DG Flugzeugbau

Aerobatic Test flights of the DG-1000S/18m

 

This article was written by Alwin Guentert of Bruchsal,
        who is one of Germanys experts in glider aerobatics

We needed to run a number of tests in order to set the stakes for a category  "A" certification (aerobatics) of the DG-1000 with 18m wingspan. Therefore I needed to check the general handling of the plane while flying upside down. After checking the general flying characteristics with 20m wingspan Swen and I took off at 10-25-2000 with 18m wingspan and a central center of gravity (approx. 380mm) for a first aerobatics check flight.

The first thing I did was a stall speed check. The plane stalled at 68 km/h IAS in normal flight. It was easy to spin after applying full elevator and rudder. The DG-1000 did approx. 1/4 more spirals after stopping the spin in a vertical flight layer. It was easy to round out the aircraft.

The next things we did were figures of the certification "utility", such as loop, turn, chandelle and lazy-eight. The entrance speeds were 180-200 km/h. The figures proved to be easy to fly and didn't demand special skills of the pilot.

I managed to fly a loop with an entrance speed of only 170 km/h without stalling in the top part.

The rudder has to be applied slowly in the direction of the intended turn until the full rudder is applied at a min. speed of 140 km/h. The DG-1000's behavior is comparable to that of an ASK 21, a Twin - Astir or a DG-500.

Slight rudder against the direction of the turn and a slight aileron movement in the direction of the turn will assist in a clean turn once a vertical flight pattern is established. The turn can then be completed at a speed of approx. 110-115 km/h. After completing these tests to our satisfaction the program came to the inverted flight.

We started by flying a half roll to the left and ended up inverted. While rolling the plane to the other side we noticed a smooth and nice reaction to the controls. The approx. rate of a full (360) role was 11 - 13 sec. / 360, which is comparable to other double seaters.

We noticed quickly that the DG-1000 is capable of a steeper angle of attack than the DG-500. Further we noticed that the stall danger is significantly reduced while flying inverted and the controls are all fine.

The flying characteristics remind me of the ASK 21, which is counted as one of the most stable gliders. The stationary inverted flight was tested at speeds from 110 to 220 IAS. (We will have to calibrate the airspeed indicator for inverted flights before making exact statements about the speeds).
 

We were happily surprised about the little amount of force that had to be used on the elevator control. (A result of the bars and weights in the control mechanism and depending on the applied trim). The stall speed in inverted flight is reached at approx. 107 IAS. It is shown by a strong shaking.

Photo by Altieri FrancescoThe plane will change to an attitude prior to stalling. The inverted flight can be carried on by reducing the elevator and allowing  the plane to pick up a speed of approx. 130 - 140 km/h. The plane can be maneuvered into an inverted spin by applying full rudder and full (pushed) elevator.  A stationary spin was reached after 1/2  turns. The spin can be stopped by applying neutral elevator and slight rudder against the direction of the spin. The plane can be easily rounded out after ending close to a vertical position. First measurements and estimates show a loss in altitude of approx. 120 - 150m / turn.

I also tested a flick roll in order to get a real perspective of the flying characteristics of the DG-1000. Flick roles have proven to be difficult especially in double seaters with good flying behaviors and al low wingspread due to their inability of causing  a dynamic stall. The flick role was entered  at 120 IAS  with a full rudder and elevator. The stall occurred after a drastic rise of the angle of attack. It happened softly and clean. The DG-1000 proceeded to an inverted pattern. The movement could be stopped by reducing the elevator and applying slight opposite rudder. We achieved the normal flying pattern by a half loop as a follow up.

The "pushed role" has to be flown at a higher speed due to the decreased lift. We entered the maneuver at 150 km/h IAS. Pushing the elevator completely forward and applying full rudder will place the DG-1000 into a normal pattern again. It can probably be improved by a slight pull on the elevator in the last part of the roll.

After going through these tests on the DG - 1000/18m I can came to the conclusion:

The DG-1000 is a perfect aircraft for aerobatics - the stable
flight characteristics are favorable for flight training.

The characteristics of inverted flying are a lot better than those of the
DG-500 Trainer (Orion) making it easier to handle than the DG - 500.

The further test flights will show the exact number and amount of allowed figures to be regarded as safe and sound to handle for every pilot. What can be said is that every figure flyable with a DG-500 can be flown with a DG-1000. And the flying will become easier.

