Topic: The side-sliping with flap extended restriction

[Rod Blievers]

So where does this restriction come from?

All the Aero Club manuals/handbooks I have clearly prohibit sideslipping with flap extended, but then again they are all written to far more conservative limits than the RAF appears to have used. My RAF Pilot's Notes are without the Limitations Section, the Flying Instructor's Handbook implies that this combination is permissable and my (purchased at hideous expense) Approved Flight Manual has no such restriction.

Over to you...

[Dean Cross]

Rod,
I think it is nonsense. I consider the full flap sideslip part of my arsenal when flying the Chipmunk in winter, keeping the front cylinder head warm while using drag against power( Airline jockey no no). The machine behaves beautifully in this config, one of the benefits of the pressure head(combined Pitot/static)  being an accurate IAS despite the slip or configuration. Even in calm conditions on a short field I like to "induce" a slip to look ahead with the nose so high at 45Kt on a 400Yard strip.
Have I got it wrong ....Please educate me???
Dec

[Rob Merrylees]

I once had pleasure of going for a flight in a Chipmunk with Russell Evans who was at the time senior examiner of airmen (NSW region) with the Australian Department of Civil Aviation.  Russ had considerable experience instructing on the DHC-1 with the Royal Newcastle Aero Club,   the first Australian Aero Club to  utilise the Chipmunk.  His affection for the type which he had not flown for some years was obvious as he asked if he could "take over " for the landing.  Flying from the rear cockpit Russ yawed the nose around and used a gentle sideslip for final approach with the flaps extended.  Russ explained that he used this technique to improve forward visibility when flying from the rear cockpit.

If this technique was good enough for the ledgendary Russell Evans I think that it is safe enough for us all to use.

[Roy Travis]

I have mentioned this point in another post but it is relevant to this discussion.
I have been told by a number of people for whom I have respect on the subject of Chipmunks, not to side slip with flaps extended. The reason being that the flap cables may not take the load. If one breaks you are then in the position of having differential flaps.
I am interested in others views on this point.

[Dean Cross]

What load? If you observe the limiting speed what is the problem?

[Roy Travis]

Declan that is a good point and I am seeking to determine whether the idea that we should not sideslip with flaps is valid or not.
So far I have found that there is no mention in the pilots's notes. I have an original copy with my model 21. On the other hand there is a strong belief existing that it is not good practice.
I first learned of it from the instructor who did my endorsement training, this was supported by the engineer who does most of the work on my aircraft.
The issue revolves around the strength of the flap cables. The physics are a bit beyond my understanding however, is it the case that when side sliping there is more pressure on one flap than the other which may cause one of the cables to fail?
I would be very happy to be confident to side slip so I look forward to being able to get a definative answer.

[Duncan]

I think the confusion is arising from the fact that  there is a perception  of asymmetric load during the sideslip and that there is a chance of more "pressure/load" on one flap than the other that would exceed the flap limit and cause a cable failure.  I cannot see how this would occur as surely there is more pressure to force the flaps up from the relative airflow working perpendicular to the surface in straight flight rather than along the surface in sideslip?

As there is no limitation in any documentation (RAF Pilots Notes Oct 2000 Edition, CAA Flight Manual or Flight Reference Cards) I suspect this is more an issue of owners/engineers introducing their own limits to protect their asset based on speculation.  The only referenced handling issue with flaps is to not raise the flaps with a tailwind component on the ground as there is a risk of the flaps being forced up and the cables jumping from the pulleys.

My own view is that if you observe the flap limiting speed then the greatest load on any surface will be within limits and will not overstress the cables whether the force is asymmetric or not.

However, I am no engineer!!!

[KMY]

During the 1960s The Royal Singapore Flying Club based at Paya Lebah Singapore operated Chipmunks for both flying training and general club use. The instructors were civilians and RAF types who happened to be based in Singapore and as far as I can recall side slipping with flaps extended was not part of the syllabus, in fact we never taught it and never even disscussed it because it was not a safe manoevure. Considering this it seems to me that what Roy Travis is saying makes sense as the penalty for a broken flap cable is too much to pay. It adds nothing to good judgement so why do it??  If in fact one elects to employ such a technique then  perhaps it is an admission of bad judgement.

  KMY

[Duncan]

As this topic has generated significant interest and discussion, I will endeavour to find out a definitive answer.

However a little research so far show the following from UK CAA Airworthiness Information Leaflet AIL00046 dated 14 June 2002:

Long Chord Rudder (de Havilland Modification H 104)

The long chord rudder was introduced at the request of the Royal Air Force to improve
handling during aerobatics. Specifically, the modified rudder enables the pilot to hold
the nose up during slow rolls, and improves control when sideslipping and during a
cross-wind take-off or landing.

Although this does not make mention of flap extension, it does discuss (and by default, endorse?) sideslipping in the Chipmunk.

I will continue to source definitive information on the use of flap and sideslip.

[Bob]

Para 39 page 109 of the Chipmunk T10 Student Study Guide;

" Having practiced the slipping turn without flap you will then practice with full flap..."

http://upload3.postimage.org/54834/photo_hosting.html

[Duncan]

Bingo!

Thanks Bob.  Can you confirm which edition you have?

[Dean Cross]

The risk of assymetric flap is ever present in Aeroplanes.The problem is,it will happen close to the ground, below 1000' in light aircraft.
Large transport types cannot be certified without flap assymetery protection systems, so dangerous is this condition.
We are not afforded this luxury in the Chipmunk so a thorough knowledge of the aircrafts limitations, current and proficient handling skills, coupled with a sound maintenance system, are our best protection.
Unfortunately mechanical systems will fail from time to time,is flying in a single engined vintage aircraft an admission of bad judgement? Many people who are not fully aware of this wonderful sport seem to think so. I meet them in the school-yard every day. Maybe if they took the time to study the subject in more detail,the world would be different.
Let us stick to the facts and not fireside stories    and hope it (flap assym)never happens.

Cannot remember where I read it but "Good judgement comes from experience ,and experience, well that comes from bad judgement!"

Let he(she) who was not born with a empty log book cast the first stone..........................................................

[Bob]

TC/250262 Dec 1969

[KMY]

Declan;

<snip>
Moderated 31 Mar 06.  This post was off topic and degrading into a political and aggressive slanging.

Keep to Chipmunking please gentlemen!

[KMY]

Duncan;

  Stifling debate by exclusion is your prerogative but is it necessary to shout ?    

  KMY.   Absit invidia.

(Reply by Duncan here to allow the thread to continue uninterupted.)

KMY,

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For as long as you abide by the Rules and Guidelines of this forum, you are welcome to post here and endulge in constructive conversation about deHavilland Chipmunks. However any provocative, insulting posts, or any breach of the Rules and Guidelines by any user may result in their account being suspended.

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