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Trials beginMeanwhile,de Havillands had received a contract number 6/acft/2525 for the loan of a Chipmunk aircraft to Boscombe Down for trials and examination (performance & landings only) in which it noted that the aircraft was not up to full T8/48 specification. As such,`KDN duly attended A & AEE from June to August 1948. The opportunity was also taken to carry out radio acceptance trials of the STR 9 VHF equipment mounted in the forward cockpit behind and below the instrument panel and the 24" whip aerial mounted on top of the fuselage some 16" forward of the tail fin. The range of the installation with the station behind the aircraft was approximately forty miles before reception in the aircraft was lost.
However, this was regained upon turning ninety
degrees, the ultimate range being found as sixty five miles.
It was therefore suggested that the aerial be moved to an underwing position in order to overcome the shadow effect of the fin and a letter giving the results of these tests was sent to the MOS on September 7th.
Following this visit, various modifications were carried out to both
`KDN & `JVD including widening the canopy at the top for increased
headroom facility and also ballooning of the side panels in the rear
cockpit for improved vision for the instructor. The opportunity was
also taken on `JVD to alter the rake angle of the undercarriage thus
moving the mainwheels forward by four inches for improved ground
handling.This also reduced the possibility of nosing over during
taxying. The flying controls also came in for some modification on both
aircraft with a chord increasement of two inches on the elevators and
the angular travel increased to give 38.5deg up and 17deg down.Rudder
travel,often a criticism with regard to aerobatics & sideslips was
also increased from 27deg to 34deg each way.
A similar, but not identical contract(7/acft/3745) was issued verbally to Fairey Aviation in respect of a Primer aircraft with Cirrus Major 3 engine for trials and after lengthy discussions specification T17/48 was agreed in early August and appeared officially dated October 10th 1948.
Following the return of `KDN from the preliminary handling trials, de Havilland now had a firm plan to work to and advised MOS on the 13th. of August that Chipmunk G-AJVD was being prepared to the stated specification required but with a Gipsy Major 10 engine; therefore, an additional part to the earlier contract was issued for a loan period of up to three months for examination and complete testing and included the use of `KDN for spinning trials.
With the issue of the various specifications, the Director of Contracts sent out letters of invitation on July 22nd. for the submission of a formal tender number 452009 to contract 6/acft/2508 for seven hundred and fifty aircraft to be completed within four years at a production rate of two hundred per year. Both companies returned their tenders well in time for the MOS meeting on 23rd. August, the de Havilland tender contained few changes from the earlier quotation with the exception that the price per unit was slightly lower at £2100.
The cost of the Primer however, had risen slightly due to some revision of the design to meet increased strength factors.They also advised that some difficulties had arisen over the applicability of T 17/48 and Air Publication 970 to the Primer aircraft in respect of crash proof tanks and jettisonable cockpit hoods and the fact that these requirements had not been notified. Therefore, the tender was for the aircraft as previously stated in May 1948 which was £2150 for the first one hundred aircraft reducing to £1380 for the last two hundred and fifty machines.
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