Topic: Wikipedia Chipmunk entry

[Chippydriver]

I notice on Wikipedia (not that I believe anything written there) that 22A's are banned from aerobatics in the UK.

Where might that statement have come from? Was there ever a proposal to ban 22A's from aeros, or indeed was there a period of time when they were banned? Could the person who made the entry be confused with Lycoming machines?

Nothing placarded or in the flight manual of course, so I shall continue to do them!

[Mark]

I was always led to believe by my aerobatic instructor that by taking out the ribs to make way for the 12 gal tanks in the Mk 22 the wing no longer had the torsional stiffness for aerobatics. Having said that, like yourself I  have never seen that written in any flight manual. I suggest this is a question for the chaps at DH support to provide the definitive answer, particularly since Chipmunk airframes are not getting any younger.

[Nigel Stevens]

I have just done the modification on the wing to take them from 9 gallon tanks to 12 gallon tanks. There is no permanent removal of any rib involved, simply the change of the tank liner from a 9 gallon to 12 gallon in the same space, with no alteration of the tortional stiffness of the wing. The liner is held in place by a handful of rivets and makes no contribution to the tortional stiffness. You have to remove the root rib, obviously, to do the work, but you put it back in afterwards.
In fact there is an enourmous void behind the 9 gallon tank. There is even space for a bigger tank probably space for up to 15 galllons although the liner and the tank do not exist for this. (A pity, IMHO)
I'm sure the historians will correct me but I thought the original design, from Canada, had 12 gallon tanks and this was reduced to 9 gallons at the request of the RAF for the T Mk 10. Comparing the parts all dH did was to shorten the metal liner and put in a smaller rubber tank.
I wonder if the Wikipedia writer was simply confused by the ban on aerobatics in the UK civil machines not fitted with the anti spin strakes?
Nigel

[Chippydriver]

Like my abandoning post, fascinating stuff. Will give Bill Taylor a call nonetheless. Cheers chaps

[john henderson]

in my opinion, Wikapedia is thoroughly unsound as a concept and is a dangerous source of mis information.

If I read the flight manual for my DHC1 22A, it sets out in the handling section that to carry out aerobatics, the aircraft must be fitted with "spin strakes" and must be placarded in the cockpit as follows: "SPIN RECOVERY MAY NEED FULL FORWARD STICK UNTIL ROTATION STOPS (also see flight manual)".  If it deos not have spin strakes, then the placard must be worded "AEROBATICS AND SPINS PROHIBITED".

This is the only limitation in the book!  As far as I know all chipmunks today have the strakes fitted.

The Mk 22A aerobats in the right hands (- not sadly in mine I hasten to add) extremely well.  No ribs are removed in converting to a 22A.  the wing is the same and only a baffle is moved to support the tank bladder in the appropriate place.

The flight manual devotes some 3 pages to handling of the spin, but leaves all other manouvres to instruction.

John h

[david burke]

The Portugese Air Force Chipmunks were not fitted with spin strakes - there are a few Chipmunks around the world flying without them. 

[chipmunkflyer]

Greetings,

I can confirm from the Type Record that in Feb 1953 a weight increase for the mk 21 was approved to 2100 lbs and at the same time the increase to 12 gallon tanks was also mentioned. It specificallly states " it is estimated that there is no effective diminution of either strength or stiffness of the wing.
The weight increase of 100lbs will mean a reduction of 5% in the reserve factors on the wing as quoted in the Type Record, but the minimum is still greater than 1.0 and the ultimate load factor of 9.0 will still be achieved.

Fly safely

Best

Rod

[Rod Blievers]

David Burke is correct - there are many (in Australia possibly the majority) Chipmunks happlily flying without the anti-spinning strakes. The are quite a few short-chord rudders to be seen too.

The "Glen Caple" metal 12 gallon tank modification does entail the removal of a rib, yet the authorities here still approve aerobatics in aircraft fitted with the strakes. The tank capacity in reality is understated (I have measured 12.7 gallons in mine) but for certification/stress and rigidity calculations  they had to have the 12 gallon capacity.

Regards,

Rod.

[Fitzy]

In reply to Nigel Steven's query I can confirm that the early model Chipmunks from Canada had 14 gallon tanks.  We have recently had some new bladders made in Canada for our aircraft.

Regards Mark Fitzgerald