Testing DE Stubby for Payload Capability and Canted Gear Consideration

[Tom H]

It seems that there have been several DEs built and flown, but I have seen only a few reports of flight testing, and very limited info on the performance when carrying a passenger. 

We've been flying DE Stubby for a few years now, but have never carried a passenger or tested it for that possibility.  One reason is we fly it from a short grass strip with trees and wires at the ends, and too much "progress", i.e., houses, in the surrounding area.  We always planned to take it to a longer runway with open area around, and we finally got it done Monday.

We flew it to a not-too-distant airport with a paved 5000 ft runway.  The weather included sun, some clouds, temp around 80 degF, dewpoint around 60-65 degF, winds around 0-3 kts., with density altitude reported at around 1500 ft.  We took note of fuel quantity, pilot weight, and added weight, 40# at at time, and flew the pattern, noting the climb rate.  Here is what we found:

Pilot alone, 230#, with around 10 gal of gas, total payload wt about 290#, Stubby usually climbs at 600-800 fpm, depending on weather.

Pilot, w/ 40 lbs wt, w/ 48# fuel, total payload = 318#, tailwheel weight loaded was 130#.  Takeoff roll to a three point takeoff seemed about normal, climb rate varied from 300-600 fpm; discounting thermals, etc., I would call it around 500-600 fpm.

With total payload = 352#, climb was about 300-400 fpm.  Tailwheel wt was 140#.  TO roll to a three point takeoff was longer, but not too bad.  Tried Pwr Off stall, just mushed.  This verified our Wt/Balance numbers that showed the CG was not aft.

Total payload = 389#, climb was about 250 fpm.  Tailwheel wt was 145#.  TO roll was longer again, lifted off, this time from a wheel takeoff.  Needed to keep in ground effect until more speed gained.  Stall test resulted in a mush.  Ground observer said rate of descent was noticeable.

Total payload = 426#,  tailwheel wt was 151#.  TO roll was definitely longer, lifted off from mains, carefully gained speed, carefully climbed out.  ROC was maybe 100-150 fpm.  I flew around after getting some altitude and it handled fine; seemed more stable.  Did not fool around with stall test.  Turns to final made with extra speed, and landing made a little faster than normal to keep sink rate low.

We had another bag of rocks to try, but decided that the last test was about the limit for that day.  I think it might fly with 460# payload or so on a nice cool day, but probably just barely, like the final test above.  Before anyone says it, Stubby is heavy at 564# empty, with an engine with all the accessories, a panel with a bunch of instruments, etc.  If we could shave off 100# or so we would be in a better position to carry two up!

Why did we measure the tailwheel weight?  Stubby was built with the canted forward main gear, due to concerns at the time that the airplane was too tipsy during ground handling.  With Stubby, after making adjustments to get the flying CG in the correct spot, we always thought the tailwheel weight was excessive.  On the ground, no pilot, the tailwheel weight is 81#.  With a pilot, the weight is probably around 125#.  As the tests show, the tailwheel weight gets to be really high, and there is no danger of tipping over forward.  In fact, there is enough load that the tailwheel swiveling was getting slightly jammed, resulting in practically no directional control at slow speed using rudder pedals alone.  Brakes were needed for turning.  At higher speed, the rudder authority was fine.

The conclusion we made is that the canted gear is not needed or desired for Stubby.  Some day we may modify it back to the straight gear legs.  Some day.

Hope this helps with the knowledge base of DE airplanes, and is useful to those building or flying the DE design.

If any others flying the DE have experience with carrying passengers or add'l load, tell us about it.

Tom H

[MrG]

Good Info Tom
I hope to be flying again by weekend if the flying gods are with me (Checking for smoke on the new wiring and
just finishing some painting)
I have been up at 1020 lbs and even thou heavy it did ok - ive done 2 flights like that but only short  hops
Simon recons we climbed out around 300 fpm, i have better instruments this time so can collect better data
Here we have to write all this in to a manual - got some work ahead
From a power of engine i do believe i have a bit more HP than than the aerovee engine as we have dynoed engines
with similar specs to mine
Hope to have you some data coming in soon as we run in the new engine

[Tom H]

Mr G, looking forward to seeing your results.

I had meant to mention it - our engine is a Great Plains 2180 (not Aerovee), with a Performance Propeller 62x26.  You probably do have more power than we do.

You all have heard it often - build it light.

[rfeenstra]

I've carried well over 400# (pilot, passenger, partial fuel). TO roll is definitely longer and climb considerably affected.  Don't have a vertical speed indicator so not sure what the numbers are.  BUT, I have a Continental A65 with a 70" prop up front.  Considerably more pulling power than the VW, but also a bit more weight. By myself, i take off from long grass in 3-400 feet if try.  I won't take a passenger from my short field.  I fly to a paved or much longer grass strip.  With passenger, TO is probably in 5 to 600 feet range on pavement with a much slower climb out.  I would guess 3 to 400 ft/ min. Alone probably 600.  this winter will see major changes to the fuse, particularly the tail.  I'm going to extend the tail by about 2 feet and add some shape to make more like a champ.  With the added wing span because of the cabin,  and about 12# lead in the tail to get the CG back,  I'm hoping the added length will actually reduce weight slightly and improve stability.  We'll see.  After 3 summers of flying, it's time to make changes!

