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Diehl XTC

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danko9

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Sep 12, 2015
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CHICAGO
Greetings Everyone,

So I just came across this beautiful airplane.

I am trying to figure out any and all lessons that were learned from the design of the XTC, and I thought that this illustrious group might be just the one to ask. Was it well-liked by pilots? Were there any glaring flaws? I wonder how easy it would have been to catch an edge flip it while landing on water? Are there any obvious improvements that could be made? Also the wings are much closer to the water than on most seaplanes. I wonder how bad a strike would be at the very slow landing speed this thing has, given its huge wing?

I read that some pilots said it was unstable in pitch; however, it seems like later versions fixed that. I am not really sure though. I also read that the original 25 hp engine was not enough.

Here is a pristine one for sale. The listing has the best pictures I've found:
Diehl XTC Amphibian Microlight | Trade Me



 

Topaz

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The XTC was one of a number of "canard" (tail-first) designs that came out at the height of the ultralight craze. If memory serves, this one appeared on the market within a year or so before FAR Part 103 came out, which regulation defined what an "ultralight" is in the United States. Again, going from memory, I believe the XTC was (and is) too heavy to qualify - empty weight must be 254 lbs or lighter. I believe that seaplanes and float planes get an extra 30 lbs. allowable in the empty weight, but the XTC may not qualify even under that looser definition. It may also have a "stall" speed to fast for the 24 knot maximum of Part 103. If you intend to fly this airplane as a US "ultralight" under Part 103, you may want to spend some attention to if it qualifies here - my memory is that it does not, although I may be wrong after so many years. The New Zealand microlight category is not the same thing, is less restrictive than Part 103, and is not transferable to our regulation.

The only other way it could be operated in the United States is as an Experimental aircraft. You'll want to check with your local FAA FSDO to see what is necessary to bring an E-Amateur-Built aircraft from another country into ours, and demonstrating that it qualifies for E-AB status here. Otherwise you're restricted to one of the other Experimental categories, and they severely restrict what you can do with the aircraft. Those latter probably aren't the way you want to go.

I remember very little about the XTC's flight characteristics - I've never seen one in person, let alone flown one - but I recall that, like many canard aircraft of the period, the early ones got a little squirrely in the stall. I think that was fixed later on. I seem to recall some comments about directional stability (yaw), but don't recall any details. You might get lucky and find a former owner here on HBA, or perhaps there's a Yahoo group (or archive of a group) where you can get more information.

Wish I could help more, but it's been a very long time since I've read anything about the aircraft. The listing is correct - this is a fairly rare bird.
 

WonderousMountain

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Apr 10, 2010
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2,143
Location
Clatsop, Or
There were some great concepts during the birth of the ultralight category. Some seemed simply to disappear without cause.

Any pictures of later versions?

LuPi
 

Topaz

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There were some great concepts during the birth of the ultralight category. Some seemed simply to disappear without cause.

Any pictures of later versions?

LuPi
I think the listed one is one of the later examples. I don't recall the original XTC having any taper on the canard.
 

danko9

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Sep 12, 2015
Messages
4
Location
CHICAGO
Very helpful Topaz, thank you! I am mostly interested in it from a design perspective; however, maybe buying one would be a good first step . . . Hopefully a unicorn will unveil himself in this thread soon.
 

Cresco750

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Nov 8, 2015
Messages
1
Location
New Zealand
Hi, sorry to chime in on an older thread, but that's me and my XTC so I guess maybe I'm the Unicorn you were hoping for? :)

I'm not the original builder but I'm happy to try and answer any questions.

In answer to some of the above:
Is it easy to catch a wave and get into trouble on takeoff or landing? Yes and no. I limit water ops to virtually flat water (flatter the better). If the waves are beginning to form a tiny white-cap I consider this to be at the upper end of the safe operating spectrum. Because the wings are very low to the surface it could be assumed that they could catch a wave but I have not found this to be an issue due to operating on flat water. If you do a search on YouTube you will find a few rather poor quality videos of me flying. On the video of the takeoff you will notice the hull slap the water three or four times just as it accelerates up onto the step. This is a known characteristic of the XTC. Its not what I would term a 'pourpoise', but a gentle nod or slap of the water.
There is a reference on the web somewhere that the XTC is very 'pitchy' in flight. After contacting the designer, Dan Diehl I came to the conclusion that this was a reference made by a journalist back in the '80's who flew one of the early prototypes. The early ones had a completely different canard, which was quickly changed to a new arrangement. I've flown a few different canard U/L's and they do all seem to share a common characteristic; they can be over controlled in pitch of the pilot fights the aircraft in turbulence. My personal thoughts on this one is that because the canard is right in the pilots field of view, he sees that part of the plane bobbing up and down in the thermals and instinctively reacts with opposite elevator in an attempt to level the aircraft. The reality is that not only does the pilot invariably feed in way too much control input, but that input may in fact be out of phase with the aircrafts movement, thereby actually aggravation the situation. I've found that if I let the stick go in light turbulence the XTC will actually fly along quite smoothly.

I have not found any adverse characteristics with the stall (mush), or there being any yaw control issues. In fact, the twin rudders are extremely effective as are the spoilers on the wings.