Author:
A. Guentert

a little Movie showing a Looping with the DG-1000

Photo by Alexander Tummes

 

Alwin Guentert operates an aircraft maintenance facility
and is the general salesman for the aerobatic gliders "Fox" and "Swift".
Guentert + Kohlmetz GmbH, Bruchsal - Tel.: +49 (0)7251 931060
http://www.segelflug.de/guentert.kohlmetz/swift.htm


A short final note:

It proved to be quite a surprise for us that the DG-1000 is better than DG-500 in aerobatics and about as easy to handle as the ASK-21. We did not expect that because the characteristics of a modern airfoil with it's improved gliding ratio generally comes along with bad flying characteristics while flying upside down. By opting for a more conservative airfoil we have apparently  built an all-round  aircraft, capable of aerobatics and good gilding and flying characteristics.


How to fly Aerobatics with the DG-1000S

If you want to know, how to fly aerobatics with the DG-1000, please have a look into the Flight Manual
under the chapter "Normal Procedures/Aerobatics" No. 4.5.8.
There is described, which maneuvers are allowed.

flugh-1000s-bs-e.pdf

Caution:
The DG-1000S is a high performance sailplane. Therefore the speed increase in the dive, especially in inverted flight is high.
Training aerobatics therefore should only be executed after a rating with an experienced pilot, or if you can master the maneuvers on other sailplane types.

In any case don't try to execute the maneuvers with entry speeds other than those listed.
Do not make full or abrupt control movement above the maneuvering speed VA=185 km/h (97 kts.). At speeds between VA and VNE= 270km/h (146 kts.) reduce the control movements accordingly. At VNE only 1/3 of the max. control movements are allowed.
 

Approved maneuvers

Entry speed 

g-loads 

Spin

-

-

Inside loop 

180 - 200 km/h 
(97 - 108 kts)

 +4,0 g

Chandelle

180 - 200 km/h 
(97 - 108 kts) 

+3,5 g

Lazy Eight 

180 - 200 km/h 
(97 - 108 kts) 

+3,5 g

Lazy Eight 

180 - 200 km/h 

+3,5 g

Stall Turn 

200 - 220 km/h
(108 - 119kts)

+4,0 g


Closing comment from the test pilot to the manual:

From my point of view, the manual can remain in the current issue.
Additional maneuvers shouldn't be authorized as they are too challenging for most of the pilots.

With the authorized maneuvers currently available an in-depth education of acrobatics is possible and even more maneuvers are not necessary.

Considering the potentials provided by the DG-1000, it displaces available two-seaters on the market!

It is fun flying with the DG-1000!
Alwin


In the meantime the DG-1000 Turbo is authorized for full acrobatics as well. It wouldn't have been worth while to do an authorization process for a limited acrobatics version.
Hence, the DG-1000T covers all areas of gliding:

  • cross-country flights with 20m and retractable gear

  • training flights with 18m

  • Acrobatics - full with 18m / limited with 20m

You can find reports from Alwin GŁntert about test flights here.

Brochure of the DG-1000 Family


Safety Advice:

The picture on the right comes from Don Woodward from Australia.
It shows the trial to fly an inside loop. It was not at all a slow roll, because for that figure the DG-1000 is certified with the short 18m wing tips only!

BTW:

In which altitude did they fly?????

 


Smoke Signals for a DG-1000

This definitely is not a "recommendation" of the manufacturer. It is a proposal only to copy it on your own responsibility.

We were asked by our customer Bastian Koppen, if it is possible to install smoke signals for aerobatic flying on the wings of a DG-1000. We did not refuse this proposal.

Now he wrote:

Dear Mr. Weber,

here you can find some photos attached. They were made last weekend during an event at our airfield  in "Bergneustadt Auf dem Duempel/GER".
Furthermore I have attached some drafts, which I already had sent to Mr. Dirks before.

The picture shows the device for the right wing.
The signals are manufactured by "Comet" and are named "Rauchsignal SOLAS 74/88".

Greetings Bastian

This is the device:

Drafts

and the result. Isn't it beautiful?

 


Mirror Flight

Here is a spectacular picture from the Lasham Gliding Club / UK.

Two DG-1000 in a mirror flight. It was astonishing for the pilots to find out that the upside-down flying DG-1000 had a better glide ratio than the normal flying one with turbo engine extracted.  They could of course have retracted the engine a little bit until both gliders have had exactly the same glide ratio, but the stunt had probably already produced enough Adrenaline for the pilots as well as the photographer Paul Haliday.


Other Articles of Interest:

 


DG-1000 - the development

 

DG-1000 - Impressions and Comments

 

Derek Piggott flies the DG-1000

 

DG-1000 Trim Box

 

DG-1000 T - the sustainer version