Part of the reason for adding some shape is to smooth the airflow back to the tail.  I experience some buffeting (not flutter) in the controls when cruising around 60.  I suspect it is because of the added cabin and the way the center section of the wing has a gap between the trailing edge and the fuse.  any thoughts are appreciated!  It'll be fun to experiment.

Hey, there may be a tail section for a DE available for sale!

[Tom H]

rfeenstra, no doubt your 65 conti has more pulling/climb power with that prop diameter.  Added wing span is probably a big help, too.  Your experience sounds good/workable.

I can see where the tail could get some turbulence from the cabin shape.  Our DE has a cabin, but not squared off like yours, and I don't recall experiencing any buffeting.  If we get around to it, I would like to add some streamlining shape to the rear of our cabin to further smooth the flow, and maybe reduce drag.  The two foot extension should help with getting CG more aft, and allow weight reduction.  Will be good to hear about the end result.

I think these various changes we are making are overall good for the design.

[Dan_]

Topic split... 

[Tom H]

Thanks, Dan, for the split.

Now, all you DE flyers out there, send in some flight experiences!!!!

[MrG]

"Thanks Also Dan " this is good data and really heaps to keep a clean thread so others can use or refer to it

Aussie - DE 8866
Dry weight 594 lb ( 270 kg ) we need to re do W/B
30 L fuel        48 lb (22 kg ?)
ME Pilot       200lb  (90kg)
Cruise 2930/2950 rpm = 58 knts / 67mph
Cruise 3050  rpm          = 65 knts / 74 mph
EGT 1200 f
CHT  300 f
Glide Slope 4.21:1 Engine Off  this will get better i hope with the drag mods on wing struts and other tubes

@3080 RPM (about 46 knts / 53 mph) 650 fpm timed and distance over 60sec and consistent with 3 attempts
We are still playing with carby (bing CV of a 912 rotax) and not making 100% power yet and its a brand new engine with 1.9hrs on it
We also have clipped wings about 8 inches shorter per side ( Higher Wing Load and Drag )

@Tom what speeds to do use when climbing for Rate and Distance, whats your RPM ? for full throttle in climb and what do you normally use
whats your static on the ground, do you know EGT/CHT numbers

I may not get another chance now due crappy weather for a week.
@Frank Johnston dam this prop is loud - Love it, they definitely know its me flying - the old engine after run in did get up to 2350 and did pull big time
The photo attached is a better look than last time i went flying.

[Dan_]

That was a quick turn around there..!

[Tom H]

Mr   G asked:  "  @Tom what speeds to do use when climbing for Rate and Distance, whats your RPM ? for full throttle in climb and what do you normally use 

whats your static on the ground, do you know EGT/CHT numbers "


From some early tests, DE Stubby's best rate of climb (Vy) is about 60 mph, and the best angle of climb (Vx) is a bit less, about 58.  We haven't done any recent testing of these numbers.


Static on ground is usually 3100 - 3200, seems dependent on weather conditions.  Climb out is usually about 3250 range, full throttle.  Cruise (3050 rpm) EGT is adjustable by mixture on the Zenith Carb from the cockpit, usually I set it a bit rich, maybe 1200 degF., but I can lean it out to 1400.  CHT is usually around 300-350 degF; lately it has been only 250, but I suspect an error in that system.  Oil temp can get all the way up to 180-190, with the whole cooler taped over.  I "un-tape" it some, and show around 170 degF oil temp usually.

[MrG]

Big thanks for that - we cant lean in flight so we doing Jetting changes so that will help heaps, im not getting the climb out rpm
as high as yours at the moment ( just need some good weather to test - but did get an extra flight in last night ) to test
Thanks Tom
hope to have some more stuff on weekend
Are the zeniths still manufactured (new) ?

----  
Extra From tonight's flight
Got my EGT up were it runs a bit better buy playing with main jet - really starting run nice (2.5hrs) on it a bit to go yet b4 it loosens up

[Tom H]

We purchased the Zenith carb from Great Plains with the engine kit, maybe 4-5 years ago.  As far as I know, they are still being manufactured.  We have the Zenith mdl 14998, which was Great Plains cat #2122, I believe.  Don't know what they are selling now that  GP ownership changed.

[MrG]

A bit more info after this afternoon's flight
Weight:  850lbs
3200 rpm = 70 knots / 80 mph
3040 rpm = 60 knots / 69 mph   my cruise RPM

Ill get some climb data in two weeks after we finish running engine in 
i did notice for me it liked 45 knots / 50 mph for climbing - i don't have an AIS normally do it of video *(time / height)

[Gjsteube]

What have you found for your Glide Ratio, Power off and Power on stalls?

[Tom H]

Gj, I don't really know the glide ratio of DE Stubby, but, when you idle the engine down, set up around 60 mph, the airplane does not go real far, but does not drop like a rock.  Sorry, that is about the best way I can describe it.  I usually come into final a bit high, knowing that it will come down fairly fast, and, if necessary, I can slip it to really lose altitude.

Power off and on stalls are mostly mushes.  I think this is due to our CG being a bit too far forward, even after a lot of work to get it to where it is, which is around 26% aft of leading edge with me flying.  I can get a power off stall break if I pull back quickly and hard, but just barely.  Search the list for CG Stubby DE, and you should find a lot that I wrote about our testing and changes, and the conclusion that the flying CG should be around 28-30%.