It really is a fun aircraft to operate off the water. Unfortunately I just have not had time to utilise it for a couple of years now, but I hope to get it out again this summer.

Regards
 
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scottperk

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Mar 5, 2011
Messages
25
Location
Atlanta, GA
I would like to add some USA FAA perspective. The XTC was the most advanced and best
performing FAA FAR 103 compliant seaplane/amphib ever designed and built. Part of the
reason is as stated it was created before the FAA settled on adjustments to the FAR103
ultralight regulations and as a result the XTC was "way under" the weight limits allowed
which provided for the ability to make many enhancements to the plane without making
it too heavy "illegal". In fact the earliest versions came in under the 254 pound weight limit
before the FAA granted a fifty pound allowance for single hull based fuselages and an additional
24 pounds parachute allowance. There was a gentleman in California who removed the
retractable landing gear ( what other UL do you know that has those ! ) to gain back
weight ( as a pure seaplane) and was able to add a Rotax 503 engine and forward
ballast for balance and still was legal in the USA ! That staggering amount of thrust
resulted in dramatically short takeoffs and climbouts when desired.
The XTC if made available today would still be ahead of its time. It had a NASA designed
airfoil (E749) and as an all composite structure,
it was impervious to water.
here is a link to the worlds largest collection of XTC photos....
made available by the designer himself

https://photos.google.com/album/AF1QipMAZnvo1PrhBeq3CQae6gOkx5TaAAFujJ81kkE

If there was one UL aircraft that someone would leave me in a will among hundreds in
the world I would pick the XTC ! For the last 15 years not a month has gone by where
I dont think how I could recreate this marvel.
 

renxxx1981

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Joined
Jan 5, 2013
Messages
40
Location
italy
I would like to add some USA FAA perspective. The XTC was the most advanced and best
performing FAA FAR 103 compliant seaplane/amphib ever designed and built. Part of the
reason is as stated it was created before the FAA settled on adjustments to the FAR103
ultralight regulations and as a result the XTC was "way under" the weight limits allowed
which provided for the ability to make many enhancements to the plane without making
it too heavy "illegal". In fact the earliest versions came in under the 254 pound weight limit
before the FAA granted a fifty pound allowance for single hull based fuselages and an additional
24 pounds parachute allowance. There was a gentleman in California who removed the
retractable landing gear ( what other UL do you know that has those ! ) to gain back
weight ( as a pure seaplane) and was able to add a Rotax 503 engine and forward
ballast for balance and still was legal in the USA ! That staggering amount of thrust
resulted in dramatically short takeoffs and climbouts when desired.
The XTC if made available today would still be ahead of its time. It had a NASA designed
airfoil (E749) and as an all composite structure,
it was impervious to water.
here is a link to the worlds largest collection of XTC photos....
made available by the designer himself

Google Photos

If there was one UL aircraft that someone would leave me in a will among hundreds in
the world I would pick the XTC ! For the last 15 years not a month has gone by where
I dont think how I could recreate this marvel.
The link seems not working for me too... I'm going to see one XTC next week and I'd like to get as much info as possible. Good to read the comments here... Reassuring!
 

WINGITIS

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Jun 24, 2020
Messages
346
Location
Wellington, New Zealand
Hi Folks

That link was from a TRADEME auction site here in New Zealand.

Its like EBAY or Craigslist, so was for sale, after the auction the listing gets deleted after a set time period.

It could have been this New Zealand registered one!?

 

cluttonfred

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Fort Walton Beach, Florida, USA
The photo link works for me and the Diehl XTC looks like a great candidate for a revival around a modern paramotor engine. The Waspair Tomcat's high-wing canard would also be an interesting configuration for a new design if you used sponsons instead of tip floats on your hull.

1611665708649.png
 

BJC

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97FL, Florida, USA
It is interesting to look at some of the old ultralights, but having seen, and examined, many of them, I suggest that you approach them very carefully. There are reasons - structural, aerodynamic, and conceptual - that they are not flying today.

Lots of young, enthusiastic, ignorant people rejected critical input, and later died in their ill-conceived ultralights. There needed an internet, an open mind, and HBA.com.


BJC
 
Last edited:

Gregory Perkins

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May 25, 2019
Messages
69
Location
Atlanta
Not denying all your assertions but the crash analysis reports from back then revealed that the majority of fatal crashes were the result of pilot error and not structural failure. That is when the dual seat instruction systems were rolled out and given great priority.
 

BJC

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Not denying all your assertions but the crash analysis reports from back then revealed that the majority of fatal crashes were the result of pilot error and not structural failure. That is when the dual seat instruction systems were rolled out and given great priority.
I did not intend to, nor did I, assert that the majority of crashes were due to structural failures. Most crashes of aircraft are due to pilot error, so I would be surprised if ultralights were different.

I don’t have reliable data to make a case either way, and I do wonder about the validity of some of the ultralight crash reports from years ago, but I do know of five different new design ultralights shown at Oshkosh that had structural failures that led to fatalities. But, as I suggested above, there were plenty of other reasons, too.

BJC
 

plncraze

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Messages
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Somewhere I read an article on the the Tomcat that said it was very flexible. The horizontal on the original warped rather than using an elevator.
Pay very close attention to the original ultra lights and their assembly. They are very light
 
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