was never designed with this mission in mind and I would urge those reading this to operate their whispers within the limits of the flight manual as none of these manoevres have been tested.

Who knows maybe we'll make an "acro" model one day - Christian you volunteering for test pilot duty? :D

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Re: Aerobatics with the Whisepr

Post by speedy » Fri Sep 05, 2008 12:05 pm

Who knows maybe we'll make an "acro" model one day - Christian you volunteering for test pilot duty?
:D Why not ... but let me first start building a whisper ... hope soon ... :wink:
operate whispers within the limits of the flight manual
You are totaly right! What's not tested and even not intended in the design should not be done!
The remaining question is: What has to be done in building to make it an acro-light model? Or would this only be possible by changing the design?

Christian

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Re: Aerobatics with the Whisepr

Post by whisper » Fri Sep 05, 2008 1:44 pm

We used CS22 as a certification basis (even though the aircraft is not certified). They require a limit load of 5.3g with a 50% reserve. The wing was designed thus to 7.95g. Our local CAA decided to change the reserve to 100% and therefore we had to show an ultimate load of 10.6g. The wing achieved this (but only just!). We kept both spar caps the same size so effectively the wing is as strong in positive as in negative g. The wings weigh roughly 80kg each. They could be made slightly lighter by reducing the negative g limits and making one spar cap smaller. They could also be built in carbon. We chose to keep the caps the same size to simplify the building process and used glass throughout for cost reasons. For comparison other motorgliders designed to similiar specs have wing weights of:
Dimona 100kg; motorfalke 80kg. It may be possible therefore (with significant re-design, load tests, more cost and quite a bit of paperwork) to get the wing weight to say 70kg. It would require another wing loading test though (In this country anyway). An easier way to keep it light I think is to be very disciplined when building when it comes to fillers, extra flox etc. It is possible to build a rotax powered whisper under 500kg. This is very light for a 10.6g (CS22 based) motorglider. I am attemting to achieve this with the http://www.whisperaircraft.blogspot.com project.
People make comparison of the whisper mass to that of "ultralight" type motorgliders such as the lambada. The design limits of these category of motorglider are much lower and hence they can achieve these very light weights.

It would be possible to design a "whisper lite" to these specs and come up with very low empty mass. This would be a great "fair weather" type aircraft but I would not like to expose it to the harsh conditions that gliders often encounter and the reason why CS22 has quite a tough set of limits (tougher than certified powered aircraft specs).

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Re: Aerobatics with the Whisepr

Post by speedy » Fri Sep 05, 2008 2:06 pm

Seems you misunderstood my last sentence.
I did not intend to make the whisper lighter (I don't like microlights) but to make is motorglider which is capable of light aerobatics - so acro-light-model :wink:
What you tell about the design basis (CS22),the identical spar caps and the wing design beeing calculated to 10.6g is very interesting for me.
10.6g - my god .... even the brandnew and factory produced DG1000 (also designed and certified for aerobatics) has only be designed for 6.4g * 1,75 = 11.2g. In the ultimate load test ist broke at 12.48g. So 10.6g is fairly nice! What's about the wing skin? Is it also identical bottom/top? For which loads has the fuselage been designed/tested?
Can't wait for the information package you wanted to send me ...

Christian

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